Trihalomethane Formation Potential Research Articles

Control of chlorination disinfection by-products in drinking water by combined nanofiltration process: A case study with trihalomethanes and haloacetic acids

Disinfection by-products (DBPs) are prevalent contaminants in drinking water and are primarily linked to issues regarding water quality. These contaminants have been associated with various adverse health effects. Among different treatment processes, nanofiltration (NF) has demonstrated superior performance in effectively reducing the levels of DBPs compared to conventional processes and ozone-biological activated carbon (O3-BAC) processes. In this experiment, we systematically investigated the performance of three advanced membrane filtration treatment schemes, namely "sand filter + nanofiltration" (SF + NF), "sand filter + ozone-biological activated carbon + nanofiltration" (SF + O3-BAC + NF), and "ultrafiltration + nanofiltration" (UF + NF), in terms of their ability to control disinfection by-product (DBP) formation in treated water, analyzed the source and fate of DBP precursors during chlorination, and elucidated the role of precursor molecular weight distribution during membrane filtration in relation to DBP formation potential (DBPFP). The results indicated that each treatment process reduced DBPFP, as measured by trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP), with the SF + O3-BAC + NF process being the most effective (14.27 μg/L and 14.88 μg/L), followed by the SF + NF process (21.04 μg/L and 16.29 μg/L) and the UF + NF process (26.26 μg/L and 21.75 μg/L). Tyrosine, tryptophan, and soluble microbial products were identified as the major DBP precursors during chlorination, with their fluorescence intensity decreasing gradually as water treatment progressed. Additionally, while large molecular weight organics (60–100,000 KDa) played a minor role in DBPFP, small molecular weight organics (0.2–5 KDa) were highlighted as key contributors to DBPFP, and medium molecular weight organics (5–60 KDa) could adhere to the membrane surface and reduce DBPFP. Based on these findings, the combined NF process can be reasonably selected for controlling DBP formation, with potential long-term benefits for human health.

Spatiotemporal dynamics of dissolved organic matter and disinfection by-products formation potential of Shengzhong Lake in southwest China.

The quality and quantity of dissolved organic matter (DOM) in lakes as well as its environmental effects associated with the unintended disinfection by-products (DBPs) have received continuous attention. This work investigated the spatiotemporal dynamics of DOM in Shengzhong Lake in southwest China and the formed DBPs during the chlorine disinfection process. The results showed that lake water in summer had significantly higher dissolved oxygen and dissolved organic carbon than that in winter. In contrast, DOM in winter demonstrated an obviously higher aromaticity and molecular weight than that in summer. Four fluorescence components, i.e., terrestrial humic-like substances (C1), protein-like substances (C2), and microbial humic-like substances (C3 and C4), were identified, and their relative abundance followed in the order of C3 > C4 > C2 > C1 in winter and C4 > C3 > C1 > C2 in summer. The formation potential of trihalomethanes and haloacetic acids in winter was higher and lower than that in summer, which was mainly ascribed to the content of aromatic and hydrophobic substances. Compared to the significant seasonal dynamic, the spatial variation of DOM and the formed DBPs was not obvious. This work sheds light on the spatial-temporal distribution of DOM and the potentially formed DBPs in Shengzhong Lake, and will be helpful for understanding the biogeochemical cycle of carbon and assessing the drinking water safety.

Biological Activated Carbon Filtration Controls Membrane Fouling and Reduces By-Products from Chemically Enhanced Backwashing during Ultrafiltration Treatment

Water purification by ultrafiltration (UF) requires regular membrane cleaning via backwashing. In the case of chemically enhanced backwashing (CEB), it can result in the formation of unwanted by-product precursors due to reactions with organic matters present in the backwashing water and accumulating on the membrane. After subsequent disinfection, these precursors are prone to generate trihalomethanes (THMs) and haloacetic acids (HAAs), posing potential risks to the chemical safety of drinking water. However, limited information was available regarding the removal of these disinfection by-products. In this study, biological activated carbon (BAC) pretreatment followed by UF with chemically enhanced backwashing (CEB) (BAC-UF-CEB) was investigated to mitigate membrane fouling and reduce by-product formation. It was tested in parallel with UF with CEB (UF-CEB) and UF with sole physical backwashing. Compared to UF-CEB, BAC pretreatment prior to UF-CEB reduced transmembrane pressure (TMP) by 49.0%. BAC achieved high removals of dissolved organic carbon (59.99%) and UV254 absorbance (80.82%) in the BAC-UF-CEB effluent. Moreover, BAC-UF-CEB substantially decreased trihalomethane and haloacetic acid formation potentials by 83.28% compared to UF-CEB. BAC alleviated irreversible membrane fouling by 78.7%. By removing disinfection by-product precursors, BAC-UF-CEB markedly improved treated water quality and chemical safety. This study demonstrates BAC pretreatment effectively mitigates membrane fouling and controls disinfection by-products during UF water treatment.

DBP-FP change of biofilm in drinking water distribution system induced by sequential UV and chlorine disinfection: Effect of UV dose and influencing mechanism

The issue of biofilm-related disinfection byproducts (DBPs) in drinking water distribution system (DWDS) has garnered significant attention. This study sought to examine the changes in biofilm-originated halogenated DBP formation potential (biofilm DBP-FP) in simulated continuous-flow DWDSs subjected to sequential UV and chlorine disinfection (UV–Cl2) treatments with varying UV doses and to propose the underlying mechanism. The formation potential of trihalomethanes (THMs), haloacetic acids (HAAs), and the total organic halogen (TOX, X = Cl and Br) produced by biofilm were measured. Results showed that the biofilm TOCl-FP was at a minimum with a UV dose of 80 mJ/cm2, corresponding to the lowest amounts of protein and polysaccharides in the extracellular polymeric substances (EPS). Sphingobium, Methylobacterium, and Sphingomonas played a crucial role in protein and polysaccharide biosynthesis. Bacterial community composition characterization together with metabolic function analysis indicated that dominant bacteria varied and metabolic function shifted due to UV-Cl2 disinfection, with Alphaproteobacteria increasing in relative abundance and Bacteroidia showing the opposite trend with increasing UV doses. Correlation analysis suggested that the UV-Cl2 disinfection process led to changes in the water matrix, including organics, inorganics, bacteria, and components that provide environmental pressure for the biofilm. These changes ultimately influenced the properties of the biofilm EPS, which had a direct impact on biofilm DBP-FP.

Total organic halogen (TOX) in drinking water: Occurrence, correlation analysis, and precursor removal during drinking water treatment

Total organic halogen (TOX) in drinking water provides a measurement of the overall organic halogenated disinfection by-products (DBPs) formed during disinfection. Yangtze River Delta is one of the regions with the highest population density, the fastest urbanization process, and the most severe water pollution in China. Collecting water samples from full-scale drinking water treatment plants (DWTPs) in this region, this study firstly surveyed TOX occurrence in drinking water. Besides, the correlation of TOX formation potential (TOXFP) and trihalomethane formation potential (THMFP) with general water quality parameters (e.g., dissolved organic carbon [DOC], UV254, and specific ultraviolet absorbance) and the removal efficiencies of TOX precursors by different water treatment processes were also investigated. TOX levels in DWTP effluents (i.e., finished water) ranged from 29 to 165 μg/L (median 67 μg/L), and those in simulated distribution system waters ranged from 101 to 276 μg/L (median 158 μg/L). There were generally higher linear regression coefficient values for raw water (R2 = 0.51–0.88) than for treated water (R2 = 0.33–0.64) in terms of the relationship between DBP formation potentials and general parameters. However, a relatively stronger correlation between THMFP and TOXFP was observed for treated water (R2 = 0.80, p < 0.001) than for raw water (R2 = 0.64, p < 0.001). The overall treatment efficiencies of investigated parameters in DWTPs generally followed the order of UV254 > DOC > TOX precursors > THM precursors. Notably, the overall removal rates of DOC and TOX precursors in summer (averaging 59 % and 54 %, respectively) were obviously higher than those in winter (averaging 39 % and 38 %, respectively), which was assumed to be related to the seasonal variation of bioactivity in sand filter. These results could expand the knowledge of TOX in drinking water, and provide valuable perspectives to water industry and DBP research.

Integrating biological ion exchange with biological activated carbon treatment for drinking water: A novel approach for NOM removal, trihalomethane formation potential, and biological stability

Ion exchange resins (IEX) are used in drinking water utilities to remove natural organic matter (NOM) from surface water; however, the disposal of used brine can be a major drawback. Recently, biological ion exchange (BIEX) has been proposed as an alternative to biological activated carbon (BAC) for removing natural organic matter (NOM). The present study is, to the best of our knowledge, the first attempt to use a hybrid BIEX and BAC (BIEX+BAC) system for drinking water treatment. The removal of NOM, assimilable organic carbon, and trihalomethane formation potential was investigated by operating four columns comprising IEX, BIEX, BAC, and BIEX+BAC with 18,000 bed volumes. The BIEX+BAC system was the most effective at removing dissolved organic carbon (59.9%). Based on fluorescence excitation-emission matrix spectroscopy, the BIEX+BAC column showed the maximum removal rates in all peak regions of T1, T2, and A. Using liquid chromatography-organic carbon detection, resin-containing columns were found to effectively remove humic substances, which are the principal precursors of trihalomethanes. The lowest potential for trihalomethane formation was observed in BIEX+BAC. BIEX+BAC also had the highest assimilable organic carbon removal efficiency (61.2%) followed by BIEX (52.3%), BAC (49.5%), and IEX (47.1%). The BIEX+BAC hybrid was found to be the most effective method for removing NOM fractions and reducing the formation of disinfection byproducts.

Emerging disinfection by-products formation of various molecular weight organic matter fractions in raw water contaminated with treated wastewater

Combining dissolved organic matter (DOM) in raw water (RW) with DOM in treated wastewater (TWW) can react with chlorine and pose emerging disinfection by-products (DBPs). This study evaluated DOM based on the molecular weight (MW) size fractionation, trihalomethane, iodinated-trihalomethane, haloacetonitrile, and trichloronitromethane formation potential (THMFP, I-THMFP, HANFP, and TCNMFP) of the RW from the U-Tapao Canal, Songkhla, Thailand and the RW mixed with TWW (RW + TWW) samples. The RW and RW + TWW were treated by coagulation with poly aluminum chloride. The DOM of RW and RW + TWW and their treated water was distributed most in the MW below 1 kDa. The MWs of 3–10 kDa and 1–3 kDa were the active DOM involved in the specific THMFP for the RW + TWW. The MW of < 1 kDa in the RW + TWW resulted in a slightly high specific I-THMFP and HANFP. The MW of 1 − 3 kDa in the coagulated samples had a high specific I-THMFP. The MW of > 10 kDa in the coagulated RW + TWW was a precursor for a particular HANFP. Monitoring systems for measuring the level of TWW mixed with RW and an effective process to enhance the efficiency of traditional water treatment must be set up to produce a consumer-safe water supply.

FexO/FeNC modified activated carbon packing media for biological slow filtration to enhance the removal of dissolved organic matter in reused water

The biological slow filtration reactor (BSFR) process has been found to be moderately effective for the removal of refractory dissolved organic matter (DOM) in the treatment of reused water. In this study, bench scale experiments were conducted using a mixture of landscape water and concentrated landfill leachate as feed water, to compare a novel iron oxide (FexO)/FeNC modified activated carbon (FexO@AC) packed BSFR, with a conventional activated carbon packed BSFR (AC-BSFR), operated in parallel. The results showed that the FexO@AC packed BSFR had a refractory DOM removal rate of 90%, operated at a hydraulic retention time (HRT) of 10 h at room temperature for 30 weeks, while under the same conditions the removal by the AC-BSFR was only 70%. As a consequence, the treatment by the FexO@AC packed BSFR substantially reduced the formation potential of trihalomethanes, and to a less extent, haloacetic acids. The modification of FexO/FeNC media raised the conductivity and the oxygen reduction reaction (ORR) efficiency of the AC media to accelerate the anaerobic digestion by consuming the electrons that are generated by anaerobic digestion itself, which lead to the marked improvement in refractory DOM removal.

Trihalomethanes formation potential of polluted tropical river water and its correlation with UV-Vis spectral ratio: A case study in Citarum River, Indonesia

The presence of natural organic matter (NOM) and anthropogenic organic matter (AOM) in polluted river water leads to the formation of carcinogenic disinfection by-products (DBPs) during the water chlorination process. This study aimed to determine trihalomethanes (THMs) formation, as the regulated DBPs, in polluted tropical river water. The samples were taken from the Citarum River, Bandung, Indonesia. The NOM and AOM were characterized using UV254, UV355, and ultraviolet-visible (UV-Vis) spectral ratio while DBPs formation was determined using THM4 formation potential. In several sampling points, the THM4 formation potential of the samples exceeded the USEPA regulation standards and had high toxicity (LC50) values. On the other hand, other sampling points had small THM4 formations. Also, the THM4 formation potential was found to have a great correlation with the spectral ratio, especially A280/A350 UV absorbances that could be further used as a surrogate parameter of THM4 formation. Citarum River, as a water source, needs sufficient treatment to remove the DBPs precursors to provide healthy and clean potable water.

Removal of NOMs by Carbon Nanotubes/Polysulfone Nanocomposite Hollow Fiber Membranes for the Control of Disinfection Byproducts (DBPs)

It has been well established that natural organic matters (NOMs) are precursors for the formation of disinfection by-products (DBPs) in drinking water supplies, thus the removal of NOMs is often used as an effective approach to limit DBPs production. In this study, we evaluated the application of oxidized multi-walled carbon nanotubes (OMWNTs)/polysulfone (PSU) nanocomposite hollow fiber membranes (HFM) for the removal of NOMs and its impact on the production of DBPs following water chlorination. Analysis of source water samples by fluorescence excitation/emission matrix (EEM) spectrometry indicated that the dominant dissolved organic matters were humic acid. Evaluation of the fabricated nanocomposite HFMs showed improved water fluxes (30~50%), better fouling resistance, and a comparable solute rejection rate when compared with the conventional PSU membranes. The flux increase was attributed to the increased surface hydrophilicity and porosity of the membrane after embedding the hydrophilic OMWNTs. The membrane filtration resulted in a reduction of UV254 by approximately 52%, 48%, and 38% for three water samples from Missouri River, Eagle Bluffs Conservation Area, and Columbia Water Treatment Plant, respectively. The corresponding reduction in trihalomethane formation potential (THMFP) reached 40%, 70%, and 27%, respectively. Overall, this study demonstrated that proper OMWNTs/PSU ultrafiltration membranes could remove a portion of NOMs from water at a relatively low cross-membrane pressure. It also illustrates the innovative concept that membrane design could be tailored for specific water quality conditions and regulatory requirements; in this particular case, to fabricate a membrane to reduce the THMFP to a level that meets the regulatory standards for trihalomethanes when the water was disinfected by chlorine.

Variations in trihalomethane formation potential of Microcystis aeruginosa under different growth conditions: Phenomenon and mechanism

Cyanobacteria and their metabolites are one of the primary precursors of disinfection by-products (DBPs) in natural water environments. However, few studies have investigated whether the production of DBPs by cyanobacteria changes under complex environmental conditions and possible mechanisms underlying these changes. Therefore, we investigated the effects of algal growth phase, water temperature, pH, illumination and nutrients on the production of trihalomethane formation potential (THMFPs) by Microcystis aeruginosa in four algal metabolic fractions, that is, hydrophilic extracellular organic matter (HPI-EOM), hydrophobic EOM (HPO-EOM), hydrophilic intracellular organic matter (HPI-IOM) and hydrophobic IOM (HPO-IOM). Additionally, correlations between THMFPs and some typical algal metabolite surrogates were analyzed. The results showed that the productivity of THMFPs by M. aeruginosa in EOM could be affected significantly by the algal growth phase and incubation conditions, while the IOM productivity varied insignificantly. M. aeruginosa in the death phase could secrete more EOM and have a higher THMFP productivity than those in the exponential or stationary phases. Cyanobacteria grown under harsh conditions could have increased THMFP productivity in EOM by increasing the reactivity of algal metabolites with chlorine, for example, under low pH conditions, and secreting more metabolites in EOM, for example, under low temperature or nutrient limitation conditions. Polysaccharides were responsible for the enhanced THMFP productivity in HPI-EOM fraction, and a significant linear correlation was found between the concentration of polysaccharides and THMFPs (r = 0.8307). However, THMFPs in HPO-EOM did not correlate with dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV254), specific UV absorbance (SUVA) and cell density. Thus, we could not specify the kind of algal metabolites that contribute to the increased THMFPs in the HPO-EOM fraction under harsh growth conditions. Compared with the case in EOM, the THMFPs in IOM were more stable and correlated with the cell density and total amount of IOM. The results implied that the THMFPs in the EOM were sensitive to growth conditions and were independent of algal density. Considering the fact that traditional water treatment plants cannot remove dissolved organics as efficiently as algal cells, the increased THMFP productivity in EOM by M. aeruginosa under harsh growth conditions could be a potentially serious threat to the safety of the water supply.

Using UV–Vis differential absorbance spectra of tropical peat water DOM fraction to determine trihalomethanes formation potential and its estimated cytotoxicity

Absorbance differential spectra could be utilized to identify dissolved organic matter (DOM) characteristics such as the disinfection by products (DBPs) formation. This research purposed to establish the relationship between absorbance differential spectra and trihalomethanes-4 (THM4) formation potential, as well as the estimated cytotoxicity of tropical peat water DOM percentage. The ion exchange resin was used to separate the DOM components from peat water. In addition, the UV–Vis spectrum was examined between 200 and 700 nm. The hydrophobic-acid (HPOA) fraction contains the highest concentration of dissolved organic carbon (DOC), THM4 production potential, and calculated cytotoxicity. On the other hand, the hydrophilic-neutral (HPIN) fraction has the lowest potential THM4 production. The UV–Vis absorbance spectra of all DOM fractions showed a comparable peak at 277 nm. The differential spectra of 277 nm (ΔA277) indicated a significant association with DOC concentration (99.6 %), trichloromethane (TCM) creation (86.6 %), total-THM4 (TTHM4) (81.3 %) formation, THM4 estimated cytotoxicity (89.7 %), and a moderate correlation with bromodichloromethane (BDCM) formation (55.6 %). Meanwhile, ΔA277 had a poor correlation with brominated THM4 formation potential (chlorodibromomethane (CDBM): 2.59, tribromomethane (TBM): 2.78 %). The absorbance differential spectra might be employed as a surrogate measure for the peat water DOM fraction and its precursor properties to form THM4 during the chlorination process, as well as its estimated cytotoxicity.

Changes in the structural characteristics of EfOM during coagulation by aluminum chloride and the effect on the formation of disinfection byproducts

The effects of coagulation on the removal efficiency of different fractions of effluent organic matter (EfOM) from wastewater treatment plants were investigated to identify changes in their structural characteristics and the influences on trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP). The results indicated that coagulation performed better for the removal of hydrophobic base (HOB) and hydrophobic neutral (HON) fractions than hydrophilic (HI) and hydrophobic acid (HOA) fractions. The removal efficiency was higher under neutral than under acidic conditions for all fractions. As a result, lower levels of THMFP and HAAFP were detected at pH7. The excitation-emission matrix spectra indicated that the HI fraction contained humic acid-like substances that reacted with chlorine to form THMs. The HON fraction contained soluble microbial byproduct-like substances with a higher potential to create HAAs. The results of Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and high-pressure size exclusion chromatography (HP-SEC) of the raw and coagulated water indicated that a higher molecular weight, α-carbon, COOH, aromatic structures, and polysaccharides were associated with a higher production of disinfection byproducts (DBP). These results elucidate the coagulation efficiencies of EfOM fractions associated with different mechanisms and facilitate the prediction of DBP formation by each fraction based on specific structural characteristics.

Correlation Analysis of the Carboxyl and Carbonyl Groups of Natural Organic Matter and the Formation Potential of Trihalomethanes and Chloral Hydrate

Natural organic matter (NOM) has always been considered the main precursor of disinfection by-products (DBPs) during the chlorine disinfection of drinking water. This research focuses on investigating the correlation between the functional group (carboxyl and carbonyl groups) content of NOM and the formation of trichloromethane (TCM) and chloral hydrate (CH). The quantitative determination of carboxyl groups, carbonyl groups, TCM, and CH were conducted during the drinking water treatment processes with different coagulant dosages and with/without pre-oxidation by KMnO4 or NaClO. The most appropriate coagulant for the removal of conventional components was polyaluminum chloride (PAC), and the dosage was 110 mg/L. Up to 43.7% and 14.5% of the carboxyl and carbonyl groups, respectively, were removed through the coagulation and sedimentation processes, which can be enhanced by increasing PAC dosage. The filtration process further increased the removal rates of these two functional groups to 59.8% and 33.5%, respectively. The formation potential of the TCM and CH decreased as the PAC dosage increased. Pre-oxidation by KMnO4 (0.8-1.0 mg/L) effectively controlled the formation of DBPs while increasing the carboxyl and carbonyl group content. Pre-oxidation by NaClO decreased the formation of TCM rather than CH, and a suitable amount (0.5-1.0 mg/L) decreased the carboxyl and carbonyl groups. It was found that there was a good linear correlation between carboxyl groups and TCM and CH. The linear fit R2 values of the carboxyl groups to TCM and CH were 0.6644 and 0.7957, respectively. The linear fit R2 values of the carbonyl groups to TCM and CH were 0.5373 and 0.7595, respectively.

Beneficial role of pre- and post-ozonation in a low rate biofiltration-ultrafiltration process treating reclaimed water

Previous studies have shown that the combination of biological and ozone oxidation processes can achieve a greater performance in treating natural surface water than each process individually. In this work, we designed and tested an ozonation–gravity-driven up-flow slow rate (0.01 m/h) biofiltration–ozonation (O3–GUSB–O3) process for the pre-treatment of reclaimed water prior to ultrafiltration (UF), with the aim of producing high quality drinking water and a significantly reduced degree of UF fouling. Results showed that O3 coupled with GUSB can effectively remove aromatic compounds (∼ 84.8%), dissolved organic carbon (DOC, ∼ 83.4%), and biopolymers in surface water. In addition, post-ozonation greatly contributed to the reduction of the UF membrane fouling (∼ 6 times greater flux). With regard to the disinfection by-product formation potential (DBPFP) of the final treated water, both trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP) were greatly reduced (86.4% and 84.8% for THMs and HAAs, respectively). The relationship between DBPFP and various spectral indexes revealed that aromatic compounds and amino acids were more likely to generate DBPs during the disinfection stage. Among these, humic substances were more likely to generate THMs, while low molecular weight carboxylate and carbonyl organic compounds were associated with the generation of HAAs. Moreover, the dosage of O3 during the post-ozonation stage was found to influence directly the generation of DBPs. Overall, this study has conducted a detailed evaluation of a novel multi-ozone biofilter UF process for treating surface water, and the results provide a valuable basis for subsequent studies at larger scale to demonstrate the potential of the treatment process for practical applications.

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 4.47mg/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.

Fertilization regime shifts the molecular diversity and chlorine reactivity of soil dissolved organic matter from tropical croplands

Soil-derived dissolved organic matter (SDOM) is an important site-specific disinfection byproduct (DBP) precursor in watersheds. However, it remains unclear how fertilization regime shifts the molecular diversity and chlorine reactivity of SDOM in cropland-impacted watersheds. Here, we analyzed the spectroscopic and molecular-level characteristics of the SDOM from croplands that had different fertilization regimes (i.e., non-fertilization, chemical fertilization, straw return, and chemical fertilization plus straw return) for 5 years and evaluated the chlorine reactivity of the SDOM by determining the 24-h chlorine consumption and specific DBP formation potential (SDBP-FP). The SDOM level decreased by chemical fertilization and was not significantly altered by straw return alone or combined with chemical fertilizer. However, all fertilization regimes elevated the molecular diversity of SDOM by increasing the abundance of protein-, lignin-, and tannin-like compounds. The chlorine reactivity of SDOM was reduced by chemical fertilization, but was significantly increased by straw return. Typically, straw return increased the formation potential of specific trihalomethane and chloral hydrate by 339% and 56% via increasing the aromatics in SDOM, whereas chemical fertilization could effectively decrease about 231% of the increased specific trihalomethane formation potential caused by straw return. This study highlights that fertilization regime can significantly shape the molecular diversity and chlorine reactivity of the SDOM in croplands and that partially replacing chemical fertilizer with crop straw is an advantageous practice for reducing DBP risks in drinking water in cropland-impacted watersheds.

The fate of microplastics and organic matter leaching behavior during chlorination.

As an emerging persistent pollutant, microplastics (MPs) have been detected in the drinking water system and its potential risk in the presence of disinfectants has received little attention. This work aimed to investigate the changes in MPs properties and the organic matter leaching behavior of MPs during chlorination. Physical and chemical changes of the chlorinated MPs were detectable by scanning electron microscope, Micro-Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Polystyrene (PS) was less resistant to chlorination than polyethylene (PE), indicated by changes in Raman peaks and O/C ratio of the XPS spectrum. Organic matter leaching behavior of MPs was explored by dissolved organic carbon (DOC) determination and disinfection byproducts formation potential measurement. The results demonstrated the stimulating effect of chlorination on the organic matters leaching from MPs, with the total leached DOC accounting for ∼0.3‰-0.5‰ of the MPs mass. The leached organic matters exhibited an appreciable potential to form trihalomethanes (THMs) and haloacetonitriles (HANs). The formation potential of THMs and HANs were 54.43-185.08μg/mg C and 3.65-11.83μg/mg C, respectively. Compared to PE, organic matter leaching behavior during chlorination was more obvious for PS. This study provides insights into the fate of chlorinated microplastics and the possible risk of organic matters leached from MPs to form disinfection byproducts during chlorination.

Minimization of halogenated disinfection by-product precursors by Al-based electrocoagulation–flotation (ECF) toward cyanobacteria-laden water

Abstract The presence of toxic algae, such as Microcystis aeruginosa (MA), in drinking water treatment plants (DWTPs) would contribute to algal organic matter (AOM) as precursors toward disinfection by-products (DBPs). Electrocoagulation–flotation (ECF) has shown promising performance in minimizing algal cells from water and dissolved AOM. This study aimed to investigate the effect of current density (CD) and pH on alumina (Al)-based ECF for removing MA cell and DBPs precursors from cyanobacteria-laden water. The performance of Al-based ECF was evaluated at various CD and pH conditions within 20 min. In addition, the total halogenated DBPs formation of the treated suspension after ECF was quantified. At pH 8, the ECF process with 5 mA/cm2 exhibits the most significant reductions in MA cell and soluble AOM, accounting for 97 and 56%, respectively. Additionally, the precursors of trihalomethanes (THMs) and haloketones (HKs) can be effectively removed with flotation despite their significant release at EC. The tremendous reduction of humic acid-like (HAL) substances in extracellular organic matter (EOM) fraction by ECF leads to the minimized THMs formation potential. In summary, Al-based ECF at pH 8 is effective to remove cyanobacteria and minimize the precursors of regulated THMs along with an insignificant reduction in regulated haloacetic acids (HAAs) precursors.

Disinfection By-product Precursor Removal by Biochar Derived from Agricultural Waste

Biochar made from agricultural waste products can be used as a low-cost adsorbent targeting dissolved organic matter (DOM). In water treatment plant (WTP), DOM reacts with chlorine-based disinfectant and forms carcinogenic disinfection by-products. The objective of this study was to investigate the applicability of bamboo biochar derived from wood vinegar production waste as an adsorbent for DOM removal and subsequently trihalomethane formation potential (THM-FP) reduction. Raw biochar (BCRaw) and 800°C post-heated biochar (BC800) was tested for its surface characteristics including scanning electron microscopy, Fourier transform infrared spectroscopy and Brunauer, Emmett and Teller analysis. The post-pyrolysis treatment increased the surface area of the biochar from 90.3 to 274 m2 g-1. Raw natural water collected from Tapra WTP, Khon Kaen, Thailand, which uses the Chi River as its water source. The adsorption capacities for dissolve organic carbon at 24-h equilibrium (Qe) of BCRaw and BC800 were 0.148 and 0.551 mg-C g-1 adsorbent, respectively. The adsorption kinetics were described well with a pseudo-second order model, which implied chemisorption and multiple adsorption mechanisms. While THM-FP was relatively unaffected by a treatment with BCRaw, a treatment with BC800 resulted in 12.4% THM-FP reduction and preferential removal of precursor to chloroform over other THMs was observed. Fluorescent excitation-emission matric spectroscopy was employed to characterize DOM before and after treatment with biochar. BC800 achieved greater removal of terrestrial humic-like and fulvic-like DOM, due to the presence of oxygen functional groups, which enhances removal capacity for aromatic compounds. Overall, this study shows the potential use of bamboo biochar derived from waste material as an adsorbent for THM precursor removal.