Anaerobic digestion of slaughterhouse wastewater using a combination sludge blanket and filter arrangement in a single reactor

A laboratory-scale anaerobic reactor, in which the bottom two-thirds were occupied by a sludge blanket and the upper one-third by submerged small cubes of polyurethane foam, was evaluated for the anaerobic treatment of slaughterhouse wastewater. The reactor was operated at 35°C during the two experimental studies. In the first study, the chemical oxygen demand (COD) concentration of the wastewater was increased from 3•74 to 10•41 g l−1 whilst maintaining a constant hydraulic retention time (HRT) of 1•5 days. In the second, the HRT was decreased from 1•35 to 0•50 days, whilst maintaining a constant influent COD concentration of 10•41 g l−1. The results showed that this type of reactor was suitable for the anaerobic treatment of this wastewater and demonstrated a high COD removal of between 90•2 and 93•4% at organic loading rates between 2•49 and 20•82 g COD l−1 day−1. At an HRT of 0•5 days, the reactor achieved a methane yield of 0•345 l CH4 STP per gram of COD removed. This yield is higher than the values reported in previous studies.