The potential of direct contact membrane distillation for industrial textile wastewater treatment using PVDF-Cloisite 15A nanocomposite membrane

Progress in membrane distillation processes for dye wastewater treatment: A review

Textile and cosmetic industries generate large amounts of dye effluents requiring treatment before discharge. This wastewater contains high levels of reactive dyes, low to none-biodegradable materials and chemical residues. Technically, dye wastewater is characterised by high chemical and biological oxygen demand. Biological, physical and pressure-driven membrane processes have been extensively used in textile wastewater treatment plants. However, these technologies are characterised by process complexity and are often costly. Also, process efficiency is not achieved in cost-effective biochemical and physical treatment processes. Membrane distillation (MD) emerged as a promising technology harnessing challenges faced by pressure-driven membrane processes. To ensure high cost-effectiveness, the MD can be operated by solar energy or low-grade waste heat. Herein, the MD purification of dye wastewater is comprehensively and yet concisely discussed. This involved research advancement in MD processes towards removal of dyes from industrial effluents. Also, challenges faced by this process with a specific focus on fouling are reviewed. Current literature mainly tested MD setups in the laboratory scale suggesting a deep need of further optimization of membrane and module designs in near future, especially for textile wastewater treatment. There is a need to deliver customized high-porosity hydrophobic membrane design with the appropriate thickness and module configuration to reduce concentration and temperature polarization (CP and TP). Also, energy loss should be minimized while increasing dye rejection and permeate flux. Although laboratory experiments remain pivotal in optimizing the MD process for treating dye wastewater, the nature of their time intensity poses a challenge. Given the multitude of parameters involved in MD process optimization, artificial intelligence (AI) methodologies present a promising avenue for assistance. Thus, AI-driven algorithms have the potential to enhance overall process efficiency, cutting down on time, fine-tuning parameters, and driving cost reductions. However, achieving an optimal balance between efficiency enhancements and financial outlays is a complex process. Finally, this paper suggests a research direction for the development of effective synthetic and natural dye removal from industrially discharged wastewater.

Clay-polymer nanocomposites for water and wastewater treatment: A comprehensive review

A majority of water pollution or contamination occurs through the discharge of effluents from industries. Wastewater treatment is crucial to protect our water sources from harmful pollutants. Therefore, a number of efforts have been made to tackle this issue by employing different techniques. Clay minerals and polymers are among these materials used extensively in wastewater treatment. While both have their own drawbacks, it is fascinating to discover that they complement each other to overcome most of their limitations. As a result, clay-polymer nanocomposites (CPNs) have been found to be highly efficient in the adsorption of pollutants from water and show promising results to be a long-term candidate for this purpose. In this paper, we discuss about different types of clay and polymers used in the preparation of CPNs. The work also focuses on the different types of clay-polymer nanocomposites, their synthesis and factors affecting their performance such as pH, temperature, contact time, pollutant concentration and adsorbent dose. In addition, the maximum adsorption capacity, mechanism and kinetics of adsorption are highlighted to assess the performance of CPNs. Various studies indicate that CPNs are only a few steps away from becoming one of the best options for wastewater treatment due to their multiple desirable properties.

Modeling and Life Cycle Assessment of a Membrane Bioreactor–Membrane Distillation Wastewater Treatment System for Potable Reuse

Wastewater treatment for indirect potable reuse (IPR) is a possible approach to address water scarcity. In this study, a novel membrane bioreactor–membrane distillation (MBR-MD) system was evaluated to determine the environmental impacts of treatment compared to an existing IPR facility (“Baseline”). Physical and empirical models were used to obtain operational data for both systems and inform a life cycle inventory. Life cycle assessment (LCA) was used to compare the environmental impacts of each system. Results showed an average 53.7% reduction in environmental impacts for the MBR-MD system when waste heat is used to operate MD; however, without waste heat, the environmental impacts of MBR-MD are significantly higher, with average impacts ranging from 218% to 1400% greater than the Baseline, depending on the proportion of waste heat used. The results of this study demonstrate the effectiveness of the novel MBR-MD system for IPR and the reduced environmental impacts when waste heat is available to power MD.

Reuse of textile wastewater for dyeing cotton knitted fabric with hybrid treatment: Coagulation/sand filtration/UF/NF-RO

The aim of this study was to investigate the usefulness of a membrane hybrid process for the treatment of real textile wastewater (TWW) and its potential reuse in the dyeing of cotton knitted fabric (DCF) process. To determine a suitable pretreatment, sand filtration, coagulation, and UF hollow fiber (UF-HF) were compared on a laboratory scale in terms of turbidity, color, and total organic carbon (TOC). Here, UF-HF provided the best removal results of 93.6%, 99.0%, and 29.0%, respectively. The second stage involves the study of UF flat sheet membranes (5, 10, 20, and 50 kDa). The 5 kDa membrane provided the best permeate quality according to the chemical oxygen demand (COD), turbidity, TOC, conductivity, and color by 54.5%, 83.9%, 94.2%, and 45.7-83.3%, respectively. The final step was treatment with nanofiltration (NF) and reverse osmosis (RO) and these effluents were reused for dyeing. Finally, the effluents from UF-HF/5 kDa UF/RO (Scenario 1) and UF-HF/5 kDa UF/NF (Scenario 2) were analyzed for turbidity, COD, TOC, biological oxygen demand, conductivity, hardness, anions and cations, and color. Both scenarios provided high removal results of 76.3-83.5%, 94.6-97.7%, 88.5-99%, 95.4-98.0%, 59.2-99.0%, 88.7-98.7%, 60.7-99.1%, and 80.0-100%, respectively. They also satisfied the DCF tests compared to the standard DCF samples. The innovative aspect of this research is as follows: 1) the complete analysis of hybrid membrane separation processes for the purpose of reuse of treated textile wastewater and 2) the proposal of a new criterion for reuse for DCF.

Modification of porous polyetherimide hollow fiber membrane by dip-coating of Zonyl® BA for membrane distillation of dyeing wastewater

Wetting and fouling have significantly affected the application of membrane distillation (MD). In this work, a dip-coating method was used for improving surface hydrophobicity of the polyetherimide (PEI) hollow fiber membrane. An air gap membrane distillation (AGMD) process was applied for treatment of the methylene blue (MB) solution. The porous PEI membrane was fabricated by a dry-wet spinning process and the hydrophobic 2-(Perfluoroalkyl) ethanol (Zonyl^® BA) was used as the coating material. From FESEM, the modified PEI-Zonyl membrane showed an open structure with large finger-like cavities. The modified membrane displayed a narrow pore size distribution with mean pore size of 0.028 μm. The outer surface contact angle of the PEI-Zonyl membrane increased from 81.3° to 100.4° due to the formation of an ultra-thin coated layer. The pure water flux of the PEI-Zonyl membrane was slightly reduced compared to the pristine PEI membrane. A permeate flux of 6.5 kg/m² h and MB rejection of 98% were found for the PEI-Zonyl membrane during 76 h of the AGMD operation. Adsorption of MB on the membrane surface was confirmed based on the Langmuir isotherm evaluation, AFM and FESEM analysis. The modified PEI-Zonyl membrane can be a favorable alternative for AGMD of dyeing wastewaters.

Carnauba Wax/Halloysite Nanotube with Improved Anti-Wetting and Permeability of Hydrophobic PVDF Membrane via DCMD

The hydrophobic membranes have been widely explored to meet the membrane characteristics for the membrane distillation (MD) process. Inorganic metal oxide nanoparticles have been used to improve the membrane hydrophobicity, but limited studies have used nano clay particles. This study introduces halloysite nanotube (HNT) as an alternative material to synthesis a hydrophobic poly(vinylidene fluoride) (PVDF)-HNT membrane. The PVDF membranes were fabricated using functionalized HNTs (e.g., carnauba wax and 1H,1H,2H,2H-perfluorooctyl-trichlorosilane (FOTS)). The results were determined by Fourier transform infrared-attenuated total reflection, scanning electron microscope, goniometer and porometer to determine the desired hydrophobic membrane for direct contact membrane distillation (DCMD). The addition of FOTS-HNT (f_s-HNT) and carnauba wax-HNT (f_w-HNT) in the PVDF membrane enhanced the water contact angle (CA) to 127° and 137°, respectively. The presence of f_w-HNT in the PVDF membrane exhibited higher liquid entry pressure (LEP) (2.64 bar) compared to f_s-HNT in the membrane matrix (1.44 bar). The PVDF/f_w-HNT membrane (Pf_w-HNT) obtained the highest flux of 7.24 L/m²h with 99.9% salt removal. A stable permeability in the Pf_w-HNT membrane was obtained throughout 16 h of DCMD. The incorporation of f_w-HNT in the PVDF membrane had improved the anti-wetting properties and the membrane performance with the anti-fouling effect.

A Mini Review on Antiwetting Studies in Membrane Distillation for Textile Wastewater Treatment

The textile industry is an important contributor to the growth of the global economy. However, a huge quantity of wastewater is generated as a by-product during textile manufacturing, which hinders the ongoing development of textile industry in terms of environmental sustainability. Membrane distillation (MD), which is driven by thermal-induced vapor pressure difference, is being considered as an emerging economically viable technology to treat the textile wastewater for water reuse. So far, massive efforts have been put into new membrane material developments and modifications of the membrane surface. However, membrane wetting, direct feed solution transport through membrane pores leading to the failure of separation, remains as one of the main challenges for the success and potential commercialization of this separation process as textile wastewater contains membrane wetting inducing surfactants. Herein, this review presents current progress on the MD process for textile wastewater treatment with particular focuses on the fundamentals of membrane wetting, types of membranes applied as well as the fabrication or modification of membranes for anti-wetting properties. This article aims at providing insights in membrane design to enhance the MD separation performance towards commercial application of textile wastewater treatment.

Heavy metal ions' poisoning behavior-inspired etched UiO-66/CTS aerogel for Pb(II) and Cd(II) removal from aqueous and apple juice

Here, inspired by the poisoning process of heavy metal in human body that the accidental ingested heavy metal can anchor to the functional groups of DNA/protein/enzyme to exert their toxicities during the rapid blood circulation, we developed the adsorbent that enveloped Etched UiO-66 with abundant functional groups into chitosan (CTS) aerogel to capture Pb(II) and Cd(II) in aqueous and apple juice. SEM, XRD and FTIR spectra were used to characterize the Etched UiO-66/CTS aerogel. The results showed that Etched UiO-66/CTS aerogel has a three-dimensional porous structure, and -OH groups of CTS interact with Zr(IV) of Etched UiO-66 to form the stable UiO-66/CTS aerogel. Benefiting from the intrinsic properties of porous and abundant functional groups, Etched UiO-66/CTS aerogel exhibits satisfactory adsorption capacities of 654.9 mg g^-1 for Pb(II) and 343.9 mg g^-1 for Cd(II) at 45 °C. Moreover, the aerogel shows excellent removal efficiencies of 98.21% for Pb(II) and 98.70% for Cd(II) with initial concentration of 1.0 mg L^-1 in apple juice with little effect on the quality of apple juice. This strategy of mimetic heavy metal ions' poisoning behavior opens up a new avenue for the removal of heavy metal ions in complex matrices.

Dye synthetic solution treatment by direct contact membrane distillation using commercial membranes

The reuse of treated dyeing wastewater has become a viable option to minimizing water scarcity problems and environmental impacts in the textile industry. The potentiality of commercial flat sheet membranes of polytetrafluoroethylene (PTFE) and polypropylene (PP) in direct contact membrane distillation (DCMD) for dye synthetic solution treatment has been explored in this work. DCMD is interesting for the textile industry since a recovery of heat by hot dyeing wastewater for thermal energy is possible. Moreover, DCMD enables water and dye reclamation with possible reuse in the textile process. The commercial availability of membranes may expedite the DCMD commercialization in the textile industry. Experiments were conducted in a laboratory-scale circulating unit with synthetic solutions containing reactive or disperse dye. High mean permeate flux up to 18.8 kg m^-2 h^-1 with complete colour rejection was obtained. The dyes tested in this study are not able to completely wet the membranes and the increase of the permeate flux when compared to distilled water is attributed to electrostatic interactions between the dyes and the membranes. Moreover, a partial wetting reduced vapour diffusion path and the permeate flux was increased. PP membrane showed higher performance due to higher porosity when compared to the PTFE membrane. In addition, an influence of dye class on permeability was observed. The results were promising when compared to other studies, which used commercial or lab-scale membranes.

Removal of fluoride in membrane-based water and wastewater treatment technologies: Performance review

The presence of excess fluoride in aqueous media above local environmental standards (e.g., the U.S. Environmental Protection Agency (EPA) standard of 4 mg/L) affects the health of aquatic life. Excess fluoride in drinking water above the maximum contaminant level (e.g., the World Health Organization (WHO) standard of 1.5 mg/L) also affects the skeletal and nervous systems of humans. Fluoride removal from aqueous solutions is difficult using conventional electrochemical, precipitation, and adsorption methods owing to its ionic size and reactivity. Thus, new technologies have been introduced to reduce the fluoride concentration in industrial wastewater effluents and various drinking water sources. Membrane technology is one of the newer technologies found to be very effective in significantly reducing fluoride to desired standards levels; however, it has received less attention than other technologies because it is perceived as a costly process. This study critically reviewed the performance of various membrane process and compared it with effluent and zero liquid discharge (ZLD) standards. The performance review has been conducted with the consideration of the theoretical background, rejection mechanisms, technical viability, and parameters affecting flux and rejection performance. This review includes membrane systems investigated for the defluoridation process but operated under pressure (i.e., reverse osmosis [RO] and nanofiltration [NF]), temperature gradients (i.e., membrane distillation [MD]), electrical potential gradients (i.e., electrodialysis [ED] and Donnan dialysis [DD]), and concentration differences (i.e., forward osmosis [FO]). Moreover, the study also addressed the advantages, limitations, & applicable conditions of each membrane based defluoridation process.

A review of membrane development in membrane distillation for emulsified industrial or shale gas wastewater treatments with feed containing hybrid impurities

Investigations on membrane materials for membrane distillation (MD) and its applications have been ongoing since the 1990s. However, a lack of materials that produce robustly stable and up-to-the-mark membranes for MD for different industrial applications remains an ongoing problem. This paper provides an overview of materials developed for MD applications. Although key aspects of published articles reviewed in this paper pertain to MD membranes synthesized for desalination, future MD can also be applied to organic wastewater containing surfactants with inorganic compounds, either with the help of hybrid treatment processes or with customized membrane materials. Many industrial discharges produce effluents at a very high temperature, which is an available driving force for MD. However, there remains a lack of cost-effective membrane materials. Amphiphobic and omniphobic membranes have recently been developed for treating emulsified and shale gas produced water, but the problem of organic fouling and pore wetting remains a major challenge, especially when NaCl and other inorganic impurities are present, which further deteriorate separation performance. Therefore, further advancements in materials are required for the treatment of emulsified industrial wastewater containing surfactants, salts, and for oil or shale gas wastewater for its commercialized reuse. Integrated MD systems, however, may represent a major change in shale gas wastewater and emulsified wastewater that are difficult to treat.

Influence of dye class on the comparison of direct contact and vacuum membrane distillation applied to remediation of dyeing wastewater

This work investigated the influence of dye class on permeate flux and color rejection by comparing direct contact membrane distillation (DCMD) and vacuum membrane distillation (VMD) applied to remediation of dyeing wastewater. The same operating system at the feed side was used and the driving force of each configuration was determined. Reactive and disperse dye solutions were considered, and a commercial membrane was employed. Final color rejection > 90.79% was obtained, and water was recovered at the permeate side (final normalized permeate flux up to 38.92 kg m^-2day^-1kPa^-1). VMD showed higher normalized permeate flux when compared to DCMD. However, the performance according to dye class depended on MD configuration. Reactive dye resulted in higher permeate flux than the disperse dye solution in DCMD. Contrarily, disperse dye solution showed higher permeate flux in VMD. The formation of a concentration boundary layer at the permeate membrane interface was suggested with disperse dye solution in DCMD, decreasing thus the driving force. In VMD, the boundary effect is negligible with disperse dye solution. This result implies that the VMD performance in the textile industry may depend more on driving force rather than the dye class of the dyeing bath.

Fouling and wetting in the membrane distillation driven wastewater reclamation process - A review

Fouling and wetting of membranes are significant concerns that can impede the widespread application of the membrane distillation (MD) process during high-salinity wastewater reclamation. Fouling, caused by the accumulation of undesirable materials on the membrane surface and pores, causes a decrease in permeate flux. Membrane wetting, the direct permeation of the feed solution through the membrane pores, results in reduced contaminant rejection and overall process failure. Lately, the application of MD for water recovery from various types of wastewaters has gained increased attention among researchers. In this review, we discuss fouling and wetting phenomena observed during the MD process, along with the effects of various mitigation strategies. In addition, we examine the interactions between contaminants and different types of MD membranes and the influence of different operating conditions on the occurrence of fouling and wetting. We also report on previously investigated feed pre-treatment options before MD, application of integrated MD processes, the performance of fabricated/modified MD membranes, and strategies for MD membrane maintenance during water reclamation. Energy consumption and economic aspects of MD for wastewater recovery is also discussed. Throughout the review, we engage in dialogues highlighting research needs for furthering the development of MD: the incorporation of MD in the overall wastewater treatment and recovery scheme (including selection of appropriate membrane material, suitable pre-treatment or integrated processes, and membrane maintenance strategies) and the application of MD in long-term pilot-scale studies using real wastewater.

Water and Wastewater Treatment Systems by Novel Integrated Membrane Distillation (MD)

The scarcity of freshwater has been recognized as one of the main challenges people must overcome in the 21st century. The adoption of an environmentally friendly, cost-effective, and energy-efficient membrane distillation (MD) process can mitigate the pollution caused by industrial and domestic wastes. MD is a thermally driven process based on vapor–liquid equilibrium, in which the separation process takes place throughout a microporous hydrophobic membrane. The present paper offers a comprehensive review of the state-of-the-art MD technology covering the MD applications in wastewater treatment. In addition, the important and sophisticated recent advances in MD technology from the perspectives of membrane characteristics and preparation, membrane configurations, membrane wetting, fouling, and renewable heat sources have been presented and discussed.

Fate and wetting potential of bio-refractory organics in membrane distillation for coke wastewater treatment

Membrane distillation (MD) has been hindered in industrial applications due to the potential wetting or fouling caused by complicated organic compositions. This study investigated the correlations between the fate and wetting potential of bio-refractory organics in the MD process, where three coke wastewater samples pre-treated with bio-degradation and coagulation served as feed solutions. Results showed that although most of the bio-refractory organics in coke wastewater were rejected by the hydrophobic membrane, some volatile aromatic organics including benzenes, phenols, quinolines and naphthalenes passed through the membrane during the MD process. Interestingly, membrane wetting occurred coincidently with the penetration of phenolic and heterocyclic organics. The wetting rate was obviously correlated with the feed composition and membrane surface properties. Ultimately, novel insights into the anti-wetting strategy of MD with bio-refractory organics was proposed, illustrating that the polyaluminum chloride/polyacrylamide coagulation not only removed contaminants which could accelerate membrane wetting, but also retarded membrane wetting by the complexation with organics. The deposition of these complexes on the membrane surface introduced a secondary hydrophilic layer on the hydrophobic substrate, which established a composite membrane structure with superior wetting resistance. These new findings would be beneficial to wetting control in membrane distillation for wastewater treatment.

Wetting phenomena in membrane distillation: Mechanisms, reversal, and prevention

Membrane distillation (MD) is a rapidly emerging water treatment technology; however, membrane pore wetting is a primary barrier to widespread industrial use of MD. The primary causes of membrane wetting are exceedance of liquid entry pressure and membrane fouling. Developments in membrane design and the use of pretreatment have provided significant advancement toward wetting prevention in membrane distillation, but further progress is needed. In this study, a broad review is carried out on wetting incidence in membrane distillation processes. Based on this perspective, the study describes the wetting mechanisms, wetting causes, and wetting detection methods, as well as hydrophobicity measurements of MD membranes. This review discusses current understanding and areas for future investigation on the influence of operating conditions, MD configuration, and membrane non-wettability characteristics on wetting phenomena. Additionally, the review highlights mathematical wetting models and several approaches to wetting control, such as membrane fabrication and modification, as well as techniques for membrane restoration in MD. The literature shows that inorganic scaling and organic fouling are the main causes of membrane wetting. The regeneration of wetting MD membranes is found to be challenging and the obtained results are usually not favorable. Several pretreatment processes are found to inhibit membrane wetting by removing the wetting agents from the feed solution. Various advanced membrane designs are considered to bring membrane surface non-wettability to the states of superhydrophobicity and superomniphobicity; however, these methods commonly demand complex fabrication processes or high-specialized equipment. Recharging air in the feed to maintain protective air layers on the membrane surface has proven to be very effective to prevent wetting, but such techniques are immature and in need of significant research on design, optimization, and pilot-scale studies.

Pilot-scale study on catalytic ozonation of bio-treated dyeing and finishing wastewater using recycled waste iron shavings as a catalyst

A pilot scale reactor with an effective volume of 2.93 m³ was built in-situ and run in both batch and continuous modes to investigate the removal for organic pollutants in bio-treated dyeing and finishing wastewater by heterogeneous catalytic ozonation under neutral pH with waste iron shavings as a catalyst. Experimental results showed that both running modes were able to reduce the chemical oxygen demand (COD) from 132–148 mg/L to a level below the discharge criteria (<80 mg/L) within 15–30 mins under several conditions. Specifically, significantly organic removal was observed with COD, soluble COD (sCOD) and dissolved organic carbon (DOC) decreased from the initial 165, 93 and 76 mg/L to 54, 28 and 16 mg/L respectively, when treated by 10.2 g-O₃/min of ozone dosage at a hydraulic retention time of 30 mins under continuous mode. 80% proteins and 85% polysaccharides were removed with a decrease in their contribution to sCOD from 69% to 43%. Mineralization as well as conversion of high molecular organic compounds was observed through Gas Chromatography-Mass Spectrometer (GC-MS) & Liquid Chromatography-Mass Spectrometer (LC-MS) analysis, which led to a decrease of inhibitory effect from 29% to 25%, suggesting a reduction in the acute toxicity.

Direct contact membrane distillation for textile wastewater treatment: a state of the art review

To meet surging water demands, water reuse is being sought as an alternative to traditional water resources. Direct contact membrane distillation (DCMD) has been increasingly studied in the past decade for its potential as an emerging cost effective wastewater treatment process and subsequent water reuse. This review presents a comprehensive overview of the current progress in the application of DCMD for textile wastewater treatment based on the available state of the art. There are already published review papers about the membrane distillation process, but the difference in the present work is that it focuses on the textile area, which consumes a lot of water and generates large amounts of wastewater, and still needs innovations in the sector. A review focused on the textile sector draws the attention of professionals to the problem and, consequently, to a solution. Current issues such as the influences of feed solution, membrane characteristics and membrane fouling and new insights are discussed. The main performance operating conditions and their effects on the separation process are given. Likewise, challenges associated with the influence of different dyes on the DCMD results are explained. This review also highlights the future research directions for DCMD to achieve successful implementation in the textile industry.

Untapped potentials of acrylonitrile-butadiene-styrene/polyurethane (ABS/PU) blend membrane to purify dye wastewater

Production of acrylonitrile-butadiene-styrene/polyurethane (ABS/PU) blend membrane with high rejection efficiency for disperse and vat dyes, is introduced as a facile and cost effective technique to purify textile wastewater. In this respect, membranes are produced using commercially available polymers, i.e. ABS and PU, with different compositions (ABS/PU: 100/0, 80/20, 70/30, 60/40 and 50/50 w/w) through wet casting. Casting solutions with concentration of 30 wt% are prepared using two different solvents, i.e. dimethylformamide (DMF) and N-methyl-2- pyrrolidone (NMP). The prepared membranes are characterized using a variety of analytical techniques including SEM imaging, FTIR spectroscopy, dry and wet gas permeation, evaluation of reusability, antifouling and mechanical properties, photostability, surface hydrophilicity and pure water permeability (PWP) of the produced membranes. According to the results, irrespective of solvent type, ABS/PU membranes with higher PU content have lower porosity and smaller pore size both of which contribute to enhanced dye rejection efficiency. This is while the impact of PU content on the photostability of ABS/PU membranes was found to be negligible. Additionally, the produced ABS/PU membranes exhibit good reusability and antifouling properties. However, the mechanical properties of ABS/PU membranes with higher PU contents are inferior to those with lower PU contents. This contrast highlights the prominence of optimum PU content to make a trade-off between dye rejection efficiency and mechanical properties. In this regard, ABS/PU (60/40 w/w) membrane is recognized as the one with optimum composition. Furthermore, it was found that regardless of PU content, membranes cast from DMF-based solutions exhibit superior rejection performance over those cast from NMP-based solutions. Overall, one can witness that employing ABS/PU membranes provides a meritorious and clean approach to refine disperse and vat dye wastewaters, a great threat to the environment and human health.