Disinfection byproducts in drinking water and regulatory compliance： A critical review

Disinfection by-products （DBPs） are regulated in drinking water in a number of countries. This critical review focuses on the issues associated with DBP regulatory compliance, including methods for DBP analysis, occurrence levels, the regulation comparison among various countries, DBP compliance strategies, and emerging DBPs. The regulation comparison between China and the United States （US） indicated that the DBP regulations in China are more stringent based on the number of regulated compounds and maximum levels. The comparison assessment using the Information Collection Rule （ICR） database indicated that the compliance rate of 500 large US water plants under the China regulations is much lower than that under the US regulations （e.g. 62.2% versus 89.6% for total trihalomethanes）. Precursor removal and alternative disinfectants are common practices for DBP regulatory compliance. DBP removal after formation, including air stripping for trihalomethane removal and biodegradation for haloacetic acid removal, have gained more acceptance in DBP control. Formation of emerging DBPs, including iodinated DBPs and nitrogenous DBPs, is one of unintended consequences of precursor removal and alternative disinfection. At much lower levels than carbonaceous DBPs, however, emerging DBPs have posed higher health risks.

Pilot study for the treatment of sodium and fluoridecontaminated groundwater by using high-pressure membrane systems

High-pressure membrane process is one of the cost-effective technologies for the treatment of groundwater containing excessive dissolved solids. This paper reports a pilot study in treating a typical groundwater in Huaibei Plain containing excessive sodium, sulfate and fluoride ions. Three membrane systems were set up and two brands of reverse osmosis （RO）, four low-pressure RO （LPRO） and one tight nanofiltration （NF） membranes were tested under this pilot study. An apparent recovery rate at about 75% was adopted. Cartridge filtration, in combination with dosing antiscalent, was not sufficient to reduce the fouling potential of the raw water. All RO and LPRO systems （except for the two severely affected by membrane fouling） demonstrated similar rejection ratios of the conductivity @98.5%）, sodium （-98.5%） and fluoride （-99%）. Membrane fouling substantially reduced the rejection performance of the fouled membranes. The tight NF membrane also had a good rejection on conductivity （95%）, sodium （94%） and fluoride （95%）. All membranes rejected sulfate ion almost completely （more than 99%）. The electricity consumptions for the RO, LPRO and NF systems were 1.74, 1.10 and 0.72 kWh·m3 treated water, respectively. The estimated treatment costs by using typical RO, LPRO and tight NF membrane systems were 1.21, 0.98 and 0.96 CNY·m 3 finished water, respectively. A treatment process consisting of either LPRO or tight NF facilities following multi-media filtration was suggested.

Using loose nanofiltration membrane for lake water treatment:A pilot study

Nanofiltration(NF)using loose membranes has a high application potential for advanced treatment of drinking water by selectively removing contaminants from the water,while membrane fouling remains one of the biggest problems of the process.This paper reported a seven-month pilot study of using a loose NF membrane to treat a sand filtration effluent which had a relatively high turbidity(∼0.4 NTU)and high concentrations of organic matter(up to 5 mg/L as TOC),hardness and sulfate.Results showed that the membrane demonstrated a high rejection of TOC(by<90%)and a moderately high rejection of two pesticides(54%–82%)while a moderate rejection of both calcium and magnesium(∼45%)and a low rejection of total dissolved solids(∼27%).The membrane elements suffered from severe membrane fouling,with the membrane permeance decreased by 70%after 85 days operation.The membrane fouling was dominated by organic fouling,while biological fouling was moderate.Inorganic fouling was mainly caused by deposition of aluminum-bearing substances.Though inorganic foulants were minor contents on membrane,their contribution to overall membrane fouling was substantial.Membrane fouling was not uniform on membrane.While contents of organic and inorganic foulants were the highest at the inlet and outlet region,respectively,the severity of membrane fouling increased from the inlet to the outlet region of membrane element with a difference higher than 30%.While alkaline cleaning was not effective in removing the membrane foulants,the use of ethylenediamine tetraacetate(EDTA)at alkaline conditions could effectively restore the membrane permeance.

Concentration levels of disinfection by-products in 14 swimming pools of China

Swimming has become a popular exercising and recreational activity in China but little is known about the disinfection by-products （DBPs） concentration levels in the pools. This study was conducted as a survey of the DBPs in China swimming pools, and to establish the correlations between the DBP concentrations and the pool water quality parameters. A total of 14 public indoor and outdoor pools in Beijing were included in the survey. Results showed that the median concentrations for total tfihalomethanes （TTHM）, nine haloacetic acids （HAA9）, chloral hydrate （CH）, four haloacetonitriles （HAN4）, 1,1- dichloropropanone, 1,1,1-trichloropropanone and trichlor- onitromethane were 33.8, 109.1, 30.1, 3.2, 0.3, 0.6 pg＇L-1 and below detection limit, respectively. The TTHM and HAA9 levels were in the same magnitude of that in many regions of the world. The levels of CH and nitrogenous DBPs were greatly higher than and were comparable to that in typical drinking water, respectively. Disinfection by chlorine dioxide or trichloroisocyanuric acid could sub- stantially lower the DBP levels. The outdoor pools had higher TTHM and HAA9 levels, but lower trihaloacetic acids （THAA） levels than the indoor pools. The TTHM and HAA9 concentrations could be moderately correlated with the free chlorine and total chlorine residuals but not with the total organic carbon （TOC） contents. When the DBP concentration levels from other survey studies were also included for statistical analysis, a good correlation could be established between the TTHM levels and the TOC concentration. The influence of chlorine residual on DBP levels could also be significant.

Membrane fouling in ultrafiltration of natural water after pretreatment to different extents

The combined fouling during ultrafiltration（UF） of surface water pretreated to different extents was investigated to disclose the roles of polysaccharides, proteins, and inorganic particles in UF membrane fouling. Both reversible and irreversible fouling decreased with enhanced pretreatment（biologically active carbon（BAC） treatment and sand filtration）. The sand filter effluent fouled the membrane very slowly. The UF membrane removed turbidity to less than 0.1 nephelometric turbidity unit（NTU）, reduced polysaccharides by 25.4%–29.9%, but rejected few proteins. Both polysaccharides and inorganic particles were detected on the fouled membranes, but inorganic particles could be effectively removed by backwashing. The increase of turbidity in the sand filter effluent to 3.05 NTU did not significantly increase the fouling rate, but an increase in the turbidity in the BAC effluent to6.11 NTU increased the fouling rate by more than 100%. The results demonstrated that the polysaccharide, not the protein, constituents of biopolymers were responsible for membrane fouling. Membrane fouling was closely associated with a small fraction of polysaccharides in the feed water. Inorganic particles exacerbated membrane fouling only when the concentration of fouling–inducing polysaccharides in the feed water was relatively high. The combined fouling was largely reversible, and polysaccharides were the predominant substances responsible for irreversible fouling.

Influence of pore size and membrane surface properties on arsenic removal by nanofiltration membranes

Nanofiltration(NF)has a great potential in removing arsenate from contaminated water.The performance including arsenate rejection,water permeability and resistance to fouling could however differ substantially among NF membranes.This study was conducted to investigate the influence of membrane pore size and surface properties on these aspects of membrane performance.Four fullyaromatic NF membranes with different physicochemical properties were adopted for this study.The results showed that surface charge,hydrophobicity,roughness and pore size could affect water permeability and/or arsenate rejection considerably.A more negative surface charge was desirable to enhance arsenate rejection rates.NF90 and a non-commercialized membrane(M#1)demonstrated the best performance in terms of arsenate rejection and water permeability.The M#1 membrane showed less membrane fouling than NF90 when used for filtration of real arsenic-containing groundwater.This was mainly due to its distinct chemical composition and surface properties.A severe membrane fouling could lead to a substantial reduction of arsenic rejection.The M#1 membrane showed the best performance,which indicated that membrane modification could indeed enhance the overall membrane performance for water treatment.

Techno-economic characteristics of wastewater treatment plants retrofitted from the conventional activated sludge process to the membrane bioreactor process

While a growing number of wastewater treatment plants(WWTPs)are being retrofitted from the conventional activated sludge(CAS)process to the membrane bioreactor(MBR)process,the debate on the techno-economy of MBR vs.CAS has continued and calls for a thorough assessment based on techno-economic valuation.In this study,we analyzed the operating data of 20 large-scale WWTPs(capacity≥10000 m^(3)/d)and compared their techno-economy before and after the retrofitting from CAS to MBR.Through cost-benefit analysis,we evaluated the net profit by subtracting the operating cost from the environmental benefit(estimated by the shadow price of pollutant removal and water reclamation).After the retrofitting,the removal rate of pollutants increased(e.g.,from 89.0%to 93.3%on average for NH3-N),the average energy consumption increased from 0.40 to 0.57 kWh/m^(3),but the operating cost did not increase significantly.The average marginal environmental benefit increased remarkably(from 0.47 to 0.66 CNY/g for NH3-N removal),leading to an increase in the average net profit from 19.4 to 24.4 CNY/mJ.We further scored the technical efficiencies via data envelopment analysis based on non-radial directional distance functions.After the retrofitting,the relative cost efficiency increased from 0.70 to 0.73(the theoretical maximum is 1),while the relative energy efficiency did not change significantly.The techno-economy is closely related to the effluent standard adopted,particularly when truncating the extra benefit of pollutant removal beyond the standard in economic modeling.The modeling results suggested that MBR is more profitable than CAS given stricter effluent standards.

Haloacetic acids in swimming pool and spa water in the United States and China

The objective of this study is to investigate the occurrence of haloacetic acids （HAAs）, a group of disinfection byproducts, in swimming pool and spa water. The samples were collected from six indoor pools, six outdoor pools and three spas in Pennsylvania, the United States, and from five outdoor pools and nine indoor pools in Beijing, China. Five HAAs （HAA5）, including monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid were analyzed. Total chlorine, pH and total organic carbon concentration were analyzed as well. Results indicated that the levels of HAA5 in swimming pools and spas in the United States ranged from 70 to 3980μg·L^-1, with an arithmetic average at 1440μg·L^-1 and a median level at 1150μg·L^-1. These levels are much higher than the levels reported in chlorinated drinking water and are likely due to organic matters released from swimmers＇ bodies. The levels of HAA5 in swimming pools in China ranged from 13 to 332μg·L^-1, with an arithmetic average at 117μg·L^-1 and a median level at 114μg·L^-1. The lower HAA levels in swimming pools in China were due to the lower chlorine residuals. Results from this study can help water professionals to better understand the formation and stability of HAAs in chlorinated water and assess risks associated with exposures to HAAs in swimming pools and spas.