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To mitigate groundwater level decline, managed aquifer recharge (MAR) with secondary treated wastewater (STWW) is increasingly considered and implemented. However, the effectiveness and potential risks of such systems need evaluation prior to implementation. In this study, we present a large-scale sand tank experiment to analyse processes related to the infiltration of real STWW through the vadose zone and subsequent mixing with oxic native groundwater. The varying composition of STWW from 15 infiltration cycles over six months of operation and the retention times were the main drivers of the observed processes, which were characterized by a wide range of analytical techniques such as in situ high-resolution oxidation-reduction potential (ORP) measurements, closed mass balances of solutes, characterization of dissolved organic carbon (DOC), stable nitrate isotopes analysis, as well as numerical flow and transport modelling. Depending on the composition and infiltration rates of the STWW, both nitrification and denitrification could be observed, even simultaneously at different locations in the tank. Furthermore, due to the variability of the real STWW we observed enhanced arsenic mobilisation during times of elevated phosphate concentrations of the infiltrating STWW. Additionally, uranium was mobilised in our experimental system via carbonate mineral dissolution caused by the infiltrating STWW which was undersaturated of calcite for all infiltration cycles. Overall, our results showed the importance of conducting studies with waters of complex matrix, such as real STWW, and considering mixing with groundwater to assess the full range of possible processes encountered at MAR field sites., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

• Time-dependent pathogen rate reduction in 3-D fracture network fractures. • 3-D E. coli transport simulation in networks of thousands of fractures. • Extended colloid filtration theory predicts pathogen BTC & 3-D plume in groundwater. • Model simulations were supported by field sampling and laboratory filtration tests. • Potential pathogen release to the bathing water is possible during floods. Microbial transport in fractured carbonate rock using enhanced solutions is a significant and neglected research topic in the literature. We propose an extended colloid filtration theory (CFT) combined with a particle-tracking following streamlines (PTFS) model for the rapid prediction of breakthrough curves (BTCs) and plumes of pathogens in three-dimensional (3-D) discrete fracture networks (DFNs). We adapted CFT in porous media to pathogen transport in fractures containing Terra Rossa (soil) deposits. As an example of the model capability, a simulation was used to predict the 3-D motion field and Escherichia coli count in groundwater originating from the Forcatella managed aquifer recharge (MAR) Facility (Brindisi, Italy) using a DFN composed of 3,900 fractures. In arid regions, MAR facilities are significant for sustaining basic human needs, such as freshwater supply for drinking and crop production. The Markov chain Monte Carlo (MCMC) technique was applied to E. coli counts in the collected water samples to increase data representativeness. The pathogen transport coefficients were further supported by batch filtration tests carried out in the CNR/IRSA Laboratory (Bari, Italy). The mean E. coli attachment rate coefficient of 0.15 × 10−8 m2 d–1 (sticking efficiency = 1.1 × 10−8 m) resulted in a 2.1 log 10 removal in 600 m of reclaimed water filtration. The simulation output visualized the E. coli 3-D pathways in groundwater and the positions of contaminated groundwater spring outflows on Forcatella Beach. The simulation results agreed with the mean MCMC output of E. coli concentrations in bathing water under unperturbed geochemical and environmental flow and transport conditions. However, results indicate that concentrations of pathogenic strains, parasites, and enteric viruses may enter the marine environment of MAR sites during flood periods. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Soil columns simulating soil aquifer treatment (SAT), fed with synthetic secondary effluent by intermittent infiltration of flooding/drying cycles, were characterized for nitrogen and organic carbon removal, and microbial ecology and biokinetics. The columns differed in the concentration ratio of chemical oxygen demand (COD) to the summed NH 4 +, NO 2 − and organic nitrogen—2 (C/N2) or 5 (C/N5). Chemical profiles along the column demonstrated a preference for COD oxidation over nitrification and coupled denitrification, with higher nitrogen loss (57% vs. 16%) in the C/N5 column. Unexpectedly, significant dominance of the genus Nitrospira over the genus Nitrobacter and ammonia-oxidizing bacteria (AOB) was strongly correlated at column depths where NH 4 + removal occurred. Moreover, the Nitrospira profile had the strongest correlation to the profile of NH 4 + (positive) and NO 3 − (negative), strongly indicating complete ammonia oxidation. 16S sequencing analysis of the topsoil in C/N2 vs. C/N5 columns revealed double the abundance of microbial aerobic potential (64% vs. 32%) vs. one-third the denitrification potential (13% vs. 31%). The concentrations and degradability levels of organic carbon were the most influential parameters shaping community structure. Niche differentiation within the biofilm attached to the soil is suggested to have an important role in the process's anoxic activity and nitrogen removal. Graphical abstract Image 1 Highlights • Higher C/N ratio in the feed resulted in significantly higher N loss. • The genus Nitrospira showed preponderance over the genus Nitrobacter and AOB. • Nitrospira correlated to ammonia removal show complete ammonia oxidation activity. • At top high C/N column microbial community reflected potential for denitrification. • Niche differentiation within the biofilm is significant in anoxic activity at SAT. [ABSTRACT FROM AUTHOR]

Abstract Two column pairs filled with 3.05-m of a sandy soil from the Upper San Gabriel Valley were operated for a period of four and ½ years on municipal effluent from the San Jose Creek Water Reclamation Plant operated by the Sanitation Districts of Los Angeles County (LACSD). One column pair was fed filtered, chlorinated effluent (tertiary effluent) for the entire period. The other pair was fed ozonated secondary effluent for 8-mo, ozonated secondary effluent filtered through biological activated carbon (O 3 /BAC) for 7-mo and tertiary effluent for 38-mo. Each column pair was operated in series, where the first column was operated for a shorter residence time and the second column for a longer residence time. Residence times tested were 5-d, 28-d, 30-d, 58-d, 60-d, 150-d and 180-d. For the last 38-mo, both pairs of columns had a residence time of 30-d in the first column and the total residence time of the two pairs was 150 and 180-d, respectively. Testing showed both of these pairs had the same long-term performance. The column pairs with a 150 to 180-d residence time, which were both fed tertiary effluent, reached an effluent total organic carbon (TOC) of 1.8 mg/L. Column pairs with a 28 to 30-d residence time, which were fed tertiary, ozonated, and O 3 /BAC effluent, reached effluent TOCs of 2.3, 2.1 and 1.8 mg/L respectively. In the latter, some TOC removal was shifted from the soil columns to the BAC. During the last 38 months of testing, using tertiary effluent as the source water, a series of sampling events was performed throughout the soil column system for N -nitrosodimethylamine (NDMA) and chemicals of emerging concern (CECs). NDMA was substantially reduced in all the columns, with a median value of 3 ng/L after 30-d and <2 ng/L after both 150 and 180-d. Twenty-one CECs were found in the majority of tertiary effluent samples, twelve of which were attenuated by the soil columns and the remaining were not. Chemicals found to be recalcitrant were 4-nonylphenol, acesulfame-k, carbamazepine, lidocaine, primidone, simazine, sucralose, sulfamethoxazole, and TCEP. Using excitation-emission matrix (EEM) techniques, soluble microbial products (SMP) peak characteristic of effluent organic matter (EfOM) is nearly eliminated after a 30-d hydraulic retention time (HRT) and completely eliminated in the 150/180-d samples. The intensity of the other peaks is significantly reduced as well, resulting in an EEM much like that of natural groundwater. Graphical abstract Image 1 Highlights • Soil columns fed tertiary effluent reduced the TOC 67% with a 150-day HRT. • NDMA was attenuated through soil columns by more than 99%. • Soil column treatment attenuated 12 of the 21 CECs found in tertiary effluent. • Soil columns were operated over four and ½ year period with tertiary effluent. [ABSTRACT FROM AUTHOR]

The long term behavior of total nitrogen and its components was investigated in a soil aquifer treatment system of the Dan Region Reclamation Project (Shafdan), Tel-Aviv, Israel. Use is made of the previous 40 years' secondary data for the main nitrogen components (ammonium, nitrate and organic nitrogen) in recharged effluent and observation wells located inside an infiltration basin. The wells were drilled to 106 and 67 m, both in a similar position within the basin. The transport characteristics of each nitrogen component were evaluated based on chloride travel-time, calculated by a cross-correlation between its concentration in the recharge effluent and the observation wells. Changes in the source of recharge effluent, wastewater treatment technology and recharge regime were found to be the main factors affecting turnover in total nitrogen and its components. During aerobic operation of the infiltration basins, most organic nitrogen and ammonium will be converted to nitrate. Total nitrogen removal in the upper part of the aquifer was found to be 47–63% by denitrification and absorption, and overall removal, including the lower part of the aquifer, was 49–83%. To maintain the aerobic operation of the infiltration fields, the total nitrogen load should remain below 10 mg/L. Above this limit, ammonium and organic nitrogen will be displaced into the aquifer. [ABSTRACT FROM AUTHOR]

The reuse of treated wastewater for irrigation and groundwater recharge can counteract water scarcity and reduce pollution of surface waters, but assessing its environmental risk should likewise consider effects associated to the soil. The present study therefore aimed at determining the impact of wastewater irrigation on the habitat quality of water after soil passage and of soil after percolation by applying bioassays and chemical analysis. Lab-scale columns of four different soils encompassing standard European soil and three field soils of varying characteristics and pre-contamination were continuously percolated with treated wastewater to simulate long-term irrigation. Wastewater and its percolates were tested for immobilization of Daphnia magna and growth inhibition of green algae ( Pseudokirchneriella subcapitata ) and water lentils ( Lemna minor ). The observed phytotoxicity of the treated wastewater was mostly reduced by soil passage, but in some percolates also increased for green algae. Chemical analysis covering an extensive set of wastewater-born organic pollutants demonstrated that many of them were considerably reduced by soil passage, particularly through peaty soils. Taken together, these results indicated that wastewater-born phytotoxic substances may be removed by soil passage, while existing soil pollutants (e.g. metals) may leach and impair percolate quality. Soils with and without wastewater irrigation were tested for growth of plants ( Avena sativa , Brassica napus ) and soil bacteria ( Arthrobacter globiformis ) and reproduction of collembolans ( Folsomia candida ) and oligochaetes ( Enchytraeus crypticus , Eisenia fetida ). The habitat quality of the standard and two field soils appeared to be deteriorated by wastewater percolation for at least one organism (enchytraeids, plants or bacteria), while for two pre-contaminated field soils it also was improved (for plants and/or enchytraeids). Wastewater percolation did not seem to raise soil concentrations of classical organic pollutants and priority substances, while a significant retention was found for zinc and several organic micropollutants, particularly in the peaty soils, thus matching these soils' observed higher removal efficiency. Overall, our results demonstrate that benefits of wastewater irrigation can come with the cost of deteriorating soil habitat quality and depend on the respective soil and considered test organism. The approach employed here represents a feasible tool to assess these integrated effects at lab-scale while being predictive for scenarios at field-scale. [ABSTRACT FROM AUTHOR]

Soil aquifer treatment is widely applied to improve the quality of treated wastewater in its reuse as alternative source of water. To gain a deeper understanding of the fate of thereby introduced organic micropollutants, the attenuation of 28 compounds was investigated in column experiments using two large scale column systems in duplicate. The influence of increasing proportions of solid organic matter (0.04% vs. 0.17%) and decreasing redox potentials (denitrification vs. iron reduction) was studied by introducing a layer of compost. Secondary effluent from a wastewater treatment plant was used as water matrix for simulating soil aquifer treatment. For neutral and anionic compounds, sorption generally increases with the compound hydrophobicity and the solid organic matter in the column system. Organic cations showed the highest attenuation. Among them, breakthroughs were only registered for the cationic beta-blockers atenolol and metoprolol. An enhanced degradation in the columns with organic infiltration layer was observed for the majority of the compounds, suggesting an improved degradation for higher levels of biodegradable dissolved organic carbon. Solely the degradation of sulfamethoxazole could clearly be attributed to redox effects (when reaching iron reducing conditions). The study provides valuable insights into the attenuation potential for a wide spectrum of organic micropollutants under realistic soil aquifer treatment conditions. Furthermore, the introduction of the compost layer generally showed positive effects on the removal of compounds preferentially degraded under reducing conditions and also increases the residence times in the soil aquifer treatment system via sorption. [ABSTRACT FROM AUTHOR]

Abstract: In this study, changes of microbial substrate metabolic patterns by BIOLOG assay were discussed through a sequential wastewater reuse process, which includes activated sludge and treated effluent in wastewater treatment plant and soil aquifer treatment (SAT), especially focussing on the surface sand layer in conjunction with the vadose zone, concerning sand depth. A SAT pilot-scale reactor, in which the height of packed sand was 237 cm (vadose zone: 17 cm and saturated zone 220 cm), was operated and fed continuously by discharged anaerobic–anoxic–oxic (A2O) treated water. Continuous water quality measurements over a period of 10 months indicated that the treatment performance of the reactor, such as 83.2% dissolved organic carbon removal, appeared to be stable. Core sampling was conducted for the surface sand to a 30 cm depth, and the sample was divided into six 5 cm sections. Microbial activities, as evaluated by fluorescein diacetate, sharply decreased with increasing distance from the surface of the 30 cm core sample, which included significant decreases only 5 cm from the top surface. A similar microbial metabolic pattern containing a high degree of carbohydrates was obtained among the activated sludge, A2O treated water (influent to the SAT reactor) and the 0–5 cm layer of sand. Meanwhile, the 10–30 cm sand core layers showed dramatically different metabolic patterns containing a high degree of carboxylic acid and esters, and it is possible that the metabolic pattern exhibited by the 5–10 cm layer is at a midpoint of the changing pattern. This suggests that the removal of different organic compounds by biodegradation would be expected to occur in the activated sludge and in the SAT sand layers immediately below 5 cm from the top surface. It is possible that changes in the composition of the organic matter and/or transit of the limiting factor for microbial activities from carbon to phosphorus might have contributed to the observed dramatic changes in SAT metabolic patterns. [Copyright &y& Elsevier]

Abstract: Ozonation is known as an efficient treatment to reduce the concentration of many trace organic compounds from WWTP effluents, but the formation of unknown and possibly persistent and toxic transformation products has to be considered. In this paper tertiary treatment of wastewater by the combination of ozone and soil aquifer treatment was investigated with respect to the removal of the antiepileptic drug carbamazepine (CBZ, 10 μg/L) and its transformation products. Batch tests and pilot experiments confirmed efficient removal of carbamazepine from secondary effluent by ozone. With typical ozone consumption of 0.7 mg O3/mg DOC0, approx. 50% of the transformed CBZ was detected as its primary product 1-(2-benzaldehyde)-4-hydro-(1H,3H)-quinazoline-2-one (BQM). Structure proposals and a formation pathway were elaborated for a total of 13 ozonation products of CBZ. In subsequent biological treatment BQM turned out to be more effectively biodegraded than CBZ. Its aldehyde group was quickly oxidized to a carboxylic acid (BaQM), which was removed in sand column experiments. Most of the minor ozonation products of CBZ persisted in sand column experiments with residence times of 5–6 days. Non-target screening of column effluent revealed no formation of persistent biotransformation products. [Copyright &y& Elsevier]

Abstract: Soil Aquifer Treatment (SAT) is a process where treated wastewater is purified during transport through unsaturated and saturated zones. Easily biodegradable compounds are rapidly removed in the unsaturated zone and the residual organic carbon is comprised of primarily high molecular weight compounds. This research focuses on flow in the saturated zone where flow conditions are predictable and high molecular weight compounds are degraded. Flow through the saturated zone was investigated with 4 reactors packed with 2 different particle sizes and operated at 4 different flow rates. The objective was to evaluate the kinetics of transformation for high molecular weight organics during SAT. Dextran was used as a model compound to eliminate the complexity associated with studying a mixture of high molecular weight organics. The hydrolysis products of dextran are easily degradable sugars. Batch experiments with media taken from the reactors were used to determine the distribution of microbial activity in the reactors. Zero-order kinetics were observed for the removal of dextran in batch experiments which is consistent with hydrolysis of high molecular weight organics where extracellular enzymes limit the substrate utilization rate. Biomass and microbial activity measurements demonstrated that the biomass was independent of position in the reactors. A Monod based substrate/biomass growth kinetic model predicted the performance of dextran removal in the reactors. The rate limiting step appears to be hydrolysis and the overall rate was not affected by surface area even though greater biomass accumulation occurred as the surface area decreased. [Copyright &y& Elsevier]

Abstract: A 2000 mm long saturated laboratory soil column was used to simulate soil aquifer treatment under saturated conditions to assess the removal of chemical and biochemical oxygen demand (COD and BOD), dissolved organic carbon (DOC), nitrogen and phosphate, using high strength artificial wastewater. The removal rates were determined under a combination of constant hydraulic loading rates (HLR) and variable COD concentrations as well as variable HLR under a constant COD. Within the range of COD concentrations considered (42 mg L−1–135 mg L−1) it was found that at fixed hydraulic loading rate, a decrease in the influent concentrations of dissolved organic carbon (DOC), biochemical oxygen demand (BOD), total nitrogen and phosphate improved their removal efficiencies. At the high COD concentrations applied residence times influenced the redox conditions in the soil column. Long residence times were detrimental to the removal process for COD, BOD and DOC as anoxic processes and sulphate reduction played an important role as electron acceptors. It was found that total COD mass loading within the range of 911 mg d−1–1780 mg d−1 applied as low COD wastewater infiltrated coupled with short residence times would provide better effluent quality than the same mass applied as a COD with higher concentration at long residence times. The opposite was true for organic nitrogen where relatively high concentrations coupled with long residence time gave better removal efficiency. [Copyright &y& Elsevier]

Soil column experiments were performed to investigate the behavior and characteristics of dissolved organic matter (DOM) during soil aquifer treatment (SAT), and to differentiate among the mechanisms responsible for the changes in the structural and functional properties of DOM during SAT. To determine the biological transformation of DOM, biodegradability tests using a biodegradation-column system were conducted. DOM was fractionated using XAD resins into 5 fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). Dissolved organic carbon (DOC) was removed by 70% during SAT, and the sorption and anaerobic biodegradation in SAT led to a DOC reduction of 27.4%. The significant changes in fluorescence properties of DOM were observed during SAT. However, the sorption and anaerobic biodegradation in SAT seemed to have no significant effect on the chemical structure of fluorescing constituents in DOM. The DOM fractions exhibited different changes in Fourier-transform infrared (FT-IR) spectra characteristics during SAT. Biodegradation resulted in the enrichment of aromatic structures and the decreased content of the oxygen-containing functional groups, such as Cx2013;O, in DOM. On the other hand, the production of C–O and amide-2 functional groups occurred as a result of the sorption combined with anaerobic biodegradation in SAT. [Copyright &y& Elsevier]

Abstract: This study investigates the relationship between soil biomass and organic carbon removal during the infiltration of conventionally treated effluents used for groundwater recharge during soil-aquifer treatment (SAT). Investigations were conducted on samples collected from full-scale SAT sites, revealing a positive correlation between biodegradable organic carbon (BOC) concentrations in the recharged effluents and total viable soil biomass concentrations in the infiltration zone of soil samples collected from respective recharge basins. Findings of this study suggest that BOC limits soil biomass growth and was able to support a steady-state concentration of viable soil biomass that is characteristic to BOC concentrations introduced with the recharged effluents. All investigated sites indicate that BOC is primarily removed within 30cm soil depth leading to a significant increase in soil biomass levels (measured as substrate induced respiration (SIR), total viable biomass, and dehydrogenase activity (DHA)). Controlled biological column studies revealed that the primary components of BOC in domestic effluents are organic colloids. Findings of this study support that hydrophobic acids, commonly believed to be recalcitrant, may also be attenuated by biological processes during soil infiltration. [Copyright &y& Elsevier]

Increased water demands have led to a notable interest in the use of treated wastewater for reuse. Typically, this results from the implementation of advanced treatment of final effluent from wastewater treatment plants prior to reuse for potable or non-potable purposes. Soil aquifer treatment (SAT) is a natural treatment process in which water from sources of varying quality is infiltrated into the soil to further improve its quality. The goal of this study was to determine the log 10 reduction values (LRVs) of viruses naturally present in treated effluent and evaluate two potential indicators of virus removal and transport, pepper mild mottle virus (PMMoV) and crAssphage, during SAT of treated effluent. Groundwater was sampled at three wells with different attributes within the Sweetwater Recharge Facility (SWRF) in Tucson, AZ. These sites vary greatly in operational parameters such as effluent infiltration rates and wetting/drying cycles, which may influence virus removal efficiency. Detection of adenovirus, enterovirus, PMMoV, and crAssphage were determined by qPCR/RT-qPCR and log 10 reduction values (LRVs) were determined. PMMoV and crAssphage were detected in groundwater associated with a set of recharge basins that exhibited shorter wetting/drying cycles and faster infiltration rates. LRVs for crAssphage and PMMoV at this site ranged from 3.9 to 5.8, respectively. Moreover, PMMoV was detected downflow of the SAT sites, indicating the potential degradation of microbial groundwater quality in the region surrounding managed aquifer recharge facilities. Overall, PMMoV and crAssphage showed potential as conservative process indicators of virus removal during SAT, particularly for attribution of LRV credits. Moreover, the detection of these viruses indicated the potential influence of wetting/drying cycles on virus removal by SAT, a parameter that has not yet been studied with respect to biological contaminants. Image 1 • Virus removal examined at three sites within soil aquifer (SAT) treatment facility. • Overall virus removal ranged from >3.4 to >6.2 • Virus detected from site with faster infiltration rates/shorter wet-dry cycles. • Pepper mild mottle virus and crAssphage have potential as process indicators of virus removal. • Pepper mild mottle virus detected in groundwater downflow of SAT facility. [ABSTRACT FROM AUTHOR]