Anaerobic Degradation of Molasses Stillage in a Pilot UASB Reactor

Abstract

The feasibility of a mesophilic anaerobic treatment of an alcohol distillery wastewater (beet molasses stillage) was studied in a 1300 l Upflow Anaerobic Sludge Blanket (UASB) reactor for a period of 180 days. The system was seeded with 600 L of mesophilic anaerobic sludge harvested from the bottom of a dairy anaerobic lagoon. Nutrients were added to acidified effluent and after adjusting the pH in an equalization tank, the system was fed with a diluted effluent containing COD in the range of 1000-11000 mg/L at 30degree C. Initially, the system had an OLR of 1 kg COD m^-3 d^-1 and upflow velocity was maintained at 0.6 m/h (HRT=6 h) throughout the study. A gradual increase in OLR, through increased feed concentration, resulted in an excessive sludge washout necessitating the addition of calcium carbonate to act as a nuclei for granule formation. After 20 days of operation and at an OLR of 5.3 kg COD m^-3 d^-1, signs of granule formation were abserved, as indicated by increased VSS at the bottom of the reactor and reduced effluent VSS. At this point, the loading to the system was increased in four stages up to 16 kg COD m^-3 d^-1 (COD removal efficiency of 95%) to evaluate the optimum operational conditions of the system. During this period, the VSS/SS ratio remained constant at 0.83 and the SLR varied from 0.14 to 0.81 kg COD kg^-1 VSS d^-1. The performance of the system, based on unit reactor volume and unit microbial mass, was 10 kg SCOD m^-3 d^-1 and 0.25 kg SCOD kg^-1 VSS d^-1, respectively.