Comparative functional microbiome profiling of various animal manures during their anaerobic digestion in biogas production processes

Anaerobic digestion (AD) for bio-methane production continues to be plagued by major problems such as acidification, ammonia inhibition, long reaction periods, and expensive biogas upgrading. In this study, the authors suggest that intrinsic microbial roles during AD have previously been understudied yet they are the basis for discovery of effective and substrate-specific strategies for biogas process improvement. A comparison of the functional microbiome profiling of fresh cow, horse, pig, and chicken manures sourced from seven farms around Gauteng in South Africa was done. Correlation of profiles of the daily and cumulative biogas and bio-methane production determined in an automatic methane potential system (AMPTS), six intermediate AD compounds (propionate, butyrate, formic acid, lactic acid, ethanol, and acetate) observed using a modular Thermo Scientific Vanquish Core high performance liquid chromatography (HPLC) system, and active microbiome observed through Illumina 16S rDNA high-throughput sequencing suggests that cow manure AD went through 2 quick and efficient phases while horse manure showed 3 phases with hydrolysis being the rate limiting step, pig manure showed 4 phases and was dominated with hydrogenotrophic methanogenesis, and chicken manure had 2 phases affected by ammonia inhibition. It was inferred from the findings, that co-digestion of the horse manure within the first 9 days with cow manure, manipulation of Methanococcus hydrogenotrophs from pig manure AD in 2 stage reactor co-digestion systems, introduction of Methanococcus-rich inoculum from a pig manure AD system (between Day 15 & Day 24) as well as trace nutrient supplementation to boost SAOB, are strategies that can improve hydrolysis & methanogenesis in horse manure AD, upgrade biogas quality from various substrates, counter ammonia inhibition in chicken manure AD as well as in other similar substrates respectively.