Biological Water Treatment Processes Research Articles

Comparing DNA isolation and sequencing strategies for 16S rRNA gene amplicon analysis in biofilm containing environments

Bacteria are primarily responsible for biological water treatment processes in constructed wetland systems. Gravel in constructed wetlands serves as an essential substrate onto which complex bacterial biofilms may successfully grow and evolve. To fully understand the bacterial community in these systems it is crucial to properly isolate biofilms and process DNA from such substrates. This study looked at how best to isolate bacterial biofilms from gravel substrates in terms of bacterial richness. It considered factors including the duration of agitation during extraction, extraction temperature, and enzyme usage. Further, the 16S taxonomy data subsequently produced from Illumina MiSeq reads (using the SILVA 132 ribosomal RNA (rRNA) database on the DADA2 pipeline) were compared with the 16S data produced from Oxford Nanopore Technologies (ONT) MinION reads (using the NCBI 16S database on the EPI2ME pipeline). Finally, performance was tested by comparing the taxonomy data generated from the Illumina MiSeq and ONT MinION reads using the same (SILVA 132) database. We found no significant differences in the effective number of species observed when using different bacterial biofilm detachment techniques. However, enzyme treatment enhanced the total concentration of DNA. In terms of wetland community profiles, relative abundance differences within each sample type were clearer at the genus level. For genus-level taxonomic classification, MinION sequencing with the EPI2ME pipeline (NCBI database) produced bacterial abundance information that was poorly correlated with that from the Illumina MiSeq and DADA2 pipelines (SILVA132 database). When using the same database for each sequencing technology (SILVA132), the correlation between relative abundances at genus-level improved from negligible to moderate. This study provides detailed information of value to researchers working on constructed wetlands regarding efficient biofilm detachment techniques for DNA isolation and 16 s metabarcoding platforms for sequencing and data analysis.

Contamination Characteristics，Detection Methods，and Control Methods of Antibiotic Resistance in Pharmaceutical Wastewater

Pharmaceutical industry wastewater contains a large number of emerging pollutants such as antibiotics， antibiotic resistant bacteria （ARBs）， and antibiotic resistance genes （ARGs）. The present biological water treatment processes cannot effectively remove these pollutants. Eventually， they are discharged into various water bodies or penetrate into soil with the effluent， causing environmental pollution and affecting human health. Therefore， exploring the pollution characteristics of antibiotics， ARBs， and ARGs in pharmaceutical wastewater and knowing the methods to detect and control antibiotic resistance pollution in wastewater are crucial for reducing the contamination of antibiotics and ARGs and assessing the ecological risks of antibiotic resistance. Aiming at the problem of antibiotic resistance pollution in a pharmaceutical wastewater treatment plant （PWWTPs）， the pollution status of antibiotics， ARBs， and ARGs in pharmaceutical wastewater was discussed. Different assessment methods of antibiotic resistance in pharmaceutical wastewater were summarized. Finally， the wastewater treatment technologies commonly used to remove antibiotics and ARGs in PWWTPs were summarized in order to provide a theoretical basis for the ecological risk assessment and scientific control of antibiotics and ARGs in the environment.

A novel method to estimate biofilm activity based on enzymatic oxygen release from hydrogen peroxide decomposition

Biofilm is central for biological water treatment processes in recirculating aquaculture systems (RAS). A lack of suitable methods for quantifying biofilm activity, however, makes it difficult to assess and compare the microbial status of biofilm. This type of information of the biofilm will be useful to assess the colonization status of nitrifying biocarriers or to evaluate the effect of disinfectants on the biofilm activity.Here we introduce a novel assay for rapid assessment of microbial activities in the biofilm attached on bioelements from a RAS biofilter. The assay consisted of an intermittent respirometer platform where biofilter elements were exposed to 10 mg/L hydrogen peroxide (H2O2) for 1 h, following concurrent measurements of oxygen release from the decomposition of H2O2 caused by biofilm-associated enzymes. A different number of colonized, mature bioelements from a moving bed biofilter in a freshwater RAS were tested with repeated H2O2 exposure, and compared against their autoclaved forms. A substantial increase in dissolved oxygen (DO) concentration (0.92–2.31 mg O2/L) occurred with mature bioelements during 1 h of H2O2 exposure, compared to small amounts of DO release (≤0.27 mg O2/L) with autoclaved bioelements. This substantiates that H2O2 decomposition by biofilm is mainly governed by microbial enzymatic activities. A monomolecular model fitted well with the observed oxygen release profiles of tested mature bioelements after H2O2 exposure (R2 > 0.98). The kinetic rate constant of net oxygen release (kor, h−1) was proportional (R2 for linear fit = 0.99) to the number of mature bioelements tested. Repeated exposure of H2O2 to the same bioelements did not change kor, which indicates that 10 mg/L H2O2 with an exposure time of 1 h does not suppress enzymatic activity in biofilm. Our study provides a new rapid method that allows simple quantification of microbial activity in biofilm samples from aquaculture systems, which could potentially be also applied to study biofilm from wastewater treatment plants and other industries.

Evidence and Mechanisms of Selenate Reduction to Extracellular Elemental Selenium Nanoparticles on the Biocathode.

Intracellular selenium nanoparticles (SeNPs) production is a roadblock to the recovery of selenium from biological water treatment processes because it is energy intensive to break microbial cells and then separate SeNPs. This study provided evidence of significantly more extracellular SeNP production on the biocathode (97-99%) compared to the conventional reactors (1-90%) using transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy. The cathodic microbial community analysis showed that relative abundance of Azospira oryzae, Desulfovibrio, Stenotrophomonas, and Rhodocyclaceae was <1% in the inoculum but enriched to 10-21% for each group when the bioelectrochemical reactor reached a steady state. These four groups of microorganisms simultaneously produce intracellular and extracellular SeNPs in conventional biofilm reactors per literature review but prefer to produce extracellular SeNPs on the cathode. This observation may be explained by the cellular energetics: by producing extracellular SeNPs on the biocathode, microbes do not need to transfer selenate and the electrons from the cathode into the cells, thereby saving energy. Extracellular SeNP production on the biocathode is feasible since we found high concentrations of C-type cytochrome, which is well known for its ability to transfer electrons from electrodes to microbial cells and reduce selenate to SeNPs on the cell membrane.

Coupling of (methane + air)-membrane biofilms and air-membrane biofilms: Treatment of p-nitroaniline wastewater

Membrane biofilm (MBf) technology is a promising biological water treatment process that combines membrane aeration with biofilms. To expand its application in the treatment of toxic organic wastewater, methane/air gas mixture-MBfs ((CH4 + Air)-MBfs) and air-MBfs were coupled to enhance the treatment of p-nitroaniline (PNA) wastewater. Based on exploration of the membrane permeability of methane and oxygen, a hybrid MBf reactor was constructed, and the degradation characteristics of PNA and the coupling effects of (CH4 + Air)-MBfs and air-MBfs were studied. The permeation flux of methane was found to be 1.114 g/(m2 d) when using a methane/air gas mixture at an aeration pressure of 10 kPa, and this result was better than that when methane was used as the aeration gas alone. Aeration with a methane/air gas mixture provided conditions for realizing aerobic methane oxidation; the aerobic methane oxidation that occurred in the (CH4 + Air)-MBfs promoted the reduction of PNA, and the intermediates of PNA degradation were further degraded by the air-MBfs. At an influent PNA membrane area load of 1.67 g/(m2 d), the PNA removal load reached 187.30 g/(m3 d). The coupling of MBfs took advantage of different matrix-based MBfs and promoted the degradation of PNA by utilizing the synergistic effects of various functional microorganisms.

Formalization of the Task of Creating a Mathematical Model of Combined Wastewater Treatment Processes

This paper focuses on the formation approach to formalize the mathematical modeling of wastewater treatment processes for further forming decision support systems for wastewater treatment facilities management on such a theoretical basis. To create an experimental model of formalization of modeling problems, research was conducted on activated sludge from municipal sewage treatment facilities by introducing an oxidant (H2O2) during standard operation of wastewater treatment facilities and introducing a toxicant (sulfur compounds). It was determined that under conditionally standard conditions, the influence of the oxidant is negative: exceeding technological standards of the concentration of dissolved oxygen in water solutions (3.0–13,7 mg/l), low water column transparency (1.4–1.6 cm), higher concentrations of ammonia nitrogen and phosphorus. With the appearance of a toxicant in the form of reduced sulfur compounds (sulfide ions and hydrogen sulfide 1.4–2.8 mg/l), on the contrary, the positive effect of H2O2 on biological water treatment processes was determined: the concentration of dissolved oxygen increases to 3.4 mg/l and the swelling of activated sludge stops. In this case, using a simplified scheme of expert evaluation as a global quality criterion of the biological stage management process of water treatment for rapid assessment of the vitality of activated sludge is justified. As parameters available for direct automatic measurement, it was proposed to use ORP and pH approximated by the regression equation. Also, a conditional scheme of the decision support system for water treatment management was proposed, which will provide two-level hierarchical control: situational and operational in real-time with a preventive response to emergencies; tactical with daily, at least daily, forecasting of the treatment plants.

Effects of stabilizers on sustainability, activity and decolorization performance of Manganese Peroxidase enzyme produced by Phanerochaete chrysosporium

Manganese Peroxidase (MnP), is one of the most promising lignin depolymerization enzymes, which has been widely used for degradation purposes. Nevertheless, MnP tends to lose activity rapidly during its maintenance phase and degradation process, especially in the inevitable presence of hydrogen peroxide. This study aimed to improve MnP efficiency produced by Phanerochaete chrysosporium, via enhancing its sustainability. In this context, the effects of MnO2, Fe3O4, PEG, Veratryl Alcohol (VA), and DMSO as stabilizing agents on MnP activity were explored both in vivo and in vitro. During in vivo experiments, heterogeneous Fe3O4 was found to be the desirable choice to enhance MnP production, obtaining a maximum MnP activity of 2149 U/L, which was a 67 % boost over the stock configuration. Also, in vitro studies demonstrated a noticeable increase in the stability of the extracted MnP from 8 days up to 14, 23, 23, 25, and 26 days by the addition of MnO2, VA, Fe3O4, PEG, and DMSO stabilizers, respectively. The efficiency of stabilizers on degradation ability of MnP was also examined; optimum conversion of model dyes viz., AO7 and CV, were improved 36.17 and 126.51 % in response to stabilizers, respectively. The inclusion of stabilizers managed to improve sustainability, performance, and cost-effectiveness of the biological water treatment process.

Removal of emerging pharmaceutical pollutants: A systematic mapping study review

Abstract The presence of certain pharmaceutical compounds in ground and surface waters may constitute a serious environmental problem, even at low concentrations. The removal of these compounds is a trending research topic that implies a wide variety of disciplines. To provide clear insight into this field of research, a Systematic Mapping Study review (SMS) has been conducted. We investigated studies reported from 1993 to 2019 in ScienceDirect library. 4164 articles have been analyzed resulting in 172 primary relevant studies and revealing the treatment of 174 molecules. This paper aims to review the existing and recent trends in techniques for the removal of pharmaceuticals present in varied aqueous matrices and also presents a brief overview of the different classes of pharmaceutical compounds investigated. Findings of this study can help the scientists to identify potential techniques aiming to reduce the impact of pharmaceuticals present in wastewater discharge and into surface water bodies. It was revealed that, antibiotics and analgesics/anti-inflammatories are the most commonly investigated, since the highest risk is posed by these classes. The biological processes were found to be the most commonly used techniques in these field of research, and the diclofenac is the most extensively compounds examined. Recent advances in the field of the combination of AOPs with biological water treatment processes for the degradation of pharmaceuticals are discussed. Finally, advantage and limitations of methods used for the elimination of target compounds are addressed.

Endogenous respiration process analysis between aMBR and UV/O3-aMBR for polluted surface water treatment

Abstract The microbial endogenous respiration process is very important in biological water treatment processes. This study analyzed and compared the endogenous respiration process in an attached growth membrane bioreactor (aMBR) system and a UV/O3 integrated aMBR system (UV/O3-aMBR) in treating polluted surface water with CODMn around 10 mg/L. The endogenous respiration activity of heterotrophic microbes and autotrophic nitrifiers activity in both systems was analyzed and compared. Results show that heterotrophic bacteria and autotrophic nitrifiers enter endogenous respiration at 6 h aeration in an aMBR and 0 h in a UV/O3-aMBR system. Biomass amount on PVA-gel in aMBR was higher than in UV/O3-aMBR in terms of specific respiration rates SOURt, SOURH, and SOURA. Substrate remained on PVA-gel in the aMBR system, but no substrate remained on PVA-gel in the UV/O3-aMBR system. Higher species of microbes, including recoverable and irrecoverable components, existed in the aMBR system as compared to the UV/O3-aMBR system. The UV/O3-aMBR system could make full use of the advanced oxidation process (AOP) and biological process, leading to a higher treatment performance, and has the potential to mitigate total energy demand. Thus, the UV/O3-aMBR system can be used as a new technology for treating polluted surface water with the co-contribution of biological process and AOP treatment.

Modeling and research of the biological water treatment process considering the temperature regime

Household waste water contains mineral and organic pollution, while industrial varies both in composition and concentration, depending of the origin. Whatever type, all waste water required to be cleaned as it contains pollutants which far exceed the permissible concentration limits. Despite the large number of investigations of the corresponding processes, the actual task is to study the interaction of active sludge with pollution under the influence of external factors such as variable temperature, etc. Another important task is the prediction of process parameters waste water treatment based on the information with incomplete data at the design stage of the purification system. The automation of processes occurring in the reactor, in particular the use of bacteria with the optimal age, the creation of conditions for the maximum absorption capacity of active sludge, minimization of economic costs are integral components of modern systems.The mathematical model of aerobic waste water treatment is developed, which describes the processes occurring in the treatment plant taking into account the mutual influences of the characteristics of the process on the characteristics of the environment. The influence of external factors for the temperature calculation on the basis of the equation of thermal balance and the laws of thermodynamics is taken into account. The solution of the corresponding model problem using the m-function pdepe of the Matlab software is found. The influence of temperature of aqueous environment, concentration of oxygen on the absorbing capacity of active sludge is investigated. The dependence of bacterial activity from water temperature is shown.

Degradation of ciprofloxacin by 185/254 nm vacuum ultraviolet: kinetics, mechanism and toxicology

Fluoroquinolone antibiotics (FQs) are highly resistant to conventional biological water treatment processes, thus, it is desirable to develop novel water treatment methods for eliminating FQs efficiently.

Degradation kinetics, mechanism and toxicology of tris(2-chloroethyl) phosphate with 185 nm vacuum ultraviolet

Organophosphorus esters (OPEs), a series of high production volume chemicals, receive increasing concerns due to their occurrence in worldwide aquatic environment and resistance to conventional biological water treatment processes. Degradation of tris(2-chloroethyl) phosphate (TCEP) was tested with 185 + 254 nm ultraviolet irradiation treatment. Transformation of TCEP followed a pseudo-first order kinetics with an apparent rate constant at 1.65 × 10−3 s−1 when [TCEP]0 = 3.51 μM, 185 vacuum ultraviolet (VUV) irradiation intensity = 0.24 mW cm−2. Degradation experiments with wavelength screening, radical scavenging and kinetic calculation revealed that the radical-based oxidation induced by 185 nm VUV was the dominant mechanism with a reaction rate constant kOH-TCEP at (3.2 ± 0.3) × 108 M−1 s−1. Radical-based addition and substitution of TCEP generated intermediate products with phosphate backbone at early stage (0–20 min). Based on the toxicology analysis including reactive oxygen species and apoptosis of Escherichia coli, these early stage products have lower toxicity than TCEP or their further small molecule products. Variable pH value and natural organic matters/anions affected the efficiency of VUV, while intrinsic VUV screening and radicals scavenging were two key inhibition mechanisms. VUV induced a radical-based oxidation of TCEP, and it will be a promising treatment method for transforming and detoxifying micro-pollutants from water.

From urban municipalities to polar bioremediation: the characterisation and contribution of biogenic minerals for water treatment.

Minerals of biological origin have shown significant potential for the separation of contaminants from water worldwide. This study details the contribution of biologically derived minerals to water treatment operations, with a focus on filtration media from urban municipalities and remote cold regions. The results support biofilm-embedded iron and manganese to be the building blocks of biogenic mineral development on activated carbon and nutrient-amended zeolites. The presence of similar iron and manganese oxidising bacterial species across all filter media supports the analogous morphologies of biogenic minerals between sites and suggests that biological water treatment processes may be feasible across a range of climates. This is the first time the stages of biogenic mineral formation have been aligned with comprehensive imaging of the biofilm community and bacterial identification; especially with respect to cold regions. Where biogenic mineral formation occurs on filter media, the potential exists for enhanced adsorption for a range of organic and inorganic contaminants and improved longevity of filter media beyond the adsorption or exchange capacities of the raw material.

Conventional drinking water treatment and direct biofiltration for the removal of pharmaceuticals and artificial sweeteners: A pilot-scale approach

The presence of endocrine disrupting compounds (EDCs), pharmaceutically active compounds (PhACs) and artificial sweeteners are of concern to water providers because they may be incompletely removed by wastewater treatment processes and they pose an unknown risk to consumers due to long-term consumption of low concentrations of these compounds. This study utilized pilot-scale conventional and biological drinking water treatment processes to assess the removal of nine PhACs and EDCs, and two artificial sweeteners. Conventional treatment (coagulation, flocculation, settling, non-biological dual-media filtration) was compared to biofilters with or without the addition of in-line coagulant (0.2–0.8mgAl3+/L; alum or PACl). A combination of biofiltration, with or without in-line alum, and conventional filtration was able to reduce 7 of the 9 PhACs and EDCs by more than 50% from river water while artificial sweeteners were inconsistently removed by conventional treatment or biofiltration. Increasing doses of PACl from 0 to 0.8mg/L resulted in average removals of PhACs, EDCs increasing from 39 to 70% and artificial sweeteners removal increasing from ~15% to ~35% in lake water. These results suggest that a combination of biological, chemical and physical treatment can be applied to effectively reduce the concentration of EDCs, PhACs, and artificial sweeteners.

Examination of possible energy conservation in a biological water treatment process using a multiple regression model

This study examined various controls and operating parameters of a sewage treatment plant by performing multiple regression analyses on the operating parameters and the effluent quality of the sewage treatment plant. For the examination, operating data from April to November, 2012, was collected from a sewage treatment plant using the media anaerobic-anoxic-oxic method. The chemical oxygen demand (CODMn) and total nitrogen (T-N) forecasting models for the secondary sedimentation basin effluent were built through multiple regression analysis and showed Mean Absolute Percentage Error (MAPE) 6.6–9.3 and 16.0–23.7, respectively. All models showed similar results to real observational data. When controlling the operating parameters of CODMn and T-N, by using the regression model and the standardization regression coefficients without violating legal water quality criteria, operating conditions can be set that save an average of 23% of power consumption. Using this result, an operating guide for low energy consumption can be provided to the operators of sewage treatment plants.

Influence of Biofilm on Activated Carbon on the Adsorption and Biodegradation of Salicylic Acid in Wastewater

This paper presents a study of the combined process of adsorption and biodegradation in solid biologically activated carbon (AC) for the removal of salicylic acid aimed at determining the influence of the presence of biofilm on the process. Adsorption on AC and biodegradation of free cell cultures were studied separately so as to compare their performance with that of the combined biosorption system. The formation of bacterial biofilm on the surface of the carbon was investigated. The study was carried out using a range of synthetic solutions containing between 15 and 500 mg/L salicylic acid simulating an industrial effluent from the pharmaceutical industry. An individual bacterium, Pseudomonas putida (DSM 4478), was used to study the differentiated effects. Filtrasorb 400 and GAC 830 ACs were used in the adsorption processes and Filtrasorb 400 in the biofilm formation and combined biosorption processes. As regards, combined adsorption/biodegradation results indicated that the bioactivated carbon system outperformed the combination of conventional AC and biological water treatment processes when working with high pollutant concentrations.

Characterization of bromate-reducing bacterial isolates and their potential for drinking water treatment

The objective of the current study was to isolate and characterize several bromate-reducing bacteria and to examine their potential for bioaugmentation to a drinking water treatment process. Fifteen bromate-reducing bacteria were isolated from three sources. According to 16S rRNA gene sequencing, the bromate-reducing bacteria are phylogenetically diverse, representing the Actinobacteria, Bacteroidetes, Firmicutes, and α-, β-, and γ- Proteobacteria. The broad diversity of bromate-reducing bacteria suggests the widespread capability for microbial bromate reduction. While the cometabolism of bromate via nitrate reductase and (per)chlorate reductase has been postulated, five of our bromate-reducing isolates were unable to reduce nitrate or perchlorate. This suggests that a bromate-specific reduction pathway might exist in some microorganisms. Bioaugmentation of activated carbon filters with eight of the bromate-reducing isolates did not significantly decrease start-up time or increase bromate removal as compared to control filters. To optimize bromate reduction in a biological drinking water treatment process, the predominant mechanism of bromate reduction (i.e., cometabolic or respiratory) needs to be assessed so that appropriate measures can be taken to improve bromate removal.

Modeling of Biological Water and Wastewater Treatment Processes Using Artificial Neural Networks

AbstractA growing world population, unrelenting urbanization, increasing scarcity of good quality water resources, and rising fertilizer applications are the driving forces behind the accelerating upward trend in the use of efficient methods of water and wastewater treatment such as biological processes. Due to the complexity of the reactions in biological processes, a few studies have been performed involving the modeling of biological removal of water pollutants. Thus, the application of the artificial neural networks (ANNs) to predict the performance of the biological systems has been attempted. ANNs are computer‐based systems that are designed to simulate the learning process of neurons in the human brain. One of the characteristics of modeling based on ANNs is that it does not require the mathematical description of the phenomena involved in the process. This review article describes the application of ANNs for modeling of biological water and wastewater treatment processes. Examples of early applications of ANNs in modeling and simulation of biological water and wastewater treatment processes in the presence of various microalgae, macroalgae, bacteria, microbes, yeasts, anaerobic sludge, aerated submerged biofilms, and submerged membrane bioreactors are reviewed.

Review of biologically active filters in drinking water applications

Biological water treatment processes are based on the growth of microbial communities capable of metabolizing contaminants through mediating oxidation–reduction reactions. Biologically active filters (BAFs) are applied in drinking water treatment for the removal of contaminants including natural organic matter, nitrate, trace organic compounds, perchlorate, sulfate, iron, and manganese. BAFs make use of a fixed film that develops on media such as sand, anthracite, granular activated carbon, or membranes. This biofilm is a diverse community, but the conventional biological treatment process basically takes a “black box” approach with respect to microbial community development. Controlling biofilm thickness and producing microbial communities fully adapted to target contaminants represent significant engineering challenges. This article discusses the advantages and applications of BAFs to remove contaminants in drinking water sources, reviews microbial communities in bulk water and biofilms, and summarizes the current fundamental knowledge about biofilm adhesion and control.

Membrane bioreactor for the drinking water treatment of polluted surface water supplies

A laboratory membrane bioreactor (MBR) using a submerged polyethylene hollow-fibre membrane module with a pore size of 0.4 μm and a total surface area of 0.2 m 2 was used for treating a raw water supply slightly polluted by domestic sewage. The feeding influent had a total organic carbon (TOC) level of 3–5 mg/L and an ammonia nitrogen (NH 3-N) concentration of 3–4 mg/L. The MBR ran continuously for more than 500 days, with a hydraulic retention time (HRT) as short as 1 h or less. Sufficient organic degradation and complete nitrification were achieved in the MBR effluent, which normally had a TOC of less than 2 mg/L and a NH 3-N of lower than 0.2 mg/L. The process was also highly effective for eliminating conventional water impurities, as demonstrated by decreases in turbidity from 4.50±1.11 to 0.08±0.03 NTU, in total coliforms from 10 5/mL to less than 5/mL and in UV 254 absorbance from 0.098±0.019 to 0.036±0.007 cm −1. With the MBR treatment, the 3-day trihalomethane formation potential (THMFP) was significantly reduced from 239.5±43.8 to 60.4±23.1 μg/L. The initial chlorine demand for disinfection decreased from 22.3±5.1 to 0.5±0.1 mg/L. The biostability of the effluent improved considerably as the assimilable organic carbon (AOC) decreased from 134.5±52.7 to 25.3±19.9 μg/L. All of these water quality parameters show the superior quality of the MBR-treated water, which was comparable to or even better than the local tap water. Molecular size distribution analysis and the hydrophobic characterisation of the MBR effluent, in comparison to the filtered liquor from the bioreactor, suggest that the MBR had an enhanced filtration mechanism. A sludge layer on the membrane surface could have functioned as an additional barrier to the passage of typical THM precursors, such as large organic molecules and hydrophobic compounds. These results indicate that the MBR with a short HRT could be developed as an effective biological water treatment process to address the urgent need of many developing countries that are plagued by the serious contamination of surface water resources.