Performance of an Anaerobic Fluidized Bed Bioreactor (AnFBR) for digestion of municipal biosolids and bioethanol wastes

The primary objective of this work was to investigate the treatability of very high suspended solids with different biodegradable particulate fractions, thin stillage (a by-product from the corn ethanol industry) as well as primary sludge, using an anaerobic fluidized bed bioreactor (AnFBR) employing zeolite with average diameter of (d_m) of 425-610 μm and specific surface area (SSA) of 26.5 m²/g as the carrier media. Due to the long-term impact of accumulation of inert suspended solids in the AnFBR and potential toxicity leading to failure, treatability of high suspended-solid streams can be very challenging. Despite the very high strength of thin stillage and primary sludge with chemical oxygen demand of 130,000 mg TCOD/L and 42,000 mg TCOD/L respectively and suspended solids of 47,000 mg TSS/L and 34,000 mg TSS/L, the AnFBR showed up to 88% and 82% TCOD and 78% and 82% TSS removal efficiencies from thin stillage and primary sludge respectively at very high organic and solids loading rates (OLR and SLR) of 29 kg COD/m³.d and 9.5 kg COD/m³.d and 10.5 kg TSS/m³.d and 10.3 kg TSS/m³.d respectively at hydraulic retention time (HRT) of 3.5 and 4 days. Maximum methane production yields of up to 40 L_CH4/L_{Thin stillage} and 9.7 L_CH4/L_PS were achieved for treating thin stillage and primary sludge respectively corresponding to biogas production rate per reactor volume of 15.8 L_gas/L_reactor.d and 1.22 L CH₄/L_reactor.d.