Anaerobic degradation of cornstarch in wastewater in two upflow reactors

Abstract

Wastewater containing high concentrations of cornstarch was treated in two 8.5-L upflow reactors: upflow anaerobic sludge blanket (UASB) and a modified anaerobic filter (AF). Both reactors were operated in parallel at 37°C and pH 6.8-7.9 over 510 d with increased loadings of chemical oxygen demand (COD). Results showed that, in spite of having different sludge concentration profiles, both reactors, with 12 h of hydraulic retention time, removed an average of 95.3% of COD from wastewater containing up to 45,000 mg-COD · L-1 (loading rates up to 90 g-COD · L-1 · d-1). At Loading rates up to 75 g-COD·L-1d-1, only 0.42% and 0.80% of starch particulates remained unhydrolyzed and were washed out by the effluent from UASB and modified AF reactors, respectively. Of the COD removed, 85.9% was converted to methane and the rest was converted to biomass with a net sludge yield of 0.10 g-VSS · g-COD-1. Both reactors failed at loading rates higher than 90 g-COD · L-1 · d-1, because of severe washout of solids. The sludge granules had a methanogenic activity of 1.90-1.92 g-methane-COD · g-VSS-1 · d-1 and consisted of various trophic bacteria in the order of 108-109 m/L.