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Degradation of Veterinary Antibiotics in Swine Manure via Anaerobic Digestion

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2018 ASABE Annual International Meeting  1801460.(doi:10.13031/aim.201801460)
Authors:   Ali Hosseini Taleghani, Teng Teeh Lim, Chung-ho Lin
Keywords:   Anaerobic digester, antibiotics removal, antimicrobial, biogas, Chlortetracycline, Tylosin

There is an increasing concern about veterinary antibiotic (VA) use and the imminent risk of antibiotic resistant microorganisms. Laboratory scale anaerobic digesters were utilized to investigate potential mitigation of VA in swine manure. The aims of the study were evaluating VA degradation, finding the threshold of removal and recognizing the joint effects of Chlortetracycline (CTC) and Tylosin combination on digestion process. Nine laboratory anaerobic digesters (AD) were kept at 39±2ºC in incubators and loaded every two days. The digesters had a working volume of 1.38 L (in 1.89-L glass jar), with a hydraulic retention time (HRT) of 21 days and loading rate of 1.0 g-VS/m3-day. Biogas produced by each AD was collected using 10-L Tedlar bags for volume measurement, which was conducted every four days. Concentration of carbon dioxide of the biogas and pH values of the digestate were measured weekly. The AD process was allowed 1.5 to 2 HRT to stabilize before adding the VAs. Tests were conducted to compare the effects of VAs onto manure nutrients, volatile solid destruction, VA degradation, and biogas production. Concentrations of VA added to the manure samples were 263 to 298 mg/L of CTC, and 88 to 263 mg/L of Tylosin respectively. Analysis of VA concentrations before and after the AD process was conducted to determine the VA degradation. The process of measuring the relatively low VA concentrations involves using LC-MS-MS methodology. Additional tests were also conducted to confirm the degradation of both VAs dissolved in water under room temperature and digester temperature. Some fluctuations of biogas production and operating variable were observed because of the VA addition. The literature concluded that CTC and Tylosin below certain thresholds could increase the biomethane potential of manure, while higher concentrations inhibited the digestion, and the CTC removal rate declined exponentially. For VA degradation, all CTC was found degraded even only after 6 days of storage in water solution, thus there was no baseline to estimate the effects of anaerobic digestion. As for Tylosin, 100% degradation was observed due to the AD (removal rate was 100%, compared with 24%-40% degradation observed in the 12-day water solution storage). In addition, complete Tylosin degradation was also observed in the digestate samples treated with a mixture of the two VAs. The Enrofloxacin internal standard resulted in highly variable results and could not be used as correction factor. Choice of isotope internal standards and the LC-MS-MS recovery of VAs should be examined and improved in the future study.

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