With their daily activities, people create waste that needs to be disposed of. As the population grows year by year, so does the amount of waste that needs to be disposed of. Most of the waste that is produced is municipal waste, and it has received the most attention in terms of disposal. A significant part of the waste is produced even when man has a positive effect on the environment, for example the treatment of wastewater. Purification removes harmful and unwanted substances from wastewater, but sludge formation is inevitable. The sludge needs to be effectively removed, further treated and disposed of because it contains various substances, many of which are harmful to the environment and living things. In addition to the harmful substances, the sludge also contains nutrients and biomass. Therefore, the sludge can be used in agriculture, but it needs to be further processed and kept clean and stable to prevent odors, which result from the biodegradation of microorganisms. Otherwise, the sludge is disposed of in landfills. In the most developed countries with modern industry, only landfilled sludge or ash is concerned. This paper will describe the physicochemical properties of sludge, sludge composition, legislation in the Republic of Croatia on sludge disposal, and the main technical procedures for sludge disposal and its use