The objective of this work was the analysis of the quality of sewage sludge from the sewage-treatment plant in Suwałki and studies into composting process of sewage sludge with organic wastes inoculated with Trigger-4 biopreparation on the usability of such sludge for natural utilisation. High quantities of organic matter and nutrients were discovered in the tested sludge. The contents of heavy metals were low and they did not exceed acceptable standards for application in agriculture and in land reclamation. No presence of live and not live eggs of nematodes, Ascaris lumbricoides, was discovered in the sewage sludge. A large Coli titre were identified in the material, at a lower presence of bacteria Clostridium perfingens. Because of this, the tested sludge cannot be utilised in agriculture. The material of sludge can only be used for land reclamation for non-agricultural use and for growing plants that will not be used for consumption or production of fodder as well as for energy crops. The experimental material was compost obtained in “Dano” technology form non-segregated solid wastes. The compost was inoculated with Trigger-4 biopreparation. The chemical changes of  compost mass were analysed during composting. It was found that the microorganism addition to the compost mass of sewage sludge and compost “Dano” caused most intensive decomposition of organic wastes. The nitrogen content of composted organic materials only increased in the initial period of the composting process. The amount of phosphorus had a small upward trend in the mass of waste enriched with the biopreparation. The effect of Trigger-4 on composting process was noted. The components of Trigger-4 such as selected active microorganisms and enzymes accelerate the decomposition of organic matter in composted mass of sewage sludge with biowaste fraction, odours are not associated with the process of composting.