Catalytic thermal treatment (catalytic thermolysis) of a biodigester effluent of an alcohol distillery plant

The catalytic thermal treatment (catalytic thermolysis) of biodigester effluent from an alcohol distillery unit was studied in the presence of CuO catalyst in batch mode in the temperature range of 100-140 degrees C and the pressure range of 1-9 bar. The catalyst mass loading, C, was varied between 2 and 5 kg/m(3). Thermal treatment at 140 degrees C with a C-w of 3 kg/m(3) gave a maximum chemical oxygen demand (COD) reduction of about 70% from its initial value of 34 kg/m(3). The biochemical oxygen demand reduction was found to be 83% from its initial value of 6.3 kg/m(3). The COD reduction-time profiles show two clearly distinct steps: a fast process followed by a slower process. A good amount of charred solid residue is obtained; which is enriched with carbon, giving a C/H atomic ratio of 1:0.947, versus a C/H atomic ratio of 1:1.146 for the effluent. The charred residue is a good fuel material with a high heating value (similar to 17.92 MJ/kg) representing 42-47% energy recovery from the digester effluent. During the thermolysis, copper gets leached to the aqueous phase. The leached out copper has its lowest concentration of 91 mg/dm(3) when the initial pH value of the biodigester effluent was adjusted to 4. The residue obtained after the treatment may be combusted and/or incinerated, and the ash, which is rich in copper, may be blended with organic manure for use in agricultural fields.