In this study, the influence of electrocoagulation pretreatment, using aluminum electrodes, of spent and prepared cutting oil emulsions (Tasfalout22B,Naftal, Algeria), at 4 % v/v, biodegradation was examined under anaerobic conditions. Moreover, non-pretreated samples were tested as well.
The Automatic Methane Potential Test System (AMPTS) contained fifteen parallel reactors; each one was connected to a volumetric gas counter with an automatic acquisition system to follow gas production during biodegradation was used. Experiments were carried out in triplicate. 500 mL batch reactors were inoculated using anaerobic sludge from a municipal digester (Saint-Brieuc, France), at an inoculum to substrate ratio (I/S) of 3:1 and 2:1 w/w of volatile solids for non-pretreated and pretreated cutting oil samples respectively. These reactors were incubated in a thermostatically-controlled water bath at 37 °C. Electrocoagulation pretreatment optimum conditions were obtained using experimental design (18 experiments), for an initial pH of 5.8, current density of 241 A / m² and a processing time of 29 min. The anaerobic biodegradation tests were then carried out. The cumulative methane production increased, when pretreatment was used, from 0.024 ± 0.007 to 0.175± 0.05 (650 %) and 0.094 ± 0.04 to 0.27 ± 0.01 Nm3 CH4 kg COD-1 (187 %) for synthetic and spent cutting oilemulsion respectively. Furthermore, anaerobic biodegradability improved as well from 6.9 to 51 % and from26.98 to 80 % for synthetic and spent cutting oil emulsion respectively. These results show the considerable improvements of cutting oil emulsion anaerobic biodegradation when electrocoagulation pretreatment was used.