Studying On Control Of Organic Phosphorus Release In Sediment Using In Situ Capping

Phosphorus pollution of water has always been an important topic in the field of environment.The source of phosphorus in water In addition to the input of external phosphorus,the release of phosphorus from the sediment is also an important source of phosphorus pollution in water.Controlling the release of endogenous phosphorus from the sediment is the key to the treatment of polluted water,and in situ capping techniques are often used to control the release of endogenous phosphorus from sediments.Current research is focused on the effection and mechanisms of controlling inorganic phosphorus(IP)release in sediments.Organophosphorus(OP)is also a significant source of phosphorus in overlying waters and there are relatively few studies which are focused on controling the organophosphorus release.Seeking effective capping materials,reasonable capping methods and application conditions,explaining the law of controlling OP release in sediment,is the key to the application of in-situ capping to control the release of OP in sediments.Therefore,controlling the release of organic phosphorus in sediments is of great significance for the treatment of endogenous pollution in rivers and lakes.In this paper,the contaminated sediment of urban river channelis is as the object of research,and the research investigated the pollution background of the river channel to determine the experimental sampling area.Through the indoor simulation experiment,the effect of the capping materials,the particle size,the thickness and the capping method of selected coverage material on the release of OP in the sediment was studied,and the best capping method was determined.On this basis,the influence of environmental factors on the release and conversion of OP in the sediment was studied.The results of the study are as follows:(1)The paper selected the typical polluted rivers first and investigated the pollution background.The results show that the COD,TN,and TP of the water body in the reach exceeds the class V criteria of surface water and the water pollution is serious.The content of total phosphorus(TP)in the sediment ranged from 283.4 to 1846.1 mg/kg,of which the content of OP accounted for 12% to 35% of TP.And the content of total nitrogen(TN)ranged from 45.6 to 1435 mg/kg,and the content of organic matter(OM)is 0.7-33.8%,and the investigation site seriously polluted is selected as the experimental sampling area.(2)By controlling the release of OP in the sediment by in-situ capping of contaminated sediments with natural red soil and river sand,the results of experiments showed that the capping of red soil and river sand can also control the release of OP in the sediment.The results show that the OP/TP value of the capping groups of red soil and river sand were 29.98% and 20.63%,respectively,which were greater than the OP/TP value of the blank group by 19%.The capping of red soil was more conducive to control the release of OP in sediments,and by capping with red soil with a particle size of 1-2 mm and a covering thickness of 3 cm,the content of OP in the sediment will increase and its average increasing rate is 1.24 mg/(kg.d).The combinatorial capping of river sand and red soil is the best way to control the release of OP in sediment.(3)Using the combination of sand and red soil capping,Incubation tests were carried out to investigate the effects of pH,temperature,DO,and other environmental factors on the release and conversion of OP.The results showed that under the aerobic environment with T=25°C,the combination of sand and red soil capping can effectively control the release of organic phosphorus to the overlying water and the content of OP in sediment increased,reducing the concentration of TP and DOP in overlying water.The results showed that the environmental factors had the greatest impact on the conversion of moderately active phosphorus(MLOP)in the sediment,the content of organic phosphorus and the ration of OP/TP increased by inhibiting the MLOP conversion in the sediment.The correlation between alkaline phosphatase activity(APA)and various forms of phosphorus in the sediment showed that APA was positively correlated with TP and OP content in sediment,and APA can indicate the process of conversion between various forms of phosphorus.(4)Red soil and sand capping can effectively inhibit the emission of OP in the sediment and reduce the release of phosphorus from the sediment to the overlying water,improving the water environment.Based on the rational coverage and application environment obtained from this study,in practical engineering projects,sand and red soil capping can be used to control the release of OP,delay the release of phosphorus in the sediment,and eliminate sudden water pollution.