Advanced Drinking Water Treatment Processes Research Articles

Assessing the efficiency of ozone-based advanced drinking water treatment processes in removing antibiotics and antibiotic-resistant genes: Pilot-scale research

With the widespread use of antibiotics, the emergence of antibiotics and antibiotic resistance genes (ARGs) poses a potential threat to public health. Drinking water plants are both the source and sink of these pollutants. In this study, we investigated and analyzed the distribution of four major types of antibiotics and ARGs in a drinking water plant with advanced treatment processes (ozone and activated carbon units) located in the central region of China. Among these treatment processes, the ozone process had significant removal effects on antibiotics and resistance genes, ranging from 15.10–91.17 % and 0.07–1.27 log, (except for ermA and qnrD) respectively. A correlation analysis of the concentrations of antibiotics and ARGs revealed a significant correlation (0.95 < r < 1) between antibiotics and ARGs, as well as between different types of ARGs. Additionally, the mechanism of ozone in the lab- and pilot-scale tests was analyzed to improve the removal capacity of ozone units for target pollutants. The experimental results showed that the removal efficiency of antibiotics and ARGs by ozone could be effectively improved by increasing the ozone dosage (5 mg/L), pH (9), and reaction time (10 min). The removal efficiency of the pollutants ranged between 36.65 % and 96.01 %. Under optimal reaction conditions, the results of the pilot-scale ozone experiment were significantly better than the actual treatment effects in drinking water plants. Our findings provide a theoretical basis for the optimization of the ozone process in actual drinking water plants.

Removal and distribution of antibiotics and resistance genes in conventional and advanced drinking water treatment processes

With the extensive detection of antibiotics and antibiotic resistance genes (ARGs) in drinking water treatment plants, the safety of drinking water has received increased attention. Therefore, the distribution and removal of antibiotics and ARGs in drinking water systems require further investigation. In this study, nine typical antibiotics, nine ARGs, and one integron in two drinking water plants were investigated by high pressure liquid chromatography with tandem mass spectrometry and real-time quantitative polymerase chain reaction analyses. Sulfonamides were the dominant antibiotic in the two drinking water treatment plants (WP-A and WP-B). The removal effect of advanced water treatment on total antibiotic concentration was significantly higher than that of conventional treatment. Sul gene was the dominant gene in the raw water of the two plants. After undergoing different treatment units, the finished water in WP-A and WP-B exhibited Sul gene concentrations of 54.06 genes/mL and 67.9 genes/mL, respectively. In the conventional treatment process, adding a sand filtration unit before the flocculation unit can improve the removal efficiency of antibiotics and ARGs. In the advanced treatment process, the post ozonization unit using the strong oxidation of O3 could effectively remove antibiotics and ARGs. Although the activated carbon unit can effectively remove antibiotics, the removal effect of ARGs is poor. Chlorination has a poor effect on the removal of antibiotics, but it can effectively remove ARGs. This study can provide a basis for understanding the fate of antibiotics and ARGs in drinking water systems.

Comparison between ferrihydrite adsorption and full-scale advanced drinking water treatment processes for controlling bacterial regrowth potential

Bacterial regrowth in drinking water systems is a threat to public health. In this study, ferrihydrite (Fh) adsorption was compared with advanced drinking water treatment processes (ADWTP) during one and a half years of sampling to test the reduction in assimilable organic carbon (AOC) and bacterial regrowth potential (BRP). Dissolved organic matter (DOM) was removed by Fh through ligand exchange and electrostatic interaction. The DOM removal was higher below pH 6 due to protonation of Fh surfaces. The ADWTP exhibited higher removal rates of DOM than Fh and lower phosphate removal rates than Fh. Excitation-emission matrix (EEM) and size exclusion chromatography (SEC) revealed that Fh removed aromatic DOM larger than 1000 Da, while the biological activated carbon (BAC) of ADWTP could remove DOM smaller than 1000 Da. These differences of organic compositions resulted in the lowest AOC of BAC treated water, and the lowest BRP of Fh-treated water, indicating that it was the most biostable water. Phosphate addition experiments illustrated that phosphorus was the primary rate limiting nutrient, indicating that the higher phosphate removal of Fh made it possible to produce waters with lower BRP than ADWTP. Therefore, BRP is considered to be a better indicator of bacterial regrowth than AOC when phosphorus is a rate-limiting nutrient, as is the case with the Fh treatment.

Occurrence and reduction of antibiotic resistance genes in conventional and advanced drinking water treatment processes

Antibiotic resistance is extensively detected in drinking water sources, threatening its safety and human health, which deserves further attention to the removal of antibiotic resistance genes (ARGs) in the drinking water system. In this study, the occurrence and reduction of integrase gene intI1 and forty-one ARG subtypes, which confers resistance to six antibiotic classes (β-lactam, aminoglycoside, macrolide, tetracycline, sulfonamide, and quinolone), were investigated in a drinking water treatment plant (DWTP). Seventeen ARG subtypes with absolute concentrations ranging from 1.4 × 100 to 7.3 × 105 and 3.9 × 104 genes/mL (intI1) were detected in the raw water; and sul1 and sul2 were the two dominant ARG subtypes. Overall, the whole DWTPs achieved 0.03–2.4 log reduction of ARGs compared with those presented in raw water. The reduction efficiencies of sul1, strA, and intI1 were the highest (1.0–2.4 log) in both conventional and advanced processes. However, the levels of sul1, sul2, and ermC still remained high (1.3 × 100–1.9 × 104 genes/mL) in finished water. The treatment units, including pre-flocculation/sedimentation/sand filtration, and ozonation units, were beneficial for the reduction of ARGs, which was mostly ascribed to the decline in biomass and the strong oxidizing properties of ozone. However, the reduction effect was subsequently counteracted by the granular activated carbon and chlorination units. This study provides basic data for ARG pollution in the drinking water system, and suggests that ARGs persist in drinking water, even after conventional chlorination or advanced treatment processes, highlighting the need for new and efficient water purification technologies.

Occurrence and removal of sulfonamide antibiotics and antibiotic resistance genes in conventional and advanced drinking water treatment processes.

Sulfonamides (SAs) and sul antibiotic resistance genes (ARGs) have been extensively detected in drinking water sources and warrant further studies on the removal of them in different drinking water treatment processes (DWTPs). The prevalence of 13 SAs, sul1, sul2 and class I integrase gene intI1 in conventional and advanced processes was investigated using HPLC-MS/MS and real-time quantitative PCR (qPCR), respectively. The most abundant SA was sulfamethoxazole, with the maximum concentration of 67.27 ng/L. High concentration of sulfamethoxazole was also measured in finished water in both conventional (22.05 ng/L) and advanced (11.24 ng/L) processes. Overall, the removal efficiency of advanced process for each SA was higher than that of conventional process, except for sulfameter. The absolute concentrations of sul1, sul2 and intI1 in raw water ranged from 1.8 × 103 to 2.4 × 105 gene abundance/mL. After treatment, the residual sul ARGs and intI1 in finished water still remained at 102 - 104 gene abundance/mL. Conventional treatment units, including flocculation/sedimentation/sand filtration, played a more important role in removing sul1, sul2 and intI1 than oxidation (chlorination or ozonation) and granular activated carbon filtration treatments. Based on this work, more investigations are needed to help improve the removal of both antibiotics and ARGs in DWTPs.

Emerging pollutants removal through advanced drinking water treatment: A review on processes and environmental performances assessment

Abstract The presence of emerging pollutants in the aquatic environment in relatively small concentrations and the fact that they cannot be removed by conventional water/wastewater treatment processes bring new challenges in terms of adequate selection of technologies from the technical, economical and environmental points of view. Generally, literature discusses emerging pollutants’ removal at significant concentrations (such as those in wastewater), while few studies consider their low concentrations occurring in raw water. This study presents a comprehensive review of the research efforts related to the occurrence, fate, health effects and impacts of emerging pollutants on advanced drinking water treatment and the environmental performance evaluation of different technological options, with a focus on pilot and full-scale installations. All presented case studies consider pollutants removed, process conditions and removal efficiencies, thus making possible comparisons between membrane processes, advanced oxidation processes and adsorption on activated carbon and other materials. The study is completed by an analysis of the environmental assessment instruments (life cycle assessment, carbon, water footprints, other type of assessments) that may be used for selecting sustainable advanced drinking water treatment processes able to remove emerging pollutants. This paper critically reviews the main research topics concerning emerging pollutants: classification, legislative framework, up-to-date removal processes and their environmental performances assessment, to offer a comprehensive analysis of the strategic issues that may constitute future research directions for sustainable water supply.

Changes in Dissolved Organic Matter Composition and Disinfection Byproduct Precursors in Advanced Drinking Water Treatment Processes.

Molecular changes in dissolved organic matter (DOM) from treatment processes at two drinking water treatment plants in Japan were investigated using unknown screening analysis by Orbitrap mass spectrometry. DOM formulas with carbon, hydrogen and oxygen (CHO-DOM) were the most abundant class in water samples, and over half of them were commonly found at both plants. Among the treatment processes, ozonation induced the most drastic changes to DOM. Mass peak intensities of less saturated CHO-DOM (positive (oxygen subtracted double bond equivalent per carbon (DBE-O)/C)) decreased by ozonation, while more saturated oxidation byproducts (negative (DBE-O)/C) increased and new oxidation byproducts (OBPs) were detected. By Kendrick mass analysis, ozone reactions preferred less saturated CHO-DOM in the same alkylation families and produced more saturated alkylation families of OBPs. Following ozonation, biological activated carbon filtration effectively removed <300 Da CHO-DOM, including OBPs. Following chlorination, over 50 chlorinated formulas of disinfection byproducts (DBPs) were found in chlorinated water samples where at least half were unknown. Putative precursors of these DBPs were determined based on electrophilic substitutions and addition reactions. Ozonation demonstrated better decomposition of addition reaction-type precursors than electrophilic substitution-type precursors; over half of both precursor types decreased during biological activated carbon filtration.

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.

The occurrence and removal of algae (including cyanobacteria) and their related organic compounds from source water in Vaalkop Dam with conventional and advanced drinking water treatment processes

Cyanobacterial bloom formation in freshwaters, such as rivers, lakes and dams, is known to occur throughout the world. The Vaalkop Dam, which serves as source to the Vaalkop drinking water treatment works (DWTW), is no exception. Blooms of cyanobacteria occur annually in Vaalkop Dam as well as in dams from which Vaalkop is replenished during low-rainfall periods. These blooms during the summer months are associated with the production of cyanotoxins and taste and odour compounds such as geosmin and MIB. The Vaalkop DWTW uses a combination of conventional and advanced water treatment processes to deal with the cyanobacteria and their related organic compounds in the source water. The overall objectives of this study were to: (i) investigate the occurrence of algae (including cyanobacteria) and cyanotoxins in the Vaalkop Dam; (ii) establish which environmental variables are responsible for the development and onset of algae, and (iii) determine whether the Vaalkop DWTW is able to eliminate the influence that algae (including cyanobacteria) may have on the drinking water. Multivariate statistical analyses revealed seasonal variation in algal assemblages in the raw water. The risk of cyanobacteria bloom formation proved to be especially high during the summer months as the nutrients needed for cyanobacterial growth are available and the temperature range is optimal, causing the production of geosmin, MIB and microcystin. The presence of Ceratium hirundinella (O.F. Muller) Dujardin, in the source water appears to exacerbate the negative effect that cyanobacteria have on the drinking water treatment process. When Ceratium hirundinella is present, floc formation is inhibited, causing more of the problematic algae to penetrate into the drinking water. Even though advanced treatment options such as ozone and granular activated carbon filters are used at Vaalkop DWTW, the effects of the organic compounds produced by cyanobacteria are not entirely eliminated during the treatment process. Keywords : potable water treatment, geosmin, MIB (2-methylisoborneol), microcystin, granular activated carbon (GAC), ozone

A cross-omics toxicological evaluation of drinking water treated with different processes

Cross-omics profiling and phenotypic analysis were conducted to comprehensively assess the toxicities of source of drinking water (SDW), effluent of conventional treatment (ECT) and effluent of advanced treatment (EAT) in a water treatment plant. SDW feeding increased body weight, and relative liver and kidney weights of mice. Hepatic histopathological damages and serum biochemical alterations were observed in the mice fed with SDW and ECT, but EAT feeding showed no obvious effects. Transcriptomic analysis demonstrated that exposure to water samples caused differential expression of hundreds of genes in livers. Cluster analysis of the differentially expressed genes which generated by both microarrays and digital gene expression showed similar grouping patterns. Proteomic and metabolomics analyses indicated that drinking SDW, ECT and EAT generated 59, 145 and 41 significantly altered proteins in livers and 8, 2 and 0 altered metabolites in serum, respectively. SDW was found to affect several metabolic pathways including metabolism of xenobiotics by cytochrome P450 and fatty acid metabolism. SDW and ECT might induce molecular toxicities to mice, but the advanced treatment process can reduce the potential health risk by effectively removing toxic chemicals in drinking water.

Molecular weight distributions of effluent organic matters and the biodegradability assessment of a typical advanced drinking water treatment plant in South China

Biodegradability and molecular weight (MW) distributions of effluent organic matters were studied. Sample units of advanced drinking water treatment processes, namely, pre-ozonation, conventional water treatment (CWT), and main ozonation/biological activated carbon (BAC), were obtained from the drinking water treatment plant in South China. Biodegradable dissolved organic carbon (BDOC) and assimilable organic carbon (AOC), which is a component of BDOC, were measured as indicators of organic matter biodegradability and biological stability in drinking water. Results showed that the high-MW organic matter in raw water was oxidized into low-MW organic matter (MW < 3 kDalton) through preozonation process, thereby enhancing the BDOC content in raw water. BDOC components were removed by the subsequent CWT process. Components of the effluent organic matters obtained from the CWT process were completely decomposed through the main ozonation process, and the remaining organic matters were simultaneously oxidized into low-MW organic matters, thus increasing the BDOC content and improving the biodegradability. Finally, the low-MW BDOC was efficiently removed through BAC process. The AOC content in user water was over 100 μg L−1, indicating that the factors contributing to biological instability remained. Additional attention should be given to BAC protection in China.

Evaluation of mutagenic activity in the Nakdong river and advanced drinking water treatment processes

The previously proved method of Ames test was followed to measure the mutagenic activity. We used Salmonella typhimurium which has special gene mutation site with a single compound characteristic and histidine operon, and measured at the four (Gumi, Gangjung, Gachang, Hyunpung) branch points of Nakdong river for one year. We used Standard Methods for general water analysis with the items as water temperature, pH, DO, BOD, COD, KMnO4, T-N, T-P, NH3-N, TOC, and AOX. Hyunpung branch, where the Nakdong and the Gumho river seems to be mixed enough, showed higher mutagenic activity than the other 3 branches. Every point of Nakdong river showed the TA98 mutagenic activity higher than 2, while TA100 was lower than 2. Most of the mutagenic activity was detected from methanol extracts. These results indicate that Nakdong river water quality is getting deteriorated, and that Nakdong river is influencing the mutagenic activity by Frame-shift type mutation and its polar substances. Correlations (R) between mutagenic activity and concentrations of water analysis items as TOC, AOX, BOD, COD, T-N, and T-P, resulted as 0.768, 0.787, 0.743, 0.688, 0.757, 0.628, respectively, and mutagenic activities of TA98 and TA100, after the treatment of ozone and activated carbon, decreased by chlorine pre-treatment. Finally, if the injected concentration of ozone was higher than 1.0 mL, TA98 and TA100 showed lower mutagenic activities than 2.