Production of Alternative Fuels Based on Municipal Sewage Sludge and Selected Types of ELV Waste

Abstract

The construction of new wastewater treatment plants and the modernization of existing ones lead to the expansion of sewage networks, resulting in a sharp increase in the volume of municipal sewage sludge, which translates into a global problem of sludge management. The solution to this problem could be the recovery of energy from sewage sludge in the cement industry to exploit its energy potential. The aim of the present study was to examine the results of laboratory research on the production of alternative fuels based on municipal sewage sludge, plastic waste from end-of-life vehicles, and wood waste (sawdust) from carpentry enterprises. The tests were carried out for waste mixtures designated as PAZO I, PAZO II, PAZO III, and PAZO IV fuels, differing in the percentage of waste used and the type of plastic waste. The following parameters were evaluated in fuels: water content, ash content, sulfur content, and calorific value. Water content of the obtained fuels ranged from 17.1% to 19.4%, the ash content ranged from 2.5% to 3.4%, while PAZO II fuel was characterized by the highest ash content, which was 17.6%, but it remained within the limits permissible for alternative fuels.The sulfur and chlorine contents did not exceed the permissible values for alternative fuels. The calorific value of alternative fuels obtained was high and ranged from 16.5 MJ/kg to 33 MJ/kg. Furthermore, the composition of the individual fuel mixtures was selected to avoid energy-intensive sludge drying, whereas the fuel met the requirements for alternative fuels. The energy properties and water content of the obtained fuels indicate that the maximum amount of sewage sludge should not exceed 25% to maintain the parameters permissible for alternative fuels. Therefore, the analysis of the results leads to the conclusion that the obtained fuels, based on municipal sewage sludge, plastic waste, and wood waste (sawdust), meet the requirements for alternative fuels used in the cement industry. Today, the fuels based on municipal sewage sludge can be more of an alternative to conventional fuels used in the cement industry. The application of the fuels produced in the cement industry eliminates the formation of combustion byproducts in the form of slag and ash since they become a component of clinker. As an additional source of energy, the use of fuels in the cement industry will create an opportunity to move toward the circular economy.