Study On The Technology Of Simultaneous Nitrogen And Phosporous Removal Based On Solid-phase Denitrification And Phosphorous Adsorption

As the nitrogen and phosphorous pollution in surface water and groundwater of China has become increasely serious, raising the discharge standard of pollution for wastewater treatment plant(WWTP) becomes the most direct and effective way to control water pollution. The concentration of organic matter in the influent of WWTP is the key factor to guarantee the removal efficiency of nitrogen and phosphorus from wastewater and to ensure the discharge to reach the relevant standard. However, the development trend of municipal sewage with low carbon source is presented, which has brought great pressure and challenges to simultaneous nitrogen and phosphorous removal in WWTP. Based on a comprehensive review of existing solutions for low carbon sewage, it is considered that it is not only because of the process technology but also the method that resulted in complex treatment procedure, higher requirement for operation and control, constrained conditions and certain limitation in application in the existing solutions for wastewater with a low C/N ratio. Therefore, it is more import to find a new method to remove nitrogen and phosphorus efficiently. Solid-phase denitrification and phosphorous dynamic adsorption, which have draw great attention from the scientist in recent years, are the new prominent wastewater treatment techniques. These novel processes can fundamentally solve the problem that the nitrogen and phosphorus removal efficiency is dependent too much on the influent organic matter, and thus provides a new idea and method to remove nitrogen and phosphorus from wastewater with low carbon source.In order to accelerate the investigation and development of the solid-phase denitrification and phosphorous dynamic adsorption process, particular to accelerate the application of the two processes for the treatment of wastewater with a low C/N ratio, continuous-flow experiment combined with batch test was carried out, and the screening of solid carbon substrate and preparation of phosphorus adsorption materials are studied. Based on the materials screened and prepared in the previous research, the solid-phase denitrification biofilter(SPDB) process and phosphorous removal adsorption bed(PRAB) process are constructed, and the effects of operation parameters are explored with the nitrate and phosphate removal efficiency as the response value. The predictive polynomial quadratic equation models are established and the operation parameters of the two processes are also optimized. To widen the application range of the two processes mentioned above, two sets of combined process, coagulation sedimentation-biological aeration filter-solid phase denitrification biofilter-phosphorous removal adsorption bed(CS-BAF-SPDB-PRAB) and sequencing batch biofilm reactor-solid phase denitrification biofilter-phosphorous removal adsorption bed(SBBR-SPDB-PRAB) are developed for the first time. The effect of operation parameters on the nitrogen removal performance of BAF-SPDB and SBBR are intensively studied, and the optimum operation conditions are determined. The mechanism of the effect of operation parameters on nitrogen removal performance is analyzed from the perspective of microbial community structure. Finally, on the basis of above researches, the simultaneous nitrogen and phosphorous removal performance of the two sets of combied processes in the actual application of treating domestic wastewater with low C/N ratio was investigated. The conclusions are as follows:(1) Material types, physico-chemial properties and filling patterns of the solid carbon substrate have significant effect on denitrification performance. The results show that, with the same molecular weight(Mw)(80,000), the biodegradability and denitrification perforamcne of polycaprolacctone(PCL) was better than that of poly(butylenes succinate)(PBS); the biodegradability and denitrification perforamcne of PCL decreased with the increase of average Mw; the physical structure and surface properties of PCL play a more important role than Mw in biological dentrification during the solid-phase denitrification process;The nitrogen removal efficiency of solid-phase denitrification reactor filled with polymer particle was much higher than that filled with inclined plate under shorter HRT conditions. Additionally, the optimum conditions for the preparation of phosphorus adsorpbent are: the volume ratio of polyurethane foam and porous hydrated calcium silicate mixture is 2.56:1, among which is 50 m L waterborne polyurethane with concentration of 100 g/L, and 12 g hydrated calcium silicate.(2) In SPDB, HRT(X1), influent NO3--N concentration(X2), influent CODCr, concentration(X3) and the interaction between X1X2 significantly affect the nitrate removal efficiency(P<0.05), while the interaction between X1X3 and X2X3 have non-significant impacts. At the same time, nitrate removal model proved to be highly significant, and the calculated values of the equation are agreed well with the experimentally tested data, suggesting that the nitrate removal efficiency of PRAB can be predicated accurately The optimum conditions obtained are HRT 3.5 h, influent NO3--N concentration 14.73 mg/L, and influent CODCr concentration 15.00 mg/L. Under the optimized conditions, the nitrate removal efficiency of the SPDB is up to 99.23%.(3) In PRAB, HRT(X1), influent PO43--P concentration(X2), temperature(X3), initial p H value(X4) and the interaction between X1X2, X1X3, X1X4, X2X3 and X2X4 have significant influences on the phosphate removal efficiency while the interaction between X1X3 have non-significant impacts. Meanwhile, Phosphate removal model proved to be highly significant, and the calculated values of the equation are agreed well with the experimentally tested data, suggesting that the phosphate removal efficiency of PRAB can be predicated accurately. In PRAB, The optimum conditions obtained are HRT 79.77 min, influent ?(PO43--P) 1.70 mg/L, Temperature 34.04 °C and initial p H value 9.68. Under the optimized conditions, the phosphate removal efficiency of the adsorption bed is found to be 93.46%.(4) In the CS-BAF-SPDB-PRAB combined process, to realize favorable nitrifying and denitrifying performance simultaneously in the BAF-SPDB unit, the influent C/N ratio and gas/water ratio of BAF should be set at 3:1 and 4:1, respectively, HRT of BAF and SPDB should be set at 3.5h and 1.5h, respectively, and the temperature should be controlled above 20 °C. In addition, the influence of the macro operation parameters on the performance of the BAF and SPDB has a direct relationship with the dynamic changes of the micro microbial community. The influence of gas/water ratio, temperature and influent ammonia nitrogen loading on nitrification performance in BAF is mainly embodied in the change of composition, amount and activity of ammonia oxidizing bacteria Candidatus Nitrospira defluvii and nitrite oxidizing bacteria Nitrosomonas sp. Nm47, while that on denitrification performance in SPDB is mainly embodied in the change of composition and amount of solid carbon substrate degrading denitrifying bacteria Pseudomonas sp, Myxobacterium AT3-03 and heterotrophic denitrifying bacteria Dechloromonas agitate, Thauera aminoaromatica, Comamonas granuli and Rubrivivax gelatinosus. In addition, the change of microbial community structure of heterotrophic nitrification and aerobic denitrification with operation conditions also play a very important role in ensuring the stable nitrification and denitrification under extreme operation conditions(low temperature and low gas/water ratio).(5) In the SBBR-SPDB-PRAB combined process, stable nitrification and high nitrogen removal can be achieved in the SBBR reactor when the operation cycle time is 3 h, and the aeration rate is 3.8 m3/(h·m3). The optimized operation parameters can significantly improve the volume removal rate of SBBR and reduce the energy consumption. SBBR also displays strong tolerance to low temperature. When the temperatue is 10 °C, the average ammonia nitrogen removal efficiency can still be maintained at 82.7%. Nitrosomonas and Nitrospira, as the key microorganism in SBBR, play a leading role in ammonia and nitrite oxidation. Thauera and Bacteroidetes are the main denitrying bacteria and phosphate accumulating bacteria in SBBR system. Trichococus and Saprospiraceae uncultured play a leading role in organic removal.(6) Low carbon domestic wastewater with CODCr concentration of 149~185.3 mg/L, NH4+-N concentration of 25.6-38.5 mg/L, and TP concentration of 3.52-7.76 mg/L is treated in the combined process of CS-BAF-SPDB-PRAB. The average removal efficiency of NH4+-N, TN and TP is up to 97.6%, 91% and 97%, respectively,and the average concentration of NH4+-N, TN, TP and CODCr in the effluent is 0.77, 3.3, 0.17 and 15 mg/L, respectively, which are much lower than the primary standard of wastewater emission control regulation.(7) Low carbon domestic wastewater with CODCr concentration of 93~140mg/L mg/L, NH4+-N concentration of 34~36 mg/L, TN concentration of 41~45mg/L and TP concentration of 3.52-7.76 mg/L is treated in the combined process of SBBR-SPDB-PRAB. The average removal efficiency of TN and TP can reach 90% and 95.6%, respectively,and the average concentration of TN, TP and CODCr in the effluent is 4.23, 0.21 and 25 mg/L, respectively, which are much lower than the primary standard of wastewater emission control regulation.