Synthesis Of Supported Nanoscale Zero-Valent Iron And Its Removal Of Phosphorus In Urban Rainwater Runoff

Rainwater runoff contains a variety of contaminants, which are becoming the mainpollution source of urban waterbody. Among those contaminants phosphorus (P) is thecontrolling factor that causes eutrophication and it can be removed by rainwaterinfiltration pond. The key of the technology is to gain materials which have highadsorption capacity at low equilibrium concentration of phosphorus. In this researchsupported nanoscale zero-valent iron (supported-nZVI) was synthetized in thelaboratory and was used to remove phosphorus, meanwhile its removal efficeny,adsorption capacity, service cycle and adsorption mechanism were investigated. Mainresults are as follows:(1) According to the monitoring results, rainwater runoff inBeijing was polluted seriously. The concentration of all the conventional pollutants washigher than the water quality standard of class V in the surface water environment, andthe concentration of most pollutants in the initial runoff was higher than class â…¢standard of urban sewage emissions, worse still, SS and COD concentrations in runofffrom grassland and road were even higher than that in the sewage;(2) cation exchangeresin supported-nZVI and active carbon supported-nZVI were successfully synthetizedby reduction method in the solution and was used to adsorb phosphorus in rainwaterrunoff. Respectively,80.0%,90.8%and88.1%of P in runoff from grassland wasremoved by cation exchange resin supported-nZVI, active carbon supported-nZVI1#and active carbon supported-nZVI3#when the dosage was8g supported-nZVI/Lrunoff, while only26.0%and33.1%of P was removed when using cation exchangeresin and active carbon under the same condition.(3) The adsorption capacity of cationexchange resin supported-nZVI increased up to89times of cation exchange resin at theequilibrium phosphorous concentration of0.42mg/L, meanwhile, adsorption capacitiesof active carbon supported-nZVI1#and active carbon supported-nZVI3#were18and19times of active carbon under the same condition;(4)100%of particulate P in roadrunoff was removed by filter column packed with active carbon while less than14%ofdissolved P was removed when hydraulic retention time (HRT) was6h or less, and theTP concentration in effluent was far higher than0.02mg/L which was set for thestandard of eutrophication control. Unlike active carbon, active carbon supported-nZVI performed well in removing both particulate and dissolved P.99%of TP could beremoved by filter column packed with active carbon supported-nZVI and the standardof0.02mg/L could be achieved when HRT was1h or more;(5) The service life wasestimated assuming that the materials were used to process the rainwater runoff inBeing and the results indicated that active carbon could be used for1.5year before itreached saturated while active carbon supported-nZVI couled be used for10.7years.(6)The absorbate dispreaded on the surface of micropore of active carbon after phosphoruswas absorbed from prepared solution. The microstructure of active carbon stayed nearlythe same after absorption but the specific surface area decreased significantly.Ca(H2PO4)2was generated during the process which demonstrated that chemicalabsorption played an important role. As for active carbon supported-nZVI, the specificsurface area was the same after absorption but nZVI supported on active carbon wasaltered from round-shaped particles into needle shaped particles due to the generation ofgoethite (FeOOH). No significant change of iron content in active carbonsupported-nZVI was determined which indicated that no iron was washed away.Pyrophosphate was generated when phosphorus was absorbed by nZVI.