Abstract
This study provides important new insights on how to achieve high sulfur selectivities and stable gas biodesulfurization process operation in the presence of both methanethiol and H2S in the feed gas. On the basis of previous research, we hypothesized that a dual bioreactor lineup (with an added anaerobic bioreactor) would favor sulfur-oxidizing bacteria (SOB) that yield a higher sulfur selectivity. Therefore, the focus of the present study was to enrich thiol-resistant SOB that can withstand methanethiol, the most prevalent and toxic thiol in sulfur-containing industrial off gases. In addition, the effect of process conditions on the SOB population dynamics was investigated. The results confirmed that thiol-resistant SOB became dominant with a concomitant increase of the sulfur selectivity from 75 mol% to 90 mol% at a loading rate of 2 mM S methanethiol day−1. The abundant SOB in the inoculum – Thioalkalivibrio sulfidiphilus – was first outcompeted by Alkalilimnicola ehrlichii after which Thioalkalibacter halophilus eventually became the most abundant species. Furthermore, we found that the actual electron donor in our lab-scale biodesulfurization system was polysulfide, and not the primarily supplied sulfide.
Highlights
Among many reduced sulfur compounds, natural gas and landfill gas streams may contain thiols (RSH) and hydrogen sulfide (H2S) at high concentrations
We present an upgraded gas biodesulfurization technology. It concerns the adsorption of thiols and H2S in a highly buffered, moderately alkaline solution pH 8–10, followed by an oxidation step, in which haloalkaliphilic sulfide-oxidizing bacteria (SOB) convert sulfide to elemental sulfur as a major and sulfate as a minor products at low redox potential created by oxygen-limited conditions (Van Den Bosch et al, 2007)
Addition of an anaerobic bioreactor to a traditional gas biodesulfurization lineup resulted in increased sulfur formation during addition of MT
Summary
Among many reduced sulfur compounds, natural gas and landfill gas streams may contain thiols (RSH) and hydrogen sulfide (H2S) at high concentrations. Important drawbacks of physicochemical methods for sour gas treatment are the formation of waste streams and the high operating costs, whereas biological conversion processes are environmentally friendly and more cost-effective (Cline et al, 2003). The latter still have room for further optimization. We present an upgraded gas biodesulfurization technology It concerns the adsorption of thiols and H2S in a highly buffered, moderately alkaline solution pH 8–10, followed by an oxidation step, in which haloalkaliphilic sulfide-oxidizing bacteria (SOB) convert sulfide to elemental sulfur as a major and sulfate as a minor products at low redox potential created by oxygen-limited conditions (Van Den Bosch et al, 2007). Elemental sulfur is the preferred end (insoluble and separated) product as the associated regeneration of hydroxide ions (needed for H2S absorption) leads to a reduction in caustic (NaOH) consumption, in a decrease in air-oxygen requirements as well as energy requirements (Van Den Bosch et al, 2007)
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