Effect of antibiotics on psychrophilic anaerobic digestion of swine manure slurry in sequencing batch reactors

The effect of antibiotics on the psychrophilic anaerobic digestion (PAD) of swine manure slurry in sequencing batch reactors (SBRs) was investigated. Six antibiotics, tylosin, lyncomycin, tetracycline, sulphamethazine, penicillin and carbadox, were individually added to the pig diet at their maximum prescribed level. Manure slurries collected from pigs receiving control and medicated diets were individually fed to pairs of SBRs at organic loading rates (OLRs) ranging from 2.2 to 3.5 g total chemical oxygen demand (TCOD) per litre of bioreactor initial sludge volume per day. Three mixtures of slurries from pigs fed on individual, antibiotics were also tested at OLRs varying between 2.5 and 3.2 g TCOD/l/d. The presence of penicillin and tetracycline in manure slurries reduced methane production by 35% and 25%, respectively. However, the slurries from pigs receiving the other antibiotics and the slurry mixtures did not significantly affect (P > 0.05) methane production. In addition, the presence of individual and combined antibiotics did not have noticeable adverse effects on process stability and treatment efficiency. Total and soluble COD (TCOD and SCOD) reduction, total and volatile solids (TS and VS) removal, pH and volatile fatty acid (VFA) concentrations in experimental units were not statistically different (P > 0.05) than in the controls. In all bioreactors, the TCOD, SCOD, TS and VS removal exceeded 62%, 76%, 65% and 75%, respectively. Crown Copyright (C) 2000 Published by Elsevier Science Ltd. All rights reserved.