Impacts Of Ignited Sediment Inhibition Of Endogenous Phosphorus Release

At present,capping method is a kind of in-situ remediation technology for controlling endogenous phosphorus,which is widely concerned by both domestic and foreign.Also,the river sediment and the water purification sludge?WPS?had a certain adsorption capacity.Therefore,it will be a new way of thinking that combining the two methods to study the river restoration.In this paper,the river sediment and the water purification sludge?WPS?were used as the object after modified with ignition,which was discussed of its adsorption of exogenous phosphorus and its distribution of different phosphorus forms in the interstitial water and sediments.The effects of the ignition mode on the adsorption properties of materials and the effects of different dosing methods on the transport and transformation of phosphorus in sediments.Sediments from Meiliang Bay in Tai Lake and Xueshi Road,water purification sludge from a waterworks in Suzhou was used as basic materials of experimentThe indoor simulated culture method was used in the experiment,and the Rhizon interstitial water sampler and Unisense microelectrode was used to determined the data of phosphorus in overlying water,interstitial water and sediments,also was used to analyze the interfacial transformation between phosphorus forms and changes of physical and microbial characteristics of micro-interfaces in sediments.The above indexes are fitted according to the model equation,the ways of exogenous phosphorus entering into sediment and the induce mechanism of endogenous phosphorus transformation in sediments was discussed after adding modified materials.The ignited sedimenthad a higher maximum adsorption capacity(S_max),and smaller phosphorus equilibrium concentration?EPC₀?and lower phosphorus saturation?DSP?after modified by Langmuir model.And the ignited water purification sludge had a higher S_max(8.55 mg·kg^-1)to the S_max(2.64 mg·kg^-1)of ignited river sediment.This result showed that the water purification sludge had a stronger ability of phosphorus adsorption and retention after ignition.It can be founded in the study of ignited river sediment that when sediments were mixed with or covered by the ignited sediments,5.985 mg and 5.978 mg of input P disappeared from the overlying water,respectively.However,when the sediments were mixed with the ignited sediments,84.18% of the input P was converted to HCl-P,whereas when they were covered by the ignited sediments,sedimentary P was released,mainly from Fe/Al-P?up to 87.50%?.This was attributed to differences in the microenvironments,because less-intense anaerobic conditions formed in the mixed sediments than in the sediments covered by the ignited sediments.This suggests that the injection of ignited sediments into existing sediments enhances their P adsorption and retention.This can be confirmed in the second part of the experiment.It can be founded in the study of water purification sludge that the contribution of P disappearance in the overlying water was almost no difference between the mixing and capping with IWPS,but this contribution wais higher obviously,compared with the control.Under the mixing,the adsorption of external P by unit IWPS was 2.3 times of that under the capping,if the contacting probability was considered between the IWPS and the overlying water.Under the capping,the DIP in the sediment interstitial water?1-2cm?was 33.17 times?average?of the mixing.It is attributed to the decrease of the dissolved oxygen penetration due to the capping.Under the mixing,the external P is favor of the formation of the Ca-P,while the percentage of the NH₄Cl-P and Fe/Al-P to Tot-P is bigger under the capping.It is suggested that the remould of the sedimentary microenvironment by the mixing with the IWPS is favor of the adsorption of the external P and the immobilization of the internal P.From all the experimental results,such as: the adsorption of exogenous phosphorus,the control of phosphorus in the interstitial water,the transformation of the microenvironment of the sediment and the conversion of endogenous phosphorus,the mixing technology still has application prospects although the construction of mixing method is more difficult than the covering method.In future studies,it may be possible to use "injecting water purification sludge" instead of mixing.