Study On The Denitrification And Phosphorus Removal In Two-sludge System Combined With Three-stage Induced Crystallization Process

The traditional wastewater treatment plant process has the problems of carbon source competition between phosphorus accumulating organisms and denitrifying bacteria,the sludge age contradiction between phosphorus accumulating bacteria and nitrifying bacteria,and the influence of nitrate in reflux sludge on phosphorus accumulating bacteria.The concentration of pollutants in effluent is difficult to meet the I-class A criteria specified in Discharge standard of pollutants for municipal wastewater treatment plant?GB18918-2002?.At the same time,precious phosphorus resources in sewage have not been recovered,and phosphate rock has been listed by the Ministry of Land and Resources as one of the 20 minerals that can not meet the needs of national economic development after 2010.That's why phosphorus recovery is particularly important.The denitrification and phosphorus removal in two-sludge system combined with induced crystallization process can not only solve the problems existing in the traditional process,but also recover phosphorus resources.The cultivation of nitrifying sludge and denitrifying phosphorus accumulating sludge is the key to the successful operation of the whole process.During the 30 days of cultivation of nitrifying sludge,the removal rate of NH₃-N increased from 47.7%to94.5%.The denitrifying phosphorus-accumulating sludge was cultured by two-stage method,which consisted of anaerobic/aerobic and anaerobic/anoxic/aerobic stages.The phosphorus removal rate of PAOs cultured in the first stage increased from about30%to more than 70%,and the ratio of phosphorus accumulating to releasing amount was about 1.26.The anaerobic phosphorus accumulating amount of denitrifying phosphorus-accumulating sludge domesticated in the second stage accounted for 95.8%of total phosphorus accumulating amount,which showed DPAOs was successfully cultured.Undomesticated aerobic phosphorus accumulating bacteria also had a certain ability of denitrifying phosphorus accumulating,but since the proportion of DPAOs was relatively small,the ability of denitrifying phosphorus accumulating was relatively weak.The domesticated denitrifying phosphorus accumulating sludge could use nitrite as electron acceptor at low concentration,but when the concentration exceeded 45 mg/L,the denitrifying phosphorus accumulating sludge was completely inhibited.Taking domestic sewage as the treatment object,the treatment effect of two-sludge process was explored,and its influence on two-sludge process was studied by changing sludge reflux ratio.The results showed that the average removal rates of COD,NH₃-N,TN and TP were 91.8%,85.6%,72.1%and 92.0%respectively.The other indicators except NH₃-N met the I-class A criteria specified in Discharge standard of pollutants for municipal wastewater treatment plant?GB18918-2002?.The removal efficiencies of COD and TP were relatively stable under different reflux ratios.The effect of sludge reflux ratio on the removal efficiencies of NH₃-N and NO₃^--N was greater.When the sludge reflux ratio was higher,the concentration of NH₃-N in effluent higher and the concentration of NO₃^--N in effluent was lower.The sludge reflux ratio had no significant effect on the removal of total nitrogen.Thus,the study showed that the removal effect was the best when sludge reflux ratio was chosen to be 0.2.Taking domestic sewage as the treatment object,the treatment effect of the denitrification and phosphorus removal in two-sludge system combined with three-stage induced crystallization process was explored.The process had good removal effects on COD and TP,with average removal rates of 92.0%and 97.3%,and phosphorus recovery rate of 65.1%.The average concentration of NH₃-N and TN in effluent was 5.82 mg/L and 13.2 mg/L,with removal rate of 86.5%and 71.8%.When analyzing the flow of COD,N and P in the process,the equilibrium ratios were 88%,97%and 93%,respectively.