Performance of an anaerobic fluidized bed bioreactor (AnFBR) for digestion of primary municipal wastewater treatment biosolids and bioethanol thin stillage

Abstract

The primary objective of this work was to investigate and compare the treatability of very high suspended solids with different biodegradable particulate fractions and COD fractionation, thin stillage (a by-product from the corn ethanol industry) as well as primary sludge from municipal wastewater treatment, using an anaerobic fluidized bed bioreactor (AnFBR) employing US Mesh 30 × 40 zeolite with a diameter of (dm) in the range of 425–610 μm and specific surface area (SSA) of 26.5 m2/g as the carrier media. Each experimental run lasted over a six-month period. Due to the long-term impact of accumulation of inert suspended solids in the AnFBR and potential active biomass washout 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 0.31LCH4/gCOD and 0.25LCH4/gCOD were achieved for thin stillage and primary sludge respectively corresponding to biogas production rate per reactor volume of 15.8 Lgas/Lreactor d and 1.22LCH4/Lreactord.