THE EFFECT OF SCALE-UP ON THE DIGESTION OF SWINE MANURE SLURRY IN PSYCHROPHILIC ANAEROBIC SEQUENCING BATCH REACTORS

Abstract

This study evaluated the effect of scale-up on the performance and stability of anaerobic sequencing batch reactors (ASBRs) treating high-strength swine manure at 20°C. The performance of three semi-industrial-scale ASBRs, with total volumes of 2.5, 8, and 12 m3, respectively, was compared to that of laboratory-scale (42 L) ASBRs. Two bioreactor configurations, cylindrical with either flat or conical bottoms, were also evaluated. There was no significant difference (P < 0.05) in methane yield between the three semi-industrial-scale ASBRs. Over the six-month experimental period, methane production averaged 0.24 ±0.04 L CH4 per g total chemical oxygen demand (TCOD) fed to the bioreactors. The total and soluble CODs were reduced by 79.5% ±5.2% and 86.8% ±2.5%, respectively. The ASBRs were not affected by elevated ammonia-nitrogen concentrations throughout the experiment and high volatile fatty acid (VFA) levels in the mixed liquor at the end of the feed period. The bioreactors maintained an adequate pH and produced a high-quality biogas, with a methane content ranging from 57% to 78%. Results were similar to those obtained with laboratory-scale ASBRs, with volumes 60 to 285 times smaller than the volumes of the semi-industrial-scale ASBRs. Therefore, further scale-up of the semi-industrial-scale ASBRs, by a factor of 20 to 40, to operate on commercial farms should not affect process efficiency and stability. Results also indicated that the conical-bottom ASBR did not perform differently from the flat-bottom ASBRs at the scale tested in this study.