Study On Combination Processes Of Watertreatment Based On Gac-Sand Filter

The micro-pollution is exist in Dongjiang source water prevalently, including organic compounds, odor compounds (2-MIB, GSM) and ammonia, and which was unable to be solved by traditional water treatment. The study mostly aimed at the removal characteristics of micro-pollution by the combination processes of enhanced coagulation, potassium permanganate pre-oxidation, powdered activated carbon sludge return with GAC-sand filter through simulating Dongjiang River in this paper, and then abtained a short depth process which suitable for Dongjiang River. The main contents and conclusions were as follows:(1)The odor compounds (GSM and 2-MIB) could be qualitative and quantitative analysed by HS-SPME. The optimal conditions of HS-SPME were as follow: extracting for 40minute, extracting at 65℃, and adding NaCl 0.1g. The temperature program for column of GC was first maintained at 50℃for 1 minute, then rose to 100℃at the rate of 10℃per minute keeping for 0.15minute, finally rose to 240℃by 5℃per minute. Under these conditions, the separate detection limits of GSM and 2-MIB were obtained with 0.2, 0.5ng / L respectively.(2) Combination process of enhanced coagulation and GAC-sand filter. The removal rates of turbidity and organic compounds could be increased significantly through adding the dosage of coagulant. Experimental showed that the better result of enhanced coagulation could be obtained when the dosages of aluminum chloride and ferric chloride were 25mg/L and 30mg/L respectively. But the removal rate of turbidity would rebound as the condition of the coagulant overdose. The performance of enhanced coagulation and sedimentation of aluminum chloride was better than ferric chloride.The better resoult of odor conpounds remove could also be abbtained by reducing pH value of raw water than changing the dosage of coagulant. The sand filtration could help to strengthen the removal of turbidity and UV254 but freedom from influence of the dosage of coagulant and the Ph of raw water, which also had less help to remove odor compounds. The GAC filter had a significant effect to remove the remaining organic matter and odor compounds, and the odor of the outlet could below the detection limits especially.In contrast, the removal rate of turbidity was difficult to increase further by GAC filter because the carbon filtration washelpless to remove the small molecules residual in water. (3) Combination process of potassium permanganate (KMnO₄) pre-oxidation and GAC-sand filter. The KMnO₄ had the effect of coagulation-supporting to remove turbidity, odor and UV₂₅₄ when it used with coagulant. The investment show that the optimum dosages of potassium permanganate were 0.7, 1.0 mg/L respectively as the coagulant was aluminum chloride and ferric chloride. The overdose of KMnO₄ could affect the coagulation effect although the removal rate of ammonia increased with the the adding of KMnO₄. In that case, the removal rates of turbidity, odor and UV₂₅₄ would rebound. Sand filtration has a good effect to turbidity and organic matter as the enhanced filter, but helpless to odor and ammonia nitrogen removal. Carbon layer still had a significant contribution on UV₂₅₄ and odor removal, but could do nothing on the ammonia nitrogen. The combination of sand filter and GAC filter had a effective removal to odor compounds.(4) Combination process of powdered activated carbon sludge return and GAC-sand filtration. The method of powdered activated carbon sludge return was feasible. The long time re-growth of flocs was beneficial to remove odor compounds, UV₂₅₄ and ammonia. Instead, the average removal rate of residual turbidity would drop because of the irreversibility of the floc breakage. The performance of the flos re-growth of aluminum chloride was better than ferric chloride. Both aluminum chloride and ferric chloride, the best removal effect could be obtained when the coagulant was and the sludge returned to the beginning of flocculation process, and all average removal rates of 2-MIB, GSM and ammonia in the effluent from settling tank would increased except UV₂₅₄ and turbidity, which could be eliminated by sand filtration for its good ability of enhanced filtration, however. Also the sand filtration had good effect to turbidity and UV₂₅₄. Additionally, GAC filtration could not only had the strong physical adsorption and retention performance, but also had the biological membrane which formed in the pore of GAC. The aerobic bacteria could biodegrade the ammonia effectively. The GAC filtration was the most important way to eliminate ammonia. The aerobic bacteria also had the comsuption of the odor coumpounds, which could reduce the odor of effluence to below the detection limit.