ELECTROSTATIC COALESCER AND CROSS FLOW ULTRAFILTRATION FOR CUTTING OIL WASTEWATER TREATMENT AND SEPARATION

Abstract

This research aims to study the performance of various treatment processes on cutting oil wastewater, which is highly stabilized and difficult to deal with. The application of chemical destabilization, conventional coalescer, and ultrafiltration (UF) were considered. Calcium chloride (CaCl2) was employed as a positively charged electrolyte for destabilizing oil droplets, in which its optimal dosage was determined by the jar-test method. For the coalescer, the polypropylene material in tubular shape was used as the two-stage coalescing media with the influent velocity of 1.2 mm/s. The UF process was conducted under a cross-flow operation mode and its optimum conditions in terms of TMP, temperature, and pH were investigated. Once these methods were independently studied, they were finally integrated into a system with liquid recirculation and their combining performance was then evaluated. Considering each process individually, the optimal ratio of the CaCl2 dose and oil concentration varied from 1:1 to 5:1 with the highest efficiency of 70%. Without oil droplet destabilization, the coalescer could reach its maximum effectiveness of 40% when dealing with oil concentrations below 0.5% w/v. However, the combination of these two processes could enhance oil separation performance of the coalescer up to 50%. For the UF process, the optimal conditions were acquired at the TMP of 3 bar and 28ºC under an alkaline state, in which more than 95% oil removal could be attained. Nevertheless, the problem of rapid membrane fouling still needs to be concerned. In case of the combined process, the coalescer with chemical adding was applied as a pretreatment for the cross-flow UF. The results indicated that this combined process could lessen half the residence time for the coalescer. Also, the membrane fouling could be retarded when the coalescer was provided upstream. Moreover, the COD removal of 97% was achieved for the effluent from this combined process. Finally, an external low electric field was applied over the media layer in order to promote the migration of oil droplet surface charges, leading to further oil droplet coalescence and enhanced overall process efficiency in terms of oil recovery and flux decline intensity.