Water Treatment Plant In China Research Articles

Long-term operation of ultrafiltration membrane in full-scale drinking water treatment plants in China: Characteristics of membrane performance

The installed capacity of ultrafiltration (UF) membranes in drinking water treatment plants (DWTPs) has increased significantly, it is necessary to summarize the long-term characteristics of UF membranes in full-scale DWTPs in China. Firstly, the characteristics of UF membranes applied in large-scale DWTPs in China were systematically evaluated based on capacity, location, membrane materials and filtration mode. By 2020, the total capacity of large-scale DWTPs using UF membranes has reached ~10 million m3/d. Polyvinylidene fluoride was the dominant UF membrane material with a proportion of 73.7 %, followed by polyvinyl chloride. Secondly, the performance of UF membranes in various typical DWTPs during long-term operation was analyzed. UF membrane in five typical treatment processes displayed good contaminant removal performance, while the combination of UF membrane with coagulation, sedimentation and filter was widely used. The fouling evolution of UF membranes during long-term operation was systematically analyzed. Then, the effect of pretreatment methods and cleaning approaches on membrane in full-scale DWTPs were assessed. The use of hydraulic cleaning, maintenance cleaning and recovery cleaning could ensure the stable operation of UF membranes, while these cleaning methods may adversely influence membrane lifetime. This study could provide useful guidance for long-term operation of UF membrane in full-scale DWTPs.

Occurrence and toxicity of halobenzoquinones as drinking water disinfection byproducts

Halobenzoquinones (HBQs) are emerging unregulated drinking water disinfection byproducts (DBPs) that are more toxic than regulated DBPs. This study aimed to determine the distribution and formation of HBQs in drinking water from water treatment plants in China, compare their chronic cytotoxicity and their induction of chromosomal damage in Chinese hamster ovary cells, and analyze the correlation of HBQ toxicity with their physicochemical parameters. Two HBQs, 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ) and 2,6-dibromo-1,4-benzoquinone (2,6-DBBQ), were detected in finished water and tap water in China. The concentrations were in the ranges of <2.6–19.70 ng/L for 2,6-DCBQ and <0.38–1.8 ng/L for 2,6-DBBQ. Chemical oxygen demand and residual chlorine were positively correlated with HBQ formation. The HBQ concentration was lower in a drinking water treatment plant using chlorine dioxide. High Ca2+ in tap water decreased the HBQ level. The rank order of HBQ by cytotoxicity was 2-chloro-1,4-benzoquinone > 2,3-diiodo-1,4-benzoquinone > 2,6-diiodo-1,4-benzoquinone > 2,6-dibromo-1,4-benzoquinone > 2,5-dibromo-1,4-benzoquinone > 2,5-dichloro-1,4-benzoquinone > 2,6-dichloro-1,4-benzoquinone > tetrachloro-1,4-benzoquinone > 2,3,6-trichloro-1,4-benzoquinone, and for their genotoxicity, 2,5-dichloro-1,4-benzoquinone > 2,6-dichloro-1,4-benzoquinone > 2,3-diiodo-1,4-benzoquinone > 2,6-diiodo-1,4-benzoquinone > tetrachloro-1,4-benzoquinone > 2,5-dibromo-1,4-benzoquinone > 2,6-dibromo-1,4-benzoquinone > 2,3,6-trichloro-1,4-benzoquinone. The cytotoxicity of six dihalo-HBQs was negatively correlated with the octanol-water partition coefficient (r = −0.971, P < 0.05), molar refractivity (r = −0.956, P < 0.05), energy of the highest occupied molecular orbital (EHOMO) (r = −0.943, P < 0.05), and polar surface area (r = −0.829, P < 0.05). The genotoxicity of these three pairs of dihalo-HBQ isomers followed the same order as their EHOMO values. This study reveals the occurrence and formation of HBQs in drinking water in China and systematically evaluates the chromosomal damage caused by nine HBQs in mammalian cells.

Performance of hollow fiber ultrafiltration membrane in a full-scale drinking water treatment plant in China: A systematic evaluation during 7-year operation

Ultrafiltration (UF) was implemented as a process upgrade in a full-scale drinking water treatment plant (DWTP) with a scale of 100,000 m3·d−1, and the performance was systematically investigated over seven years of operation. The results showed that the UF system exhibited excellent rejection of particles and improved the removals of organics by 9.0–14.7%. The annual average UF flux decreased from 28.37 to 16.51 L·m−2·h−1, and it was necessary to employ various cleaning approaches at an increasing frequency for maintaining stable operation. Compared to the initial scenario, the total cost per m3 of water for the UF system after 7-year operation increased by 55%. The cost of membrane replacement, energy, waste water and chemicals played a decisive role on operating cost in the lifecycle of the UF system. The content of cations (i.e., Mg, Al, Si, Ca, Mn and Fe), biological metabolites and organic substances in the cake layer increased significantly during long-term UF filtration, which not only aggravated membrane fouling but also affected the organic composition of the drinking water. The excellent integrity of the UF membrane during the 7-year operation was sufficient to prevent breakthrough of the organic substances from metabolic activity of microorganisms and to ensure biological safety of the permeate.

Composition and Dynamics of Bacterial Communities in a Full-Scale Mineral Water Treatment Plant.

The aim of this study was to gain insight into the bacterial composition and dynamics in a mineral water treatment system (MWTS). The bacterial community of a full-scale mineral water treatment plant in the Maofeng Mountain, South China, was studied using high-throughput sequencing combined with cultivation-based techniques in both the dry and wet season. Overall, adenosine tri-phosphate (ATP) concentration (6.47 × 10-11 – 3.32 × 10-8 M) and heterotrophic plate counts (HPC) (3 – 1.29 × 103 CFU/mL) of water samples in the wet season were lower than those (ATP concentration 5.10 × 10-11 – 6.96 × 10-8 M, HPC 2 – 1.97 × 103 CFU/mL) in the dry season throughout the whole MWTS. The microbial activity and biomass of water samples obviously changed along with treatment process. All 300 isolates obtained using cultivation-based techniques were distributed in 5 phyla, 7 classes, and 19 genera. Proteobacteria accounted for 55.7% (167) of the total isolates, among which predominant genus was Pseudomonas (19.3%). Illumina sequencing analysis of 16s rRNA genes revealed 15 bacterial phyla (relative abundance >0.1%) as being identified in all water samples. Among these, Proteobacteria constituted the dominant bacteria microbiota in all water samples. A large shift in the proportion of Bacteroidetes, Actinobacteria, and Firmicutes was obtained during the treatment process, with the proportion of Bacteroidetes, Actinobacteria decreasing sharply, whereas that of Firmicutes increased and predominated in the final water product. The core microbiome, which was still present in whole MWTS comprised several genera including Pseudomonas, Acinetobacter, Clostridium, and Mycobacterium, that contain species that are opportunistic pathogens, suggesting a potential threat for mineral water microbiology safety. This study is the first to investigate the bacterial community of a full-scale mineral water treatment plant in China. The results provided data regarding the bacteria composition and dynamics in an MWTS, which will contribute to the beneficial manipulation of the mineral water microbiome.

Occurrence and fate of PPCPs in typical drinking water treatment plants in China.

In this study, the occurrence and removal of twenty-nine pharmaceuticals and personal care products (PPCPs) in two water treatment plants (WTPs) in China were investigated. WTP1 employed ozonation and granular active carbon (GAC) filtration after coagulation and sedimentation, while WTP2 applied anthracite and GAC filtration instead. In the influent, six and four selected PPCPs with total concentrations of 554.97 and 12.94ng/L were detected in WTP1 and WTP2, respectively (in October), among which, sulfamethoxazole and erythromycin were detected with highest concentrations due to their widely used as both human and veterinary medicines. PPCPs removal varied significantly among compounds and treatment units. In general, coagulation, filtration and single GAC units worked inefficiently and removed the detected PPCPs by less than 50%, as they were not hydrophobic. Ozonation was capable to eliminate a majority of PPCPs by more than 90%, which, however, presented limited mineralization and generated a certain amount of degradation by-products. To seek the improvement of PPCPs removal by coagulation and flocculation, the feasibility of adding hydrogen peroxide (H2O2) into the coagulation process (Fe2+ or Fe3+) to trigger the Fenton reaction was investigated. Results indicated that only under acidic condition, Fe2+ combined H2O2 efficiently removed PPCPs, while Fe3+/H2O2 also showed some removal capacity compared to coagulation process only. It will be impractical to employ this process under neutral pH. But when acidic wastewater is involved, this process may have its potential application.

Tracking changes in composition and amount of dissolved organic matter throughout drinking water treatment plants by comprehensive two-dimensional gas chromatography–quadrupole mass spectrometry

Dissolved organic matter (DOM) can affect the performance of water treatment processes and produce undesirable disinfection by-products during disinfection. Several studies have been undertaken on the structural characterization of DOM, but its fate during drinking water treatment processes is still not fully understood. In this work, the nontargeted screening method of comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry (GC×GC-qMS) was used to reveal the detailed changes of different chemical classes of compounds in DOM during conventional and advanced drinking water treatment processes at three drinking water treatment plants in China. The results showed that when the dissolved organic carbon removal was low, shifts in the DOM composition could not be detected with the specific ultraviolet absorbance at 254nm, but the changes were clear in the three-dimensional fluorescence excitation-emission matrix or GC×GC-qMS analyses. Coagulation-sedimentation processes selectively removed 37–59% of the nitrogenous compounds, alcohols and aromatic hydrocarbons but increased the concentrations of halogen-containing compounds by 17–26% because of the contact time with chlorine in this step. Filtration was less efficient at removing DOM but preferentially removed 21–60% of the acids. However, other organic matter would be released from the filter (e.g., nitrogenous compounds, acids, and aromatic hydrocarbons). Biological activated carbon (BAC) treatment removed most of the compounds produced from ozonation, particularly ketones, alcohols, halogen-containing compounds and acids. However, it should be noted that certain highly polar or high molecular weight compounds not identified in this study might be released from the BAC bed. After the whole treatment processes, the concentrations of nitrogenous compounds, alcohols, alkenes, aromatic hydrocarbons and ketones were decreased more by the advanced treatment processes than by the conventional treatment processes. Alcohol and ketone removals were probably related to the reduction in protein-like materials. Alkane removal was probably related to the reduction in fulvic acid-like and humic acid-like materials.

Raw water quality assessment for the treatment of drinking water

Changes in the quality of raw water can significantly affect the treatments necessary for drinking water. Generally, raw water quality assessments are carried out to classify the pollution level of raw waters and cannot be used directly as a control for drinking water treatments. In order to improve the adaptability of drinking water treatments and to stabilize the overall quality of treated water, a raw water quality assessment technique that is specifically related to drinking water treatments is developed in this study. First, a drinking water treatment-oriented raw water quality assessment standard is proposed, based on historical environmental information and an analysis of operational data from drinking water treatments. A raw water quality assessment model is then set up to assess the raw water quality in real time. Finally, the results from this assessment are used to compute feedforward compensation for real-time control of the chemical dosing process, including both alum and ozone in the drinking water treatment. In this way, drinking water treatment can be adjusted according to the temporal changes in raw water quality, thereby stabilizing the quality of treated waters. Experimental implementation of this technique has been carried out in the chemical dosing process control systems of a drinking water treatment plant in China, and the results obtained demonstrate the effectiveness of the raw water quality assessment method proposed herein. This development will be helpful in satisfying the basic requirement of safe drinking water under a worsening global water environment.

Removal of typical antibiotics in the advanced treatment process of productive drinking water

This study investigated the fate of six artificial antibiotics during treatment process of an industrial-scale drinking water treatment plant in China. The results showed that all the antibiotics can be effectively removed by the advanced treatment process. The average concentrations of the six antibiotics ranged from 1 to 43 ng/L in the influent while from non-detected to 6 ng/L in the effluent. The antibiotic removal efficiencies were 91% for total antibiotics, 85% for amoxicillin, 92% for tetracycline, 86% for oxytetracycline, and approximately 100% for sulfamethoxazole, sulfamethazine, and erythromycin in the integrated water treatment process. Of all treatment units in the plant, it was found that ozonation and biological activated carbon treatment were the most effective treatment to remove antibiotics.

Using coagulation to restrict microbial re-growth in tap water by phosphate limitation in water treatment

Extensive microbial re-growth in a drinking water distribution system can deteriorate water quality. The limiting factor for microbial re-growth in a tap water produced by a conventional drinking water treatment plant in China was identified by determining the microbial re-growth potential (MRP) by adding different nutrients to stimulate growth of a natural microbial consortium as inoculum and flow-cytometric enumeration. No obvious change of MRP was found in tap water after addition of carbon, whereas, a 1- to 2-fold increase of MRP was observed after addition of phosphate (P). This clearly demonstrated that microbial re-growth in this tap water was limited by P. Most of the re-grown microbial flora (>85%) consisted of high nucleic acid content cells.A subsequent investigation of the MRP in the actual water treatment plant demonstrated that coagulation was the crucial step for decreasing MRP and producing P-limited water. Therefore, a comparison concerning the control of MRP by three different coagulants was conducted. It showed that all the three coagulants efficiently reduced the MRP and shifted the limitation regime from C to P, but the required dose was different. The study shows that it is feasible to restrict microbial re-growth by P limitation using coagulation in water treatment.

An Optimized Analytical Method for the Simultaneous Detection of Iodoform, Iodoacetic Acid, and Other Trihalomethanes and Haloacetic Acids in Drinking Water

An optimized method is presented using liquid-liquid extraction and derivatization for the extraction of iodoacetic acid (IAA) and other haloacetic acids (HAA9) and direct extraction of iodoform (IF) and other trihalomethanes (THM4) from drinking water, followed by detection by gas chromatography with electron capture detection (GC-ECD). A Doehlert experimental design was performed to determine the optimum conditions for the five most significant factors in the derivatization step: namely, the volume and concentration of acidic methanol (optimized values = 15%, 1 mL), the volume and concentration of Na2SO4 solution (129 g/L, 8.5 mL), and the volume of saturated NaHCO3 solution (1 mL). Also, derivatization time and temperature were optimized by a two-variable Doehlert design, resulting in the following optimized parameters: an extraction time of 11 minutes for IF and THM4 and 14 minutes for IAA and HAA9; mass of anhydrous Na2SO4 of 4 g for IF and THM4 and 16 g for IAA and HAA9; derivatization time of 160 min and temperature at 40°C. Under optimal conditions, the optimized procedure achieves excellent linearity (R2 ranges 0.9990–0.9998), low detection limits (0.0008–0.2 µg/L), low quantification limits (0.008–0.4 µg/L), and good recovery (86.6%–106.3%). Intra- and inter-day precision were less than 8.9% and 8.8%, respectively. The method was validated by applying it to the analysis of raw, flocculated, settled, and finished waters collected from a water treatment plant in China.

Molecular weight distribution variation of assimilable organic carbon during ozonation/BAC process

Assimilable organic carbon (AOC) was measured combined with molecular weight (MW) distribution during a long time operation of a pilot scale ozonation/BAC (biological activated carbon) process in a water treatment plant in China. The AOC measurement was done on different samples: raw water, water samples after sedimentation, sand filtration, ozonation and BAC filtration. MW distribution variation of AOC during ozonation/BAC process was evaluated. Results showed that AOC was mainly related to the NOM (natural organic matter) with MW < 1 kDa. The fraction of the NOM with MW < 1 kDa corresponds to 53-67% of the dissolved organic carbon (DOC) to all the samples while AOC corresponds to 2.7-5.9% of DOC. So just a small part of the fraction with MW < 1 kDa was AOC. This indicates that ozonation/BAC process removing a large part of DOC will not necessarily result in a great reduction in AOC.

Nitrite accumulation in an attapulgas clay biofilm reactor by fulvic acids

As a result of seriously polluted raw water sources, some water-treatment plants in China are intending to apply the biofilm process as a pretreatment prior to the traditional drinking water-treatment systems. These polluted raw waters contain higher total organic matter and ammonium than unpolluted waters. It has been reported that synthetic organic matter can cause nitrite accumulation. However, there have been few reports about the influence of fulvic acids on nitrification. Fulvic acids are the main part of the natural organic matter in waters, and nitrite is a toxic substance which has been paid attention to recently, especially in the treatment of drinking water, so it is necessary to study the effect of fulvic acids on the nitrification process. In this experiment, a so-called `attapulgas clay' biofilm reactor was set up, in which attapulgas clay was packed as the support medium for biological growth. After 40 days start-up, a multi-species biofilm developed in the reactor. The influence of fulvic acids on nitrite accumulation was investigated. Nitrite accumulation in the biofilm process was related to fulvic acids loadings. When the fulvic acids loading was less than 0.002 kg (TOC)/h·m 3, no nitrite build-up appeared; but when the loading was in the range of 0.002–0.02 kg (TOC)/h·m 3, nitrite built up and the concentration of nitrite could reach as high as 11.4 mg/l. When the loading was above 0.07 kg (TOC)/h·m 3, the nitrification process was completely inhibited.