Anaerobic digestion of tannery waste: Semi-continuous and anaerobic sequencing batch reactor processes

Disposal of the vast amounts of tannery waste that are currently generated is a significant problem. Anaerobic treatment of different types of tannery waste (fleshings, skin trimmings and wastewater sludge) was investigated. The biochemical methane potential is the same at 37 °C or 55 °C and an assay of this was shown to be an appropriate screening tool with which to estimate the susceptibility of a substrate to anaerobic digestion. The start-up procedure of a tannery waste thermophilic anaerobic digestion in 100 days using seed from mesophilic digester processing municipal sludge is presented. The specific methane production potential at 55 °C is estimated to be 0.617 m3 kg−1 of volatile suspended solids for tannery waste sludge, 0.377 m3 kg−1 for tannery waste trimmings and 0.649 m3 kg−1 for tannery waste fleshings. Additional concerns such as chromium content, salinity and temperature fluctuations were also addressed. Chromium content and salinity showed no adverse effects; however a reactor temperature reduction of 4.4 °C led to a drop in biogas production of 25%, indicating a requirement to keep the temperature constant at 55 °C.