Degradation of Sulfamethazine in Swine Manure via Anaerobic Digestion

Abstract. Antimicrobial resistance is becoming an imminent danger for human health, in part because of excessive consumption of antibiotics in the animal industry. Food and Drug Administration reports that in 2017, veterinary antibiotic (VA) use was more than five thousand tons. Anaerobic digesters were utilized to investigate the potential removal of VA in ‎swine manure. The goals of the study were evaluating VA degradation due to anaerobic digestion, and finding the best removal concentration range. Nine ‎laboratory anaerobic digesters (AD) were kept at 39±2oC in incubators and were 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 a ‎loading rate of 1.0 g-VS/m3-day. Biogas was collected using 10-L Tedlar bags for volume ‎measurement, which was measured and emptied every four days. Carbon dioxide concentration of the biogas and pH ‎values of the digestate as indicators digester performance were measured weekly. The AD process was allowed 1.5 to 2 HRT to stabilize before adding ‎the target VA, Sulfamethazine. Tests were conducted to compare the effects of Sulfamethazine onto manure nutrients, volatile solid destruction, VA ‎degradation, and biogas production. Concentrations of Sulfamethazine added to the manure samples were 674, ‎‎770 and 866 mg/L with two replicates for each concentration. 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. Further tests were also performed to approve the ‎degradation of both VAs dissolved in water under room temperature and digester temperature. Some fluctuations ‎of biogas production and operating variables were observed because of the Sulfamethazine addition. The literature suggested ‎that sulfamethazine concentrations below certain levels have no inhibitory effect, while our tests showed that for all three concentration levels, biogas production declined. Lastly, metagenomics analysis performed on each group by using 50 most variable operational taxonomic units (OTUs)s and perfect discriminations were detected between groups. The effect of administration period and dosage of VAs on Phyla Firmicutes Proteobacteria, Synergistetes and Phylum Bacteroides was investigated. Then statistical analysis of the effect of different treatments on samples performed. Random forest analysis applied to obtain the most suitable OTUs as the biomarkers using “MeanDecreaseAccuracy”. These biomarkers' abundance can be employed to predict the sample‘s treatment group.