In many industries especially oil companies in Iraq consumed large quantities of water which will produce oil-contaminated water which can cause major pollution in agricultural lands and rivers. The aim of the present work is to enhance the efficiency of dispersed air flotation technique by using highly effective and cost-efficient coagulant to treating gas oil emulsion. The experimental work was carried out using bubble column made of Perspex glass (5cm I.D, 120cm height). A liquid was at depth of 60cm. Different dosage of sawdust +bentonite at ratio 2:1 (0.5+ 0.25; 1+ 0.5 and 2+1) gm and alum at concentration (10,20and30mg/l) at different pH ( 4 and 7) were used to determine optimum dosages of coagulant. Jar test experiment has showed that optimum dosage of (sawdust +bentonite) was (1+0.5gm) and alum concentration was 30 mg/l at pH=4.  

  The present study was conducted to evaluate the effect of various parameters pH (3, 4,7and 9); air flow rate (300, 500, 1000, and 1500 cc/min); initial oil concentration (300 up to 1000 ppm); concentration of Sodium dodecylsulphat surfactants ,SDS (25, 75and 150mg/l); and the effect of the addition coagulant (sawdust + bentonite at ratio 2:1) and alum (30mg/l) in the removal efficiency of oil from wastewater by coagulation –flotation process.

   The study has showed that the removal efficiency of COD, oil content and turbidity were related to the initial oil concentration; additive concentration of SDS and dosage of coagulants. It was found that the flotation rate increases when using coagulants, the fastest removal rate was obtained when pH 4 and also the higher removal efficiency achieved was for flotation (87%) and (95.7%) sawdust +bentonite; (97%) for alum in coagulation – flotation process.