Trihalomethane Formation Potential Removal Research Articles

Reductions of dissolved organic matter and disinfection by-product precursors in full-scale wastewater treatment plants in winter

The reductions of dissolved organic matter (DOM) and disinfection byproduct precursors in four full-scale wastewater treatment plants (WWTPs) (Liaoning Province, China) where different biological treatment processes were employed in winter were investigated. The total removal efficiencies of dissolved organic carbon (DOC), ultraviolet light at 254 nm (UV-254), trihalomethane formation potential (THMFP), and haloacetic acid formation potential (HAAFP) were in the range of 70.3–76.0%, 49.6–57.3%, 54.4–65.0%, and 53.7–63.8% in the four WWTPs, respectively. The biological treatment was the predominant process responsible for the removal of DOC, THMFP, and HAAFP in WWTPs. Differences in the reduction of UV-254 were not significant (p > 0.05) among biochemical reaction pool, secondary sedimentation tank, and disinfection tank. Biological aerated filter and suspended carrier activated sludge processes achieved higher DOM removal than the conventional active sludge and anaerobic–anoxic–oxic processes. Hydrophobic neutral and hydrophilic fraction were removed to a higher degree through biological treatment than the other three DOM fractions. HAAFP removal was more efficient than THMFP reduction during biological treatment. During primary treatment, fluorescent materials in secondary sedimentation tanks were preferentially removed, as compared to the bulk DOM. Humic-like fluorescent compounds were not readily eliminated during biological treatment. The fluorescent materials were more susceptible to chlorine than nonfluorescent compounds.

Effects of ozone as a stand-alone and coagulation-aid treatment on the reduction of trihalomethanes precursors from high DOC and hardness water

This study investigates the effect of ozone as a stand-alone and coagulation aid on the removal of dissolved organic carbon (DOC) from the water with a high level of DOC (13.8 mgL−1) and calcium hardness (270 mgL−1) CaCO3.Natural water collected from the Assiniboine River (Manitoba, Canada) was used in this study.Effectiveness of ozone treatment was evaluated by measurement of DOC, DOC fractions, UV254, and trihalomethane formation potential (THMFP). Additionally, zeta potential and dissolved calcium concentration were measured to discern the mechanism of ozone reactions.Results indicated that 0.8 mg O3/mg DOC ozone stand-alone can cause up to 86% UV254 reduction and up to 27% DOC reduction.DOC fractionation results showed that ozone can change the composition of DOC in the water samples, converting the hydrophobic fractions into hydrophilic ones and resulting in the reduction of THMFP. Also, ozone caused a decrease in particle stability and dissolved calcium concentration. These simultaneous ozonation effects caused improved water flocculation and enhanced removal of DOC. This resulted in reduction of the coagulant dosage when ozone doses higher than 0.2 mg O3/mg DOC were applied prior to coagulation with ferric sulfate. Also, pre-ozonation-coagulation process achieved preferential THMFP removal for all of the ozone doses tested (0–0.8 mg O3/mg DOC), leading to a lower specific THMFP in pre-ozonated-coagulated waters than in the corresponding ozonated waters.

Reducing THMFP by H2O2/UV oxidation for humic acid of small molecular weight

In this study, the merits of using H2O2/UV oxidation for reducing trihalomethane formation potential (THMFP), colour, and dissolved organic carbon (DOC) of smaller molecular humic acid were investigated, especially the energy consumption based on EEO. The results show that THMFP decreases by increasing oxidation time, H2O2 dose and UV intensity. The reaction constant in descending order is kColour > kDOC > kTHMFP. Furthermore, EEO shows three trends. First, it decreases as H2O2 dose increases. That is, by increasing the amount of H2O2 dose, the electrical energy efficiency becomes better. Second, EEO,9 W > EEO,13 W, implying that higher UV power would result in a higher electrical energy efficiency. Third, EEO,THMFP > EEO,DOC > EEO,colour. That is, the electric energy efficiency is the best for colour removal, second for DOC removal, and third for THMFP reduction. The operation costs for 90% removal of colour, DOC, and THMFP are from 0.31 to 0.69, from 0.78 to 1.72, and from 1.11 to 2.29 US$/m3, respectively. However, reducing THMs to Taiwan's drinking water standard of 80 µg/L needs only 0.25–0.60 US$/m3. Therefore, the condition with UV of 9 W, H2O2 of 50 mg/L, and oxidation time of 23 min can be applied for THMs reduction as the cost is the smallest of 0.25 US$/m3, even lower than current Taiwan's drinking water price of 0.3 US$/m3.

Dissolved organic carbon and trihalomethane formation potential removal during coagulation of a typical UK upland water with alum, PAX-18 and PIX-322

This paper considers the removal of dissolved organic carbon (DOC) from a typical UK upland reservoir water using three different coagulants; aluminium sulphate/alum (Al2(SO4)3(aq)), polyaluminium chloride/PAX-18 (Aln(OH)mCl3n-m(aq)) and ferric sulphate/PIX-322 (Fe2(SO4)3(aq)). A comparison of DOC quality including fractional character, colour, specific ultraviolet absorption (SUVA) and molecular weight was made between the source water and the supernatants obtained following its coagulation in each case. Trihalomethane formation potential (THMFP) was compared before and after treatment to assess which coagulant performed best in terms of THM amelioration. The conditions (coagulant dose and pH) required to obtain optimal DOC removal were established using bench-scale jar tests. Statistically significant differences in DOC removal rates were observed between the different coagulants. THMFP removal was linked to a combination of high net DOC removal and the preferential removal of THM precursors. This selectivity may also be responsible for the increase in brominated THM species (BrTHMs) observed following treatment.

Advanced oxidation of bromide-containing drinking water: A balance between bromate and trihalomethane formation control

Addition of H2O2 has been employed to repress bromate formation during ozonation of bromide-containing source water. However, the addition of H2O2 will change the oxidation pathways of organic compounds due to the generation of abundant hydroxyl radicals, which could affect the removal efficacy of trihalomethane precursors via the combination of ozone and biological activated carbon (O3-BAC). In this study, we evaluated the effects of H2O2 addition on bromate formation and trihalomethane formation potential (THMFP) reduction during treatment of bromide-containing (97.6–129.1 μg/L) source water by the O3-BAC process. At an ozone dose of 4.2 mg/L, an H2O2/O3 (g/g) ratio of over 1.0 was required to maintain the bromate concentration below 10.0 μg/L, while a much lower H2O2/O3 ratio was sufficient for a lower ozone dose. An H2O2/O3 (g/g) ratio below 0.3 should be avoided since the bromate concentration will increase with increasing H2O2 dose below this ratio. However, the addition of H2O2 at an ozone dose of 3.2 mg/L and an H2O2/O3 ratio of 1.0 resulted in a 43% decrease in THMFP removal when compared with the O3-BAC process. The optimum H2O2/O3 (g/g) ratio for balancing bromate and trihalomethane control was about 0.7–1.0. Fractionation of organic materials showed that the addition of H2O2 decreased the removal efficacy of the hydrophilic matter fraction of DOC by ozonation and increased the reactivity of the hydrophobic fractions during formation of trihalomethane, which may be the two main reasons responsible for the decrease in THMFP reduction efficacy. Overall, this study clearly demonstrated that it is necessary to balance bromate reduction and THMFP control when adopting an H2O2 addition strategy.

Characteristics of DOM and Removal of DBPs Precursors across O3-BAC Integrated Treatment for the Micro-Polluted Raw Water of the Huangpu River

The aim of this study is to determine the impact upon dissolved organic matter (DOM) and removal of disinfection by-product (DBP) precursors of adding an ozone-biological activated carbon (O3-BAC) process after the conventional treatment process (CTP) using water from the Huangpu River in Shanghai, east China. Several metrics, including size fractionation, dissolved organic carbon (DOC) and trihalomethane formation potential (THMFP), were employed to accomplish this goal. In the raw water collected from the Huangpu River, the low molecular weight (MW) molecules (MW <3 kDa) were absolutely dominant in DOM, accounting for more than 55% of total DOC, and the DOM resulted in a high THMFP level of 472.91 ± 4.63 µg/L after an excessive chlorination. The CTP reduced high MW molecules (MW >10 kDa) by 61% and the low MW molecules (MW <3 kDa) by only 8%. The O3-BAC presented an accumulated DOC removal efficiency of approximately 50%, in particular, showing a high degree of the removal effectiveness of low MW molecules. Samplings from the CTP, ozone and BAC were subjected to excessive chlorination to determine the THMFP, and the measured concentrations were 211.89 ± 4.58 µg/L, 169.52 ± 4.55 µg/L, and 124.42 ± 4.27 µg/L, respectively. Therefore, coupled with the THMFP removal rate of 74%, the addition of the O3-BAC process after an existing CTP improved the water quality of the effluent, particularly, in terms of the improved reduction in the precursors of DBPs.

Dissolved organic carbon and trihalomethane precursor removal at a UK upland water treatment works

The removal of dissolved organic carbon (DOC) during potable water treatment is important for maintaining aesthetic water quality standards, minimising concentrations of micro-pollutants, controlling bacterial regrowth within distribution systems and, crucially, because it contains a sub-component that can act as trihalomethane (THM) precursors. In this study, the concentration and characteristics of raw water DOC and THM formation potential (THMFP) entering an upland potable water treatment works were analysed over twelve months. Correlations between raw water DOC characteristics, standardised THMFP (STHMFP) and % DOC removal were also investigated. DOC and THM precursor removal during a series of treatment stages was examined over this period, as well as potential selectivity in the removal of DOC fractions, to assess the importance of different treatment stages for DOC removal and THM amelioration. Though THMFP removal remained high and fairly stable throughout the study period (83–89%), the data suggest that this was mostly the result of high DOC removal rates rather than the selective removal of THM precursors. Whilst this chemical agnosticism makes DOC removal more robust, it may make the overall process more vulnerable to exceeding permissible THM concentrations under changing climatic conditions. The kinetics of the reaction between DOC and chlorine appeared to vary seasonally, indicating temporal changes in the proportions of fast- and slow-reacting precursors with implications for THM concentrations at the point of delivery to the consumer. The initial treatment stages, comprising coagulation–flocculation and dissolved air floatation (DAF) were by far the most important in terms of bulk DOC removal and the preferential removal of THM precursors, though, surprisingly, DOC quality was also modified following chlorination and secondary rapid gravity filtration (RGF). Though net THM concentration decreased following initial treatment stages, a doubling in the proportion of brominated THMs (BrTHMs), which are reported to be more carcinogenic, was also observed.

Evaluation of temperature impacts on drinking water treatment efficacy of magnetic ion exchange and enhanced coagulation

Magnetic ion exchange (MIEX ® ) is an emerging technology for disinfection by-product (DBP) precursor removal in the drinking water industry. Although recent research has demonstrated that this technology is capable of achieving excellent natural organic matter (NOM) removal, there is paucity of published research showing the efficacy of ion exchange (IX) technology in cold water conditions. The overall objective of this research was to evaluate at bench-scale the potential impact of cold water operating conditions on enhanced coagulation with alum, MIEX ® and a combination of MIEX® and low dose alum. All three treatments were evaluated at 1 and 20 °C with settled water quality compared in terms of turbidity, UV254, dissolved organic carbon (DOC), specific UV absorbance (SUVA), trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP). The results of the study showed that all three technologies evaluated were significantly impacted by cold water operating conditions in terms of turbidity removal, and UV254 removal was significantly reduced in both the MIEX ® and MIEX ® -Alum processes. However, treatment of the surface water with the combined process resulted in the highest removal of DBP precursor material and lowest THMFP and HAAFP concentrations at both temperatures compared to the individual unit operations.

Influence of Preozonation on the Formation of Chlorination Disinfection By-products – A Case Study: The Úzquiza Reservoir Water

The influence of preozonation on the formation of chlorination disinfection by-products (DBPs) is studied for three different types of water: a natural water from the Úzquiza Reservoir (Burgos, Spain), synthetics waters prepared using natural fulvic and humic acids extracted from the Úzquiza Reservoir and a synthetic water prepared using a commercially supplied humic acid. The main factors intervening in this process have been reviewed: the delay time between ozonation and chlorination, the ozone reaction pathway, the type of NOM, the applied ozone dose and the presence of bromide ion. Preozonation decreases trihalomethane formation potential (THMFP) for both humic and fulvic acids, being this effect more significant for the humic acids. The molecular pathway of ozone seems to be more selective than the radical pathway for THMFP removal from humic acids. Ion bromide content of the raw water greatly influences the effect of preozonation on THMFP. The influence of preozonation on the formation of some minority DBPs has been studied too.

Removal of organics and control of bromate for a southern china water supply

A pilot plant with successive preozonation, coagulation‐sedimentation, sand filtration, postozonation, and biological activated carbon was operated for more than six months to treat reservoir water containing 15–38 μg/L of bromide in southern China. Preozonation enhanced the removal of chemical oxygen demand using potassium permanganate as the oxidant (CODMn) and ultraviolet light absorbance at 254 nm (UV254) using coagulation‐sedimentation but did not improve total organic carbon (TOC)‐removal effectively. However, preozonation markedly enhanced the removal of trihalomethane formation potential (THMFP) by the conventional process, and THMFP removal by the combination of preozonation and conventional treatment was 57% using an ozone dose of 0.8 mg/L. Almost no bromate formed during preozonation. An ozone dose of 2.0 mg/L (0.5 mg/L and 1.5 mg/L for pre‐ and postozonation, respectively) was found to be the optimal dosage for the maximum removal of organics (65% of THMFP, 52% of TOC, 63% of CODMn, and 84% of UV254) while keeping bromate under 5 μg/L. A combination of conventional treatment with preozonation should be a suitable alternative if the primary goal is to remove THMFP.

Removal of natural organic matter and THM formation potential by ultra- and nanofiltration of surface water

Natural organic matter (NOM) and trihalomethane formation potential (THMFP) removal were evaluated by ultrafiltration (UF) and nanofiltration (NF). Ten different raw water sources in Alicante province (SE Spain) were analysed. Five types of membranes of different materials were tested with a dead-end-type stirred UF cell. Additional measurements, such as dissolved organic carbon, ultraviolet absorbance (254 nm), THMFP, ion concentration, pH, conductivity, etc. were made on raw water, permeates and concentrates. The SUVA value was used to determine the hydrophobicity of the water analysed. The elimination of NOM and THMFP is correlated with the molecular weight (MW) of NOM determined by size exclusion chromatography (SEC). The flux decline trends were correlated with cation concentration. NOM removal by UF is low, which correlates with the average MW determined by SEC with an average value of 922 g/mol (between 833 and 1031 g/mol). However, the NOM removal obtained with the NF90 and NF270 NF membranes for all water sources is almost complete (90%). THMFP removal is related to hydrophobicity and permeability of membrane. The NFT50 membrane removes almost 100% of the THMFP of more hydrophobic waters.

Evaluation of a pilot scale dual media biological activated carbon process for drinking water

This study was carried out to optimize a dual media BAC (biological activated carbon) process for DOC removal and DBPs (disinfection by-products) control. Pilot scale tests were coducted at the Tukdo water treatment plant in Seoul, Korea. The dual media BAC process is highly efficient in the removal of DOC and THMFP, and is more capable of sustaining microorganisms than a single layer filter. The bottom layer of the sand filter functioned as a screen for turbidity, microorganisms, and other biological material. Total DOC removal efficiency was 13 to 25%, and the corresponding THMFP (trihalomethane formation potential) removal efficiency was approximately 20 to 33%. Turbidity and DOC leakage continued for 40 min after backwashing in all reactors. Breakthrough occurred from 24-72 hours in each reactor. Ten species of microorganisms were identified in the activated carbon filled in BAC reactors. The predominant species were Clavibactor and Corynebacterium and microbial species were simple at the lower end.

Enhanced coagulation under changing alkalinity-hardness conditions and its implications on trihalomethane precursors removal and relationship with UV absorbance

This study evaluates the effectiveness of aluminium sulphate (alum) and polyaluminium chloride (PACl) as coagulants for the treatment of surface water with low DOC (2.1–2.4 mg/L) and at two alkalinity–hardness levels. Effectiveness was evaluated by measurement of DOC, UV absorbance at 254 nm (UV 254), and different trihalomethane formation potential (THMFP) tests. PACl showed higher removal efficiency for all the analyzed variables and under both high and low alkalinity–hardness conditions. Results also showed that alum coagulation is more sensitive to operational conditions, especially pH. Maximum differences between coagulants were observed in the removal of final THMFP with average values ( n = 48) being 48 and 31%. This difference was maximum when coagulation–flocculation was carried out at pH 8.0. Comparison of full scale Plant data and jar test data revealed that optimization based on DOC and UV 254 removal does not ensure optimum results for THMs precursors removal. Solution pH above 6.0 units ensures acceptable residual levels of dissolved aluminium (<0.2 mg Al 3+/L). Precursor removal optimization did not compromise residual aluminium requirements. After treatment a noticeable increase in the contribution of low molecular weight molecules to the THMFP was observed. Under high alkalinity–hardness conditions bromine incorporation factor (BIF) of treated water is much more sensitive to the type of coagulant used. Results of BIF suggest that at higher alkalinity–hardness levels hydrophilic natural organic matter (NOM) is better removed. Finally, the relationship between removal of UV absorbance and removal of THMFP was investigated. Results suggest that this relationship is more accurate and more reliable when PACl is used.

Transformation of Dissolved Organic Matter During Ozonation: Effects on Trihalomethane Formation Potential

Transformation of dissolved organic matter (DOM) during ozonation results in a higher reduction in trihalomethane formation potential (THMFP) relative to dissolved organic carbon (DOC). This study was conducted to determine the effect of DOM transformation after ozonation on THM formation and to elucidate the difference in THMFP and DOC removal. Changes in DOC, THMFP, reactivities of the hydrophilic and hydrophobic DOC, and phenolic-OH were determined to explain the difference in THMFP and DOC removal after ozonation. Higher reduction in THMFP (24–46%) relative to DOC (10–16%) was obtained and was attributed to the following: transformation of DOM from a more reactive hydrophobic DOC (μg THM produced per mg organic carbon) to a less reactive hydrophilic DOC and to the decrease in the reactivities of both the hydrophobic and hydrophilic DOC after ozonation. The results also showed decrease in phenolic-OH indicating the oxidation of some reactive sites like resorcinol or meta-dihydroxy benzene ring structures, which are prone to chlorine substitution, consequently decreasing the reactivity of the organic carbon to form THM. These changes in DOM led to a significant decrease in THMFP with no remarkable removal in DOC.

Effect of HRT and MLSS on THM precursor removal in the activated sludge process

This study was conducted to evaluate the effect of hydraulic retention time (HRT) and mixed liquor suspended solids (MLSS) on trihalomethane (THM) precursor removal in the activated sludge process and to determine the effect of chemical properties of the organic components on trihalomethane formation potential (THMFP). A laboratory-scale reactor for the activated sludge process was used with synthetic domestic wastewater as influent. Experimental conditions, HRT and MLSS, were varied and the effluents were evaluated in terms of DOC and THMFP. Hydrophilicity, hydrophobicity and chemical functional groups were analyzed to determine the chemical parameters that may affect THMFP. Optimum removal of THMFP was achieved at HRT 24 h and at MLSS of ca. 2500 mg l −1. Due to the organic metabolites produced in the activated sludge floc, better DOC or THMFP removal was not observed at longer HRTs and larger MLSS. Decrease in DOC did not result in comparable removal of THMFP. This was attributed to two factors: the higher reactivity of the hydrophobic organic carbon (18.5 μg THMFP mg −1 C) compared to the hydrophilic organic carbon (6.2 μg THMFP mg −1 C) and the nonremoval of the remaining hydrophobic THM precursors in HRTs longer than 8 h. The activated sludge process preferentially removed the hydrophilic organic substances which was shown to have less potential to form THM. The activated sludge process effluents exhibited similar chemical characteristics compared with various types of treated industrial wastewaters determined in a previous study. The activated sludge process effluents contained larger amounts of the hydrophilic organic substances compared to the hydrophobic fractions. Larger amounts of the carboxylic and phenolic-OH functional groups were determined in the hydrophilic fractions than in the hydrophobic fractions. The equation obtained for THMFP prediction based on bulk parameters and specific functional groups of the treated industrial wastewaters was also found to be applicable on the activated sludge process effluents. The equation suggests that bulk THMFP was influenced by UV 260 and organic nitrogen of both the hydrophilic and the hydrophobic fractions, and phenolic-OH of the hydrophilic fractions.

Comparison of ozonation and AOPs combined with biodegradation for removal of THM precursors in treated sewage effluents

The efficiency of ozonation (O3) and advanced oxidation processes (AOPs) such as O3/UV, O3/H2O2, H2O2/UV and O3/H2O2/UV was examined for removal of trihalomethane (THM) precursors in treated sewage effluents. A low-pressure mercury (Hg) lamp (maximum wavelength 253.7 nm; intensity 2.6 × 10−6 Einstein s−1) was employed for AOPs using ultraviolet light. The efficiency of the processes employed was examined by both direct mineralization of target compounds and the formation of biodegradable compounds, based on the removal of dissolved organic carbon (DOC), UV absorbance at 260 nm (UV260), and THM formation potential (THMFP). The contribution of ozonation was relatively small for mineralization of DOC, but was larger for the increase in biodegradability of residual DOC. On the other hand, AOPs were effective for both mineralization and increase in biodegradability. A longer reaction time with AOPs resulted to an increase in mineralization but not to an increase in biodegradable components possibly because the biodegradable components were also decomposed by AOPs. The removal of UV260 was obtained by chemical/photolytic processes and not by biodegradation. The rate of THMFP removal by ozonation, AOPs, and biodegradation was higher than that of DOC removal.

Comparison of ozonation and AOPs combined with biodegradation for removal of THM precursors in treated sewage effluents

The efficiency of ozonation (O3) and advanced oxidation processes (AOPs) such as O3/UV, O3/H2O2, H2O2/UV and O3H2O2/UV was examined for removal of trihalomethane (THM) precursors in treated sewage effluents. A low-pressure mercury (Hg) lamp (maximum wavelength 253.7 nm; intensity 2.6 × 10−6 Einstein s−1) was employed for AOPs using ultraviolet light. The efficiency of the processes employed was examined by both direct mineralization of target compounds and the formation of biodegradable compounds, based on the removal of dissolved organic carbon (DOC), UV absorbance at 260 nm (UV260), and THM formation potential (THMFP). The contribution of ozonation was relatively small for mineralization of DOC, but was larger for the increase in biodegradability of residual DOC. On the other hand, AOPs were effective for both mineralization and increase in biodegradability. A longer reaction time with AOPs resulted to an increase in mineralization but not to an increase in biodegradable components possibly because the biodegradable components were also decomposed by AOPs. The removal of UV260 was obtained by chemical / photolytic processes and not by biodegradation. The rate of THMFP removal by ozonation, AOPs, and biodegradation was higher than that of DOC removal.

BEHAVIOR OF ORGANIC HALIDES PRECURSOR IN ACTIVATED SLUDGE PROCESS

In order to investigate the behavior of the organic halides precursor in the activated sludge process, bench scale reactors were operated at various organic loadings. Trihalomethane formation potential (THMFP) and total organic halides formation potential (TOXFP) were measured as the organic halides precursor. The effluent from the reactor fed by potato starch which has not THMFP produced THMs with the reaction of chlorine. In the experiments using primary settled municipal sewage or its 8μm filtrate, the removal of THMFP was mainly associated with the removal of particulate precursor. THMFP of the effluent was related with a hard biodegrable organics in the influent and biological metabolic by-products. The ratio of THMFP/TOC of the effluent was increased than that of the influent, since the removal efficiency of THMFP was lower than that of TOC. TOXFP removal efficiency was almost the same as TOC removal efficiency.

Control of Trihalomethane Precursors in Drinking Water: Granular Activated Carbon With and Without Preozonation

In a pilot study that lasted 80 weeks, unozonated and ozonated waters were fed to granular activated carbon (GAC) columns to compare the removal of trihalomethane formation potential by GAC treatment with that by ozone‐GAC treatment. The results were comparable for these treatments.

Cationic polyelectrolytes as primary coagulants for removing trihalomethane precursors

Four cationic polymers were tested as sole coagulants for removing trihalomethane precursors from synthetic and natural waters. Waters synthesized from humic acid were more amenable to polymer coagulation than those synthesized from fulvic acid. The presence of kaolinite appeared to improve removal of trihalomethane formation potential (THMFP) from these waters. In general, the performances of the polymers were comparable. For the natural waters, the effectiveness of polymer coagulation in THMFP reduction varied as a function of raw water source. Ambient pH of the water appeared to influence polymer performance. For both types of water, the reductions in THMFP were generally greater than the corresponding decreases in total organic carbon.