F. Wang

The fate of H2O2 during managed aquifer recharge: A residual from advanced oxidation processes for drinking water production

The fate of H2O2 residual from advanced oxidation process (AOP) preceding managed aquifer recharge (MAR) is of concern because H2O2 could lead to undesired effects on organisms in the MAR aquatic and soil ecosystem. The objective of this study was to distinguish between factors affecting H2O2 decomposition in MAR systems, simulated in batch reactors with synthetic MAR water and slow sand filter sand. The results showed that pure sand and soil organic matter had no considerable effect on H2O2 decomposition, whereas naturally occurring inorganic substances on the surface of sand grains and microbial biomass are the two main factors accelerating H2O2 decomposition in MAR systems. Additionally, the results showed that the H2O2 decompositions with different initial concentrations fitted first-order kinetics in 2-6 h in a mixture of slow sand filter sand (as a substitute for sand from a MAR system) and synthetic MAR water with high bacterial population. An estimation indicated that low concentrations of H2O2 (<3 mg/L) could decompose to the provisional standard of 0.25 mg/L in the first centimeters of MAR systems with the influent water containing high microbial biomass 38 ng ATP/mL.

Effective removal of bromate in nitrate-reducing anoxic zones during managed aquifer recharge for drinking water treatment: Laboratory-scale simulations

The removal of bromate (BrO3-) as a by-product of ozonation in subsequent managed aquifer recharge (MAR) systems, specifically in anoxic nitrate (NO3-)-reducing zones, has so far gained little attention. In this study, batch reactors and columns were used to explore the influence of NO3- and increased assimilable organic carbon (AOC) due to ozonation pre-treatment on BrO3- removal in MAR systems. 8 m column experiments were carried out for 10 months to investigate BrO3- behavior in anoxic NO3--reducing zones of MAR systems. Anoxic batch experiments showed that an increase of AOC promoted microbial activity and corresponding BrO3- removal. A drastic increase of BrO3- biodegradation was observed in the sudden absence of NO3- in both batch reactors and columns, indicating that BrO3- and NO3- competed for biodegradation by denitrifying bacteria and NO3- was preferred as an electron acceptor under the simultaneous presence of NO3- and BrO3-. However, within 75 days absence of NO3- in the anoxic column, BrO3- removal gradually decreased, indicating that the presence of NO3- is a precondition for denitrifying bacteria to reduce BrO3- in NO3--reducing anoxic zones. In the 8xa0m anoxic column set-up (retention time 6 days), the BrO3- removal achieved levels as low as 1.3xa0μg/L, starting at 60xa0μg/L (98% removal). Taken together, BrO3- removal is likely to occur in vicinity of NO3--reducing anoxic zones, so MAR systems following ozonation are potentially effective to remove BrO3-.

Effect of residual H2O2 from advanced oxidation processes on subsequent biological water treatmen: A laboratory batch study

H2O2 residuals from advanced oxidation processes (AOPs) may have critical impacts on the microbial ecology and performance of subsequent biological treatment processes, but little is known. The objective of this study was to evaluate how H2O2 residuals influence sand systems with an emphasis on dissolved organic carbon (DOC) removal, microbial activity change and bacterial community evolution. The results from laboratory batch studies showed that 0.25xa0mg/L H2O2 lowered DOC removal by 10% while higher H2O2 concentrations at 3 and 5xa0mg/L promoted DOC removal by 8% and 28%. A H2O2 dosage of 0.25xa0mg/L did not impact microbial activity (as measured by ATP) while high H2O2 dosages, 1, 3 and 5xa0mg/L, resulted in reduced microbial activity of 23%, 37% and 37% respectively. Therefore, DOC removal was promoted by the increase of H2O2 dosage while microbial activity was reduced. The pyrosequencing results illustrated that bacterial communities were dominated by Proteobacteria. The presence of H2O2 showed clear influence on the diversity and composition of bacterial communities, which became more diverse under 0.25xa0mg/L H2O2 but conversely less diverse when the dosage increased to 5xa0mg/L H2O2. Anaerobic bacteria were found to be most sensitive to H2O2 as their growth in batch reactors was limited by both 0.25 and 5xa0mg/L H2O2 (17-88% reduction). In conclusion, special attention should be given to effects of AOPs residuals on microbial ecology before introducing AOPs as a pre-treatment to biological (sand) processes. Additionally, the guideline on the maximum allowable H2O2 concentration should be properly evaluated.

Rapid degradation of brominated and iodinated haloacetamides with sulfite in drinking water: Degradation kinetics and mechanisms

The effective removal of haloacetamides (HAMs) as a group of emerging disinfection by-products is essential for drinking water safety. This study investigated the degradation of 10 HAMs, including chlorinated, brominated, and iodinated analogues, by sodium sulfite (S(IV)) and the mechanism behind it. The results indicated that all HAMs, excluding chlorinated HAMs, decomposed immediately when exposed to S(IV). The reductive dehalogenation kinetics were well described by a second-order kinetics model, first-order in S(IV) and first-order in HAMs. The degradation rates of HAMs increased with the increase of pH and they were positively correlated with sulfite concentration, indicating that the reaction of S(IV) with HAMs mainly depends on sulfite. The rank order and relative activity of the reaction of sulfite with HAMs depends on bimolecular nucleophilic substitution reaction reactivity. The order of the reductive dehalogenation rates of HAMs versus the substitution of halogen atoms was iodo-u202f>u202fbromo-u202f>>u202fchloro-. During reductive dehalogenation of HAMs by sulfite, the α-carbon bound to the amide group underwent nucleophilic attack at 180° to the leaving group (halide). As a consequence, the halide was pushed off the opposite side, generating a transition state pentacoordinate. The breaking of the C-X bond and the formation of the new C-S bond occurred simultaneously and HAM sulfonate formed as the immediate product. Results suggest that S(IV) can be used to degrade brominated and iodinated HAMs in drinking water and therefore should not be added as a quenching agent before HAM analysis to accurately determine the HAM concentrations produced during water disinfection.

The contribution of atmospheric particulate matter to the formation of CX3R-type disinfection by-products in rainwater during chlorination

Atmospheric particulate matter (PM) can be scavenged by rainfall and contribute dissolved organic matter (DOM) to rainwater. Rainwater may serve as a part or the whole of drinking water sources, leading to the introduction of PM-derived DOM into drinking water. However, little information is available on the role of PM-derived DOM as a remarkable precursor of CX3R-type disinfection by-products (DBPs) in rainwater. In this study, samples were collected from ten occurrences of rainfall in Shanghai and batch experiments were executed to explore the contribution of PM-derived DOM to CX3R-type DBP formation in rainwater and to further understand some of unknowns regarding its characteristics. Results revealed that a part of PM was scavenged by rainfall and the scavenge performance was better for smaller PM. The formation potentials (FPs) of individual CX3R-type DBP were similar among size-isolated PM. TCM was predominant (around 0.5-4.5u202fμg-C/mg-C) and TCAA was the secondary (around 0.6-3.2u202fμg-C/mg-C) among all detectable CX3R-type DBPs. Based on the PM removal data and DBP FP results, the contribution of PM-derived DOM to CX3R-type DBP formation in rainwater was modeled. Furthermore, aromatic proteins and soluble microbial product-like compounds were found to be significant compositions, which were reported to be DBP precursors. And low molecular weight (< 10u202fkDa) DOM derived from total PM and rainwater exhibited higher CX3R-type DBP FPs. DOM fractions with higher SUVA254 and SUVA285 values gave relatively higher yields of CX3R-type DBPs, indicating that aromatic compounds played an important role in DBP formation.