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Microbial processes and carbon utilization in high sulfate waters and sediments Schmidtova, Jana


The application of microorganisms for treating high sulfate effluents is proving to be an effective approach although the processes involved are not well understood. One example is the use of anaerobic passive systems such as mine pit lakes and subsurface flow wetlands. This work addresses the missing information on microbial processes in two high sulfate environments: a permanently stratified fjord and a subsurface flow wetland treating mine waste. In Nitinat Lake fjord, although sulfide was present, no significant sulfate reduction occurred and quantitative polymerase chain reaction (qPCR) of the dissimilatory sulfite reductase gene (dsr) detected very few sulfate-reducing bacteria (SRB). Instead, the small subunit rRNA phylogenetic analysis revealed almost complete domination by novel Arcobacter-related species in deep anoxic water. In contrast, substantial sulfate reduction was measured in the fjord sediments. A rate of 250 ± 60 nmol cm⁻³ d⁻¹ was determined, and 8.7 ± 0.7 x 10⁶ copies of dsr mL⁻¹ were found using quantitative PCR (qPCR). When the sediments were amended with carbon sources (acetate, lactate, or a mixture of compost, silage and molasses), acetate stimulated the highest rate of sulfate reduction. An operating passive treatment system remediating metal-containing seepage near the Teck smelter in Trail, B.C. was used for a study of five carbon materials (silage, pulp mill biosolids, compost, molasses with hay, and cattails) as potential substrates for passive systems. Phylogenetic analyses of SSU rRNA and dsr genes were performed, as well as qPCR and chemical analyses of carbon parameters including easily degradable material (EDM), dissolved and particulate organic carbon (DOC and TOC), particulate nitrogen (PN), and carbon to nitrogen ratio C/N. Silage showed highest sulfate-reducing potential. The results showed that the initial C/N ratio of organic materials correlated positively with the SRB activity. However, phylogenetic analysis determined that the majority of bacterial species belonged to Bacteroidetes and Firmicutes phyla likely involved in complex carbon degradation. The lack of SRB in the actual system suggests that processes other than sulfate reduction are responsible for metal removal. This study contributed to the understanding of microbial processes and therefore aids in improving design and monitoring of passive treatment systems.

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