Treatment of lubricant oily emulsion wastewater by combining flotation and coagulation process

Abstract

The objective of this work is to study the treatment of stabilized lubricant oily emulsion wastewater containing with anionic (SDS), cationic (CTAB), and nonionic (Tween20) surfactants at concentration equal to 1 CMC (Critical Micelle Concentration). The Modified Induced Air Flotation process (MIAF), which is the combined process between the Induced Air Flotation (IAF) process and the coagulation process, were applied and also compared with those obtained with the IAF and coagulation processes. The study has shown that the removal efficiencies were related with the alum dosage, pH value and air flow rate. For the IAF process, optimal treatment conditions for oil emulsion with SDS, CTAB, and Tween20 were obtained at 30 s of aeration time and at 0.3, 0.3, and 0.5 l/min of air flow rate: these provide the treatment efficiencies equal to 33.33%, 74.44% and 25.00%, respectively. Due to the coagulation process, the highest removal efficiencies from oily-emulsion wastewaters with SDS, CTAB, and Tween20 equal to 61.82%, 59.77% and 37.66% were achieved at pH 8 and at alum concentration 400, 200, and 150 mg/l. respectively. The concentration of surfactant used for preparing oil-emulsion, size of oil droplets and surface charge of oil droplets were proven to be the important parameters. For the MIAF process, the highest treatment efficiencies were obtained with the oily-emulsion wastewater with SDS: this was chosen in order to study, in detail, in term of kinetic and bubble hydrodynamic characteristics. The optimal operating conditions were 300 mg/l of alum concentration, 0.3 l/min of air flow rate, and 30 minutes of aeration time and thus 75% of treatment efficiencies can be obtained. The reaction rate constant (log k) and reaction order (n) related with coagulant concentration can be applied for proposing the simple model for predicting the treatment efficiency with average difference about 25%. Moreover, the ratio between interfacial area and the velocity gradient (a/G) have been proven to be the important parameter for controlling the flotation process efficiency in term of collision/attachment and of chemical mixing condition. The linear equation of treatment efficiencies and a/G ratio can be possibly applied as the important parameter for well controlling floatation process.