Basic Study On Short-cut Denitrifying Phosphorus Removal

The standard of wastewater discharge was controlled more strictly with the severe eutrophication question occurred. Therefore, the wastewater techniques developed gradually from the period of pure COD removal to the period of simultaneous COD, nitrogen and phosphorus removal. Today, the nitrogen and phosphorus removal technology aimed for eutrophication control has been the study focus in the wastewater treatment area. The process of denitrification phosphorus removal using nitrite as electron acceptor had many advantages not only with high effective phosphorus removal, the good settling ability of active sludge and easy to dewater, but also with less energy consumption, less carbon source consumption and less sludge yield. combined with the short-cut nitrification can realize two stages activated sludge systems together-short-cut nitrification-denitrifying phosphorus removal using nitrite, but at present there are many problems in the denitrifying phosphorus removal technique using nitrite, such as the inhibitory degree of nitrite nitrogen on the anoxic phosphorus uptake, nitrite nitrogen effects on phosphorus release and the effects of COD on the anoxic phosphorus absorb and so on, all the problems are critical issues which should be studied. Based on the investigation of domestication and factors for denitrifiaction phosphorus removal bacterium aimed at the reactor used to treat the synthetic wastewater, the feasibility of the process of denitrification phosphorus removal was involved too. The main results of this thesis were as followings:1) Denitrifying dephosphatation process using nitrite as electron acceptor could be realized fully, the short-cut denitrifying phosphorus removal system was successfully started up in 77d based on the enriched denitrifying dephosphatation sludge using nitrite, and adopting continuous flow reactor. The results show that the system has a good operational stability and nitrogen and phosphorus removal. The removal rates of COD, PO43--P and NO2-N reached 77%,73.3% and 86.7%, if the influent COD, PO43--P and NO2--N were 296.2mg/L,16.07mg/L and 30.46mg/L. Compared with the traditional biological nutrient removal technology (ie anaerobic/ aerobic phosphorus removal, full nitrification-denitrification), there were effectively reduction of COD demand, oxygen consumption and sludge production removing the same amount of nutrients. It is a sustainable wastewater treatment process2) Under the experimental conditions, nitrite can serve as electron acceptor instead of oxygen. With anoxic nitrite concentration increasing, the phosphate removal rate is increased. When the influent NO--N concentration was 5mg/L, 15mg/L, the phosphorus emancipation of the second anoxic occurs. The system was not disturbed when the NO2--N concentration reached as high as 55 mg/L. The effect of denitrifying phosphorus removal was the best if NO2--N concentration and PO43--P were in the 25-35mg/L.3) With the electron acceptor exist in anaerobic conditions, the short-range and short-denitrifying bacteria denitrifying phosphorus bacteria compete the external organic carbon sources, which releases the phosphorus and maximum phosphorus releasing rate. In order to ensure high efficient phosphorus release, the NO2--N concentration was kept below 1.5mg/L.4) Denitrifying phosphorus removal system, high and low influent COD concentration of the denitrifying phosphorus removal has a great influence. When the influent COD concentration is high, remaining at the end of the outer anaerobic organic carbon concentration was higher, leading to short-range and short-denitrifying bacteria denitrifying phosphorus bacteria compete on the electron acceptor to reduce phosphorus removal, when the Progressive COD concentration of water is too low, the anaerobic denitrifying phosphorus removing bacteria within the carbon absorption of organic synthesis of PHB is very small residual organic matter less, resulting in removal of phosphate and nitrite are very low. Too high or too low inlet COD concentration has great impact on denitrifying phosphorus removal technique using nitrite, the inlet COD concentration should be restricted in about 300mg/L in this experiment..5) pH value have a significant effect on the uptake, releasing of the phosphorus. With the pH value increased, the emancipation of phosphorus was increasing in the anaerobic. anoxic pH 7.2, the effluent PO43--P concentrations of the lowest. pH Value has great influence on phosphorus release and uptake, the results showed that the optimum pH value of 8.0 in anaerobic stage, the optimum pH value of 7.0 in anoxic stage. Therefore, the response to short-denitrifying phosphorus removal system, effective control of pH value in order to avoid anaerobic phosphorus release-the process of oxygen uptake interference pH values.