The sewage treatment plant is a kind of production plant, where, except products, the waste material come into being. The main wastes of the sewage treatment plant are sewage sludge. The basic algorithm of the sewage sludge utilization provides for waste storage on the storage yard, composting after mechanical dehydration and natural utilization. The biogas which is a product of the sludge fermentation can be also take as the waste from the sewage treatment plant The simplest form of the biogas utilization is the combustion on the torch. The more complicated algorithm provides for the energy utilization of the sewage sludge. It causes of the technical, economical and ecological problems. These problems basing on experiences of the sewage treatment plant in Rzeszow were presented in the present work. As one of problems of the sewage sludge energy utilization is the procedure of the determining of the sewage sludge higher heating value HHV and sewage sludge lower heating value LHV. Because the moisture content of the sewage sludge is very high, the modification of the calorimetric method to determined HHV and LHV is necessary. Chosen results of the sewage sludge HHV and LHV measurements on different stages of their transformation were presented. The other problem presented in the paper is the problem of the biogas energy utilization. It is connected with the inclusive of the combined heat and power units (CHP) feeding by biogas into the energy system of the sewage sludge treatment plant. Values of parameters describing applied CHP systems in the sewage treatment plant in Rzeszow were presented. In the conclusion one found that the energy utilization of the waste from the sewage treatment plant should be oriented first of all on the biogas utilization. The energy, economic and ecological advantages are large in this case. The energy biogas utilization is connected with the utilization of the digested sludge which must be dried. It can be done using the solar energy (drying of the sewage sludge in the greenhouse) and the excess thermal energy of the biogas from the CHP system.