The potential of advanced treatment methods for sewage sludge

Excess sludge is an inevitable drawback of the waste‐activated sludge process. Both the reduction of the amount of sludge produced and improving its dewaterability are of paramount importance. With more stringent environmental and legislative constraints, increasing sludge production and limited disposal options, new reduction alternatives have to be found. This paper presents different advanced sludge treatment (AST) processes, i.e. thermal hydrolysis (neutral, acid, alkaline) and chemical oxidation using H₂O₂. Semi‐pilot and pilot‐scale experiments are conducted in order to achieve optimum treatment conditions (T, pH, concentration of reagent, catalyst, etc.) with respect to sludge dewaterability. Additional targets are the removal of heavy metals and pathogens from the sludge so that the residual filter cake can be used for land application. Although all methods are promising, peroxidation gave the best results with respect to improving sludge dewaterability and product quality of the residual filter cake. The amount of dry solids per equivalent‐inhabitant per day (DS/IE.d) was reduced from 60g DS/IE.d to 33g DS/IE.d and the percentage DS of the sludge cake was 47 per cent, which is a significant improvement of traditional sludge dewatering yields. This results in a significantly reduced energy for subsequent drying (94kJ/IE.d compared to 437kJ/IE.d for the traditional treatment).