Effect of Amoxicillin on Biogas Production and the Eschericia coli Population in Biogas Systems Treating Swine Wastewater

The effect of amoxicillin concentrations (0, 200 and 400 ppm) on biogas production and the Eschericia coli population in lab-scale biogas systems treating swine wastewater was examined. Three anaerobic fermentation reactors (with an available volume of 25 1), containing wastewater collected from a swine farm and free from antibiotics, were operated for eight weeks. After eight weeks, the cumulative yields of biogas and methane in the control group (0 ppm) were the highest (11,563 ml of biogas and 542 ml of methane, as 100%). The cumulative biogas yields in the group 1 (400 ppm) and group 2 (200 ppm) decreased to 70.5% and 90.04% compared to the control group, respectively. Moreover, group 1 and group 2 had cumulative methane yields decreased to 31.9% and 65.3% respectively, compared to the control group. The total suspended solids (TSS) and chemical oxygen demand (COD) were highest for the group 1 (352 and 930 mg/l, respectively) and subsequently decreased for the group 2 (308 and 570 mg/l, respectively) and the control group (121 and 275 mg/l, respectively). Volatile fatty acid (VFA) concentrations were the highest in the control group (563 mg/l), and decreased in other treatment groups (488 and 225 mg/l in group 2 and 1, respectively). The pH values did not change for any group. In addition, it was found that Escherichia coli decreased over time in all groups. Over a five week period, amoxicillin concentrations decreased each week from 400 to 178, 99.1, 88.23, and 2.12 ppm respectively (group 1) as well as from 200 to 140.6, 55.36, 36.23 ppm and no detection respectively (group 2). These results illustrate that although the concentration of detectable amoxicillin decreases over time, its presence results in a decrease in the cumulative biogas and methane produced. However, based upon the analytical assay, the concentration of detectable amoxicillin is decreasing in the biogas systems.