Sustainable Utilization of Paper Sludge for Energy Conversion: Economic Potential and Environmental Feasibility

In the context of sustainable development, the assessment of the role the paper industry is of paramount importance. In the last years, the efforts of the paper industry towards ecologically sustainable paper recycling have faced growing problems of waste management since recovered paper processing leads to the production of considerable amount of waste (sludge) requiring disposal. The work outlines the current state of the utilisation of paper sludge for energy conversion. Focus of the paper is the assessment of the environmental feasibility of energy recovery from paper sludge associated with toxic emissions (like NOx, SO2, N2O, chlorinated organic compounds); the fate of some toxic metals (like Hg, Pb, Cd, Zn, Mn) deriving from dyes, fillers, and toxic pigments is discussed based on new research combustion data. The environmental impact of burning paper sludge is discussed showing the interdependence between sludge properties and combustion conditions. Recent data concerning co-combustion of paper sludge, particularly in conjunction with different biomass fuels (like wood and straw), are reported. Differences related to usage of paper sludge as a fuel in paper mill boilers and industrial power plants and their economic implications are presented. Future possible scenarios for paper sludge utilisation in energy recovery are also discussed.