Low Molecular Weight Organic Matter Research Articles

Removal of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) by coagulation: Influence of coagulant and dosing conditions

Per- and polyfluoroalkyl substances (PFAS) pose significant risks to the environment and human health. Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are two of the most frequently detected PFAS in the environment. In most surface water drinking water treatment works (WTW), coagulation is the first processes exposed to a range of contaminants, including PFAS. While not designed to be a process for removal of micropollutants, it is important to understand the fate of PFAS in coagulation processes, intended or otherwise, to determine whether water treatment sludge can be a significant sink for this group of micropollutants. This work advances understanding of PFAS removal in coagulation processes by comparing the removal of PFOA and PFOS by four metal coagulants (Zr, Zn, Fe, and Al) from real water matrices. The coagulant performance followed the order Al > Fe > Zr > Zn. Al was taken forward for further evaluation, with significant removal of PFAS (>15 % for PFOA and > 30 % for PFOS) being observed when the pH<5.5 and the dose was > 5 mg Al·L-1. The adsorption of PFOA and PFOS onto flocs through hydrophobic interaction was the primary removal route. The impacts of background matrix on the mechanisms of coagulation for PFAS were explored using five organic compounds. Macromolecular organic compounds contributed to an increase in removal due to the sorption of PFAS and subsequent removal of the organic-PFAS aggregate during coagulation. Low molecular weight organic matter inhibited the removal of PFAS due to the ineffective removal of these compounds during coagulation.

Advanced oxidation of bio-treated incineration leachate by persulfate combined with heat, UV254 nm, and UV365 nm: Kinetics, mechanism, and toxicity

This study compared and evaluated the ultraviolet/persulfate (UV/PS) at 254 or 365 nm and heat/persulfate (heat/PS) systems for advanced treatment of biologically pre-treated incineration leachate. The UV365 nm/PS system with the highest removal reduced chemical oxygen demand (COD) by 81.7%, total organic carbon by 73.8%, NH3-N by 96.8%, total nitrogen by 47.3%, and color by 98.6% within 24 h, separately. Kinetics tests suggested that a highest concentrations of 4.8 × 10−10 M for [SO4·-]ss and 2.8 × 10−11 M for [·OH]ss were reported in UV365/PS and UV254/PS systems, respectively. Characterization of leachate organic matter species revealed that low molecular weight organic matter < 5 kDa was preferentially degraded in three systems. Ketones are relatively easily degraded by both heat/PS and UV/PS systems, whereas esters were the most recalcitrant. Three-dimensional fluorescence analysis revealed > 99% humic acid and fulvic acid removal in all three systems. In practical applications, it is crucial to consider the pH and toxicity of SR-AOPs in the treatment of bio-treated incineration leachate. Furthermore, the ecotoxicity of MBR effluent treated by the heat/PS system and UV365 nm/PS system increased, which was caused by the strong acidity exhibited in the systems. In addition, we found that PS could interfere with 3.3% of the COD’s detection. The findings of this study suggest that secondary effects of PS on water quality at high doses should be investigated in future research.

Novel insight into secondary effluent quality improvement and ultrafiltration fouling mitigation by UV/peracetic acid pretreatment

Ultrafiltration (UF) technology is widely used in the treatment for deep purification of municipal secondary effluent, however, the membrane fouling and low removal of N, P, and organic matter during actual operation have been the main bottlenecks limiting its wide-spread application. To address the above problems, this study employed peracetic acid (PAA) and UV/PAA to evaluate the effects of PAA-based pre-oxidation on ultrafiltration membrane fouling and secondary effluent water quality. The results demonstrated that the activated PAA pre-oxidation could prominently enhance the hydrophilicity of effluent organic matter, effectively destroy the high molecular weight organic matter and mineralize the low molecular weight organic matter. PAA and its metabolites, as well as the by-products of EfOM, increased the C/P ratio in water samples from 118 to 563 and the C/N ratio from 0.86 to 8.53. After UV/20 mg/L PAA pretreatment, the reversible and irreversible membrane fouling resistance significantly decreased by 55.97 % and 65.67 %, respectively. Moreover, the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory showed lower adhere potential of the foulants to the membrane surface. In general, UV/PAA as ultrafiltration pretreatment has a huge potential for secondary effluent treatment for membrane fouling mitigation and water quality improvement.

Fate of low molecular weight organic matters in reverse osmosis and vacuum ultraviolet process for high-quality ultrapure water production in the semiconductor industry

Ultrapure water (UPW) is essential in the semiconductor industry for rinsing and cleaning products. With the growing demand for UPW, various feed water sources such as tap water, surface water, and wastewater are utilized to produce UPW. However, these feed water sources contain various low molecular weight organic matters (LMWOMs), which can adversely affect the quality of semiconductors when present in treated UPW. Therefore, achieving the complete removal of LMWOMs is crucial in the UPW production process. However, the current reverse osmosis (RO) and vacuum ultraviolet (VUV) processes employed for UPW production have limitations in achieving complete LMWOM removal. Therefore, this study is conducted to investigate the mechanisms of LMWOM removal in RO and the performance of VUV for high-quality UPW production. Six LMWOMs found in the semiconductor industry were tested for lab- and pilot-scale experiments. The result showed that size exclusion is the main mechanism of LMWOM removal in the RO process. However, methanol, ethanol, and urea were not efficiently removed by RO membranes. In addition, a lab-scale VUV experiment was performed under accelerated conditions to examine the oxidation mechanism of LMWOM. The LMWOM with low reactivity to hydroxyl radicals, such as tetramethylammonium hydroxide (TMAH) and urea, were not removed perfectly within 60 min and 180 min, respectively. Furthermore, a pilot-scale VUV experiment was performed to examine the oxidation of LMWOM under real UPW production conditions. Despite observing a correlation in the pseudo-first-order rate constants between the lab-scale and pilot-scale experiments, the removal of TMAH and urea was still not achieved even with a lamp power of 320 W. As urea was not completely removed by either RO or VUV, strategies for UPW production using current water sources are discussed to develop future UPW technologies.

The disinfectant residues promote the leaching of water contaminants from plastic pipe particles

Disinfection treatment is an indispensable water purification process, but it can leave trace concentrations of disinfectant in the purified water. Disinfectants oxidation can age plastic pipes and release hazardous microplastics and chemicals into drinking water. Lengths of commercially-available unplasticized polyvinyl chloride and polypropylene random copolymer water pipe were ground into particles and exposed to micro-molar concentrations of ClO2, NaClO, trichloroisocyanuric acid, or O3 for up to 75 days. The disinfectants aged the plastic and changed its surface morphology and functional groups. Meanwhile, disinfectants could significantly promote the release of organic matter from plastic pipes into the water. ClO2 generated the highest concentrations of organic matter in the leachates from both plastics. Plasticizers, antioxidants and low molecular weight organic matter were detected in all of the leachates. Leachate samples inhibited the proliferation of CT26 mouse colon cancer and induced oxidative stress in the cells. Even trace concentrations of residual disinfectant can constitute a drinking water risk.

Iron oxides act as an alternative electron acceptor for aerobic methanotrophs in anoxic lake sediments

Conventional aerobic CH4-oxidizing bacteria (MOB) are frequently detected in anoxic environments, but their survival strategy and ecological contribution are still enigmatic. Here we explore the role of MOB in enrichment cultures under O2 gradients and an iron-rich lake sediment in situ by combining microbiological and geochemical techniques. We found that enriched MOB consortium used ferric oxides as alternative electron acceptors for oxidizing CH4 with the help of riboflavin when O2 was unavailable. Within the MOB consortium, MOB transformed CH4 to low molecular weight organic matter such as acetate for consortium bacteria as a carbon source, while the latter secrete riboflavin to facilitate extracellular electron transfer (EET). Iron reduction coupled to CH4 oxidation mediated by the MOB consortium was also demonstrated in situ, reducing 40.3% of the CH4 emission in the studied lake sediment. Our study indicates how MOBs survive under anoxia and expands the knowledge of this previously overlooked CH4 sink in iron-rich sediments.

Construction of anti-swelling circuit board-like activated graphene oxide lamellar nanofilms with functionalized heterostructured 2D nanosheets

The assembly of 2D nanosheets into graphene nanofilm is attracting great interests because of their distinctive properties. However, it remains a big challenge to break through the unfixed interlayer channels caused by swelling for selective separation. In this study, novel activated graphene oxide lamellar nanofilms fixed by functionalized heterostructured MEA-C3N4 nanosheets with superior anti-swelling ability were successfully synthesized via post-synthesis activation (PSA) and alignment oriented slow deposition (AOSD). Different from traditional cross-linking by random packing, the structure-directed g-C3N4 nanosheets can not only be immobilized on activated GO to eliminate unstable interlayer structures by forming strong ionic and covalent bondings, but also act as building block to organize circuit board-like structure with highly interconnected microporosity by varying the thickness of electrical layer and the deposition rate. The strong interactions generated between building blocks reinforced the stability of interlayer sub-nanochannels and greatly suppressed swelling during cross-flow filtration for at least 120 h, in which the difference of interlayer spacing in dry condition and in water was as low as 0.2 Å. The prepared nanofilms with unique structure exhibited ultrahigh rejection (≥99.5%) toward low molecular weight organic matters. Meanwhile, due to the unique circuit board-like structure, very high water permeance (25.6 L m-2h-1 bar-1) and competitive rejection (91.0 %) for Na2SO4 were achieved, surpassing most reported GO-based or commercial nanofiltration membranes. Importantly, the permselectivity of constructed nanofilms can easily be adjusted by varying the space and type of intercalated nanosheets. The results indicate that this promising route will offer more opportunities in the synthesis of various 2D membranes with oriented structure for versatile applications.

Molecular characterization of disinfection byproduct precursors in filter backwash water from 10 drinking water treatment plants

Organic matter reacts with chlorine forming disinfection byproducts (DBPs) including trihalomethanes (THMs), haloacetamides (HAMs), haloacetic acids (HAAs), and haloacetonitriles (HANs). Filter backwash water (FBW) is either released back to the environment or recycled to the head of the treatment plant after solids settling and the remaining dissolved organic matter is a significant pool of DBP precursors that are not well understood. We characterized dissolved organic matter in FBW from 10 treatment plants and low molecular weight (MW < 1 kDa) organic matter contributed the most to DBP formation. We demonstrated overall similarity of the molecular composition (e.g., elemental ratios, m/z, DBE) of the 10 samples of FBW by Fourier transform ion cyclotron resonance mass spectrometry. Aromatic and more highly oxidized compounds preferentially reacted with chlorine, forming DBPs. Low MW (<450 Da) aliphatic compounds, and highly unsaturated and phenolic compounds were the primary precursors of THMs, HANs, and HAMs, and the formation potentials (FPs) of these groups of DBPs were correlated with multiple individual molecular formulae. HAA FPs were correlated with low MW, highly unsaturated and phenolic compounds. These advances in the understanding of the molecular composition of DBP precursors in FBW may develop the effective strategies to control DBP formation and limit impacts on the quality of finished water, and can be expanded to understanding DBP precursors in drinking water sources.

Enhancement effects and pathways of nitrogen removal by plant-based carbon source in integrated vertical flow constructed wetlands

Nitrogen removal in integrated vertical flow constructed wetlands (IVCW) is often limited by denitrification processes due to the lack of carbon sources. This study aims to elucidate the enhancement effects and mechanisms of alkali pretreated reeds as plant-based carbon source on the nitrogen removal process of IVCW. The results show near-complete removal of both COD and NH4+-N, with removal efficiencies of circa 98.0%. The alkali pretreated reeds were demonstrated to increase the removal efficiencies of NO3−-N and TN from −15.97% and 53.13% to 95.5% and 93.7%. The plant-based carbon source release organic matter primarily composed of tryptophan-like, fulvic acid-like and humic acid-like substances. Among these substances, the low molecular weight organic matter closely related to the carboxyl functional group showed high bioavailability. 16S rRNA gene sequencing demonstrated the plant-based carbon source to increase the relative abundance of nitrogen removal functional microbial genera up to 24.12%. Consequently, total nitrogen (TN) removal increased notably from 47.77% to 89.10%, primarily driven by a significant increase in denitrification from 0.16 mg/L to 14.11 mg/L. The TN removal was further enhanced by a considerable increase in anaerobic ammonia oxidation from 0.18 mg/L to 1.73 mg/L. The findings could support efficient nitrogen removal in CW via the enhancement of denitrification pathways.

Enhanced short-chain fatty acids production through a short-term anaerobic fermentation of waste activated sludge: Synergistic pretreatment of alkali and alkaline hydrolase blend

Short-chain fatty acids (SCFAs) recovery through anaerobic fermentation is a promising pathway to achieve economic benefits and carbon-emission reduction in waste activated sludge management. Although numerous pretreatment approaches have been investigated, alkaline hydrolase blend (AHB) incubation at initial pH 10.0 condition for enhancing anaerobic fermentation has rarely been reported. In this study, the sludge flocs were disintegrated into electronegative particle fragments with extracellular polymeric substance disruption and microbial cell lysis, owing to the synergistic effect of alkali-triggered sludge solubilization and AHB-catalyzed hydrolysis. Substantial sludge hydrolysis and biodegradable organic matter release were thereby induced. After pH 10 + AHB pretreatment for 2 h, numerous SCOD release of 5109 mg/L was achievable, which was approximately 12.4, 2.02, and 1.19 times higher than those in control, pH 10 and pH 10+alkaline protease pretreatments, respectively. Meanwhile, the AHB boosted hydrolysis and biodegradation of dissolved organic matters, promoting a low molecular weight shift in molecular weight distribution. The dissolved organic matter compositions tended to low molecular weight organic matters, accelerating the overall anaerobic fermentation process. Correspondingly, considerable SCFAs of 528.9 mg COD/g VSS was produced through a short-term anaerobic fermentation (3 days), which was 5.6, 1.7 and 1.1 times higher than the maximum SCFAs production by control, pH 10 and pH 12–10+alkaline protease pretreatments, respectively. The produced SCFAs were mostly composed of acetate (58.7%), which could be recovered as biodegradable carbon source. By adopting the AHB-based strategy, economic benefits of 392.4–580.6 CNY/ton sludge SS and carbon-emission reduction of 0.207–0.521 ton CO2/ton sludge SS were achievable. Apparently, the AHB-based strategy is a cost-effective and carbon-beneficial technology for sludge management.

Effect of Oxidation on the Formation of Disinfectant By-products of Low Molecular Weight Organic Matter

Some natural organic compounds (NOC) such as aromatic compounds can trigger the formation of disinfection by-products (DBPs). In chlorination (disinfectant) process resultant water quality depletes. Some safe alternative oxidants are needed for cleaning water pollutants. KMnO4 had shown better oxidation results, especially for reducing aromatic and non-aromatic organic compounds present in water. The aim of this study was to analyze the effect of KMnO4 and Ca(OCl)2 oxidants on the concentration of high and low molecular weight organic matter including aromatic compounds in the water sample. In this experiment, artificial organic compounds, namely sinapic acid (high molecular weight aromatic compound) and resorcinol (low molecular weight aromatic compound) were used to identify the characteristic of organic matter under different molecular weights. Sinapic acid and resorcinol were oxidized by using KMnO4 and Ca(OCl)2 with a minimum contact time of 60 minutes. Samples were analyzed for aromatic contents and total organic carbon (TOC) before and after completion of the experiment by using UV-Vis spectrophotometer at 254 nm wavelength (UV254). It has been observed that both oxidants increased TOC concentration. Ca(OCl)2 produces a higher percentage of organic matter degradation by-products (DBPs) such as chloroform (CHCl3) a highly toxic compound than KMnO4. Since Ca(OCl)2 has a higher oxidation potential than KMnO4. It has been observed that KMnO4 is a safer oxidant than Ca(OCl)2 as potassium permanganate produces less amount of DBPs.

Impact of freeze-thaw cycles on organic carbon and metals in waters of permafrost peatlands

Despite the importance of soil and surface waters freezing in permafrost landscapes, the behaviour of dissolved organic carbon (DOC), nutrients and metals during periodic freeze-thaw cycles (FTC) remains poorly known. The on-going climate warming is likely to increase the frequency of FTC in continental aquatic settings, which could modify the chemical composition of waters. In this study, we conducted 9 repetitive cycles of overnight freezing (−20 °C) and 5 h thawing (4 °C) in the laboratory using representative 0.22 μm-filtered waters from NE European permafrost peatland: leachates of vegetation and soil, and natural surface waters (depression, thermokarst lake and river). Only minor (<5%–15%) changes of DOC concentrations, SUVA254 and molecular weight were observed in all leachates and the depression water. In contrast, several trace elements (Fe, Al, P, Mn, As, and REE) exhibited sizable variations during FTC (>10%). The leachates and the depression water were enriched in trace elements, whereas the thermokarst lake and the river demonstrated a decrease in concentration of Fe (−39 and −94%, respectively), Al (−9 and −85%), and Mn (−10 and −79%) during FTC. Overall, the observations demonstrated an increase in aliphatic low molecular weight organic matter (OM), and the precipitation of Fe, Al hydroxides and organo-mineral particles. Therefore, enhanced of frequency of FTC can favour the release of metals and toxicants from acidic OM-rich surface waters and maintain stable OM-metals-colloids in large lakes and rivers, thus regulating aquatic transport of DOC and metals from soils to the Arctic Ocean.

Enhancement of PAHs biodegradation in biosurfactant/phenol system by increasing the bioavailability of PAHs

The poor bioavailability of polycyclic aromatic hydrocarbons (PAHs) is the main limiting factor for their biodegradation in contaminated sites. The addition of biosurfactant is an effective method for enhancing the bioavailability of PAHs. Suitable low molecular weight (LMW) organic matters have been shown to increase the bioavailability of PAHs. Therefore, we investigated the effect of phenol, which often co-exists with PAHs, on the biodegradation of PAHs in biosurfactant solution. The results show that the critical micelle concentration (CMC) of the biosurfactant decreased after phenol was added. The formation of mixed micelles resulted in enhancement of PAHs dissolution. The weight solubilization ratio (WSR) values of biosurfactant for Phe, Pyr and BaP in phenol solution are approximately 1.34, 1.40 and 1.67 times that of the control group, respectively. Phenol, therefore, can assist biosurfactant to increase the availability of PAHs by microbes. The bioavailability of PAHs in sludge increased from 27.7% to 43.1% after the biosurfactant was added, and reached a maximum of 49.2%, following the simultaneous addition of phenol and biosurfactant. Phenol also improved the degradation of PAHs by Stenotrophomonas sp. N5 in biosurfactant solution.

Pretreatment for capacitive deionization: Feasibility tests using activated filter media and granule activated carbon filtration

Dissolved organic matter and scaling are the main causes of electrode fouling, blocking activated carbon pores and reducing their performance. However, limited information exists on fouling by low molecular weight organic matter in the capacitive deionization (CDI) process. This study therefore systematically investigated for the first time a pretreatment process to prevent the accumulation of organic and inorganic matter as well as scaling in the CDI process. During various pretreatments, activated filter media and granule activated carbon were considered promising for drinking water treatment. The higher the turbidity and organic matter concentration in the CDI feed solution was, the greater the reduction of salt removal efficiency, production rate, and energy consumption became. Divalent ions, such as Ca2+, had no noticeable effect on CDI treatment performance because of the neutralization effect of the dispersant, whereas iron had a noticeable effect on CDI electrode fouling. The results of this study are foreseen to help minimize its negative impact by reducing organic matter fouling and enabling water reuse.

Application of heat-activated peroxydisulfate pre-oxidation for degrading contaminants and mitigating ultrafiltration membrane fouling in the natural surface water treatment

Membrane fouling is posing a critical obstacle limiting the widespread application of ultrafiltration (UF). Among the numerous membrane foulants, natural organic matter (NOM) is one of the most problematic since it exists ubiquitously in natural waters and can cause severe membrane fouling. This study investigated the removal of NOM in surface water and the mitigation of membrane fouling using heat-activated peroxydisulfate (PDS) as a pretreatment for UF process. The results demonstrated that the NOM was efficiently removed, with ultraviolet absorbance (UV254) and dissolved organic carbon (DOC) decreasing by approximately 71% and 52%, respectively, at a PDS dose of 0.8 mM within 60 min (80 °C). The chromatograms of high performance size exclusion chromatography (HPSEC) indicated that some high molecular weight humic substances with a peak at approximately 10 kDa were oxidized to low molecular weight organic matters distributed in the range of < 100 Da during the pretreatment process. Moreover, three-dimensional fluorescence parallel factor analysis (PARAFAC) indicated that humic-like substances were much more easily degraded by heat-activated PDS pretreatment than protein-like substances. These results indicated that some unsaturated NOM fractions were first degraded and then mineralized to carbon dioxide during pretreatment. Meanwhile, the destroyed structure of humic substances might hinder its binding with high valence cations to reduce the possibility of high valence cations deposited on the membrane surface, thereby reducing membrane fouling. Therefore, membrane fouling could be significantly mitigated due to the shifts of NOM concentration and structure by heat-activated PDS pretreatment in the surface water treatment.

Characterization of Algal Organic Matter of Microcystis sp.: Disinfection By-Product (DBP) Formation Potential and Treatability

Objectives This study was evaluated the disinfection by-product formation potential (DBPFP) in the algal organic matter of Microcystis sp. (M-AOM), which lives in the downstream Maeri area of Nakdong River, and the removal efficiency by each drinking water treatment process. Methods M-AOM were prepared by ultrasound/extraction/filtration using Microcystis sp. from Maeri area in the downstream of Nakdong River. M-AOM and Nakdong river water sample (N-NOM) were compared to removal efficiency of dissolved organic matter (DOM) and DBPFP in the coagulation/settlement (Coag./Sedi.), biological activated carbon (BAC) and granular activated carbon (GAC) processes. The treatment efficiency characteristics of DOM were evaluated by LC-OCD and fluorescence spectrophotometer. DBPFP was analyzed for trihalomethane formation potential (THMFP), haloacetic acids FP (HAAFP), haloacetonitrile FP (HANFP) and chloral hydrate FP (CHFP), respectively. Jar-tester was used for the Coag./Sedi., the BAC and GAC process were conducted using a laboratory scale acrylic column with an empty bed contact time (EBCT) of 20 min. Results and Discussion The contents of humic substances (HS) was high at 50.9% in N-NOM, whereas it was content 26.0% of biopolymers (BP) and LMW-acid (LMW-A) was high at 30.6% in M-NOM. In case of DBPFP, THMFP accounted for 59.5% of the total in N-NOM but CHFP and HANFP accounted for 49.6% and 23.3%, respectively in M-AOM. Thus, There were many differences in the composition of DOM and DBPFP of N-NOM and M-AOM. Both N-NOM and M-AOM showed a high removal efficiency of high molecular weight (HMW) organic matters (BP and HS) during the Coag./Sedi. process, whereas low molecular weight (LMW) organic matters (BB and LMW-org) was high during the GAC and the BAC processes, and the removal efficiency was somewhat different. Residual BP after Coag./Sedi. process was more easily removed by the biodegradation in BAC process rather than GAC process. THMFP and HAAFP which originated from AOM, were able to eliminated about 90% by the Coag./Sedi. process, which was very similar to the removal rate of BP and HS among DOM constituents and they were judged to be involved in THM formation. However, the removal rate of HANFP and CHFP was low, and it could be suspected that HANFP and CHFP formation were occurred in LMW organic matters showing low removal rate by the Coag./Sedi. process. The removal rates of CHFP and HANFP relatively high in the BAC process and total DBPFP showed high removal efficiency in the GAC process. Conclusions N-NOM had high contents of HS (50.9%), but M-AOM had high contents of BP (26.0%) and LMW-A (30.6%). THMFP accounted for 59.5% in total DBPFP of the N-NOM and CHFP (49.6%) and HANFP (23.3%) occupied high rate in the DBPFP of M-AOM. N-NOM and M-AOM were high removal from HMW organic matters (BP, HS) showed high removal efficiency by the Coag./Sedi. process, LMW organic matters showed high removal efficiency in the GAC and BAC processes. Also, residual BP after Coag./Sedi. was easily removed by biodegradation in the BAC rather than adsorption in the GAC process. THM and HAA formed in M-AOM could be removed about 90% by Coag./Sedi. process, whereas it was difficult to remove HANFP and CHFP by Coag./Sedi. process. CHFP and HANFP had relatively high removal efficiency in the BAC process and DBPFP removal was excellent overall in the GAC process. Key words: Microcystis sp., Algal Organic Matter (AOM), Disinfection By-Product, Drinking Water Treatment Process, Treatability

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.

Quorum quenching in anaerobic membrane bioreactor for fouling control

Quorum quenching (QQ) is an effective method to control membrane biofouling in aerobic membrane bioreactors (AeMBRs). However, it is not clear if QQ is feasible in an anaerobic membrane bioreactor (AnMBR). In this study, Microbacterium. sp that has QQ capability was embedded in alginate beads, known as QQ beads (QQB), and applied in a lab-scale AnMBR to investigate their potential in fouling control. With the addition of QQB, the operating period of AnMBR-QQB reactor was prolonged by about 8–10 times at constant flux operation before reaching the pre-set maximum transmembrane pressure (TMP). The concentration of Acyl-homoserine lactones (AHLs) in the bulk liquid was significantly higher during the ‘TMP jump’ period compared to QQB and control phases, while AHLs in the membrane foulants were remarkably lower in QQB phase compared to control phase. Furthermore, a much lower level of soluble microbial production (SMP) was observed in QQB phases. Extracellular polymeric substance (EPS), protein in particular, was reduced by 39.73–80.58% in the cake layer of the membrane from QQB phases. Significant changes of organic functional groups were observed in cake layer from QQB membrane as compared with that from control membrane. At the end of operation, bio-polymer (BP), building blocks (BB) and low molecular weight (LMW) organic matters increased in the foulant from control phases but such increase was not observed in QQB phase. After long-term operation, revival of QQB is required due to the declined activity for AHLs degradation.

Reduction of organic matter and disinfection byproducts formation potential by titanium, aluminum and ferric salts coagulation for micro-polluted source water treatment

Typical Chinese source water has high content of low molecular weight and aromatic protein-like organic matter which is difficult to remove and poses a great challenge to conventional coagulation/flocculation. To investigate coagulation performance of this typical water, this research focused on organic matter removal characteristics and the associated disinfection byproducts formation potentials (DBPFPs) during the coagulation process by titanium salts compared with traditional aluminum and ferric salts. Results showed that based on the dissolved organic matter (DOM) removal, the optimal coagulant dosages of AlCl3, FeCl3 and TiCl4 were 0.5 mM and the optimal initial pH values were 8, indicating that the DOM in the typical Chinese water could be effectively removed through sweeping and adsorption by metal hydroxides rather than the complexation and charge neutralization effect under acidic conditions. Compared these three coagulants, the highest ultra violet absorbance at 254 nm removal rate of 72.9% was achieved by TiCl4. The three-dimensional excitation emission matrix results showed that the removal ability of humic acids by AlCl3 was poorer than FeCl3 and TiCl4. The removal rate of low molecular weight components (1600 Da) by TiCl4 was 20% higher than using AlCl3 and 14% higher than FeCl3. Comparing with AlCl3 and FeCl3, TiCl4 had a better performance on the control of DBPFPs, especially for chloroform and dichloroacetic acid, due to its higher removal ability of aromatic organics. The trihalomethane formation potentials removal rate by TiCl4 was three times higher than that by AlCl3 and twice by FeCl3, by which could be inferred that titanium salts achieved better removal of low molecular weight organic matter than aluminum and ferric salts.

Removal of Trihalomethane Precursors by Nanofiltration in Low-SUVA Drinking Water

Trihalomethanes (THMs) are prevalent disinfection by-products. High THM formation is usually associated with natural organic matter with high molecular weight and aromatic characteristics, which is efficiently removed by nanofiltration (NF). In the Sea of Galilee and the Israeli National Water Carrier (NWC), water shows high THM formation potential, although it mainly contains low molecular weight and hydrophilic organic matter with low aromaticity. In the present study, NF removal abilities were tested on treated NWC water using three different spiral wound membranes (NF90, NF270, and DL). Rejections and fluxes were tested as a function of pressure, water recovery, and membrane type. Feed and permeate dissolved organic carbon (DOC), UVA254, total THM formation (THMF), and total THM formation potential (THMFP), as well as alkalinity, conductivity, hardness, Ca2+, Mg2+, and Cl− were measured to evaluate rejection and THM formation reduction. The results demonstrated that NF can efficiently remove natural organic matter (NOM) and reduce THM formation, even in this challenging type of water. At low water recovery, membranes showed average rejection of about 70–85% for THMFP and THM. Upon elevating recovery, average THM and THMFP rejection decreased to 55–70%, with THM content still well below regulation limits. Of the membranes tested, the higher permeability of NF270 appears to make it economically favorable for the applications tested in this work.