Decomposition of two haloacetic acids in water using UV radiation, ozone and advanced oxidation processes.

The decomposition of two haloacetic acids (HAAs), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), from water was studied by means of single oxidants: ozone, UV radiation; and by the advanced oxidation processes (AOPs) constituted by combinations of O(3)/UV radiation, H(2)O(2)/UV radiation, O(3)/H(2)O(2), O(3)/H(2)O(2)/UV radiation. The concentrations of HAAs were analyzed at specified time intervals to elucidate the decomposition of HAAs. Single O(3) or UV did not result in perceptible decomposition of HAAs within the applied reaction time. O(3)/UV showed to be more suitable for the decomposition of DCAA and TCAA in water among the six methods of oxidation. Decomposition of DCAA was easier than TCAA by AOPs. For O(3)/UV in the semi-continuous mode, the effective utilization rate of ozone for HAA decomposition decreased with ozone addition. The kinetics of HAAs decomposition by O(3)/UV and the influence of coexistent humic acids and HCO(3)(-) on the decomposition process were investigated. The decomposition of the HAAs by the O(3)/UV accorded with the pseudo-first-order mode under the constant initial dissolved O(3) concentration and fixed UV radiation. The pseudo-first-order rate constant for the decomposition of DCAA was more than four times that for TCAA. Humic acids can cause the H(2)O(2) accumulation and the decrease in rate constants of HAAs decomposition in the O(3)/UV process. The rate constants for the decomposition of DCAA and TCAA decreased by 41.1% and 23.8%, respectively, when humic acids were added at a concentration of 1.2mgTOC/L. The rate constants decreased by 43.5% and 25.9%, respectively, at an HCO(3)(-) concentration of 1.0mmol/L.

[Analysis of haloacetic acids in drinking water by gas chromatography-mass spectrometry].

Based on liquid-liquid micro-extraction and acidic methanol derivatization methods from EPA Method 552.3, a gas chromatographic-mass spectrometric (GC-MS) method has been studied for determining haloacetic acid (HAAs) in drinking water using ultrapure water instead of methyl tert-butyl ether (MTBE) as solvent for preparing standard stock solution. The results showed that the peaks of 1,2-dibromo propane (internal standard) and HAAs were separated very well. With the improved method, the recoveries for HAAs (82% - 103%) were high at concentrations ranging from 5 to 80 microg/L, the detection limits for dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) were 0.72 and 0.44 microg/L. With the improved method, the runtime could be also significantly reduced without compromising the analytical resolutions. It is also demonstrated that the stock standard was stable under storage for 2 month at 4 degrees C.

[Effect of DO distribution on contaminated urban stream water treatment performance in constructed wetland].

We evaluated the effect of dissolved oxygen (DO) on the performance of two pilot-scale constructed wetlands in treating contaminated water from an urban stream. The aim of this study was to investigate a more effective DO distribution in contaminated stream water treatment wetland that may aid future constructed wetland design effort. The results show poor natural aeration condition and inadequate DO in wetland directly result in the deterioration of effluent water quality. Natural waterfall is an effective aeration way and can improve DO concentration in wetland. The aeration capability of waterfall can be evaluated by oxygen deficit ratio (the ratio of difference between concentration of saturated DO and DO measured before and after waterfall). The distributions of DO obviously correlated with the quantity distribution of micrdorganism and removal rate of organic contaminants in wetland, however there was no obvious relationship between DO and TP removal rate. Results of the study also indicate setting multi-waterfall in plug-flow wetland can balance the distribution of DO and improve the nitrification.

[Adsorption performance of haloacetic acids onto 5 GACs from water].

Adsorption performance of 5 GACs were compared on two abundant haloacetic acids (HAAs) as disinfection by-products (dichloroacetic acid and trichloroacetic acid). The adsorption behaviours of the two HAAs were well correlated with Langmuir equation. When the two HAAs co-existed, trichloroacetic acid tended to be adsorbed more easily. The adsorption capacity of a foreign GAC-A for dichloroacetic acid was 4.4-5.7 times that of domestic GACs, and 3.8 times that of another foreign GAC-B, while the adsorption capacity of a foreign GAC-A for trichloroacetic acid was 4.0-5.4 times that of domestic GACs, and 2.6 times that of another foreign GAC-B. The equilibrium study of competitive adsorption between dichloroacetic acid and trichloroacetic acid on GAC-A demonstrates that the relative adsorption capacity of HAAs has a linear increase with their relative equilibrium concentration. The adsorption capacity for trichloroacetic acid is sensitive to changes at its equilibrium concentration greater than that for dichloroacetic acid.