In-situ Chemical Control Experimental Study On The Sediment Phosphorus

In recent years, the eutrophication of lakes and reservoirs is very serious in ourcountry. Nitrogen and phosphorus are the main factors that cause eutrophication. Afterthe nutrients are uptaken in water,some will deposit down to the sediment with the deathof microorganisms. With the more efforts in management sewage, the external sourcenitrogen and phosphorus has very little. But nitrogen and phosphorus in the sedimentsbecome the main factors that cause eutrophication. Control the release of phosphorus insediments is an essential to treat eutrophic waters.More and more attention are paid to the in situ control technology of sedimentphosphorus release. However, a systematic study is still required. Taking No.2LakeDistrict sediments of Yan Ming Lake as the research object in simulated laboratoryconditions, the paper studied the disciplines of phosphorus release in the interface ofsediment pore water and the interface of sediments-water and also investigated thecontrol effects of different in situ control technologies including calcium nitrate, zeolitecapping and the combination of aeration and zeolite capping technology. The mainresults and conclusions are as follow.(1) Temperature and pH have a very significant impact on the phosphorus releaseof sediment. With temperature（25℃）increasing，phosphorus releasing from sedimentis faster and total phosphorus concentration in the pore water is higher. Alkalineconditions and acidic conditions are favorable for phosphorus release to the pore water,as pH is5,7and9, the maximum total phosphorus concentration in the pore water was1.030mg/L，0.915mg/L，1.175mg/L respectively.(2) In the interface of sediments overlying water, temperature, pH, DO anddisturbance have a great influence on the phosphorus release With temperature rising,phosphorus release would increase. When temperature was25℃, The biggestphosphorus concentration of the overlying water was0.380mg/L,it was1.49times astemperature was5℃. And the higher the temperature was,the faster the totalphosphorus concentration achieved the maximum. The pH influence on the phosphorusreleasing was mainly reflected in that in the neutral condition, the phosphorus releasewas smallest, and alkaline or acidic conditions would promote phosphorus release.Control phosphorus release, the effect of DO was the most obvious. Oxygenation madethe sediment in the aerobic state, can be very good inhibition for the phosphorus release.Total phosphorus concentration of the overlying water was within the scope of0～0.205mg/L. Under anaerobic conditions, the concentration of total phosphorus inoverlying water maintained at4.205to4.335mg/L after360hours. When thedisturbance intensity was low, most of the sediment was not resuspended, only made thespread of phosphorus in the overlying water. When disturbance intensity was enough,sediment resuspension occurs, resulting in total phosphorus concentration of theoverlying water increased.(3)Calcium nitrate can control phosphorus release from sediments. When thedosage was greater, the control effect was better and the timeliness was longer.(4) Natural zeolite barrier had some effect in controlling sediment phosphorusrelease. The effect of control phosphorus release, CaCl2modified zeolite is best,followed by NaCl modified zeolite. The higher the temperature (25℃)was, the worsethe control effect was. When the particle size was smaller and the barrier was thicker,the control effect was better.(5) At the beginning of the experiment, the air can not reach the sediment surface,but the emerged disturbance made the total phosphorus concentrations in the overlyingwater higher than that under anaerobic conditions. However, with time going, aerationon the zeolite barrier would be better than merely using zeolite barriers on effect ofcontrol phosphorus release from sediment. The combination techniques of aeration andzeolite barrier for controlling sediment phosphorus release had a very good result.