Soil Aquifer Treatment Research Articles

Feasibility of long-term irrigation as a treatment method for municipal wastewater using natural soil in Kuwait

Passing treated wastewater through soil is a natural and economic means to improve the quality of wastewater. The United Agricultural Production Company (UAPCO) farm located in the Sulaibiya area of Kuwait has been irrigated with tertiary treated wastewater since 1976. A field investigation at the farm has been conducted by the Kuwait Institute for Scientific Research (KISR) to assess the applicability of the natural soil treatment method, in the long term, to improve the quality of the treated wastewater under the conditions prevailing in Kuwait. The collected data have been analyzed to assess the degree of improvement in quality of the infiltrated water with respect to the tertiary wastewater used for irrigation. The data analysis indicates that in spite of low clay content of the soil, improvement in the quality of the tertiary treated wastewater through soil aquifer treatment by the removal of ammonia (>90%), iron (>80%), organic carbon (>90%), biological oxygen demand (BOD) (100%) and bacteria (50–100%, depending on its type), can be expected over a long-term period. Soil leaching, however, tends to increase the total dissolved solids of the infiltrated water and the nitrification process increases the nitrate content.

Feasibility of Soil Aquifer Treatment for Removal Chemical Pollutants of Wastewater

Feasibility of Soil Aquifer Treatment for Removal Chemical Pollutants of Wastewater

Fate of secondary effluent dissolved organic matter during soil-aquifer treatment

The reduction of mass and trihalomethane formation potential (THMFP) of dissolved organic matter (DOM) and its fractions from secondary effluent during laboratory-scale soil-aquifer treatment (SAT) soil columns were studied. Reduction in dissolved organic carbon (DOC), absorbance of ultraviolet light at 254 nm (UV-254), biodegradable dissolved organic carbon (BDOC) and nonbiodegradable dissolved organic carbon (NBDOC) for the bulk DOM averaged 72.35%, 53.98%, 97.49% and 35.33% across the soil columns, respectively. Using XAD-8 and XAD-4 resins, DOM was fractionated into 3 fractions: hydrophobic acid (HPO-A), transphilic acid (TPI-A) and hydrophilic fraction (HPI). HPO-A was removed by 61.06%, TPI-A by 54.86% and HPI by 74.95% as DOC as a consequence of the laboratory-scale SAT, respectively. The reduction of THMFP from HPO-A, TPI-A and HPI was 27.24%, 26.24% and 36.08%, respectively. Proton nuclear magnetic resonance (1H-NMR) spectra revealed that the HPO-A isolated from the secondary effluent contained more aromatic functional groups than the corresponding TPI-A. Fourier-transform infrared (FT-IR) spectrum analysis illustrated that TPI-A had decreased hydrocarbon and increased aromatics content in the SAT columns. Specific ultraviolet light absorbance (SUVA) and specific THMFP for each DOM fraction increased across the soil columns and HPI exhibited greater increase in both than HPO-A and TPI-A. The most problematic THM precursor was found to be HPO-A with its high quantity present in recharged water and high chlorine reactivity.

GIS-based multi-criteria analysis for potential wastewater aquifer recharge sites

GIS and expert knowledge are used as a decision support system to determine adequate potential soil aquifer treatment (SAT) sites for groundwater recharge of Hammamet–Nabeul aquifer located in ‘Cap Bon’ peninsula in North East of Tunisia. These sites are identified using a single-objective multi-criteria analysis. All criteria selected are assumed to be constraints. The acceptable range of each criterion is determined by a critical threshold value, corresponding to standards or normative statements. Based on these acceptable ranges, all criteria are expressed in a Boolean map: excluded areas are coded 0 and those open for consideration are coded 1. Multi-criteria evaluation were performed combining all Boolean maps by means of intersect operator in order to select sites meeting all the criteria. The selection of criteria and acceptable ranges is based on national expert consulting and international published guidelines and technical documents. The resulting map of this GIS-based multi-criteria analysis shows extended potential sites for SAT, exceeding 1000 ha, which indicates a possible use of treated wastewater for groundwater recharge; 8 ha could be supplied by Hammamet Sud plant, 764 ha by SE3 and 347 ha by SE4. 109 ha of these areas could be supplied by both SE3 and SE4. These potential sites are mostly located at rivers banks, around Grand-Nabeul urban area and in some agricultural domains and coastal dunes.

Removal and transformation of organic matter during soil-aquifer treatment

This study investigated the removal and transformation of organic matter through laboratory-scale soil-aquifer treatment (SAT) soil columns over a 110-day period. Reductions in total organic carbon (TOC), dissolved organic carbon (DOC), biodegradable dissolved organic carbon (BDOC), nonbiodegradable dissolved organic carbon (NBDOC) and absorbance of ultraviolet light at 254 nm (UV-254) averaged 71.46%, 68.05%, 99.31%, 33.27% and 38.96% across the soil columns, respectively. DOC/TOC ratios increased slightly with depth while BDOC/DOC ratios showed a converse trend. DOC exiting the soil-column system contained only a very small biodegradable fraction. SAT decreased the concentration of DOC present in feed water but increased its aromaticity, as indicated by specific ultraviolet light absorbance (SUVA), which increased by 50%∼115% across the soil columns, indicating preferential removal of non-aromatic DOC during SAT. Overall, laboratory-scale SAT reduced trihalomethane formation potential (THMFP), although specific THMFP increased. THMFP reduction was dominated by removal in chloroform. All samples exhibited a common general relationship with respect to weight: chloroform>dichlorobromomethane >dibromochloromethane>bromoform.

Manganese Mobilization and Enrichment during Soil Aquifer Treatment (SAT) of Effluents, the Dan Region Sewage Reclamation Project (Shafdan), Israel

The composition of groundwater reclaimed from tertiary soil aquifer treatment systems reflects the dynamic processes taking place in the subsurface, between the infiltration basin and the production wells. At the end of year 2000, following more than a decade of operation, high Mn concentrations (2 micromol L(-1) < or = Mn < or = 40 micromol L(-1)) appeared in the reclaimed effluents of the Dan Region Sewage Reclamation Project (Shafdan), Israel. A mass balance indicates that the high Mn excess originated from the aquifer rocks, most likely following reduction of sedimentary Mn-oxides under suboxic conditions. The subsequent adsorption of the Mn2+ results in a slow Mn2+ front that advances in the direction of groundwater flow only when all the Mn2+ exchangeable sites are saturated. A retardation factor obtained from two independent estimates based on a simple reduction-adsorption-advection model yields a value of about 10. This explains the delayed appearance of the high Mn concentrations at a distance of only -500 m from the infiltration basin.

Transport and Adhesion of Escherichia coli JM109 in Soil Aquifer Treatment (SAT): One-Dimensional Column Study

Bacteria transport and adhesion experiments under water-saturated and partially saturated conditions were examined over a wide range of ionic strength, from 1 to 100 mM KCl, CaCl(2), and MgCl(2), and at water contents of 0.15 and 0.22 in sand columns packed with three different sands, baked, sterilized, and raw sands in order to investigate the effects of ionic strength, water content, and porous media type on the microbial adhesion in soil aquifer treatment (SAT). Well-characterized Escherichia coli JM109 were used as model bacterial cells in this study. Column study results showed that bacterial deposition rates increased with increasing ionic strength and decreasing water content, and were higher in raw sand columns than those in other sand columns. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was applied to experimental results in order to consider the interaction energies between the bacterial cells and collector grains; results revealed that a considerable amount of bacterial cells was weakly deposited onto the solid surfaces in secondary minimum.

Character of Organic Matter in Soil-Aquifer Treatment Systems

The objective of this study was to investigate the character and fate of bulk organics in reclaimed water used for groundwater recharge via soil-aquifer treatment (SAT). The study design followed a watershed guided approach considering hydraulically corresponding samples of drinking water sources, SAT-applied wastewater effluents, and subsequent post-SAT samples representing a series of different travel times in the subsurface. Water samples were fractionated into hydrophobic acids, transphilic acids, and hydrophilic carbon using a XAD resin-based protocol. Extensive characterization of organic carbon in the different samples was performed using state-of-the-art analytical techniques including excitation–emission matrix fluorescence spectroscopy, size exclusion chromatography, carbon-13 nuclear magnetic resonance spectroscopy ( C-NMR 13 ) , Fourier transform infrared spectroscopy (FTIR), and elemental analysis. During SAT, transphilic and hydrophilic organic matter were preferentially removed. The results...

Soil Aquifer Treatment (SAT) as a Natural and Sustainable Wastewater Reclamation/Reuse Technology: Fate of Wastewater Effluent Organic Matter (EfOM) and Trace Organic Compounds

Through the use of innovative analytical tools, the removal/transformation of wastewater effluent organic matter (EfOM) have been tracked through soil aquifer treatment (SAT). While the total amount of EfOM is significantly reduced by SAT, there are trends of shorter term versus longer term removals of specific EfOM fractions. The preferential removal of non-humic components (e.g., proteins, polysaccharides) of EfOM occurs over shorter travel times/distances while humic components (i.e., humic substances) are removed over longer travel times/distances, with the removal of both by sustainable biodegradation. Dissolved organic nitrogen (DON), a surrogate for protein-like EfOM, is also effectively removed over shorter term SAT. There is some background humic-like natural organic matter (NOM), associated with the drinking water source within the watershed, that persists through SAT. While most effluent-derived trace organic compounds are removed to varying degrees as a function of travel time and redox conditions, a few persist even through longer term SAT.

Nitrogen Transformations during Soil–Aquifer Treatment of Wastewater Effluent—Oxygen Effects in Field Studies

Depth-dependent oxygen concentrations and aqueous-phase total ammonia and nitrate/nitrite ion concentrations were measured in the field during the infiltration of wastewater effluent. Measurements illustrated the dependence of nitrogen fate and transport on oxygen availability. Infiltration basins were operated by alternating wet (infiltration) and dry periods. During infiltration periods, ammonia was removed within the top few feet of sediments via adsorption. Biochemical activity rapidly eliminated residual molecular oxygen in the infiltrate, making the soil profile anoxic. During dry periods, oxygen reentered the basin profile and sorbed ammonia was converted to nitrate via nitrification. Oxygen penetrated to a depth of about 0.6m(2ft) within the first few days of dry periods. At greater depths, oxygen levels increased more slowly due to a combination of slow transport kinetics and biochemical (nitrogenous) oxygen demand. During normal wet/dry basin cycles consisting of about 4 wet and 4 dry days, the local vadose zone remained anoxic at depths greater than about 1.5m(5ft) below land surface. As a consequence, conditions for denitrification were satisfied in the deeper sediments. That is, the nitrate nitrogen produced in near surface sediments moved freely downward with infiltrating water where it encountered an extensive anoxic zone before reaching local monitoring or extraction wells. The relative importance of dissolved organics and sorbed ammonia as electron donors for denitrification reactions remains to be established.

Occurrence and biodegradability studies of selected pharmaceuticals and personal care products in sewage effluent

It is important to determine the behavior of constituents in treated sewage during soil aquifer treatment for water recycling. A collaborative project with Herman Bouwer published in 1984 documented the fate and occurrence of Priority Pollutants during groundwater recharge using wastewater with application to water reuse and agricultural systems. New compounds are continually being manufactured and released to the environment. The interest today has shifted to the behavior of emerging contaminants. One important class of emerging contaminants is pharmaceuticals and personal care products (PPCPs). The hazards to the environment and human health of trace levels of PPCPs in water supplies are poorly understood. A multi compound method using solid phase extraction and chemical derivatization with pentafluorobenzylbromide, followed by analysis via gas chromatography/mass spectrometry was used to study the occurrence and removals of 18 PPCPs in a local wastewater treatment plant (WWTP). Overall, 16 out of the 18 selected PPCPs, which span a range of therapeutic classes and some commonly used personal care products, were detected in raw sewage samples collected from the Baltimore Back River WWTP. Ten of the 18 selected PPCPs were detected in the treated sewage effluent, signifying incomplete removal for the majority of the PPCPs during the wastewater treatment processes. The majority of the target analytes were detected in both the influent and effluent WWTP samples at μg/L levels, although some PPCPs (e.g., naproxen and ibuprofen) were encountered at μg/L levels. Biodegradation is an important process for wastewater and soil aquifer treatment. Aerobic batch biodegradation (using activated sludge as microbial inocula) experiments were conducted to gain insight into the biodegradation behavior of our target PPCPs at initial concentrations of 50, 10, and 1 μg/L. Sterile control studies showed no loss of our target PPCPs during the entire incubation period, and sorption to the biomass was found to be negligible for all testing conditions. Biodegradation results were not sensitive to the initial concentration and showed that 13 of the 18 PPCPs tested exhibited biotransformations greater than 80% after 50 days of incubation. Phenytoin, 5-fluorouracil, and diclofenac were the only three compounds with removals less than 60%. The occurrence study revealed the presence of PPCPs in sewage effluents, and the biodegradation study suggests that biotransformation is a possible removal mechanism for PPCPs during groundwater recharge or soil aquifer treatment for water recycling.

EDTA, NTA, Alkylphenol Ethoxylate and DOC Attenuation during Soil Aquifer Treatment

Removals of dissolved organic carbon (DOC), ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA) and carboxylated alkylphenol polyethoxylate metabolites (APECs) were studied at the Sweetwater (Tucson, Ariz.) soil aquifer treatment site that treated chlorinated secondary effluent. The site was operated in a first phase by flooding irregularly for weeks interrupted by days of drying and in a second phase by a regular schedule of flooding for 3 days and drying for 4 days. The average hydraulic loading rates were 0.13 and 0.17 m∕day in the first and second phases, respectively. During drying, oxygen intruded at least 3 m deep into the unsaturated subsurface causing nitrification of the ammonium that was retained in the top layer during flooding. Nitrification increased nitrate concentrations to >200 mg∕L but most was removed to <10 mg∕L during transport to 38 m depth. At 38 m depth, removals of DOC, EDTA, NTA, and APECs during the first phase were 85, 80, 90, and 98%, slightly higher (<7%) than...

Studies of P accumulation in soil/sediment profiles used for large‐scale wastewater reclamation

AbstractWe studied the long‐term accumulation processes and material balances of phosphorus (P) in the soil/sediment profiles of large‐scale effluent recharge basins used for wastewater reclamation by the soil aquifer treatment (SAT) system. The objective was to quantify and clarify the long‐term performance of soil/sediment in the SAT system as a sorbent to filter out P from the recharged effluent. Total P concentration in the soil/sediment profiles of the Shafdan wastewater treatment plant (WWTP) increased over 25 years of operation (1977–2001) by 20–220 mg kg−1, as a result of adding loads of 0.17–6.2 kg m−2 of P. Retained P in the 0–2.0 m soil layer increased from 0.06 to 0.31 kg m−2 with increasing cumulative load of P while the retained percentage gradually decreased from 19 to 5% of the cumulative P load. Accumulation rate of P in the 0–0.15 m horizon in the basins was inversely proportional to recharge time, decreasing from ∼28 mg P kg−1 year−1 during the first 3 years of operation, to &lt;2.3 mg P kg−1 year−1 between the 20th and 25th years of operation. Thus, P content in this horizon approached a steady state after about 10–15 years of effluent recharge under the operational conditions of the Shafdan WWTP. Phosphorus concentration in deeper horizons increased at constant rates of approximately 7.8, 5.9 and 2.9 mg P kg −1 year−1 in the 0.15–0.30, 0.30–0.60 and 1.80 to 2.10‐m horizons, respectively, over the 25 years of effluent recharge. However, the accumulation front of P appears gradually to have moved deeper in the soil profile. In general, this phenomenon may be explained by kinetic limitations to the achievement of full adsorption equilibrium for P between the flowing solution and the solid phase components of the soil. In addition, both the increase of EPC0(the equilibrium P concentration in solution at which there is no sorption or desorption to or from the soil under the given conditions), caused by long‐term effluent recharge, and gradual decrease of the annual average concentration of P in the effluent input after 1995, may result in the steady‐state level of P in the topsoil of the basin.

Phosphorous retardation and breakthrough into well water in a soil-aquifer treatment (SAT) system used for large-scale wastewater reclamation

Retardation and breakthrough of phosphorous in the soil/sediment profiles of a SAT system at the Shafdan wastewater treatment plant, Israel, were investigated in situ. Area-weighted average effluent load to the whole site was 65 m yr −1. Annual average concentrations of P in the recharged effluent ranged between about 1.5 and 7.7 mg L −1 during 25 yr of operation, while P in groundwater remained ⩽0.05 mg L −1 in most wells. Recharge is done through an overlying layer of >40 m sandy soil/sediment formations. By combining results of isotherm tests, long-term monitoring of phosphorous (P) in solid and liquid phases of the recharge site, a simple multi-cell tracer-movement model and measured chloride breakthrough curves to the groundwater we calculated P distribution coefficients and estimated the retardation factor of P. Laboratory measured, isotherm-based distribution coefficient, K d I , was about 4–6 L kg −1 at equilibrium P concentration <6 mg L −1, while field-based K d F was considerably higher, reaching about 20–55 L kg −1 after a load of around 1800 m effluent was recharged. Measured P breakthrough times into two shallow observation wells were 19–21 yr. Calculated P breakthrough times using K d F data agreed with observations while those calculated using K d I grossly underestimated retardation and predicted much shorter breakthrough times. This validated the approach and model used. Estimated P breakthrough times to the deeper observation wells and the recovery wells are more than 100 yr and 400–1100 yr, respectively. These estimates show that P contamination of the reclaimed effluents in the Shafdan plant will not be a problem in the foreseeable future.

Evaluation of steel slag for organic and inorganic removals in soil aquifer treatment

Basic oxygen furnace slag (BOFS) was evaluated as an additive to the soil aquifer treatment (SAT) in the laboratory column tests and the characteristic behaviors of organics and inorganic compounds through the columns were examined with both natural soil and the mixture of soil and slag. It was obvious that the slag could contribute more removals of DOC under both unsaturated and saturated conditions of SAT operation possibly due to its larger surface area. The molecular weight fractions of less than 1 kDa was greatly degraded during the unsaturated SAT operation by biodegradation and the molecular weight fractions of higher than 10 kDa was also significantly reduced after unsaturated SAT by adsorption. It was indicated that the steel slag seemed to play an effective role in reducing the refractory organics during saturated SAT. The macroporous XAD resin isolations showed the increase of hydrophilic fractions with a decrease in the hydrophobic and transphilic fractions through SAT. The use of steel slag resulted in adverse effect on the nitrification due to high pH (about 11) and the relative redox potential measurement showed that the steel slag provided a non-oxidative environment in SAT columns. Almost complete removal of phosphate was achieved during unsaturated and saturated SAT operations with a relatively low hydraulic loading rate and effective adsorption by steel slag. A 20–30% increase of sulfate was observed in slag-containing unsaturated columns whereas the saturated 100% slag columns exhibited 68% decrease of sulfate concentration.

Using soil biomass as an indicator for the biological removal of effluent-derived organic carbon during soil infiltration

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 30 cm 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.

Role of aquifer storage in water reuse

Two case studies are described that explain the role, value, limitations and policy requirements for storing reclaimed water in aquifers for indirect reuse. The first case involves aquifer storage and recovery of water, the product of tertiary treated municipal sewage effluent, via a single injection and recovery well at Bolivar, South Australia. The recovered water, like the source water for injection, is used for unrestricted irrigation of horticulture. A limestone aquifer at a depth of 100 to 160 m confined by clay and containing brackish groundwater provides the storage zone. In the second case, located at Alice Springs, trials are proceeding to assist in the design and establishment of a soil–aquifer treatment system which will allow water derived from secondary treatment of municipal sewage effluent to be stored in an unconfined alluvial aquifer for irrigation of horticulture. Intermittent infiltration from basins provides supplementary water treatment. In each case, the motivations, choice of methods, required investigations, public consultation processes, and economics of subsurface storage are presented. The lessons learned that may assist with development of policies to facilitate environmentally sustainable subsurface storage of water in water reuse projects are discussed.

Effect of Long-Term Effluent Recharge on Phosphate Sorption by Soils in a Wastewater Reclamation Plant

The Soreq recharge basins, used for wastewater reclamation employing the Soil-Aquifer Treatment (SAT) system, have been recharged, on average, by about 1,800 m depth of secondary effluent during their operation period of ∼25 years. An estimated amount of ∼6 kg P m−2 was added to the soil/sediment column during this period. The objective of this study was to compare phosphorous sorption characteristics of representative pristine soils in the Soreq recharge site to those of the basin soils sampled after a long period of effluent recharge. Batch isotherm experiments were conducted: samples of one g of soil were equilibrated with 25 mL of 0.02 M NaCl solution containing 0–3.2 mM of phosphate for 7 days at 25± 1∘C and P sorption was measured. Long-term effluent recharge significantly decreased the maximum P sorption capacity of the top sandy soil (0.15–0.3 m) and only very slightly decreased maximum P isotherm capacity of the deep clayey-sand soil (10–10.5 m). The retention of P in the basin sandy soil primarily involved sorption and surface precipitation reactions on soil carbonates. In the basin clayey-sand soil, P was retained by its sorption on surfaces of Fe, Al, Mn oxide/hydroxides and clay minerals. Long-term effluent recharge increased EPC0, (the equilibrium P concentration in solution at which there is no sorption or desorption to or from the soil under the given conditions), of the basin soils compared to the pristine soils. Due to loading of the top horizons with P by prolonged recharge and reduced P concentration in the effluent, EPC0 of the basin sandy soil is now equal to the average P concentration of the recharged effluents. If effluent P concentration will decrease further, the top sandy soil will become a source of P to the reclaimed water, rather than a sink. The clayey-sand layers and lenses in the vadose zone of the SAT system of the Soreq site offer a large capacity for P adsorption. With gradual leaching of carbonate minerals and synthesis of secondary clay minerals, driven by long-term effluent recharge, P retention mechanisms in the basin soil may be changed, but this process would be extremely slow.

Water quality dependence on the depth of the vadose zone in SAT-simulated soil columns

Three soil aquifer treatment (SAT) columns were operated for five months to investigate the dependence of the treated water quality upon the depth of unsaturated vadose zone in terms of its organics, nitrogen and phosphorus contents. It was found that DOC removal was independent of the unsaturated vadose zone depth except during the initial flooding period when the effluent was injected into each column. From tests to study the nitrate profile, it was found that the pattern of nitrification was dependent on the depth of the unsaturated zone during the initial periods of SAT flooding. However, no further nitrification occurred at the end of the flooding since the injection of the effluent continued to provide a high loading concentration to the SAT columns. The lack of phosphate removal in this study indicates that its removal is more dependent upon the soils and aquifer characteristics than on the depth of unsaturated zone.

Fate of Wastewater Effluent hER-Agonists and hER-Antagonists during Soil Aquifer Treatment

Estrogen activity was measured in wastewater effluent before and after polishing via soil-aquifer treatment (SAT) using both a (hER-beta) competitive binding assay and a transcriptional activation (yeast estrogen screen, YES) assay. From the competitive binding assay, the equivalent 17alpha-ethinylestradiol (EE2) concentration in secondary effluent was 4.7 nM but decreased to 0.22 nM following SAT. The YES assay indicated that the equivalent EE2 concentration in the same effluent sample was below the method-detection limit (<2.5 x 10(-3) nM) but increased to 0.68 nM in effluent polished via SAT processes. It was hypothesized thattest-dependent differences arose because the competitive binding assay responds positively to both estrogen mimics and anti-estrogens; the YES assay responds to estrogen mimics, but test response is inhibited by anti-estrogens. The hypothesis was supported when organics extracted from wastewater effluent inhibited the YES test response to EE2 (anti-estrogenic effect). A similar extract prepared from SAT-polished effluent augmented the EE2 curve (agonist response). When hydrophobic organics in secondary effluent were fractionated, assay results indicated that several physically distinct anti-estrogens were present in the sample. From this work, it is evident that transcription-activation bioassays alone should not be relied upon to measure estrogenic activity in complex environmental samples because the simultaneous presence of both agonists and antagonist compounds can yield false negatives. Multiple in vitro bioassays, sample fractionation or tests designed to measure anti-estrogenic activity can be used to overcome this problem. It is also clear that there are circumstances under which SAT does not completely remove estrogenic activity during municipal wastewater effluent polishing.