The goal of the thesis is to optimize the exploitation costs and parameters of a Chemical-Pharmaceutical Industry's WWTP in Switzerland. After having described the WWTP's scheme and its performance over time, an economical assessment was made. The two major costs components were found to be the excess sludge disposal and the energy consumed by the air compressors in the biological basins: the rest of the thesis focuses on trying to reduce these costs. First, a feasibility study, a lab test and a pilot test were done on a decanter in order to evaluate the economical advantage that a dehydration treatment step could have.