Capping With Calcined Water Treatment Plant Sludge For Controlling The Phosphorus Release From The Sediment

The controlling of eutrophication of water body is one of the research focus in China and abroad.Phosphorus concentration is an important restriction factor of water eutrophication.When the external phosphorus was controlled,the internal phosphorus was easily to release from the contaminated sediment,which was the main contributor to water eutrophication.Capping could effectively reduce the release of phosphorus which was easily released from the contaminated sediment.The calcined water treatment plant sludge(C-WTPS)developed by the research group has a strong capacity for phosphorus fixation.Therefore,the control effect of internal phosphorus release from the contaminated sediment using capping with C-WTPS was investigated through a series of laboratory-scale static and dynamic simulating experiments.The effects of dose rates of C-WTPS,dissolved oxygen(DO)concentration less than 1 mg/L in overlying water,the secondary capping and hydraulic residence time(HRT)on the control effect of internal phosphorus release were discussed.The phosphorus sorption capacity and phosphorus forms of C-WTPS were analyzed.The migration and transformation of phosphorus in C-WTPS and sediment were explored.In addition,the re-release possibilities of phosphorus saturated adsorption in C-WTPS under the condition of different initial pH value and low oxidation-reduction potential(ORP)were preliminarily studied.The main results were as follows.(1)The control effect of phosphorus using C-WTPS capping:(1)static simulation test:When the release rate of total phosphorus(TP)from the sediment was2.26~9.19mg/(m~2·d),the average reduction efficiency of TP using C-WTPS capping of dose rate of 2 kg/m~2 was 92.14%.(2)dynamic simulation test:from 0-44 days,the TP concentration in overlying water using C-WTPS capping of dose rate of 2 kg/m~2reduced 3.55 to 0.18 mg/L,and from 45-95 days,the TP concentration was at a lower level.(2)The factors of the control effect of phosphorus using C-WTPS:(1)Dose rate of C-WTPS:When the TP release rate from the contaminated sediment was6.25~10.87 mg/(m~2·d),the average reduction efficiency of TP using C-WTPS capping of dose rate of more than 1 kg/m~2 was over 90%.(2)DO concentration less than 1mg/L in overlying water:When the release rate of TP from the contaminated sediment under the condition of DO concentration less than 1 mg/L in overlying water was2.30~21.56mg/(m~2·d),the average reduction efficiency of TP using C-WTPS capping of dose rate of 2.00kg/m~2 was 88.36%.(3)The secondary capping:When the TP release rate from contaminated sediments was 4.07~14.04 mg/(m~2·d),and the thickness of the secondary capping of sediment were 0,2,4,7,10 and 15 mm,respectively,the average reduction efficiencies of TP using C-WTPS capping of dose rate of 2.00 kg/m~2 were 87.57%,72.42%,58.21%,48.48%,41.93%and 32.11%,respectively.(4)HRT:When the HRT were 0.5~3d and the TP release rate from contaminated sediment was 2.27~9.37 mg/(m~2·d),the average reduction efficiency of TP using C-WTPS capping of dose rate of 2.00 kg/m~2 was over 90%.(3)Phosphorus forms and the pathways of migration and transformation in C-WTPS and sediment.The changes of five phosphorus forms in C-WTPS and sediment before and after testing were determined by the Standard Measurements and Testing(SMT),and the results showed that the phosphate forms by C-WTPS adsorption were mainly non-apatite inorganic phosphorus(NAIP)of inorganic phosphorus(IP),and the phosphorus that released from the sediment was also NAIP mainly,which migrated to C-WTPS with being fixed.(4)The re-release possibilities of phosphorus saturated adsorption in C-WTPS:(1)pH value:When the initial pH value was 5,6,7,8,9 and 10,respectively,the average release efficiencies of phosphorus from the C-WTPS were 0.23%,0.25%,0.21%,0.25%,0.3%and 0.82%,respectively,which the phosphorus adsorption capability was 6.23 mg/g.(2)Low ORP:the phosphate of C-WTPS adsorption would not be released to the overlying water,and the C-WTPS could reduce the release of phosphorus from the contaminated sediment in the natural and low ORP environments where ORP were 117~210 mV and-237~53 mV.