Aquifer Treatment Research Articles

Design of a bioaugmented soil aquifer treatment for efficient removal of p‐nitrophenol

AbstractSecondary effluent reclamation and reuse is an effective solution to the water shortage problem, and the safety of reused water is a matter of increasing concern. p‐Nitrophenol (PNP), a common secondary effluent pollutant, can be efficiently removed using the eco‐friendly bioaugmented soil aquifer treatment (SAT) system at the laboratory scale. In this study, a sewage treatment plant in Changchun was selected as a case study to apply the bioaugmented SAT system for field scenarios efficiently. The bioaugmented SAT system was simulated using HYDRUS‐1D code. Biodegradation and adsorption coefficient were conducted from the batch experiment. Based on the degradation experiments, the concentration of bacteria injected into SAT system was designed to be 6 × 1018 colony‐forming units (CFU) m−3. To enhance the efficiency of the bioaugmented SAT system, the key parameters were optimized based on the sensitivity analysis and the response surface methodology, which showed that the optimal operating conditions were an initial concentration of 86.11 mg L−1, a medium of 4.27‐m thickness, and a wet/dry ratio of 0.28. Specifically, alternated wetting–drying conditions and increasing the medium thickness reduced PNP within a specific range. This work demonstrates the performance and applicability of the bioaugmented SAT system for removal PNP in secondary sewage effluent.

Effects of Operating and Media Conditions on the Change of Reclaimed Water Quality in Soil Aquifer Treatment (SAT) System: Experimental and Simulation Study

Effects of Operating and Media Conditions on the Change of Reclaimed Water Quality in Soil Aquifer Treatment (SAT) System: Experimental and Simulation Study

Impacts of autochthonous particulate organic matter on redox-conditions and elimination of trace organic chemicals in managed aquifer recharge

Autochthonous carbon fixation by algae and subsequent deposition of particulate organic matter can have significant effects on redox conditions and elimination of trace organic chemicals (TOrCs) in managed aquifer recharge (MAR). This study investigated the impacts of different algae loadings (0–160 g/m2) and infiltration rates (0.06–0.37 m/d) on overall oxygen consumption and elimination of selected TOrCs (diclofenac, formylaminoantipyrine, gabapentin, and sulfamethoxazole) in adapted laboratory sand columns. An infiltration rate of 0.37 m/d in conjunction with an algae load of 80 g/m2 (dry weight) sustained oxic conditions in the sand bed and did not affect the degradation of TOrCs. Thus, the availability of easily degradable organic carbon from algae did not influence the removal of TOrCs at an influent concentration of 1 µg/L. In contrast, a lower infiltration rate of 0.20 m/d in combination with a higher algae loading of 160 g/m2 caused anoxic conditions for 30 days and significantly impeded the degradation of formylaminoantipyrine, gabapentin, sulfamethoxazole, and diclofenac. Especially the elimination of gabapentin did not fully recover within 130 days after pulsed algae deposition. Hence, measures like micro-sieving or nutrient control are required at bank filtration or soil aquifer treatment sites with low infiltration rates.

Using integrative samplers to estimate the removal of pharmaceuticals and personal care products in a WWTP and by soil aquifer treatment enhanced with a reactive barrier

The need and availability of freshwater is a major environmental issue, aggravated by climate change. It is necessary to find alternative sources of freshwater. Wastewater could represent a valid option but requires extensive treatment to remove wastewater-borne contaminants, such as contaminants of emerging concern (CECs). It is urgent to develop not only sustainable and effective wastewater treatment techniques, but also water quality assessment methods. In this study, we used polar organic chemical integrative samplers (POCIS) to investigate the presence and abatement of contaminants in an urban wastewater treatment plant (WWTP) and in soil aquifer treatment (SAT) systems (a conventional one and one enhanced with a reactive barrier). This approach allowed us to overcome inter-day and intraday variability of the wastewater composition. Passive sampler extracts were analyzed to investigate contamination from 56 pharmaceuticals and personal care products (PPCPs). Data from the POCIS were used to estimate PPCPs' removal efficiency along the WWTP and the SAT systems. A total of 31 compounds, out of the 56 investigated, were detected in the WWTP influent. Removal rates along WWTP were highly variable (16-100 %), with benzophenone-3, benzophenone-1, parabens, ciprofloxacin, ibuprofen, and acetaminophen as the most effectively removed chemicals. The two SAT systems yielded much higher elimination rates than those achieved through the primary and secondary treatments together. The SAT system that integrated a reactive barrier, based on sustainable materials to promote enhanced elimination of CECs, was significantly more efficient than the conventional one. The removal of the recalcitrant carbamazepine and its epoxy- metabolite was especially remarkable in this SAT, with removal rates between 69–81 % and 63–70 %, respectively.

Manganese and cobalt metals interrelations with ammonium performance in soil aquifer treatment

This study aimed to discover and explore the impacts and interactions of applying Mn2+ and Co2+ metals in NH4 removal performance under nitrification conditions through soil aquifer treatment. A laboratory scale column was used to simulate the soil aquifer treatment system using quartz sand as packed media to infiltrate the synthetic wastewater mixture from 35 mg/L of NH4, 60 mg/L Mn2+ and 40 mg/L of Co2+ concentrations. The experimental and linear regression model results demonstrate a significant relationship between NH3-N concentration with Mn2+ and Co2+ concentration with a p-value < 0.05, indicating a substantial influence of Mn2+ and Co2+ presence on ammonium bioremediation. Co2+ has a negative correlation interaction with NH3-N, which means Co2+ has increased ammonium oxidation by stimulating the degradation bacteria and cell growth to supplement and improve the activity of ammonium degradation bacteria. However, applying a high concentration of Mn2+ works as an inhibitor for NH3-N bioremediation. Using a high concentration of Mn2+ negatively impacts bacteria, causing a toxic effect and decreasing the bacteria's degradability for ammonium.

Wastewater reuse through soil aquifer treatment: regulations and guideline for feasibility assessment

Wastewater reuse through soil aquifer treatment: regulations and guideline for feasibility assessment

Design of an Enhanced SAT Using Zeolite for the Removal of Ammonia Nitrogen at a Bengbu Aquatic Farm in China

As one of the artificial recharge technologies, the soil–aquifer treatment (SAT) system is used for the removal of nitrogen pollution from aquaculture wastewater. An adsorption-enhanced SAT system was designed to reduce the level of nitrogen pollution below the threshold stipulated by the standards. Adsorption kinetics experiments were used to measure the adsorption capacity of zeolite and activated carbon for ammonia nitrogen. Both adsorbents can be well described by the Lagergren pseudo-second-order model, and the adsorption rates of zeolite and activated carbon for ammonia nitrogen were 72.16% and 31.40%, respectively. Combining the experimental data and the actual situation, the medium-packing method was determined and the influence of wastewater characteristics and hydrodynamic conditions on the adsorption and retention capacity of the SAT system were considered. Finally, the feasibility of the adsorption-enhanced SAT site design scheme was verified by Hydrus-1D model simulation. The study found that the design scheme for the situation in the study area was feasible; however, the surrounding underground environment still had a risk of pollution during the operation of the site. Therefore, further research is needed for the nitrogen pollution to be completely removed within the scope of the SAT site.

Typical Sulfonamide Antibiotics Removal by Biochar-Amended River Coarse Sand during Groundwater Recharge.

The high porosity of medium-coarse sand (MCS) layers in groundwater recharge areas presents a high environmental risk. Sulfamethoxazole (SMX) and trimethoprim (TMP) are two common sulfonamide antibiotics in surface water that have a high propensity to migrate into groundwater. In this study, four biochars were prepared and biochar-amended soil aquifer treatment (SAT) columns were constructed to remove SMX and TMP. Batch experiments demonstrated that the sorption isotherms conformed to the Freundlich model. The maximum adsorptions of biochars prepared at 700 °C were 54.73 and 67.62 mg/g for SMX and 59.3 and 73.38 mg/g for TMP. Electrostatic interaction may be one of the primary mechanisms of adsorption. The column experiments showed that the SMX and TMP removal rate of the biochar-amended SAT was as high as 96%, while that of the MCS SAT was less than 5%. The addition of biochar greatly improved the retention capacity of the pollutants in the MCS layer in the groundwater recharge area and effectively reduced environmental risk.

Mechanism of downward migration of quinolone antibiotics in antibiotics polluted natural soil replenishment water and its effect on soil microorganisms

Reclaimed water is widely concerned as an effective recharge of groundwater and surface water, but trace organic pollutants produced by traditional wastewater treatment plants (WWTPs) would cause environmental pollution (water and soil) during infiltration. Therefore, the effects of reclaimed water containing ofloxacin (OFL) and ciprofloxacin (CIP) in antibiotics polluted natural soil (APNS) were investigated by simulating soil aquifer treatment systems (SATs). The experiment results showed that OFL and CIP in water were adsorbed and microbially degraded mainly at 30 cm, and the concentration of OFL and CIP in soil increased with depth, which were mainly due to the desorption from APNS. Concurrently, the change in replenishment water concentration also significantly affected OFL and CIP in pore water and soil. Although OFL and CIP inhibited the diversity of soil microbial community, they also promoted the growth of some microorganisms. As the dominant bacteria, Proteobacteria and Acidobacteriota can effectively participate in the degradation of OFL and CIP. The degradation effects of soil microorganisms on OFL and CIP were 45.48% and 42.39%, respectively, indicating that soil microorganisms selectively degraded pollutants. This experiment was carried out on APNS, which provided a reference for future studies on the migration of trace organic pollutants under natural conditions.

Quantitative microbial risk assessment (QMRA) for setting health-based performance targets during soil aquifer treatment.

A quantitative microbial risk assessment was conducted to assess the health risks associated with the exposure of agricultural workers to tertiary treated wastewater in irrigated fields through soil ingestion in Cyprus. Three pathogenic microorganisms were chosen, particularly E. coli (bacteria), rotavirus (viruses) and Cryptosporidium. Two extreme exposure scenarios were investigated. Monte Carlo simulations were performed using input data from literature, and the model outputs were compared to the health standards of the World Health Organization (WHO). The results suggested that additional treatment is required for all pathogens to satisfy the health standards. Sensitivity analysis identified the source concentration and pathogen reduction due to soil aquifer passage as the most influential factors in the model outputs. Additional computations were performed to evaluate the minimum pathogen reduction due to soil aquifer passage so that the health targets are achieved for the 95 % of the output values. Rotavirus and Cryptosporidium were found to require more treatment than E. coli. The inclusion of these reference pathogens to the monitoring network of the local authorities is recommended, and the role of soil aquifer passage is emphasized on reducing the concentration of the contaminants.

Enhanced electrokinetic remediation of heterogeneous aquifer co-contaminated with Cr(VI) and nitrate by rhamnolipids

Electrokinetic remediation is an in situ remediation technique that is gaining increasing attention in the field of groundwater contaminant removal. Aquifers co-contaminated with hexavalent chromium (Cr(VI)) and nitrate are becoming more common and research on the remediation of this pollutant is attracting worldwide attention owing to the considerable human health hazards of Cr(VI) and nitrate, including carcinogenicity, genotoxicity, and cytotoxicity. Electrokinetic remediation technology has significant advantages for the treatment of heterogeneous aquifers. This is the first study on the electrokinetic remediation of an aquifer co-contaminated with toxic heavy metals and inorganic salts. This study investigated the feasibility of electrokinetic remediation for layered heterogeneous aquifers co-contaminated with Cr(VI) and nitrate in the presence of groundwater flow, and it also assessed the ability of the anionic biosurfactant rhamnolipid to enhance the remediation effect. Changes in the pH, electrical conductivity, Cr(VI), nitrate, electric current, and the distribution of energy consumption and the voltage contour were analyzed through seven sets of experiments. The highest removal rates of Cr(VI) and nitrate were 97.30% and 87.08%, respectively. Rhamnolipids greatly enhanced the electrokinetic remediation process, especially in medium with moderately low permeability: 1) rhamnolipids improved Cr(VI) removal(from 1.62% of EK3 to 85.57% of EK6 and from 48.42% of EK4 to 94.18% of EK7) through migration and reduction; and 2) rhamnolipids improved nitrate removal (from 13.03% of EK3 to 71.72% of EK6 and from 23.69% of EK4 to 78.43% of EK7) through enhanced migration.

Pathways and efficiency of nitrogen attenuation in wastewater effluent through soil aquifer treatment

Soil Aquifer Treatment (SAT) is used to increase groundwater resources and enhance the water quality of wastewater treatment plant (WWTP) effluents. The resulting water quality needs to be assessed. In this study, we investigate attenuation pathways of nitrogen (N) compounds (predominantly NH4+) from a secondary treatment effluent in pilot SAT systems: both a conventional one (SAT-Control system) and one operating with a permeable reactive barrier (PRB) to provide extra dissolved organic carbon to the recharged water. The goal is to evaluate the effectiveness of the two systems regarding N compounds by means of chemical and isotopic tools. Water chemistry (NO3−, NH4+, Non-Purgeable Dissolved Organic Carbon (NPDOC), and O2) and isotopic composition of NO3− (ẟ15N–NO3- and ẟ18O–NO3-) and NH4+ (ẟ15N–NH4+) were monitored in the inflow and at three different sections and depths along the aquifer flow path. Chemical and isotopic results suggest that coupled nitrification-denitrification were the principal mechanisms responsible for the migration and distribution of inorganic N in the systems and that nitrification rate decreased with depth. At the end of the study period, 66% of the total N in the solution was removed in the SAT-PRB system and 69% in the SAT-Control system, measured at the outlet of the systems. The residual N in solution in the SAT-PRB system had an approximately equal proportion of N–NH4+ and N–NO3- while in the SAT-Control system, the residual N in solution was primarily N–NO3-. Isotopic data also confirmed complete NO3− degradation in the systems from July to September with the possibility of mixing newly generated NO3− with the residual NO3− in the substrate pool.

Transfer of trace organic compounds in an operational soil-aquifer treatment system assessed through an intrinsic tracer test and transport modelling.

Soil Aquifer Treatment (SAT) can provide supplementary treatment of trace organic compounds (TrOCs) such as pharmaceutical and industrial compounds present in Secondary Treated Wastewater (STWW). Concern on presence of unregulated TrOCs in natural systems has raised recently as well as the interest in SAT systems for remediation. The present study quantifies, at the field scale over35 m of lateral groundwater flow, the effectiveness of the Agon-Coutainville SAT system (Manche, Normandy, France) for TrOCs removal by sorption and biodegradation through monitoring of seven TrOCs (oxazepam, carbamazepine, benzotriazole, tolyltriazole, caffein, paracetamol, ibuprofen) and major inorganic compounds as intrinsic tracers in STWW and groundwater during a 34-day STWW infiltration experiment during operational use of the SAT. Cationic exchanges and mixing between groundwater and STWW during the experiment were highlighted by major ions and geochemical simulations. Due to the low thickness of the unsaturated zone, a 1D analytical solution of the advection-dispersion equation (ADE) was applied on chloride data. Chloride was used as conservative intrinsic tracer to calibrate the horizontal flow and transport parameters such as the aquifer dispersion coefficient (D) and the average pore water velocity (ν) allowing estimation of the groundwater residence time. Transport and attenuation of the TrOCs were simulated assuming first-order degradation constant (μ) and linear retardation coefficient (R), calibrated to simulate the observed temporal changes in the breakthrough of TrOCs. Sorption was found to play a role in the transport of TrOCs, notably for oxazepam with a higher linear retardation coefficient value of 2.2, whereas no significant differences of retardation were observed for carbamazepine, tolyltriazole, benzotriazole (1.37, 1.35, 1.36 respectively). Estimated first order degradation rate constants, between 0.03d-1 for carbamazepine and 0.09d-1 for tolyltriazole, were generally high compared to the literature, possibly due to favourable redox conditions and important microbial activities within the system. This study provides evidence of the efficiency of the Agon-Coutainville SAT system for the removal of TrOCs.

Assessing the Wastewater Pollutants Retaining for a Soil Aquifer Treatment using Batch Column Experiments

In this study, the Secondary Treated Waste-Water (STWW) to infiltrate through the soil matrix, hence eliminating the contaminants in the effluent. For this study, three types of soil, such as loamy sand, fine sand, and clayey soil, were subjected to two cycles of wetting and drying to assess the type of soil that removes the maximum contaminants under which cycle. At diverse locations, soil samples were collected and examined to determine the soil types. Likewise, STWW was collected from Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB) and Perungudi Sewage Treatment Plant (PSTP) to illustrate the quality of water before Soil Aquifer Treatment (SAT). About 1.5 m in height and 8 mm in diameter of fabricated acrylic material columns are used for the soil aquifer treatment efficiency studies. Water quality parameters, namely pH, TDS, and turbidity, were monitored throughout the study. All the organic compounds present in water were reduced to a higher level only in the fine sand in the one-day wetting/drying cycle. pH was reduced from 8.55 to 7.5, TDS was reduced from 1580 mg/l to 850 mg/l, and Turbidity was reduced from 7.24 to 4.04 NTU. This proposed method is to minimize the amount of water pollution from the environment. It is an effective way to manage aquifer recharge (MAR). SAT is the easiest method, aquifer and/or soil-based treatment systems improve the effluent quality of wastewater by removing the trace elements in the aquifer during the recharge of groundwater. It is likewise attractive for technologically advanced as well as emerging countries, and it is supple enough to allow adaptation to home-grown requirements by uniting it with predictable natural or bringing about water and technologies of wastewater treatment. Doi: 10.28991/CEJ-2022-08-07-011 Full Text: PDF

Effects of the chlorination on organic matter removal and microbial communities during soil aquifer treatment for wastewater reclamation

ABSTRACT Soil aquifer treatment (SAT) has been widely applied for wastewater reclamation, which cooperates secondary treatment (i.e. A2O process) and disinfection treatment (chlorination) in wastewater treatment plants (WWTPs), to remove organic matter. This study compared dissolved organic carbon (DOC) characteristics, substrate utilisation patterns, and microbial communities between pre-chlorination SAT and SAT columns, and effective removals of DOC were observed in the pre-chlorination SAT and SAT columns. However, the composition of HiA in SAT columns without chlorination was less than in pre-chlorination SAT columns for DOC fraction. In comparison to A2O effluent, different metabolic patterns and the composition of the microbial community were demonstrated by the top layer of SAT column and pre-chlorination SAT column. Furthermore, deeper layers showed similarities in the metabolic pattern and composition of the microbial community. Overall, pre-chlorination minimised the change of the microbial communities from A2O effluent in the top layer of SAT except for deeper layers, and DOC concentrations decreased in pre-chlorination SAT column. Thus, the cooperation of SAT and wastewater treatments could be suitable for wastewater reclamation.

Nitrogen Removal Capacity of Microbial Communities Developing in Compost- and Woodchip-Based Multipurpose Reactive Barriers for Aquifer Recharge With Wastewater.

Global water supplies are threatened by climate changes and the expansion of urban areas, which have led to an increasing interest in nature-based solutions for water reuse and reclamation. Reclaimed water is a possible resource for recharging aquifers, and the addition of an organic reactive barrier has been proposed to improve the removal of pollutants. There has been a large focus on organic pollutants, but less is known about multifunctional barriers, that is, how barriers also remove nutrients that threaten groundwater ecosystems. Herein, we investigated how compost- and woodchip-based barriers affect nitrogen (N) removal in a pilot soil aquifer treatment facility designed for removing nutrients and recalcitrant compounds by investigating the composition of microbial communities and their capacity for N transformations. Secondary-treated, ammonium-rich wastewater was infiltrated through the barriers, and the changes in the concentration of ammonium, nitrate, and dissolved organic carbon (DOC) were measured after passage through the barrier during 1 year of operation. The development and composition of the microbial community in the barriers were examined, and potential N-transforming processes in the barriers were quantified by determining the abundance of key functional genes using quantitative PCR. Only one barrier, based on compost, significantly decreased the ammonium concentration in the infiltrated water. However, the reduction of reactive N in the barriers was moderate (between 21 and 37%), and there were no differences between the barrier types. All the barriers were after 1 year dominated by members of Alphaproteobacteria, Gammaproteobacteria, and Actinobacteria, although the community composition differed between the barriers. Bacterial classes belonging to the phylum Chloroflexi showed an increased relative abundance in the compost-based barriers. In contrast to the increased genetic potential for nitrification in the compost-based barriers, the woodchip-based barrier demonstrated higher genetic potentials for denitrification, nitrous oxide reduction, and dissimilatory reduction of nitrate to ammonium. The barriers have previously been shown to display a high capacity to degrade recalcitrant pollutants, but in this study, we show that most barriers performed poorly in terms of N removal and those based on compost also leaked DOC, highlighting the difficulties in designing barriers that satisfactorily meet several purposes.

Accelerating Microbial Activity of Soil Aquifer Treatment by Hydrogen Peroxide

Soil aquifer treatment (SAT), as a gravity-based wastewater reuse process, is limited by oxygen availability to the microbial community in the soil. Using oxygen from enzymatic degradation of H2O2 to generate hyper-oxygen conditions can exceed solubility limitations associated with aeration, but little is known about the effect of hyper-oxygen conditions on the microbial community and the dominant bio-reactions. This study examined the impact of H2O2 addition on the community structure and process performance, along with SAT depth. Overall, two soil columns were incrementally fed synthetic secondary effluents to simulate infiltration through SAT. The experimental column received 14 mg/L hydrogen peroxide to double the level of natural oxygen available. The microbial kinetics of nitrifiers and heterotrophs were evaluated. We found that all of the H2O2 was degraded within the top 10 cm of the column, accompanied by a higher removal of COD (23 ± 0.25%) and ammonia (31 ± 3%) in comparison to the reference column. Higher nitrogen removal (23 ± 0.04%) was obtained for the whole process using H2O2. Analysis of nitrifiers indicated that ammonia-oxidizing bacteria were most influenced, obtaining higher concentration and abundance when exposed to H2O2. DNA sequencing analysis of samples exposed to H2O2 revealed significant community structure and diversity differences among heterotrophs. This study shows that not only aerobic, but also anoxic, microbial activity and process performance in a SAT system could be accelerated in existing infrastructure with H2O2, which could significantly decrease the associated environmental footprint.

Continuous monitoring of a soil aquifer treatment system's physico-chemical conditions to optimize operational performance

Abstract. Soil aquifer treatment (SAT) is a tertiary process for wastewater treatment, where the wastewater infiltrates through a thick vadose zone for purification and storage in the underneath aquifer. SAT infiltration basins are typically flooded intermittently, while maintaining a fixed ratio between the wetting and the drying stages. However, infiltration basins exhibit different physical and chemical properties, limiting the generalization of SAT operation to attain optimal efficiency. Since frequent sampling of the soil pore water to verify the SAT's biodegradation efficiency can be arduous, continuous monitoring of the SAT vadose zone's physico-chemical conditions is required. In this study, redox potential (Eh) was continuously monitored, together with other variables, such as volumetric water content (θ), soil temperature, and gaseous oxygen (O2), at multiple depths of a SAT vadose zone throughout the year and while the system was constrained to different operational modes. Hydrological models were calibrated and validated to water content observations, and they illustrated the seasonal changes in water infiltration. Furthermore, it was shown that, under long wetting stages during winter, there was a reduction in the SAT's drainage capabilities. The Eh observations, under long wetting stages, demonstrated larger variability and very negative values as ambient temperature increased. Assembling the daily Eh observations illustrated that a wetting stage should cease after about 30 h, once suboxic conditions are established. A drying stage's optimal duration should be 36 h, according to the Eh and O2 observations during summer and winter. Ultimately, the study shows that the length of wetting and drying stages should be defined separately, rather than by adhering to the wetting / drying ratio.

HYDRUS-2D simulations of typical pollutant migration in a soil aquifer system in the Zibo-Weifang funnel area of China

To clarify the removal trends of typical pollutants in recharged water samples during soil aquifer treatment (SAT), especially the recharging performances in the funnel areas of arid regions, the Zibo-Weifang funnel area of China was selected as an example where the effects of dry-wet ratio (DWR, the ratio of the dry period to irrigation period), wet period duration (WPD, duration of one irrigation period), irrigation side length (ISL) and irrigation depth (ID) on the 50-year SAT performance were simulated using HYDRUS-2D. Experimental results revealed that the operational parameters of the DWR, WPD, ISL and ID exhibited significant effects on the bulk removal of chemical oxygen demand (COD), nitrate (NO3−), ammonium (NH4+), total phosphorus (TP) and hexavalent chromium (Cr6+). Eventually, the optimal conditions with a DWR of 3, WPD of 7 d, ISL of 100 m, and ID of 200 cm were selected for the SAT based on the simulations, and irrigation loads as high as of 84.12 m/yr were obtained. During the 50-year irrigation simulation, as much as 256 Mm3/yr of new water would be recharged into the Shandong Plain, which would be accompanied by the effective removal of COD, NH4+, TP and Cr6+. In contrast, the NO3− concentrations within the obtained SAT effluent (50 m depth) were higher than those of the influent, which were closely related to the insufficient carbon sources in the deep soil and poor soil adsorption capacity. Thus, a more stringent threshold value for the nitrate reinjection concentration (e.g., 12 mg/L) was proposed. In addition, the pollutants, NO3−, NH4+, TP and Cr6+ all exhibited a penetration potential and posed potential pollution threats, especially under higher irrigation loads. Therefore, appropriate pretreatment measures should be strongly considered for the practical operation of SAT systems.

Experimental study on soil aquifer treatment for water quality improvement

Laboratory fabricated soil column experiments were performed to differentiate among the mechanisms (i.e., adsorption, filtration, biodegradation) responsible for the changes in the water quality during Soil Aquifer Treatment (SAT). This study focuses on collecting and analyses the soil samples for its characterization. Similarly, treated wastewater was collected from sewage treatment plant, to characterize the quality before SAT. Then the study has been carried out with columns that are one meter in height and 6 cm diameter to understand the efficiency of the Soil Aquifer Treatment. Entire experiment has been carried out in the presence of sun light. Secondary treated wastewater has poured into soil column and collected at the outlet. Effluent from the column has been analyzed after SAT. After that the clogging layer specimens has taken from soil column and then the soil microbial concentration was estimated. The soil hydraulic conductivity was estimated, to characterize the mechanical and hydraulic behaviour of the clogging layer for before and after SAT. The relative significance of hydraulic loading in soil aquifer treatment system was analyzed and also the changes in the major soil components: Iron(Fe) and Manganese (Mn) oxides resulted from SAT application was measured. Maximum Chemical Oxygen Demand (COD) was reduced in 1.5 m unsaturated Vadoze depth Sandy Clay Loam (SCL) soil from 50.1 mg/l to 18.1 mg/l. During first wetting cycle of SAT, Dissolved Organic Carbon (DOC) was reduced from 12.5 mg/l to 6.5 mg/l. Nitrate(NO-3) and Nitrite(NO-2) was reduced 26 mg/l to 11.25 mg/l and 1.37 mg/l to 1 mg/l respectively. From adsorption studies, it was observed the clay soil has higher adsorption distribution coefficient. The relative hydraulic conductivity decline in SCL mixed clay soil was larger than SCL soil.