Pilot-scale studies on the treatment of tannery effluents by electroflotation

A pilot-scale electroflotation system with a treatment capacity of 0.8 m(3) per hour has been designed and built. The system is equipped with a conditioning tank, a rectifier, flow meters, an energy meter and pumps. Iron, aluminium and titanium coated with oxides of tantalum, ruthenium and iridium were used as electrodes. The system was installed within the premises of the Common Effluent Treatment Plant (CETP), which receives effluents from nearly 200 tanneries. The effectiveness of electroflotation for the separation of suspended solids, sulphur species, chromium and other chemicals contributing to COD and BOD were studied. The separation of suspended solids and chromium by electroflotation was nearly complete (> 95%) and their concentration in the processed samples can be maintained well below the discharge limits. The removal of COD was observed to be 15-20% greater than with conventional chemical coagulation. Furthermore, the entire spectrum of pathogenic bacteria was eliminated to the extent of 99.97% by subjecting the effluent to electroflotation.