Preparation Of Slow-release Calcium Peroxide Material Based On Water Purification Sludge And Its Effect On Inhibiting The Release Of Internal Phosphorus

Phosphorus is one of the most important factors to control eutrophication in water.More and more phosphorus adsorbents have been applied to in-situ capping technology.Calcium peroxide?CaO₂?,as an environmental friendly material with high energy peroxide covalent bond,releases oxygen in contact with water and improves anaerobic condition,has been widely used in adsorbing phosphorus in water,dissolve inorganic phosphorus and inhibition of phosphorus release from sediment.However,due to the excessive speed of oxygen generated by CaO₂ in contact with water,CaO₂ consumes too fast and supplies more oxygen exceed microorganisms need,resulting in waste of available oxygen and excessive alkalinity of water.Therefore,it is very important to prepare a slow-release calcium peroxide material for effective treatment of phosphorus.Calcium peroxide modified material?ACPM?was tested by phosphorus isothermal adsorption.The optimum proportion of ACPM was calcium peroxide:water purification sludge:cement=5:3:2?mass ratio?;the optimum technological conditions were:drying at 100 C for 2 hours,the maximum phosphorus adsorption capacity reached 29.28 mg P g^-1,and the correlation coefficient R² obtained by Langmuir model was higher than 0.98.The dissolved oxygen release rate showed that the oxygen release rate of ACPM was significantly lower than that of pure CaO₂,and the oxygen supply period was effectively prolonged.Scanning electron microscopy analysis showed that the powder dispersed CaO₂ was transformed into a cluster with porous structure,which reduce the contact area between CaO₂ and water in ACPM and prolong the effective oxygen release time.The contents of Si,Al,Fe,Mg and other metal ions were increased,and more phosphorus adsorption potential points were provided.In order to explore the effect of ACPM on the adsorption of phosphorus in the overlying water and the control of phosphorus release in sediment,one-month simulation experiment was conducted by adding ACPM and CaO₂ with the same effective content in a typical eutrophic river by capping method.The results show that ACPM could effectively reduce the DIP content in the interstitial water.Compared with the pure CaO₂ experiment,the DIP content in the interstitial water was reduced by0.966 mg P L^-1.In addition,ACPM had significant removal effects on NH₄⁺-N and Fe²⁺in pore water.After capping with ACPM,NH₄⁺-N and Fe²⁺decreased from 29.17mg/L and 2.71 mg/L to 3.05 mg/L and 0.38 mg/L,respectively.This indicate that slow-release of oxygen of ACPM lead to the change of sediment from anaerobic to aerobic,and promote the removal of reducing substances.The addition of ACPM resulted in the transformation of easily released phosphorus to refractory phosphorus,in which Fe/Al-P and Res-P decreased significantly,while Ca-P increased significantly,accounting for 64%of total phosphorus.On the other hand,the addition of ACPM reduced the content of bioavailable phosphorus in sediment,and the ratio of bioavailable phosphorus account for total phosphorus decreased from 17.27%to 7.21%,which reduced the risk of endogenous phosphorus release.To explore the effect of different ACPM dosages on the inhibition of phosphorus release from sediment,the sediment was capped with different dosage ratios(P_mobile:ACPM)from 1:1 to 1:4.The results show that with the increase of dosage,ACPM result in DIP in overlying water and DIP,NH₄⁺-N and Fe²⁺in pore water decreased significantly,which was obviously lower than that in control.Under the condition of1:4 dosage ratio,the removal rate of DIP in overlying water reached 61.9%,and that of DIP,NH₄⁺-N and Fe²⁺in pore water reached 81%,74%and 69%,respectively.The removal of NH₄⁺-N and Fe²⁺and the increase of DO in interstitial water indicate that ACPM promotes the transformation of sediment micro-environment from anaerobic to aerobic.This may lead to enhancement of phosphorus adsorption capacity and retention capacity of surface sediment.The phosphorus adsorption isotherm experiment showed that the maximum phosphorus adsorption capacity(S_max)of surface sediment increased from 3.002 mg g^-1?1:1?to 8.143 mg g^-1?1:4?,and was significantly higher than that of the control experiment(3.002 mg g^-1).In addition,the equilibrium phosphorus concentration?EPC₀?of surface sediment decreased significantly from 0.382 mg g^-1?1:1?to 0.034 mg g^-1?1:4?,which was significantly lower than that of the control experiment(0.601 mg g^-1).ACPM capping also has a significant impact on the active phosphorus(P_mobile)in sediment,P_mobileobile decreased from 691.26 mg kg^-11 to 467.03 mg kg^-1?the average of four coverage ratios?,and refractory phosphorus?Ca-P,Al-P and Res-P?increased from 238.12 mg kg^-1to 1130.88 mg kg^-1.The former was significantly lower than the control,while the latter was significantly higher than the control.Among the four dosage ratios,1:4 was the best.In summary,the slow-release modification of CaO₂ by water purification sludge enhance the penetration depth of dissolved oxygen,improve the anaerobic environment of sediment,remold the surface sediment,promote the transformation of activated phosphorus into refractory phosphorus,and improve the retention capacity of sediment to phosphorus.In practical application,mixing a certain material with calcium peroxide may be the best recommendation for the use of calcium peroxide.