Effect Of In-situ Physical Elution On The Properties Of Nitrogen& Phosphorus Release Of The Polluted Sediments And Restoration Of Aquatic Plants

During the treatment process of urban polluted rivers,it should be considered not only the restoration of contaminated sediments,but also the restoration of damaged ecosystems especially submerged plants communities.This subject aimed at an in-situ remediation technology to sediment,in-situ physical elution technology.The sediment of Liangshui River in Beijing was taken as the research object.Physical&chemical indexes,typical pollutants,nitrogen（N）and phosphorus（P）forms in sediment were compared between treatment group and control group both for on-site and simulate test.So as the release characteristics of N and P.Furthermore,two treatments of aeration and hydraulic elution were simulated in the laboratory to study the change of simulated treatments on the physical&chemical characteristics of sediment as well as the differences of germination and growth features of an submerged macrophyte,Vallisneria natans within the sediments before and behind the treatments.The results were as follows:（1）Significant change of physical&chemical indexes and typical pollutants in sediment happened in specified depth range（on-site test:depth in 0～5 cm;simulated test:depth in 10 cm）with the in-situ physical elution technology,such as the increase of p H and oxidation-reduction potential（ORP）as well as the decrease of moister content;The removal rate of organic matter（OM）,TN,TP were reached 70.12±4.80%,66.85±1.98%and 43.14±3.12%in simulated treatment,respectively.（2）In-situ physical elution technique has significantly changed the distribution of nitrogen and phosphorus in the 0～10 cm sediment.The removal of TN and TP in 0～10cm sediment with in-situ physical elution is mainly achieved by removing particulate organic nitrogen（PON）and Al bound phosphorus（Al-P）,organic phosphorus（OP）:the contribution ratios of PON to TN-removal reached 55.0%and 73.6%respectivel during on-site and simulation test,and the contribution ratios of Al-P,OP to TP-removal reached37.0%,66.7%and 31.3%,43.6%,respectively.（3）In-situ physical elution technology showed a significant inhibitory effect on the release of NH₄⁺-N,PO₄^3--P and TP from sediment to overlying water:on the 30th day of release test,the average release rates of NH₄⁺-N,PO₄^3--P and TP were reduced by 98.6%,68.6%and 91.9%of the control group,respectively.The in-situ physical elution technology has changed the redox environment of interface between sediment and overlying water as well as achieved the removal of organic nitrogen and phosphorus forms such as PON and OP,which contributing the significant inhibitory effect for the release of NH₄⁺-N and PO₄^3--P to overlying water.（4）Aeration elution and hydraulic elution simulation treatment significantly improved the redox environment of the sediment,including significant improvement of ORP value in different depths in sediment and the reduction of the content of NH₄⁺-N and acid volatile sulfide（AVS）;Removal of OM,TN and TP in sediment were significant by both of the treatments;Hydraulic elution treatment showed more increase of the final cumulative germination rate and germination speed（GS）than those in aeration elution treatment,and the increase was drived by the ORP values（range from 1 to 3 cm）,w（NH₄⁺-N）,d（0.1）,d（0.9）,etc,in sediment;The plant height（h_p）,number of roots（n_r）,number of leaves（n_l）and average root length（l_r）of the plant seedlings both in 2 treatment groups;The growth indexes of the plant in hydraulic elution treatment showed the greater significance than those in aeration elution treatment,and the increase was drived by the d（0.5）,w（TN）,w（NH₄⁺-N）,w（Al-P）and w（AVS）,especially the removal of NH₄⁺-N and AVS might lead to the relief of the stress of hypoxic environment on the growth of Vallisneria natans.