[show abstract][hide abstract] ABSTRACT: This work studies the inhibitory effects and fate of the antibiotics oxytetracycline (OTC) and chlortetracycline (CTC) during the anaerobic digestion of pig manure. Both substances were added together in batch assays at concentrations of 10, 50 and 100mgL(-1). Control assays only with antibiotics (abiotic) as well as without antibiotics (biotic) were also conducted. Methane production was reduced by 56%, 60% and 62% at OTC and CTC concentrations of 10, 50 and 100mgL(-1), respectively. The IC(50) level calculated from these experiments was estimated to be around 9mgL(-1), a significant value considering the reported concentrations of these compounds in pig manure samples (up to 136mgL(-1)). Strong adsorption to solid matter was observed, which increased the stability of both substances. Antibiotic degradation was thus much higher in control assays, without solids, than those determined from assays including inoculum and manure substrate.
[show abstract][hide abstract] ABSTRACT: An optimisation protocol for maximising methane production by anaerobic co-digestion of several wastes was carried out. A linear programming method was utilised to set up different blends aimed at maximising the total substrate biodegradation potential (L CH(4)/kg substrate) or the biokinetic potential (L CH(4)/kg substrate d). In order to validate the process, three agro-industrial wastes were considered: pig manure, tuna fish waste and biodiesel waste, and the results obtained were validated by experimental studies in discontinuous assays. The highest biodegradation potential (321 L CH(4)/kg COD) was reached with a mixture composed of 84% pig manure, 5% fish waste and 11% biodiesel waste, while the highest methane production rate (16.4 L CH(4)/kg COD d) was obtained by a mixture containing 88% pig manure, 4% fish waste and 8% biodiesel waste. Linear programming was proved to be a powerful, useful and easy-to-use tool to estimate methane production in co-digestion units where different substrates can be fed.