Changes in Performance and Active Microbial Communities Due to Single and Multiple Effects of Mixing and Solid Content in Anaerobic Digestion Process of OTC Medicated Cattle Manure

Oxytetracycline (OTC) is used in animal husbandry which is poorly metabolized and excreted in manure. In this study, effect of two operational parameters (mixing rate and solid content) and presence of OTC on dynamics of active microbial populations were investigated along with inhibition on biogas production and elimination of OTC. Anaerobic digester studies were carried out batch-wise in 1000 ml digesters with active volume of 600 ml for 30 days. Two different sets were conducted by diluting blank and medicated manures to 5-6% and 8-9% Volatile solid (VS) content. Inoculum seed from a manure digester was added at a ratio of 1:10. Manure slurries were digested then at mixing rates of 90 rpm and 120 rpm at 37 0 C. In all digesters, VS content decreased by 30%-50% after 20 days as biogas yields of medicated manure digesters decreased by 14%-24% in respect to control digesters after 30 days.  Decrease in biogas yield was lower (14%-17%) in high VS content digesters compared to decrease in low VS content digesters (20%-24%). Methane content of biogas was determined as 62±3% in all digesters. OTC concentration decreased by 55-70% indicating a half life of 22-27 days during anaerobic digestion. FISH analyses showed an increase in activity with time and mixing rate. Activity of microbial cells were decreased with increased VS content and presence of OTC. Digesters were dominated by hydrogenotrophic methanogens where acetoclastic methanogens were represented by Methanosarcina spp.