Long term effects of the ozonation of the sludge re cycling stream on excess sludge reduction and biomass activity at full-scale

This paper presents a full-scale experience of sludge minimization by means of short contact time ozonation in a WWTP mainly fed on textile wastewater. WWTP performance over a 5-year operational data series was analyzed and compared with a one-year operation with sludge ozonation. Lab-scale respirometric tests were also performed to characterize biomass activity before and after the ozone contact reactor. Results suggest that sludge ozonation: (1) is capable to decrease excess sludge production by 17%; (2) partially decreases both N removal, by lowering the denitrification capacity, and P removal, by reducing biomass synthesis; (3) increases the decay rate from the typical value of 0.62 d-1 to 1.3 d-1; (4) decreases the heterotrophic growth rate from the typical value of 0.67 to 0.58 gCOD/gCOD