Study On Enhancing Phosphorus Adsorption Of Sediment In Estuary Wetland

Enhancing the phosphorus adsorption ability of sediment is the key toimprove the phosphorus removal rate in wetland, because the adsorptionand transformation of phosphorus by sediment is the crucial pathway toremove phosphorus from water body. The sediment of Luoshijiang Riverwetland in Yunnan Province was the experiment subject. Different methodswere used to improve sediment’s phosphorus adsorption ability. Theformation distribution and transformation of phosphorus entering thesediment was also studied. The results were as follows.(1) Water aerationaccelerated phosphorus adsorption and also improved DO concentration inoverlying water. No obvious extra improvement was discovered under alonger aeration duration (120min/d), which indicated that an appropriateaeration duration should be chose to balance effect and cost in actualapplication. Aeration accelerated the formation of Fe-P and Ca-P, while Al-P was showed not to be affected.(2) Resuspension accelerated phosphorusadsorption and SRP dropped dramatically to0.01-0.04mg/L at the thirdday. DO was consumed considerably by sediment stirring, lower than1mg/L all the time. Sediment aeration favored reoxygenation and average DO was5.81mg/L. Due to different DO levels, more Al-P formed in stirredsediment and more Fe-P formed in aerated sediment. Two kinds ofresuspension both accelerated the formation of Ca-P.(3) The addition ofFeCl3and AlCl3caused a higher increase on the sediment’s adsorptionenergy (K), maximum adsorption capacity (Qm), and maximum bufferingcapacity (MBC), and meanwhile, a more obvious decrease on equilibriumphosphorus concentration (EPC0), compared to CaCl2. EPC0of FeCl3added sediment was lower than that of AlCl3at the minimum dosage, whilethe other adsorption parameters(KF、KL、Qm、MBC)improvementofAlCl3were better than those of FeCl3.(4)Among different heat treatmenttemperatures(150,350,550,750℃),150℃and750℃both improved KL,KFand MBC values and decreased EPC0value of sediment. Heat treatmentimproved S/L-P, Al-P and Ca-P contents. Fe-P content decreased sharplyby49%and68%under550℃and750℃heat treatment, respectively,which showed a tendency of transforming into S/L-P, Al-P and Ca-P.(5)Among different concentrations hydrochloric acid, samples treated by0.1mol/L acid had the highest adsorption capacity. KL, KF, Qmand MBCvalues were improved by50%,60%,140%and236%. But EPC0valueincreased a little. The lost of Ca-P increased along with the acidconcentration increased. Al-P and Fe-P content increased first, reaching thepeak at0.1mol/L acid treatment (1.8and3.6times of initial sample,respectively), and then decreased. This was the reason that0.1mol/L was the best one.(6)During11weeks after phosphorus entering the sediment,S/L-P increased only0.80-1.00mg/kg. Ca-P and O-P contents increasedcontinuously with small fluctuation. Increase of Al-P and Fe-P contentsduring the first week accounted for more than half of the phosphoruscontent entering the sediment. Al-P content kept between39.43and43.98mg/kg. Fe-P content decreased during later period, which showed atendency of transforming into Ca-P and O-P. Among the five methods,water aeration, resuspension and phosphorus-fixing reagents are valuableto engineering application.