Abstract
Trace elements (TEs) are vital for anaerobic digestion (AD), due to their role as cofactors in many key enzymes. The aim of this study was to evaluate the effects of specific TE deficiencies on mixed microbial communities during AD of soluble polymer-free substrates, thus focusing on AD after hydrolysis. Three mesophilic (37 °C) continuous stirred-tank biogas reactors were depleted either of Co, Ni, or a combination of Se and W, respectively, by discontinuing their supplementation. Ni and Se/W depletion led to changes in methane kinetics, linked to progressive volatile fatty acid (VFA) accumulation, eventually resulting in process failure. No significant changes occurred in the Co-depleted reactor, indicating that the amount of Co present in the substrate in absence of supplementation was sufficient to maintain process stability. Archaeal communities remained fairly stable independent of TE concentrations, while bacterial communities gradually changed with VFA accumulation in Ni- and Se-/W-depleted reactors. Despite this, the communities remained relatively similar between these two reactors, suggesting that the major shifts in composition likely occurred due to the accumulating VFAs. Overall, the results indicate that Ni and Se/W depletion primarily lead to slower metabolic activities of methanogenic archaea and their syntrophic partners, which then has a ripple effect throughout the microbial community due to a gradual accumulation of intermediate fermentation products.
Highlights
Anaerobic digestion (AD) is an important biotechnology for combining organic waste treatment with renewable energy recovery [1]
Operational performance of Rctrl and RCo remained at stable state in terms of biogas production, volatile fatty acid (VFA) concentrations, pH, and total volatile solid (TVS) contents throughout the experiment (Figure 1)
The results show that the process performances, microbial community compositions, and overall functions of the reactors in this study were similar during the experimental period before trace elements (TEs) depletion
Summary
Anaerobic digestion (AD) is an important biotechnology for combining organic waste treatment with renewable energy recovery [1]. Cobalt (Co) is essential for the functioning of acetogens and methanogens due to its involvement in cobamide coenzymes, responsible for methyl group transfers [7,8]. Nickel (Ni) is vital for methanogenesis due to its functional role in porphyrinoid F430, a prosthetic group of the active site of methyl coenzyme M reductase, which catalyses the formation of methane [9]. Selenium and tungsten (Se and W) are important for acetogens and hydrogenotrophic methanogens due to their role in the function of hydrogenases and formate dehydrogenase, which transforms formate to CO2 and H2 [10,11]
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