Removal of precursors of typical nitrogenous disinfection byproducts in ozonation integrated with biological activated carbon (O3/BAC)

Effects of running time on biological activated carbon filters: water purification performance and microbial community evolution

Ozone-biologically activated carbon (BAC) filtration is an advanced treatment process that can be applied to remove recalcitrant organic micro-pollutants in drinking water treatment plants (DWTPs). In this study, we continuously monitored a new and an old BAC filter in a DWTP for 1 year to compare their water purification performance and microbial community evolution. The results revealed that, compared with the new filter, the use of the old BAC filter facilitated a slightly lower rate of dissolved organic carbon (DOC) removal. In the case of the new BAC filter, we recorded general increases in the biomass and microbial diversity of the biofilm with a prolongation of operating time, with the biomass stabilizing after 7 months. For both new and old BAC filters, Proteobacteria and Acidobacteria were the dominant bacterial phyla. At the genus level, the microbial community gradually shifted over the course of operation from a predominance of Herminiimonas and Hydrogenophaga to one predominated by Bradyrhizbium, Bryobacter, Hyphomicrobium, and Pedomicrobium, with Bradyrhizobium being established as the most abundant genus in the old BAC filter. Regarding spatial distribution, we detected reductions in the biomass and number of operational taxonomic units with increasing biofilm depth, whereas there was a corresponding increase in microbial diversity. However, compared with the effects of time, the influence of depth on the composition of the biofilm microbial community was considerably smaller. Furthermore, co-occurrence network analysis revealed that the microbial community network of the new filter after 11 months of operation was the most tightly connected, although its modular coefficient was the lowest of those assessed. We speculate that the positive and negative interactions within the network may be attributable to symbiotic or competitive relationships among species. Moreover, there may have been a significant negative interaction between SWB02 and Acidovorax, plausibly associated with a competition for substrates.

Effect of micropollutants on disinfection byproducts and antibiotic resistance genes in drinking water in the process of biological activated carbon treatment

The biofilm stress response of biological activated carbon (BAC) was investigated under prolonged exposure to sulfadiazine and 2,4-Dichlorophenoxyacetic acid, simulating complex emerging organic contaminants (EOCs) that are mainly involved in the formation of nitrogenous disinfection byproducts (N-DBPs) and antibiotic resistance genes (ARGs). Under trace complex EOCs condition (2 µg/L), N-DBP precursors and abundance of ARGs increased significantly in BAC effluent. The total formation potential of haloacetonitriles (HANs) and halonitromethanes (HNMs) was 751.47 ± 2.98 ng/L, which was much higher than the control group (440.67 ± 13.38 ng/L without EOCs). Similarly, the relative abundance of ARGs was more than twice that in the control group. The complex EOCs induce excessive extracellular polymeric substance secretion (EPS), thereby causing more N-DBP precursors and stronger horizontal gene transfer. Metagenome analysis revealed that functional amino acid and protein biosynthesis genes were overexpressed compared to the control group, causing more EPS to be secreted into the external environment. Complex EOCs promote Cobetia, Clostridium, and Streptomyces dominance, contributing to the production of N-DBP precursors and ARGs. For the first time, in addition to the direct hazards of the EOCs, this study successfully revealed the indirect water quality risks of complex EOCs from the microbial stress response during BAC treatment. Synergistic regulation of EOCs and microorganisms is important for tap water security.

Exploring the impacts of service life of biological activated carbon on dissolved organic nitrogen removal

The biological activated carbon (BAC) process has been widely used in drinking water treatment to improve the removal of pollutants, including the precursors of nitrogenous disinfection byproducts (N-DBPs). Nevertheless, old BAC filter effluent DON concentration is heightened, increasing the highly toxic N-DBPs formation potential. Herein, the variation of dissolved organic nitrogen (DON) was comprehensively explored during one backwashing cycle, focusing on four BAC age (0.3, 2, 5, and 10 years) for BAC filters in drinking water. Comparatively, the removal rate of DON by four BAC followed the order 0.3-yr BAC (39.69%-66.96%) >2-yr BAC (10.10%-39.78%) >5-yr BAC (-4.18%-29.63%)>10-yr BAC (-20.88%-19.87%). When at day 7 after backwashing, 10-yr BAC filter effluent increased at least 13.71% of DON and considerably elevated the N-DBPs formation potential, which was attributed to the ultimate production of more various proteins/amino sugars-like compounds by microbes. In comparisons of microbial community between all BAC samples, Rhizobials were more prevalent in 10-yr BAC and could produce microbe-derived DON associated with amino acids. Moreover, microbes regulated metabolic pathways, including amino acid biosynthesis, TCA cycle, purine metabolism, and pyrimidine metabolism, to enhance the adaptive cellular machinery in response to environmental stressors, and therefore accelerated microbial secretion of microbe-derived DON. Structural equation model (SEM) analysis investigated that BAC age had bio-effects on N-DBPs formation potential, which were delivered via the linkage of " BAC age, microbial community, microbial metabolism, and DON molecular characteristics". Our findings demonstrate the necessity of reconsidering the feasibility of BAC filters for long-time operation, which has implications for future N-DBPs precursors control in drinking water.

Insight into the temporal dynamics of microbial succession and ecology mechanisms in biological activated carbon tanks

Biological activated carbon (BAC) has long been applied in China to guarantee water quality and to achieve drinking water regulations. However, a knowledge gap remains regarding the temporal dynamics of microbial communities, particularly microbe-based assembly and co-occurrence patterns. Accordingly, this study investigated the evolution of BAC microbial communities using a pilot-scale system and examined by multivariate ecological combined with high-throughput Illumina sequencing and statistical methods. The results showed that BAC microbial diversity reached its peak in 2 years and declined thereafter. Microbial communities composition was accompanied by significant temporal evolution in the BAC biofilm. Deterministic processes gained in importance along with time, especially homogeneous selection which contributed 59.09 %-75.63 % to the community assembly in 8-yr, 9-yr, and 10-yr BAC. According to co-occurrence network analysis, microbial networks have more unstable structures over time, as evidenced by higher modularity, heightened connectivity, and fewer keystones. Moreover, the interaction between microbial taxa tended to have a higher proportion of competitive relationships during the operation of the BAC tank, ranging from 13.51 % to 76.35 %. Based on these dynamic ecological processes, microbial community succession in BAC biofilm might undergo four phases: community establishment (Years 0-2); community stability (Years 2-5); community quasi-degradation (Years 5-8); community degradation (Years 8-10). The performance of BAC was greatly influenced by community development, and contaminant removal gradually decreased as community succession proceeded. These results add to our knowledge of microbial ecology and provide the basis for further research into microbial communities' regulation strategies in BAC tanks.

Microplastics toxicity, detection, and removal from water/wastewater

The world has witnessed massive and preeminent microplastics (MPs) pollution in water bodies due to the inevitable continuous production of plastics for various advantageous chemical and mechanical features. Plastic pollution, particularly contamination by MPs (plastic particles having a diameter lesser than 5 mm), has been a rising environmental concern in recent years due to the inappropriate disposal of plastic trash. This study presents the recent advancements in different technologies for MPs removal in order to gain proper insight into their strengths and weaknesses, thereby orchestrating the preparation for innovation in the field. The production, origin, and global complexity of MPs were discussed. This study also reveals MPs' mode of transportation, its feedstock polymers, toxicities, detection techniques, and the conventional removal strategies of MPs from contaminated systems. Modification of conventional methods vis-à-vis new materials/techniques and other emerging technologies, such as magnetic extraction and sol-gel technique with detailed mechanistic information for the removal of MPs are presented in this study. Conclusively, some future research outlooks for advancing the MPs removal technologies/materials for practical realization are highlighted.

A new process to further remove dissolved organic matter and disinfection by-product formation potential during drinking water treatment

Biological activated carbon (BAC) will produce soluble microbial products (SMPs), which affect effluent quality. To clarify the mechanism by which BAC affects effluent water quality, the processes of a drinking water plant in Jiangsu Province were investigated. It was found that during the O₃-BAC process, although ozonation could remove dissolved organic matter (DOC) to a certain extent, the DOC increased from 4.44 to 4.47 mg/L after BAC. Dissolved organic matter (DOM) in effluent from different processes was divided into five fractions based on hydrophilicity and hydrophobicity by resin fractionation. Through fluorescence excitation-emission matrix (EEM) spectroscopy combined with DOC analysis, it was found that SMPs are mainly included in transitional hydrophilic neutral (TPIN) fraction, which was the main cause of the DOC increase. Therefore, a new combined process was designed to remove TPIN effectively by coagulation after biological treatment, and found that coagulation had a good removal rate (13.2%) on TPIN. The trihalomethane formation potential (THMFP) of TPIN could be reduced effectively by 44.9% after coagulation. Compared with the old process, the new combined process had a higher removal rate (14.2-30.0%) of DOC, as well as a greater reduction of THMFP (29.0-78.6%) and haloacetic acid formation potential (HAAFP) (46.4-75.3%). This study aims to reveal the mechanism by which SMPs affect effluent water quality and exacerbate health risks, and to propose a solution to provide theoretical support for the design and optimization of drinking water treatment processes.

Effects of biological activated carbon filter running time on disinfection by-product precursor removal

Biological activated carbon (BAC) filtration is usually considered to be able to decrease formation potentials (FPs) of disinfection by-products (DBPs) in drinking water treatment plant (DWTP). However, BAC filters with long running time may release microbial metabolites to effluents and therefore increase FPs of nitrogenous DBPs with high toxicity. To verify this hypothesis, this study continuously tracked BAC filters in a DWTP for one year, and assessed effects of old (running time 8-9 years) and new (running time 0-13 months) BAC filters on FPs of 15 regulated and unregulated DBPs. Results revealed that dissolved organic carbon (DOC) removal was slightly higher in the new BAC than the old one. All fluorescent components of dissolved organic matter evidently declined after new BAC filtration, but fulvic acid-like and soluble microbial product-like substances increased after old BAC filtration, which could be caused by microbial leakage. Correspondingly, new BAC filter generally removed more DBP FPs than the old one. 46.5% HAA₇ FPs from chlorination and 44.3% THM₄ FPs from chloramination were removed by new BAC filter. However, some DBP FPs, especially HAN FPs, were poorly removed or even increased by the old BAC filter. Proteobacteria could be a main contributor for DBP precursor removal in BAC filters. Herminiimonas, most abundant genera in new BAC filter, may explain its better DOC and UV₂₅₄ removal performance and lower DBP FPs, while Bradyrhizobium, most abundant genera in old BAC filter, might produce more extracellular polymeric substances and therefore increased N-DBP FPs in old BAC effluent. This study provided insight into variations of DBP FPs and microbial communities in the new and old BAC filters, and will be helpful for the optimization of DWTP design and operation for public health.

Unraveling dissolved organic matter in drinking water through integrated ozonation/ceramic membrane and biological activated carbon process using FT-ICR MS

The performance of an integrated process comprising coagulation, ozonation, and catalytic ceramic membrane filtration (CMF) followed by treatment with biological active carbon (BAC) was evaluated in a pilot-scale (96 m³/d) experiment to understand the biostability and quality of the finished water. The fate of dissolved organic matter (DOM) at the molecular level was explored using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Biostable finished water with an assimilable organic carbon (AOC) concentration of 30.2-45.4 µg/L was obtained by the integrated process, and the high hydraulic retention time (HRT) (≥ 45 min) of the BAC filter was necessary to provide biostable finished water. The coagulation/O₃/CMF unit efficiently transformed nitrogen-containing polyaromatic hydrocarbons (PAH) with aromaticity and large molecular weight (Mw) (500-1000 Da) into CHO-type highly unsaturated phenolic compounds (HuPh) with less aromaticity and medium Mw (300-500 Da), which were effectively removed by subsequent BAC filtering. The main reaction was oxygen addition, followed by deamination and dealkylation of the coagulation/O₃/CMF unit and decarboxylation of the BAC filter. Principal component analysis revealed that N-containing and large-Mw PAH are potential AOC precursors, and the chemical characteristics of CHO-type and medium-Mw HuPh make them AOC candidates (correlation coefficients > 0.96). This study provides insights into the management of drinking water biostability and its suitability for the practical application of the integrated coagulation/O₃/CMF-BAC process in drinking water treatment plants.

Pilot-Scale Biological Activated Carbon Filtration–Ultrafiltration System for Removing Pharmaceutical and Personal Care Products from River Water

Biological activated carbon (BAC) biofilter coupling ultrafiltration (UF) is a promising process for the treatment of river water contaminated by pharmaceutical and personal care products (PPCPs). However, the pilot-scale study should be conducted to reveal the long-term removal performance and the respective contributions of BAC and UF. In this study, a BAC-UF system with treatment capacity of 0.16 m3 h−1 was operated for 130 days. The water quality was analyzed in terms of CODMn, UV254, NH4+-N, and PPCPs. The results showed that both BAC and UF were related to the removal of organic matter (CODMn and UV254), achieving the removals of 56.00% and 55.25%, respectively. Similarly, BAC and UF were both relevant to the removal effects of ammonia nitrogen, nitrite, and nitrate. Moreover, the BAC-UF process was featured with a high efficiency in the removal of PPCPs, and the average removal of total PPCPs reached 47.84%, especially anhydroerythromycin, sulfachloropyridazine, sulfadiazine, trimethoprim, and caffeine. Besides, it was found that the BAC unit played a key role in PPCPs removal and the UF unit also degraded them by the biomass on UF membranes. Therefore, this study proved the removal performance of BAC-UF for treating popular pollutants from river water, and the BAC-UF process in this work can be considered as a feasible method of producing clean drinking water.

Removal of microplastics from wastewater: available techniques and way forward

Microplastics are the newly emerged contaminants with a presence in almost every part of the globe. Despite being small in size, microplastic particles have proved to be harmful for plants, animals, humans, and for the ecosystem in general. Water is one of the most important routes through which microplastics transfer from one place to another. Moreover, water is also an important route for the ingestion of microplastics in human, which results in various health issues, such as cancer, mutagenic and teratogenic abnormalities. Thus, microplastics in water is an emerging public health issue which needs attention and, hence, it is important to investigate removal techniques for microplastics in wastewater. Although, there are some biological, chemical/electrochemical, and physical techniques to remove microplastics, their wide scale applicability and cost-effectiveness is an issue. In this review, we have discussed the existing and upcoming treatment technologies for the removal of microplastics from wastewater and also tried to present an overview for the future approaches.

A comparison of removal efficiencies of conventional drinking water treatment and advanced treatment equipped with ozone-biological activated carbon process

ABSTRACTUsing raw water from a shallow water supply reservoir located in the lower Yangtze River region, the removal efficiencies of conventional treatment on dissolved organic matter (DOM) and disinfection by-products formation potential (DBPFP) were compared with an advanced treatment that equipped with ozone-biological activated carbon (O₃-BAC) process. The results showed that the advanced treatment was more efficient than the conventional treatment at removing dissolved organic carbon (DOC; 40-67% removal), UV₂₅₄ (61-81% removal), the trihalomethane formation potential (THMFP; 37-70% removal) and the haloacetic acid formation potential (HAAFP; 35-89% removal). The sand filter in the conventional treatment process was identified as the main contributor to decreasing DOC, UV₂₅₄ and DBPFP. The O₃-BAC in advanced treatment was found to decrease THMFP and HAAFP, with removal rates of 17-40% and 22-59%, respectively. To improve the water quality of effluents, advanced treatment with O₃-BAC should be used to treat raw water from the shallow water supply reservoir in lower Yangtze River. However, the increased DBPFP yield, which is proportional to the potential health risks, should not be ignored.

Control of disinfection byproducts in drinking water treatment plants: Insight into activated carbon filter

The removal efficiencies of disinfection byproducts formation potentials (DBPFPs) and generated DBPs under pre-chlorination condition (pre-generated DBPs) during different drinking water treatment trains in eight full-scale drinking water treatment plants (WTPs) were investigated through field and laboratory studies. Haloacetic acids (HAAs) and haloacetonitriles (HANs) were identified to be two representative DBPs based on cytotoxicity and genotoxicity assessments. The performances of advanced treatment train for HAAs and HANs were better than that of conventional treatment train. However, the efficacy of ozone - biological activated carbon (O₃-BAC) was affected by its service time and position in the water treatment process. In addition, the consumption of free chlorine by activated carbon in old granular activated carbon (GAC) filter was higher than that in new one under pre-chlorination condition, resulting in the increase of HAAs and HANs in the GAC filter effluent. This demonstrated that the organic matter adsorbed on older activated carbon generated more HAAs and HANs during pre-chlorination, which inhibited the adsorption of pre-generated DBPs. The ability of GAC/O₃-BAC to remove HAAs and HANs was consistent with that of protein-like and low molecular weight organic substances, which could predict the performance of GAC and O₃-BAC in treating DBPs.

Substrate Pre-loading Influences Initial Colonization of GAC Biofilter Biofilms

Microbial community composition and stability affect pollutant removal for biological/granular activated carbon (BAC/GAC) processes. Here, we pre-loaded the organic carbon substrates sucrose, lactose, and Lysogeny Broth (LB) medium onto new GAC prior to use and then tested whether this substrate pre-loading promoted development of biofilms with high coverage that remained stable for prolonged operational periods. Temporal dynamics of the biomass and microbial community on the GAC were monitored via flow cytometry (FCM) and sequencing, respectively, in both batch and continuous-flow experiments. In comparison with the non-loaded GAC (control), the initial biofilm biomass on substrate-loaded GAC was 3–114 times higher, but the initial richness was considerably lower (only accounting for 13–28% of the control). The initial community compositions were significantly different between batch and continuous-flow column experiments, even when loaded with the same substrates. In the continuous-flow column experiments, both biomass and microbial community composition became remarkably similar to the control filters after 64 days of operation. From these findings, we conclude that substrate-loaded GAC could enhance initial colonization, affecting both biomass and microbial community composition. However, the biomass and composition did not remain stable during long-term operation due to continuous dispersal and competition from influent bacteria.

Ecological insights into assembly processes and network structures of bacterial biofilms in full-scale biologically active carbon filters under ozone implementation

To address the adverse effects of harmful algal blooms, there are increased demands over the implementation of ozone coupled with biologically active carbon (BAC) filters in the drinking water treatment plants. Although the microbial biofilms are vital elements to support the proper performance of BAC filters, except for taxonomic affiliations, little is known about the assembly mechanisms of microbial communities in the full-scale BAC filters. This study aimed to examine how the assembly processes and their associated factors (e.g., influent characteristics, biological interactions) drive the temporal dynamics of bacterial communities in full-scale BAC filters, which underwent ozone implementation (five consecutive seasons from 2017 to 2018). The results revealed that along with the increase of bacterial taxonomic richness and evenness, stochastic processes became more crucial to determine the bacterial community assembly in the summer and autumn after ozone implementation (relative contribution: 61.23% and 83.75%, respectively). Moreover, their corresponding networks possessed simple network structures with lower modularity than other seasons, which implied lesser biological interactions among bacterial populations. The correlation between taxonomic and predicted functional diversities using functional redundancy index indicated that relatively high levels of bacterial functional redundancy (>0.83) were generally present in BAC filters. However, compared to other seasons, significantly higher degrees of functional redundancy existed in the summer and autumn after ozone implementation (0.85 ± 0.01 and 0.86 ± 0.01, respectively). Overall, this work improves our understanding of the microbial ecology of full-scale BAC filters by providing a conceptual framework that characterizes bacterial biofilm assembly processes relevant to performance optimization of full-scale BAC filters.

Precursors of typical nitrogenous disinfection byproducts: Characteristics, removal, and toxicity formation potential

The emergence of nitrogenous disinfection byproducts (N-DBPs) in drinking water has become a widespread concern. In this study, dichloroacetonitrile (DCAN), dicholoacetamide (DCAcAm) and trichloronitromethane (TCNM) were chosen as representatives to clarify the characteristics of N-DBP precursors in the raw waters of Taihu Lake, the Yangtze River, and Gaoyou Lake. Removal of DCAN and DCAcAm precursors must focus on nonpolar and positively charged organics, but more attention should be paid to micromolecular, polar and non-positively charged organics as TCNM precursors. Compared to molecular weight (MW) and hydrophilicity fractionation, polarity and electrical classification have higher selectivity to intercept N-DBP precursors. The properties of N-DBP precursors are relatively fixed and traceable in water systems, which could contribute to their targeted removal. Based on investigation of their characteristics, the removal efficiency and preferences of organic precursors under different processes were studied in three drinking water treatment plants (DWTPs). The TCNM precursors produced in preozonation can be effectively removed during coagulation. The cumulative removal efficiency of conventional processes on N-DBP precursors was approximately 20-30%, but O₃/BAC process improved removal by about 40%. The key to improving the removal efficiency of N-DBP precursors by O₃/BAC is that it can significantly remove low-MW, nonpolar, positively charged, hydrophilic and transphilic organics. In combined toxicity trials, both cytotoxicity and genotoxicity showed a synergistic effect when DCAN, DCAcAm, and TCNM coexisted, which means that low-level toxicity enhancement in the actual water merits attention. DCAN precursors dominated in the toxicity formation potential (TFP), followed by TCNM precursors. In addition, the removal rate of total N-DBP precursors may be higher than that of TFP, leading to overly optimistic evaluation of precursor removal in water treatment practice. Therefore, the removal effect on TFP must also be considered.

Haloacetonitriles and haloacetamides precursors in filter backwash and sedimentation sludge water during drinking water treatment

Haloacetonitriles (HANs) and haloacetamides (HAMs) are nitrogenous disinfection byproducts that are present in filter backwash water (FBW) and sedimentation sludge water (SSW). In many cases FBW and SSW are recycled to the head of drinking water treatment plants. HAN and HAM concentrations in FBW and SSW, without additional oxidants, ranged from 6.8 to 11.6 nM and 2.9 to 3.6 nM of three HANs and four HAMs, respectively. Upon oxidant addition to FBW and SSW under formation potential conditions, concentrations for six HANs and six HAMs ranged from 92.2 to 190.4 nM and 42.2 to 95.5 nM, respectively. Therefore, at common FBW and SSW recycle rates (2 to 10% of treated water flows), the precursor levels in these recycle waters should not be ignored because they are comparable to levels present in finished water. Brominated HAN and chlorinated HAM were the dominant species in FBW and SSW, respectively. The lowest molecular weight ultrafiltration fraction (< 3 kDa) contributed the most to HAN and HAM formations. The hydrophilic (HPI) organic fraction contributed the greatest to HAN precursors in sand-FBW and SSW and were the most reactive HAM precursors in both sand- or carbon-FBWs. Fluorescence revealed that aromatic protein-like compounds were dominant HAN and HAM precursors. Therefore, strategies that remove low molecular weight hydrophilic organic matter and aromatic protein-like compounds will minimize HAN and HAM formations in recycled FBW and SSW.

Formation and interdependence of disinfection byproducts during chlorination of natural organic matter in a conventional drinking water treatment plant

It is crucial to explore the source, formation process and interdependence of disinfection byproducts (DBPs) to reduce their risk on public health. In this investigation, a source water was chlorinated to evaluate the initial formation rates and the maximum yields of trichloromethane (TCM), dichloroacetic acid (DCAA), and trichloroacetic acid (TCAA) based on a hyperbola model. The results showed that TCM achieved the highest initial formation rate and maximum theoretical concentration compared with DCAA and TCAA. The TCM yield can be used to forecast the yields of DCAA and TCAA throughout the whole reaction process, and the yields of chloral hydrate (CH), dichloroacetonitrile (DCAN) and 1,1,1-trichloropropanone (1,1,1-TCP) within the initial reaction stage. Besides, the raw water, settled water and filtered water collected from a drinking water treatment plant were divided into five fractions, respectively, by ultrafiltration membranes to evaluate their DBP formation after chlorination. Compared with the medium molecular weight species, high and low molecular weight organic matters exhibited relatively high specific regulated and unregulated DBP yields (expressed as μg/mg C), respectively. Humic acid-like compositions predominantly contributed to regulated DBP yields, while soluble microbial by-product-like compounds preferentially generated DCAN. The correlation study revealed that the TCM could also serve as an indicator for the measured DBPs from chlorination of sample fractions with different molecular weight. Finally, it was found that the theoretical cytotoxicity was enhanced during chlorination of filtered water compared with chlorination of settled water.

Transformation of N-Methylamine Drugs during Wastewater Ozonation: Formation of Nitromethane, an Efficient Precursor to Halonitromethanes

Potable reuse of wastewater is expanding, and ozonation for water reuse is becoming more common, either as a preoxidant before membranes or as part of ozone/biological activated carbon (O₃/BAC) systems. However, previous research has demonstrated that ozone drastically increases the formation potential of genotoxic halonitromethanes (HNMs), including during O₃/BAC. Chloropicrin, the most common HNM, is synthesized by chlorinating nitromethane, suggesting that nitromethane may be the immediate precursor of chloropicrin, although nitromethane is unlikely to occur naturally in wastewater. We hypothesized that wastewater ozonation forms nitromethane, which would be the key intermediate toward HNMs. Ozonation of wastewater effluent was shown to form abundant nitromethane, which explained the majority (in one case, all) of subsequent chloropicrin formation. Next, we investigated a suspected category of nitromethane precursor: stimulant drugs, such as ephedrine and methamphetamine, and certain antidepressants. These drugs all feature N-methylamine functional groups, and certain N-alkylamines have been shown to produce primary nitroalkanes upon ozonation. Ozonation of N-methylamine drugs ubiquitously formed nitromethane, typically at >50% yield. Subsequent chlorination converted nitromethane to chloropicrin. The reaction mechanism was investigated to understand the variation in nitromethane yield between different precursors. These results suggest that nitromethane fate during reuse and nitromethane control should be investigated.

Occurrence and removal of microplastics in an advanced drinking water treatment plant (ADWTP)

Microplastics (MPs) have attracted worldwide attention as the emerging persistent pollutants. Since they have been detected in raw water and the treated water of drinking water treatment plants (DWTPs), there was an urgent need to explore the properties and fates of microplastics in DWTPs. The characteristics of the effluent MPs from each treatment unit in an advanced drinking water treatment plant (ADWTP) were studied, and the relationship between the variations of MPs and the removal performances of treatment processes was also explored. Overall, both the coagulation combined with sedimentation and the granular activated carbon (GAC) filtration performed well in removing microplastics. The former had a removal efficiency of about 40.5-54.5%, mainly for fibres' removal, and the presence of GAC filtration reduced the microplastic abundance by about 56.8-60.9%, mainly for small-sized MPs. It was worthy of attention that a larger amount of polyacrylamide (PAM) was detected in the effluent of the sedimentation compared to raw water, which was caused by the usage of coagulant containing PAM. Specially, the number of 1-5 μm MPs in the effluent of ozonation tank was increased by 2.8-16.0%, resulting in a negative removal efficiency in ozonation. The removals of microplastics were depended primarily on their physical properties (size and shape).

Different removal efficiency of disinfection-byproduct precursors between dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm) by up-flow biological activated carbon (UBAC) process

Up-flow biological activated carbon (UBAC) filter has been widely used in waterworks due to its less hydraulic loss, stronger biodegradation ability, and the prevention of excessive biomass growth relative to down-flow BAC treatment. In this study, the different removal efficiency (DRE) of disinfection byproduct precursors between dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm) was evaluated when UBAC filter was used as advanced treatment process. Results showed that the UBAC filter with approximately 36 months of usage time had a poor performance in the removal of DCAcAm formation potential (FP) (i.e. 9.3-19.1%) compared to DCAN FP (i.e., 22.5-34.1%). After chlorination of UBAC effluent, the hydrolysis of DCAN to form DCAcAm only partly contributed to the DRE variations of both DCAN FP and DCAcAm FP. Using the high-throughput sequencing technology and the redundancy analysis (RDA), the second dominant genus Bacillus in UBAC filter, which may transform precursors of DCAN into inorganic matters, could be another reason that led to the DRE in DCAN and DCAcAm FP. The formation and leakage of soluble microbial products (SMPs) was identified by excitation-emission matrix (EEM) peak intensities as well as variation of biological index (BIX). The SMPs released into UBAC effluent, favoring the formation of DCAcAm, also contributed to the precursors of both DCAN and DCAcAm, causing a poor removal performance in DCAcAm FP by UBAC filter.