Does Reduction of Sludge Processes / Ozonation, Thermal Treatment have an Impact on Wastewater Treatment Efficiency?

Reducing Excess Sludge Production seems to be a very appealing solution to cope with the severe restrictions on conventional sludge disposal options. However, the treatment efficiency must be maintained. In this work, a thermal treatment or an ozonation were combined to an activated sludge process to reach a significant (more than 50%) sludge production reduction. The main objective was to study by batch and continuous experiments the effect of these combined treatment on the pollution removal efficiency. Thermal or oxidative treatments of sludge led to a COD release that depended on the stress dosage. In the case of ozonation, this released COD is entirely easily biodegradable and can be used for nutrient removal though a competition with the oxygen accumulated during ozonation must be taken into account. For thermal treatment, only 50% of the released COD is biodegradable and can be used for nutrient removal. Complete denitrification should be achieved considering the favourable N-TKN/COD ratio measured on the treated flow. On continuous pilot of the combined treatment systems, nitrification efficiency was around 95% though for thermal treatment a decrease on nitrifier cell concentration due to thermal stress was pointed out. Phosphorus should be removed by precipitation but, in the case of ozonation, because no cell deactivation occurred during the oxidative stress, a P concentration could be achieved via the PAO metabolism.