Controlling Technology Of Nitrogen And Phosphorus Release From Reservoir Sediments

Chanzhi Reservoir is the main municipal water supply of Laixi and Qingdao city, playing an vital role in water occupies of Laixi and Qingdao city. With the rapid development of industrial and agricultural production, pollutants flowed in Chanzhi Reservoir increased. Some irrational development activities also made a negative impact on the environment, leading the water pollution become increasingly prominent. The field survey shows that endogenous pollution and point source pollution are the two main pollution sources of Chanzhi Reservoir. Although point source is the largest pollution source, it can be treated more easily than endogenous pollution which locates at the bottom of reservoir and its treatment become an difficulty. However, endogenous pollution loads a significant share in the reservoir pollutant. Therefore, it is especially significant to control nitrogen and phosphorus pollution in Chanzhi Reservoir.This article, based on the natural environment survey of the region, executed a large number of indoor and outdoor tests, analyzed the pollution characteristics of water body, and studied correlations and flux of nitrogen and phosphorus in the sediments and interstitial water. Through attapulgite modification, adsorption isotherms and kinetics of nitrogen and phosphorus in water has been discussed. Finally, the inhibitory effect of modified attapulgite controlling nitrogen and phosphorus release and the influence of different barrier thickness, temperature and particle size were researched. The conclusions are as follows:(1) Current water pollution status was analyzed and water quality was evaluated.The study results show that nitrogen and phosphorus contents are high in autumn and winter and low in rainy season overall; water quality changes Significantly over time, and water quality level falls from classâ…¢to classâ…¤; Organic nitrogen occupy a high proportion of TN, and organic nitrogen pollution is serious in Chanzhi Reservoir.(2) Pollution characteristics of reservoir sediment were discussed and correlations of nitrogen and phosphorus between sediments and interstitial water were analyzed.Moisture content and organic matter of the sediment in Chanzhi Reservoir are high on the surface and decrease with depth. The surface sediments are loose and instable, which are vulnerable to storms and other external disturbances and have impacts on the overlying water. Recently, with the increase of human activities, endogenous nitrogen and phosphorus load increase. Correlations of TN and TP between sediments and interstitial water are notable and to some extent, nitrogen and phosphorus contents in sediments decide their contents in interstitial water.(3) Through indoor experiments, nitrogen and phosphorus flux in sediments were caculated in order to estimate nitrogen and phosphorus release quatity from reservoir sediment.According to nitrogen and phosphorus flux caculation, it is knowed that point source is the largest pollution source of Chanzhi Reservoir and occupy a certain proportion. Consequently, it is necessary to control endogenous pollution to improve reservoir water.(4) Natural attapulgite were modified by thermal, acid and salt means.The modification results show that particle size of natural attapulgite has decreased, resulting a larger surface area and better adsorption. Among those modifization, acid modification has the best adsorption effect.(5) Adsorption isotherms and kinetics of ammonia nitrogen and phosphate on modified attapulgite has been studied.Results show that adsorption of ammonia nitrogen and phosphate on attapulgite increase gradually with concentration of balanced ammonia solution. Compared with unmodified attapulgite, modified attapulgite can significantly adsorb more ammonia nitrogen and phosphate, and the adsorption of thermal and acid modified attapulgite are much better. Freundlich equation can describe the adsorption isotherms of nitrogen and phosphate on modified attapulgite. These 4 modified attapulgite react quickly against ammonia, slowly against phosphate. Temperature is conducive to adsorption. As the pH increase from 2 to 13, the equilibrium concentrations of ammonia and phosphate solution decline at first and then increase.(6) Influence of different barrier types, thickness, temperature and particle size on sediment nitrogen and phosphorus release were discussed comprehensively. Results show that compared with non-barrier, sand and modified attapulgite barriers are both able to control nitrogen and phosphorus release from the sediment, and the former is better than the later. The barrier has a high release inhibition for TP, NH4+-N and NO3-N, but low TP. When the barrier is thicker, the temperature is lower and grain size is smaller, control of nitrogen and phosphorus from sediments by barrier are better.