Effluent treatment for alcohol distillery: Catalytic thermal pretreatment (catalytic thermolysis) with energy recovery

The sugarcane molasses-fed distillery wastewater (DWW) has very high biochemical and chemical oxygen demand (BOD and COD) and has to be treated to meet the regulatory discharge standards and to recover its energy content. The catalytic thermal pretreatment (or catalytic thermolysis, CT) is a novel pretreatment process to recover the majority of its energy content with consequent COD and BOD removal. The present paper deals with the CT of DWW using CuO catalyst. Experiments were conducted in a 1 dm3 stainless steel pressure reactor in a batch mode in the temperature range of 100–140 °C and corresponding autogenous pressure with CuO mass loading in the range of 2–5 kg/m3. The initial pH (pH0) is found to have profound impact on the efficiency of thermolysis in COD removal and the optimum pH0 is found to be 2. At 140 °C with 3 kg/m3 catalyst loading and pH0 2, a maximum of 60% COD could be reduced. The CT process follows a two step mechanism: each step obeys the first order reaction kinetics with respect to COD and a fractional order 0.37 and 0.29 with respect to catalyst mass loading for the first and second steps, respectively. The CT process results in the formation of settleable solid residue and the slurry obtained after the thermolysis exhibited very good filtration characteristics. At 140 °C and pH0 2, the solid residue had a C:H atomic ratio of 1:1.08 with a heating value of 21.77 MJ/kg. The residue can be used as a fuel in the combustion furnaces and the ash obtained can be blended with organic manure and used in agriculture/horticulture.