A through investigation of energy recovery from tannery effluent in the context of circular economy

The tanning wastewater effluent raises environmental concerns since it consists a complex mixture of organic and inorganic pollutants. Physicochemical and biological methods are applied to treat such a wastewater, so solids and potentially hazardous substances to be isolated. The produced sludge from the previous treatment is rich in organic matter and Cr(III), a metal which is primarily used in tanning process. Certain alternatives have been proposed, tested and implemented for the exploitation and/or safe disposal of tannery sludge on a pilot and industrial scale. Land application after stabilization, composting, anaerobic digestion, combustion for energy recovery, pyrolysis, chromium recovery and employment in ceramics are some of the proposed methods. The main treatment process of sludge is dehydration, in order to reduce its volume and achieve the appropriate moisture content required for landfill disposal. However, there is no universal solution for the reuse/management of sludge, while legislation and practices vary from country to country (UNIDO 2011). A proper tannery sludge management is crucial for the sustainable operation of a relevant plant and according to European Union guidelines, energy recovery from tannery sludge are recommended, fulfilling the principles of circular economy (EU 2013). Therefore, aim of this study is to explore the possibility of energy recovery through tannery sludge combustion and to define the optimum conditions in order to fully exploit its potential.