Ozonation of industrial and sewage sludge is a suitable process for minimizing the sludge production of activated sludge processes. The ozonation has the advantage for complete oxidation of volatile suspended solids (VSS) of combining partial sludge oxidation with subsequent biological oxidation. This paper describes the evaluation of two full-scale sewage sludge ozonation investigations for subsequent aerobic stabilisation as well as for subsequent anaerobic stabilisation compared to different sludge treatment processes. For both the anaerobic and aerobic application, sludge liquefying by release of 110 and 160 mg COD per g total suspended solids (TSS) has been reached at specific ozone consumption of 0.03 and 0.06 kg O3 per kg TSS, respectively. The subsequent biological treatment has reached a mass reduction of 20-35% for the aerobic and 19% for the anaerobic stabilisation. For both applications the specific ozone consumption was about 0.05 kg O3 per kg TSS to be treated. A comparison with mechanical and thermo-chemical sludge mass reduction methods shows that the mass reduction potential of ozonation is presently higher. Even though costs for sludge ozonation are higher compared to other methods, the optimisation potential for cost reduction of sludge ozonation is obvious from the results presented in this paper.

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