Pretreatment processes for the recycling and reuse of sewage sludge

This paper focuses on mechanical disintegration and will compare its results to thermal and ozone treatment. Several mechanical methods can be used for disintegration of sewage sludge. The methods differ in energy consumption and suitability of the machines for practical application, which is of great influence on the selection of the method. Thermal disintegration processes have a higher energy consumption than mechanical methods, but they can use low cost thermal energy instead of electrical energy. The highest solution of organic components is achieved using ozone treatment. Several reuse options of disintegrated sludge in aerobic and anaerobic processes are explained. An acceleration and enhancement of the anaerobic stabilisation process is observed, especially if excess sludge is used. Mechanical disintegration leads to better results than thermal treatment in the range of 60 to 130 degreesC. For the aerobic process the substitution of external proton donors is of special interest. High denitrification rates can be achieved, if the sludge is adapted to the substrate. Increasing the concentration of nitrogen and phosphorus in the supernatant, in order to recycle these valuable compounds, mechanical disintegration and ozone treatment seem to be more suitable than thermal disintegration.