Mathematical analysis of a batch electrocoagulation reactor

Abstract

Electrocoagulation treats water by delivering coagulant from a sacrificial anode (aluminium) in an electrochemical cell. Hydrogen is evolved from the inert cathode. In the batch electrocoagulation reactor numerous interactions occur with settling and flotation identified as the dominant removal paths. Current determines both coagulant dosage and bubble production rate. The bubbles influence the mixing, and hence mass diffusion within the reactor. Rate of flotation and settling were experimentally determined for currents 0.25-2.0 A and pollutant loading 0.1-1.7 g/L. The performance of the electrocoagulation reactor was quantified by analysis of experimental results. First-order ordinary differential equations were developed to describe the pollutant's settling and flotation behaviour. Kinetic rate constants were calculated considering this pair of irreversible reactions. At low current (0.25A), sedimentation dominates with slow release of coagulant and gentle agitation provided by low bubble production. Removal is slow and hence the low rate constants calculated were appropriate. At high currents (1.0 and 2.0 A) faster removal occurs due to greater bubble density. This resulted in greater mass floated to the surface and higher rate constants were observed. Thus the developed rate equations successfully quantified the reactor's performance over a variety of conditions.