Disinfection By-product Formation Potential Research Articles

Characteristics and disinfection by-product formation potential of dissolved organic matter in reservoir water in cold area.

The severe cold in winter with harsh natural conditions in Northeastern China seriously affect the water quality of the reservoir, showing the increased content and more complex types of organic matter, which brings severe challenges to the control of disinfection by-products (DBPs) in drinking water treatment with reservoir water as the water source. In this study, the fractions of dissolved organic matter (DOM) in source water at before ice formation period (P1), ice-age period (P2), and ice begin to melt period (P3) were separated by membrane separation technology. Subsequently, the contributions of DOM fractions with different molecular weights (MW) to DOC, UV254, and SUVA254, and their disinfection by-product formation potential (DBPFP) were evaluated. Although DOM with high MW (5-10kDa) contributed the most to dissolved organic carbon (DOC) and UV254, but the contribution of DOM with low MW (0-1kDa) to DBPs formation could not be ignored, especially during ice-age period. There was no significant difference in the total numbers of DOM formula belonged to low MW fraction at these three periods, mainly including lignin, followed by N-containing saturated compounds and tannins. Additionally, redundancy analysis revealed that DOC and UV254 as the predictors had good correlation with DBPFP, while SUVA254 could not be used as a single indicator to predict the generation potential of DBPs, and could be used as the prediction factors together with AImodwa parameter closely related to DBPFP. The study provided key information for controlling the DBPs formation of DOM in water, especially in the ice-age period, and provided the theoretical basis for water plant production.

Identification of key precursors contributing to the formation of CX3R-type disinfection by-products along the typical full-scale drinking water treatment processes

Identification and characterization of disinfection by-product (DBP) precursors could help optimize drinking water treatment processes and improve the quality of finished water. This study comprehensively investigated the characteristics of dissolved organic matter (DOM), the hydrophilicity and molecule weight (MW) of DBP precursor and DBP-associated toxicity along the typical full-scale treatment processes. The results showed that dissolved organic carbon and dissolved organic nitrogen content, the fluorescence intensity and the SUVA254 value in raw water significantly decreased after the whole treatment processes. Conventional treatment processes were in favor of the removal of high-MW and hydrophobic DOM, which are important precursors of trihalomethane and haloacetic acid. Compared with conventional treatment processes, Ozone integrated with biological activated carbon (O3-BAC) processes enhanced the removal efficiencies of DOM with different MW and hydrophobic fractions, leading to a further decrease in almost all DBP formation potential and DBP-associated toxicity. However, almost 50% of the detected DBP precursors in raw water has not been removed after the coagulation-sedimentation-filtration integrated with O3-BAC advanced treatment processes. These remaining precursors were found to be mainly hydrophilic and low-MW (< 1.0 kDa) organics. Moreover, they would largely contribute to the formation of haloacetaldehydes and haloacetonitriles, which dominated the calculated cytotoxicity. Since current drinking water treatment process could not effectively control the highly toxic DBPs, the removal of hydrophilic and low-MW organics in drinking water treatment plants should be focused on in the future.

Granular activated carbon caps - A potential treatment barrier for drinking water cyanotoxins

Incorporation of granular activated carbon (GAC) in rapid media filtration has been shown to serve as an effective means to mitigate cyanotoxin exposure via extracellular adsorption. Control of organics, including dissolved organic carbon (DOC), may also improve via adsorption followed by biological treatment. Although beneficial, complete replacement of filter media with GAC is often associated with high capital costs. A seven-month pilot study conducted at a water treatment facility located in Eugene, Oregon examined the benefits of replacing the top 15 cm of anthracite media with GAC “caps” to enhance control of a cyanotoxin as well as DOC, disinfection by-product formation potential (DBP FP), and chlorine demand. Removal of cylindrospermopsin by GAC cap adsorption was assessed via simulated cyanotoxin events utilizing orange II dye as a surrogate over a 4-month period. A pilot-scale filter incorporating a GAC cap demonstrated up to 40% higher reduction throughout the study when compared to a control. This reduction however decreased to 9% as operation time increased. While installation of a GAC cap increased biomass density (ATP concentration), it did not improve DOC or DBP FP removal or chlorine demand at this facility, likely due to the low EBCT (1.2 min) in the GAC layer. This study presents evidence that incorporation of GAC caps may provide a cost-efficient, albeit low capacity, barrier for cylindrospermopsin exposure following several months of continuous operation.

Impact of simulated wildfire on disinfection byproduct formation potential

Impact of simulated wildfire on disinfection byproduct formation potential

Effects of different types of nitrogen sources in water on the formation potentials of nitrogenous disinfection by-products in chloramine disinfection process based on isotope labeling

Nitrogenous disinfection by-products (N-DBPs) raise increasing concerns because of their high genotoxicity, cytotoxicity, and carcinogenicity compared to carbonaceous disinfection by-products (C-DBPs). Nitrogen-containing disinfectants, dissolved organic nitrogen (DON), and inorganic nitrogen may all promote the formation of N-DBPs. Therefore, it is urgent to explore the dominant nitrogen source of N-DBPs under the coexistence of multiple nitrogen sources. In this study, the effects of amino acids, nitrate, ammonia, and chloramine as different types of nitrogen sources on the formation of five N-DBPs were investigated systematically, including chloroacetonitrile (CAN), dichloroacetonitrile (DCAN), bromochloroacetonitrile (BCAN), dibromoacetonitrile (DBAN) and dichloroacetamide (DCAcAm). L-Aspartic acid (L-Asp) as the organic nitrogen source showed a high potential on the formation of N-DBPs by forming acetonitrile intermediates. Ammonia as the inorganic nitrogen source consumed oxidants and changed the existing form of chloramine, thus inhibiting the formation of N-DBPs. Instead of providing nitrogen to N-DBPs, nitrate as a salt promoted the volatilization of N-DBPs, thereby reducing the detected N-DBPs. Furthermore, an isotope labeling method was applied to clearly trace the nitrogen sources of N-DBPs via GC–MS with electron ionization. 15N-chloramine, 15N-amino acid, 15N-nitrate and 15N-ammonia were selected as the corresponding isotopic nitrogen sources. The results indicated that chloramine was the major nitrogen contributor to five N-DBPs during the chloramination of L-Asp under the coexistence of multiple nitrogen sources, ranging from 61 % to 79 %. The influence of environmental factors (reaction time, pH, and bromide) on the formation of N-DBPs during chloramination was also investigated. There was competition between brominated N-DBPs and chlorinated N-DBPs in chloramination. With the increase of reaction time or bromine, the formation potentials of chlorinated N-DBPs gradually decreased, while brominated N-DBPs gradually increased. Moreover, higher pH inhibited the generation of N-DBPs.

Dissolved organic matter derived from aquatic plants in constructed wetlands: Characteristics and disinfection byproducts formation

Constructed wetlands are used to improve water quality in the drinking water sources, but aquatic plants planted in constructed wetlands may be a source of disinfection by-product (DBP) precursors. This study explored the characteristics of aquatic plant-derived dissolved organic matter (DOM) and DBP formation in micro-polluted raw water treated by constructed wetlands. A simulated surface flow wetland (SSFW) planted with the typical aquatic plants Lythrum salicaria and Acorus calamus was studied. Raw water, control samples, effluent, and Suwannee River natural organic matter (SRNOM) were analyzed. via ultraviolet-visible (UV-Vis) spectroscopy, three-dimensional excitation emission matrix (3D-EEM) fluorescence combined with a parallel factor (PARAFAC) analysis, liquid chromatography-organic carbon detection (LC-OCD), principal component analysis (PCA), and other detection and analysis methods. A DBP formation potential (DBPFP) index was also constructed. Treatment by the SSFW increased the effluent dissolved organic carbon (DOC), UV254, trihalomethane formation potential (THMFP), haloacetic acid formation potential (HAAFP) by 72.2%, 171.4%, 83.7% and 88.6%, respectively. Planting aquatic plants in surface wetlands will negatively affect the water quality of micro-polluted raw water, with the plants being an important source of increased DBP precursors in wetland effluent. The effluent properties were similar to those of SRNOM, and had a higher degree of aromatization and larger molecular weight than raw water. The increased DBP precursors were mainly fulic acid and humus with higher aromatic and molecular weight, which derived from the growth and metabolism of aquatic plants. Humic substances (HS) accounted for the highest proportion of DOM in this study, with the average molecular weight of HS increasing from 648 to 698 g·mol−1 as the DOM content increased. Results from this study are particularly applicable to the establishment of constructed wetlands planted with aquatic plants in the drinking water sources, and the DOM derived from aquatic plants in constructed wetlands may be important precursors in the subsequent water disinfection process.

Developing the large-area manganese-based catalytic ceramic membrane for peroxymonosulfate activation: Applications in degradation of endocrine disrupting compounds in drinking water

Endocrine disrupting compounds (EDCs) in the aquatic systems are of growing concerns that could undermine drinking water safety. In this study, manganese (III) oxide (Mn2O3) based catalytic ceramic membrane (CCM) was developed for the activation of peroxymonosulfate (PMS), and its applicability has been tested in degrading the ten different EDCs (including bisphenol analogs (BPs)) in drinking water. The CCMs were synthesized at different calcination temperatures i.e., 850, 950, and 1150 °C. Optimal performance of CCMs/PMS was achieved at a higher degree of calcination. The CCMs/PMS has shown a potential to effectively degrade the EDCs at higher concentrations (mg/L) to trace levels (ng/L). The CCMs/PMS system adopted a non-radical pathway of degrading the EDCs through the extensive generation of singlet oxygen (1O2), as confirmed using quenching experiments and electron paramagnetic resonance (EPR) spectroscopy. 1O2-based oxidation process showed special selectivity for the decontamination of phenols and bisphenols. The long-term performance of CCMs/PMS showed good stability in degradation of the EDCs in drinking water, also with efficient mineralization (TOC removal >55%) and negligible release of Mn (0.004 wt%Mn/min). CCMs/PMS system also showed high potential in improving water quality by reducing the disinfection byproducts (DBPs) formation potential, highest recorded for bromodichloromethane (CHCl2Br, 100%) and lowest for dichloroacetic acids (TCAA, ∼50%). The study provided a highly efficient catalytic ceramic membrane based advanced oxidation process (AOPs) for effective degradation multiple of EDCs in drinking water, and the findings of this work can be a baseline for full-scale water treatment applications.

Insights into graphene oxide/ferrihydrite adsorption as pretreatment during ultrafiltration: Membrane fouling mitigation and disinfection by-product control

In this study, a novel adsorbent of graphene oxide (GO) incorporated ferrihydrite (FH) was fabricated and integrated with ultrafiltration (UF) to remove natural organic matter (NOM), the crucial cause of membrane fouling and major precursor of disinfection by-products (DBPs). Compared with FH and powdered activated carbon (PAC), GO/FH exhibited superior removal for high molecular weight (HMW) humic- and fulvic-like substances and low molecular weight (LMW) protein. The cake layer formed by GO/FH alleviated the deposition of NOM on membrane surface or inside membrane pores. Therefore, GO/FH reduced 89% and 95% total fouling resistance and irreversible membrane resistance, respectively, together with the lowest increment of transmembrane pressure. Pearson correlation analysis indicated that DOC, rather than specific ultraviolet absorbance (SUVA) and UV254, was significantly correlated to the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) when SUVA was below 4 L/mg-C.m. Whilst the HMW NOM (1–20 kDa) was highly related to dibromochloromethane (DBCM) (r = 0.98–1), the LMW fraction (< 1 kDa) was correlated with dibromochloromethane (TCAA) and dichloroacetic acid (DCAA) (r = 0.88–0.98). Inspiringly, GO/FH-UF reduced 90% of carbonaceous DBPs, the concentrations of which well met the WHO Guidelines. In summary, GO/FH-UF substantially alleviated membrane fouling and dramatically reduced DBP formation potential.

Formation of disinfection byproducts in an ammonia-polluted source water with UV/chlorine treatment followed by post-chlorination: A pilot-scale study

This study investigated the formation of disinfection byproducts (DBPs) from a real ammonia-polluted source water treated by a pilot-scale ultraviolet (UV)/chlorine process with subsequent post-chlorination. The experimental results indicated that UV/chlorine treatment enhanced the formation of trihalomethanes (THMs), haloacetic acids (HAAs), and haloacetonitriles (HANs) in post-chlorination, compared to UV or chlorine applied alone under parallel experimental conditions. DBP formation was observed to depend on pH values, chlorine doses, and reaction times. THM formation was higher at pH 9.0 than pH 6.0, while HAAs and HANs were produced more readily at pH 6.0 rather than 9.0. A higher chlorine dose led to a higher amount of DBPs formed after the treatment of UV/chlorine followed by post-chlorination. The concentration of DBPs increased with the UV/chlorine treatment time increasing from 2 to 15 s and then presented a decrease trend with the reaction time prolonging to 30 s. In addition, changes in natural organic matter (NOM) properties were evaluated using three-dimensional fluorescence spectra and parallel factor analysis (PARAFAC) UV/chlorine treatment effectively destroyed humic-like and tyrosine-like components in waters with the maximum fluorescence intensity ( FI m a x ) reduced by 51.4% and 64.6%, respectively, compared to the raw water sample. The decrease of fluorescence of waters exhibited a positive correlation with the formation of DBP-FP in UV/chlorine treatment. Overall, DBP formation from the ammonia-polluted source water caused by UV/chlorine treatment could be managed by carefully determining chlorine doses and contact times to be used in the UV/chlorine process. • Micro-polluted water was treated by a pilot-scale UV/chlorine process. • DBP formation potential in UV/chlorine was strongly pH dependent. • Reducing chlorine dosage offset the increase of DBP formation. • The destruction of fluorescence components related with the formation of DBPs. • Fulvic-like components could be used as an indicator for DBP formation.

Comparison of Organic Matter Properties and Disinfection By-Product Formation between the Typical Groundwater and Surface Water

The disinfection by-product (DBP) formation was affected by the dissolved organic matter (DOM). Therefore, the DOM properties and DBP formation potential of the two most widely used source waters: groundwater (GW) and surface water (SW), were comparatively studied in this work. The results suggested that the GW mainly consisted of protein-like organics with smaller molecular weight (Mw) less than 3000 Da, while the SW contained the humic- and fulvic-like substances with larger Mw. The tap water DBP concentration of GW as source water was lower than that of SW as well as the cytotoxic index (CI). The total DBP formation potential of the SW under chlorine and chloramine disinfection was higher than that of GW, especially the trihalomethanes (THMs) and haloacetic acid (HAAs). The higher THM and HAA formation potential of the SW was mainly attributed to the relatively hydrophobic and aromatic humic and fulvic substances. The halonitromethanes (HANs) formation was mainly due to the less hydrophobic protein-like components with smaller Mw. In addition, the total CI of the GW was lower than the SW under both chlorine and chloramine disinfection. Therefore, for the DBPs control, using the GW as source water was more beneficial to human health.

Micropollutant removal and disinfection byproduct control by sequential peroxymonosulfate-UV treatment in water: A case study with sulfamethoxazole

UV/peroxymonosulfate (UV/PMS) advanced oxidation process has attracted significant attention for removal of micropollutants in water. However, during practical water treatment applications, the PMS treatment must be performed before the UV treatment to achieve full contact. In this study, sulfamethoxazole (SMX) was selected as the target micropollutant. Four different operational approaches, including UV alone, PMS alone, simultaneous UV/PMS and sequential PMS-UV, were compared for their differences in SMX removal and disinfection by-product (DBP) formation potentials during chlorine-driven disinfection. Among the four approaches, UV/PMS and PMS-UV achieved over 90% removal efficiencies for SMX without substantial differences. For raw water, the trichloronitromethane (TCNM) formation potential after treatment with PMS-UV was lower than that after UV/PMS treatment. The time interval over which the PMS-UV process was conducted had little effect on the final removal efficiency for SMX. However, a brief (5 min) pre-PMS treatment significantly reduced the TCNM formation potential and the genotoxicity from DBPs. The formation risk for TCNM during chlorination increased markedly with increasing PMS dosages, and the appropriate dosage under these experimental conditions was suggested to be 0.5–1.0 mmol/L. Under alkaline conditions, PMS-UV treatment can enhance SMX degradation as well as dramatically reduced the formation potentials for haloketones, haloacetonitriles and halonitromethanes. This study suggests that proper optimization of UV/PMS processes can remove SMX and reduce its DBP formation.

Determination of cost-effective optimum coagulant dosage for removal of disinfection by-product precursors in water treatment based on the theory of elasticity

Determination of coagulant dosage in drinking water treatment is related to the requirements for drinking water quality as well as the treatment costs. Selection of appropriate coagulant dosages has been an issue for water treatment utilities, though empirical approaches were normally considered or employed. Inspired by the theory of elasticity in microeconomics, this study explored a novel approach for the cost-effective optimum coagulant dosage. This could enable water utilities to achieve the maximum possible removal efficiency of precursors for disinfection byproducts (DBPs) while maintain an economical dosage without incurring an excessive cost. The relationships between DBP formation potential (DBPFP) and several relevant water quality parameters were first examined and evaluated. UV254 was found the most appropriate DBPFP indicator with the highest correlation coefficients. Based on the relationship of UV254 and DBPFP, an approach for determination of cost-effective optimum coagulant dosage was delineated. The results showed that use of the cost-effective optimum coagulant dosage, which account for approximately 33% of optimum coagulant dosage, could achieve 79% of maximum removal efficiencies of UV254 for the source waters tested, thereby substantially reducing the formation of DBPs. Further increase the coagulant dosage was believed uneconomical since the increase in UV254 removal was limited. Similar results were obtained with different coagulants and with raw water samples with diverse water qualities. The results suggest that the proposed approach could provide a mathematical tool for cost-effective optimum coagulant dosage control which could at the same time achieve sufficient removal of natural organic matter to reduce DBPs formation.

Fermentation liquid as a carbon source for wastewater nitrogen removal reduced nitrogenous disinfection byproduct formation potentials of the effluent

Sludge alkaline fermentation liquid (SAFL) is an alternative to sodium acetate (NaAc) in enhancing wastewater nitrogen removal. Upon SAFL addition, dissolved organic nitrogen (DON) can be externally introduced or biologically synthesized during nitrogen removal, which is an important precursor to toxic nitrogenous disinfection by-products (N-DBPs). This study aims to evaluate the effects of different carbon source addition on effluent DON concentration, composition, and N-DBP formation potentials. A lab-scale A2O system treating real municipal wastewater was operated with NaAc or SAFL as external carbon sources. DON molecules and potential N-DBP precursors were identified by Orbitrap mass spectrometry. Subsequently, major microorganisms contributing to DON biosynthesis were suggested based on metagenomics. It was found that effluent DON was higher with SAFL as the carbon source than NaAc (1.51 ± 0.24 v.s. 0.56 ± 0.08 mg N/L, p < 0.05). Nevertheless, dichloroacetonitrile and nitrosamine formation potentials (7.14 ± 1.02 and 1.57 ± 0.07 μg/mg DON-N, respectively) of the effluent with SAFL addition were 42.79 ± 2.42% and 54.89 ± 1.70% lower than those of NaAc. Protein- and lignin-like compounds were the most abundant DON molecules in the effluent, where alanine, glycine and tyrosine were important precursors to N-DBPs. Azonexus and Flavobacterium spp. were positively correlated with these precursors, and possessed key genes involved in precursor synthesis. SAFL is a promising carbon source, not only for achieving efficient inorganic nitrogen and DON removals, but also for reducing N-DBP formation potentials of chlorinated effluent.

The role of medium molecular weight organics on reducing disinfection by-products and fouling prevention in nanofiltration

Nanofiltration (NF) is utilized in water treatment for controlling disinfection by-products formation potential (DBPFP) and disinfection by-products (DBPs). Attention regarding NF-based technology has been paid on membrane fouling of NF and the rejection efficiency of contaminants by NF membranes. Natural organic matter (NOM) presenting in surface waters is one main removal target in drinking water treatment by NF-based technology, and is thereby a contributor to the membrane fouling of NF. In application, pretreatments of other membrane filtration (e.g., microfiltration (MF) and ultrafiltration (UF)) has been taken prior to NF, resulting in the separation of NOM of specific molecular weight. Meanwhile, it is well known that NOM is composed of organic compounds of different molecular weights. However, the effect of NOM of specific molecular weight has been seldom investigated from the aspects of membrane fouling and the resulting DBPFP after membrane filtration. By using combinations of MF and UF (molecular weight cut-off of 100K or 20K) as pretreatment prior to NF, the NOM of various molecular weight on DBPFP and DBPs in the NF-treated water were investigated. The experiments were conducted with two real-world surface water samples and one tap water sample. It was found that medium molecular weight NOM, defined as NOM that passed UF100K but did not pass UF20K in this study, reduced fouling of the NF membrane. This is supported by the excitation and emission matrix (EEM) fluorescence spectra, size exclusion chromatography (SEC) and flux analysis. In addition, the medium molecular weight NOM also reduced the DBPFP in the NF treated water and eventually the DBPs by participating in forming a protective layer on the NF surface, blocking the transfer of small molecular weight NOM into the NF filtrate, thereby reducing the DBPFP of the NF filtrate since small molecular weight NOM was the major contributor to DBPFP in this study.

Formation of disinfection byproducts from chlorinated soluble microbial products: Effect of carbon sources in wastewater denitrification processes

Carbon sources are crucial for biological denitrification in wastewater treatment that significantly affects the production of soluble microbial products (SMPs), thereby affecting the formation of disinfection byproducts (DBPs) during subsequent chlorination. However, the effect of carbon sources on DBPs formation has not been studied. In this work, sodium acetate, sodium lactate, and glucose were used as carbon sources, and denitrifying SMPs derived from different carbon sources were used as DBPs precursors to investigate the formation potential (FP) of 16 carbonaceous DBPs and 19 nitrogenous DBPs. Results showed that the carbonaceous DBPs FP of SMPs derived from acetate, lactate, and glucose were 502.1–584.3, 250.3–288.9, and 374.7–439.1 μg/L, respectively, and the nitrogenous DBPs FP were 19.1–45.6, 12.8–21.9, and 7.9–9.0 μg/L, respectively. After chlorination, the genotoxicity of SMPs measured by the SOS/umu test was also evaluated with 364 ng 4-NQO/L for acetate, 212 ng 4-NQO/L for lactate, and 138 ng 4-NQO/L for glucose. Based on X-ray photoelectron spectroscopy, chemical structures of SMPs were characterized, and their relationship with DBPs FP was investigated to explain the mechanism of DBPs formation. Aromatic C and C-O were found to be the major precursor structures to form carbonaceous DBPs, and their lowest proportions in lactate-derived SMPs caused the lowest carbonaceous DBPs FP. Organic nitrogen, including aromatic N, amide/peptide N, and primary amine N, was the precursor of nitrogenous DBPs. The lowest concentration of dissolved organic nitrogen for glucose-derived SMPs caused the lowest nitrogenous DBPs FP and genotoxicity. Glucose may be a better choice among the three carbon sources in terms of reducing genotoxicity.

Identification of the key biochemical component contributing to disinfection byproducts in chlorinating algogenic organic matter

Disinfection byproducts (DBPs) remains an ongoing issue because of their widespread occurrence and toxicity. Various organic substances in Algogenic organic matter (AOM) can produce DBPs in the chlorination process. To provide specific suggestions for the targeted removal of DBP precursors in AOM, the main biochemical components in AOM were qualitatively and quantitatively analyzed. An accurate model for predicting the DBP formation potentials (DBPFPs) of AOM was herein developed based on the dissolved organic carbon of the five main biochemical components in AOM and the DBPFPs of their corresponding surrogates. The contributions of each biochemical component to the three DBP species were evaluated, and the key components were identified. The results showed that lipids, proteins, carbohydrates, humic acid-like substances, and fulvic acid-like substances were the main biochemical components in AOM. Thereof, proteins (71.2 ± 2.1%) and carbohydrates (53.1 ± 2.1%) were the major contributor to the carbon content in intracellular organic matter and extracellular organic matter, respectively. The contribution results of biochemical components to the formation of DBPs showed that proteins were the key contributor to DBPs, suggesting that the targeted removal of proteins before the chlorination process would effectively reduce DBPs from AOM.

Removal of Small-Molecular-Weight Organic Matter by Coagulation, Adsorption, and Oxidation: Molecular Transformation and Disinfection Byproduct Formation Potential

Removal of Small-Molecular-Weight Organic Matter by Coagulation, Adsorption, and Oxidation: Molecular Transformation and Disinfection Byproduct Formation Potential

Synergistic Control of Nitrogenous Disinfection By-products and Opportunistic Pathogens in Drinking Water by Iron-Modified Quartz Sand Filtration

The main function of quartz sand in drinking water treatment has been to remove turbidity, while the microbial effect of its solid-liquid interface has been ignored. In order to solve the limitations of control of the disinfection by-products (DBPs) and opportunistic pathogens (OPs) in common quartz sand, the common quartz sand was modified to iron sand. The maximum DBPs formation potential of typical nitrogenous disinfection by-products (N-DBPs) and carbonaceous disinfection by-products was determined using gas chromatography-ECD. Compared with those of sand, the inhibition effects of halonitromethanes, haloacetamides, and haloacetonitriles by the Fe-sand were increased by 51.51%, 43.66%, and 90.6%, respectively. In addition, the gene copy numbers of Hartmanella vermiformis, Legionella spp., Mycobacterium spp., M. avium, and Naegleria spp. were detected via quantitative qPCR, and the results indicated that the Fe-sand did have a similar significant inhibitory effect on OPs. The Fe-sand had limited ability to enhance the removal of NOM. However, the Fe-sand effectively inhibited the continuous contribution of biofilm to N-DBPs and opportunistic pathogens. The distribution of biofilms on the surface of the Fe-sand filter media was uniform, not likely to fall off, and more stable; however, the suspended biofilms in the effluent were more difficult to aggregate. In addition, the α-helix of the secondary structure in the extracellular protein disappeared in the effluent of the Fe-sand. Therefore, the whole suspended biofilm was easily penetrated by chlorine. The Fe-sand solid-liquid interface did significantly change the microbial community structure and suspended biofilm characteristics, which provides a new concept to ensure the safety of drinking water quality and plays a good theoretical supporting role in the improvement and transformation of the existing process in drinking water treatment plants.

Permanganate/Bisulfite Pre-Oxidation of Natural Organic Matter Enhances Nitrogenous Disinfection By-Products Formation during Subsequent Chlorination

The permanganate/bisulfite (PM/BS) process is a novel oxidation process, which can degrade micropollutants within several seconds. As natural organic matter (NOM) ubiquitously exists in an aquatic environment, the PM/BS process will inevitably react with NOM, which may impact the disinfection-by-products (DBPs) formation during subsequent chlorination. This study investigated the effect of PM/BS pre-oxidation of NOM on DBP formation. It was found that TOC removal reached a plateau when the molar ratio of PM to BS was 1:5. Increasing ratios of PM to BS decreased the intensity and area of fluorescence spectroscopy. PM and BS doses, pre-oxidation time, pH of solutions and concentration of Br− impacted the formation potential of various DBPs. PM/BS pre-oxidation decreased the formation of TCM while increasing the yields of N-DBPs, thus increasing the risk of water quality. Calculated toxicity analysis showed that a general increase in CTI was observed with PM/BS pre-oxidation, indicating that PM/BS pre-oxidation had a negative effect on risk control of overall cytotoxicity. Although the PM/BS process could accelerate the degradation of micropollutants, the elevated DBPs formation, especially highly toxic N-DBPs, needs enough attention to control water-quality risk.

Characterization of molecular dissolved organic matter removed by modified eucalyptus-based biochar and disinfection by-product formation potential using Orbitrap mass spectrometric analysis

Biochar is an alternative adsorbent, with similar characteristics to activated carbon, that can be applied to water treatment to remove dissolved organic matter (DOM) as disinfection by-product (DBP) precursors with comparable efficiency and better cost-effectiveness and sustainability relative to commercial alternatives. We applied non-targeted analysis with Orbitrap mass spectrometry to investigate changes in molecular DOM and DBP formation after treating DOM-containing water with biochar. Two surface water sources, Phong River (PR) in Khon Kaen, Thailand and Suwannee river (SR), USA, were tested using three types of eucalyptus-derived biochar (i.e., KOH-modified, calcined, and both) were selected as adsorbents and compared to commercial coconut-based activated carbon (ccAC). The results showed that calcination increased the surface area, pore volume, and functional groups of biochar responsible for adsorption. The calcined biochar achieved higher DOC removal efficiencies for both rivers than other adsorbents. PR contains more adsorbable DOM as over 800 molecules with carbon, hydrogen, and oxygen (CHO) features that were decreased or totally removed by all adsorbents. In contrast, for SR treatment, KOH-modified and calcined biochar was found to decrease over 800 CHO features, compared to around 500 and 400 CHO features for calcined biochar and ccAC, respectively. However, numerous background CHO features with reduced character (i.e., low degree of oxidation) were found after water treatment by calcined biochar, resulting in higher DBP formation after chlorination compared to the other adsorbents. The results of this study have important implications for future preparation of biochar for water treatment.