Experimental Research On Enhanced Coagulation Flotation Of Pretreating Coal Gasification Wastewater Based On Excess Sludge Addition

Coal gasification wastewater contains a large amount of oil pollution.Considering that the oil pollution has inhibitory effect to the metabolism activity of microbial,we should remove oil pollution from wastewater before it get into biological treatment unit process.The content of oil pollution should be lower than 20 mg/L.In order to cut back the dosage of coagulant and improve the efficiency of coagulation-flotation,this program started an experimental research on enhanced coagulation–flotation of coal gasification wastewater based on excess sludge addition.The research is divided into three stages.First,through the coagulation flotation preliminary test,the method of adding excess sludge was established.The optimal dosage of coagulation agent and excess sludge was verified,and the optimal operation parameters of dissolved air floation was verified,too.Then,three kinds of excess sludge were used to strengthen the coagulation flotation to verify its treatment efficiency by adjusting the coagulation flotation pilot test equipment.Finally,the change of flocculation structure and the interactio n mechanism between excess sludge and air floating microbubbles were analyzed.First,the stage of coagulation-floatation preliminary test.The best way to adding excess sludge was to add the excess sludge together with the coagulant.And the optimal amount of the excess sludge was 1200 mg/L.The treatment efficiency of the coagulant polyaluminium chloride was better than that of polyferric sulfate,the optimum dosage of polyaluminium chloride was 150 mg/L,and the optimal dosage of polyacrylamide was 2 mg/L.The optimal operating parameters of the air flotation device were verified: the pressure of flotation is 0.4 MPa,the flow rate of the backflow pump is 0.8 L /min,and the time of flotation is 15 min.At this point,the oil content,total phenol and COD removal rate of the coagulation flotation process strengthened by excess sludge are 66.4%,30.4% and 22.2%,respectively.Second,the stage of coagulation floatation pilot test.The pump of coagulation floatation was tested.The optimal operation parameters for the floatation device were verified: the pressure of flotation is 0.5 MPa,the flow rate of gas is 0.67 L/min,the gas water ratio is 20%,and the reflux ratio of wastewater is 100%.Under the water flow rate of 0.2 m3/h,the removal rate of oil content,total phenol and COD of coagulation floatation process strengthened by aerobic excess sludge are 84.0%,27.9% and 39.1%,respectively.The content of oil is 15.7 mg/L,meet the requirement of the oil content of the follow-up biological treatment process.Which require the content of oil should be lower than 20 mg/L.By scanning electron microscopy(sem)analysis of excess sludge floc structure changes before and after reinforcement,the diffenence of air-flotation scum produced by different excess sludge were found.If the sludge floc structure is loose,the scum will be easier to form sheet stack structure,which may enhance the adsorption effect of oil pollutants in water.After the reinforcement of aerobic excess sludge,the average diameter of microbubble in oil-water separation area is 32.1 ?m,it is 33% smaller in average diameter than of conventional microbubble,and its stable time is also 1.5 times less than that of conventional microbubbles.The process established in this paper: enhanced coagulation flotation based on excess sludge addition,can effectively remove the oil pollution in the coal gasification wastewater.It can also improve the biodegradability of wastewater,and make it meet the requirements of water quality of the follow-up biological treatment process.This research has important reference value for practical engineering of coal gasification wastewater treatment.