Reduction Of Trihalomethane Formation Potential Research Articles

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

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

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

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

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

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

Efficiencies of O-MBR and A/O-MBR for Organic Matter Removal from and Trihalomethane Formation Potential Reduction in Domestic Wastewater.

Lab-scale anoxic/oxic membrane bioreactor (A/O-MBR) and oxic membrane bioreactor (O-MBR) systems using a submerged polysulfone hollow-fiber membrane module with a pore size of 0.01 μm and a total surface area of 1.50 m2 were used to treat domestic wastewater. The sludge retention time (SRT) of each system was examined by setting the SRT to 10, 20, and infinity (no sludge withdrawal). The results showed that the total nitrogen removal efficiency of the A/O-MBR was more significant than that of the O-MBR at a SRT of infinity, with figures of 72.3% and 33.1% being found, respectively. The COD removal efficiencies of the A/O-MBR system with a SRT of 10 days, 20 days, and infinity were 82.4%, 84.3%, and 91.5%, respectively. The COD removal efficiencies of the O-MBR system with a SRT of 10 days, 20 days, and infinity were 79.3%, 81.5%, and 89.8%, respectively. An increase in the SRT resulted in an increase in the COD removal efficiency. The FEEM peak of the influent tended to decrease after an increase in the SRT for both systems (A/O-MBR and O-MBR). For the A/O-MBR system, the trihalomethane formation potential (THMFP) was significantly reduced by 88.91% (at a SRT of infinity). The THMFP declined significantly by 85.39% for the O-MBR system at a SRT of infinity. The A/O-MBR system showed a slightly higher efficiency than the O-MBR system in terms of the COD removal and the THMFP reduction. These results indicated that the MBR process, and the A/O-MBR system, in particular, could be used as an effective wastewater treatment process for many developing countries that are troubled by the emerging contamination of water and wastewater.

Evaluation of enzyme activity for monitoring biofiltration performance in drinking water treatment

Many water providers monitor adenosine triphosphate (ATP) as an indicator of biological acclimation of their biofilters; however, strong correlations between ATP concentration and filter performance (e.g., organic matter or disinfection by-product precursor removal) are not typically observed. As an alternative, this study evaluated the use of enzyme activity for monitoring biological processes within filters. Recent studies have proposed that enzyme activity may be used as an indicator of biofilter function as it provides a means to quantify biodegradation which may allow for a more accurate measure of degradation potential and to gain a better understanding of biofilter performance. Sampling was completed from full- and pilot-scale biofilters to assess impacts associated with pre-treatments, varying sources waters, as well as pre-treatment and operating conditions. Enzyme activity (carboxylic esterase, phosphatase, ß-glucosidase, α-glucosidase, ß-xylosidase, chitinase, and cellulase) and ATP were measured from the top 5 cm of biofilter media representative of typical full-scale sampling; water quality parameters included dissolved organic carbon (DOC) and disinfection by-products (DBPs): trihalomethane (THM) formation potential (FP), and haloacetic acid FP (HAA FP). Results confirmed that ATP was not a reliable monitoring tool for DOC and DBP FP reduction in biofilters. A strong relationship was observed between esterase activity and DOC reduction; chitinase activity significantly correlated to THM FP reduction for filters treating three different source waters and HAA FP reduction achieved by filters treating the same source water with a range of pre-treatment and backwash conditions. This study showed that enzyme activity may be appropriate for monitoring biological processes within drinking water filters and may act as a surrogate for the removal of organic compounds.

Study on the removal of humic acid by ultraviolet/persulfate advanced oxidation technology.

Humic acid (HA) in water is the main precursor of disinfection by-products in the chlorination process of drinking water. In this study, an ultraviolet/persulfate (UV/PS) process, in a laboratory-scale system, is successful in the degradation of HA. The results showed that HA was significantly degraded (UV254 removal rate of ~ 89%) and partially mineralized (~ 62.5%) by UV/PS treatment at a PS dose of 0.4mM, pH of 7.12, and UV irradiation time of 160min. The trihalomethane formation potential (THMFP) was also significantly reduced (THMFP reduction of ~ 85.4%). A strong linear relationship was observed between UV254 and dissolved organic carbon. The removal rate of HA at low pH was better than that at high pH conditions, and the inhibition by Cl- slowed down after an initial increase, and the inhibition was weaker than HCO3-. By analyzing the fluorescence spectrum of two humic-like substances, the fluorescent compounds C1 and C2 in HA were significantly degraded, and the change in C1 and C2 concentration was correlated with the decrease of THMFP. The degradation of different fractions of natural organic matter in real-world water samples indicated that UV/PS has significant potential to decrease HA in water.

Impact of TiO2/UVA photocatalysis on THM formation potential

In drinking water treatment plants, reduction of trihalomethane formation potential (THMFP) can be reached through precursor removal prior chlorine disinfection. In this work, the impact of TiO2/UVA photocatalytic process on THMFP has been studied using different phenolics (phenol, resorcinol, catechol, hydroquinone and gallic acid) and citric acid as NOM surrogates. A solution of each surrogate was photocatalytically treated at pH 7 applying different UVA doses and then chlorinated. Resorcinol oxidation by TiO2/UVA and THMFP reduction go hand in hand, indicating that the intermediates hardly form THMs when chlorinated. For the rest of surrogates, intermediates with medium-high specific THMFP (maximum values 40–120 μg CHCl3 (mg DOC)−1 for phenols; and ∼1000 μg CHCl3 (mg DOC)−1 for citric acid) are initially formed and disappear at higher UVA doses. TiO2/UVA treatment of water matrices with high and low specific UV absorption at 254 nm (SUVA254) (Sigma-Aldrich humic acid, pH 7; and water from Villar del Rey reservoir; Badajoz-Spain), was also investigated. For surface water UVA doses higher than 5 kWh m−3 were needed to achieve a THMFP below 100 μg THM L−1. During water treatment, an initial negative impact of AOPs in general and TiO2/UVA in particular on THMFP is expected.

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.

Algal removal from cyanobacteria-rich waters by preoxidation-assisted coagulation–flotation: Effect of algogenic organic matter release on algal removal and trihalomethane formation

The cyanobacteria-bloom in raw waters frequently causes an unpredictable chemical dosing of preoxidation and coagulation for an effective removal of algal cells in water treatment plants. This study investigated the effects of preoxidation with NaOCl and ClO2 on the coagulation–flotation effectiveness in the removal of two commonly blooming cyanobacteria species, Microcystis aeruginosa (MA) and Cylindrospermopsis raciborskii (CR), and their corresponding trihalomethane (THM) formation potential. The results showed that dual dosing with NaOCl plus ClO2 was more effective in enhancing the deformation of cyanobacterial cells compared to single dosing with NaOCl, especially for CR-rich water. Both preoxidation approaches for CR-rich water effectively reduced the CR cell count with less remained dissolved organic carbon (DOC), which benefited subsequent coagulation–flotation. However, preoxidation led to an adverse release of algogenic organic matter (AOM) in the case of MA-rich water. The release of AOM resulted in a poor removal in MA cells and a large amount of THM formation after oxidation-assisted coagulation–flotation process. The reduction in THM formation potential of CR-rich waters is responsible for effective algae and DOC removal by alum coagulation. It is concluded that the species-specific characteristic of cyanobacteria and their AOM released during chlorination significantly influences the performance of coagulation–flotation for AOM removal and corresponding THM formation.

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.

Disinfection byproduct precursor removal by enhanced coagulation and their distribution in chemical fractions

Raw water from the Songhua River was treated by four types of coagulants, ferric chloride (FeCl3), aluminum sulfate (Al2(SO4)3), polyaluminum chloride (PACl) and composite polyaluminum (HPAC), in order to remove dissolved organic matter (DOM). Considering the disinfection byproduct (DBP) precursor treatability, DOM was divided into five chemical fractions based on resin adsorption. Trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP) were measured for each fraction. The results showed that hydrophobic acids (HoA), hydrophilic matter (HiM) and hydrophobic neutral (HoN) were the dominant fractions. Although both HoN and HoA were the main THM precursors, the contribution for THMFP changed after coagulation. Additionally, HoA and HiM were the main HAA precursors, while the contribution of HoN to HAAFP significantly increased after coagulation. HoM was more easily removed than HiM, no matter which coagulant was used, especially under enhanced coagulation conditions. DOC removal was highest for enhanced coagulation using FeCl3 while DBPFP was lowest using PACl. This could indicate that not all DOC fractions contained the precursors of DBPs. Reduction of THMFP and HAAFP by PACl under enhanced coagulation could reach 51% and 59% respectively.

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.

Removal of DOC and its fractions from surface waters of the Canadian Prairie containing high levels of DOC and hardness

In this paper removal of dissolved organic carbon (DOC) and its fractions by chemical coagulation was studied. Raw water was collected from the Red River (Manitoba, Canada). This source water has a DOC concentration ranging from 8 to 12 mg L−1 and total hardness of about 400 mg L−1 CaCO3, which represents a typical surface water quality of the Canadian Prairie. Four coagulants were tested at different pH levels: alum, ferric sulfate, ferric chloride and titanium sulfate. Coagulation effectiveness was evaluated by removal of DOC, DOC fractions, specific UV absorbance (SUVA), and trihalomethane formation potential (THMFP) of the coagulated water. The water DOC was separated into six fractions based on hydrophobicity and acid base functionality: hydrophobic acid (HPOA), hydrophobic base (HPOB), hydrophobic neutral (HPON), hydrophilic acid (HPIA), hydrophilic base (HPIB), and hydrophilic neutral (HPIN). Results showed that ferric sulfate had the highest total DOC removal of 66% while ferric chloride had the lowest DOC reduction of 54%. Although the THMFP was found to be lowered significantly with all four coagulants the ferric chloride showed the greatest THMFP reduction. Fractionation results found a significant reduction in the HPOA fraction for all coagulants with 91% for ferric chloride as the highest removal value. Poor removal of hydrophilic fractions was found for all coagulants. The result of this study showed that total DOC reduction cannot guarantee THMFP reduction and coagulation should be optimized to remove DOC fractions which form most THMs.

응집과 막여과 공정에서 응집제에 따른 유기물 및 THMFP제거

Integrated process with coagulation and microfiltration as an advanced water treatment has been expanded its application in recent years due to its superb removal of particles and natural organic matter. In usual, effectiveness of coagulation sometimes determines performance of the whole system. Several new polymeric coagulants introduced to water utilities for better efficiency were studied in this paper. Three polymeric coagulants (i.e., PACl, PACs, and PAHCs) along with alum were evaluated for removal of natural organic matter, especially for reduction of trihalomethane formation potential, for which regulation has become stringent. Turbidity removal was closely related to pH variation showing the reduced turbidity removal by PACs due to the decreases in the pH of supernants at high doses. The four coagulants showed different organic matter removal during coagulation and affected the removal in microfiltration. For instance, DOC concentration was not reduced by microfiltration when PAHCs were used however 10 % of DOC removal was observed by microfiltration with alum coagulation. Coagulation pretreatment also impacted the THM removals, i.e., approximately 30 % of THMs and 13 % of DOC was removed by microfiltration only, but 40 to 67 % of THMs and 30 % of DOC was removed by the integrated process. Strategies on selection of coagulants are needed depending on characteristics of target pollutants in raw waters.

Removal of DOM and THM formation potential of tropical surface water by ceramic microfiltration

Dissolved organic matter (DOM) and trihalomethane formation potential (THMFP) removal by ceramic microfiltration (CMF) under different operating conditions was investigated and compared with the performance of a conventional water treatment plant at Bangkhen, Thailand. The tropical surface raw water for all the experiments was taken from Chaophraya River, Bangkok, Thailand. CMF studies were conducted with both pilot scale (Pilot-CMF) and laboratory scale (Lab-CMF) units. Observations indicate that the properties of raw water such as dissolved organic carbon (DOC) concentration and specific ultraviolet absorbance (SUVA) vary with time. Under these varying raw water conditions, the conventional water treatment process demonstrates varying THMFP removals. The Pilot-CMF provides better and steady THMFP removals compared to conventional process. Bangkhen water treatment plant (BWTP) filtrate SUVA (2.01 ± 1.07) and Pilot-CMF filtrate SUVA (3.22 ± 0.98) were significantly lower compared to raw water SUVA (4.79 ± 1.39). This SUVA reduction indicated a higher removal of aromatic DOMs through both treatment processes. Pilot-CMF manifest a grater removal of hydrophilic DOM compared to filtrate from BWTP. This corresponds to a higher reduction of THMFP by Pilot-CMF over BWTP. It was found that higher removal of DOC by Pilot-CMF is associated with coagulation process, effects of suspended solids and membrane properties.

Reduction of dissolved organic matter and trihalomethane formation potential during laboratory‐scale soil‐aquifer treatment

AbstractDissolved organic matter (DOM) in recovered groundwater from soil‐aquifer treatment (SAT) has the potential to generate harmful disinfection by‐products. This study investigated the reduction of mass and trihalomethane formation potential (THMFP) of DOM fractions from secondary effluent during laboratory‐scale SAT. Using XAD‐8 and XAD‐4 resins, DOM was fractionated into three fractions: hydrophobic acid (HPO‐A), transphilic acid (TPI‐A) and hydrophilic fraction (HPI). HPO‐A was removed by 61.1%, TPI‐A by 54.9% and HPI by 75.0% as dissolved organic carbon (DOC) during the laboratory‐scale SAT, respectively. The reduction of THMFP from HPO‐A, TPI‐A and HPI was 27.24, 26.24 and 36.08%, respectively. Specific THMFP for each DOM fraction increased across the soil columns. HPO‐A was found to be the major precursor of THMs. THMFP was strongly correlated to ultraviolet light at 254 nm (UV‐254) for HPO‐A and HPI, while the relationship between THMFP and UV‐254 for TPI‐A was significantly poor.

Fate of secondary effluent dissolved organic matter during soil-aquifer treatment

The reduction of mass and trihalomethane formation potential (THMFP) of dissolved organic matter (DOM) and its fractions from secondary effluent during laboratory-scale soil-aquifer treatment (SAT) soil columns were studied. Reduction in dissolved organic carbon (DOC), absorbance of ultraviolet light at 254 nm (UV-254), biodegradable dissolved organic carbon (BDOC) and nonbiodegradable dissolved organic carbon (NBDOC) for the bulk DOM averaged 72.35%, 53.98%, 97.49% and 35.33% across the soil columns, respectively. Using XAD-8 and XAD-4 resins, DOM was fractionated into 3 fractions: hydrophobic acid (HPO-A), transphilic acid (TPI-A) and hydrophilic fraction (HPI). HPO-A was removed by 61.06%, TPI-A by 54.86% and HPI by 74.95% as DOC as a consequence of the laboratory-scale SAT, respectively. The reduction of THMFP from HPO-A, TPI-A and HPI was 27.24%, 26.24% and 36.08%, respectively. Proton nuclear magnetic resonance (1H-NMR) spectra revealed that the HPO-A isolated from the secondary effluent contained more aromatic functional groups than the corresponding TPI-A. Fourier-transform infrared (FT-IR) spectrum analysis illustrated that TPI-A had decreased hydrocarbon and increased aromatics content in the SAT columns. Specific ultraviolet light absorbance (SUVA) and specific THMFP for each DOM fraction increased across the soil columns and HPI exhibited greater increase in both than HPO-A and TPI-A. The most problematic THM precursor was found to be HPO-A with its high quantity present in recharged water and high chlorine reactivity.

Removal and transformation of organic matter during soil-aquifer treatment

This study investigated the removal and transformation of organic matter through laboratory-scale soil-aquifer treatment (SAT) soil columns over a 110-day period. Reductions in total organic carbon (TOC), dissolved organic carbon (DOC), biodegradable dissolved organic carbon (BDOC), nonbiodegradable dissolved organic carbon (NBDOC) and absorbance of ultraviolet light at 254 nm (UV-254) averaged 71.46%, 68.05%, 99.31%, 33.27% and 38.96% across the soil columns, respectively. DOC/TOC ratios increased slightly with depth while BDOC/DOC ratios showed a converse trend. DOC exiting the soil-column system contained only a very small biodegradable fraction. SAT decreased the concentration of DOC present in feed water but increased its aromaticity, as indicated by specific ultraviolet light absorbance (SUVA), which increased by 50%∼115% across the soil columns, indicating preferential removal of non-aromatic DOC during SAT. Overall, laboratory-scale SAT reduced trihalomethane formation potential (THMFP), although specific THMFP increased. THMFP reduction was dominated by removal in chloroform. All samples exhibited a common general relationship with respect to weight: chloroform>dichlorobromomethane >dibromochloromethane>bromoform.

Reduction of dissolved organic matter in terms of DOC, UV-254, SUVA and THMFP in industrial estate wastewater treated by stabilization ponds

The aim of this research was to monitor the influent and effluent water quality of the aeration, facultative and oxidation water treatment ponds of an industrial estate. This industrial estate, the largest in northern Thailand, has proposed to utilization of reclaimed treated wastewater in their raw water supply so as to cope with the yearly water shortage during the dry season. Water samples were collected four times from four sampling points and evaluated for their dissolved organic matter (DOM) content in terms of dissolved organic carbon (DOC), ultraviolet light absorbance at 254 nm (UV-254), specific ultraviolet absorption (SUVA), trihalomethane formation potential (THMFP) and trihalomethane (THM) species. Average values of DOC, UV-254, SUVA and THMFP in the influent wastewater of 12.9 mg L(-1), 0.165 cm(-1), 1.29 L mg(-1) m(-1) and 1.24 mg L(-1), respectively, were observed. The aeration ponds produced the best results: a 54% reduction of DOC, a 33% reduction of UV-254, and a 57% reduction of THMFP. However, SUVA in the aeration pond effluent showed a moderate increase. The facultative ponds and oxidation ponds did not take part in the reduction of DOC, UV-254, SUVA and THMFP. Average DOC, UV-254, SUVA and THMFP value of the treated wastewater were 5.8 mg L(-1), 0.107 cm(-1), 1.85 L mg(-1) m(-1) and 468 microg L(-1), respectively. Chloroform, at 72.6% of total THMFP, was found to be the predominant THM species.