| As a type of waste generated in water purification,water treatment sludges,especially those produced in waterworks,have been proved to have efficient phosphorus adsorption performance,and have broad application prospects in sewage phosphorus removal.However,there are many difficulties in the application of water treatment sludge,such as hard to recycling,easy to clogging and so on.Many researches have granulated water treatment sludge in order to solve the above problems and broaden its application.In this paper,sludge ceramsite with excellent phosphorus adsorption performance was prepared by non-sintering natural curing method.Waterworks sludge is the main body of ceramsite,while cement,fly ash,steel slag and mineral powder are used as raw materials.The phosphorus adsorption performance of ceramsite under static and dynamic conditions was studied.The main conclusions are shown below:(1)The range of adding ratio of raw materials was determined according to the compressive strength of ceramicite,and on this basis,the mixing design was carried out to determine the optimal ratio.The compressive strength and apparent density of ceramicite were taken as response values,and the optimal ratio of ceramicite was obtained through response optimization: waterworks sludge=48.92%,cement=34.01%,mineral powder=8.53%,fly ash=5.70%,steel slag=2.84%.The characterization of sludge ceramsite showed that the indicators of sludge ceramsite were in line with the requirements specified in Artificial Ceramsite Filter Material for Water Treatment(CJ/T 299-2008,China).SEM results showed that sludge ceramsite had pore structure.XRD results showed that the main crystal minerals of sludge ceramsite were quartz,calcite and larnite.The toxicity analysis of leached metal showed that the content of heavy metal leached by sludge ceramic was far lower than the limit specified in the relevant standard.(2)The adsorption capacity of sludge ceramsite to phosphorus was studied by static adsorption experiment.The results showed that acidic environment,high temperature conditions and high initial phosphorus concentration were more conducive to the phosphorus adsorption process.The fitting results of adsorption kinetics showed that the phosphorus adsorption process of sludge ceramics was more consistent with the second-order adsorption rate equation,and the fitting results of adsorption isotherm showed that the adsorption process was more consistent with Freundlich adsorption isotherm equation.The maximum phosphorus adsorption capacity of ceramics was 46.50 mg/g by Langmuir fitting results.The morphology of phosphorus on ceramsite showed that Ca-P,Al+Fe-P and physical adsorption form of phosphorus accounted for 61.22%,22.93% and 1.49% of the total adsorption phosphorus,respectively.This indicates that the adsorption of phosphorus by sludge ceramsite mainly depends on chemical adsorption,and Ca,Al and Fe play an important role in the process of phosphorus adsorption by sludge ceramsite.(3)Dynamic adsorption experiments were carried out with sludge ceramsite as filler.Under the conditions of total packing height of 30 cm,influent phosphorus concentration of 3 mg/L and influent flow rate of 6m L/min,the sludge ceramsite filler adsorption column experienced the process of starting adsorption to complete penetration during the 40-day operation cycle.The effluent p H was 9.48 in the early,then gradually decreases and finally stabilized at 7.20.As for the influence of different packing height,with the increase of packing height,the phosphorus removal performance of effluent got better,and the longer the time required for penetration of column was.The adsorption penetration curve fitting was carried out for dynamic adsorption at different packing heights.The results showed that the dynamic adsorption process at packing heights of 10,20 and30 cm was consistent with Thomas model and Yoon-Nelson model,and the R2 of two models were both greater than 0.95. |
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