Inhibition Of Phosphorus Release From Sediment By Zeolite/Hydrous Metal Oxide

Recently,the eutrophication gained increasing attention,and the release of internal phosphorus became the main source of this phenomenon.In this study,two materials:zeolite/hydrous aluminum oxide（ZHAO）and zeolite/hydrous lanthanum（ZHLO）have been prepared from coal fly ash.ZHAO was investigated to cap sediment to reduce P concentration in an urban pond which was stratified or was not easy to be disturbed using batch and 28-day sediment core incubation experiments.And ZHLO was used to amend the sediment of Lake Taihu which belongs to shallow lake.As for the results of ZHAO on controlling the release of phosphorus from sediment:1)The adsorption isotherm studies illustrated that the maximum adsorption capacity of phosphate,ammonium and manganese（II）ions on ZHAO were 11.88,7.74 and 13.23 mg/g,which were 7.3,10.3,and 10.5 times greater than those of sediment,respectively.This suggested that ZHAO was a unique material to block the release of not only anionic P,but also cationic NH₄⁺and Mn²⁺from sediment.2)ZHAO was able to reduce SRP level from pond water and increasing pH led to decreased removal performance.3)P fractionation measurements demonstrated that adding ZHAO resulted in the reduction of release-sensitive P fractions（labile-P fraction and reductant-soluble P fraction）in sediment and diminished the release of P under anaerobic conditions.4)We also found that,during the 28-day sediment core incubation period,ZHAO treatment was more efficient（reducing TP and SRP in the pond water overlying the sediment cores by more than 90%）and durable than the traditional alum treatment which has been used for decades worldwide.ZHAO is a promising sediment amendment material to control the internal P loading in eutrophic lakes/ponds.As for the result of zeolite/hydrous lanthanum oxide on controlling the release of phosphorus from sediment:1)The adsorption capacity of phosphate and the P release from amended and raw sediments under different pH and anaerobic conditions have been investigated.The results showed that,after adding 24‰zeolite/hydrous lanthanum oxide into sediments,the maximum adsorption capacity of phosphorus reached 3.02mg/g,which was equivalent to twice the adsorption capacity of raw sediment.The calculated maximum adsorption capacity of phosphorus by zeolite/hydrous lanthanum oxide was 61.44 mg/g,which was much higher than other materials used to amend sediments in previous literatures.2)In light of the results of P fractionation,zeolite/hydrous lanthanum oxide was able to transform highly unstable or medium unstable P forms to stable P forms（HCl-P and Res-P）.3)The alkaline condition（pH>9）,the high temperature and the anaerobic condition significantly promoted the release of phosphorus from sediment,however,the release could be inhibited by adding zeolite/hydrous lanthanum oxide into the sediment.4)In addition,although Mn²⁺and ammonium ions those are harmful for aquatic organisms released under the anaerobic condition,we found that the release could also be controlled by adding zeolite/hydrous lanthanum oxide.5)Finally,zeolite/hydrous lanthanum oxide-amended sediment performed well to reduce P level in the presence of actual lake water.Therefore,zeolite/hydrouslanthanumoxideisapromising sediment-capping material to inhibit P release from sediments and to manage eutrophication in water bodies.In conclusion,the absorption mechanism,environmental factors and the application on the study of controlling the release of phosphorus from sediment was investigated.It proves that these two materials have the strong ability to effectively control the release of internal phosphorus,as well as reducing the phosphate concentration in the overlying water.In addition,these materials were prepared by fly ash which is one of the primary solid waste of our country so that the disposal of the fly ash could be also solved.Therefore,the eutrophication controlled by zeolite/hydrous aluminum oxide or zeolite/hydrous lanthanum oxide has a great prospect.