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Trihalomethane formation in contaminated surface water and its control by membrane bio-reactor

by Chu, Hiu-ping

Abstract (Summary)
(Uncorrected OCR) Abstract of thesis entitled Trihalomethane Formation in Contaminated Surface Water and Its Control by Membrane Bio-Reactor submitted by Hiu Ping CHU for the degree of Doctor of Philosophy at the University of Hong Kong in February 2003 Most drinking water quality problems, such as turbidity, odor, taste, bio-instability, and the formation of trihalomethanes (THMs), are closely related to organic impurities in source waters. In the present laboratory study, the THM formation potentials (THMFPs) of the organic impurities from both natural sources and sewage discharge were characterized. The natural organic matter (NOM) concentrated from the raw water of Hong Kong had a unit carbon THMFP of around 22 ? /mg in terms of total organic carbon (TOC). Based on the molecular weight fractionation by ultrafiltration, the THMFP of the NOM fraction was found to increase with its apparent molecular weight (AMW). However, in contrast to the results for pure humic matter, where the predominant THMFP came from large AMW (>30,000) fractions, nearly half of the THMFP of the NOM was attributable to small AMW (<3,000) fractions. Pre-ozonation appeared to be effective for the water with a high calcium concentration of 80 mg/L. The presence of bromide ions brought about by seawater intrusion considerably increased the rate and potential of THM formation in water. As the bromide content increased from 0 to 3.40 mg/L in the raw waters of Hong Kong and Macao with a TOC of about 2.0 mg/L, the total THMFP increased from 145 to 260 ?/L. Discharges of inadequately treated sewage have become the main source of organic impurities in surface waters in many developing countries. The sewage organics obtained from a local treatment works had a unit carbon THMFP ranging from 30 to 67 ?/mg for raw sewage and from 52 to 233 ?/mg for its secondary effluent. To treat a raw water supply slightly polluted by domestic sewage, a laboratory membrane bioreactor (MBR) with a submerged hollow-fiber membrane module was used for more than 750 days with a hydraulic retention time (HRT) as short as 1 hr. The feeding influent had a TOC level of 3 - 5 mg/L and a NH3-N concentration of 3 - 4 mg/L. Sufficient organic degradation and complete nitrification were achieved in the MBR effluent with a TOC of less than 2 mg/L and a NH3-N of below 0.2 mg/L. The process was also highly effective in eliminating conventional water impurities, as demonstrated by decreases in turbidity from 4.50 ?1.11 to 0.08 ?0.03 NTU and UV254 absorbance from 9.8 ?1.9 to 3.6 ?0.7 m-1. THMFP was significantly reduced from 239.5 ?43.8 to 60.4 ?23.1 ?/L. All of these water quality parameters indicate the superior quality of MBR treated water, which was comparable to or even better than local tap water. It is suggested that a dynamic sludge layer on the membrane surface could function as an additional barrier to the passage of typical THM precursors, such as large organic molecules and hydrophobic compounds. The experimental results showed the promise of the MBR as an effective biological water treatment technology to solve the urgent problems of developing countries beset by the serious contamination of their surface water resources. An abstract of exactly 494 words
Bibliographical Information:

Advisor:

School:The University of Hong Kong

School Location:China - Hong Kong SAR

Source Type:Master's Thesis

Keywords:trihalomethanes membrane reactors water purification biological treatment

ISBN:

Date of Publication:01/01/2003

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