To assess the impact on greenhouse gas emission, different process schemes for municipal sludge treatment were evaluated based on the data from pilot-scale experiments and review of annual operation reports. A modified anaerobic digestion process with partial ozonation of digested sludge to improve biological degradability and the conventional anaerobic digestion process were compared with respect to the energy demand in each process schemes. Options for beneficial use of biogas included (1) application of biogas for power production and (2) recovery as an alternative to natural gas utilization. The analysis indicated that the partial ozonation process with power production led to minimal greenhouse gas emission because the extra energy production from this scheme was expected to cover all of the energy demand for the plant operation. Moreover, the final amount of dewatered sludge cake was only 40% of that expected from the conventional process, this significantly minimizes the potential for greenhouse gas emission in the subsequent sludge incineration processes.

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