Simultaneous microalgae separation and COD reduction from landfill leachate using electrocoagulation-flotation

Simultaneous microalgae separation and COD reduction from landfill leachate using electrocoagulation-flotation | 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 Simultaneous microalgae separation and COD reduction from landfill leachate using electrocoagulation-flotation Marvin Bruns, Alexander Kuss, Peter Kern, Christian Wolf, Himanshu Himanshu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8360370/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 10 You are reading this latest preprint version Abstract Microalgae-based wastewater treatment holds potential for nutrient recovery and carbon capture, but efficient biomass harvesting remains energy-intensive. This study evaluates electrocoagulation-flotation (ECF) for simultaneous microalgae separation and chemical oxygen demand (COD) reduction in real landfill leachate. A mixed microalgal consortium (Chlorella-dominated) was cultivated directly in landfill leachate at low and high biomass densities (OD 680 0.3 and 2.2) and treated in a 0.5 L batch ECF reactor operated under a low-duty pulsed-voltage regime (5.0 V for 0.1 s and 1.5 V for 29.9 s, 30 min). ECF achieved 99.7% and 94.7% separation at low and high biomass, corresponding to 0.22-0.40 kWh kg-1 total solids and 0.33-0.38 kWh m-3. COD for low biomass microalgae decreased from 715 ± 12 mg O 2 L-1 (raw leachate) to 564 ± 14 mg O 2 L-1 after ECF i.e. 21% relative to raw leachate. These findings demonstrate that ECF effectively integrates microalgae harvesting with partial organic pollutant removal in a challenging wastewater matrix, offering a promising low-energy strategy for combined treatment and resource recovery in landfill leachate management. Microalgae separation electrocoagulation landfill leachate Circular economy wastewater Chlorella Figures Figure 1 Figure 2 1. Introduction Microalgae can play a significant role in advancing the circular economy, offering proven potential for wastewater treatment and the recovery of key nutrients such as carbon, nitrogen, and phosphorus (Li et al. 2019 ; Molitor et al. 2024 ). In addition to these benefits, microalgae provide valuable ecosystem services, including carbon capture, storage, and utilization through CO 2 absorption, while simultaneously producing value-added products such as biofuels and nutraceuticals (Ezhumalai et al. 2024 ). However, despite these advantages, the large-scale adoption of microalgae-based processes is limited by challenges in downstream processing. Notably, biomass separation and harvesting can account for up to 30% of process costs and 20–30% of the total process energy input, due to the difficulty of separating small, near-neutrally buoyant microalgae cells (Renuka et al. 2013 ; Chen et al. 2021 ; Shaikh et al. 2021 ). Several technologies have been developed for microalgae separation, each with distinct advantages and disadvantages. For example, sedimentation is highly energy efficient 0.05–0.1 kWh m − 3 and has low capital costs (€0.03 m − 3 ), but it achieves only modest concentrations of 0.5-3 g L − 1 total suspended solids and requires long retention times due to the low intrinsic settling velocity (~ 1 cm h − 1 ) of microalgae cells, which have a density similar to water (Vandamme 2017 ). Chemical flocculation can achieve high separation efficiency (95–99%) with relatively low energy requirements, as energy is primarily needed for mixing. However, it faces significant drawbacks for large-scale application, including high operational costs for organic flocculants (e.g. chitosan 20–50 USD kg − 1 (Xu et al. 2021 ), and contamination of the recovered microalgae due to residual flocculants. Inorganic flocculants (alum, ferric chloride) can leave behind residual salts and metal ions, while organic polymers (chitosan, polyacrylamide) may introduce residual polymer chains that complicate downstream biomass utilization (Zhu et al. 2018 ). Centrifugation offers high separation efficiency (90–98%) with short treatment times (minutes), but requires the highest specific energy (8–20 kWh m − 3 ) among common methods and involves significant capital costs (Abu-Shamleh and Najjar 2020 ; McGrath et al. 2024 ). Electrocoagulation flotation (ECF) has emerged as a technology for microalgae separation that offers high separation efficiency, low energy demand, short treatment times, and low operational costs. For example Guldhe et al. ( 2016 ) reported 91% separation efficiency of Ankistrodesmus falcatus in 30 minutes, outperforming chitosan at 55% and alum at 86% after 60 minutes. The same study reported ECF energy consumption can be orders of magnitude lower than centrifugation i.e. 1.8 kWh kg − 1 for ECF versus 65.3 kWh kg − 1 for centrifugation at similar recovery. Lucakova et al. ( 2021 ) reported that adding an electrocoagulation pre-concentration step (using stainless steel cathode and carbon steel anode for Chlorella ) before centrifugation reduced total separation energy to 0.136 kWh kg − 1 , energy savings of up to 89% relative to stand-alone centrifugation. In addition Lucakova et al. ( 2021 ), using ECF with iron electrodes, demonstrated the harvested Chlorella biomass had the iron content within food/feed safety limits. Mechanistically, during ECF aluminum and/or iron is oxidized at the anode, releasing Al 3+ and Fe 2+ /Fe 3+ ions that produce metallic hydroxides which destabilise negatively charged microalgae cells by charge neutralisation and sweep flocculation. Simultaneously, cathodically produced hydrogen microbubbles attach to the flocs and float them to the surface for easy skimming. Unlike chemical coagulation, ECF does not introduce additional anions into the solution beyond OH − generated at the cathode and the in-situ release of multivalent cations be tightly controlled by controlling the current reducing the risk of overdosing (Visigalli et al. 2021 ). Electrocoagulation has also been reported as an effective treatment for wastewaters, including for chemical oxygen demand (COD) reduction. For example Asefaw et al. ( 2024 ) reported 98% COD removal from coffee wastewater using electrocoagulation. In landfill leachate Rookesh et al. ( 2022 ) reported a reduction of 30% COD and 84% NH 4 + using electrocoagulation with Fe–graphite electrodes. The mechanism for COD reduction is similar to that for microalgae separation: Al 3+ generated at the anode hydrolyses to form amorphous Al(OH) 3 , which destabilizes colloids and adsorbs dissolved organics, while H 2 produced at the cathode assists flotation. However, in the case of landfill leachate, COD reduction is primarily driven by adsorption and sweep-flocculation of dissolved organics into Al(OH) 3 , and in chloride-rich matrices at higher anode potentials, indirect oxidation via in situ chlorine/hypochlorite may also occur (Jotin et al. 2012 ). Despite these advances, several gaps remain in the application of ECF for microalgae separation in real wastewaters. Most studies have focused on single species in synthetic media or clean water, limiting the transferability of results to coloured, saline and highly conductive real-life wastewaters such as landfill leachates (Visigalli et al. 2021 ). Additionally, energy reporting is often incomplete, as many studies do not log time-resolved voltage and current to accurately integrate the true electrical energy input. Only a limited number of studies have reported both volumetric (kWh m − 3 ) and mass-based (kWh kg − 1 dry biomass) normalisations. Recent guidelines recommends using specific electro-energy consumption per unit dry mass (kWh kg TS − 1 ) for comparability and volumetric electro-energy consumption (kWh m − 3 ) for reactor-scale context (Visigalli et al. 2021 ). Finally, to date, there are no reports in the literature on simultaneous microalgae separation using ECF/electrocoagulation and COD reduction in real landfill leachate. The aim of this study is to evaluate ECF in real landfill leachate to achieve simultaneous microalgae separation and COD reduction, using a mixed microalgal consortium grown in the same leachate. To the author’s knowledge, this provides the first demonstration of simultaneous microalgae separation and COD reduction in real landfill leachate using ECF. 2. Materials and methods 2.1 Matrix and microalgae Landfill leachate was collected at the :metabolon site (Lindlar, Germany) and inoculated with a working culture consisting of indigenous Chlorella sorokiniana collected from this landfill site and adapted to growth in the same leachate matrix, without any micro- or macronutrient supplementation. The microalgae was identified by nuclear ribosomal ITS sequences determined from three different strains available under GenBank accession numbers PX210920-PX210922 (Kuss et al. 2025 ). The microalgae biomass was produced at two different optical densities i.e. OD 680 0.3 (L1, L2 and L3) and 2.2 (H1, H2 and H3). The microalgae were grown in sealed 1-L Erlenmeyer flasks at 22 ± 2°C and continuously mixed with a magnetic stirrer at 150–200 rpm and illuminated by LED lights at an intensity of 150–200 µmol m − 2 s − 1 in a 14/10 h light-dark cycle. 2.2 ECF experimental setup All ECF batch tests were performed in triplicate in a custom acrylic reactor with internal dimensions 100 × 95 × 65 mm and a working volume of 0.5 L. Unless stated otherwise, values are reported as arithmetic mean ± standard deviation (SD). n denotes the number of independent biological replicates, defined here as independent ECF batch runs performed on independently prepared cultures for each condition (L1L3 for low biomass; H1–H3 for high biomass; n = 3 per condition). The electrochemical cell comprised two parallel aluminium plates mounted in a 3D-printed holder, separated by an inter-electrode gap of 2 mm. The effective anode area was 75 cm² (50 × 75 mm facing surfaces on both sides). UNI-T UDP3305S-E laboratory power supply operated in voltage mode delivered a low-duty pulsed waveform for 30 minutes with each 30 s cycle comprised 5.0 V applied for 0.1 s followed by 1.5 V for 29.9 s (duty 0.33%). For the high-biomass runs (H1–H3), voltage and current were logged at 1 Hz from the power supply. For the low-biomass runs (L1–L3), a logging fault occurred with automatic recorder, so the current and voltage were documented by manual readings taken every 6 minutes. Integrated electrical energy and charge for L1–L3 were computed from the manual reading. The 1 Hz sampling and 0.1 s pulse on-time mean that only a fraction of individual pulses appear in the time series and the peak capture is probabilistic and does not reflect instability. During ECF the microalgae culture was mixed at 250 rpm with a magnetic stirrer. After the 30 minute ECF test the mixing was stopped and the foam/floc layer was allowed to form for 60 minutes. The clarified growth medium was then collected using a pipette from below the foam/floc layer. The residual foam/floc layer was dried at 105°C for 48 hours to determine the dry matter content. The total COD of raw landfill leachate, low biomass density microalgae culture i.e. optical density at 680 nm (OD 680 ) 0.3 (after 24 hour of incubation) and the clarified culture medium after ECF was analysed by the dichromate method (ISO 6060/DIN 38409 H41/H44) using Hach-Lange LCK514 (100–2000 mg O 2 L − 1 ). pH measured before and after ECF treatment using Si analytics tritroline 6000. Mean current density was obtained by dividing the time-averaged current by the effective anode area of 75 cm 2 . Specific energy demand per unit treated volume (kWh m − 3 ) was calculated by dividing the integrated electrical work by the treated volume. Specific energy per unit of biomass separated (kWh kg − 1 TS) was calculated by dividing the integrated electrical work by the product of capture efficiency, treated volume and initial biomass concentration expressed as total solids. Capture efficiency was determined from the reduction in OD₆₈₀ of the supernatant between the initial and final samples. Electrode mass loss and residual aluminium in the effluent were not measured in this preliminary study. However, the theoretical aluminium dose was computed using Eq. 1 from Faraday’s law where Q is electric charge in coulomb (C), t is time in seconds, M is molar mass of aluminium (26.98 g mol − 1 ), z is the valence of Aluminum ions i.e. 3 and F is the Faraday’s constant (96485 C mol − 1 ) and is reported as mg L − 1 per run (Visigalli et al. 2021 ). \(\:{m}_{Al}\left(mg{\:L}^{-1}\right)=\frac{QM1000}{zFV\left(L\right)}\) (Eq. 1) 3. Results ECF achieved a consistently high level of microalgae separation efficiency in both low- (99.7%) and high-biomass (94.75%) microalgae cultures (Table 1 ). The specific electro-energy consumption per unit dry mass for low- and high-biomass cultures was 0.395 ± 0.014 kWh kg − 1 TS and 0.222 ± 0.025 kWh kg − 1 TS, respectively and volumetric electro-energy consumption was 0.332 kWh m − 3 and 0.383 kWh m − 3 , respectively. The reported figures include only electrical work at the electrodes and exclude supply losses, mixing and controls The mean current density under the imposed waveform was ~ 3 mA cm − 2 (referenced to the 75 cm² anode area). Figure 1 shows the current profile for high-biomass microalgae culture. The baseline rose during the first 3–5 min then remained near 0.20–0.26 A over 30 min. Single-point peaks appear when the 1 Hz sample coincided with the 0.1 s, 5.0 V pulse. The peak incidence varies with logger-pulse phase and does not indicate instability. Theoretical aluminium release was calculated from the time-integrated current using Faraday’s law with aluminium valency of 3. As shown in Table 1 the calculated average aluminium doses were 78.4 ± 2.4 mg L − 1 and 85.0 ± 12.1 mg L − 1 for low and biomass microalgae cultures, respectively. The corresponding charges were 420.6 ± 13 C and 456.5 ± 65 C, respectively. Residual dissolved aluminium in the clarified phase and gravimetric electrode mass loss were not measured in this study. The total COD of the landfill leachate increased from 715.0 ± 12.3 mg O 2 L − 1 in the raw leachate to 808.5 ± 11.5 mg O 2 L − 1 after incubation with microalgae for the low biomass microalgae culture. Following the ECF treatment, the COD of the clarified (unfiltered) landfill leachate without microalgae declined to 564.3 ± 13.6 mg O 2 L − 1 (Fig. 2 ). This corresponds to a reduction of roughly 30% relative to the culture and 21% relative to the raw landfill leachate. Expressed as specific energy per unit COD removed, the ECF process consumed 1.35 kWh kg − 1 COD, calculated from the volumetric energy (0.33 kWh m − 3 ) divided by the mass-based COD removal (244.2 mg L − 1 = 0.2442 kg COD m − 3 ). The pH of landfill leachate did not change during the ECF treatment and it was 8.3 for both raw and ECF treated leachate. Table 1 Charge, energy input and theoretical aluminium dose during ECF. Values are from three independent biological replicates per condition (L1–L3 and H1–H3; n = 3). Mean (SD) is reported in parentheses. TS = total solids. Theoretical Al dose calculated from Faraday’s law; separation efficiency from OD 680 reduction ID Biomass Charge Q (C) Energy input (mWh) Theoretical Al dose (mg L − 1 ) Specific energy (kWh m − 3 ) Specific energy (kWh kg − 1 TS) Separation efficiency (%) L1 Low 423.0 176.3 78.9 0.353 0.404 99.7 L2 Low 432.0 180.0 80.5 0.360 0.380 99.4 L3 Low 406.8 141.3 75.8 0.283 0.380 99.9 Mean (SD) 420.6 (13) 165.9 (21.4) 78.4 (2.4) 0.332 (0.04) 0.395 (0.01) 99.7 (0.2) H1 High 477.0 198.5 88.9 0.397 0.233 96.6 H2 High 508.2 215.7 94.7 0.431 0.240 94.9 H3 High 383.0 159.6 71.4 0.319 0.194 92.7 Mean (SD) 456.5 (65) 191.3 (28.7) 85.0 (12.1) 0.383 (0.06) 0.222 (0.03) 94.7 (1.9) 4. Discussion This study tested whether ECF, in real landfill leachate, can simultaneously deliver microalgal separation and COD reduction. ECF achieved high microalgae separation efficiencies for both biomass concentrations, with a slightly lower efficiency observed at higher biomass. This reduction is likely due to increased floc loading and carry-through in the clarified layer, rather than ineffective destabilization. The high separation efficiencies are comparable to the high recoveries for ECF reported in literature for the conductive media and optimised ECF processes by Vandamme et al. ( 2011 ), Visigalli et al. ( 2021 ), and de Morais et al. ( 2023 ). The presence of various constituents e.g. dissolved organics, salts etc in the landfill leachate did not prevent efficient microalgae aggregation and flotation while these constituents have been reported to sometimes inhibit flocculation (Vandamme et al. 2013 ). The separation efficiency of the present study is comparable to state-of-the-art high-separation-efficiency methods, such as chemical flocculation, but without the need for chemical flocculants. For example, chitosan flocculation of Chlorella sorokiniana achieved > 99% clarification efficiency (Xu et al. 2021 ), while the present study achieved 94.7–99.7% separation efficiency. The separation efficiency of present study compared to some of the established mechanical microalgae separation methods e.g. centrifugation are very similar but the energy requirement for ECF is one to two order of magnitude lower than centrifugation (Danquah et al. 2009 ; Guldhe et al. 2016 ). For comparison among ECF methods for microalgae separation, the specific energy demand for both high and low biomass concentration cultures in this study is an order of magnitude lower than typical energy consumptions reported for freshwater media. e.g. Vandamme et al. ( 2011 ) reported a specific energy requirement of 2 kWh kg − 1 for Chlorella vulgaris in fresh culture. However, the specific energy requirements observed here are comparable to those in saline conditions, where Vandamme et al. ( 2011 ) reported 0.3 kWh kg − 1 for Phaeodactylum tricornutum separation in seawater. The mass-based specific energy decreased at higher biomass because more dry solids were removed per unit electrical work, while the volumetric energy remained similar since the batch electrical work was comparable (Table 1 ). Baseline current in the logged runs for high biomass microalgae culture remained stable over 30 minutes, with occasional single-point peaks when sampling coincided with the 0.1 s pulse (Fig. 1 ). The lack of current drift suggests sustained electrode activity, likely due to reduced buildup of insulating oxide on the aluminium anode, which can occur during constant DC voltage application (Jotin et al. 2012 ). Another advantage of pulsed voltage application is that the interrupted current promotes rapid nucleation and detachment of small bubbles, which can improve attachment to fine microalgae flocs. Smaller bubbles provide a larger total surface area, thereby improving flotation efficacy (Khosla et al. 1991 ). The total COD of the treated landfill leachate decreased 30% relative to the microalgae culture and 21% relative to the raw landfill leachate. This decrease likely combines removal of microalgal particulates formed during incubation with adsorption and sweep-flocculation of dissolved organics by in situ Al(OH) 3 formed at the anode, aided by H 2 flotation at the cathode. These mechanisms and their pH-dependent speciation are well established for EC in leachate, with COD removal generally maximised between pH 4 and 8 when amorphous Al(OH) 3 dominates the speciation (Jotin et al. 2012 ). The COD reduction is comparable to EC studies using iron electrode e.g. 32.4% COD reduction by Rookesh et al. ( 2022 ) and 35% COD reduction by Ilhan et al. ( 2008 ) in landfill leachate at near-neutral pH. However, the present COD reduction is lower than the EC studies which have used Al electrodes e.g. 74% COD reduction by Jotin et al. ( 2012 ) and 70% COD reduction by Dia et al. ( 2017 ). The lower COD reduction efficiency is probably because the present study didn’t optimise the pH, ECF treatment time and voltage and current input. Although the COD removal was modest (21%), the specific energy requirement to achieve it was 1.35 kWh kg − 1 COD which is lower than the specific energy reported for some other landfill leachate treatment technologies. For example, electro-Fenton achieved 91.90-93.35% COD removal at 3.32–6.24 kWh kg − 1 COD (Li et al. 2022 ), electrochemical ceramic membrane filtration achieved 70.8% removal at 49.3 kWh kg − 1 and combined bipolar flocc-oxidation with electrobioreactor systems achieved 94.7% removals at 32.02 kWh kg − 1 COD (He et al. 2023 ). Although these comparative technologies target higher COD removals, the low specific energy requirement of ECF for moderate COD reduction suggests it may be a low-energy method for simultaneous microalgae separation and wastewater treatment. Aged landfill leachate contains high levels of recalcitrant humic and fulvic substances that impart COD and colour. Traditional biological treatment often struggles with these compounds, as indicated by BOD 5 /COD ratios that decline with landfill age from 0.5-1.0 (young) to 0.1 (aged) (Foo and Hameed 2009 ), reflecting the shift toward non-biodegradable organic matter. Studies comparing native and non-native biomass demonstrate that only indigenous organisms adapted to leachate can achieve > 75% COD removal, while conventional biomass achieves only ~ 40% due to inhibitory effects of humic substances (Corsino et al. 2020 ). ECF can aid in reduction of this recalcitrant COD through adsorption and sweep flocculation mechanisms. 5. Conclusions This study shows that ECF can recover microalgae from real landfill leachate at low electrical energy, achieving replicated recovery of 94.7–99.7% at 0.22–0.40 kWh kg − 1 TS, while delivering a measurable reduction in COD. Performance was demonstrated in a demanding matrix using time-resolved voltage–current logging and dual normalisation, providing a replicable benchmark. The combined microalgae separation and COD reduction support integration of microalgal processes into landfill leachate treatment for simultaneous waste treatment and resource recovery enabling circular economy at landfill sites. Declarations Code availability - Not Applicable . Competing interests – All authors declare no competing interests Funding - This contribution was jointly funded by Technische Hochschule Koln’s Initialförderung funding initiative and the project PLan_CV. The project PLan_CV (reference number 03FHP109) is funded by the German Federal Ministry of Education and Research (BMBF) and Joint Science Conference (GWK). Author Contribution Conceptualisation: Marvin Bruns, Himanshu Himanshu; Methodology: Marvin Bruns, Himanshu Himanshu, Alexander Kuss; Investigation: Marvin Bruns, Himanshu Himanshu; Formal analysis: Marvin Bruns, Himanshu Himanshu; Data curation: Marvin Bruns, Himanshu Himanshu; Visualisation: Marvin Bruns, Himanshu Himanshu; Writing – original draft: Marvin Bruns, Himanshu Himanshu; Writing – review and editing: Marvin Bruns, Himanshu Himanshu, Christian Wolf, Peter kern; Supervision: Himanshu Himanshu; Funding acquisition: Christian Wolf, Himanshu Himanshu, Acknowledgement The authors acknowledge the technical and logistical assistance provided by the landfill operator (Bergischer Abfallwirtschaftsverband, Engelskirchen). Data Availability Data supporting the findings of this study are available within the article. Raw data are available on request from the authors. References Abu-Shamleh A, Najjar YSH (2020) Optimization of mechanical harvesting of microalgae by centrifugation for biofuels production. Biomass Bioenergy 143:105877. https://doi.org/10.1016/j.biombioe.2020.105877 Asefaw KT, Bidira F, Desta WM, Asaithambi P (2024) Investigation on pulsed-electrocoagulation process for the treatment of wet coffee processing wastewater using an aluminum electrode. Sustainable Chemistry for the Environment 6:100085. https://doi.org/10.1016/j.scenv.2024.100085 Chen M, Chen Y, Zhang Q (2021) A review of energy consumption in the acquisition of bio-feedstock for microalgae biofuel production. Sustainability 13:8873. doi: 10.3390/su13168873 . Corsino SF, Capodici M, Di Trapani D, Torregrossa M, Viviani G (2020) Assessment of landfill leachate biodegradability and treatability by means of allochthonous and autochthonous. Journal of Chemical Technology and Biotechnology 55:91–97. https://doi.org/10.1016/j.nbt.2019.10.007 Danquah MK, Ang LM, Uduman N, Moheimani N, Forde GM (2009) Dewatering of microalgal culture for biodiesel production: exploring polymer flocculation and tangential flow filtration. J Chem Technol Biotechnol 84:1078–1083. https://doi.org/10.1002/jctb.2137 de Morais EG, Sampaio ICF, Gonzalez-Flo E, Ferrer I, Uggetti E, García J (2023) Microalgae harvesting for wastewater treatment and resources recovery: a review. N Biotechnol 78:84–94. https://doi.org/10.1016/j.nbt.2023.10.002 Dia O, Drogui P, Buelna G, Dubé R, Ben Salah Ihsen (2017) Electrocoagulation of bio-filtrated landfill leachate: fractionation of organic matter and influence of anode materials. Chemosphere 168:1136–1141. https://doi.org/10.1016/j.chemosphere.2016.10.092 Ezhumalai G, Arun M, Manavalan A, Rajkumar R, Heese K (2024) A holistic approach to circular bioeconomy through the sustainable utilization of microalgal biomass for biofuel and other value-added products. Microbial Ecology 87:61. https://doi.org/10.1007/s00248-024-02376-1 Foo KY, Hameed BH (2009) An overview of landfill leachate treatment via activated carbon adsorption process. Journal of Hazardous Materials 171:54–60. https://doi.org/10.1016/j.jhazmat.2009.06.038 Guldhe A, Misra R, Singh P, Rawat I, Bux F (2016) An innovative electrochemical process to alleviate the challenges for harvesting of small size microalgae by using non-sacrificial carbon electrodes. Algal Research 19:292–298. https://doi.org/10.1016/j.algal.2015.08.014 He H, Zhang C, Yang X, Huang B, Zhe J, Lai C, Liao Z, Pan X (2023) The efficient treatment of mature landfill leachate using tower bipolar electrode flocculation-oxidation combined with electrochemical biofilm reactors. Water Research 230:119544. https://doi.org/10.1016/j.watres.2022.119544 Ilhan F, Kurt U, Apaydin O, Gonullu MT (2008) Treatment of leachate by electrocoagulation using aluminum and iron electrodes. J Hazard Mater 154:381–389. https://doi.org/10.1016/j.jhazmat.2007.10.035 Jotin R, Ibrahim S, Halimoon N (2012) Electro coagulation for removal of chemical oxygen demand in sanitary landfill leachate. International Journal of Environmental Sciences 3:921–930. Khosla NK, Venkatachalam S, Somasundaran P (1991) Pulsed electrogeneration of bubbles for electroflotation. Journal of Applied Electrochemistry 21:986–990. https://doi.org/10.1007/BF01077584 Kuss A, Beszteri B, Beese-Vasbender P, Rehorek, A, Sartor, M. Growth and nutrient uptake of site-adapted microalgae in undiluted, high-strength landfill leachates. Journal of Applied Phycology (2025). https://doi.org/10.1007/s10811-025-03678-8 Li K, Liu Q, Fang F, Luo R, Lu Q, Zhou W, Huo S, Cheng P, Liu J, Addy M, Chen P, Chen D, Ruan R (2019) Microalgae-based wastewater treatment for nutrients recovery: a review. Bioresource Technology 291:121934. https://doi.org/10.1016/j.biortech.2019.121934 Li M, Zhou M, Qin X (2022) A feasible electro-Fenton treatment of landfill leachate diluted by electro-Fenton effluent: evaluation of operational parameters, effect of dilution ratio and assessment of treatment cost. Journal of Water Process Engineering 47:102754. https://doi.org/10.1016/j.jwpe.2022.102754 Lucakova S, Branyikova I, Kovacikova S, Pivokonsky M, Filipenska M, Branyik T, Ruzicka MC (2021) Electrocoagulation reduces harvesting costs for microalgae. Bioresource Technology 323:124606. https://doi.org/10.1016/j.biortech.2020.124606 McGrath SJ, Laamanen CA, Senhorinho GNA, Scott JA (2024) Microalgal harvesting for biofuels – options and associated operational costs. Algal Research 77:103343. https://doi.org/10.1016/j.algal.2023.103343 Molitor HR, Kim GY, Hartnett E, Gincley B, Alam MM, Feng J, Avila NM, Fisher A, Hodaei M, Li Y, McGraw K, Cusick RD, Bradley IM, Pinto AJ, Guest JS (2024) Intensive microalgal cultivation and tertiary phosphorus recovery from wastewaters via the EcoRecover process. Environmental Science & Technology 58:8803–8814. https://doi.org/10.1021/acs.est.3c10264 Renuka N, Sood A, Ratha SK, Prasanna R, Ahluwalia AS (2013) Nutrient sequestration, biomass production by microalgae and phytoremediation of sewage water. International Journal of Phytoremediation 15:789–800. https://doi.org/10.1080/15226514.2012.736436 Rookesh T, Samaei MR, Yousefinejad S, Hashemi H, Derakhshan Z, Abbasi F, Jalili M, Giannakis S, Bilal M (2022) Investigating the electrocoagulation treatment of landfill leachate by iron/graphite electrodes: process parameters and efficacy assessment. Water 14:205. https://doi.org/10.3390/w14020205 Shaikh SMR, Hassan MK, Nasser MS, Sayadi S, Ayesh AI, Vasagar V (2021) A comprehensive review on harvesting of microalgae using polyacrylamide-based flocculants: potentials and challenges. Separation and Purification Technology 277:119508. https://doi.org/10.1016/j.seppur.2021.119508 Vandamme D, Foubert I, Muylaert K (2013) Flocculation as a low-cost method for harvesting microalgae for bulk biomass production. Trends in Biotechnology 31:233–239. https://doi.org/10.1016/j.tibtech.2012.12.005 Vandamme D (2017) Harvesting, thickening and dewatering processes. In: Pires JCM (ed) Microalgae as a Source of Bioenergy: Products, Processes and Economics (Recent Advances in Renewable Energy, Vol 1). Bentham Science Publishers, pp 202–223. https://doi.org/10.2174/9781681085227117010010 Vandamme D, Pontes SCV, Goiris K, Foubert I, Pinoy LJJ, Muylaert K (2011) Evaluation of electro-coagulation-flocculation for harvesting marine and freshwater microalgae. Biotechnology and Bioengineering 108:2320–2329. https://doi.org/10.1002/bit.23199 Visigalli S, Barberis MG, Turolla A, Canziani R, Berden Zrimec M, Reinhardt R, Ficara E (2021) Electrocoagulation–flotation (ECF) for microalgae harvesting – a review. Separation and Purification Technology 271:118684. https://doi.org/10.1016/j.seppur.2021.118684 Xu K, Zou X, Mouradov A, Spangenberg G, Chang W, Li Y (2021) Efficient bioflocculation of Chlorella vulgaris with a chitosan and walnut protein extract. Biology 10:352. https://doi.org/10.3390/biology10050352 Zhu L, Li Z, Hiltunen E (2018) Microalgae Chlorella vulgaris biomass harvesting by natural flocculant: effects on biomass sedimentation, spent medium recycling and lipid extraction. Biotechnology for Biofuels 11:183. https://doi.org/10.1186/s13068-018-1183-z Additional Declarations No competing interests reported. Supplementary Files CurrentPlot.xlsx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 12 Feb, 2026 Reviews received at journal 15 Jan, 2026 Reviews received at journal 24 Dec, 2025 Reviewers agreed at journal 23 Dec, 2025 Reviewers agreed at journal 19 Dec, 2025 Reviewers agreed at journal 18 Dec, 2025 Reviewers invited by journal 18 Dec, 2025 Editor assigned by journal 18 Dec, 2025 Submission checks completed at journal 16 Dec, 2025 First submitted to journal 14 Dec, 2025 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-8360370","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":563230188,"identity":"b4b8c858-e294-4b2d-b35a-65726252fbf6","order_by":0,"name":"Marvin Bruns","email":"","orcid":"","institution":"Metabolon Institute, TH Köln - University of Applied Sciences","correspondingAuthor":false,"prefix":"","firstName":"Marvin","middleName":"","lastName":"Bruns","suffix":""},{"id":563230190,"identity":"ef7247ec-86d5-4ced-b1c1-cb43315c9d88","order_by":1,"name":"Alexander Kuss","email":"","orcid":"","institution":"Metabolon Institute, TH Köln - University of Applied Sciences","correspondingAuthor":false,"prefix":"","firstName":"Alexander","middleName":"","lastName":"Kuss","suffix":""},{"id":563230192,"identity":"8b096675-8447-4a27-8746-9be72a9f218e","order_by":2,"name":"Peter Kern","email":"","orcid":"","institution":"Metabolon Institute, TH Köln - University of Applied Sciences","correspondingAuthor":false,"prefix":"","firstName":"Peter","middleName":"","lastName":"Kern","suffix":""},{"id":563230194,"identity":"6196f395-fa67-4753-8aa8-112dbcf598fe","order_by":3,"name":"Christian Wolf","email":"","orcid":"","institution":"Metabolon Institute, TH Köln - University of Applied Sciences","correspondingAuthor":false,"prefix":"","firstName":"Christian","middleName":"","lastName":"Wolf","suffix":""},{"id":563230200,"identity":"344f5f54-aaca-4de4-abf9-099bccb38388","order_by":4,"name":"Himanshu Himanshu","email":"data:image/png;base64,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","orcid":"","institution":"Metabolon Institute, TH Köln - University of Applied Sciences","correspondingAuthor":true,"prefix":"","firstName":"Himanshu","middleName":"","lastName":"Himanshu","suffix":""}],"badges":[],"createdAt":"2025-12-14 22:08:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8360370/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8360370/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":98899203,"identity":"aac8bed4-b71a-4dc3-b26e-0f17f9676f87","added_by":"auto","created_at":"2025-12-23 18:41:24","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":86286,"visible":true,"origin":"","legend":"","description":"","filename":"Bruns2025SimultaneousmicroalgaeNoendnotev1.2.docx","url":"https://assets-eu.researchsquare.com/files/rs-8360370/v1/ffb62fe29621c7060e6e25ff.docx"},{"id":99309874,"identity":"2c39b818-5691-4411-9102-86fbb3b35320","added_by":"auto","created_at":"2025-12-31 16:11:19","extension":"json","order_by":1,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":6706,"visible":true,"origin":"","legend":"","description":"","filename":"0a2987669c5748a486a15ca2865fe44b.json","url":"https://assets-eu.researchsquare.com/files/rs-8360370/v1/ed5a31318f654b29c265f757.json"},{"id":99310025,"identity":"8d59d988-79c7-49fa-9db9-67e54dd1bb9b","added_by":"auto","created_at":"2025-12-31 16:11:40","extension":"xlsx","order_by":2,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":396181,"visible":true,"origin":"","legend":"","description":"","filename":"CurrentPlot.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-8360370/v1/ece52cef3260133794b87e31.xlsx"},{"id":98899210,"identity":"47f60d01-4c22-48f4-bd49-14d7adec635e","added_by":"auto","created_at":"2025-12-23 18:41:24","extension":"xml","order_by":3,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":88473,"visible":true,"origin":"","legend":"","description":"","filename":"0a2987669c5748a486a15ca2865fe44b1enriched.xml","url":"https://assets-eu.researchsquare.com/files/rs-8360370/v1/ce0cf3a252bffe12af105801.xml"},{"id":98899204,"identity":"6f37e402-cbb8-4b05-af47-55e748c98e4e","added_by":"auto","created_at":"2025-12-23 18:41:24","extension":"png","order_by":4,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":46362,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8360370/v1/4905a5307b40e0d2d303dc82.png"},{"id":99787941,"identity":"52cf7926-5501-4a83-9c96-2e73bc3c8c96","added_by":"auto","created_at":"2026-01-08 12:42:01","extension":"png","order_by":5,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":4879,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8360370/v1/3bcc42f6fb6597dadbaf6912.png"},{"id":98899207,"identity":"d97cee17-7ff7-4802-b800-8f61ac9413f6","added_by":"auto","created_at":"2025-12-23 18:41:24","extension":"png","order_by":6,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":38546,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8360370/v1/7314f9b253b35d3aebf78056.png"},{"id":99309663,"identity":"509503f3-b50c-480a-8ed4-d60d1d1ee835","added_by":"auto","created_at":"2025-12-31 16:10:55","extension":"png","order_by":7,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":3806,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8360370/v1/8d84e856a87d755a2c2afab1.png"},{"id":98899212,"identity":"19d8e354-7985-48a7-a23d-b84b2f24e133","added_by":"auto","created_at":"2025-12-23 18:41:24","extension":"xml","order_by":8,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":89069,"visible":true,"origin":"","legend":"","description":"","filename":"0a2987669c5748a486a15ca2865fe44b1structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8360370/v1/e41769b45d088d03f42b6a36.xml"},{"id":98899213,"identity":"20748b4c-207b-48af-90e5-dadb2741603f","added_by":"auto","created_at":"2025-12-23 18:41:24","extension":"html","order_by":9,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":93533,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8360370/v1/8f00b5c3d935260f8171c08b.html"},{"id":98899202,"identity":"59ef38e9-df67-4ec5-b456-b2bd7b2f0cdd","added_by":"auto","created_at":"2025-12-23 18:41:23","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":46362,"visible":true,"origin":"","legend":"\u003cp\u003eCurrent profile during ECF of high-biomass culture in real landfill leachate. Voltage mode: 5.0 V for 0.1 s and 1.5 V for 29.9 s per 30 s cycle. Current sampled at 1 Hz. Baseline remained stable at about 0.20–0.26 A over 30 minutes. Single-point peaks occur when sampling coincides with the 0.1 s pulse. Full raw logs are provided in Supplementary\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8360370/v1/ec5037a1a8ead7ddf7eaf12c.png"},{"id":99309894,"identity":"945e9c7e-a3ca-42af-abc7-d640ee64202a","added_by":"auto","created_at":"2025-12-31 16:11:20","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":12116,"visible":true,"origin":"","legend":"\u003cp\u003eTotal COD for raw leachate, leachate after 24 h microalgae (low biomass concentration) growth and post ECF landfill leachate. Bars show mean ± SD, n=3\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8360370/v1/9e45610955395c8095c247c5.png"},{"id":100803962,"identity":"73031f91-32a5-4bcc-b9df-8a486a706000","added_by":"auto","created_at":"2026-01-21 14:31:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":654866,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8360370/v1/293fb48a-12b0-496b-b8ce-cb01ab92763e.pdf"},{"id":98899209,"identity":"3d7c6e4b-8f18-48a0-8a3b-17596ceda85d","added_by":"auto","created_at":"2025-12-23 18:41:24","extension":"xlsx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":396181,"visible":true,"origin":"","legend":"","description":"","filename":"CurrentPlot.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-8360370/v1/a6a77a6797bee6f5645650c0.xlsx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Simultaneous microalgae separation and COD reduction from landfill leachate using electrocoagulation-flotation","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eMicroalgae can play a significant role in advancing the circular economy, offering proven potential for wastewater treatment and the recovery of key nutrients such as carbon, nitrogen, and phosphorus (Li et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Molitor et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). In addition to these benefits, microalgae provide valuable ecosystem services, including carbon capture, storage, and utilization through CO\u003csub\u003e2\u003c/sub\u003e absorption, while simultaneously producing value-added products such as biofuels and nutraceuticals (Ezhumalai et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). However, despite these advantages, the large-scale adoption of microalgae-based processes is limited by challenges in downstream processing. Notably, biomass separation and harvesting can account for up to 30% of process costs and 20\u0026ndash;30% of the total process energy input, due to the difficulty of separating small, near-neutrally buoyant microalgae cells (Renuka et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Chen et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Shaikh et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSeveral technologies have been developed for microalgae separation, each with distinct advantages and disadvantages. For example, sedimentation is highly energy efficient 0.05\u0026ndash;0.1 kWh m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e and has low capital costs (\u0026euro;0.03 m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), but it achieves only modest concentrations of 0.5-3 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e total suspended solids and requires long retention times due to the low intrinsic settling velocity (~\u0026thinsp;1 cm h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) of microalgae cells, which have a density similar to water (Vandamme \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Chemical flocculation can achieve high separation efficiency (95\u0026ndash;99%) with relatively low energy requirements, as energy is primarily needed for mixing. However, it faces significant drawbacks for large-scale application, including high operational costs for organic flocculants (e.g. chitosan 20\u0026ndash;50 USD kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Xu et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), and contamination of the recovered microalgae due to residual flocculants. Inorganic flocculants (alum, ferric chloride) can leave behind residual salts and metal ions, while organic polymers (chitosan, polyacrylamide) may introduce residual polymer chains that complicate downstream biomass utilization (Zhu et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Centrifugation offers high separation efficiency (90\u0026ndash;98%) with short treatment times (minutes), but requires the highest specific energy (8\u0026ndash;20 kWh m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) among common methods and involves significant capital costs (Abu-Shamleh and Najjar \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; McGrath et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eElectrocoagulation flotation (ECF) has emerged as a technology for microalgae separation that offers high separation efficiency, low energy demand, short treatment times, and low operational costs. For example Guldhe et al. (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) reported 91% separation efficiency of \u003cem\u003eAnkistrodesmus falcatus\u003c/em\u003e in 30 minutes, outperforming chitosan at 55% and alum at 86% after 60 minutes. The same study reported ECF energy consumption can be orders of magnitude lower than centrifugation i.e. 1.8 kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for ECF versus 65.3 kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for centrifugation at similar recovery. Lucakova et al. (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) reported that adding an electrocoagulation pre-concentration step (using stainless steel cathode and carbon steel anode for \u003cem\u003eChlorella\u003c/em\u003e) before centrifugation reduced total separation energy to 0.136 kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, energy savings of up to 89% relative to stand-alone centrifugation. In addition Lucakova et al. (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), using ECF with iron electrodes, demonstrated the harvested \u003cem\u003eChlorella\u003c/em\u003e biomass had the iron content within food/feed safety limits.\u003c/p\u003e \u003cp\u003eMechanistically, during ECF aluminum and/or iron is oxidized at the anode, releasing Al\u003csup\u003e3+\u003c/sup\u003e and Fe\u003csup\u003e2+\u003c/sup\u003e/Fe\u003csup\u003e3+\u003c/sup\u003e ions that produce metallic hydroxides which destabilise negatively charged microalgae cells by charge neutralisation and sweep flocculation. Simultaneously, cathodically produced hydrogen microbubbles attach to the flocs and float them to the surface for easy skimming. Unlike chemical coagulation, ECF does not introduce additional anions into the solution beyond OH\u003csup\u003e\u0026minus;\u003c/sup\u003e generated at the cathode and the \u003cem\u003ein-situ\u003c/em\u003e release of multivalent cations be tightly controlled by controlling the current reducing the risk of overdosing (Visigalli et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eElectrocoagulation has also been reported as an effective treatment for wastewaters, including for chemical oxygen demand (COD) reduction. For example Asefaw et al. (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) reported 98% COD removal from coffee wastewater using electrocoagulation. In landfill leachate Rookesh et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) reported a reduction of 30% COD and 84% NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e using electrocoagulation with Fe\u0026ndash;graphite electrodes. The mechanism for COD reduction is similar to that for microalgae separation: Al\u003csup\u003e3+\u003c/sup\u003e generated at the anode hydrolyses to form amorphous Al(OH)\u003csub\u003e3\u003c/sub\u003e, which destabilizes colloids and adsorbs dissolved organics, while H\u003csub\u003e2\u003c/sub\u003e produced at the cathode assists flotation. However, in the case of landfill leachate, COD reduction is primarily driven by adsorption and sweep-flocculation of dissolved organics into Al(OH)\u003csub\u003e3\u003c/sub\u003e, and in chloride-rich matrices at higher anode potentials, indirect oxidation via \u003cem\u003ein situ\u003c/em\u003e chlorine/hypochlorite may also occur (Jotin et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDespite these advances, several gaps remain in the application of ECF for microalgae separation in real wastewaters. Most studies have focused on single species in synthetic media or clean water, limiting the transferability of results to coloured, saline and highly conductive real-life wastewaters such as landfill leachates (Visigalli et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Additionally, energy reporting is often incomplete, as many studies do not log time-resolved voltage and current to accurately integrate the true electrical energy input. Only a limited number of studies have reported both volumetric (kWh m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) and mass-based (kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e dry biomass) normalisations. Recent guidelines recommends using specific electro-energy consumption per unit dry mass (kWh kg TS\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) for comparability and volumetric electro-energy consumption (kWh m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) for reactor-scale context (Visigalli et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Finally, to date, there are no reports in the literature on simultaneous microalgae separation using ECF/electrocoagulation and COD reduction in real landfill leachate.\u003c/p\u003e \u003cp\u003eThe aim of this study is to evaluate ECF in real landfill leachate to achieve simultaneous microalgae separation and COD reduction, using a mixed microalgal consortium grown in the same leachate. To the author\u0026rsquo;s knowledge, this provides the first demonstration of simultaneous microalgae separation and COD reduction in real landfill leachate using ECF.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Matrix and microalgae\u003c/h2\u003e \u003cp\u003eLandfill leachate was collected at the :metabolon site (Lindlar, Germany) and inoculated with a working culture consisting of indigenous \u003cem\u003eChlorella sorokiniana\u003c/em\u003e collected from this landfill site and adapted to growth in the same leachate matrix, without any micro- or macronutrient supplementation. The microalgae was identified by nuclear ribosomal ITS sequences determined from three different strains available under GenBank accession numbers PX210920-PX210922 (Kuss et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). The microalgae biomass was produced at two different optical densities i.e. OD\u003csub\u003e680\u003c/sub\u003e 0.3 (L1, L2 and L3) and 2.2 (H1, H2 and H3). The microalgae were grown in sealed 1-L Erlenmeyer flasks at 22\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C and continuously mixed with a magnetic stirrer at 150\u0026ndash;200 rpm and illuminated by LED lights at an intensity of 150\u0026ndash;200 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in a 14/10 h light-dark cycle.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 ECF experimental setup\u003c/h2\u003e \u003cp\u003eAll ECF batch tests were performed in triplicate in a custom acrylic reactor with internal dimensions 100 \u0026times; 95 \u0026times; 65 mm and a working volume of 0.5 L. Unless stated otherwise, values are reported as arithmetic mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD). n denotes the number of independent biological replicates, defined here as independent ECF batch runs performed on independently prepared cultures for each condition (L1L3 for low biomass; H1\u0026ndash;H3 for high biomass; n\u0026thinsp;=\u0026thinsp;3 per condition). The electrochemical cell comprised two parallel aluminium plates mounted in a 3D-printed holder, separated by an inter-electrode gap of 2 mm. The effective anode area was 75 cm\u0026sup2; (50 \u0026times; 75 mm facing surfaces on both sides). UNI-T UDP3305S-E laboratory power supply operated in voltage mode delivered a low-duty pulsed waveform for 30 minutes with each 30 s cycle comprised 5.0 V applied for 0.1 s followed by 1.5 V for 29.9 s (duty 0.33%). For the high-biomass runs (H1\u0026ndash;H3), voltage and current were logged at 1 Hz from the power supply. For the low-biomass runs (L1\u0026ndash;L3), a logging fault occurred with automatic recorder, so the current and voltage were documented by manual readings taken every 6 minutes. Integrated electrical energy and charge for L1\u0026ndash;L3 were computed from the manual reading. The 1 Hz sampling and 0.1 s pulse on-time mean that only a fraction of individual pulses appear in the time series and the peak capture is probabilistic and does not reflect instability. During ECF the microalgae culture was mixed at 250 rpm with a magnetic stirrer. After the 30 minute ECF test the mixing was stopped and the foam/floc layer was allowed to form for 60 minutes. The clarified growth medium was then collected using a pipette from below the foam/floc layer. The residual foam/floc layer was dried at 105\u0026deg;C for 48 hours to determine the dry matter content. The total COD of raw landfill leachate, low biomass density microalgae culture i.e. optical density at 680 nm (OD\u003csub\u003e680\u003c/sub\u003e) 0.3 (after 24 hour of incubation) and the clarified culture medium after ECF was analysed by the dichromate method (ISO 6060/DIN 38409 H41/H44) using Hach-Lange LCK514 (100\u0026ndash;2000 mg O\u003csub\u003e2\u003c/sub\u003e L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). pH measured before and after ECF treatment using Si analytics tritroline 6000.\u003c/p\u003e \u003cp\u003eMean current density was obtained by dividing the time-averaged current by the effective anode area of 75 cm\u003csup\u003e2\u003c/sup\u003e. Specific energy demand per unit treated volume (kWh m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) was calculated by dividing the integrated electrical work by the treated volume. Specific energy per unit of biomass separated (kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e TS) was calculated by dividing the integrated electrical work by the product of capture efficiency, treated volume and initial biomass concentration expressed as total solids. Capture efficiency was determined from the reduction in OD₆₈₀ of the supernatant between the initial and final samples.\u003c/p\u003e \u003cp\u003eElectrode mass loss and residual aluminium in the effluent were not measured in this preliminary study. However, the theoretical aluminium dose was computed using Eq.\u0026nbsp;1 from Faraday\u0026rsquo;s law where Q is electric charge in coulomb (C), t is time in seconds, M is molar mass of aluminium (26.98 g mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), z is the valence of Aluminum ions i.e. 3 and F is the Faraday\u0026rsquo;s constant (96485 C mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and is reported as mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e per run (Visigalli et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{m}_{Al}\\left(mg{\\:L}^{-1}\\right)=\\frac{QM1000}{zFV\\left(L\\right)}\\)\u003c/span\u003e \u003c/span\u003e (Eq.\u0026nbsp;1)\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cp\u003eECF achieved a consistently high level of microalgae separation efficiency in both low- (99.7%) and high-biomass (94.75%) microalgae cultures (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The specific electro-energy consumption per unit dry mass for low- and high-biomass cultures was 0.395\u0026thinsp;\u0026plusmn;\u0026thinsp;0.014 kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e TS and 0.222\u0026thinsp;\u0026plusmn;\u0026thinsp;0.025 kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e TS, respectively and volumetric electro-energy consumption was 0.332 kWh m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e and 0.383 kWh m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, respectively. The reported figures include only electrical work at the electrodes and exclude supply losses, mixing and controls The mean current density under the imposed waveform was ~\u0026thinsp;3 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (referenced to the 75 cm\u0026sup2; anode area). Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the current profile for high-biomass microalgae culture. The baseline rose during the first 3\u0026ndash;5 min then remained near 0.20\u0026ndash;0.26 A over 30 min. Single-point peaks appear when the 1 Hz sample coincided with the 0.1 s, 5.0 V pulse. The peak incidence varies with logger-pulse phase and does not indicate instability.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTheoretical aluminium release was calculated from the time-integrated current using Faraday\u0026rsquo;s law with aluminium valency of 3. As shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e the calculated average aluminium doses were 78.4\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 85.0\u0026thinsp;\u0026plusmn;\u0026thinsp;12.1 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for low and biomass microalgae cultures, respectively. The corresponding charges were 420.6\u0026thinsp;\u0026plusmn;\u0026thinsp;13 C and 456.5\u0026thinsp;\u0026plusmn;\u0026thinsp;65 C, respectively. Residual dissolved aluminium in the clarified phase and gravimetric electrode mass loss were not measured in this study.\u003c/p\u003e \u003cp\u003eThe total COD of the landfill leachate increased from 715.0\u0026thinsp;\u0026plusmn;\u0026thinsp;12.3 mg O\u003csub\u003e2\u003c/sub\u003e L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the raw leachate to 808.5\u0026thinsp;\u0026plusmn;\u0026thinsp;11.5 mg O\u003csub\u003e2\u003c/sub\u003e L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e after incubation with microalgae for the low biomass microalgae culture. Following the ECF treatment, the COD of the clarified (unfiltered) landfill leachate without microalgae declined to 564.3\u0026thinsp;\u0026plusmn;\u0026thinsp;13.6 mg O\u003csub\u003e2\u003c/sub\u003e L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This corresponds to a reduction of roughly 30% relative to the culture and 21% relative to the raw landfill leachate. Expressed as specific energy per unit COD removed, the ECF process consumed 1.35 kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e COD, calculated from the volumetric energy (0.33 kWh m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) divided by the mass-based COD removal (244.2 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e = 0.2442 kg COD m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e). The pH of landfill leachate did not change during the ECF treatment and it was 8.3 for both raw and ECF treated leachate.\u003c/p\u003e \u003cp\u003e \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\u003eCharge, energy input and theoretical aluminium dose during ECF. Values are from three independent biological replicates per condition (L1\u0026ndash;L3 and H1\u0026ndash;H3; n\u0026thinsp;=\u0026thinsp;3). Mean (SD) is reported in parentheses. TS\u0026thinsp;=\u0026thinsp;total solids. Theoretical Al dose calculated from Faraday\u0026rsquo;s law; separation efficiency from OD\u003csub\u003e680\u003c/sub\u003e reduction\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=\"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=\"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=\"char\" char=\".\" 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\"\u003e \u003cp\u003eID\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBiomass\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCharge Q (C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eEnergy input (mWh)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTheoretical Al dose\u003c/p\u003e \u003cp\u003e(mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSpecific energy\u003c/p\u003e \u003cp\u003e(kWh m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSpecific energy\u003c/p\u003e \u003cp\u003e(kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e TS)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eSeparation efficiency\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eL1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLow\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e423.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e176.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e78.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.353\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.404\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e99.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eL2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLow\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e432.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e180.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e80.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.360\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.380\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e99.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eL3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLow\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e406.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e141.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e75.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.283\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.380\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e99.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean (SD)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e420.6 (13)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e165.9 (21.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e78.4 (2.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.332 (0.04)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.395 (0.01)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e99.7 (0.2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHigh\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e477.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e198.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e88.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.397\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.233\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e96.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHigh\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e508.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e215.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e94.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.431\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.240\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e94.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHigh\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e383.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e159.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e71.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.319\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.194\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e92.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean (SD)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e456.5 (65)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e191.3 (28.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e85.0 (12.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.383 (0.06)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.222 (0.03)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e94.7 (1.9)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThis study tested whether ECF, in real landfill leachate, can simultaneously deliver microalgal separation and COD reduction. ECF achieved high microalgae separation efficiencies for both biomass concentrations, with a slightly lower efficiency observed at higher biomass. This reduction is likely due to increased floc loading and carry-through in the clarified layer, rather than ineffective destabilization. The high separation efficiencies are comparable to the high recoveries for ECF reported in literature for the conductive media and optimised ECF processes by Vandamme et al. (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), Visigalli et al. (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), and de Morais et al. (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The presence of various constituents e.g. dissolved organics, salts etc in the landfill leachate did not prevent efficient microalgae aggregation and flotation while these constituents have been reported to sometimes inhibit flocculation (Vandamme et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe separation efficiency of the present study is comparable to state-of-the-art high-separation-efficiency methods, such as chemical flocculation, but without the need for chemical flocculants. For example, chitosan flocculation of \u003cem\u003eChlorella sorokiniana\u003c/em\u003e achieved\u0026thinsp;\u0026gt;\u0026thinsp;99% clarification efficiency (Xu et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), while the present study achieved 94.7\u0026ndash;99.7% separation efficiency. The separation efficiency of present study compared to some of the established mechanical microalgae separation methods e.g. centrifugation are very similar but the energy requirement for ECF is one to two order of magnitude lower than centrifugation (Danquah et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Guldhe et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). For comparison among ECF methods for microalgae separation, the specific energy demand for both high and low biomass concentration cultures in this study is an order of magnitude lower than typical energy consumptions reported for freshwater media. e.g. Vandamme et al. (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) reported a specific energy requirement of 2 kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for \u003cem\u003eChlorella vulgaris\u003c/em\u003e in fresh culture. However, the specific energy requirements observed here are comparable to those in saline conditions, where Vandamme et al. (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) reported 0.3 kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for \u003cem\u003ePhaeodactylum tricornutum\u003c/em\u003e separation in seawater. The mass-based specific energy decreased at higher biomass because more dry solids were removed per unit electrical work, while the volumetric energy remained similar since the batch electrical work was comparable (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBaseline current in the logged runs for high biomass microalgae culture remained stable over 30 minutes, with occasional single-point peaks when sampling coincided with the 0.1 s pulse (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The lack of current drift suggests sustained electrode activity, likely due to reduced buildup of insulating oxide on the aluminium anode, which can occur during constant DC voltage application (Jotin et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Another advantage of pulsed voltage application is that the interrupted current promotes rapid nucleation and detachment of small bubbles, which can improve attachment to fine microalgae flocs. Smaller bubbles provide a larger total surface area, thereby improving flotation efficacy (Khosla et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1991\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe total COD of the treated landfill leachate decreased 30% relative to the microalgae culture and 21% relative to the raw landfill leachate. This decrease likely combines removal of microalgal particulates formed during incubation with adsorption and sweep-flocculation of dissolved organics by \u003cem\u003ein situ\u003c/em\u003e Al(OH)\u003csub\u003e3\u003c/sub\u003e formed at the anode, aided by H\u003csub\u003e2\u003c/sub\u003e flotation at the cathode. These mechanisms and their pH-dependent speciation are well established for EC in leachate, with COD removal generally maximised between pH 4 and 8 when amorphous Al(OH)\u003csub\u003e3\u003c/sub\u003e dominates the speciation (Jotin et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). The COD reduction is comparable to EC studies using iron electrode e.g. 32.4% COD reduction by Rookesh et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) and 35% COD reduction by Ilhan et al. (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) in landfill leachate at near-neutral pH. However, the present COD reduction is lower than the EC studies which have used Al electrodes e.g. 74% COD reduction by Jotin et al. (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) and 70% COD reduction by Dia et al. (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The lower COD reduction efficiency is probably because the present study didn\u0026rsquo;t optimise the pH, ECF treatment time and voltage and current input.\u003c/p\u003e \u003cp\u003eAlthough the COD removal was modest (21%), the specific energy requirement to achieve it was 1.35 kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e COD which is lower than the specific energy reported for some other landfill leachate treatment technologies. For example, electro-Fenton achieved 91.90-93.35% COD removal at 3.32\u0026ndash;6.24 kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e COD (Li et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), electrochemical ceramic membrane filtration achieved 70.8% removal at 49.3 kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and combined bipolar flocc-oxidation with electrobioreactor systems achieved 94.7% removals at 32.02 kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e COD (He et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Although these comparative technologies target higher COD removals, the low specific energy requirement of ECF for moderate COD reduction suggests it may be a low-energy method for simultaneous microalgae separation and wastewater treatment.\u003c/p\u003e \u003cp\u003eAged landfill leachate contains high levels of recalcitrant humic and fulvic substances that impart COD and colour. Traditional biological treatment often struggles with these compounds, as indicated by BOD\u003csub\u003e5\u003c/sub\u003e/COD ratios that decline with landfill age from 0.5-1.0 (young) to 0.1 (aged) (Foo and Hameed \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2009\u003c/span\u003e), reflecting the shift toward non-biodegradable organic matter. Studies comparing native and non-native biomass demonstrate that only indigenous organisms adapted to leachate can achieve\u0026thinsp;\u0026gt;\u0026thinsp;75% COD removal, while conventional biomass achieves only\u0026thinsp;~\u0026thinsp;40% due to inhibitory effects of humic substances (Corsino et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). ECF can aid in reduction of this recalcitrant COD through adsorption and sweep flocculation mechanisms.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eThis study shows that ECF can recover microalgae from real landfill leachate at low electrical energy, achieving replicated recovery of 94.7\u0026ndash;99.7% at 0.22\u0026ndash;0.40 kWh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e TS, while delivering a measurable reduction in COD. Performance was demonstrated in a demanding matrix using time-resolved voltage\u0026ndash;current logging and dual normalisation, providing a replicable benchmark. The combined microalgae separation and COD reduction support integration of microalgal processes into landfill leachate treatment for simultaneous waste treatment and resource recovery enabling circular economy at landfill sites.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCode availability\u003c/strong\u003e - \u003cem\u003eNot Applicable\u003c/em\u003e.\u003c/p\u003e\u003cp\u003e \u003ch2\u003e \u003cb\u003eCompeting interests\u003c/b\u003e \u0026ndash;\u003c/h2\u003e \u003cp\u003eAll authors declare no competing interests\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding -\u003c/h2\u003e \u003cp\u003eThis contribution was jointly funded by Technische Hochschule Koln\u0026rsquo;s Initialf\u0026ouml;rderung funding initiative and the project PLan_CV. The project PLan_CV (reference number 03FHP109) is funded by the German Federal Ministry of Education and Research (BMBF) and Joint Science Conference (GWK).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualisation: Marvin Bruns, Himanshu Himanshu; Methodology: Marvin Bruns, Himanshu Himanshu, Alexander Kuss; Investigation: Marvin Bruns, Himanshu Himanshu; Formal analysis: Marvin Bruns, Himanshu Himanshu; Data curation: Marvin Bruns, Himanshu Himanshu; Visualisation: Marvin Bruns, Himanshu Himanshu; Writing \u0026ndash; original draft: Marvin Bruns, Himanshu Himanshu; Writing \u0026ndash; review and editing: Marvin Bruns, Himanshu Himanshu, Christian Wolf, Peter kern; Supervision: Himanshu Himanshu; Funding acquisition: Christian Wolf, Himanshu Himanshu,\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors acknowledge the technical and logistical assistance provided by the landfill operator (Bergischer Abfallwirtschaftsverband, Engelskirchen).\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData supporting the findings of this study are available within the article. Raw data are available on request from the authors.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAbu-Shamleh A, Najjar YSH (2020) Optimization of mechanical harvesting of microalgae by centrifugation for biofuels production. Biomass Bioenergy 143:105877. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.biombioe.2020.105877\u003c/span\u003e\u003cspan address=\"10.1016/j.biombioe.2020.105877\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAsefaw KT, Bidira F, Desta WM, Asaithambi P (2024) Investigation on pulsed-electrocoagulation process for the treatment of wet coffee processing wastewater using an aluminum electrode. Sustainable Chemistry for the Environment 6:100085. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scenv.2024.100085\u003c/span\u003e\u003cspan address=\"10.1016/j.scenv.2024.100085\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen M, Chen Y, Zhang Q (2021) A review of energy consumption in the acquisition of bio-feedstock for microalgae biofuel production. Sustainability 13:8873. doi:\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/su13168873\u003c/span\u003e\u003cspan address=\"10.3390/su13168873\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCorsino SF, Capodici M, Di Trapani D, Torregrossa M, Viviani G (2020) Assessment of landfill leachate biodegradability and treatability by means of allochthonous and autochthonous. Journal of Chemical Technology and Biotechnology 55:91\u0026ndash;97. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.nbt.2019.10.007\u003c/span\u003e\u003cspan address=\"10.1016/j.nbt.2019.10.007\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDanquah MK, Ang LM, Uduman N, Moheimani N, Forde GM (2009) Dewatering of microalgal culture for biodiesel production: exploring polymer flocculation and tangential flow filtration. J Chem Technol Biotechnol 84:1078\u0026ndash;1083. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/jctb.2137\u003c/span\u003e\u003cspan address=\"10.1002/jctb.2137\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ede Morais EG, Sampaio ICF, Gonzalez-Flo E, Ferrer I, Uggetti E, Garc\u0026iacute;a J (2023) Microalgae harvesting for wastewater treatment and resources recovery: a review. N Biotechnol 78:84\u0026ndash;94. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.nbt.2023.10.002\u003c/span\u003e\u003cspan address=\"10.1016/j.nbt.2023.10.002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDia O, Drogui P, Buelna G, Dub\u0026eacute; R, Ben Salah Ihsen (2017) Electrocoagulation of bio-filtrated landfill leachate: fractionation of organic matter and influence of anode materials. Chemosphere 168:1136\u0026ndash;1141. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.chemosphere.2016.10.092\u003c/span\u003e\u003cspan address=\"10.1016/j.chemosphere.2016.10.092\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEzhumalai G, Arun M, Manavalan A, Rajkumar R, Heese K (2024) A holistic approach to circular bioeconomy through the sustainable utilization of microalgal biomass for biofuel and other value-added products. Microbial Ecology 87:61. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00248-024-02376-1\u003c/span\u003e\u003cspan address=\"10.1007/s00248-024-02376-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFoo KY, Hameed BH (2009) An overview of landfill leachate treatment via activated carbon adsorption process. Journal of Hazardous Materials 171:54\u0026ndash;60. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jhazmat.2009.06.038\u003c/span\u003e\u003cspan address=\"10.1016/j.jhazmat.2009.06.038\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuldhe A, Misra R, Singh P, Rawat I, Bux F (2016) An innovative electrochemical process to alleviate the challenges for harvesting of small size microalgae by using non-sacrificial carbon electrodes. Algal Research 19:292\u0026ndash;298. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.algal.2015.08.014\u003c/span\u003e\u003cspan address=\"10.1016/j.algal.2015.08.014\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHe H, Zhang C, Yang X, Huang B, Zhe J, Lai C, Liao Z, Pan X (2023) The efficient treatment of mature landfill leachate using tower bipolar electrode flocculation-oxidation combined with electrochemical biofilm reactors. Water Research 230:119544. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.watres.2022.119544\u003c/span\u003e\u003cspan address=\"10.1016/j.watres.2022.119544\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIlhan F, Kurt U, Apaydin O, Gonullu MT (2008) Treatment of leachate by electrocoagulation using aluminum and iron electrodes. J Hazard Mater 154:381\u0026ndash;389. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jhazmat.2007.10.035\u003c/span\u003e\u003cspan address=\"10.1016/j.jhazmat.2007.10.035\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJotin R, Ibrahim S, Halimoon N (2012) Electro coagulation for removal of chemical oxygen demand in sanitary landfill leachate. International Journal of Environmental Sciences 3:921\u0026ndash;930.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKhosla NK, Venkatachalam S, Somasundaran P (1991) Pulsed electrogeneration of bubbles for electroflotation. Journal of Applied Electrochemistry 21:986\u0026ndash;990. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/BF01077584\u003c/span\u003e\u003cspan address=\"10.1007/BF01077584\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKuss A, Beszteri B, Beese-Vasbender P, Rehorek, A, Sartor, M. Growth and nutrient uptake of site-adapted microalgae in undiluted, high-strength landfill leachates. Journal of Applied Phycology (2025). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s10811-025-03678-8\u003c/span\u003e\u003cspan address=\"10.1007/s10811-025-03678-8\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi K, Liu Q, Fang F, Luo R, Lu Q, Zhou W, Huo S, Cheng P, Liu J, Addy M, Chen P, Chen D, Ruan R (2019) Microalgae-based wastewater treatment for nutrients recovery: a review. Bioresource Technology 291:121934. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.biortech.2019.121934\u003c/span\u003e\u003cspan address=\"10.1016/j.biortech.2019.121934\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi M, Zhou M, Qin X (2022) A feasible electro-Fenton treatment of landfill leachate diluted by electro-Fenton effluent: evaluation of operational parameters, effect of dilution ratio and assessment of treatment cost. Journal of Water Process Engineering 47:102754. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jwpe.2022.102754\u003c/span\u003e\u003cspan address=\"10.1016/j.jwpe.2022.102754\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLucakova S, Branyikova I, Kovacikova S, Pivokonsky M, Filipenska M, Branyik T, Ruzicka MC (2021) Electrocoagulation reduces harvesting costs for microalgae. Bioresource Technology 323:124606. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.biortech.2020.124606\u003c/span\u003e\u003cspan address=\"10.1016/j.biortech.2020.124606\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMcGrath SJ, Laamanen CA, Senhorinho GNA, Scott JA (2024) Microalgal harvesting for biofuels \u0026ndash; options and associated operational costs. Algal Research 77:103343. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.algal.2023.103343\u003c/span\u003e\u003cspan address=\"10.1016/j.algal.2023.103343\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMolitor HR, Kim GY, Hartnett E, Gincley B, Alam MM, Feng J, Avila NM, Fisher A, Hodaei M, Li Y, McGraw K, Cusick RD, Bradley IM, Pinto AJ, Guest JS (2024) Intensive microalgal cultivation and tertiary phosphorus recovery from wastewaters via the EcoRecover process. Environmental Science \u0026amp; Technology 58:8803\u0026ndash;8814. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/acs.est.3c10264\u003c/span\u003e\u003cspan address=\"10.1021/acs.est.3c10264\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRenuka N, Sood A, Ratha SK, Prasanna R, Ahluwalia AS (2013) Nutrient sequestration, biomass production by microalgae and phytoremediation of sewage water. International Journal of Phytoremediation 15:789\u0026ndash;800. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/15226514.2012.736436\u003c/span\u003e\u003cspan address=\"10.1080/15226514.2012.736436\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRookesh T, Samaei MR, Yousefinejad S, Hashemi H, Derakhshan Z, Abbasi F, Jalili M, Giannakis S, Bilal M (2022) Investigating the electrocoagulation treatment of landfill leachate by iron/graphite electrodes: process parameters and efficacy assessment. Water 14:205. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/w14020205\u003c/span\u003e\u003cspan address=\"10.3390/w14020205\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShaikh SMR, Hassan MK, Nasser MS, Sayadi S, Ayesh AI, Vasagar V (2021) A comprehensive review on harvesting of microalgae using polyacrylamide-based flocculants: potentials and challenges. Separation and Purification Technology 277:119508. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.seppur.2021.119508\u003c/span\u003e\u003cspan address=\"10.1016/j.seppur.2021.119508\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVandamme D, Foubert I, Muylaert K (2013) Flocculation as a low-cost method for harvesting microalgae for bulk biomass production. Trends in Biotechnology 31:233\u0026ndash;239. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.tibtech.2012.12.005\u003c/span\u003e\u003cspan address=\"10.1016/j.tibtech.2012.12.005\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVandamme D (2017) Harvesting, thickening and dewatering processes. In: Pires JCM (ed) Microalgae as a Source of Bioenergy: Products, Processes and Economics (Recent Advances in Renewable Energy, Vol 1). Bentham Science Publishers, pp 202\u0026ndash;223. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2174/9781681085227117010010\u003c/span\u003e\u003cspan address=\"10.2174/9781681085227117010010\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVandamme D, Pontes SCV, Goiris K, Foubert I, Pinoy LJJ, Muylaert K (2011) Evaluation of electro-coagulation-flocculation for harvesting marine and freshwater microalgae. Biotechnology and Bioengineering 108:2320\u0026ndash;2329. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/bit.23199\u003c/span\u003e\u003cspan address=\"10.1002/bit.23199\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVisigalli S, Barberis MG, Turolla A, Canziani R, Berden Zrimec M, Reinhardt R, Ficara E (2021) Electrocoagulation\u0026ndash;flotation (ECF) for microalgae harvesting \u0026ndash; a review. Separation and Purification Technology 271:118684. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.seppur.2021.118684\u003c/span\u003e\u003cspan address=\"10.1016/j.seppur.2021.118684\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXu K, Zou X, Mouradov A, Spangenberg G, Chang W, Li Y (2021) Efficient bioflocculation of \u003cem\u003eChlorella vulgaris\u003c/em\u003e with a chitosan and walnut protein extract. Biology 10:352. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/biology10050352\u003c/span\u003e\u003cspan address=\"10.3390/biology10050352\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhu L, Li Z, Hiltunen E (2018) Microalgae \u003cem\u003eChlorella vulgaris\u003c/em\u003e biomass harvesting by natural flocculant: effects on biomass sedimentation, spent medium recycling and lipid extraction. Biotechnology for Biofuels 11:183. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1186/s13068-018-1183-z\u003c/span\u003e\u003cspan address=\"10.1186/s13068-018-1183-z\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\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":"","identity":"journal-of-applied-phycology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"10811","submissionUrl":"https://submission.nature.com/new-submission/10811/3","title":"Journal of Applied Phycology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Microalgae separation, electrocoagulation, landfill leachate, Circular economy, wastewater, Chlorella","lastPublishedDoi":"10.21203/rs.3.rs-8360370/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8360370/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Microalgae-based wastewater treatment holds potential for nutrient recovery and carbon capture, but efficient biomass harvesting remains energy-intensive. This study evaluates electrocoagulation-flotation (ECF) for simultaneous microalgae separation and chemical oxygen demand (COD) reduction in real landfill leachate. A mixed microalgal consortium (Chlorella-dominated) was cultivated directly in landfill leachate at low and high biomass densities (OD 680 0.3 and 2.2) and treated in a 0.5 L batch ECF reactor operated under a low-duty pulsed-voltage regime (5.0 V for 0.1 s and 1.5 V for 29.9 s, 30 min). ECF achieved 99.7% and 94.7% separation at low and high biomass, corresponding to 0.22-0.40 kWh kg-1 total solids and 0.33-0.38 kWh m-3. COD for low biomass microalgae decreased from 715 ± 12 mg O 2 L-1 (raw leachate) to 564 ± 14 mg O 2 L-1 after ECF i.e. 21% relative to raw leachate. These findings demonstrate that ECF effectively integrates microalgae harvesting with partial organic pollutant removal in a challenging wastewater matrix, offering a promising low-energy strategy for combined treatment and resource recovery in landfill leachate management.","manuscriptTitle":"Simultaneous microalgae separation and COD reduction from landfill leachate using electrocoagulation-flotation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-23 18:41:18","doi":"10.21203/rs.3.rs-8360370/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-02-12T11:00:27+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-16T02:48:03+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-25T02:23:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"32642897921552973954271924219011217495","date":"2025-12-23T09:51:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"315305138878085527820236404696279843090","date":"2025-12-20T01:17:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"201901753680835773389191169925771622135","date":"2025-12-18T11:51:32+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-18T05:37:00+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-18T05:24:09+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-16T12:08:21+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Applied Phycology","date":"2025-12-14T21:57:51+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"","identity":"journal-of-applied-phycology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"10811","submissionUrl":"https://submission.nature.com/new-submission/10811/3","title":"Journal of Applied Phycology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"b9710507-753c-4b10-9157-4d6cb4374853","owner":[],"postedDate":"December 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-03-07T06:24:49+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-23 18:41:18","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8360370","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8360370","identity":"rs-8360370","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}