Anaerobic Degradation of Cornstarch in Wastewater in Two Upflow Reactors

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$\dot{s}$L ⁻¹ (loading rates up to 90 g-COD$\dot{s}$L ⁻¹ $\dot{s}$d ⁻¹ ). At loading rates up to 75 g-COD$\dot{s}$L ⁻¹ $\dot{s}$d ⁻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$\dot{s}$g-COD ⁻¹ . Both reactors failed at loading rates higher than 90 g-COD$\dot{s}$L ⁻¹ $\dot{s}$d ⁻¹, because of severe washout of solids. The sludge granules had a methanogenic activity of 1.90–1.92 g-methane-COD$\dot{s}$g-VSS ⁻¹ $\dot{s}$d ⁻¹ and consisted of various trophic bacteria in the order of 10 ⁸ –10 ⁹ m/L.