Biological Removal of Groundwater’s Nitrate under Sterile and Non-sterile Soil Conditions (Lab Experiment and Simulation)

Abstract Nitrate is potentially harmful in an aquatic environment however it can be converted into more dangerous forms by microbial activities. In this research, we tested the efficiency of nitrate removal by using a denitrification bed (DB) containing in sterile soil (SS) and non-sterile soil (NSS) media. A Marriott column and a Plexiglas column filled with a clay loam soil were used as the water resource and DB, respectively. Potassium nitrate used to make different nitrate concentrations including 24, 50 and 100 (mg l-1). The nitrate was injected up to ten pore volumes (PV), when the soil was sterile, only active surfaces within the soil matrix acted as an adsorbent. The number of bacteria and the bacteria growth was investigated at the end of each experiment. The solute transfer parameters were estimated by using soil hydraulic parameters at HYDRUS model. As result, the growth of bacteria and the concentration of pollutants in the output of the column decreased in SS media. In the NSS with a concentration of 100 mg nitrate, the number of bacteria increased to the highest, 80000 bacterial number. The presence of rival anions in the solution has a negative impact on reducing the adsorption rate and removal of nitrate. In NSS with nitrate concentration of 24 (mg l-1), the removal nitrate efficiency nearly 99.5 (%). There was a significant difference between nitrate concentration of the SS and NSS conditions (p<0.05). The value of the diffusion coefficient is 4.99 (cm). Sensitivity analyses demonstrated that saturated hydraulic conductivity had the greatest effect on the variations of nitrate concentration. Besides, the correlation coefficient between simulated values and observed values by the HYDRUS-1D model varied between 0.90 and 0.99.