Characterization of NOM in the Han River and evaluation of treatability using UF-NF membrane

Characterization of Dissolved Organic Matter and Its Derived Disinfection Byproduct Formation along the Yangtze River

The Yangtze River basin covers one-fifth of China's land area and serves as a water source for one-third of China's population. During long-distance water transport from upstream to downstream, various sources of dissolved organic matter (DOM) lead to considerable variation in DOM properties, significantly impacting water treatability and disinfection byproduct (DBP) formation after chlorination. Using size-exclusion chromatography and fluorescence spectroscopy, the spatial variation in DOM characteristics was comprehensively investigated on a basin scale. The formation of 36 DBPs and speciated total organic halogen in chlorinated samples was determined. Overall, the Yangtze River waters featured a high proportion of terrestrially derived humic substances that served as important precursors for trihalomethanes and haloacetic acids, which was responsible for the increase in total DBP formation along the Yangtze River. The downstream waters were characterized by high levels of microbially derived protein-like biopolymers, which significantly contributed to the formation of haloacetaldehydes and haloacetonitriles that dominated DBP-associated mammalian cell cytotoxicity. Moreover, the precursors of haloacetaldehydes and haloacetonitriles in downstream waters were highly hydrophilic, posing a challenge for water treatment. This study presents an extensive basin-scale study, providing insights into DOM variations along the Yangtze River, illustrating the impact of DOM properties on drinking water from a DBP perspective.

The inactivation of bacteriophage MS2 by sodium hypochlorite in the presence of particles

The inactivation of bacteriophage MS2 by sodium hypochlorite was investigated to understand the effect of solution chemistry on the disinfection efficacy in the presence of particles. Kaolinite and Microcystis aeruginosa (M. aeruginosa) were used as the models of inorganic and organic particles to simulate high turbidity and algal cells, respectively, in drinking water sources. In both particle-containing solutions, lower pH, the presence of cations (di-valent Ca²⁺) and natural organic matters (NOM) were regarded as the main factors to influence the aggregation and inactivation of MS2. The results showed that MS2 aggregated in all solutions at pH 3.0, protecting the inner viruses. At pH 7.0, the presence of Na⁺ cations (0-200 mmol/L) did not affect the inactivation efficacy of MS2, which always followed the order of particles-free ≈ kaolinite > M. aeruginosa. The inactivation efficacy of MS2 in the presence of Ca²⁺ cations followed the order of kaolinite > particles-free > M. aeruginosa at 0-50 mmol/L Ca²⁺ cations, while the inactivation efficacy remained almost constant in the range of 100-200 mmol/L Ca²⁺ cations. By contrast, kaolinite offered not enough protection to adsorbed MS2, but MS2 aggregation decreased disinfection efficacy at a high concentration of Ca²⁺ cations. Moreover, the presence of humic acid as NOM decreased the inactivation of MS2 more significantly than M. aeruginosa due to the more consumption of free chlorine from humic acids. Therefore, the co-existence of NOM and di-valent Ca²⁺ cations are potential challenges for the inactivation of viruses by sodium hypochlorite in safe drinking water.

An overview of the uses of high performance size exclusion chromatography (HPSEC) in the characterization of natural organic matter (NOM) in potable water, and ion-exchange applications

Natural organic matter (NOM) constitutes the terrestrial and aquatic sources of organic plant like material found in water bodies. As of recently, an ever-increasing amount of effort is being put towards developing better ways of unraveling the heterogeneous nature of NOM. This is important as NOM is responsible for a wide variety of both direct and indirect effects: ranging from aesthetic concerns related to taste and odor, to issues related to disinfection by-product formation and metal mobility. A better understanding of NOM can also provide a better appreciation for treatment design; lending a further understanding of potable water treatment impacts on specific fractions and constituents of NOM. The use of high performance size-exclusion chromatography has shown a growing promise in its various applications for NOM characterization, through the ability to partition ultraviolet absorbing moieties into ill-defined groups of humic acids, hydrolysates of humics, and low molecular weight acids. HPSEC also has the ability of simultaneously measuring absorbance in the UV-visible range (200-350 nm); further providing a spectroscopic fingerprint that is simply unavailable using surrogate measurements of NOM, such as total organic carbon (TOC), ultraviolet absorbance at 254 nm (UV₂₅₄), excitation-emission matrices (EEM), and specific ultraviolet absorbance at 254 nm (SUVA₂₅₄). This review mainly focuses on the use of HPSEC in the characterization of NOM in a potable water setting, with an additional focus on strong-base ion-exchangers specifically targeted for NOM constituents.

Pilot-scale spiral wound membrane assessment for THM precursor rejection from upland waters

The outcomes of a pilot-scale study of the rejection of trihalomethanes (THMs) precursors by commercial ultrafiltration/nanofiltration (UF/NF) spiral-wound membrane elements are presented based on a single surface water source in Scotland. The study revealed the expected trend of increased flux and permeability with increasing pore size for the UF membranes; the NF membranes provided similar fluxes despite the lower nominal pore size. The dissolved organic carbon (DOC) passage decreased with decreasing molecular weight cut-off, with a less than one-third the passage recorded for the NF membranes than for the UF ones.

The yield (weight % total THMs per DOC) varied between 2.5% and 8% across all membranes tested, in reasonable agreement with the literature, with the aromatic polyamide membrane providing both the lowest yield and lowest DOC passage. The proportion of the hydrophobic (HPO) fraction removed was found to increase with decreasing membrane selectivity (increasing pore size), and THM generation correlated closely (R² = 0.98) with the permeate HPO fractional concentration.

Kinetics and equilibrium of adsorption of dissolved organic matter fractions from secondary effluent by fly ash

Fly ash was used as a low-cost adsorbent for removing dissolved organic matter (DOM) in secondary effluent. Batch experiments were conducted under various adsorbent dosages, pH, contact time, temperatures and DOM fractional characteristics. Under the optimum conditions of fly ash dosage of 15 g/L, temperature of 303 K and contact time of 180 min, a removal of 22.5% of the dissolved organic carbon (DOC), 23.7% of UV-254, 25.9% of the trihalomethanes precursors in secondary effluent was obtained. The adsorption of DOM fractions onto fly ash all followed the pseudo second-order kinetic model, and the hydrophilic fraction adsorption by fly ash also fitted the intraparticle diffusion model quite well. Freundlich and Langmuir models were applicable to the fly ash adsorption and their constants were evaluated. The maximum adsorption capacities of the adsorptions revealed that fly ash was more effective in adsorbing hydrophilic fraction than the acidic fractions. Structure changes of the DOM fractions after fly ash adsorption were also characterized via spectrum analyzing. Those mechanisms presented critical step toward improved efficiencies of fly ash adsorption via further surface-modification.

Reduction of trihalomethane precursors of dissolved organic matter in the secondary effluent by advanced treatment processes

Wastewater effluent collected from the Wenchang Wastewater Treatment Plant (Harbin, China) was used as source water for advanced treatment and reclamation. Since dissolved organic matter (DOM) in the secondary effluent contains a high concentration of trihalomethanes (THMs) precursors, several processes of advanced treatments including granular activated carbon (GAC) adsorption, sand column biodegradation, horizontal subsurface flow wetland (HSFW) treatment, laboratory-scale soil aquifer treatment (SAT) and GAC+SAT were used in this study to compare and differentiate the removal mechanisms of DOM. DOM in the secondary effluent and the treated effluents was fractionated into five classes using XAD resins: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N), and hydrophilic fraction (HPI). Results showed that HPO-A and HPI were two main fractions of the DOM in the secondary effluent, accounting for 30.0% and 45.5% of the bulk DOM, respectively. HPO-A exhibited higher trihalomethane formation potential (THMFP) and specific THMFP (STHMFP) than HPI during the chlorination process. The order of the dissolved organic carbon (DOC) removal with respect to different advanced treatments was observed to be GAC+SAT>SAT>GAC>sand column>HSFW. As for the DOM removal mechanisms, the advanced treatment processes of GAC adsorption, SAT and GAC+SAT tended to adsorb more HPO-A, HPO-N and TPI-A and could reduce the aromaticity of those DOM fractions efficiently. Correspondingly, the advanced treatment processes of sand column, SAT, HSFW and GAC+SAT removed more HPI and TPI-N through biodegradation and each of the DOM fractions had an increased aromaticity. The removal order of the THMs precursor by the advanced treatment processes was GAC+SAT>GAC>SAT>sand column>HSFW. The adsorption reduced the STHMFP of the DOM fractions effectively, whereas the biodegradation mechanism of the treatments (sand column, SAT, GAC+SAT and HSFW) showed a converse trend. Moreover, the THMFP and STHMFP of the DOM in the HSFW effluent were obviously affected by the DOM derived from the leaves and roots.

Tracing the sources of nitrate in the Han River watershed in Korea, using delta15N-NO3- and delta18O-NO3- values

The dissolved nitrate concentrations and their nitrogen and oxygen isotopic ratios were analyzed in seasonal samples from Korea's Han River to ascertain the seasonal and spatial variations of dissolved nitrate and its possible sources. Nitrate concentrations in the South Han River (SHR) were much higher than those in the North Han River (NHR), probably because of the more extensive distribution of agricultural fields, residential areas and animal farms in the SHR drainage basin. The nitrogen isotopic composition of dissolved nitrate indicates that nitrate-nitrogen (NO(3)(-)-N) is derived mainly from atmospheric deposition and/or soil organic matter in the NHR but comes principally from manure or sewage, with only a minor contribution from atmospheric deposition or soil organic matter, in the SHR. The oxygen isotopic compositions of dissolved nitrate suggest that most atmospheric nitrate undergoes microbial nitrification before entering the river.

Study of natural organic matter fractions in water sources of Tehran

Natural Organic Matters (NOMs) are abundant in natural water resources and in many ways may affect the unit operations in water treatment. Although, NOMs are considered harmless but they have been recognized disinfection by-products precursors (DBP(s)) during the chlorination process. Formation of DBP(s) highly depends on the composition and concentration of NOM, which can be broadly divided into two fractions of hydrophobic (humic) and hydrophilic (non-humic) substances. The objective of this study was to determine Natural organic matter and its fractions concentration in the surface water sources of Tehran. Water sampling was conducted monthly between May to July 2006 in three rivers Lar, Jajrood and Karaj as the main drinking water supplying sources in Tehran. Quantitative parameters of pH, EC, UV254 and DOC were studied based on to standard methods. The XAD-7 resin method was used for fractionation of NOM. Results showed that NOM concentrations in Lar, Jajrood and Karaj rivers were 8.53, 12.9 and 11.3 mg L(-1), respectively. The HPO (hydrophobic) fraction was predominant compared to the HPI (hydrophilic) fraction in the all of water samples. The mean of total percent of HPO and HPI fractions were about 57 and 43%, respectively. Since the hydrophobic NOM fraction exhibits higher trihalomethane formation potential (THMFP) than hydrophilic NOM, Tehran water chlorination exhibits higher THMFP than haloacetic acid formation potential (HAAFP). The information obtained from this study may be further employed in the design of the control technique and management strategies for the water treatment plant, especially for DBP(s) reduction.