The aim of this study was to investigate the effect of a common veterinary antibiotic in biogas plants. 20 mg/kg of oxytetracycline was intramuscularly injected into a cow and its concentration in manure, which was sampled daily during the following 20 days, was measured. A total of 20 % of the injected oxytetracycline was detected in manure. Collected manure samples on days 1, 2, 3, 5, 10, 15, and 20 were digested in triplicate serum bottles at 37 °C for 30 days. Control serum bottles produced 255 ± 13 mL biogas, whereas 50-60 % inhibitions were obtained for the serum bottles operated with samples collected for the 5 days after medication. Multivariate statistics used for the evaluation of FISH results showed that Methanomicrobiales were the main methanogenic group responsible for most of the biogas production. Numbers of active Bacteria and Methanomicrobiales were negatively correlated with the presence of oxytetracycline, whereas Methanosarcinales and Methanobacteriales were less affected.
Summary
Biogas residues contain microbial biomass, which contributes to the formation of soil organic matter. Whether the potential of biogas residues to increase soil organic matter can be enhanced by co‐application with compost, biochar or manure is unknown, however. The aim of this paper is to evaluate the effects of co‐amendment on the mineralization of biogas residues, carbon dioxide emissions and the carbon flow within the microbial food web. We determined the fate of 13C‐labelled microbial biomass present in biogas residues applied together with compost, biochar and manure to soil, by analysing CO2 and biomarker phospholipid fatty acids. Although the rate of mineralization constant of the slowly degrading carbon pool was not affected by co‐amendments, co‐amendment with manure resulted in a larger rate of mineralization constant of the readily degrading carbon pool of biogas residues. The incorporation of carbon was mainly to Gram‐negative biomass and was the smallest with manure co‐amendment, which indicated differences in bioavailability of the carbon source.
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