The formation of malodorous dimethyl oligosulphides in treated groundwater: The role of biofilms and potential precursors

Water distributed from the Wanneroo Groundwater Treatment Plant intermitten tly contains dimethyl trisulphide (DMTS). The compound is responsible for a "swampy odour" in the water. DMTS production from potential precursors was insignificant in the absence of biofilms when compared with DMTS productio n from precursors in the presence of biofilms in a biofilm reactor. Greates t dimethyl disulphide (DMDS) and DMTS production (> 3000 ng L-1 DMTS) occur red in the reactors when supplied with methane thio-containing compounds, s uch as methionine, S-methyl cysteine and methyl-3-(methylmercapto)-propiona te, Abiotic DMTS production from oligosulphides also occurred through the a ddition of the methylating agents, methyl iodide or methyl-p-toluene sulpho nate. Significant DMTS production also occurred with Wanneroo water that co ntained added omega -thio-containing compounds such as cysteine (1400 ng L- 1 DMTS), and 3-mercaptopropionate (210 ng L-1). Biomethylation, a ubiquitou s response by microorganisms for the detoxification of toxic compounds, gen erated DMDS/TS from biofilm oligosulphides. Biofilms exposed to the toxic c ompounds selenate or 2,4,6-trichlorophenol methylated oligosulphides in add ition to the toxins. Sodium sulphide also stimulated DMTS production. Easil y Biodegradable Dissolved Organic Carbon (BDOC) probably contributed indire ctly to DMTS production by the biofilms, although whether this was a result of its stimulation of greater microbial activity or consumption of oxygen, or both, remains unresolved. Stagnation of water in the biofilm reactors a lso increased DMTS production, which was concomitant with depletion of oxyg en concentrations in the bulk water. Many processes, such as degradation of methane thio-containing compounds, methylation of sulphides and oligosulph ides, and changes in contributions of different metabolic pathways upon dep letion of oxygen concentrations upon water stagnation, probably contribute simultaneously to "swampy odour" production in the distribution system. Cro wn Copyright (C) 2001 Published by Elsevier Science Ltd, All rights reserve d.