New Biofilm-micro Flocculation Filter Synergistic Removal Of Nitrogen And Phosphorus Production Test And Related Mechanism Research

In the case of the low total carbon source of wastewater plants in the southern region of China,there is limited room for reduction of total nitrogen and total phosphorus using whole process biological system renovation to meet the increasingly stringent nitrogen and phosphorus emission targets.The upgrading of urban wastewater requires the study of more advanced treatment processes to provide deeper treatment of nitrogen and phosphorus.This topic addresses the limited space for the activated sludge treatment system to enhance nitrogen removal and phosphorus removal,and the lack of technology to integrate nitrogen removal,SS removal,and phosphorus removal in the existing tailwater treatment methods of urban wastewater plants,and proposes a new biofilm-micro flocculation filter synergistic nitrogen removal and phosphorus removal process.The optimal operating parameters of the new biofilm-micro flocculation filter were obtained,the mechanism of nitrogen removal and phosphorus removal in the filter was analyzed,and the changes of the population structure and abundance of microorganisms in the filter were studied.The test site is located in a town wastewater treatment plant in Fuzhou,and the daily treatment design scale is 120 m³/d,the test raw water is the secondary biological treatment effluent of the plant,the test water quality indicators are:COD ranged from 12 to 23 mg/L,TN from 7.8 to 15.5 mg/L,NO₃^--N from 6.6 to 12.5 mg/L,NH₄⁺-N from 0.5 to 2.1 mg/L,TP from 0.19 to 0.44 mg/L,PO₄^3--P from 0.14 to 0.38 mg/L,and SS from 14 to 23 mg/L.The main study contents and conclusions are as follows:（1）The new biofilm filter was started up by the optimized inoculation and membrane hanging method,which was judged according to the effluent quality and the change of microbial population structure,and the filter was started up successfully after 15 days.The TN removal rate was>80%,COD removal rate was>70%,NO₃^--N removal rate was>90%,and TP removal rate was about 19-21%after the start-up.（2）The appropriate C/N was beneficial to the denitrification of the biofilm filter.The TN removal rate reached 81.8%,COD removal rate reached 75.1%,and NO₃^--N removal rate was 92.4%when the C/N was 5.34.The highest nitrogen removal rate of the filter reached 79-81%when the HRT was 1.06 h.The change of HRT had less effect on the changes of COD removal rate and DO.（3）Without the addition of flocculant,the biofilm filter had limited phosphorus removal efficiency,and the TP removal rate was only 19-21%.The biofilm-micro flocculation filter was used for synergistic denitrification and phosphorus removal by adding PAC,and the TP removal rate reached 76.0%,and PO₄^3--P removal rate reached 86.7%at 5mg/L.The addition of PAC had no significant effect on denitrification and carbon removal.（4）The maximum hydraulic load that the filter tank could withstand for efficient denitrification was 4.13 m³/（m²·h）.The high hydraulic load did not significantly reduce the phosphorus removal efficiency of the filter tank,indicating that the new biofilm-micro flocculation filter tank is suitable for phosphorus removal under high hydraulic load conditions.（5）The new biofilm-micro flocculation filter adopts the combined backwashing mode of gas flushing,combined gas-water backwashing,and water flushing,with a backwashing cycle of 7 d.The water flushing intensity is 5-10 L/（s m²）,and the gas flushing intensity is10-15 L/（s m²）.The air flushing,combined air-water flushing,and water flushing times were 2～4 min,4～6 min,and 5～8 min,respectively,with a total backwashing time of about15 min.The treatment effect could be restored to the stabilization period within 40 min after backwashing.（6）The NO₃^--N removal rate can reach more than 80%stably,and the TP concentration in the effluent can still be reduced to less than 0.15 mg/L under the condition that the water temperature is about 9～13℃in the winter period.On the basis of ensuring the NO₃^--N and COD removal effect,the NH₄⁺-N removal rate can be improved by turning on the aeration equipment in the middle of the filter tank and adjusting the HRT and air-to-water ratio.Under the stage aeration with HRT of 1.4 h and the gas-water ratio of 8,the NH₄⁺-N removal rate is about 40～45%,NO₃^--N removal rate is 70～76%,and TN removal rate is about 57～62%at this time.（7）A kinetic model for the clogging of the biofilm filter was derived and established as（?）,It shows that the head loss of the filter cell is closely related to the filtration speed and operation time of the filter cell.（8）The study compared the new biofilm-micro flocculation filter with the existing high-efficiency sedimentation tank-fiber carousel filter in the wastewater plant,and the effluent quality of the new biofilm-micro flocculation filter was better than the existing process,and the cost per ton of water treated was 0.039 Yuan/m³lower than that of the combined process.The results showed that the effluent from the new biofilm-micro flocculation filter was less polluting to the surface water environment.（9）An economic assessment of the production-scale pilot plant showed that the unit wastewater construction cost was about 2353 Yuan/（m³/d）,and the ton water treatment cost,including ton water electricity consumption and chemical cost,was about 0.207 Yuan/m³.（10）Sequencing analysis of the microbial diversity of the new biofilm filter showed that the activated microorganisms were dominated by the phylum Aspergillus at the phylum level and two dominant denitrifying genera,Hydrogenophaga and Dechloromonas,werepresent at the genus level.Backwashing had no significant effect on the abundance ofmicrobial population structure but caused a decrease in the number of microbial populations;the addition of PAC reduced the abundance of Bacteroidetes but had basically no effect onProteobacteria,several denitrifying genera with higher abundance decreased insignificantly,and the relative abundance of denitrifying genera could still reach 48.76%.