Enhancing biomass fuel properties of municipal sewage sludge with carbon-rich and low ash energy crops common reed and miscanthus

Wastewater treatment plant effluents, sewage sludge, and purified water are important resources for producing renewable energy and implementing a carbon-neutral green energy policy due to their richness in organic matter and nutrients for energy crops. In the present study, the biomass energy potential, fuel quality, and combustion emission characteristics of sewage sludge and the energy plants Arundo donax and Miscanthus×giganteus and their mixtures were investigated to improve the combustion properties of sewage sludge. The plant biomass is produced using sewage treatment plant effluent as a nutrient source. The proximate and ultimate analysis results showed that adding plant biomass shifted the fuel value of the mixtures, mainly reducing the ash content and increasing the volatile matter and carbon content in the solid biofuel. The regression analysis showed that heating values of 25, 50, and 75 % biomass in sewage sludge mixtures linearly increased HHV and LHV values. The increase in volatile matter significantly improved the ignitability index of sewage sludge, reaching the optimum value of 35 at 75 % biomass mixtures for both crops. The NOx and SO2 emissions of the mixtures were lower than those of sewage sludge. Overall, the results indicate a synergistic effect between the combustion of biomass from energy crops and sewage sludge. A comprehensive comparison of proximate, ultimate, heating value, fuel indices, and gaseous emissions shows that the mixed fuels of 50 % biomass and 50 % sewage sludge can promote combustion and reduce emissions. Arundo had better biofuel properties than Miscanthus. [Display omitted] •Combustion of sewage sludge with Arundo and Miscanthus was investigated.•Energy potential with various mixture ratios were examined.•The changes of fuel quality indices with proportional mixture were determined.•Fuel quality and incineration of sewage sludge can be improved by co-combustion.