The process of combustion of the briquettes produced from compost of liquid wastes originating from a municipal sewage-treatment plant as a substitute or supplement for fossil fuel is presented. The experiments were carried out in a laboratory-scale combustion chamber which simulated a fixed-grate boiler. The laboratory stand was equipped with apparatus enabling measurement of thermal parameters of the combustion process, as well as emission into the atmosphere of various components such as fly ash, nitrogen oxide, carbon oxide, sulfur dioxide, and heavy metals. It was established that the briquettes can be used as fuel and that similar combustion and thermal conditions to combustion of brown coal were achieved with an essential benefit of lower air pollution.