Basic Study On Short-cut Denitrifying Phosphorus Removal

The process of denitrifying phosphorus removal using nitrite as electron acceptor has the characteristics of short cycling period and rapid phophorus uptake rate, 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,the inhibitory mechanism of nitrite nitrogen on the anoxic phosphorus uptake and the kinetics of denitrifying phosphorus removal using nitrite, and so on,all the problems are critical issues which should be studied.The effect of different start-up modes starting up a batch denitrifying phosphorus removal process using nitrite was contrasted,and adopting sequencing batch reactor(SBR);the effect of sludge retention time(SRT),nitrite concentration,carbon resource organism and pH Value on denitrifying phosphorus removal technique using nitrite was explored, respectively;meanwhile the kinetic parameters of a batch denitrifying phosphorus removal process using nitrite were determined.The main results were as follows:1) The start-up of denitrifying phosphorus removal technique using nitrite by adopting PAOs can't achieve the perfect result.After anaerobic/sedimentation and displacement/anoxic/sedimentation and displacemen stages,the denitrifying phosphorus removal sludge using nitrite was successfully enriched in 58d by directly putting nitrite into the system,the removal rates of COD,PO₄^3--P and NO₂^--N reached 75.4%,81.8%and 97.4%,respectively,the activated sludge had the color of black and brown and a good adaptability for higher nitrite concentration in the reactor, it was in good condition.2) By measuring anoxic productivity oxidation efficiency of nitrite k_NO,η_NO and the ratio of quantity of phosphorus uptaken/consumption of nitrite,the denitrifying phosphorus removal ability can be evaluated,and the feasibility of denitrifying phosphorus removal technique can be determined.The average values of anoxic productivity oxidation efficiency of nitrite and anoxic respiration efficiency were 27.1%,9.4%for denitrifying phosphorus removing bacteria using nitrite induced by PAOs,and were 39.3%,9.2%for denitrifying phosphorus removing bacteria using nitrite enriched by directly putting nitrite into the system.In the suitable operating conditions,the latter could ensure the long-term stable effect of denitrogenation and dephosphorization.3) Denitrifying dephosphatation process using nitrite as electron acceptor could be realized fully,the short-cut denitrifying phosphorus removal system was successfully started up in 31d based on the enriched denitrifying dephosphatation sludge using nitrite,and adopting sequencing batch reactor(SBR).The removal rates of COD,PO₄^3--P and NO₂^--N reached 69.6%,79.2%and 98.9%,respectively,the ratio of phosphorus uptake to nitrite consumption was 1.39mgP/mgN under anoxic condition.4) The steady operation of denitrifying phosphorus removal technique using nitrite as electron acceptor was affected by the factors of sludge retention time(SRT),nitrite concentration,carbon resource organism and pH Value,the sludge retention time should be restricted within 16～20d,the system was not disturbed when the NO₂^--N concentration reached as high as 45 mg/L,the effect of denitrifying phosphorus removal was the best if influent COD,NO₂^--N and PO₄^3--P were about 350,35 and 8.50.In order to ensure high efficient phosphorus release,the NO₂^--N concentration was kept below 2mg/L.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 within 300～400mg/L in this experiment. There was great difference of the transformaing rule of medium in different carbon sources,the degradation pathway of acetic sodium was similar to that of butyric acid, and was different from that of glucose,nitrogen and phosphorus removal effect was better acetic sodium or butyric acid as carbon source than that of glucose,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.5) Through analysising on the mathematics model of SBR,we could obtain the stoichiometric coefficient between organic matter and phosphate(γ) 0.206,the absorption constant of organic matter(k) 0.0613h^-1,the organic removal saturated concentration(k_s) 97.087mg/L in anaerobic stage,the maximum phosphate specific consumption rate((?)) 0.435d^-1,the phosphate removal saturated concentration(K_s,PO4^3-)49.648 mg/L,the maximum yield coefficient of denitrifying phosphate accumulating organisms using nitrite(Y_max,p)0.906,the sludge decay coefficient of denitrifying phosphate accumulating organisms using nitrite(b_p) 0.0015d^-1,the denitrification rate coefficient(k_NO2^-)3.108 mg/(gMLSS·h) in anoxic stage.By comparing the kinetic parameters of denitrifying phosphate accumulating organisms using nitrite and denitrifying phosphate accumulating organisms using nitrate,the absorption capacity of the organic matter,the anaerobic phosphorus release ability and the phosphorous absorbing ability of the former were stronger than them of the latter,but denitrifying capacity was opposite.