Effect of Hydraulic Retention Time on Up-flow Anaerobic Stage Reactor Performance at Constant Loading in the Presence of Antibiotic Tylosin

The present investigation was aimed at determining the impact of the macrolide antibiotic Tylosin in reduced HRT at constant organic loading rate (OLR) by varying feed substrate concentration in an up-flow anaerobic stage reactor (UASR). The antibiotic concentration was maintained at 200 mg.L, at constant OLR of 1.88 kg COD.m.d, by varying feed substrate concentration to the UASR and the HRT was decreased gradually from 4 to 1 d. Throughout the operation period, brewery wastewater was used as simple feed substrate to elevate the concentration of easily biodegradable carbon in comparison with the concentrations of more recalcitrant Tylosin substrate. The reactor alkalinity was controlled in all the stages of UASR by adding 1000 – 2000 mg.L CaCO3. Results showed the total COD removal efficiency at 4 d HRT was around 92%, after which point there was a slight decrease at 3 and 2 d HRT (average 82%), and this was reduced further (average 77%) at a HRT of 1 d. The UASR showed stable operation with effluent volatile fatty acid (VFA) less than 300 mg.L throughout the experimental period (HRT 4 – 1 d). Moreover, the average methane yield (CH4.kg CODr) showed a relatively constant profile and was largely unaffected by HRT in all the stages of UASR. These results show that bacteria were readily adapted to wastewater containing Tylosin at lower HRTs and did not affect the reactor performance substantially.