Influence of cefazolin contamination on performance of two-stage and single stage anaerobic batch digesters

Anaerobic digestion of animal waste is a well-established technology for on-farm waste management and energy generation. Animal wastes often contain toxic substances such as antibiotic, which have been shown to cause varying degrees of biogas inhibition in single stage (SS) digestion system. Currently, useful information on influence of antibiotic contamination of substrates, particularly cefazolin (CFZ), on two-stage (TS) digestion system is limited. The effect of CFZ antibiotic on performance of two-stage and single batch systems digesting mixture of manure and milk from dairy cow was investigated. Batch experiments were conducted at 55 °C in TS (5 and 15 days for first and second stages, respectively) and SS (20 days) digesters. Cefazolin was added at concentration of 5, 10, 20, 40 and 80 mg/l. Control experiments, with no addition of CFZ were also conducted. In TS system, all concentrations of CFZ exhibited complete or near complete inhibition of hydrogen production in the first stage, with methane reductions of 9.2-56.0% in the second stage as compared with control treatment. Corresponding biogas inhibitions for the system ranged from 7.3-29.1%. The inhibition resulted in reduction of energy recovery by 16.7-60.6%. For SS system, CFZ addition reduced 39.8-68.3% of methane production while total biogas inhibition ranged 24.0-39.0%. The inhibition also resulted in reduction of energy recovery by 39.7-68.3%. Evidently, lower biogas inhibitions and reduction in energy recovery were experienced in TS system as compared with SS system. The results thus suggest that TS system can be an alternative to conventional SS system for on-farm management of CFZ contaminated wastes.