A process to improve anaerobic biodegradation of wastewater treatment sludges is investigated. Recalcitrant organic compounds which are contained in biologically stabilized digested sludge become biodegradable by partial oxidation using ozone and ozone in combination with hydrogen peroxide respectively. By oxidation with ozone, cell walls of microorganisms were destroyed and cytoplasm dissolved in sludge water. Water insoluble substances with high molecular weight were split into smaller, water soluble and biodegradable fragments. Sludge matrix composition regarding protein, lipid and polysaccharide content changed. After ozone consumption of 0.2 gram ozone per gram organic dry matter, the degree of biodegradation of organic matter during the following anaerobic treatment increased to 42%. Due to the oxidizing pretreatment, the dewatering results of the sludges after biological decomposition deteriorated. The polymer demand to reach isoelectric point increased with ozone consumption. Compared to mechanical, thermal and thermochemical disintegration, partial oxidation by ozone achieved highest degrees of organic matter decomposition in the following anaerobic biodegradation.

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