Assessing main process mechanism and rates of sulfate reduction by granular biomass fed with glycerol under sulfidogenic conditions

X Zhou,E Fernández-Palacios,A.D Dorado,X Gamisans,D Gabriel

doi:10.1016/j.chemosphere.2021.131649

X Zhou, E Fernández-Palacios + Show 3 more

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https://doi.org/10.1016/j.chemosphere.2021.131649

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Abstract

Sulfate-reducing bioreactors for sulfide production are the initial stage of processes targeting elemental sulfur recovery from sulfate-rich effluents. In this work, the principal reactions involved in glycerol fermentation and sulfate reduction using glycerol and its fermentation products as electron donors were assessed together with their specific consumption/production rates. A battery of batch activity tests with and without sulfate were performed with glycerol and with each fermentation product using a non-methanogenic but sulfidogenic granular sludge from an up-flow anaerobic sludge blanket (UASB) reactor operated under long-term while fed with crude glycerol. As a result, a mechanistic approach based on the experimental observations is proposed in this work. Glycerol was mainly fermented to 1,3-propanediol, ethanol, formate, propionate and acetate by fermentative bacteria. All organic intermediates were found to be further used by sulfate reducing bacteria (SRB) for sulfate reduction except for acetate. The most abundant genus detected under sulfidogenic conditions were Propionispora (15.2%), Dysgonomonas (13.2%), Desulfobulbus (11.6%) and Desulfovibrio (10.8%). The last two SRB genera accounted for 22.4% of the total amount of retrieved sequences, which were probably performing an incomplete oxidation of the carbon source in the sulfidogenic UASB reactor. As single substrates, specific sulfate reduction rates (SRRs) using low molecular weight (MW) carbon sources (formate and ethanol) were 39% higher than those using high-MW ones (propionate, 1,3-propanediol and butanol). However, SRRs in glycerol-fed tests showed that 1,3-propanediol played a major role in sulfate reduction in addition to formate and ethanol.

Highlights

Sulfate is an anion widely present in natural environments
Activity tests presented were performed to study the sulfate reduction mechanism using glycerol as carbon source using sludge collected from the reactor when it was performing under sulfidogenic conditions
From day 200 to day 400, only volatile fatty acids (VFAs) were considered as the intermediate products of glycerol degradation, but a significant carbon imbalance was found during the process of glycerol fermentation

Summary

Introduction

Sulfate is an anion widely present in natural environments. high concentrations of sulfate can be toxic to aquatic life (Karjalainen et al, 2021). Sulfate can be reduced to hydrogen sulfide by sulfate-reducing bacteria (SRB) under anaerobic conditions generating further problems since hydrogen sulfide is poisonous and corrosive. As an alterna tive to costly physical-chemical technologies, environmentally friendly, biological processes arose recently, some considering the valorization of S-rich emissions into elemental sulfur (biosulfur) (Mora et al, 2020a), a value-added product currently obtained from the petrochemical in dustry. Since microbial communities able to reduce sulfate directly to biosulfur have not been described yet, one biological-based alternative relies on a two-stage process (Mora et al, 2020a). Sulfate is reduced to sulfide in an upflow anaerobic sludge blanket (UASB) bioreactor, and subsequently, sulfide is partially oxidized to elemental sulfur in a second bioreactor under microaerobic or anoxic conditions. Further fundamental analysis is warranted to reveal the un derlying mechanisms in the UASB to develop a more robust, transferable technology to field applications

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