TREATMENT OF SOLUBLE OIL-WATER EMULSIONS

Abstract

Oil-Water (o/w) emulsions are formed due to dispersion of small stable droplets (dp < 3 p m) and/or the mixture of the soluble oils in water. Soluble oils in aqueous solution are used extensively in the engineering and metal working industries, as coolants and/or lubricants. Hysol- X is a general-purpose cutting oil used in 1- 10 % concentration in aqueous solution. After prolonged use, the oil-water emulsion properties are adversely affected and the emulsion is discharged after treatment. Central Pollution Control Board (CPCB), Delhi has prescribed effluents standards for oil/greases: 10 mg/1 for the effluents discharge into sewers. In view of the CPCB Effluent standards, it is necessary that the oil-water emulsion, before its discharge, treated to remove/recover oil. So as to conform to the effluent standards of 10 mg/1 of oil and grease in the supernatant aqueous phase for discharge into sewers. Although, chemical treatment (flocculation and coagulation) is widely used technique, electrocoagulation has gained currency. The efficiency of electrocoagulation technique is dependent on various parameters like pH, current density, inter-electrode spacing, depth of the electrodes in the treatment vessel, number of electrodes etc. The present dissertation reports the work on batch and continuous treatment of Hysol-X-water emulsion. The dissertation reviews the current knowledge on electrocoagulation reported in literature and reports on the experimental programme and the results. The optimum condition for a batch system has been found as pH 6.50, current 3.50 A (current density 138.8 A/m2), electrode spacing 0.5 cm and electrode is fully submerged condition and, the 4 electrodes system. However, single stage treatment has been found to be inadequate. A two-stage treatment is to produce aqueous supernatant meeting the prescribed effluent limit of 10 mg/1 of oil. The second stage treatment requires small electrolysis time compared to the first stage treatment. The treatment of 1% o/w emulsions resulted in 99.54% oil removal in the first stage. Two-stage treatment resulted in 99.93% oil removal. For constant current density of 65 A/m2, it has been found that as the number of electrodes increases, the electrolysis time decreases and the removal of oil increases. iii The pH of the treated o/w emulsion increases by nearly one unit. The conductivity of the treated o/w emulsion changed with degree of demulsification. The percent removal of oil and turbidity is high for low concentration of oil in o/w emulsion, for the same degree of demulsification. The effect of temperature on the electrocoagulation process has been studied and was found that temperature increases above 40 °C, increases the oil removal efficiency. The effect of temperature on the stability of oil water emulsions was studied using Absorption Technique and was found that at 40 °C the oil-water emulsion has maximum absorbance at any pH. The pH decreased by increasing the temperature. The aluminum concentration in the treated water is found to be low (0.001 mg/i). The continuous runs operating at the optimum conditions obtained as in batch process show satisfactory results as those of the batch runs for the 4 and 12 electrodes system with varying flow rate.