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The efficiency of ultrafiltration membranes at removing TOC and THMFP in a British Columbia surface water

University of British Columbia

This research investigated the efficiency of membrane filtration technology at reducing the total trihalomethane formation potential in a British Columbia drinking water. Trihalomethanes are formed in drinking water as a result of chlorination of natural organic matter present in the source water. They are halogen substituted single-carbon compounds which are suspected human carcinogens. Chloroform, most frequently detected and at the highest concentrations in drinking water, often serves as an estimate for total trihalomethanes. In a national survey of 70 water supplies serving 38% of Canada's population, conducted in the winter of 1976/1977, chloroform concentrations 800 m downstream from point of chlorination, averaged 22.7 μg/L (ranging from 0 to 121 μg/L). The current Canadian guideline for total trihalomethanes is 100 μg/L. The United States' guideline (to be implemented January 2002) is 80 μg/L. Many water suppliers will not be able to meet this guideline. Both Canada and the US, state that the preferred method of controlling trihalomethanes is precursor removal (removal of naturally occurring organic matter), and the best method of precursor removal is organics removal. The present research evaluated the removal patterns of TOC and THMFP under different treatment conditions for Seymour Reservoir water in Vancouver, British Columbia. The TOC and THMFP removal patterns as measured for raw water, microfiltration (MF) filtered water, coagulated and MF filtered water, ultrafiltration (UF) filtered water, and powdered activated carbon (PAC) treated and UF filtered water were evaluated with respect to their removal efficacy. Additionally, the removal patterns were evaluated to determine if DBP production was primarily humic acid- or fulvic acid-controlled, and to determine the usefulness of TOC as a surrogate parameter. Other surrogate parameters, UV254, specific UVA (SUVA) and differential UV were also evaluated for the same waters. This research demonstrated that organic removal does not equate to a trihalomethane production reduction (estimated using chloroform production measurements). And the technologies effective at organics removal (membrane filtration technology with and with out applied pretreatments) are not always effective at removing trihalomethane formation potential. TOC removal did not equal THMFP removal. Tests demonstrated that coagulation effectively removed organics of above molecular above 10 000 Daltons but the greatest THMFP remained with organics of molecular weight <3000 Daltons. The pilot plant study also showed that TOC removal and THMFP removal are not equated. The MF membrane removed an average of 12.9% of the raw water TOC and an average of 27.2% of the raw water THMFP, while the UF membrane removed 30.9% of the raw water TOC but only 18.5% of the raw water THMFP. The water appears to be controlled by humic acids. The treatment process which removes organic material in the humic acid range (coagulation) showed the largest chloroform formation potential reductions.

Thesis/Dissertation

application/pdf

2009-08-12

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http://hdl.handle.net/2429/12111

Civil Engineering

University of British Columbia

UBCV

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