Tetracycline resistance genes in activated sludge wastewater treatment plants

The development and proliferation of antibiotic resistance in pathogenic, commensal, and environmental microorganisms is a major public health concern. The extent to which human activities contribute to the maintenance of environmental reservoirs of antibiotic resistance is poorly understood. In the current study, wastewater treatment plants (WWTPs) were investigated as possible sources of tetracycline resistance via qualitative PCR and quantitative PCR (qPCR). Various WWTPs and two freshwater lakes were surveyed for the presence of an array of 10 tetracycline resistance determinants (tet(R)): tet(A)-(E), tet(G), tet(M), tet(O), tet(Q), tet(S). All WWTP samples contained more different types of tet(R) genes, as compared to the lake water samples. Gene copy numbers of tet(G) and tet(Q) in these samples were quantified via qPCR and normalized to both the volume of original sample and to the amount of DNA extracted per sample (a proxy for bacterial abundance). Concentrations of tet(Q) were found to be highest in wastewater influent while tet(G) concentrations were highest in activated sludge. Investigation of the effects of UV disinfection on wastewater effluent showed no reduction in the number of detectable tet(R) gene types.     

Pharmaceutical chemicals and endocrine disrupters in municipal wastewater in Tokyo and their removal during activated sludge treatment

We measured six acidic analgesics or anti-inflammatories (aspirin, ibuprofen, naproxen, ketoprofen, fenoprofen, mefenamic acid), two phenolic antiseptics (thymol, triclosan), four amide pharmaceuticals (propyphenazone, crotamiton, carbamazepine, diethyltoluamide), three phenolic endocrine disrupting chemicals (nonylphenol, octylphenol, bisphenol A), and three natural estrogens (17beta-estradiol, estrone, estriol) in 24-h composite samples of influents and secondary effluents collected seasonally from five municipal sewage treatment plants in Tokyo. Aspirin was most abundant in the influent, with an average concentration of 7300 ng/L (n = 16), followed by crotamiton (921 ng/L), ibuprofen (669 ng/L), triclosan (511 ng/L), and diethyltoluamide (503 ng/L). These concentrations were 1 order of magnitude lower than those reported in the USA and Europe. This can be ascribed to lower consumption of the pharmaceuticals in Japan. Aspirin, ibuprofen, and thymol were removed efficiently during primary + secondary treatment (> 90% efficiency). On the other hand, amide-type pharmaceuticals, ketoprofen, and naproxen showed poor removal (< 50% efficiency), which is probably due to their lower hydrophobicity (logKow < 3). Because of the persistence of crotamiton during secondary treatment, crotamiton was most abundant among the target pharmaceuticals in the effluent. This is the first paper to report ubiquitous occurrence of crotamiton, a scabicide, in sewage. Because crotamiton is used worldwide and it is persistent during secondary treatment, it is a promising molecular marker of sewage and secondary effluent.     

Heterotroph anoxic yield in anoxic aerobic activated sludge systems treating municipal wastewater

As input to the steady state design and kinetic simulation models for the activated sludge system, the correct value for the heterotroph anoxic yield is essential to provide reliable estimates for the system denitrification potential. This paper examines activated sludge anoxic yield values in the literature, and presents experimental data quantifying the value. In the literature, in terms of the structure of ASM1 and similar models, theoretically it has been shown that the anoxic yield should be reduced to approximately 0.79 the value of the aerobic yield. This theoretical value is validated with data from corresponding aerobic OUR and anoxic nitrate time profiles in a batch fed laboratory scale long sludge age activated sludge system treating municipal wastewater. The value also is in close agreement with values in the literature measured with both artificial substrates and municipal wastewater. Thus, it is concluded that, in ASM1 and similar models, for an aerobic yield of 0.67mg COD/mg COD, the anoxic yield should be about 0.53 mg COD/mg COD. Including such a lower anoxic yield in ASM1 and similar models will result in a significant increase in denitrification potential, due to increased denitrification with wastewater RBCOD as substrate. In terms of the structure of ASM3, for the proposed substrate storage yields and the aerobic yield of 0.63 mg COD/mg COD, experimental data indicate that the corresponding anoxic yield should be about 0.42 mg COD/mg COD. This is significantly lower than the proposed value of 0.54 mg COD/mg COD, and requires further investigation.     

Biological degradation of pharmaceuticals in municipal wastewater treatment: proposing a classification scheme

A simple classification scheme is suggested to characterize the biological degradation of micropollutants such as pharmaceuticals, musk fragrances and estrogens during wastewater treatment. The scheme should be a basis for the discussion about potential removal efficiencies. Hence, the biological degradation of 25 pharmaceuticals, hormones and fragrances was studied in batch experiments at typical concentration levels using activated sewage sludge originating from nutrient-eliminating municipal wastewater treatment plants. Since pseudo first-order degradation kinetics was observed for all compounds down to ng L(-1) levels, the removal rates can be predicted for various reactor configurations. Therefore dilution of wastewater (e.g. by extraneous water) is expected to reduce the degree of biological removal. Wastewater segregation and treatment at the source are therefore to be favoured for elimination of persistent micropollutants over centralized end-of-pipe treatment. For reactor configurations typical for nutrient removal in municipal wastewater, the derived formula for predicting removal allows the identification of three groups of micropollutants according to their degradation constant k(biol): compounds with k(biol)<0.1 L g(SS)(-1)d(-1) are not removed to a significant extent (<20%), compounds with k(biol)>10 L g(SS)(-1)d(-1) transformed by >90% and in-between moderate removal is expected. Based on the degradation of a heterogeneous group of 35 compounds (including literature data), state of the art biological treatment schemes for municipal wastewater are not efficient in degrading pharmaceuticals: only 4 out of 35 compounds are degraded by more than 90% while 17 compounds are removed by less than 50%.     

Simulation and optimization of chemically enhanced primary/activated sludge treatment for small communities

Over the last two decades, the use of coagulation and flocculation has been emphasized for the enhancement of primary sedimentation in municipal wastewater treatment plants. This work is concerned with the development of an approach for the simulation and optimization of a chemically enhanced primary treatment (CEPT)/activated sludge scheme for municipal wastewater treatment using ferric chloride as a coagulant. A mathematical model has been developed which comprises empirical relations for the CEPT stage based on reported experimental data. The activated sludge model has been based on reported rules of thumb.

Optimization has been undertaken using the BOX Complex Routine to minimize a cost objective function with controlling parameters. The effect of varying operating cost components on the cost function has been also assessed via sensitivity analysis.

Results indicate that, for small communities, the addition of a CEPT stage is recommended based on technical and economic consideration for current and prospective costs and prices.     

ICEAS工艺启动及活性污泥培养驯化应用实例

结合福州市金山污水处理厂工艺及及活性污泥培养驯化实例,分析总结ICEAS工艺启动及活性污泥培养驯化经验。     

Influence of pharmaceutical residues on the structure of activated sludge bacterial communities in wastewater treatment bioreactors

Concern is growing over contamination of the environment with pharmaceuticals because of their widespread use and incomplete removal during wastewater treatment, where microorganisms drive the key processes. The influence of pharmaceuticals on bacterial community structure in activated sludge was assessed in small-scale wastewater treatment bioreactors containing different concentrations (5, 50, 200 and 500 μg L⁻¹) of several commonly used pharmaceuticals (ibuprofen, naproxen, ketoprofen, diclofenac and clofibric acid). T-RFLP analyses of the bacterial 16S rRNA genes indicated a minor but consistent shift in the bacterial community structure in the bioreactor R50 supplied with pharmaceuticals at a concentration of 50 μg L⁻¹, compared to the control reactor R0, which was operated without addition of pharmaceuticals. In the reactors operated with higher concentrations of pharmaceuticals, a greater structural divergence was observed. Bacterial community composition was further investigated by preparation of two clone libraries of bacterial 16S rRNA genes from reactors R0 and R50. Most clones in both libraries belonged to the Betaproteobacteria, among which Thauera, Sphaerotilus, Ideonella and Acidovorax-related spp. dominated. Nitrite-oxidizing bacteria of the genus Nitrospira sp., which are key organisms for the second stage of nitrification in wastewater treatment plants, were found only in the clone library of the reactor without pharmaceuticals. In addition, diversity indices were calculated for the two clone libraries, indicating a reduced diversity of activated sludge bacterial community in the reactor supplied with 50 μg L⁻¹ of each of selected pharmaceuticals.     

Performance comparison of a pilot-scale UASB and DHS system and activated sludge process for the treatment of municipal wastewater

This study compares the performance of a pilot-scale combination of UASB and DHS system to that of activated sludge process (ASP) for the treatment of municipal sewage. Both systems were operated in parallel with the same sewage as influent. The study was conducted for more than 300 days, which revealed that organic removal efficiency of UASB+DHS system was comparable to that of ASP. Unfiltered BOD removal by both systems was more than 90%. However, UASB+DHS system outperformed ASP for pathogen removal. In addition, volume of excess sludge production from UASB+DHS was 15 times smaller than that from ASP. Moreover, unlike ASP, there is no requirement of aeration for the operation of UASB+DHS system, which makes it an economical treatment system. Considering the above observations, it was concluded that UASB+DHS system can be a cost-effective and viable option for the treatment of municipal sewage over ASP, especially for low-income countries.     

活性污泥在天津港污水处理中常见问题的分析

论述了活性污泥的主要指标、水质管理监测项目等,归纳了活性污泥在天津港污水处理运行中常见的问题,并分析了其产生的原因,提出相应的解决措施,最后指明污水处理日常管理运行的关键。     

Characterization and treatability of aerobic bacterial thermophilically treated wastewater by a conventional activated sludge and granular activated carbon

An industrial wastewater that was pretreated by an aerobic thermophilic bacterial consortium (THE) was subjected to additional treatability studies by granular activated carbon (GAC) and a conventional activated sludge (CAS). The removal of dissolved organic carbon (DOC) in both systems was generally found to be similar. While GAC was able to attain better effluent concentrations of toluene and methyl isobutyl ketone (MIBK), the CAS was much more efficient at removing acetone. Furthermore, unlike the GAC, the performance of the CAS was not influenced by the high degree of variability in the influent wastewater. Characterization of the influent thermophilic wastewater using gas chromatography-mass spectroscopy (GC/MS) was performed to quantify the micropollutants as well as to evaluate removal efficiencies from the GAC and CAS systems.     

Fate and distribution of pharmaceuticals in wastewater and sewage sludge of the conventional activated sludge (CAS) and advanced membrane bioreactor (MBR) treatment

In this paper we report on the performances of full-scale conventional activated sludge (CAS) treatment and two pilot-scale membrane bioreactors (MBRs) in eliminating various pharmaceutically active compounds (PhACs) belonging to different therapeutic groups and with diverse physico-chemical properties. Both aqueous and solid phases were analysed for the presence of 31 pharmaceuticals included in the analytical method. The most ubiquitous contaminants in the sewage water were analgesics and anti-inflammatory drugs ibuprofen (14.6-31.3 μg/L) and acetaminophen (7.1-11.4 μg/L), antibiotic ofloxacin (0.89-31.7 μg/L), lipid regulators gemfibrozil (2.0-5.9 μg/L) and bezafibrate (1.9-29.8 μg/L), β-blocker atenolol (0.84-2.8 μg/L), hypoglycaemic agent glibenclamide (0.12-15.9 μg/L) and a diuretic hydrochlorothiazide (2.3-4.8 μg/L). Also, several pharmaceuticals such as ibuprofen, ketoprofen, diclofenac, ofloxacin and azithromycin were detected in sewage sludge at concentrations up to 741.1, 336.3, 380.7, 454.7 and 299.6 ng/g dry weight. Two pilot-scale MBRs exhibited enhanced elimination of several pharmaceutical residues poorly removed by the CAS treatment (e.g., mefenamic acid, indomethacin, diclofenac, propyphenazone, pravastatin, gemfibrozil), whereas in some cases more stable operation of one of the MBR reactors at prolonged SRT proved to be detrimental for the elimination of some compounds (e.g., β-blockers, ranitidine, famotidine, erythromycin). Moreover, the anti-epileptic drug carbamazepine and diuretic hydrochlorothiazide by-passed all three treatments investigated.Furthermore, sorption to sewage sludge in the MBRs as well as in the entire treatment line of a full-scale WWTP is discussed for the encountered analytes. Among the pharmaceuticals encountered in sewage sludge, sorption to sludge could be a relevant removal pathway only for several compounds (i.e., mefenamic acid, propranolol, and loratidine). Especially in the case of loratidine the experimentally determined sorption coefficients (K_ds) were in the range 2214-3321 L/kg (mean). The results obtained for the solid phase indicated that MBR wastewater treatment yielding higher biodegradation rate could reduce the load of pollutants in the sludge. Also, the overall output load in the aqueous and solid phase of the investigated WWTP was calculated, indicating that none of the residual pharmaceuticals initially detected in the sewage sludge were degraded during the anaerobic digestion. Out of the 26 pharmaceutical residues passing through the WWTP, 20 were ultimately detected in the treated sludge that is further applied on farmland.     

Pathways and metabolites of microbial degradation of selected acidic pharmaceutical and their occurrence in municipal wastewater treated by a membrane bioreactor

Laboratory degradation tests with five acidic pharmaceuticals using activated sludge as inocculum under aerobic conditions were performed and microbial metabolites were analysed by liquid chromatography-mass spectrometry (LC-MS). Ketoprofen was partly mineralized as a sole source of carbon and energy and the metabolites determined by LC-MS suggest microbial ketoprofen degradation to proceed along the pathway known for biphenyls and related compounds. Bezafibrate, naproxen and ibuprofen were degraded only cometabolically whereas no transformation was obtained for diclofenac. Some biodegradation intermediates in these batch tests could be tentatively identified by means of LC-MS. The first step in microbial bezafibrate degradation appears to be the hydrolytic cleavage of the amide bond, generating well degradable 4-chlorobenzoic acid as one of the hydrolysis products. As previously found for mammals, ether cleavage and formation of desmethylnaproxen was the initial step in microbial degradation of naproxen. Two isomers of hydroxy-ibuprofen were detected as intermediates in the mineralization of ibuprofen. Laboratory studies suggest that naproxen and ibuprofen can be fully mineralized whereas more stable metabolites occur in microbial ketoprofen and bezafibrate transformation, that may deserve further attention. A LC-MS method for the trace analysis of these metabolites in water was developed and applied to municipal wastewater. Municipal wastewater treatment by a membrane bioreactor may gradually improve the removal of these pharmaceuticals.     

Effects of chromium on activated sludge and on the performance of wastewater treatment plants: A review

Chromium is a heavy metal of commercial importance, thus significant amounts are released in wastewaters. Chromium in wastewaters and in the aquatic environment is primarily encountered in oxidation stages +3 (Cr^(III)) and +6 (Cr^(VI)). Recent publications suggest that Cr^(VI) compounds are more toxic than Cr^(III) ones, while Cr^(III) has been identified as trace element, at least for complex organisms. With respect to chromium species mobility, Cr^(VI) can cross cellular membranes, which then may be oxidized to Cr^(III) and react with intracellular biomolecules. Clear conclusions cannot be derived about the critical chromium concentrations that affect activated sludge growth, as the latter is a function of a number of factors. Broadly, may be supported that activated sludge growth is stimulated at Cr^(III) concentrations up to 15 mg L⁻¹, above which is inhibited, with lethal doses lying above 160 mg Cr^(III) L⁻¹. On the other hand, literature data on Cr^(VI) effects on activated sludge are even more controversial. A number of reports support that Cr^(VI) is toxic to activated sludge at concentrations above 5 mg L⁻¹, while others report growth stimulation at concentrations up to 25 mg L⁻¹. However, all reports agree that Cr^(VI) is definitely an activated sludge growth inhibitor at higher concentrations, while 80 mg Cr^(VI) L⁻¹ have been identified as lethal dose. A number of factors have been identified to influence chromium toxicity on activated sludge, such as, pH, biomass concentration, presence of organic substances or other heavy metals, acclimation process, exposure time, etc. Naturally, the presence of chromium species in wastewaters may affect the performance of wastewater treatment plants often causing malfunctions, particularly for industrial wastewaters containing relatively high chromium concentrations. The present work reviews in a critical way the published literature on chromium effects on activated sludge, and on the operation of wastewater treatment plants.     

Degradation of phthalate esters in an activated sludge wastewater treatment plant

Efficient removal of phthalate esters (PE) in wastewater treatment plants (WWTP) is becoming an increasing priority in many countries. In this study, we examined the fate of dimethyl phthalate (DMP), dibutyl phthalate (DBP), butylbenzyl phthalate (BBP), and di-(2-ethylhexyl) phthalate (DEHP) in a full scale activated sludge WWTP with biological removal of nitrogen and phosphorus. The mean concentrations of DMP, DBP, BBP, and DEHP at the WWTP inlet were 1.9, 20.5, 37.9, and 71.9 μg/L, respectively. Less than 0.1%, 42%, 35%, and 96% of DMP, DBP, BBP, and DEHP was associated with suspended solids, respectively. The overall microbial degradation of DMP, DBP, BBP, and DEHP in the WWTP was estimated to be 93%, 91%, 90%, and 81%, respectively. Seven to nine percent of the incoming PE were recovered in the WWTP effluent. Factors affecting microbial degradation of DEHP in activated sludge were studied using [U-¹⁴C-ring] DEHP as tracer. First order rate coefficients for aerobic DEHP degradation were 1.0×10⁻², 1.4×10⁻², and 1.3×10⁻³ at 20, 32, and 43 °C, respectively. Aerobic degradation rates decreased dramatically under aerobic thermophilic conditions (<0.1×10⁻² h⁻¹ at 60 °C). The degradation rate under anoxic denitrifying conditions was 0.3×10⁻² h⁻¹, whereas the rate under alternating conditions (aerobic-anoxic) was 0.8×10⁻² h⁻¹. Aerobic DEHP degradation in activated sludge samples was stimulated 5-9 times by addition of a phthalate degrading bacterium. The phthalate degrading bacterium was isolated from activated sludge, and maintained a capacity for DEHP degradation while growing on vegetable oil. Collectively, the results of the study identified several controls of microbial PE degradation in activated sludge. These controls may be considered to enhance PE degradation in activated sludge WWTP with biological removal of nitrogen and phosphorus.     

Fate of antibiotics in activated sludge followed by ultrafiltration (CAS-UF) and in a membrane bioreactor (MBR)

The fates of several macrolide, sulphonamide, and trimethoprim antibiotics contained in the raw sewage of the Tel-Aviv wastewater treatment plant (WWTP) were investigated after the sewage was treated using either a full-scale conventional activated sludge (CAS) system coupled with a subsequent ultrafiltration (UF) step or a pilot membrane bioreactor (MBR) system. Antibiotics removal in the MBR system, once it achieved stable operation, was 15-42% higher than that of the CAS system. This advantage was reduced to a maximum of 20% when a UF was added to the CAS. It was hypothesized that the contribution of membrane separation (in both systems) to antibiotics removal was due either to sorption to biomass (rather than improvement in biodegradation) or to enmeshment in the membrane biofilm (since UF membrane pores are significantly larger than the contaminant molecules). Batch experiments with MBR biomass showed a markedly high potential for sorption of the tested antibiotics onto the biomass. Moreover, methanol extraction of MBR biomass released significant amounts of sorbed antibiotics. This finding implies that more attention must be devoted to the management of excess sludge.     

活性污泥中原生动物的特征和作用

通过对活性污泥中原生动物的基本生物特征,观察分析方法,在不同环境条件下的种类、数量、活性的表述及其数量和组成的分析,总结出不同种属的原生动物在污水处理过程中的指导作用。     

Assessment of activated sludge microbial community analysis in full-scale biological wastewater treatment plants using patterns of fatty acid isopropyl esters (FAPEs)

This investigation introduces the application of a relatively rapid technique to obtain information about the dynamic nature of microbial communities in activated sludge. The objective has been to consider variability due to measurement errors and protocol changes within the same quantitative framework as the analysis of systematic differences in microbial communities in large-scale aerobic activated sludge secondary wastewater treatment systems. Adjustments to the methodology were considered due to their potential for simplifying and shortening the analysis procedure. All modifications to the protocols used to assay the composition of microbial fatty acids (MFAs) of activated sludge imposed some bias to the chromatographic data. This methodological bias was similar in magnitude to the level of discrimination between activated sludge microbial community structures that were considered as part of the present study. MFA analysis supported the expectations of subtle but systematic community structure differences and shifts in activated sludge based on the current understanding of these wastewater treatment systems. A standardized MFA methodology was shown to be sensitive to minor systematic changes in activated sludge communities due the anticipated underlying factors of selective pressures from the process configuration, history, operational conditions and/or nutrient status. The chemometric approach of fatty acid isopropyl ester analysis of activated sludge can provide a routine tool for meaningful and quantitative information of changes in activated sludge quality in full-scale treatment systems.     

Influence of wastewater treatment on sludge production and processing

The challenge of stricter wastewater standards is resulting in configuration changes to wastewater treatment. As facilities upgrade, the type of sludge produced is changing, with growing quantities of secondary and chemical sludge at the expense of primary sludge. It is already understood that secondary sludge is harder to treat than its primary equivalent; therefore, increasing the quantity of this type of sludge will have detrimental impacts downstream. As legislation tightens further, extended aeration times may be required during processing to remove more nutrients. Work has shown that extended aeration further exacerbates the treatability of secondary sludge. This paper explains how tightening wastewater legislation fundamentally alters the nature of the sludge produced, and how these alterations impact further processing, especially with respect to sludge production and type; sludge energy content; performance of anaerobic digestion and dewatering, and potential for thermal energy recovery.     

Effects of sonication on bacteria viability in wastewater treatment plants evaluated by flow cytometry--fecal indicators, wastewater and activated sludge

The application of sonication to wastewater or sludge contributes to the dispersion of aggregates, the solubilisation of particulate matter with an increase in its biodegradability, the damage of microorganisms due to the loss of cellular membrane integrity. This research is aimed at investigating the effects of sonication at 20kHz frequency on viability of microorganisms present in raw wastewater and activated sludge taken from a municipal wastewater treatment plant, as well as pure strains of Escherichia coli and E. faecalis. Flow cytometry was applied for the identification and quantification of viable and dead bacteria free in the bulk liquid, after the fluorescent staining of cellular nucleic acids. The main results showed that: (i) cells of E. coli were highly sensitive to sonication, even at low specific ultrasonic energy (E(s)), and disintegration of a large amount of cells was observed; (ii) on the contrary E. faecalis were more resistant than E. coli, even if high levels of E(s) were applied; (iii) bacteria in raw wastewater exhibited a dynamic of viable and dead bacteria similar to E. coli; (iv) in activated sludge samples, low levels of E(s) produced a prevalent disaggregation of flocs releasing single cells in the bulk liquid, while disruption of bacteria was induced only by very high levels of E(s).     

Removal of antibiotics in conventional and advanced wastewater treatment: implications for environmental discharge and wastewater recycling

Removal of 28 human and veterinary antibiotics was assessed in a conventional (activated sludge) and advanced (microfiltration/reverse osmosis) wastewater treatment plant (WWTP) in Brisbane, Australia. The dominant antibiotics detected in wastewater influents were cephalexin (med. 4.6 microg L(-1), freq. 100%), ciprofloxacin (med. 3.8 microg L(-1), freq. 100%), cefaclor (med. 0.5 microg L(-1), freq. 100%), sulphamethoxazole (med. 0.36 microg L(-1), freq. 100%) and trimethoprim (med. 0.34 microg L(-1), freq. 100%). Results indicated that both treatment plants significantly reduced antibiotic concentrations with an average removal rate from the liquid phase of 92%. However, antibiotics were still detected in both effluents from the low-to-mid ng L(-1) range. Antibiotics detected in effluent from the activated sludge WWTP included ciprofloxacin (med. 0.6 microg L(-1), freq. 100%), sulphamethoxazole (med. 0.27 microg L(-1), freq. 100%) lincomycin (med. 0.05 microg L(-1), freq. 100%) and trimethoprim (med. 0.05 microg L(-1), freq. 100%). Antibiotics identified in microfiltration/reverse osmosis product water included naladixic acid (med. 0.045 microg L(-1), freq. 100%), enrofloxacin (med. 0.01 microg L(-1), freq. 100%), roxithromycin (med. 0.01 microg L(-1), freq. 100%), norfloxacin (med. 0.005 microg L(-1), freq. 100%), oleandomycin (med. 0.005 microg L(-1), freq. 100%), trimethoprim (med. 0.005 microg L(-1), freq. 100%), tylosin (med. 0.001 microg L(-1), freq. 100%), and lincomycin (med. 0.001 microg L(-1), freq. 66%). Certain traditional parameters, including nitrate concentration, conductivity and turbidity of the effluent were assessed as predictors of total antibiotic concentration, however only conductivity demonstrated any correlation with total antibiotic concentration (p=0.018, r=0.7). There is currently a lack of information concerning the effects of these chemicals to critically assess potential risks for environmental discharge and water recycling.