I am often questioned by customers of the impact of the elemental sulfur in digester headspace (by biological sulfide oxydation treatment) that falls back into sludge digester.
my customers often observe very high H2S concentration in biogas when large amounts of elemental sulfur from headspace falls in the digestate. I thought it was caused by the sulfate/sulfite or even organic sulfur fraction in these elemental sulfur congregation, but now, I doubt it.
Does anyone know of the fate of elemental sulfur in digester sludge? Does biological sulfur reduction occur and enrich digestate in HS- (and therefore digester headspace in H2S, again!)?
How rich are sulfur congregation in digester headspace in organic sulfur, sulfite and or sulfate (in case of oxygen excess)?
Thanks in advance.
Gilles ADAM
Sulfur reduction uses elemental sulfur (S0) and generates hydrogen sulfide (H2S) as the main end product. This metabolism is largely present in extreme environments where, especially in recent years, many microorganisms have been isolated, bringing new and important data on the subject.Hydrogen sulfide is generated in anaerobic digesters primarily through the decomposition of organic matter and the use of sulfate as a terminal electron acceptor by sulfate-reducing bacteria (SRB).A significant source of sulfur in anaerobic digesters comes from the hydrolysis and fermentation of proteins and associated amino acids, resulting in a release of both hydrogen sulfide and methylated sulfurs.The H2S concentration in unprocessed biogas ranges from 50 to 10,000 parts per million (ppm), depending upon the feedstock’s. The hypothesis that H2S oxidation rates are limited, in part, by the surface area available for oxygen transfer, and can be increased by growth of bio films containing H2S oxidizing bacteria.At aeration rates corresponding to 2% to 10% of air per volume of biogas, residual oxygen levels in the biogas ranged from 0.1 to 3%. Although we predicted that any amount of excess oxygen would indicate complete oxidation of H2S, H2S levels in the biogas were consistently less than 500 ppmv only when residual oxygen levels within the biogas were ≥ 0.3% (v/v) . With respect to the effect of biogas oxygen concentrations above 1%, the results are less clear because of relatively few (and variable) results under these conditions
Sure does and is not rare. Sulfur can be used as an electron sink (like oxygen) under anoxic conditions.
"Most sulfate-reducing bacteria can also reduce other oxidized inorganic sulfur compounds, such as sulfite, thiosulfate, or elemental sulfur (which is reduced to sulfide as hydrogen sulfide)."
https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Boundless)/05%3A_Microbial_Metabolism/5.09%3A_Anaerobic_Respiration/5.9C%3A_Sulfate_and_Sulfur_Reduction
Hello Gilles Adam ,
Biogenic elemental sulfur S° is produced by partial oxidation of sulfide S-- and can be considered as stable and inert in the normal operating conditions (pH, ORP, temperature) of anaerobic digesters. The S° can be removed/recovered from the liquid digestate as solids. This partial oxidation and separation method is also applied to remove H2S from the biogas.