Membrane Bioreactor For Wastewater Treatment Research Articles

Membrane bioreactors for wastewater treatment: A review of microbial quorum sensing and quenching to control membrane biofouling based on engineering quorum quenching bacteria

Membrane bioreactor (MBR) is a kind of reputable and prospective technology for wastewater treatment and reformation applications. However, membrane fouling caused by the formation of biofilm on the membrane surface, especially biofouling, is a major obstacle that limits the energy-saving operation and maintenance of the membrane bioreactor (MBR). Microbial communication (known as Quorum Sensing (QS)) is the cause of this fouling phenomenon. A new strategy called Quorum Quenching (QQ) seems to have been successfully used for biological pollution control in wastewater treatment MBR. This review summarizes the latest findings regarding membrane fouling, QS mechanisms and QQ applications. We discussed the opportunities for further practical application of self-cleaning engineering QQ bacteria in MBR.

Powdered Activated Carbon Exacerbates Fouling in MBR Treating Olive Mill Wastewater

Membrane fouling is a major obstacle in membrane bioreactors (MBRs) that treat wastewater. The addition of powdered activated carbon (PAC) is commonly suggested as a way to improve the MBR wastewater treatment process with respect to membrane fouling and effluent quality. Integrating the PAC addition into the MBR may also improve the stability of the acclimated microbial community for biodegrading the recalcitrant organic compounds that can also enhance membrane fouling. In this study, the ability of the MBR-PAC system to decrease membrane fouling was evaluated. Two pilot-scale reactors were operated: one reactor was supplemented with suspended PAC, and one was operated under similar conditions, without PAC. The feed to the reactors comprised domestic and olive oil mill wastewater. Surprisingly, the permeate flux and the membrane permeability decreased faster in the MBR supplemented with PAC compared to the control reactor. Corroborating these MBR fouling results, soluble microbial products (SMPs), originating from the PAC-supplemented reactor, were found to be more adhesive to an ultrafiltration membrane mimetic surface (polyether sulfone) as analyzed in a quartz crystal microbalance with dissipation monitoring (QCM-D). While the PAC had almost no effect on the dissolved organic carbon in the MBR, it altered the molecular weight distribution of the organic molecules in the SMP as observed with gel permeation chromatography: The fractions of 577–789 kDa and the one bigger than 4 × 103 kDa, were elevated and reduced, respectively, by the addition of PAC. A biofilm formation analysis using a confocal laser scanning microscopy showed a higher amount of biofilm on the membrane taken from the PAC reactor, but this membrane showed no traces of PAC particles when analyzed with a scanning electron microscope (SEM). Taken together, altering the composition of the dissolved organic matter in the MBR by PAC addition promoted its adhesion to the membrane, induced biofilm formation, and more prominently, decreased membrane permeability.

In-situ graft-polymerization modification of commercial ultrafiltration membranes for long-term fouling resistance in a pilot-scale membrane bioreactor

Despite significant advances in the design of submerged membrane bioreactors for wastewater treatment, membrane organic- and biofouling remain major obstacles to effective operation, decreasing process performance and membrane lifetime. In this work, we report an improved methodology to minimize fouling in commercial polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes using redox-initiated copolymer grafting. To effectively bind a copolymer that possesses oppositely charged groups to the surface, we modified the membranes during filtration using positively charged [2-(methacryloyloxy)ethyl]-tri-methylammonium (MOETMA) and negatively charged 3-sulphopropyl methacrylate (SPM) monomers, which provide the polyampholyte coating. The binding of the grafted copolymer was verified using Fourier-transform infrared spectroscopy and contact angle measurements. Bench-scale dynamic fouling experiments were employed to optimize the modification time and verify the effectiveness of the modification in mitigating fouling from soluble microbial products and extracellular polymeric substances extracted from municipal wastewater. After demonstrating fouling resistance at the bench scale, membrane fibers were tested in a custom-made membrane bioreactor treating municipal wastewater. During 22 days of testing, fouling was consistently reduced in the case of modified membranes due to the presence of the polyampholyte copolymer barrier that hinders foulant adsorption. At the end of the testing period, the flux of modified fibers was 123% higher than that of the PVDF control. Overall, this work demonstrates a facile and effective modification technique to reduce fouling in ultrafiltration with proven performance during long-term treatment of municipal wastewater.

Comparative study of suspended and attached growth in membrane bioreactors for wastewater treatment

AbstractThe performance of laboratory scale experiments in treating synthetic domestic wastewater were conducted with suspended growth (SG) (without media) and attached growth (AG) (with moving media) membrane bioreactors (MBRs). The aim of this study is to compare fouling and the treatment performance of attached growth membrane bioreactor (AGMBR) with suspended growth membrane bioreactor (SGMBR) by assessing the removal of chemical oxygen demand (COD), nitrate, nitrite and ammonia. The finding shows that with 10% of attached growth media, average COD, nitrate, nitrite and nitrogen ammonia removal efficiency for AGMBR were found to be greater than the SGMBR system. AGMBR significantly increased critical flux, (Jc) up to 48 L m−2 h−1, hence producing low final transmembrane pressure (TMP) after cleaning and decreased the total resistance at 5.69 × 1011 m−1. Addition of cylindrical polythene media resulted in slow TMP increment that prolonged filtration process. In conclusion, AGMBR gave a better treatment performance and could minimize the membrane fouling problem.

Comparison of NLDH and g-C3N4 nanoplates and formative Ag3PO4 nanoparticles in PES microfiltration membrane fouling: Applications in MBR

Development of antifouling membranes for wastewater treatment technology can serve as an economic and efficient approach urgently demanded. Attempts have been made to develop cost-effective blended microfiltration membranes containing ZnAlCu nanolayered double hydroxide (NLDH) or g-C3N4 nanosheets, and Ag3PO4 and NH2-Ag3PO4 nanoparticles with the view of finding the effect of their chemical and structural properties on the membranes performance. The obtained ZnAlCu-NLDH/polyethersulfone (PES) and g-C3N4/PES nanocomposite membranes exhibited the significant flux recovery ratio (FRR), as an antifouling index, of 75.8 and 70.7%, respectively, as compared with the pristine PES membrane having 50.9% of FRR. Inclusion of Ag3PO4 and NH2–Ag3PO4 nanoparticles remarkably increased the permeate flux of the membranes, so that the pure water flux of nanoparticles blended membranes at the pressure of 0.5bar was found to be 292.6 and 319.5Lm−2h-1, respectively, as compared with 229.2Lm−2h-1 for the pristine PES microfiltration membrane. Moreover, the fabricated membrane containing Ag3PO4/NLDH and NH2–Ag3PO4/g–C3N4 nanofillers showed a high flux, wettability and antifouling properties, with regard to the prevention of the interaction of the organic foulant and the hydrophilic membranes. Consequently, the self-cleaning property of nanocomposite blended membranes and the low leaching of nanocomposites could lead to the fabrication of a promising mixed matrix membrane for practical wastewater treatment in membrane bioreactors (MBRs). The increase in the critical flux (CF) also showed the desirable application of the nanocomposite microfiltration (MF) in MBR.

Impact of sludge recirculation ratios on the performance of anaerobic membrane bioreactor for wastewater treatment

The performance of a lab scale anaerobic membrane bioreactor (AnMBR) was evaluated for wastewater treatment. The efficacy of the system was determined at different operating conditions in terms of fluxes and recirculation ratios (R); 10.28 L/m2 h (R = 1, Phase I), 8.8 L/m2 h (R = 2, Phase II and R = 3, Phase III) and 6 L/m2 h (R = 2, Phase IV and R = 3, Phase V), respectively. In comparison with all the operating conditions tested, optimum efficacy of the system was found at flux of 6 L/m2 h and R of 3 in terms of highest COD removal (96.7%), and maximum biogas yield (0.44 L/g CODremoved). The MLSS and MLVSS concentrations under optimum phase were 6.23 and 4.83 g/L, respectively at OLR of 0.46 kg COD/m3 day. The system also exhibited significant reduction of foulants i.e. extracellular polymeric substances (EPS) and soluble microbial products (SMP) resulting in longer membrane runs in optimized phase.

High‐density polyethylene membranes embedded with carboxylated and polyethylene glycol‐grafted nanodiamond to be used in membrane bioreactors

ABSTRACTIn this work, neat and modified nanodiamond (ND) particles were embedded into high‐density polyethylene (HDPE) membranes to improve hydrophilicity and antifouling properties. The membranes were prepared via thermally induced phase separation (TIPS) method and used for pharmaceutical wastewater treatment in membrane bioreactors (MBR) system. To prevent the agglomeration of ND, it was modified using two methods: thermal carboxylation (ND‐COOH) and grafting with polyethylene glycol (ND‐PEG). Membranes with different concentration of ND‐COOH and ND‐PEG nanoparticles ranging from 0.00 to 1.00 wt % were prepared and characterized using a set of analyses including water contact angle, pure water flux, tensile strength, differential scanning calorimeter, field emission scanning electron microscopy, and energy dispersive X‐ray spectroscopy. It was found that the optimum contents of ND‐COOH and ND‐PEG nanoparticles were 0.50 wt % and 0.75 wt %, respectively. The interfacial interaction between nanoparticles and HDPE matrix was studied based on Pukanzsky model. To examine the performance of membranes, critical flux, filtration experiment in the MBR, and fouling analysis of membranes were carried out. The results showed that among the fabricated membranes, 0.75 wt % HDPE/ND‐PEG membrane had the highest water flux and the best antifouling properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47914.

Fe(II)-dosed ceramic membrane bioreactor for wastewater treatment: Nutrient removal, microbial community and membrane fouling analysis

Ferrous dosing is used to reduce phosphorus concentration and alleviate polymeric membrane fouling in membrane bioreactor (MBR). However, limited studies have been conducted to investigate the impacts of ferrous dosing on ceramic membrane fouling, nutrient removal efficiency and microbial community. Accordingly, the aim of this study was to investigate the effect of intermittent ferrous dosing with Fe/P molar ratios of 2 and 1 (with a dosing frequency of every two days) on the overall nutrient removal, functional microbial changes and membrane fouling in ceramic membrane bioreactors (CMBR) in treatment of wastewater. TP concentration of 10 mg/L in influent decreased to 1.94 ± 0.62 mg/L (control), 0.38 ± 0.22 mg/L (Fe/P = 1) and 0.31 ± 0.18 mg/L (Fe/P = 2) in the effluent, respectively. Meanwhile, the effluent total nitrogen (TN) concentrations with Fe/P = 1 treatment (6.80 ± 2.02 mg/L) and Fe/P = 2 treatment (5.12 ± 2.28 mg/L) were lower than that of the control (7.72 ± 2.36 mg/L). Compared to Fe/P = 1, the TN removal performance was better for Fe/P = 2 mainly due to the increased abundance of denitrifying bacteria (Zoogloea and Acinetobacter). In addition, excess iron dose might have toxic effects on bacterial physiology, however the Fe concentrations that cause cell damage vary for different bacteria. The relative abundance of Zoogloea (aerobic denitrifying bacteria) continuously increased with ferrous addition (Fe/P = 2), while other bacteria including Dechloromonas, Hyphomicrobium and Thauera (anoxic denitrifying bacteria), Nitrospira (nitrifying bacteria) and Candidatus Accumulibacter (phosphorus accumulating organism) decreased sharply. Furthermore, membrane fouling was effectively moderated by ferrous dosing and Fe/P = 1 treatment showed improved membrane fouling mitigation than Fe/P = 2. Overall, intermittent ferrous addition in CMBR with Fe/P molar ratio of 1 was beneficial to the removal of nutrients (TP, TN and organics), enhanced succession of microbial community and membrane fouling mitigation.

Calibration and validation of an activated sludge model for membrane bioreactor wastewater treatment plants

ABSTRACTA mathematical model to simulate the biological processes occurring in a membrane bioreactor (MBR) is presented. The model accounts for different MBR technical features by introducing specific permeability parameters for the applied membrane system. The model considers for the heterotrophic storage process and the formation of soluble microbial products. The introduction of an inhibition coefficient influencing the anoxic kinetics enables the model to simulate the particular operating conditions of the plant, such as a high or low dissolved oxygen concentration in the denitrification tank. The model was applied at the MBR wastewater treatment plant of Vila Nova do Ceira (Portugal) which uses a classic pre-denitrification cycle. Data for calibration and validation were sampled at the same wastewater treatment plant. Calibration was achieved by varying the kinetic parameters of the model to match the simulation results to the experimental data. The values of the kinetic parameters were similar to those found in the literature. The validation was performed by two different methodologies to analyse the model response to diverse operating conditions, and to evaluate the resilience of the MBR. Calibration and validation results were evaluated with mean average error, root mean square error and fractional mean bias as performance indexes. In most cases, these indexes confirmed the high accuracy of the model. Overall, the results of the calibration and validation steps enriched the proposed model by providing an effective biological description of the processes characterizing the MBR. Thus, the model is a reliable tool for the management and designing of MBR.

Ultrafiltration with intermittent relaxation using colloidal silica and humic acid as model foulants

Crossflow microfiltration and ultrafiltration are widely used in membrane bioreactors for wastewater treatment and applications in the food, biotechnology and process industries. Membrane fouling is an endemic problem in these operations that can be mitigated by backwashing and intermittent relaxation of the pressure or flux. Intermittent relaxation offers advantages relative to backwashing since it does not alter the membrane morphology or damage susceptible membranes, provides a more uniform removal of the foulant cake layer, and is potentially more energy-efficient. This paper reports a study of intermittent relaxation to mitigate fouling under both constant flux and constant pressure operation using a regenerated cellulose flat sheet ultrafiltration membrane (MWCO 30 kDa) and two model foulants: colloidal silica that is completely rejected and highly compressible and metastable; and, humic acid that is partially rejected and thereby can cause internal pore fouling and is relatively incompressible. Intermittent relaxation more effectively mitigated humic acid fouling owing to the compressibility and metastability of colloidal silica. An optimum relaxation frequency exists owing to the counterbalancing effects between increasing the permeation flux and reducing the time for permeation, which is determined for both constant flux and constant pressure operation. Design heuristics are advanced for the operation of intermittent relaxation.

Application of membrane bioreactor in wastewater treatment: A mini review

Membrane bioreactor (MBR) is credible and promising technology methods for industrial wastewater treatment and recycle it to use in different applications. Today MBR has many domestic and industrial applications and it is popular among the types of conventional treatment methods. The main drawback in the operation of MBR is membrane fouling, that drive to the decrease in permeate flux so need some technique to clean the membrane. In spite of more than a decade of significant advances in improvement of fouling reduction technique, various physical and mechanical methods are still necessary to be improved to limit the membrane fouling problems. In this review, the advantages and disadvantages of membrane bioreactor, fundamental of membrane fouling that is affected by some factors and methods of controlling membrane fouling were discussed.

Cost aspects of membrane bioreactors for wastewater treatment

There is a tendency of more and more intensive annual growth of popularity of membrane process reactor technology. Membrane bioreactors (MBRs) have become serious competitors to other methods on the part of the quality of water cleaning. This is the new and perspective technology; however it is still rather expensive, although not so complicated to operate it. The choice of such a technology demands taking into account all its advantages and disadvantages. Nowadays customers are able to choose between different varieties of configurations of MBRs, smart choice of which may provide economic efficiency.

Development of a combined anaerobic and aerobic membrane bioreactor for wastewater treatment and reclamation in terrestrial-based controlled ecological life support system

Abstract A novel wastewater treatment and reuse system (WTRS) combining an anaerobic membrane bioreactor (AnMBR) and an aerobic membrane bioreactor (MBR) with the design capacity of 115 L/d was developed for a terrestrial-based controlled ecological life support system (CELSS). Results clearly showed that the WTRS realized mineralization of organic compounds and reservation of nitrogenous nutrient, therefore converting the effluent into replenishment for the hydroponic system. Trace gas emission from the WTRS could meet requirements for the whole CELSS. Compared with physico-chemical processes, the specific consumables consumption of the WTRS was advantageous but its specific energy consumption is still in need of improvement. Results of microbial community analysis were consistent with the running state of the AnMBR and the MBR.

Recent developments in biofouling control in membrane bioreactors for domestic wastewater treatment

• Biofouling is a long-standing problem in MBR for wastewater treatment. • Recent advances in anti-biofouling technologies in MBR are critically reviewed. • Integration of MBR with hybrid approach can mitigate biofouling effectively. • Biofouling properties are compared between aerobic and anaerobic MBR systems. • Biofouling is controlled by functionalized media in particle-sparged MBR. Biofouling is a long-standing problem in membrane bioreactors (MBRs) for domestic wastewater treatment because it deteriorates membrane permeability, thus demanding frequent chemical cleaning which can shorten membrane life-time. Recently, several anti-biofouling strategies have been suggested under scientific and engineered attentions from aerobic or anaerobic MBR systems. Nevertheless, researches are still needed to better understand biofouling and develop novel approaches to control this inevitable phenomenon. In this review, recent advances and emerging issues associated with biofouling control in aerobic and anaerobic MBR technologies are critically discussed. Existing challenges and future research perspectives are also addressed to achieve MBR sustainability with biofouling control. This also suggests that integration of MBR with hybrid approach could effectively enhance MBR performance in terms of biofouling mitigation. Future works should elucidate biofouling behavior in integrated MBRs more clearly for sustainable wastewater treatment applications.

Wastewater treatment in membrane bioreactors. Features and application

Membrane bioreactors nowadays are intensively applied in wastewater treatment worldwide. Such type of treatment systems have a large scope of implementation at facilities of different capacity. Small space demand allows placing them in conditions of limited area available. Treatment using of MBR is a combination of sludge treament and membrane filtration. Although the idea of replacing the conventional sedimentation tank activated sludge was attractive, it was difficult to adjust complex process operation of wastewater treatment due to three factors: high cost of membranes, low economic value of grey wastewater, as well as the rapid loss of membrane performance due to the pollution of her pores. Membrane module is used for the separation of sludge liquor that is an alternative to common sedimentation in secondary clarifiers. The article reveals the main features of membrane bioreactors application, concerning its advantages and disadvantages.

Stopping Autoinducer-2 Chatter by Means of an Indigenous Bacterium ( Acinetobacter sp. DKY-1): A New Antibiofouling Strategy in a Membrane Bioreactor for Wastewater Treatment.

Bacterial quorum quenching (QQ) by means of degrading signaling molecules has been applied to antibiofouling strategies in a membrane bioreactor (MBR) for wastewater treatment. However, the target signaling molecules have been limited to N-acyl homoserine lactones participating in intraspecies quorum sensing. Here, an approach to disrupting autoinducer-2 (AI-2) signaling molecules participating in interspecies quorum sensing was pursued as a next-generation antibiofouling strategy in an MBR for wastewater treatment. We isolated an indigenous QQ bacterium ( Acinetobacter sp. DKY-1) that can attenuate the expression of the quorum-sensing (QS) response through the inactivation of an autoinducer-2 signaling molecule, 4,5-dihydroxy-2,3-pentanedione (DPD), among four kinds of autoinducer-2 QS bacteria. DKY-1 released AI-2 QQ compounds, which were verified to be hydrophilic with a molecular weight of <400 Da. The addition of DKY-1 entrapping beads into an MBR significantly decreased DPD concentration and remarkably reduced membrane biofouling. This new approach, combining molecular biology with wastewater engineering, could enlarge the range of QQ-MBR for antibiofouling and energy savings in the field of wastewater treatment.

Energy analysis and optimization of hollow fiber membrane contactors for recovery of dissolve methane from anaerobic membrane bioreactor effluent

This work presents an energy analysis and optimization of the hollow fiber membrane contactors for the recovery of dissolved methane (CH4) in effluents of anaerobic membrane bioreactor wastewater treatment processes. The obtained CH4 could be merged with biogas for further purification or used with a micro-turbine for electricity generation to achieve an energy self-sufficient wastewater treatment process. A mathematical model considering simultaneous CH4 and carbon dioxide (CO2) desorption was used to estimate the membrane area required to remove the dissolved CH4, as well as quality of the outlet gas from the membrane contactor. Energy balance between electrical energy obtained from the recovered CH4 and energies consumed by vacuum and liquid pumps for the operation of membrane contactor were investigated and reported as a Net Electricity obtained per m3 of effluent or simply Net E. Results revealed that a combination of a high strip gas flow rate and slightly low vacuum condition closed to the atmospheric pressure can provide the highest Net E at 0.178 MJ/m3. This value is 85.37% of the total electrical energy that can generated from a 90% recovery of dissolved CH4 using an effluent saturated with a 60 vol% CH4 biogas and flow rate at 2 m3/day. The calculation was made based on the assumptions that 1) the membrane contactor is operated in a non-wetting mode where membrane properties remain constant, 2) flux decline due to the membrane fouling is not considered and 3) the energy required for membrane cleaning and other relevant activities are not factored into the energy analysis. Based on our results, to obtain a high CH4 mole fraction at the gas outlet, a low strip gas flow rate is recommended, however, the operating gas pressure needs to be lowered by applying a vacuum condition to improve the Net E. In addition, it was found that the Net E could be improved by increasing the number of membrane fibers, and lowering the liquid flow rate. The CH4 recovery efficiency could also be optimized to obtain an optimal Net E.

Modelling approach to better control biofouling in fluidized bed membrane bioreactor for wastewater treatment

A mathematical model has been developed to better understand fouling mitigation mechanisms in particle-sparged membrane bioreactor. The model developed herein assumes two fouling mechanisms, (i) the pore blocking leading to the decrease in membrane surface porosity and (ii) the progressive development of compressible cake layer on the membrane surface. The model has been validated by comparison with trans-membrane pressure data registered from the bioreactor filtering a synthetic solution consisting of bentonite, sodium alginate and bovin serum albumine (BSA). Two nonporous media have been tested, Polyethylene terephthalate (PET) beads and silica particles with different dosage (0, 10, 30, 50 and 70% (v/v)). Compared to the experimental data, the model shows satisfactory fitting with R2 ≥ 93%. For both media tested, an optimal dosage to minimize fouling rate was observed at 50% (v/v). Even if both fouling mechanisms have been mitigated by adding fluidized media, pore blocking was more pronounced than cake formation. Moreover, better pore blocking mitigation was observed with PET media (50% (v/v)) having bigger size and lower density than silica particles.

A comparison between two full-scale MBR and CAS municipal wastewater treatment plants: techno-economic-environmental assessment.

A holistic assessment procedure has been used in this study for comparing conventional activated sludge (CAS) and membrane bioreactor (MBR) processes for the treatment of municipal wastewater. Technical, social, administrative, economic and environmental impacts have been evaluated based on 1year of operational data from three full-scale lines (one MBR and two CAS) working in parallel in a large municipal treatment plant. The comparative assessment evidences a slight advantage of the conventional process in the studied case, essentially due to lower costs, complexity and energy consumption. On the other hand, the MBR technology has a better social acceptance and similar overall environmental footprint. Although these results are influenced by site-specific parameters and cannot be generalized, the assessment procedure allowed identifying the most important factors affecting the final scores for each technology and the main differences between the compared technologies. Local conditions can affect the relative importance of the assessed impacts, and the use of weighting factors is proposed for better tailoring the comparative assessment to the local needs and circumstances. A sensitivity analysis on the weighted final scores demonstrated how local factors are very important and must be carefully evaluated in the decision making process.

QAC modified PVDF membranes: Antibiofouling performance, mechanisms, and effects on microbial communities in an MBR treating municipal wastewater

Biofouling remains as a critical issue limiting the widespread applications of membrane bioreactors (MBRs). The use of antibiofouling membranes is an emerging method to tackle this issue. In this study, a polyvinylidene fluoride (PVDF) membrane was modified using a quaternary ammonium compound (QAC) to create an antibiofouling membrane. The membrane was used in an MBR and the performance, mechanisms, and effects on microbial communities of this membrane were compared to a control operated in parallel. Results showed that the membrane exhibited a significantly reduced transmembrane pressure increase rate of 0.29 kPa/d compared with 0.91 kPa/d of the control. Analysis using a confocal laser scanning microscope (CLSM) revealed almost complete lack of living microbes on the antibiofouling membrane in contrast to the control. However, specific oxygen uptake rate and dehydrogenase activity analyses demonstrated no adverse impacts on microbial viability of the bulk activated sludge. Bacterial population analysis using the Illumina Miseq platform added further evidence that the use of antibiofouling membrane did not exert negative influences on richness, diversity and structure of the bacterial community. Effluent quality of the test MBR also exhibited minimal difference from that of the control reactor. The amount of polysaccharides and proteins in the biofouling layer was also significantly reduced. Quartz crystal microbalance with dissipation monitoring suggested that the antibiofouling membrane only allowed organic matter with strong adhesion properties to attach onto the membrane surfaces. These findings highlight the potential of the antibiofouling membrane to be used in MBRs for wastewater treatment and reclamation.