Nitrogen And Phosphorus Removal In Hybrid Ecological Filters

Pollution by nitrogen and phosphorus are widespread in the world and it has become a prominent problem affecting the improvement of water quality.Water eutrophication caused by nitrogen and phosphorus pollution has affected agriculture,fishery,tourism and many other industries,and even threatened public health security.Aiming at the control of nitrogen and phosphorus pollution in water with low C/N ratio,this paper carried out a study on the efficiency of nitrogen and phosphorus removal in ecological filters.The research results are expected to provide theoretical support and practical reference for the control of nitrogen and phosphorus pollution in similar water environments.In this study,sponge iron was modified to improve its phosphorus adsorption capacity,and its regeneration and phosphorus recovery technology were explored.Small test system of sponge iron phosphorus removal filter and "steel slag+sponge iron" phosphorus removal filter were constructed to study its phosphorus adsorption capacity and adsorption capacity after regeneration.The hybrid ecological filter,the control group filler,and hybrid ecological filter dosing Fe2+strengthen denitrification were carried out.The effects of nitrogen load,organic load,hydraulic residence time,and water inlet mode on the filters were investigated,obtained the optimum condition under different water conditions.The similarities and differences of microbial population structure under various working conditions were analyzed.A experimental demonstration project of hybrid ecological filters was set up,and the removal performance of total nitrogen(TN),total phosphorus(TP),ammonia nitrogen(NH4+-N)and chemical oxygen demand(COD)by upflow filter and downflow filter was investigated.The study of sponge iron phosphorus removal filter shows that the theoretical maximum phosphorus adsorption capacity of modified sponge iron was increased from 4.17 mg/g to 18.18 mg/g.The saturated sponge iron was regenerated with a 98%activity recovery after treatment using 1 mol/L sodium hydroxide and 6%sulfuric acid sequentially.The sponge iron fiter has good dynamic phosphorus removal performance.The accumulated phosphorus in the sponge iron filter attained 11.49 kg/m3 which accumulated before and after regeneration,and that of"sponge iron+steel slag" filter attained 2.41 kg/m3.Phosphorus could be recovered from the desorption solution from the sponge iron regeneration in the form of struvite,and a maximum phosphorus recovery of 97.8%was achieved at the optimal generation condition of pH=10,n(Mg2+):n(PO43-):n(NH4+)=1.3:1:1.1.Under optimal conditions,the phosphorus recovery rate attained 97.8%.The study of nitrogen removal in hybrid ecological filters shows that,the hybrid ecological fiters can remove nitrogen and COD pollutants by Fe-C micro-electrolysis coupled autotrophic/heterotrophic microbial reaction under mixotrophic conditions.When worked for a long time,it still had good denitrification performance after more than 400 days of experiments,and the control group hrbrid ecological fiter invalid after continuous opera 100 days.The influent way has a great influence on the removal of different forms of nitrogen.It is beneficial for ammonia nitrogen removal to adopt downward flow inlet method and nitrate nitrogen removal to adopt upward flow inlet method.When the HRT was 10h and the COD was 40 mg/L,the average removal rate of nitrate nitrogen,ammonia and COD in the downward flow was 57.2%,96.9%and 88.1%respectively.The average removal rate of nitrate nitrogen,ammonia nitrogen and COD in the upward flow were 79.7%,75.7%and 88.7%respectively.Adding Fe2+to the hybrid ecological fiter can enhance the removal of nitrate nitrogen.When the water is free of COD,HRT is 10 h,and n(Fe2+):n(NO3-)is 10:1,the average removal rate of nitrate nitrogen is 91.4%and the average removal rate of ammonia nitrogen is 50.2%.The microbial population analysis shows that the main microbial reaction in the filters was autotrophic denitrification.Autotrophic denitrifying bacteria were mainly Thiobacillus,unclassified_f_Gallionellaceae and Denitratisoma.In the filter of the control group,the structure of the bacterias was different from that of the former two.Experimental demonstration project of hrbrid ecological fiter were build for treating river water.It attained good removal of pollutants the condition under which the inflow has low C/N ratio.The average TN concentration of the influent water is 7.69 mg/L,the average TN removal rate of the upflow is 41.2%,and the average TN removal rate of the downflow is 31.0%.When the average concentration of COD in the influent is 38.89 mg/L,the average removal rate of COD in the upflow hrbrid ecological fiter is 47.5%;the average removal rate of COD in the downflow hrbrid ecological fiter is 47.2%.The ammonia nitrogen in the effluent was kept at 0-0.27 mg/L.The average concentration of TP in the influent is 0.19 mg/L,the average removal rate of TP in the effluent in the upflow hrbrid ecological fiter is 68.2%,and the average removal rate of TP in the effluent of downflow hrbrid ecological fiter is 68.4%.