Study On Treatment Of Polluted Raw Water By Integrated Flotation And Biological Contact Oxidation Technique

In resent years, the pollution of water resource is increasingly serious. The traditional water purification technique can not satisfy the requirement of polluted raw water treatment. Among the various methods of polluted raw water treatment, more attention has been paid to biological contact oxidation technique because it can efficiently remove pollutants such as ammonia nitrogen, organic matter etc. However, the pollutants removal of this method is influenced when the temperature of water is lower than 10℃. Therefore, the combination with the biological contact oxidation technique and other methods will be one of the methods that increase the efficiency of biological pretreatment. The technology of dissolved air flotation can remove algae and ammonia nitrogen, and reduce COD. And each of biological contact oxidation process and dissolved air flotation process in series has its efficiency of pollutant removal, which has been constructed in our country.This study introduced a process of flotation in advance and biological contact oxidation process after, which is a new method of integrated flotation and biological contact oxidation. Flotation can not only exert the characteristic of this process in efficiently removing the turbidity, ammonia nitrogen, COD_Mn, algae, UV₂₅₄ etc, but also provide necessary dissolved oxygen and a certain kind of buffer for the latter processes, thus utilize the biological contact oxidation to remove pollutants in further, for lightening the burden of latter processes and increasing the effluent water quality.The experiment primarily established the parameters of flotation process through the coagulation experiment with beakers in the lab and the pilot-scale experiment; and then analyzed start-up process of the technique in the condition of natural biomembrance culturing. Further more, it respectively investigated the efficiency of pollutant removal in flotation process, biological contact oxidation technique and the overall flow of integration, and analyzed the effective actors in pollutant removal. At last, some problems met during the experiment were discussed and some meaningful results about practical process have been obtained.The test shows that: the adoption of 10% circumfluence rate of dissolved air water, 15mg/L dosage of Poly-Aluminium Chloride and 3.4m³/m²Â·h surface loading in flotation is feasible. It also confirmed that dynamic natural biomembrance culturing is effective for this device for polluted raw water treatment. When the temperature of water is condign (25～30℃, the average is 27℃) and oxygen provided is enough (DO in water keeps about 6mg/L), 3 weeks is needed to mature biomembrance. This integrated process can efficiently remove the turbidity, ammonia nitrogen, COD_Mn, UV₂₅₄ and algae etc. of polluted raw water. The temperature of water is the main influence factor of efficiency of pollutant removal. In order to keep the efficiency when the temperature was low, the experiment augmented the quantity of oxygen provided and prolongs the effective HRT of the biological contact oxidation process properly. Working with a low temperature, and high loading of ammonia nitrogen, the equipment would accumulate the nitrite. If this equipment is turned off for 3 days, it may need a week to reach the elimination effect, while turned off for 40 days, 20 days is needed. Lymnaea staynalis appeared and grew largely on the fillers of biological contact oxidation tank. The result showed that flotation in advance to avoid lymnaea staynalis entering into the tank is the credible method to prevent it from growing largely. Furthermore, the new filler used by the equipment, type TF mesh screen spin bio-filler, makes against clinging of lymnaea staynalis through rotating itself.Comparing with the existing process of biological contact oxidation and flotation in series, the integrated technique is more efficient in the treatment of polluted raw water. And it is a technique with the advantages of less occupying land and less energy cost. This technique has a good future for application.