A preliminary study of fuel mixtures of industrial sludge, bottom ash, and municipal solid waste for co-firing in coal boilers

Wastewater treatment in the textile factory produces sludge classified as toxic and hazardous waste, which is harmful if left untreated. This study assessed the potential of utilizing sludge from a textile factory in Bandung Regency, Indonesia, as a co-firing fuel in coal boiler furnaces employed in the factory. The study aimed to improve the performance of sludge to meet the required standards for fuel substitution. The analysis involved proximate, ultimate, and ash element tests with correlation of the results with calorific values. The sludge was mixed with coal bottom ash produced by the textile factory and biomass (local refuse-derived fuel) at different ratios. An environmental impact analysis was also carried out with the toxicity characteristic leaching procedure (TCLP) and air emission testing. The results showed that the sludge did not meet the fuel substitution requirements if it was used as a single material. However, the sludge could be used as a substitute for coal by mixing it with bottom ash and biomass; the optimum composition was a ratio of 20% sludge, 40% bottom ash, and 40% biomass by weight. TCLP and air emission test results showed that this mixture was safe for human health and the environment and met the fuel substitution requirements. This study provides a practical solution to the problem of reducing toxic and hazardous waste.