Competition Between Chemolithotrophic Acetogenesis and Hydrogenotrophic Methanogenesis for Exogenous H2/CO2 in Anaerobically Digested Sludge: Impact of Temperature.

Bo Fu,Ralf Conrad,Xin Jin,He Liu,Hongbo Liu

doi:10.3389/fmicb.2019.02418

Abstract

Anaerobic digestion is a widely applied technology for sewage sludge treatment. Hydrogen and CO2 are important degradation products, which serve as substrates for both hydrogenotrophic methanogenesis and chemolithotrophic acetogenesis. In order to understand the competition between these processes for H2/CO2, sludge samples were incubated under H2/CO2 headspace at different temperatures, and analyzed with respect to turnover of H2, CO2, CH4 and acetate including their δ13C values. At 15°C, 13C-depleted acetate (δ13C of −41 to −43‰) and transient acetate accumulation were observed under H2/CO2, and CH4 accumulated with δ13C values increasing from −53 to −33‰. The copy numbers of the fhs gene, which is characteristic for acetogenic bacteria, were at 15°C one order of magnitude higher in the H2/CO2 incubations than the N2 control. At 30°C, however, acetate did not accumulate in the H2/CO2 incubation and the δ13C of CH4 was very low (−100 to −77‰). At 50°C, isotopically enriched acetate was transiently formed and subsequently consumed followed by the production of 13C-depleted CH4. Collectively, the results indicate a high contribution of chemolithotrophic acetogenesis to H2/CO2 utilization at 15°C and 50°C, while H2/CO2 was mainly consumed by hydrogenotrophic methanogenesis at 30°C. Fermentative production and methanogenic consumption of acetate were active at 50°C.

Highlights

Anaerobic digestion has been widely used for stabilization and energy recovery of sewage sludge (Kelessidis and Stasinakis, 2012)
Anaerobic digestion of organic matter is achieved in four steps: hydrolysis, fermentation, acetogenesis, and methanogenesis (Adekunle and Okolie, 2015)
Methanogenic archaea and acetogenic bacteria were quantified by amplification of the mcrA and fhs genes, respectively using primers listed in fhs-f /fhs-r Table 1 (Angel et al, 2011; Xu et al, 2015)

Summary

Introduction

Anaerobic digestion has been widely used for stabilization and energy recovery of sewage sludge (Kelessidis and Stasinakis, 2012). Anaerobic digestion of organic matter is achieved in four steps: hydrolysis, fermentation, acetogenesis, and methanogenesis (Adekunle and Okolie, 2015). Acetate and CH4 are the respective products of chemolithotrophic acetogensis (4 H2 + 2 CO2 → CH3COOH + 2 H2O) and hydrogenotrophic methanogenesis (4 H2 + CO2 → CH4 + 2 H2O). Competition Between Acetogenesis and Methanogenesis directly with hydrogenotrophic methanogens for H2/CO2 as substrates (Lopes et al, 2015; Liu et al, 2016). The emission of CO2 and CH4 during anaerobic digestion of sewage sludge has received attention because of the greenhouse effect (Niu et al, 2013). The generation of acetate instead of CH4 from sewage sludge is a promising technology for waste recycling and reduction of greenhouse gas emission (Agler et al, 2011)

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