Inhibitory effects and biotransformation of acrylic acid in computer-controlled pH-stat CSTRs

In this study, the inhibitory effects and anaerobic biotransformation of ac rylic acid in computer-controlled pH-stat completely stirred tank reactors (CSTRs) with two different cultures, namely unacclimated and acrylate-accli mated acetate-enriched Methanosarcina and homogenized (crushed) granular cu ltures, were investigated. The microbial acclimation, influent concentratio n, and loading rate of acrylic acid were studied in the experiments. The ex perimental results revealed that methanogenic cultures at a concentration o f 3200 +/- 80 mg/L as volatile suspended solids (VSS) could be acclimated t o acrylic acid up to a loading rate of 220 mg/L per day (0.068 g acrylic ac id/g VSS per day) in the presence of a constant acetate concentration of 20 00 +/- 200 mg/L as the primary substrate after 300 days of acclimation. The same cultures (680 +/- 80 mg/L as VSS), after 80 days of acclimation to ac rylic acid as the sole carbon source, transformed acrylic acid up to the lo ading rate of about 200 mg/L per day (0.29 g acrylic acid/g VSS per day) al most completely (>99%) to acetic and propionic acid, but could not effectiv ely metabolize these intermediate products. Acrylate-acclimated homogenized granular cultures (6900 +/- 80 mg/L as VSS) effectively metabolized 2200 m g/L per day (0.32 g acrylic acid/g VSS per day) of acrylic acid, as the sol e carbon source, after 50 days of severe inhibition. (C) 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 62: 200-207, 1999.