Experimental Study On Nitrogen Removal Efficiency Of Hybrid Oxidation Ditch And Algal-bacterial Symbiotic System

With the development of economic and society, water pollution problems in our country become more and more serious. On one hand, low treatment rate results in large amounts of sewage can’t get resourceful utilization. On the other hand, the treated sewage still contains much nitrogen and phosphorus nutrients that may cause water eutrophication.As a kind of wastewater treatment technology, activated sludge process is widely used. Oxidation ditch is a variation of the activated sludge process. It has many advantages, like good effluent quality, stable operation and low cost. But the oxidation ditch mainly uses aeration to transform organic compounds into CO2, and then discharges from the system. The algae is autotroph that can depend on light as energy, and then use nitrogen, phosphorus and CO2 to synthesis of own complex organic compounds and release O2. Therefore, from the sustainable development point, using algae to treat sewage can not only save aeration cost, but also can absorb and fix CO2 arounding the environment. It has environmental, economic advantages and meets the natural ecological cycle.(1) This paper uses orthogonal experiment method and chooses filler fling ways, filler fling rate and SRT to study the efficiency of hybrid oxidation when treats artificial wastewater. Then get the optimal running conditions of this system. This paper also study the efficiency of algal-bacterial symbiotic system for sewage under different algae, sludge concentration and illumination time conditions. And this paper obtains the following conclusions.The results show that filler fling rate is significant factor of COD removal rate, filler fling way and filler fling rate are significant factors of NH4+-N removal rate, filler fling rate and SRT are significant factors of TN and TP removal rate. The optimal running conditions of this system are when fling 30 percents filler in the anaerobic zone and anoxic zone and keeps the system for 20 days SRT.(2) In the same culture conditions, chlorella grows better and is easier to form algal-bacterial symbiotic system. By extending illumination time can make up the effect of mixture’s low light transmittance to the growth of algae and there is a higher algae content when the sludge concentration is higher. During the experiment, the algae content of the mixture reaches maximum and the COD, NH4+-N, TN content of the effluent are lowest when the sludge concentration is 3000mg/L and the illumination time is 24 hours.(3) Under the optimal running conditions, the average removal efficiency of COD,NH4+-N, TN,TP of hybrid oxidation ditch and algal-bacterial symbiotic system are η(COD) = 91.57%, η(NH4+-N) = 92.70%, η(TN) = 69.12%, η(TP) = 71.62%. The average effluent qualities are ρ(COD) = 33 mg / L, ρ(NH4+-N) = 2.02 mg / L, ρ(TN) = 10.40 mg / L, ρ(TP) = 1.13 mg / L. The hybrid oxidation ditch and algal-bacterial symbiotic system has a better removal efficiency of COD,NH4+-N, TN and TP compares with single hybrid oxidation ditch, especially the removal efficiency of TP.