Trihalomethane Precursors Research Articles

Effect of Ozonation and UV Irradiation with Direct Filtration on Disinfection and Disinfection by-Product Precursors in Drinking Water Treatment

Pilot plant studies were conducted to evaluate the effect of pre-ozonation and ultraviolet irradiation on disinfection, disinfection by-product precursors and water quality in a direct filtration water treatment system. Disinfection parameters including total coliforms, faecal coliforms and heterotrophic plate count were investigated. Total organic carbon (TOC), trihalomethanes (THMs), total organic halides (TOX), filtered water turbidity and colour were also evaluated. It was found that advanced pre-oxidation processes (ozonation and UV irradiation) significantly increase the level of disinfection of raw water. Removal of total trihalomethanes and total organic halides precursors improved with ozonation and UV irradiation, compared to no oxidation treatment in direct filtration and/or in conventional water treatment. All coliforms (total and faecal) were completely destroyed by ozonation alone, and also with ozonation in conjunction with UV irradiation. However, the heterotrophic plate count was not significantly reduced at an ozone residual concentration of 0.1 mg l−1. This suggests that disinfection efficiency is strongly influenced by competition reactions of organic and inorganic compounds with ozone. Precursors of total trihalomethanes and total organic halides were reduced by 90% and 98%, respectively, with advanced pre-oxidation processes. Water quality parameters were improved by the pre-ozonation and UV irradiation treatment system.

Role of cupric ions in the H 2O 2/UV oxidation of humic acids

The purpose of this study is to reveal the role of cupric ions as a natural water contaminant in the H 2O 2/UV oxidation of humic acids. Humic acids are naturally occurring organic matter and exhibit a strong tendency of complexation with some transition metal ions. Chlorination of humic acids causes potential health hazards due to formation of trihalomethane (THM). The removal of THM precursors has become an issue of public concern. The H 2O 2/UV process is capable of mineralizing humic acids due to formation of a strong oxidant, hydroxyl radicals, in reaction solution. Experiments were conducted in a re-circulated photoreactor. Different cupric concentrations (0–3.8 mg/l) and different pH values (4–9) were controlled to determine their effects on the degradation of humic acids, UV light absorbance at 254 nm, and H 2O 2. The presence of cupric ions inhibits humic mineralization and decreases the rate of destruction of humic acids which absorb UV light at 254 nm. On the other hand, the higher the cupric concentration, the lower the H 2O 2 decomposition rate. In the studied pH range, the minimum of total organic carbon (TOC) removal occurs at pH=6 in the presence of 2.6 mg/l of cupric ions; both acidification (pH=4) and alkaline condition (pH=9) lead to a better removal of TOC. It is inferred from this study that the cupric-complexed form of humic acids is more refractory than the non-complexed one.

Effect of functional groups of humic substances on uf performance

The role of different functional groups present in humic substances on the membrane flux is unclear. This study is undertaken to (1) separate the carboxyl and phenolic groups from a humic solution, and (2) evaluate the effect of each fractionated humic substances on the ultrafiltration (UF) performance. A weak-base amine resin was used for the adsorption (pH 7) and the subsequent desorption (pH 13) of the phenolic groups from a commercial humic solution. These fractions were evaluated qualitatively (via Fourier transform infrared spectroscopy) and quantitatively (titration); they were further subjected to the analyses of the trihalomethane formation potential (THMFP) and ultrafiltration performance. Although, a complete separation of the phenolic and carboxyl groups is not possible, the results nevertheless provide useful information about their effects on UF performance. The fraction with a higher content of the phenolic OH group exhibits the highest THMFP (190 μg/mg C), whereas the fraction with a higher content of the carboxyl groups exhibits more flux decline. The UF system evaluated is unable to remove a significant portion of THM precursors, resulting in high THMs in permeate. The use of powdered activated carbon for the pretreatment of these fractions fails to improve membrane fouling. The pore size of UF membrane does not appear to affect the membrane flux, and the switch from the hydrophobic to hydrophilic membrane only slight improves the permeate flux.

Effects of Nanofiltration on Trihalomethane and Haloacetic Acid Precursor Removal and Speciation in Waters Containing Low Concentrations of Bromide Ion

A study was undertaken to determine trihalomethane (THM) and haloacetic acid (HAA) precursor removal by nanofiltration (NF). Cross-flow experiments were conducted with three NF membranes and six natural waters spanning total organic carbon (TOC) concentrations in the range 3.3−13.1 mg/L and bromide ion concentrations in the range 0.5−2.3 μM. Permeate and feedwaters were analyzed for all nine HAA species containing bromine and chlorine. The rejection of THM and HAA precursors decreased with increasing feedwater recovery suggesting that the transport of these materials is controlled by molecular diffusion across the polymeric membranes rather than by physical sieving at membrane surfaces. Therefore, the maximum feedwater recovery in NF systems designed for disinfection byproduct control may be limited by deteriorations in permeate water quality in addition to fouling caused by precipitation of sparingly soluble salts. High rejections of TOC coupled to low removals of bromide ion by some NF membranes resulted in a shift toward more brominated THM and HAA species in permeate waters upon chlorination. Concentrations of selected highly brominated species are shown to increase upon NF under certain conditions. Empirical equations relating THM and HAA bromine incorporation factors in feed and permeate waters to pH, Br-/TOC, and Cl2/TOC ratios are also presented.

Advanced adsorption of humic acid for trihalomethanes control

For advanced trihalomethanes control, the removal of humic acid, which is one of trihalomethanes precursors, was investigated. The smaller the particle size of activated carbon, the more humic acid was adsorbed. It will be presumed that the contact surface area dominates the amount of humic acid adsorbed. Moreover, the humic acid solution was treated with ozone, and the adsorption removal by activated carbon was investigated. The amount of humic acid adsorbed increased with ozonization time. It is assumed that degradation to lower molecular weight fragments by ozonolysis contributed to the increase in the amount adsorbed onto activated carbon. It was concluded that preozonation was effective in removing humic acid.

Effects of humic substance characteristics on UF performance

The role of humic substances in general and hydrophobicity of humic substances in particular on membrane permeate flux is unclear. The main goal of the present study is to evaluate the effect of fractionated humic substances on ultrafiltration (UF) performance. A commercial humic solution was subjected to a hydrophobic resin for fractionation of the hydrophobic and hydrophilic fraction. These fractions were further fractionated into different molecular wight groups, using gel filtration chromatography. The hydrophobic fraction accounts for 85% organic carbon recovered and has a significantly high THM (trihalomethane) formation potential, or 190 μg/mg C. The hydrophilic fraction exhibits the worst flux decline despite little solute rejection. The results of molecular weight fractionation of both hydrophobic and hydrophilic fractions further indicate that those molecules with the largest molecular weight (6.5–22.6 kDa) exhibit the worst flux decline. The UF system evaluated is unable to remove a significant portion of THM precursors, resulting in potentially high THMs in the permeate. The use of powdered activated carbon (PAC) for the pretreatment of hydrophobic/hydrophilic humic substances or in an integrated PAC-UF system exhibits an enhanced membrane fouling.

Particulate and THM Precursor Removal with Ferric Chloride

Pilot-scale experiments were performed to investigate the effectiveness of enhanced coagulation in removing particles and trihalomethane (THM) precursors from two surface source waters: California ...

Formation of trihalomethanes from humic acid by ozone and activated carbon fibers treatments

Humic acid, which is a trihalomethane precursor, was produced by the putrefaction of withered leaves. Trihalomethanes are produced by chlorine disinfection when tap water is treated with ozone and activated carbon in a purification plant. The amount of chloroform produced from humic acid by adding chlorine after the ozone and activated carbon fiber treatments was investigated. Humic acid was degraded by ozone to polar and acidic organic compounds by the addition of hypochlorite. The amount of chloroform produced increased with increasing treatment temperature, while it decreased with increasing ozonization time. It was also lowered by the addition of activated carbon fibers after the ozonization.

Effects of polydiallyldimethyl ammonium chloride coagulant on formation of chlorinated by products in drinking water

The objectives of this research work was to evaluate the reduction of THM precursors by cationic p-DADMAC and determine the correlations between the chlorine demand and trihalomethane formation in the presence of electrolyte solutions and ambient light. The chlorine demand was found to be significantly reduced provided that the H 2SO 4 electrolyte was fed to the sample solutions. The amount of CHCl 3 formation was also decreased when the Na 2SO 4 electrolyte was introduced in spite of the levels of light intensity. The p-DADMAC can not only effectively remove the turbidity but also reduce the formation of CHCl 3. The optimum dosage of p-DADMAC for reducing the turbidity TOC and CHCl 3 in the humic acid and source water samples was determined and depended upon the nature of organics.

Carbon isotopic constraints on the contribution of plant material to the natural precursors of trihalomethanes

The δ 13C values of individual trihalomethanes (THM) formed on reaction of chlorine with dissolved organic carbon (DOC) leached from maize (corn; Zea maize L.) and Scirpus acutus (an aquatic bulrush), and with DOC extracted from agricultural drainage waters were determined using purge and trap introduction into a gas chromatograph-combustion-isotope ratio monitoring mass spectrometer. We observed a 16.8‰ difference between the δ 13C values of THM produced from the maize and Scirpus leachates, similar to the isotopic difference between the whole plant materials. Both maize and Scirpus formed THM 12‰ lower in 13C than whole plant material. We suggest that the low value of the THM relative to the whole plant material is evidence of distinct pools of THM-forming DOC, representing different biochemical types or chemical structures, and possessing different environmental reactivity. Humic extracts of waters draining an agricultural field containing Scirpus peat soils and planted with maize formed THM with isotopic values intermediate between those of maize and Scirpus leachates, indicating maize may contribute significantly to the THM-forming DOC. The difference between the δ 13C values of the whole isolate and that of the THM it yielded was 3.9‰, however, suggesting diagenesis plays a role in determining the δ 13C value of THM-forming DOC in the drainage waters, and precluding the direct use of isotopic mixing models to quantitatively attribute sources.

Assessment of disinfection by-products in drinking water in Korea.

The main purpose of applying the chlorination process during water treatment is for disinfection. Research results, however, indicate that disinfection byproducts (DBPs) including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), haloketones (HKs), and chloropicrin (CP) can be produced by the chlorination process. Some of these DBPs are known to be potential human carcinogens. This 3-year project is designed to establish a standard analysis procedure for DBPs in drinking water of this country and investigate the distribution and sources of specific DBPs. The occurrence level of DBPs in drinking water was below 50 micrograms/l in most cases. THMs in plant effluent accounted for 60% of all DBPs measured, whereas HAAs accounted for 20%, HANs 12%, HKs 5% and CP 3%. Chloroform was found to be the major THMs compound (77%), followed by bromodichloromethane (BDCM, 18%) and bromoform (BF, 3%). The concentration of DBPs formed in distribution systems increased from those detected in plant effluent. Comparison of humic acid and sewage as precursors for THMs formation showed that humic acid was the major THMs precursor. Results would play an important role in exposure assessment as a part of the risk assessment process, and would give basic information for establishment of DBPs reduction and management procedures.

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.

Removal of THMP by nanofiltration: Effects of interference parameters

An experimental investigation is conducted to evaluate the effects of interference parameters on the performance of nanofiltration for removal of trihalomethane precursors (THMPs). The influence of operating pressure, feed THMPs concentration, pH, presence of other ions (Ca 2+ and Mg 2+), and suspended solids on nanofiltration performance are determined. The effect of membrane precompaction is studied as well. Membrane performance for reversible and irreversible compaction is compared. Pretreated surface water from a pond is used as the feed water in the study to simulate the practical conditions in water treatment industries. Experimental results show that precompacted membrane has a higher rejection capacity. Higher pressure, feed THMP concentration, and suspended solids increase rejection. However, overall flux variation due to these parameters is found to be negligible. On the other hand presence of divalent ions reduce the rejection capacity. Generally rejection is found to be greater than 90% for a precompacted membrane, which turned out to be well suited for industrial scale application of nanofiltration for removal of THMPs.

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.

A Modeling Analysis of THM Precursors for a Eutrophic Reservoir

ABSTRACT Mass balance modeling analyses were conducted for trihalomethane (THM) precursors in eutrophic Cannonsville Reservoir to resolve the contributions of allochthonous and autochthonous inputs to the reservoir's precursor pool, and to move toward a predictive tool that would support related managementactions. The analyses focus on the April-November interval of 1995, and are supported by detailed external loading (Stepczuk et al. 1998a) and reservoir water column (Stepczuk et al. 1998b) data for precursors. Net autochthonous production of precursors in the epilimnion, apparently driven by primary productivity, was a major source of precursors for the reservoir, representing about two-thirds of the cumulative mass input over the April-mid-summer interval. An undefined loss process(es) operated simultaneously during the study period. Major differences in behavior of the dissolved organic carbon (DOC) and THM precursor pools of the reservoir, depicted by the modeling analysis, are not supportive of the use of DOC as a surrogate estimator of precursor concentration. A preliminary mechanistic precursor model, developed by adding a primary production-based source term and a first order loss/decay term to a eutrophication model for the reservoir (Doerr et al. 1998), performed reasonably well in matching the precursor patterns observed for the lacustrine zone of the reservoir in 1995. An analysis conducted with this model indicates the need to resolve differences in the lability of allochthonous and autochthonous inputs within the model framework.

Spatial and Temporal Patterns of THM Precursors in a Eutrophic Reservoir

ABSTRACT Temporal and spatial patterns of trihalomethane (THM) precursors (measured as THM formation potential, THMFP) are described and analyzed for eutrophic Cannonsville Reservoir, NY, based on monitoring conducted weekly over the April to November interval of 1995 at three sites along the main axis of the reservoir. Ninety-eight percent of the precursors formed chloroform, and 94% were in a dissolved (0.45-μm filtrate) form. Distinct seasonal, vertical and longitudinal patterns were observed. Progressive increases in THMFP occurred from spring (~170 μg · L−1) through midsummer (~360 μg·L−1) in the epilimnion of the lacustrine zone of die reservoir, followed by subsequent decreases through early fell. Progressive, but smaller, increases in THMFP occurred in the hypolimnion throughout the period of stratification. Vertical patterns in dissolved THMFP within the hypolimnion indicate the sediments were not an important source of precursors to the water column. Summer epilimnetic concentrations of THMFP were substantially higher than those reported for the inflows (Stepczuk et al. 1998a), establishing the operation of autochtonous sources. Features of the THMFP patterns, including epilimnetic enrichment, the seasonality, and higher concentrations in the more eutrophic riverine zone, and the results of a single laboratory experiment, indicate a linkage between primary production and autochthonous production of precursors. Dissolved organic carbon was not a good surrogate measure of THMFP.

Allochthonous Contributions of THM Precursors to a Eutrophic Reservoir

ABSTRACT Temporal patterns in trihalomethane (THM) precursor concentrations (measured as THM formation potential, THMFP) and loads are documented for West Branch Delaware River (WBDR), the primary tributary for Cannonsville Reservoir, NY, and a secondary tributary, for a 12-month period. The analysis was supported by routine and runoff event-based (11 events) sampling at the mouth of WBDR, and 3 synoptic surveys along its length. Ninety-eight percent of the precursors from WBDR formed chloroform, and 94% were in a dissolved form (DTHMFP). Temporal variations on a seasonal scale, as well as during runoff events, are reported. The range in DTHMFP was 151 to 325μg · L−1. Increases in precursor concentration observed (from 140 to 240 μg · L−1) moving from upstream toward the mouth of WBDR may reflect anthropogenic contributions. A time series of daily loads of DTHMFP from WBDR to die reservoir is presented for the April-December interval of 1995. The volume-weighted concentration for this period was 228 μg · L−1. Dissolved organic carbon had only limited value as a surrogate measure of THM precursor concentration.

Natural organic matter coagulation in Valencia water supply. Pilot plant studies

: To reduce disinfection by-product (DBP) formation in drinking water treatment, the presence of natural organic matter in surface waters must be minimised. This paper describes pilot plant studies carried out on two surface waters to assess the effectiveness of coagulation in organic matter removal, the Turia and Jucar rivers, which supply the city of Valencia (1m inhabitants). The experiments were conducted with different coagulants (iron sulphate, polyaluminium chloride (PACl)) and treatment schemes. Process effectiveness was evaluated in terms of effluent turbidity, presence of residual metal in final water, and organic matter removal. Four parameters were used to quantify organic matter concentration: total organic carbon (TOC), trihalomethane precursors, ultraviolet absorbance at 254 nm, and oxidability to permanganate. Iron sulphate yielded better results than PACl. Finally, some mathematical relationships were established between coagulant dosages and organic matter removal. This paper involves a preliminary study on controlling DBP formation in conventional treatment. Future work will set out the results obtained using GAC filtration and ozonation.

Removing particles and THM precursors by enhanced coagulation

A pilot‐scale study shows that enhanced coagulation removes both particles and THM precursors.The effectiveness of enhanced coagulation for removing particles and trihalomethane (THM) precursors at various alum dosages and coagulation pH values was assessed. Samples of both source water and filter effluent were examined by counting particles and measuring particle size distribution, turbidity, total organic carbon, ultraviolet light absorbance at 254 nm (UV254), and THM formation potential. Removal of particles and turbidity increased substantially at alum dosages above 20 mg/L. Particle removal was not significantly different at adjusted pH (5.5) compared with ambient pH. Filter effluent particle counts were consistent with residual turbidity data; however, particle counting provided more information on the efficiency of the solid‐liquid separation. Significantly more THM precursors were removed by enhanced coagulation at pH 5.5 than at ambient pH. Higher dosages were needed to achieve acceptable removal of THM precursors than were needed for removal of particles.

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.