The effect of lauric acid shock loads on the biological and physical performance of granular sludge in UASB reactors digesting acetate

Abstract

Abstract The specific activity of acetotrophic methanogens and the physical behaviour of granular sludge in laboratory‐scale upflow anaerobic sludge bed (UASB) reactors subjected to shock loads of lauric acid in the absence and presence of calcium were studied. In the absence of calcium, lauric acid completely inhibited acetotrophic methanogens above a threshold level of 100 mg C 12:0 dm −3 , whereas no inhibition occurred below this threshold concentration. Addition of an equivalent amount of calcium to wastewater containing lauric acid prevented inhibition of acetotrophic methanogens at least up to 1500 mg C 12:0 dm −3 . Addition of less than an equivalent amount of calcium apparently removed more than a stoichiometric amount of lauric acid: 50 % inhibition occurred at approximately 700 mg ‘free’ or excess C 12:0 dm −3 . The results indicate that complete sludge wash‐out from conventional UASB reactors is likely to occur within 2‐8 h if the system is overloaded with an influent containing more than 100 mg C 12:0 dm −3 . Calcium did not prevent wash‐out.