Anaerobic digestion of ozonized biosolids

The effect of an oxidative pretreatment on the anaerobic digestion of sewage sludge was investigated. Sewage sludge from a domestic wastewater treatment plant was partially oxidized by ozone. The pretreatment could alter up to 67% of the organic matter: 29±3% was solubilized, 38±9% was removed. Anaerobic degradability tests indicated that the pretreatment step enhanced the subsequent anaerobic sludge digestion. The methane production was increased by a factor of 1.8 after an ozone treatment at a dose of 0.1 g O3/g chemical oxygen demand (COD), while the methane production rate was 2.2 times higher compared to the untreated sludge. Higher ozone doses, although still positive, were found to have a less pronounced effect. Limited ozone treatment appears compatible with subsequent digestion of biosolids and economically feasible.