deterrent effect of ampicillin and gentamicin antibiotics on methanogenic activity of anaerobic biomass

background: the high percentage of consumed antibiotics by humans and animals is excreted with other residues from the body after its performance. by entering these compounds to the wastewater, they can disrupt the anaerobic treatment process. in this study, deterrent behavior of two ampicillin and gentamicin antibiotics are investigated on specific methanogenic activity (sma) of anaerobic biomass. methods: a total of 18 sma (specific methanogenic activity) tests were done using 120-mlvials in batch mode. in each vial 40%, 37% and 23% (v/v) of substrate, biomass and biogas were placed respectively. each test lasted in range of 20 to 25 days. produced methane was measured by gas replacement with 2n koh solution as co2 absorbent. three volatile fatty acids (vfas) including acetic, propionic, and butyric acids were used as co-substrate. findings: in this study, in the concentrations of 200, 500 and 1000 mg/l of  ampicillin, the cumulative sma were 25, 35, and 46 ml ch 4 /g vss.d for propionic acid, 66, 101, and 154 ch 4 /g vss.d for acetic acid and 198,140, and 245 ch 4 /g vss.d for butyric acid, respectively. also, in the concentrations of 100, 500 and 1000 mg/l of gentamicin the cumulative sma were 54, 72, and 71 ml ch 4 /g vss.d for propionic acid, 141, 204, and 257 ml ch 4 /g vss.d for acetic acid, and 139, 74, and 85.5 ml ch 4 /g vss.d for butyric acid, respectively. conclusion: at the same concentrations, ampicillin has more deterrence effect on anaerobic biomass than gentamicin. on vfas, the deterrence of propionic acid is greater than acetic and butyric acids.