Ozonation for sludge reduction and improved biological nutrient removal

Municipal wastewater is often treated at a centralized treatment facility based on Activated Sludge Process (ASP) where the production of (excess) activated sludge (bio-solids) is mostly not desired and further sludge handling often contributes to a large fraction of the total operational cost, depending upon the applicable legislation and/or sludge treatment and disposal practices. Further, the Biological Nutrient Removal (BNR) based on ASPs often pose extra cost due to the need for external carbon source (acetate, methanol etc.) for the optimal performance of denitrification and biological phosphorous removal. In this research, the excess sludge was ozonated and the filtrates were used in activity batch tests for anaerobic P-release, aerobic P-uptake and denitrification. Experimental results have shown that the ozone dose in the range of 0.1-0.2 g O3/g MLSS leads to a good degree of bio-solids destruction (sludge reduction) resulting in highly biodegradable organics. The use of ozonated sludge at those ozone doses as carbon source in the activity tests revealed that the soluble biodegradable organics can be successfully used for improved denitrification and biological P-uptake. Further, the process cost analysis showed the economic feasibility under complete sludge treatment scenario, where about 42% of sludge reduction is achieved and about 30% of the total operational cost reduction may be possible under assumed conditions