Haloacetic Acid Formation Potential Research Articles

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

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

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

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

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

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

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

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

Contribution of filtration and photocatalysis to DOM removal and fouling mechanism during in-situ UV-LED photocatalytic ceramic membrane process

The use of ceramic membranes and ultraviolet light-emitting diodes (UV-LEDs) has advanced the application of photocatalytic membrane for water treatment. We systematically evaluated the contribution of filtration and photocatalysis to dissolved organic matter (DOM) removal and fouling mechanism during in-situ UV-LED photocatalytic ceramic membrane filtration. The results showed that physical rejection primarily led to removal of 4–15 kDa molecules and photocatalysis further increased the removal of 1-4 kDa molecules, causing small sized microbial humic-like or protein-like materials in the permeate. In-situ UV-LED photocatalysis had an excellent effect on membrane fouling mitigation regardless of DOM sources. The dominant fouling mechanism changed from partial blockage to gel layer formation with increasing Ca2+ concentration but did not change with UV treatment. Correlation analysis revealed that the removal of 1-4 kDa molecules contributed to the mitigation of both reversible and irreversible fouling resistance, and the small molecules were the major cause of irreversible fouling resistance. Removal of 1–4 kDa terrestrial humic acid-like contributed to the pore blockage mechanism for synthetic water. Removal of 4-15 kDa protein-like materials was closely correlated to the pore blockage mechanism for real water. Trihalomethanes (THMs) and haloacetic acids (HAAs) formation potential (FP) were both significantly reduced after photocatalytic ceramic membrane process, but precursors of nitrogenous disinfection by-products (N-DBPs) with high toxicity were not removed by filtration or by photocatalysis, which deserves attention. Membrane rejection made higher contribution to better DBPFP control than photocatalysis. This study provides novel insights into the impact of UV-LED on DOM removal, DBPFP control and fouling mitigation, promoting the development of photocatalytic ceramic membrane filtration.

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

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

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

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

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.

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

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

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

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

Pretreatment strategies for ion exchange to control brominated disinfection byproducts in potable reuse

The application of ion exchange (IX) resins to remove disinfection byproduct (DBP) precursors in wastewater effluents is challenging due to relatively high concentrations of competing anions. This study examined various pretreatment strategies to target competing ions to improve IX removal of DBP precursors, bromide and dissolved organic matter (DOM), measured as trihalomethane and haloacetic acid formation potentials (THMFP and HAAFP). IX batch experiments were performed with four commercial anion exchange (AIX) resins selective for bromide (BrP), DOM (A860), sulfate (MTA) and PFOA/PFOS (PFA), and one cation exchange (CIX) resin selective for iodide (CT). For single AIX treatments the bromide removal ranking was the following: PFA (58%) > MTA (51%) > BrP (43%) > A860 (16%), which corresponded with decreasing brominated THMFP removals and increasing bromine incorporation factors. For dual AIX combinations (PFA and BrP, MTA and BrP), either simultaneous or sequential treatments had the highest bromide (PFA + BrP [69%], MTA + BrP [67%], (PFA→BrP [77%], MTA→BrP [74%]) and Br-THMFP (THMFP [∼80%]) and Br-HAAFP (HAAFP [∼77%]) removals, and therefore the lowest fractions of brominated DBPs (Br-DBPs). Despite ozone (O3), biological active carbon (BAC), and granular activated carbon (GAC) pretreatments reducing the overall DOM concentration (33%), these pretreatment steps did not improve the bromide removals of the resins, although it did increase the Br-THMFP and Br-HAAFP removals by 2–38% and 13–20%, respectively. Nanofiltration (NF) pretreatment significantly removed sulfate (97%) resulting in an increased bromide removal of 19% by the AIX resins, which led to increased removal of Br-THMFP and Br-HAAFP by 93% and 96%, respectively. Among all the IX resins the CT resin had the highest bromide removal (83%) and lowest fraction of Br-DBPs. The results reveal pretreatment with existing technologies including AIX, O3/BAC/GAC, or NF can potentially enhance the removal of brominated DBP precursors by IX resins during potable reuse applications.

Quantitative and qualitative characteristics of dissolved organic matter derived from biochar depending on the modification method and biochar type

With the increasing utilization of biochar (BC), various modification methods have been developed; the evaluation of the environmental impact of modified BC is insufficient. In this study, three types of BC (rice husk, wood chip, and mixture) were modified through five different methods (oxidation, acidification, alkalinization, and impregnation of MnOx and FeOx), and the quantitative and qualitative characteristics of modified BC derived from dissolved organic matter (DOM) were evaluated. Quantitative analysis revealed that the yield of dissolved organic carbon (DOC) derived from modified BC was significantly lower than from BCraw, suggesting that DOM derived from BC was reduced following the modification of BC. In wood BC, the DOC yield was different from that of other types of BC, confirming that the quantitative characteristics of released DOC from modified BC depend on its type. DOM derived from BCoxidic, BCalkaline, and BCMnOx was characterized by highly condensed aromatic humic-like substances, with high trihalomethane and haloacetic acid formation potential. In contrast, DOM from BCacidic and BCFeOx showed a low degree of humification and disinfection by-product formation potential, suggesting that the qualitative properties and environmental impact of BC-derived DOM differ depending on the modification method. Overall, our findings extend our understanding of environmental impact and differences in BC-derived DOM depending on the BC types and modification methods.

Organic matter removal with bicarbonate-form ion exchange: water quality, kinetics and mass transfer mechanisms

Ion Exchange (IEX) has been widely explored for the removal of organic matter. Chloride is traditionally used as counter-ion, but its release into water can increase the risk of corrosion. Research has shown that bicarbonate IEX can be an efficient alternative, and whilst some studies have compared its efficiency to chloride IEX, none have compared their performance in relation to the potential for disinfection by-product (DBPs) formation. The differences in organic matter removal between the two regenerants were assessed by looking at the molecular weight fractions derived from liquid chromatography organic carbon detection (LC-OCD) and dissolved organic carbon (DOC). Uptake kinetics, resin age and mass transfer diffusion were also investigated. DOC removal was similar for both chloride and bicarbonate resins, achieving ca 50% DOC removal. LC-OCD analysis revealed that organic matter between 0.35 and 1 kDa was the most efficiently removed, with slightly better uptake with bicarbonate IEX. However, these differences did not impact DBP formation potential. Trihalomethane (THM) and haloacetic acid (HAA) formation potentials followed the trends of DOC removal with up to 70% reduction after IEX treatment with both resin forms. However, the bromine substitution factor (BSF) increased with resin age -from 5 to 10% for THMs and from 4 to 7% for HAAs. Resin age resulted in up to 20% decrease in the organic matter uptake rates (from 0.19 to 0.15 min−1) and up to 34% decrease in pore diffusivities (from 9.4 × 10−12 to 7.1 × 10−12 m2/s for chloride IEX and from 1.0 × 10−11 to 6.6 × 10−11 m2/s).

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.

Haloacetic Acids Formation Potential of Tropical Peat Water DOM Fractions and Its Correlation with Spectral Parameters

Haloacetic Acids Formation Potential of Tropical Peat Water DOM Fractions and Its Correlation with Spectral Parameters

Effects of temperature and microorganism densities on disinfection by-product formation

This study investigated the role of microorganisms on the correlation between temperature changes and disinfection by-product formation in natural waters. Climate changes have resulted in an increase in the global surface temperature. Studies have revealed that increases in temperature may change the composition of dissolved organic matter (DOM), which may contain major disinfection by-product (DBP) precursors. This change in the DOM composition may affect DBP formation after conventional water treatment processes. Understanding the role of microorganisms in DOM composition as well as DBP formation and speciation is critical for controlling DBP formation. In this study, laboratory stimulatory experiments were conducted on water samples from various sources, at various temperatures, and with various microbial concentrations. The results revealed a decreasing trend of dissolved organic carbon (DOC), trihalomethane formation potential (THMFP), and haloacetic acid formation potential (HAAFP) at high temperature incubations irrespective of microbial concentrates. This result may be attributed to the fact that microorganism activities or concentrations in water increase at higher temperatures, which may result in higher DOC consumption and lower DBP formation. Water samples spiked with bacteria concentrates exhibited higher THMFP or HAAFP reduction than did samples without bacteria concentrates. A higher biomass in water may contribute to a higher consumption of DOC and consequently lower DBP formation potentials, especially at high incubation temperatures.

Changes in structural characteristics of humic and fulvic acids under chlorination and their association with trihalomethanes and haloacetic acids formation

The effects of chlorination on 16 humic and fulvic acids (HAs and FAs, respectively) extracted from six different soil samples from Korea and two purchased soil samples (Canadian peat moss, Elliott Silt Loam Soil) were investigated to identify the changes in their structural characteristics and their effects on trihalomethane formation potential (THMFP) and haloacetic acid formation potential. The effect of chlorination was also investigated in fractionated samples (Aldrich HA, F1–F5) based on molecular weight (MW). Total organic carbon (TOC), specific UV absorbance (SUVA), fulvic-like fluorescence (%FLF), terrestrial humic-like fluorescence (%THLF), weight-average molecular weight (MWw), and carbon structures (13C NMR) were measured for each sample before and after chlorination, and factors relating to the chlorination mechanism were examined using principal component analysis (PCA). The results showed that the changes in the structural characteristics and the disinfection by-product formation of chlorinated HA and FA differed critically. For chlorinated HA, TOC and %FLF decreased due to oxidation, whereas %THLF was reduced via incorporation; MW also affected the structural changes and THMFP generation. In the PCA results, high SUVA, low MW, low N/C, and low O groups of aromatic C were associated with high THMFP production in HA, whereas low O groups of aliphatic C in FA were associated with both oxidation and incorporation in terms of THMFP. These results elucidate the mechanisms associated with the effects of chlorination in HA and FA and will support the prediction of THMFP generation in HA and FA based on their specific structural characteristics.

Using potassium ferrate control hazardous disinfection by-products during chlorination.

The generation of hazardous disinfection by-product is one of the major problems in drinking water chlorination. This study aims to investigate the potential of potassium ferrate (K2FeO4) on by-product control. Filtered raw water from a water treatment plant in Jinan was used to evaluate the effects of K2FeO4 dose, pH, ammonia nitrogen, and Br- concentration on trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP). The results present that 3 mg/L K2FeO4 effectively reduced ultraviolet absorbance at 254 nm (UV254) by 45%, but removed little dissolved organic carbon (DOC) by 12% at pH 7.40, since K2FeO4 tends to attack the electron-rich part of organic matter molecules but with restricted mineralization ability. Fluorescence excitation-emission matrix (EEM) analyses indicate the effective removal of fulvic acid and humic acid. Increasing K2FeO4 dose reduced THMFP but increased HAAFP, due to their precursors reacting with K2FeO4 in different pathway, while the rising pH or Br- concentration increased THMFP but decreased HAAFP. Both THMFP and HAAFP decrease with increasing ammonia nitrogen concentrations. Additionally, it was found that under alkaline conditions, trihalomethanes (THMs) were dominated by haloacetic acids (HAAs).

Impact of UV irradiation on disinfection by-product formation and speciation from post-chlorination of dissolved organic matter

Abstract The objective of this study was to investigate the effects of combined low-pressure ultraviolet (UV)irradiation and chlorination on the formation of disinfection by-products (DBPs) from different dissolved organic matter (DOM) as DBP precursors. Commercially available humic acid (HA), extracellular organic matter (EOM) from green algae, cyanobacteria, and diatom, namely Scenedesmus quadricauda (SQ), Merismopedia sp. (Msp), and Phaedactylum tricornutum (PT), were used as the sources of DOM. The DBP formation increased with increasing total residual chlorine; EOM from PT presented the highest formation potential followed by HA, Msp, and SQ. The low dosage of 40 mJ/cm2 UV irradiation is insignificant to change the DBP formation from HA and SQ; however, it decreased the DBP formation from bromide-containing EOM of PT and promoted the DBP formation from EOM of Msp at various total residual chlorines. The DBP formation of each DOM correlated well with total residual chlorine. The maximum DBP formation potential (DBPFP) reduction of 42.25 and 13.75% for haloacetic acid formation potential (HAAFP) and trihalomethane formation potential (THMFP) was obtained at the UV irradiation dosage of 300 mJ/cm2 for EOM of PT. However, for the EOM derived from Msp, a maximum increase of 58.1 and 51.1% for HAAFP and THMFP was observed after UV-chlorination.

Effects of ozonation on disinfection by-product formation potentials and biostability in a pilot-scale drinking water treatment plant with micro-polluted water

ABSTRACT The accelerated urbanization in China has caused intensified micro-pollution problems for drinking water sources, severely challenging drinking water treatment efficiencies and its biostability. This study mainly investigated the effects of ozonation on disinfection by-product formation potentials (DBPFPs) and biological dissolved organic carbon (BDOC) in a pilot-scale ozonation-biological activated carbon advanced drinking water treatment plant with micro-polluted raw water. The results indicated that the micro-polluted water would be effectively treated in the advanced treatment processes with DBPFPs significantly eliminated. The total removal rates of trihalomethane formation potentials (THMFPs) and haloacetic acid formation potentials (HAAFPs) increased with the elevated ozone dosage to finally a relatively stable stage, and the maximum removal rates of 77.3% and 57.0%, respectively, were achieved at the ozone dosage of 2 mg/L. The bromine incorporation in total THMFPs (TTHMFPs) was dramatically suppressed after integrated advanced treatment processes, while that in total HAAFPs (THAAFPs) was promoted with the corresponding increment of up to 25.3% for bromine incorporation factor, which caused relatively high brominated HAAFP proportions in the treated water than in the raw water. In addition, the BDOC generation rate and THAAFP removal rate during the post-ozonation treatment displayed apparent positive correlation, and a similar relationship was observed for the BDOC degradation rate and TTHMFP removal rate during the BAC treatment in the studied ozone dosage (1 ∼ 5 mg/L). The findings strongly implied a promising alternative to measure DBPFP removal rate instead of BDOC level for more sensitive and convenient monitoring of the biostability in the reclaimed water.