The feasibility of combining an electrocoagulation process and a biological treatment for the degradation of cutting oil emulsions

This present study considered the evaluation of the feasibility of combining an electrocoagulation (EC) process with a biological treatment for cutting oil emulsions (COE) biodegradation. The optimization of the EC process by means of the second-order model obtained using a central composite design methodology led to the following optimal conditions: an initial pH of 5.8, a current density of 241 A m–2 and an electrolysis time of 29 min. Under these optimal conditions, chemical oxygen demand (COD), and turbidity reductions were, respectively, 97.42% and 99.97%. Despite the significant reduction in pollution, the final COD values remained always high. Therefore, the effluents pretreated by electrocoagulation were then treated in an aerobic bioreactor coupled to a sequential respirometer for 52 d. The obtained results were very satisfactory showing an additional COD reduction of more than 98.5%, accompanied by a good biomass activity (40 mg O2 L–1 h–1) for the pretreated COE. Moreover, the non-pretreated COE solutions reached COD reduction of 94% during 33 d of running after 52 d of the biomass acclimatization period. A total COD removal of 99.8% was obtained with a residual value of 177 mg L–1, indicating the success of a biological treatment combined to an electrocoagulation pretreatment process.