Application Of Rapid Phosphorus Reduction And Long-term Control Methods In Urban Lakes

The high phosphorus concentration in urban lake waters and its massive release from sediment are the main causes for eutrophication.Therefore,the reduction of phosphorus concentration plays an important role in improving the water environment of urban lakes.This paper carried out the rapid removal of particulate phosphorus in water and the long-term control technology of internal phosphorus in sediment.In the reserach,the clay mineral-attapulgite(AT)was used as the carrier to prepare modified flocculation materials and phosphorus inactivation materials by compounding technology,and then they were further used for the rapid removal of particulate phosphorus in suspended particles and the control of phosphorus release from sediment,respectively.Taking the heavily polluted sediments of urban lakes as the research object,the control effect of phosphorus inactivation materials,submerged plants and their coupling on the internal phosphorus of sediments at different pollution levels and different seasons was explored by indoor simulation and field site remediation experiments,in order to find an effective technical way for the rapid reduction and long-term control of phosphorus in urban lakes.Firstly,a series of flocculation materials were prepared by mixing attapulgite with polyaluminum(PAC)and polyacrylamide(PAM),which were used for the removal of turbidity and algae in water.The effects of raw material composition,compound ratio and important factors on coagulation effect were discussed.The experimental results showed that the flocculation effect of AT-PAC-PAM was better than that of AT-PAC.When the addition amounts of PAC and PAM were 20% and 0.2% of the mass of attapulgite,respectively,the flocculation effect was the best.The AT-PAC-PAM modified material achieved 95.06%turbidity removal from a 1500 mg/L kaolin suspension at p H=7 and a concentration of 5 mg/L.Under the same conditions,92.57% turbidity removal from actual lake water could be achieved.The indoor simulation experiment set four different treatments: control group,Vallisneria Spiralis group,phosphorus inactivation material group and Vallisneria Spiralis+phosphorus inactivation material group to explore the control effect of Vallisneria spiralis,phosphorus inactivation material and their combination on controling phosphorus release and active phosphorus in sediment with different pollution levels(low,medium,high and extremely high phosphorus concentrations).The results showed that the control effect of the Vallisneria Spiralis+phosphorus inactivation material group on the concentration of nitrogen and phosphorus in overlying water,porewater water and phosphorus form in sediment was better than that of the phosphorus inactivation material group and the Vallisneria Spiralis group.After 120-day experiment,it was found that the average concentrations of total phosphorus(TP)and phosphate(SRP)were controlled at 0.029–0.084 mg/Land0.003–0.03 mg/L,respectively,and the average concentrations were 0.062 mg/L and 0.015 mg/L,respectively,which were reduced by 72.22% and 80.51% compared with the control group.Compared with the control group,the phosphorus inactivation material group,the Vallisneria Spiralis group and the Vallisneria Spiralis+phosphorus inactivation material group could reduce the release of SRP in the sediment interstitial water,and the Vallisneria Spiralis+phosphorus inactivation material group performed the best,with the removal rate reaching 94.7% compared with the blank group.Through detailed analysis and comparison of phosphorus speciation changes in surface sediment before and after treatment,it was preliminarily proved that the main reason why phosphorus release in sediment could be effectively controlled by phosphorus inactivation materials and the treatment methods of litter+phosphorus inactivation materials was that mobile-P in sediment could be significantly reduced and partially converted into inert calcium phosphate(Ca-P)and residual phosphorus(Res-P).Finally,in order to further confirm the actual performance of the combined process of Vallisneria Spiralis and phosphorus inactivation materials on phosphorus removal,a field enclosure experiment was conducted in Mochou Lake,Nanjing.The experimental results showed that the Vallisneria Spiralis,phosphorus inactivation materials and their combinations have different degrees of control effect on phosphorus in water,and the Vallisneria Spiralis+phosphorus inactivation material group has the best control effect on phosphorus release in water and sediment.During 120 days of the experimentays,the average concentration of total phosphorus in water was 0.072 mg/L,which was 77.44% lower than that in the control group.The average SRP concentration was 0.021 mg/L,which was 73.7%lower than that of the control group,and their correponding SRP release flux in interstitial water were reduced by 99.77-99.96%.The Mobile-P content in 0–2 cm surface layer of sediment in the Vallisneria Spiralis+phosphorus inactivation material group were decreased by 60.08%,52.7% and 33.3% in different months,respectively,and the contents of Ca-P and Res-P in the inert phosphorus increased by 10.5%–28.5% and 5.7%–8%,respectively.