Temperature and Flow Velocity Dependency of Biological Screen- Slot Clogging in Injection Wells

Temperature and Flow Velocity Dependency of Biological Screen- Slot Clogging in Injection Wells | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Temperature and Flow Velocity Dependency of Biological Screen- Slot Clogging in Injection Wells Shun Okihara, Yoshitaka Sakata, Katsunori Nagano, Hideki Sato This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5190067/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 03 Nov, 2025 Read the published version in Geothermal Energy → Version 1 posted 9 You are reading this latest preprint version Abstract Biological clogging in injection wells for Groundwater Heat Pump (GWHP) systems presents a significant operational challenge. The initial stage of clogging involves bacterial fouling attaching to the screen slots of well pipes. However, the relationship between fouling and horizontal groundwater flow through the slots has not been thoroughly investigated. This study conducted a tank experiment by inserting two slotted steel plates into an acrylic tank. Untreated groundwater from the bottom was supplied and groundwater with adjusted temperature and dissolved oxygen from the top were introduced. The mass increase of iron-oxidation biofouling on the slotted steel plates was measured under varying conditions of injection water temperature and flow velocity through the slots. Results showed that higher flow rates and elevated injection water temperatures increased biofouling mass. Specifically, the mass increased by up to 1.6 times due to differences in flow rate and by up to 2.7 times due to differences in injection temperature. These results indicate that iron-oxidizing bacteria are activated by rising injection temperatures, as corroborated by previous studies, and that faster flow rates provide a greater supply of substrates in the groundwater. Finally, the relationship between biofouling mass and injection temperatures was analyzed using an Arrhenius plot. This analysis yielded apparent activation energy values of 62.6 kJ/mol at a flow rate of 1 m/d and 54.5 kJ/mol at a flow rate of 0.1 m/d, with respective determination coefficients of 0.94 and 0.95. Biological clogging Groundwater flow Steel pipe well Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1 Introduction The Ground-Source Heat Pump (GSHP) System is divided into two systems: a closed-loop system known as the Ground-Coupled Heat Pump (GCHP) system and an open-loop system known as the Groundwater Heat Pump (GWHP) system. The GCHP system utilizes heat exchangers buried vertically, horizontally, or diagonally underground to indirectly exchange heat with the ground. The GWHP system directly uses pumped groundwater as a heat source for the heat pump, returning the water to the aquifer or lake after heat extraction (ASHRAE, 2023 ). The GWHP system operates efficiently by directly extracting heat from pumped groundwater. According to the European standard EN 15450, the seasonal performance factor (SPF) target value when introducing the GWHP in new buildings ranges from 3.5 to 4.0, approximately 1.5 times higher than the value for GSHP (German Institute for Standardization 2007 ). The GWHP system also offers several advantages over the GSHP system, including the maintenance of the required flow rate and less extensive drilling of boreholes and installation of long ground heat exchangers, which reduces initial costs, especially for large-scale systems (ASHRAE, 2023 ; Christodoulides et al., 2024 ). However, clogging in the wells used for pumping and injecting groundwater poses a significant barrier to adopting GWHP systems. Blockages in well-screen openings and decreased porosity of grout and soils around the screens caused by clogs lead to excessive changes in water levels during pumping or injection. In severe cases, this can make the system difficult to operate (Johnston et al., 2013 ). Annual cleaning of wells is required (Gjengedal et al., 2020), and severe clogging is more common in injection wells than in pumping wells. This disparity arises due to the sedimentation of fine particles stirred up during the pumping process and the dissolution of oxygen into the water caused by defects in the piping. This leads to the accumulation of precipitates formed when dissolved oxygen reacts with mineral ions in the water (Takizawa, 2011 ). Clogging in groundwater wells is classified into three types: 1) physical clogging caused by the accumulation of suspended solids in source water, 2) chemical clogging due to the precipitation of minerals such as calcium carbonates, sulfates, and phosphates, and 3) biological clogging with fouling caused by activated bacteria due to changes in water quality, including dissolved oxygen, water temperature, and other ion materials, particularly when the aquifers for pumping and injection are different. These types of clogging increase maintenance costs (Jeong et al. 2018 ), and biological clogging is the most uncertain in the planning and designing of GWHP due to the clog being triggered by a combination of factors regarding groundwater, well structure, and geothermal utilization (Dupin & McCarty 2000 ; Shi et al. 2024 ). Figure 1 is a schematic of an injection well with clogging, demonstrating the process of injecting warmed water into the well during the cooling season. Groundwater is pumped from the pumping well, undergoes surface heat exchange, and then returns to the injection well at a temperature approximately 5°C different from the original groundwater temperature. The water is injected from the injection pipe, descends through a steel pipe, and passes through a screen into the aquifer. As illustrated in Fig. 1 , groundwater flow creates an imbalance in water and heat transferred to the aquifer. Biological clogging is classified into two types: screen-slot clogging, where floc adhesion clogs the well screen, and well-bore clogging, where microorganisms proliferate and attach to the grout’s pores and the surrounding soil, causing the well to clog (van Beek, 2011). Previous studies from laboratory experiments on well-bore clogging have demonstrated a permeability reduction of porous materials such as grout and soil (Seki et al. 2005 ; Kim et al. 2010 ). However, bacteria are more likely to activate on the surface of well pipes than in the grout and soils, especially when the pipe is made of steel, which is conducive to the growth of iron-oxidizing bacteria, as shown in Fig. 1 . Camprovin et al. ( 2017 ) conducted experiments by passing groundwater through an apparatus containing ST52 steel pieces used as screens at Aquifer Storage and Recovery (ASR) sites, placed atop glass bead-filled columns. Over time, the screen became covered with orange-brown fine viscous sediments, and the head loss in the column increased linearly, reducing by up to 15% after 30 days. Li et al. ( 2020 ) investigated the decrease in permeability due to hydrate deposition by continuously passing a mixture of deionized water and methane gas through a screen mesh. Rovira et al. ( 2019 ) passed supernatant from waste through filters and analyzed the permeability reduction and its collected materials. Fukuda et al. ( 2000 ) passed kaolin-containing sample water through microporous membranes, confirming permeability reduction and developing a fouling progression prediction model. These experiments are mainly conducted in the water treatment field, with few studies focusing on wells and incorporating groundwater flow in permeability experiments. Various well screen products are available, the stainless steel wire-wound screens offer high opening and necessary strength while having the demerits of being expensive. SGP slit screens are cost-effective despite having a low opening (Romanova et al. 2014 ; Nyer 1992 ) since these are still used in Japan. Field studies have reported biological clogging as problematic for SGF wells, due to iron-oxidizing bacteria activating in environments attached to steel material (e.g., Bloetscher et al. 2014 ; Gjengedal et al. 2020 ). This study demonstrated a laboratory tank experiment simulating screen-slit clogging on the screen, primarily focusing on slitted SGP screens. Two slitted SGP panels were set in a water tank filled with groundwater. Clogging on the panels was measured in water flowing through panels at different velocities. The same groundwater at various temperatures was injected to evaluate the sensitivity of the clogging and to reveal the temperature and flow velocity dependency of screen-slot clogging in injection wells. 2 Methods 2.1 Site description The groundwater used for this experiment was sourced from a test well located at coordinates 43°03′06″ N and 141°15′25″ E at Hokkaido University, Sapporo, Japan. This site is located near the boundary separating the northern alluvial fan and the southern lowlands. The geological formation of the site consists primarily of unsaturated fine deposits at depths of 0 to 5 meters, alluvial fan gravel deposits at depths of 5 to 45 meters, and alternating fine and coarse sediments at depths of 45 to 80 meters (Sagayama et al., 2007 ; Sakata et al., 2017 ) The groundwater for this experiment was extracted from depths ranging from 36–60 meters, primarily from highly permeable layers of coarse sediments. These depths are consistent with those examined in the author’s previous study on clogging analysis in injection wells located approximately 1 km east of the current site. In the context of the GWHP system implemented in Sapporo, Hokkaido, issues such as increased water levels during injection and decreased permeability around the well have been observed (Sakata et al. 2024 ). In the study done by Sakata et al., referenced in the preceding section, clogging substances adhering to the injection well of the GWHP were collected for microbiome analysis. The results revealed a high abundance of iron-oxidizing bacteria, including the genus Ferriphaselus , suggesting that biological clogging, particularly due to iron-oxidizing bacteria, was the primary cause of clogging in the region. The groundwater sampled in June 2019 from the test well was deemed acceptable for drinking, except for its iron concentration. The iron level was measured at 4.9 mg/L, 16 times higher than the Ministry of Health's standard for drinking water, set at 0.3 mg/L. 2.2 Pre-immersion experiments In this study, pre-immersion experiments were conducted to confirm the occurrence of screen-slot clogging and identify factors contributing to clogging mediated by iron-oxidizing bacteria. The groundwater used for this experiment was diluted with pure water and the iron concentration was adjusted to 0.3 mg/L. Using an incubator, the sample water was placed in 1-liter beakers and maintained at a constant temperature of 12°C, corresponding to the natural groundwater temperature in Sapporo. To facilitate microbial activation within the groundwater, the samples were continuously stirred with a magnetic stirrer throughout the experiment. The experimental setup included six distinct conditions: (1) placing one 5×10 cm steel plate in a 1-liter beaker, (2) placing two steel plates, (3) placing four steel plates, (4) placing a 10 cm square wire-wound plate made of stainless steel with a slot size of 1.5 mm and an open area of 39%, (5) without placing any iron plates, and (6) adjusting the iron concentration to 3.0 mg/L, which is ten times the standard value, by using FeCl₃ standard solution without the usage of iron plates. After four days, water samples were collected from each condition. The iron concentrations and chromaticity were measured using a spectrophotometer to evaluate the occurrence of biological clogging. Iron concentrations and chromaticity were measured using a spectrophotometer to investigate the occurrence of biological clogging. The results indicated significant variations in iron concentration among different conditions. Table 1 presents the iron concentrations and chromaticity measurements taken from each sample on the first and third days of the experiment. Samples with steel plates (Samples 1, 2, and 3) exhibited large amounts of iron concentration, significantly higher than the initial value of 0.3 mg/L. Precisely, 8.0 mg/L for one plate, 20.6 mg/L for two plates, and 30.3 mg/L for four plates. In contrast, the sample with the stainless steel plate (Sample 4) showed a relatively low iron concentration of 1.4 mg/L, and the samples without any plates (Samples 5 and 6) had iron levels that remained unchanged from the initial value. A similar trend was observed for chromaticity. Samples with steel plates recorded high values of 1150 for one plate, 1380 for two plates, and 956 for four plates. In contrast, the sample with the stainless steel plate showed a lower value of 264, and samples without any plates had measurements of 27 and 0. These results suggest that steel plates, particularly ones that are solid-phase iron, play a crucial role in the occurrence of clogging. Table 1 Pre-immersion experiment results Inserted Plate Iron Concentration (mg/L) Chromaticity (-) Sample Material number Initial 3rd day Initial 3rd day 1 Steel 1 0.3 8.0 43 1150 2 Steel 2 0.3 20.6 43 1380 3 Steel 4 0.3 30.3 43 956 4 Stainless 1 0.3 1.4 43 264 5 - 0 0.3 0.2 43 27 6 - 0 3 3.0 43 0 2.3 Tank experiment Based on the results of the pre-immersion experiments, tank experiments were conducted to investigate the dependence of biological clogging progression on temperature and flow velocity within the screen. Figure 2 provides a schematic diagram of the experiment, the experimental setup, and the overall layout of the tank. The experiment was conducted in a temperature-controlled room measuring approximately 5 square meters, where the indoor temperature was constantly maintained at 12°C. This setup assembled a steady flow inside the tank, groundwater was pumped from the test well from the bottom using Well Pump 2 and injected continuously into an acrylic water tank with dimensions of 1.95 meters in length, 0.21 meters in width, and 0.39 meters in height. The water flowed through two screens positioned in the center of the tank and was discharged from the top on the opposite side. An injection port was located in the center of the screen to introduce water, with its temperature adjusted by a chiller. The injection flow rate was maintained at a constant rate of q 2 = 1.2 L/min, corresponding to the flow rate per unit surface area when injecting approximately 100 L/min into an injection well with a 200 mm diameter and a 16.5 m screen, as described in the previous section about the GWHP system. The injected water was pumped from the same well by Well Pump 1, stored in the chiller tank, and either cooled in the chiller or heated using a controlled heater placed in the chiller. Additionally, the injected water was stirred and aerated in the chiller tank, until the dissolved oxygen concentration reached near saturation. Initially, the dissolved oxygen levels were 1mg/L when pumped up, then reached 9mg/L after stirring and aerating. To ensure smooth groundwater flow within the tank while preventing air accumulation from moving downstream, the upstream side of the tank was tilted downward at a gradient of 16°. The experiment utilized plates that simulate commonly used well screens: an SGP slit plate (with 100 × 8 mm slots, 5 mm thickness, and approximately 10% open area), and a stainless steel wound-wire plate. The flow of groundwater from the bottom of the tank and water injection from the top were continuously maintained throughout the experiment. By varying the combination of simulated groundwater flow velocity u (flow rate q 1 from upstream) and the injection water temperature T in , biofouling caused by iron-oxidizing bacteria was measured as the weight change Δ w of the screen before and after the experiment. The experiment was conducted in three major stages: Under the same conditions with a flow velocity of 1m/d in the tank (injection water volume q 1 = 0.05L/min) and an injection water temperature T in of 12°C (the same as the original groundwater temperature), the weight change over time was measured using slotted SGP plates, which readily form fouling. This experiment measured the weight change over one, two, three, four, and seven days after the initial injection. A four-day test under the same conditions was repeated twice to confirm the replicability of the results. Additionally, the experiment was repeated using the wound-wire stainless steel screen instead of the slit SGP plate to compare the differences in weight change between the two screens. To investigate the dependence on temperature and flow velocity, experiments were conducted under eight different conditions, with the injection water temperature T in varying to 7°C, 12°C, 14.5°C, and 17°C and the flow velocity u to 1m/d and 0.1m/d (injection water volume 0.005L/min). The weight changes under different temperature and flow velocity conditions were compared afterward. 3 Result 3.1 Experimental days Table 2 and Fig. 3 depict the relationship between weight change and the number of experimental days. The weight change increased progressively: 4.9 g on Day 1, 8.2 g on Day 2, 23.3 on Day 3, and 63.9 g on Day 7, indicating a linear trend. When the weight changes between the upstream and downstream panels were compared, the downstream panel consistently exhibited greater weight change, except on Day 1 when the weight change was minimal. The most significant weight difference of 21% was observed after Day 3. Based on the observed trend and experimental schedule, a four-day period was deemed optimal for subsequent experiments. Table 2 Weights (g) of Slot-Screen Plates as Experimental days increased Experimental days Upstream panel Downstream panel Δ w = Δ w 1 + Δ w 2 Before After Δ w 1 Before After Δ w 2 1 3540.2 3544 3.8 3542.1 3543.2 1.1 4.9 2 3540.2 3544.9 4.6 3542.1 3546.7 4.6 9.2 3 3540.2 3550.5 10.3 3542.1 3555.1 13 23.3 4 3537.3 3354.8 17.5 3535.4 3554.8 19.4 36.9 7 3540.2 3570.8 30.6 3542.1 3575.1 33.3 63.9 3.2 Reproducibility, Screen material Table 3 and Fig. 4 present the results of repeating the experiment twice with a flow velocity of 1 m/d in the tank and an injection water temperature T in of 12°C over four days. These results were compared with those from the previous section under the same conditions, along with the results from using the stainless steel plate. The average weight change after three repetitions with the SGP plate was 36.1 g, with a minimal error of 4.0% across three trials. This indicates that high reproducibility can be achieved with a single experiment, obviating the necessity for repeated trials. It confirms the precise control of conditions, such as temperature and flow rate, and the stability of microbial conditions in the groundwater during the experiment. When comparing weight changes between the upstream and downstream panels, the downstream side exhibited greater weight change, except during the second experiment, where the upstream side showed a slightly greater change of 0.1 g. The maximum difference, 10%, was observed in the first experiment. The stainless steel plate had an average weight change of 7.2 g, nearly 20% of the weight observed on an SGP plate. This trend aligns with pre-immersion experiments and further indicates the significance of solid-phase iron in biological clogging formation. Additionally, Fig. 4 (b) shows the condition of the stainless steel screen after the experiment. Red-brown substances adhered to the slits of the screen, corroborating findings from investigations of biologically clogged injection wells (e.g., Shi et al., 2024 ). Table 3 Weights(g) of Slot-Screen Plates and Stainless Steel Plates Condition Upstream panel Downstream panel Δ w = Δ w 1 + Δ w 2 Material Number Before After Δ w 1 Before After Δ w 2 SGP 1 3537.3 3554.8 17.5 3535.4 3554.8 19.4 36.9 SGP 2 3533.6 3552.3 18.7 3535.2 3553.8 18.6 37.3 SGP 3 3530.2 3546.9 16.7 3531.2 3548.6 17.4 34.1 Stainless 1 2033.1 2035.5 2.4 2034.6 2036.6 2 4.4 Stainless 2 2037.5 2040 2.5 2034.4 2040.6 6.2 8.7 Stainless 3 2037.5 2040.7 3.2 2034.4 2039.7 5.3 8.5 3.3 Flow velocity, Injection temperature Table 4 and Fig. 5 illustrate the weight changes observed under varying flow velocities (1 m/d and 0.1 m/d) and injection water temperatures (7°C, 12°C, 14.5°C, and 17°C). The results indicate that weight change increased with rising injection water temperatures under both flow velocity conditions, suggesting enhanced activity of iron-oxidizing bacteria at higher temperatures. The difference in weight change between the lowest temperature (7°C) and the highest (17°C) was 2.7 times greater at a flow velocity of 1 m/d and 2.2 times greater at 0.1 m/d. When comparing weight changes due to variations in flow velocity, the weight change at 1 m/d was consistently greater than at 0.1 m/d. This is likely due to the increased flow velocity supplying more substrates to the biofouling (Kim et al., 2010 ). At temperatures between 7°C and 14.5°C, the differences ranged from 3.2 g to 6.6 g. However, a substantial difference of 25.6 g was observed at 17°C. This significant difference at 17°C is attributed to the high-temperature injection water activating iron-oxidizing bacteria, along with the slower supply of oxygen and substrates in the low-flow environment becoming a limiting factor. Similar to the previous experiments, the downstream side exhibited greater weight change when comparing the weight differences between the upstream and downstream panels at a flow velocity of 1 m/d, except in the case of 14.5°C. Notably, at 17°C, a significant weight difference of 11.9 g (30%) was observed. Conversely, at 0.1 m/d, the largest difference was 1.4 g at 7°C. Especially when comparing higher temperatures, there was almost no difference between the upstream and downstream sides compared to the 1 m/d flow velocity. In this experiment, the flow direction between the injection water and the groundwater is anticipated to be reversed in the upstream panel. As shown in Fig. 1 , the flow velocity of the injection water decreases, reducing the supply of dissolved oxygen and substrates contained in the injection water. In the downstream panel, the flow direction of the injection water and the groundwater source water are aligned, causing an increase in flow velocity and consequently amplifying the supply of substrates. At a flow velocity of 1 m/d, the attenuation and amplification effects of the injection water were significant, resulting in a large difference between the upstream and downstream sides. However, at 0.1 m/d, these effects were minimal, and the flow induced by the injection water predominated. As a result, the difference in flow velocity between the upstream and downstream sides was minimal, leading to smaller weight change differences between the two sides. These findings suggest that in environments with faster groundwater flow, there may be significant differences in the progression of biological clogging between the upstream and downstream sides. Table 4 Weights(g) of Slot-Screen Plates When Varying the Flow Velocity Inside the Tank and the Injection Temperature Condition Upstream panel Downstream panel Δ w = Δ w 1 + Δ w 2 u (m/d) T in (°C) Before After Δ w 1 Before After Δ w 2 1 7 3532.6 3544.4 11.8 3534 3546.9 12.9 24.7 1 12 3537.3 3554.8 17.5 3535.4 3554.8 19.4 36.9 1 14.5 3530.3 3552.5 22.2 3529.5 3549.6 20.1 42.3 1 17 3535.2 3562.6 27.4 3533.5 3572.8 39.3 66.7 0.1 7 3530.2 3540.1 9.9 3531.2 3539.7 8.5 18.4 0.1 12 3532.4 3548.3 15.9 3530 3547 17 32.9 0.1 14.5 3530.3 3548.3 18 3529.5 3547.2 17.7 35.7 0.1 17 3530.2 3550 19.8 3531.2 3552.5 21.3 41.1 4 Discussion In the pre-immersion experiments, notable changes in chromaticity and iron concentration were observed upon the introduction of steel plates. This observation suggests that solid-phase iron in water is one of the conditions for bacterial proliferation. Based on these results, the conditions for the tank experiments were established. The tank experiments further demonstrated that changes in screen weight varied with water temperature and flow velocity. This finding implies that injecting water, which has undergone temperature changes after heat exchanges by the GWHP system, could trigger microbial activation even in groundwater that maintains a constant temperature. Based on these insights, the biological clogging process in a typical injection well using SGP pipes was estimated. Groundwater pumped from the pumping well passes through the well and surface piping, enters the heat exchanger, and undergoes heat exchange, cooling during heating operations, and heating during cooling operations. In this process, if there are design defects or damage in any part of the piping, air may enter and dissolve into the groundwater, causing an increase in the dissolved oxygen concentration. Furthermore, at the start of the system, the injection pipe to the injection well is often drained, allowing air to enter the pipe. Consequently, during the water injection, the air in the pipe is pushed into the well, increasing the dissolved oxygen concentration in the well water. This water then descends vertically towards the screens placed at the deeper sections of the well. As groundwater descends with its altered temperature and dissolved oxygen concentration, iron-oxidizing bacteria adhered to the inner walls of the well are activated, leading to proliferation and the production of metabolic byproducts. The bacterial colonies increase in size due to the increment in bacterial numbers, secretion of metabolic products, and the attachment of suspended bacteria, eventually forming flocs (Camprovin et al. 2017 ). When these flocs are dislodged by water movement within the well and reach the deeper screens, and the floc size exceeds the screen slit size or combines with other flocs, forming larger masses, it cannot pass through the screen and remain inside, causing the screen-slot clogging. Even if the flocs pass through the screen, it may remain in the soil pores, leading to well-bore clogging. This is the biological clogging process caused by iron-oxidizing bacteria. Furthermore, the Arrhenius plot was created to examine the relationship between the change in screen weight and the injection water temperature. While the Arrhenius equation is commonly used to estimate the rate of chemical reactions, it is also frequently employed to assess the growth rate of microorganisms. Studies that have estimated the iron oxidation rate and growth rate of iron-oxidizing bacteria using the Arrhenius plot include Ahonen and Tuovinen ( 1989 ), who cultured iron-oxidizing bacteria with ferrous sulfate as the substrate for up to 300 hours in a temperature range of 4–46°C and obtained the activation energy of 83 kJ/mol, and Ferroni et al. ( 1986 ), who cultivated T. ferredoxins in a temperature range of 2–35°C and estimated the activation energy of 95 kJ/mol (Ahonen and Tuovinen 1989 ). These research findings suggest that the Arrhenius equation could potentially be applied to the progression of biological clogging due to the growth of iron-oxidizing bacteria and, therefore used in this study. The Arrhenius equation is shown below. $$\:k=A\:exp\left(-\frac{{E}_{a}}{RT}\right)$$ Here, k is the reaction rate constant, A is the pre-exponential factor, E a is the activation energy, R is the gas constant, and T is the absolute temperature. By taking the logarithm of both sides and plotting \(\:ln\:k\:\) against the reciprocal of T , a straight line with a slope of E a / R is obtained, allowing the determination of the E a value. In this study, k represents the increase in the amount of substance adhering to the screen (hr − 1 ), and the apparent activation energy E a (kJ/mol) required for clogging formation was determined. Figure 6 shows the Arrhenius plot. E a was determined to be 62.6 kJ/mol when the flow velocity in the tank was 1 m/d and 54.5 kJ/mol when the flow velocity was 0.1 m/d. These values fall within the range of E a values (39–88 kJ/mol) obtained in various experimets conducted under different conditions (Nicholson et al. 1988 ). It is also closely comparable to the activation energy of 14.4 kcal/mol (approximately 60 kJ/mol) for microbial iron oxidation reported by De et al. ( 1996 ) under temperature conditions of 5–18°C. This suggests that in low-temperature environments, such as the environment assembled for this study, iron-oxidizing bacteria do not highly activate, leading to relatively higher activation energy values. This study conducted experiments by introducing raw groundwater from the bottom of the tank and groundwater with varying temperatures from the top. This setup may result in a complex interaction of various bacteria. This includes Ferriphaselus , as described in the Site Description, leading to the formation of screen slit clogging. The coefficients of determination (R²) for the Arrhenius plots were 0.94 at 1 m/d and 0.95 at 0.1 m/d, indicating a strong correlation. This suggests that the Arrhenius equation effectively expresses the weight change due to biological clogging. The results show that the Arrhenius equation may represent the temperature dependence of biological clogging forming on the screen. 5 Conclusion The study investigated the factors contributing to the formation of biological clogging on healthy screens and evaluated the effects of temperature and flow rate on clogging formation. The experiments involved inserting two SGP panels, each with slits, into a tank filled with groundwater. The flow rate within the tank and the temperature of the injected water at the top of the tank were varied during the experiments. The results showed that over a maximum test period of seven days, the weight change of the screen increased linearly with time. When comparing the SGP slitted plate with a stainless steel wound-wire plate, the weight change on the stainless steel screen was only about 20% of that observed on the SGP plate, indicating the presence of solid-phase iron being a crucial factor in the formation of biological clogging. Additionally, increasing the flow rate within the tank resulted in a maximum weight change increase of 1.7 times, while raising the temperature of the injected water led to a maximum increase of 2.7 times. The Arrhenius plot was created to examine the relationship between the temperature of the injected water and the weight change. The apparent activation energy values under two different flow velocity conditions were calculated and found to be generally consistent with those reported in previous studies on iron oxidation in low-temperature environments. Moreover, the high coefficients of determination in the Arrhenius plots under both flow rate conditions suggest that the temperature dependency of biological clogging on-screen slits can potentially be explained using the Arrhenius equation. During this study, only two flow rate patterns within the tank were tested, allowing the trend that faster flow rates result in significant amounts of clogging to be observable. However, this relationship could not be quantified. Therefore, experiments with various flow velocity patterns should be conducted in future research to quantify the relationship between flow rate and clogging. Further experiments should be conducted over a broader range of flow rates to investigate the variety of clogging levels across different flow velocities. Conducting experiments focused on specific bacterial species will also be essential. In this study, groundwater was pumped and then subjected to changes in temperature and dissolved oxygen concentration, suggesting that multiple species may have been present in the groundwater, even if it is limited to iron-oxidizing bacteria. Due to the mechanisms of biological clogging and its responses to temperature vary between bacterial species, it is necessary to conduct experiments specific to each species, elucidate their respective temperature characteristics, and integrate these findings to address the complex processes involved. Furthermore, future experiments will involve more precise measurements and control of various parameters, such as iron concentration and dissolved oxygen levels in the water. The weight change in plates was calculated as the weight of deposits for this study, however further research will have to cover the detailed analyses. This includes the weight change in plates after removing deposits to investigate further effects of corrosion, compositional analysis of the deposits, and identification of bacterial species through microbial analysis. Moreover, similar experiments will be conducted using a sand-filled tank to simulate groundwater flow and evaluate well-bore clogging more accurately. Abbreviations GSHP Ground source heat pump GCHP Ground coupled heat pump GWHP Ground water heat pump ASR Aquifer storage and recovery SGP Steel gas pipe List of symbols q 1 Water injection rate to the bottom of the tank q 2 Water injection rate to the top of the tank u Flow velocity within the tank T in Temperature of the water injected at the top of the tank Δ w Change in screen weight before and after the experiment (amount of clogging on the screen) k Reaction rate constant A Frequency factor E a Apparent activation energy R Gas constant T Absolute temperature Declarations Acknowledgments Not applicable. Author contributions Shun Okihara: conceptualization, methodology, formal analysis, investigation, data curation, writing―original draft, writing―review and editing. Yoshitaka Sakata: conceptualization, supervision. Katsunori Nagano: supervision. All the authors read and approved the final manuscript. Funding No funding was received. Data availability No funding was received. Competing interests The authors declare that they have no conflict of interest. Ethics and Consent to Participate declarations Not applicable References Ahonen L, Tuovinen OH. Microbiological Oxidation of Ferrous Iron at Low Temperatures. Applied and Environmental Microbiology logo. 1989;55:312–6. https://doi.org/10.1128/aem.55.2.312-316.1989 . ASHRAE. 2023 ASHRAE Handbook - HVAC Applications: ASHRAE; 2023. Bloetscher F, Sham CH, DankoⅢ JJ, Ratick S. Lessons Learned from Aquifer Storage and Recovery (ASR) Systems in the United States. Journal of Water Resource and Protection. 2014;6:1603–29. https://doi.org/10.4236/jwarp.2014.617146 . Camprovin P, Hernandez M, Fernandez S, Martin-Alonso J, Galofre B, Mesa J. Evaluation of Clogging during Sand-Filtered Surface Water Injection for Aquifer Storage and Recovery (ASR): Pilot Experiment in the Llobregat Delta (Barcelona, Spain). Water. 2017;9:263. https://doi.org/10.3390/w9040263 . Christodoulides P, Christou C, Florides GA. Ground Source Heat Pumps in Buildings Revisited and Prospects. Energies. 2024;17:3329. https://doi.org/10.3390/en17133329 . De GC, Oliver DJ, Pesic BM. Effect of silver on the ferrous iron oxidizing ability of Thiobacillus ferrooxidans. Hydrometallurgy. 1996;41:211 – 29. https://doi.org/10.1016/0304-386X(95)00057-N . Dupin HJ, McCarty PL. Impact of Colony Morphologies and Disinfection on Biological Clogging in Porous Media. Environmental Science & Technology. 2000;34:1513–20. https://doi.org/10.1021/es990452f . Ferroni GD, Leduc LG, Todo M. Isolation and Temperature Characterization of Psychrotrophic Strains of Thiobacillus Ferrooxidans from The Environment of a Uranium Mine. The Journal of General and Applied Microbiology. 1986;32:169–75. https://doi.org/10.2323/jgam.32.169 . Fukuda S, Tsuji T, Minegishi T, Yamamoto S, Itazawa T, Matsumoto K. Fouling performance in the filtration of water containing humic acid and/or kaolin with microporous membrane. Water Science & Technology. 2000;41:317–25. https://doi.org/10.2166/wst.2000.0671 . German Institute for Standardization. Heating systems in buildings - Design of heat pump heating systems; German version EN 15450:2007: German Institute for Standardization; 2007. Gjengedal S, Stenvik LA, Ramstad RK, Ulfsnes JI, Hilmo BO, Frengstad BS. Online remote-controlled and cost-effective fouling and clogging surveillance of a groundwater heat pump system: A case study from Lena Terrace in Melhus, Norway. Bulletin of Engineering Geology and the Environment. 2021;80:1063–72. https://doi.org/10.1007/s10064-020-01963-z . Jeong HY, Jun SC, Cheon JY, Park M. A review on clogging mechanisms and managements in aquifer storage and recovery (ASR) applications. Geosciences Journal. 2018;22:667–79. https://doi.org/10.1007/s12303-017-0073-x . Johnston K, Martin M, Higginson S. Case Study: Recharge of Potable and Tertiary-treated Wastewater into a Deep, Confined Sandstone Aquifer in Perth, Western Australia. In: Martin R editors. Clogging Issues Associated With Managed Aquifer Recharge Methods. IAH Commission on Managing Aquifer Recharge; 2013. 174–183. Kim JW, Choi H, Pachepsky YA. Biofilm morphology as related to the porous media clogging. Water Research. 2010;44:1193 – 201. https://doi.org/10.1016/j.watres.2009.05.049 . Li Y, Wu N, Ning F, Gao D, Hao X, Chen Q, Liu C, Sun J. Hydrate-induced clogging of sand-control screen and its implication on hydrate production operation. Energy. 2020;206:118030. https://doi.org/10.1016/j.energy.2020.118030 . Nicholson RV, Gillham RW, Reardon EJ. Pyrite oxidation in carbonate-buffered solution: 1. Experimental kinetics. Geochimica et Cosmochimica Acta. 1988;52:1077–85. https://doi.org/10.1016/0016-7037(88)90262-1 . Nyer EK. Groundwater Treatment Technology. 2nd ed: Wiley; 1992. Romanova UG, Gillespie G, Sladic J, Ma T. A Comparative Study of Wire Wrapped Screens vs. Slotted Liners for Steam Assisted Gravity Drainage Operations. World Heavy Oil Congress 2014. 2014. Rovira AM, Geeting JGH, Allred JR, Shimskey RW, Burns CA, Peterson RA, Colosi KA. Media comparison of filtration with hanford tank AP-107 supernate. Separation Science and Technology. 2019;54:1912–21. https://doi.org/10.1080/01496395.2019.1575419 . Sagayama T, Igarashi Y, Kondo T, Kamada K, Yoshida M, Chitoku T, Tonosaki T, Kudo C, Okumura, S, Kato M. Quaternary stratigraphy of the 150 m core in the central part of Sapporo, Japan. The Journal of the Geological Society of Japan. 2007;113:391–405. https://doi.org/10.5575/geosoc.113.391 . Sakata Y, Katsura T, Nagano K, Ishizuka M. Field Analysis of Stepwise Effective Thermal Conductivity along a Borehole Heat Exchanger under Artificial Conditions of Groundwater Flow. Hydrology. 2017;4:21. https://doi.org/10.3390/hydrology4020021 . Sakata Y, Okihara S, Sato H, Nagano K, Matsuura N. Monitoring and Analysis of Annually Clogging Development in Injection Water Wells for Shallow Geothermal Utilization. Journal of the Geothermal Research Society of Japan. 2024; 46:2: 85–93. Seki K, Kamiya J, Miyazaki T. Temperature Dependence of Hydraulic Conductivity Decrease due to Biological Clogging under Ponded Infiltration. Trans. of JSIDRE. 2005;2005:213–9. https://doi.org/10.11408/jsidre1965.2005.213 . Shi M, Yang Y, Wu Y, Wang Q, Gao L, Lu Y. Mechanisms of well iron clogging in groundwater heat pump systems: Insights from video imaging, hydrogeochemical analysis, and geochemical modeling. Journal of Environmental Management. 2024;365:121535. https://doi.org/10.1016/j.jenvman.2024.121535 . Takizawa S. Techniques for Ground Thermal Energy System 8. Water quality issues for ground thermal energy system. Journal of Groundwater Hydrology. 2011;53:401–9. https://doi.org/10.5917/jagh.53.401 . C.G.E.M. (Kees) van Beek. Cause and Prevention of Clogging of Wells Abstracting Groundwater from Unconsolidated Aquifers: IWA; 2011. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 03 Nov, 2025 Read the published version in Geothermal Energy → Version 1 posted Editorial decision: Revision requested 26 Aug, 2025 Reviews received at journal 14 Aug, 2025 Reviews received at journal 04 Aug, 2025 Reviewers agreed at journal 16 Jul, 2025 Reviewers agreed at journal 14 Jul, 2025 Reviewers invited by journal 17 Apr, 2025 Editor assigned by journal 10 Oct, 2024 Submission checks completed at journal 10 Oct, 2024 First submitted to journal 01 Oct, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5190067","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":364529601,"identity":"d0e9dd00-8527-45e3-a3a7-7a4d3fc3da65","order_by":0,"name":"Shun Okihara","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwUlEQVRIiWNgGAWjYHACZobEBiDF3sDM2MDARooWngOkaGEEaZFIYAbTBIF8A/Nhg4c77PL5Zz5/bDiDgS+PoBaDA2zJCYlnki1n3M4xTtzAwFZMWIv8G+MDiW3MBgy3c5gPPmBgSyToOPkGHpCWegP5m8cfE6eF4QCPcUJi22EDgxsMYIcR1gLyi0Fi23EDwzM5xoYzDIjwCyjEJH+2VRvIHT/+WLKn4hjhEEO39FgCqVoYakjXMgpGwSgYBcMeAABM4DtzO4mXAAAAAABJRU5ErkJggg==","orcid":"","institution":"Hokkaido University","correspondingAuthor":true,"prefix":"","firstName":"Shun","middleName":"","lastName":"Okihara","suffix":""},{"id":364529603,"identity":"c8b066cd-df35-43ce-8c85-f78af201987d","order_by":1,"name":"Yoshitaka Sakata","email":"","orcid":"","institution":"Kanazawa University","correspondingAuthor":false,"prefix":"","firstName":"Yoshitaka","middleName":"","lastName":"Sakata","suffix":""},{"id":364529605,"identity":"0529a431-4719-4102-bac3-4a0234341183","order_by":2,"name":"Katsunori Nagano","email":"","orcid":"","institution":"Hokkaido University","correspondingAuthor":false,"prefix":"","firstName":"Katsunori","middleName":"","lastName":"Nagano","suffix":""},{"id":364529607,"identity":"d427a420-b96b-45f1-9dcb-793b51f7710f","order_by":3,"name":"Hideki Sato","email":"","orcid":"","institution":"SANKEN SETSUBI KOGYO CO., Ltd","correspondingAuthor":false,"prefix":"","firstName":"Hideki","middleName":"","lastName":"Sato","suffix":""}],"badges":[],"createdAt":"2024-10-02 01:08:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5190067/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5190067/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s40517-025-00365-2","type":"published","date":"2025-11-03T15:58:02+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":66548274,"identity":"545718dc-332f-4300-9ef4-dfc4db0a0316","added_by":"auto","created_at":"2024-10-14 08:44:22","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":70732,"visible":true,"origin":"","legend":"\u003cp\u003eClogging in a well injecting warm water into groundwater flows\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-5190067/v1/5a4d0ddced8d855c8743e3c7.png"},{"id":66546993,"identity":"6b1d4ac8-9f02-486e-8745-d565ec7ab688","added_by":"auto","created_at":"2024-10-14 08:36:22","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1011301,"visible":true,"origin":"","legend":"\u003cp\u003e(a)\u003cstrong\u003e \u003c/strong\u003eSchematic Diagram of the Entire Tank Experiment, (b) Overall Appearance Diagram of the Experiment, (c) Photograph of the Inside of the Incubator, (d) Conceptual Diagram of the Acrylic Aquarium\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-5190067/v1/94ee71782dd6585d7054976e.png"},{"id":66546989,"identity":"bf22a93c-3ff6-4107-829f-1c747ba80862","added_by":"auto","created_at":"2024-10-14 08:36:22","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":16771,"visible":true,"origin":"","legend":"\u003cp\u003eTransition of Δ\u003cem\u003ew\u003c/em\u003e When Varying the Number of Experimental Days\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-5190067/v1/ea067442116bd163fe2593db.png"},{"id":66546996,"identity":"cc736133-7380-4098-8551-1b7ef1ac96b3","added_by":"auto","created_at":"2024-10-14 08:36:22","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":382377,"visible":true,"origin":"","legend":"\u003cp\u003e(a)\u003cstrong\u003e \u003c/strong\u003eMeasurement Results of Δ\u003cem\u003ew\u003c/em\u003eWhen Varying the Screen Material, (b) Picture of the Screen after the Experiment\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-5190067/v1/e754155b5b68482294e0776a.png"},{"id":66548271,"identity":"c8db6cbf-cb65-45fb-92d2-b8fd44e0a24f","added_by":"auto","created_at":"2024-10-14 08:44:22","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":19322,"visible":true,"origin":"","legend":"\u003cp\u003eMeasurement Results of Δ\u003cem\u003ew \u003c/em\u003eWhen Varying the Flow Speed Inside the Aquarium and the Injection Temperature\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-5190067/v1/9dc12cb10c66447a8f77f571.png"},{"id":66546990,"identity":"4bdee06e-b638-4054-b10d-5bba6d758899","added_by":"auto","created_at":"2024-10-14 08:36:22","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":30162,"visible":true,"origin":"","legend":"\u003cp\u003eArrhenius Plot of the Increase Rate of Adhesion to the Screen Under Different Flow Velocity Environments\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-5190067/v1/734e5d918b1638b82462da52.png"},{"id":95564202,"identity":"016aa1c0-fae5-464e-9a79-bb8c9b1afef1","added_by":"auto","created_at":"2025-11-10 16:08:53","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2907133,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5190067/v1/173d5191-e204-4b84-84df-bfcbe12cde9e.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Temperature and Flow Velocity Dependency of Biological Screen- Slot Clogging in Injection Wells","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe Ground-Source Heat Pump (GSHP) System is divided into two systems: a closed-loop system known as the Ground-Coupled Heat Pump (GCHP) system and an open-loop system known as the Groundwater Heat Pump (GWHP) system. The GCHP system utilizes heat exchangers buried vertically, horizontally, or diagonally underground to indirectly exchange heat with the ground. The GWHP system directly uses pumped groundwater as a heat source for the heat pump, returning the water to the aquifer or lake after heat extraction (ASHRAE, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The GWHP system operates efficiently by directly extracting heat from pumped groundwater. According to the European standard EN 15450, the seasonal performance factor (SPF) target value when introducing the GWHP in new buildings ranges from 3.5 to 4.0, approximately 1.5 times higher than the value for GSHP (German Institute for Standardization \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The GWHP system also offers several advantages over the GSHP system, including the maintenance of the required flow rate and less extensive drilling of boreholes and installation of long ground heat exchangers, which reduces initial costs, especially for large-scale systems (ASHRAE, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Christodoulides et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHowever, clogging in the wells used for pumping and injecting groundwater poses a significant barrier to adopting GWHP systems. Blockages in well-screen openings and decreased porosity of grout and soils around the screens caused by clogs lead to excessive changes in water levels during pumping or injection. In severe cases, this can make the system difficult to operate (Johnston et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Annual cleaning of wells is required (Gjengedal et al., 2020), and severe clogging is more common in injection wells than in pumping wells. This disparity arises due to the sedimentation of fine particles stirred up during the pumping process and the dissolution of oxygen into the water caused by defects in the piping. This leads to the accumulation of precipitates formed when dissolved oxygen reacts with mineral ions in the water (Takizawa, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eClogging in groundwater wells is classified into three types: 1) physical clogging caused by the accumulation of suspended solids in source water, 2) chemical clogging due to the precipitation of minerals such as calcium carbonates, sulfates, and phosphates, and 3) biological clogging with fouling caused by activated bacteria due to changes in water quality, including dissolved oxygen, water temperature, and other ion materials, particularly when the aquifers for pumping and injection are different. These types of clogging increase maintenance costs (Jeong et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), and biological clogging is the most uncertain in the planning and designing of GWHP due to the clog being triggered by a combination of factors regarding groundwater, well structure, and geothermal utilization (Dupin \u0026amp; McCarty \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Shi et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e is a schematic of an injection well with clogging, demonstrating the process of injecting warmed water into the well during the cooling season.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eGroundwater is pumped from the pumping well, undergoes surface heat exchange, and then returns to the injection well at a temperature approximately 5\u0026deg;C different from the original groundwater temperature. The water is injected from the injection pipe, descends through a steel pipe, and passes through a screen into the aquifer. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, groundwater flow creates an imbalance in water and heat transferred to the aquifer. Biological clogging is classified into two types: screen-slot clogging, where floc adhesion clogs the well screen, and well-bore clogging, where microorganisms proliferate and attach to the grout\u0026rsquo;s pores and the surrounding soil, causing the well to clog (van Beek, 2011).\u003c/p\u003e \u003cp\u003ePrevious studies from laboratory experiments on well-bore clogging have demonstrated a permeability reduction of porous materials such as grout and soil (Seki et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Kim et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). However, bacteria are more likely to activate on the surface of well pipes than in the grout and soils, especially when the pipe is made of steel, which is conducive to the growth of iron-oxidizing bacteria, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Camprovin et al. (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) conducted experiments by passing groundwater through an apparatus containing ST52 steel pieces used as screens at Aquifer Storage and Recovery (ASR) sites, placed atop glass bead-filled columns. Over time, the screen became covered with orange-brown fine viscous sediments, and the head loss in the column increased linearly, reducing by up to 15% after 30 days. Li et al. (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) investigated the decrease in permeability due to hydrate deposition by continuously passing a mixture of deionized water and methane gas through a screen mesh. Rovira et al. (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) passed supernatant from waste through filters and analyzed the permeability reduction and its collected materials. Fukuda et al. (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2000\u003c/span\u003e) passed kaolin-containing sample water through microporous membranes, confirming permeability reduction and developing a fouling progression prediction model. These experiments are mainly conducted in the water treatment field, with few studies focusing on wells and incorporating groundwater flow in permeability experiments.\u003c/p\u003e \u003cp\u003eVarious well screen products are available, the stainless steel wire-wound screens offer high opening and necessary strength while having the demerits of being expensive. SGP slit screens are cost-effective despite having a low opening (Romanova et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Nyer \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1992\u003c/span\u003e) since these are still used in Japan. Field studies have reported biological clogging as problematic for SGF wells, due to iron-oxidizing bacteria activating in environments attached to steel material (e.g., Bloetscher et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Gjengedal et al. \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThis study demonstrated a laboratory tank experiment simulating screen-slit clogging on the screen, primarily focusing on slitted SGP screens. Two slitted SGP panels were set in a water tank filled with groundwater. Clogging on the panels was measured in water flowing through panels at different velocities. The same groundwater at various temperatures was injected to evaluate the sensitivity of the clogging and to reveal the temperature and flow velocity dependency of screen-slot clogging in injection wells.\u003c/p\u003e"},{"header":"2 Methods","content":"\n\u003ch3\u003e2.1 Site description\u003c/h3\u003e\n\u003cp\u003eThe groundwater used for this experiment was sourced from a test well located at coordinates 43\u0026deg;03\u0026prime;06\u0026Prime; N and 141\u0026deg;15\u0026prime;25\u0026Prime; E at Hokkaido University, Sapporo, Japan. This site is located near the boundary separating the northern alluvial fan and the southern lowlands. The geological formation of the site consists primarily of unsaturated fine deposits at depths of 0 to 5 meters, alluvial fan gravel deposits at depths of 5 to 45 meters, and alternating fine and coarse sediments at depths of 45 to 80 meters (Sagayama et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Sakata et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) The groundwater for this experiment was extracted from depths ranging from 36\u0026ndash;60 meters, primarily from highly permeable layers of coarse sediments. These depths are consistent with those examined in the author\u0026rsquo;s previous study on clogging analysis in injection wells located approximately 1 km east of the current site. In the context of the GWHP system implemented in Sapporo, Hokkaido, issues such as increased water levels during injection and decreased permeability around the well have been observed (Sakata et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the study done by Sakata et al., referenced in the preceding section, clogging substances adhering to the injection well of the GWHP were collected for microbiome analysis. The results revealed a high abundance of iron-oxidizing bacteria, including the genus \u003cem\u003eFerriphaselus\u003c/em\u003e, suggesting that biological clogging, particularly due to iron-oxidizing bacteria, was the primary cause of clogging in the region.\u003c/p\u003e \u003cp\u003eThe groundwater sampled in June 2019 from the test well was deemed acceptable for drinking, except for its iron concentration. The iron level was measured at 4.9 mg/L, 16 times higher than the Ministry of Health's standard for drinking water, set at 0.3 mg/L.\u003c/p\u003e\n\u003ch3\u003e2.2 Pre-immersion experiments\u003c/h3\u003e\n\u003cp\u003eIn this study, pre-immersion experiments were conducted to confirm the occurrence of screen-slot clogging and identify factors contributing to clogging mediated by iron-oxidizing bacteria. The groundwater used for this experiment was diluted with pure water and the iron concentration was adjusted to 0.3 mg/L. Using an incubator, the sample water was placed in 1-liter beakers and maintained at a constant temperature of 12\u0026deg;C, corresponding to the natural groundwater temperature in Sapporo. To facilitate microbial activation within the groundwater, the samples were continuously stirred with a magnetic stirrer throughout the experiment. The experimental setup included six distinct conditions: (1) placing one 5\u0026times;10 cm steel plate in a 1-liter beaker, (2) placing two steel plates, (3) placing four steel plates, (4) placing a 10 cm square wire-wound plate made of stainless steel with a slot size of 1.5 mm and an open area of 39%, (5) without placing any iron plates, and (6) adjusting the iron concentration to 3.0 mg/L, which is ten times the standard value, by using FeCl₃ standard solution without the usage of iron plates. After four days, water samples were collected from each condition. The iron concentrations and chromaticity were measured using a spectrophotometer to evaluate the occurrence of biological clogging. Iron concentrations and chromaticity were measured using a spectrophotometer to investigate the occurrence of biological clogging. The results indicated significant variations in iron concentration among different conditions.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents the iron concentrations and chromaticity measurements taken from each sample on the first and third days of the experiment. Samples with steel plates (Samples 1, 2, and 3) exhibited large amounts of iron concentration, significantly higher than the initial value of 0.3 mg/L. Precisely, 8.0 mg/L for one plate, 20.6 mg/L for two plates, and 30.3 mg/L for four plates. In contrast, the sample with the stainless steel plate (Sample 4) showed a relatively low iron concentration of 1.4 mg/L, and the samples without any plates (Samples 5 and 6) had iron levels that remained unchanged from the initial value. A similar trend was observed for chromaticity. Samples with steel plates recorded high values of 1150 for one plate, 1380 for two plates, and 956 for four plates. In contrast, the sample with the stainless steel plate showed a lower value of 264, and samples without any plates had measurements of 27 and 0. These results suggest that steel plates, particularly ones that are solid-phase iron, play a crucial role in the occurrence of clogging.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePre-immersion experiment results\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eInserted Plate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eIron Concentration (mg/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003eChromaticity (-)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003enumber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eInitial\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3rd day\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eInitial\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3rd day\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSteel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1150\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSteel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1380\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSteel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e30.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e956\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStainless\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e264\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e27\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003e2.3 Tank experiment\u003c/h3\u003e\n\u003cp\u003eBased on the results of the pre-immersion experiments, tank experiments were conducted to investigate the dependence of biological clogging progression on temperature and flow velocity within the screen. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e provides a schematic diagram of the experiment, the experimental setup, and the overall layout of the tank. The experiment was conducted in a temperature-controlled room measuring approximately 5 square meters, where the indoor temperature was constantly maintained at 12\u0026deg;C. This setup assembled a steady flow inside the tank, groundwater was pumped from the test well from the bottom using Well Pump 2 and injected continuously into an acrylic water tank with dimensions of 1.95 meters in length, 0.21 meters in width, and 0.39 meters in height. The water flowed through two screens positioned in the center of the tank and was discharged from the top on the opposite side. An injection port was located in the center of the screen to introduce water, with its temperature adjusted by a chiller. The injection flow rate was maintained at a constant rate of \u003cem\u003eq\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1.2 L/min, corresponding to the flow rate per unit surface area when injecting approximately 100 L/min into an injection well with a 200 mm diameter and a 16.5 m screen, as described in the previous section about the GWHP system.\u003c/p\u003e \u003cp\u003eThe injected water was pumped from the same well by Well Pump 1, stored in the chiller tank, and either cooled in the chiller or heated using a controlled heater placed in the chiller. Additionally, the injected water was stirred and aerated in the chiller tank, until the dissolved oxygen concentration reached near saturation. Initially, the dissolved oxygen levels were 1mg/L when pumped up, then reached 9mg/L after stirring and aerating. To ensure smooth groundwater flow within the tank while preventing air accumulation from moving downstream, the upstream side of the tank was tilted downward at a gradient of 16\u0026deg;. The experiment utilized plates that simulate commonly used well screens: an SGP slit plate (with 100 \u0026times; 8 mm slots, 5 mm thickness, and approximately 10% open area), and a stainless steel wound-wire plate.\u003c/p\u003e \u003cp\u003eThe flow of groundwater from the bottom of the tank and water injection from the top were continuously maintained throughout the experiment. By varying the combination of simulated groundwater flow velocity \u003cem\u003eu\u003c/em\u003e (flow rate \u003cem\u003eq\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e from upstream) and the injection water temperature \u003cem\u003eT\u003c/em\u003e\u003csub\u003ein\u003c/sub\u003e, biofouling caused by iron-oxidizing bacteria was measured as the weight change Δ\u003cem\u003ew\u003c/em\u003e of the screen before and after the experiment. The experiment was conducted in three major stages:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eUnder the same conditions with a flow velocity of 1m/d in the tank (injection water volume \u003cem\u003eq\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.05L/min) and an injection water temperature \u003cem\u003eT\u003c/em\u003e\u003csub\u003ein\u003c/sub\u003e of 12\u0026deg;C (the same as the original groundwater temperature), the weight change over time was measured using slotted SGP plates, which readily form fouling. This experiment measured the weight change over one, two, three, four, and seven days after the initial injection.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eA four-day test under the same conditions was repeated twice to confirm the replicability of the results. Additionally, the experiment was repeated using the wound-wire stainless steel screen instead of the slit SGP plate to compare the differences in weight change between the two screens.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eTo investigate the dependence on temperature and flow velocity, experiments were conducted under eight different conditions, with the injection water temperature \u003cem\u003eT\u003c/em\u003e\u003csub\u003ein\u003c/sub\u003e varying to 7\u0026deg;C, 12\u0026deg;C, 14.5\u0026deg;C, and 17\u0026deg;C and the flow velocity \u003cem\u003eu\u003c/em\u003e to 1m/d and 0.1m/d (injection water volume 0.005L/min). The weight changes under different temperature and flow velocity conditions were compared afterward.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"3 Result","content":"\n\u003ch3\u003e3.1 Experimental days\u003c/h3\u003e\n\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e depict the relationship between weight change and the number of experimental days. The weight change increased progressively: 4.9 g on Day 1, 8.2 g on Day 2, 23.3 on Day 3, and 63.9 g on Day 7, indicating a linear trend.\u003c/p\u003e \u003cp\u003eWhen the weight changes between the upstream and downstream panels were compared, the downstream panel consistently exhibited greater weight change, except on Day 1 when the weight change was minimal. The most significant weight difference of 21% was observed after Day 3. Based on the observed trend and experimental schedule, a four-day period was deemed optimal for subsequent experiments.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eWeights (g) of Slot-Screen Plates as Experimental days increased\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eExperimental\u003c/p\u003e \u003cp\u003edays\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eUpstream panel\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eDownstream panel\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eΔ\u003cem\u003ew\u003c/em\u003e\u0026thinsp;=\u0026thinsp;Δ\u003cem\u003ew\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;Δ\u003cem\u003ew\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBefore\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAfter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eΔ\u003cem\u003ew\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBefore\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAfter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eΔ\u003cem\u003ew\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3540.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3544\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3542.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3543.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e4.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3540.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3544.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3542.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3546.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e9.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3540.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3550.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e10.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3542.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3555.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e23.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3537.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3354.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e17.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3535.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3554.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e19.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e36.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3540.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3570.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e30.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3542.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3575.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e33.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e63.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003e3.2 Reproducibility, Screen material\u003c/h3\u003e\n\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e present the results of repeating the experiment twice with a flow velocity of 1 m/d in the tank and an injection water temperature \u003cem\u003eT\u003c/em\u003e\u003csub\u003ein\u003c/sub\u003e of 12\u0026deg;C over four days. These results were compared with those from the previous section under the same conditions, along with the results from using the stainless steel plate. The average weight change after three repetitions with the SGP plate was 36.1 g, with a minimal error of 4.0% across three trials. This indicates that high reproducibility can be achieved with a single experiment, obviating the necessity for repeated trials. It confirms the precise control of conditions, such as temperature and flow rate, and the stability of microbial conditions in the groundwater during the experiment. When comparing weight changes between the upstream and downstream panels, the downstream side exhibited greater weight change, except during the second experiment, where the upstream side showed a slightly greater change of 0.1 g. The maximum difference, 10%, was observed in the first experiment.\u003c/p\u003e \u003cp\u003eThe stainless steel plate had an average weight change of 7.2 g, nearly 20% of the weight observed on an SGP plate. This trend aligns with pre-immersion experiments and further indicates the significance of solid-phase iron in biological clogging formation. Additionally, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e (b) shows the condition of the stainless steel screen after the experiment. Red-brown substances adhered to the slits of the screen, corroborating findings from investigations of biologically clogged injection wells (e.g., Shi et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eWeights(g) of Slot-Screen Plates and Stainless Steel Plates\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eCondition\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003eUpstream panel\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c8\" namest=\"c6\"\u003e \u003cp\u003eDownstream panel\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eΔ\u003cem\u003ew\u003c/em\u003e\u0026thinsp;=\u0026thinsp;Δ\u003cem\u003ew\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;Δ\u003cem\u003ew\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNumber\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBefore\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAfter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eΔ\u003cem\u003ew\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBefore\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAfter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eΔ\u003cem\u003ew\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSGP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3537.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3554.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e17.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3535.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e3554.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e19.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e36.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSGP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3533.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3552.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e18.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3535.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e3553.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e18.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e37.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSGP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3530.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3546.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e16.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3531.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e3548.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e17.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e34.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStainless\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2033.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2035.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2034.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e2036.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStainless\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2037.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2040\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2034.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e2040.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e6.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e8.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStainless\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2037.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2040.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2034.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e2039.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e5.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e8.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003e3.3 Flow velocity, Injection temperature\u003c/h3\u003e\n\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e illustrate the weight changes observed under varying flow velocities (1 m/d and 0.1 m/d) and injection water temperatures (7\u0026deg;C, 12\u0026deg;C, 14.5\u0026deg;C, and 17\u0026deg;C). The results indicate that weight change increased with rising injection water temperatures under both flow velocity conditions, suggesting enhanced activity of iron-oxidizing bacteria at higher temperatures. The difference in weight change between the lowest temperature (7\u0026deg;C) and the highest (17\u0026deg;C) was 2.7 times greater at a flow velocity of 1 m/d and 2.2 times greater at 0.1 m/d. When comparing weight changes due to variations in flow velocity, the weight change at 1 m/d was consistently greater than at 0.1 m/d. This is likely due to the increased flow velocity supplying more substrates to the biofouling (Kim et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). At temperatures between 7\u0026deg;C and 14.5\u0026deg;C, the differences ranged from 3.2 g to 6.6 g. However, a substantial difference of 25.6 g was observed at 17\u0026deg;C. This significant difference at 17\u0026deg;C is attributed to the high-temperature injection water activating iron-oxidizing bacteria, along with the slower supply of oxygen and substrates in the low-flow environment becoming a limiting factor.\u003c/p\u003e \u003cp\u003eSimilar to the previous experiments, the downstream side exhibited greater weight change when comparing the weight differences between the upstream and downstream panels at a flow velocity of 1 m/d, except in the case of 14.5\u0026deg;C. Notably, at 17\u0026deg;C, a significant weight difference of 11.9 g (30%) was observed. Conversely, at 0.1 m/d, the largest difference was 1.4 g at 7\u0026deg;C. Especially when comparing higher temperatures, there was almost no difference between the upstream and downstream sides compared to the 1 m/d flow velocity.\u003c/p\u003e \u003cp\u003eIn this experiment, the flow direction between the injection water and the groundwater is anticipated to be reversed in the upstream panel. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the flow velocity of the injection water decreases, reducing the supply of dissolved oxygen and substrates contained in the injection water. In the downstream panel, the flow direction of the injection water and the groundwater source water are aligned, causing an increase in flow velocity and consequently amplifying the supply of substrates. At a flow velocity of 1 m/d, the attenuation and amplification effects of the injection water were significant, resulting in a large difference between the upstream and downstream sides. However, at 0.1 m/d, these effects were minimal, and the flow induced by the injection water predominated. As a result, the difference in flow velocity between the upstream and downstream sides was minimal, leading to smaller weight change differences between the two sides.\u003c/p\u003e \u003cp\u003eThese findings suggest that in environments with faster groundwater flow, there may be significant differences in the progression of biological clogging between the upstream and downstream sides.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eWeights(g) of Slot-Screen Plates When Varying the Flow Velocity Inside the Tank and the Injection Temperature\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eCondition\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003eUpstream panel\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c8\" namest=\"c6\"\u003e \u003cp\u003eDownstream panel\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eΔ\u003cem\u003ew\u003c/em\u003e\u0026thinsp;=\u0026thinsp;Δ\u003cem\u003ew\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;Δ\u003cem\u003ew\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eu\u003c/em\u003e (m/d)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003ein\u003c/sub\u003e (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBefore\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAfter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eΔ\u003cem\u003ew\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBefore\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAfter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eΔ\u003cem\u003ew\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3532.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3544.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e11.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3534\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3546.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e12.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e24.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3537.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3554.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e17.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3535.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3554.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e19.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e36.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3530.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3552.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3529.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3549.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e20.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e42.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3535.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3562.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e27.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3533.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3572.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e39.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e66.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3530.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3540.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e9.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3531.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3539.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e8.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e18.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3532.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3548.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3530\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3547\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e32.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3530.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3548.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3529.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3547.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e17.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e35.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3530.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3550\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e19.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3531.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3552.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e21.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e41.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"4 Discussion","content":"\u003cp\u003eIn the pre-immersion experiments, notable changes in chromaticity and iron concentration were observed upon the introduction of steel plates. This observation suggests that solid-phase iron in water is one of the conditions for bacterial proliferation. Based on these results, the conditions for the tank experiments were established. The tank experiments further demonstrated that changes in screen weight varied with water temperature and flow velocity. This finding implies that injecting water, which has undergone temperature changes after heat exchanges by the GWHP system, could trigger microbial activation even in groundwater that maintains a constant temperature.\u003c/p\u003e \u003cp\u003eBased on these insights, the biological clogging process in a typical injection well using SGP pipes was estimated. Groundwater pumped from the pumping well passes through the well and surface piping, enters the heat exchanger, and undergoes heat exchange, cooling during heating operations, and heating during cooling operations. In this process, if there are design defects or damage in any part of the piping, air may enter and dissolve into the groundwater, causing an increase in the dissolved oxygen concentration. Furthermore, at the start of the system, the injection pipe to the injection well is often drained, allowing air to enter the pipe. Consequently, during the water injection, the air in the pipe is pushed into the well, increasing the dissolved oxygen concentration in the well water. This water then descends vertically towards the screens placed at the deeper sections of the well.\u003c/p\u003e \u003cp\u003eAs groundwater descends with its altered temperature and dissolved oxygen concentration, iron-oxidizing bacteria adhered to the inner walls of the well are activated, leading to proliferation and the production of metabolic byproducts. The bacterial colonies increase in size due to the increment in bacterial numbers, secretion of metabolic products, and the attachment of suspended bacteria, eventually forming flocs (Camprovin et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). When these flocs are dislodged by water movement within the well and reach the deeper screens, and the floc size exceeds the screen slit size or combines with other flocs, forming larger masses, it cannot pass through the screen and remain inside, causing the screen-slot clogging. Even if the flocs pass through the screen, it may remain in the soil pores, leading to well-bore clogging. This is the biological clogging process caused by iron-oxidizing bacteria.\u003c/p\u003e \u003cp\u003eFurthermore, the Arrhenius plot was created to examine the relationship between the change in screen weight and the injection water temperature. While the Arrhenius equation is commonly used to estimate the rate of chemical reactions, it is also frequently employed to assess the growth rate of microorganisms. Studies that have estimated the iron oxidation rate and growth rate of iron-oxidizing bacteria using the Arrhenius plot include Ahonen and Tuovinen (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1989\u003c/span\u003e), who cultured iron-oxidizing bacteria with ferrous sulfate as the substrate for up to 300 hours in a temperature range of 4\u0026ndash;46\u0026deg;C and obtained the activation energy of 83 kJ/mol, and Ferroni et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1986\u003c/span\u003e), who cultivated T. ferredoxins in a temperature range of 2\u0026ndash;35\u0026deg;C and estimated the activation energy of 95 kJ/mol (Ahonen and Tuovinen \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1989\u003c/span\u003e). These research findings suggest that the Arrhenius equation could potentially be applied to the progression of biological clogging due to the growth of iron-oxidizing bacteria and, therefore used in this study. The Arrhenius equation is shown below.\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:k=A\\:exp\\left(-\\frac{{E}_{a}}{RT}\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eHere, \u003cem\u003ek\u003c/em\u003e is the reaction rate constant, \u003cem\u003eA\u003c/em\u003e is the pre-exponential factor, \u003cem\u003eE\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e is the activation energy, \u003cem\u003eR\u003c/em\u003e is the gas constant, and \u003cem\u003eT\u003c/em\u003e is the absolute temperature. By taking the logarithm of both sides and plotting \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:ln\\:k\\:\\)\u003c/span\u003e\u003c/span\u003e against the reciprocal of \u003cem\u003eT\u003c/em\u003e, a straight line with a slope of \u003cem\u003eE\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e/\u003cem\u003eR\u003c/em\u003e is obtained, allowing the determination of the \u003cem\u003eE\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e value. In this study, \u003cem\u003ek\u003c/em\u003e represents the increase in the amount of substance adhering to the screen (hr\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and the apparent activation energy \u003cem\u003eE\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e (kJ/mol) required for clogging formation was determined.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the Arrhenius plot. \u003cem\u003eE\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e was determined to be 62.6 kJ/mol when the flow velocity in the tank was 1 m/d and 54.5 kJ/mol when the flow velocity was 0.1 m/d. These values fall within the range of \u003cem\u003eE\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e values (39\u0026ndash;88 kJ/mol) obtained in various experimets conducted under different conditions (Nicholson et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). It is also closely comparable to the activation energy of 14.4 kcal/mol (approximately 60 kJ/mol) for microbial iron oxidation reported by De et al. (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1996\u003c/span\u003e) under temperature conditions of 5\u0026ndash;18\u0026deg;C. This suggests that in low-temperature environments, such as the environment assembled for this study, iron-oxidizing bacteria do not highly activate, leading to relatively higher activation energy values.\u003c/p\u003e \u003cp\u003eThis study conducted experiments by introducing raw groundwater from the bottom of the tank and groundwater with varying temperatures from the top. This setup may result in a complex interaction of various bacteria. This includes \u003cem\u003eFerriphaselus\u003c/em\u003e, as described in the Site Description, leading to the formation of screen slit clogging. The coefficients of determination (R\u0026sup2;) for the Arrhenius plots were 0.94 at 1 m/d and 0.95 at 0.1 m/d, indicating a strong correlation. This suggests that the Arrhenius equation effectively expresses the weight change due to biological clogging. The results show that the Arrhenius equation may represent the temperature dependence of biological clogging forming on the screen.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"5 Conclusion","content":"\u003cp\u003eThe study investigated the factors contributing to the formation of biological clogging on healthy screens and evaluated the effects of temperature and flow rate on clogging formation. The experiments involved inserting two SGP panels, each with slits, into a tank filled with groundwater. The flow rate within the tank and the temperature of the injected water at the top of the tank were varied during the experiments. The results showed that over a maximum test period of seven days, the weight change of the screen increased linearly with time. When comparing the SGP slitted plate with a stainless steel wound-wire plate, the weight change on the stainless steel screen was only about 20% of that observed on the SGP plate, indicating the presence of solid-phase iron being a crucial factor in the formation of biological clogging. Additionally, increasing the flow rate within the tank resulted in a maximum weight change increase of 1.7 times, while raising the temperature of the injected water led to a maximum increase of 2.7 times.\u003c/p\u003e \u003cp\u003eThe Arrhenius plot was created to examine the relationship between the temperature of the injected water and the weight change. The apparent activation energy values under two different flow velocity conditions were calculated and found to be generally consistent with those reported in previous studies on iron oxidation in low-temperature environments. Moreover, the high coefficients of determination in the Arrhenius plots under both flow rate conditions suggest that the temperature dependency of biological clogging on-screen slits can potentially be explained using the Arrhenius equation.\u003c/p\u003e \u003cp\u003eDuring this study, only two flow rate patterns within the tank were tested, allowing the trend that faster flow rates result in significant amounts of clogging to be observable. However, this relationship could not be quantified. Therefore, experiments with various flow velocity patterns should be conducted in future research to quantify the relationship between flow rate and clogging. Further experiments should be conducted over a broader range of flow rates to investigate the variety of clogging levels across different flow velocities. Conducting experiments focused on specific bacterial species will also be essential. In this study, groundwater was pumped and then subjected to changes in temperature and dissolved oxygen concentration, suggesting that multiple species may have been present in the groundwater, even if it is limited to iron-oxidizing bacteria. Due to the mechanisms of biological clogging and its responses to temperature vary between bacterial species, it is necessary to conduct experiments specific to each species, elucidate their respective temperature characteristics, and integrate these findings to address the complex processes involved.\u003c/p\u003e \u003cp\u003eFurthermore, future experiments will involve more precise measurements and control of various parameters, such as iron concentration and dissolved oxygen levels in the water. The weight change in plates was calculated as the weight of deposits for this study, however further research will have to cover the detailed analyses. This includes the weight change in plates after removing deposits to investigate further effects of corrosion, compositional analysis of the deposits, and identification of bacterial species through microbial analysis. Moreover, similar experiments will be conducted using a sand-filled tank to simulate groundwater flow and evaluate well-bore clogging more accurately.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eGSHP Ground source heat pump\u003c/p\u003e \u003cp\u003eGCHP Ground coupled heat pump\u003c/p\u003e \u003cp\u003eGWHP Ground water heat pump\u003c/p\u003e \u003cp\u003eASR Aquifer storage and recovery\u003c/p\u003e \u003cp\u003eSGP Steel gas pipe\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eList of symbols\u003c/strong\u003e \u003cp\u003e \u003cem\u003eq\u003c/em\u003e \u003csub\u003e1\u003c/sub\u003e Water injection rate to the bottom of the tank\u003c/p\u003e \u003cp\u003e \u003cem\u003eq\u003c/em\u003e \u003csub\u003e2\u003c/sub\u003e Water injection rate to the top of the tank\u003c/p\u003e \u003cp\u003e \u003cem\u003eu\u003c/em\u003e Flow velocity within the tank\u003c/p\u003e \u003cp\u003e \u003cem\u003eT\u003c/em\u003e \u003csub\u003ein\u003c/sub\u003e Temperature of the water injected at the top of the tank\u003c/p\u003e \u003cp\u003eΔ\u003cem\u003ew\u003c/em\u003e Change in screen weight before and after the experiment (amount of clogging on the screen)\u003c/p\u003e \u003cp\u003e \u003cem\u003ek\u003c/em\u003e Reaction rate constant\u003c/p\u003e \u003cp\u003e \u003cem\u003eA\u003c/em\u003e Frequency factor\u003c/p\u003e \u003cp\u003e \u003cem\u003eE\u003c/em\u003e \u003csub\u003ea\u003c/sub\u003e Apparent activation energy\u003c/p\u003e \u003cp\u003eR Gas constant\u003c/p\u003e \u003cp\u003e \u003cem\u003eT\u003c/em\u003e Absolute temperature\u003c/p\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eShun Okihara: conceptualization, methodology, formal analysis, investigation, data curation, writing―original draft, writing―review and editing. Yoshitaka Sakata: conceptualization, supervision. Katsunori Nagano: supervision. All the authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo funding was received.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo funding was received.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics and Consent to Participate declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAhonen L, Tuovinen OH. Microbiological Oxidation of Ferrous Iron at Low Temperatures. 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Cause and Prevention of Clogging of Wells Abstracting Groundwater from Unconsolidated Aquifers: IWA; 2011.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"geothermal-energy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"geen","sideBox":"Learn more about [Geothermal Energy](https://geothermal-energy-journal.springeropen.com/about)","snPcode":"40517","submissionUrl":"https://submission.springernature.com/new-submission/40517/3","title":"Geothermal Energy","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Biological clogging, Groundwater flow, Steel pipe well","lastPublishedDoi":"10.21203/rs.3.rs-5190067/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5190067/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBiological clogging in injection wells for Groundwater Heat Pump (GWHP) systems presents a significant operational challenge. The initial stage of clogging involves bacterial fouling attaching to the screen slots of well pipes. However, the relationship between fouling and horizontal groundwater flow through the slots has not been thoroughly investigated. This study conducted a tank experiment by inserting two slotted steel plates into an acrylic tank. Untreated groundwater from the bottom was supplied and groundwater with adjusted temperature and dissolved oxygen from the top were introduced. The mass increase of iron-oxidation biofouling on the slotted steel plates was measured under varying conditions of injection water temperature and flow velocity through the slots. Results showed that higher flow rates and elevated injection water temperatures increased biofouling mass. Specifically, the mass increased by up to 1.6 times due to differences in flow rate and by up to 2.7 times due to differences in injection temperature. These results indicate that iron-oxidizing bacteria are activated by rising injection temperatures, as corroborated by previous studies, and that faster flow rates provide a greater supply of substrates in the groundwater. Finally, the relationship between biofouling mass and injection temperatures was analyzed using an Arrhenius plot. This analysis yielded apparent activation energy values of 62.6 kJ/mol at a flow rate of 1 m/d and 54.5 kJ/mol at a flow rate of 0.1 m/d, with respective determination coefficients of 0.94 and 0.95.\u003c/p\u003e","manuscriptTitle":"Temperature and Flow Velocity Dependency of Biological Screen- Slot Clogging in Injection Wells","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-10-14 08:36:17","doi":"10.21203/rs.3.rs-5190067/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-26T21:04:13+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-14T16:13:49+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-04T09:42:06+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"151367572597335821545622812335384505586","date":"2025-07-16T07:24:06+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"106959179395351439583979424449291334068","date":"2025-07-14T13:00:08+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-17T16:54:46+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-10-10T10:16:15+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-10-10T10:14:53+00:00","index":"","fulltext":""},{"type":"submitted","content":"Geothermal Energy","date":"2024-10-02T00:55:20+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"geothermal-energy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"geen","sideBox":"Learn more about [Geothermal Energy](https://geothermal-energy-journal.springeropen.com/about)","snPcode":"40517","submissionUrl":"https://submission.springernature.com/new-submission/40517/3","title":"Geothermal Energy","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"205332a0-15fb-4d4e-8e5d-e606c5eae601","owner":[],"postedDate":"October 14th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-11-10T16:05:38+00:00","versionOfRecord":{"articleIdentity":"rs-5190067","link":"https://doi.org/10.1186/s40517-025-00365-2","journal":{"identity":"geothermal-energy","isVorOnly":false,"title":"Geothermal Energy"},"publishedOn":"2025-11-03 15:58:02","publishedOnDateReadable":"November 3rd, 2025"},"versionCreatedAt":"2024-10-14 08:36:17","video":"","vorDoi":"10.1186/s40517-025-00365-2","vorDoiUrl":"https://doi.org/10.1186/s40517-025-00365-2","workflowStages":[]},"version":"v1","identity":"rs-5190067","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5190067","identity":"rs-5190067","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}