Hydrogen sulphide removal in the anaerobic digestion of sludge by micro-aerobic processes: pilot plant experience

Abstract

H(2)S removal from biogas produced in anaerobic digestion of sludge through the introduction of oxygen under micro-aerobic conditions is studied. Research was carried out in two pilot plant reactors (working volume, 200 L each) treating sludge from WWTP with HRT of 20 days. Mixing was provided via sludge or biogas recirculation. Introduction of very low oxygen flow (0.013-0.024 L/L(reactor) d) successfully removed H(2)S content in biogas with an efficiency above 99%. Reactor performance during micro-aerobic operation in terms of biogas production, methane yield and COD removal were not affected by the amount of oxygen supplied, remaining stable and similar to the anaerobic behaviour. Sludge recirculation ( approximately 50 L/h) and biogas recirculation ( approximately 3.5 L/min) as mixing methods were found not significant in H(2)S removal from biogas while biogas recirculation reduced by 10 times dissolved sulphide concentration compared to sludge recirculation.

Oxygen Effects in Anaerobic Digestion – A Review

“…This may improve the economy of biogas generation plants enhancing the dissemination of such sustainable solutions. Partial aeration assisted anaerobic digestion has been recognized as a possible way to enhance AD performance [27][28][29][30].…”

“…Several studies [29,80,86,98] have demonstrated that limited aeration can be used to oxidize the sulfides generated in anaerobic digesters operating on S containing wastes. In anaerobic digestion, S compounds are reduced to HS -and H 2 S by the biological activity of anaerobic sulfate reducing bacteria (SRB) [99].…”

“…In anaerobic digestion, S compounds are reduced to HS -and H 2 S by the biological activity of anaerobic sulfate reducing bacteria (SRB) [99]. Minimizing the sulfides content benefits the process by minimizing the toxic effect of aqueous sulfides on methanogenic and acetogenic organisms [29,48,80,98] and also eliminates the formation of toxic, odorous and corrosive H 2 S gas [11,86]. SRB organisms compete with methanogens for organic substrates including acetate and hydrogen.…”

“…Introduction of a low oxygen flow (0.013 -0.024 L O 2 /L. d) into pilot scale CSTR reactors (200 L) fed with waste-water treatment plant (WWTP) sludge was capable of removing H 2 S in biogas almost completely without affecting the biogas generation, methane content or COD removal efficiency, according to a study carried out by Polanco et al [29]. They pointed out that the contact between O 2 and the aqueous sulfides or the mass transfer also play an important role in the overall success of the approach.…”

xygen Effects in Anaerobic Digestion - II

“…Recent research suggests, however, that a limited availability of free oxygen can be beneficial in a number of ways to make AD more efficient and flexible as a waste treatment and energy generation scheme (Johansen and Bakke, 2006;Polanco et al, 2009;Botheju et al, 2010a,b). Studying effects of limited oxygen supply in operation of AD is relevant also since maintaining meticulously anaerobic systems is often not easy.…”