Utilization of Sewage Sludge of Leather Industry. Energy Prospects

The growing amount of tannery sludge generated by leather processing often undergoes uncontrolled landfilling, or open dumping, releasing a significant volume of harmful pollutants, including carcinogenic chromium (Cr) into the air, water, and soil. Therefore, sustainable TS management through advanced valorization technologies becomes vital to align with the Sustainable Development Goals (SDGs) and mitigate the adverse environmental, health, and social impacts. Tannery sludge, as biomass, can be considered a renewable energy source for bioenergy generation which could be a viable solution for meeting contemporary environmental standards and expediting the transition towards a circular economy. Tannery sludge is an available resource that has been successfully used in anaerobic digestion, biogas, biodiesel, and industrial oil production. We offered a critical review of tannery sludge valorization technologies towards energy recovery. Many studies have shown that typical anaerobic digestion of tannery sludge requires a long period with low utilization efficiency and biogas yield. Chromium leaching is a major problem in composting and anaerobic digestion of this waste. Overall, the use of tannery sludge is proving to be a very promising alternative for biodiesel production. We also explored the environmental hazards of chrome-containing tannery sludge. Tannery sludge valorization is sensitive and critical due to the potential risk of transforming Cr(III) to Cr(VI) during the process. Therefore, there exists an urgent need for considering efficient and holistic tannery sludge valorization technologies in the design, implementation, and operations phases to avoid any environmental and health hazards.