污水磷酸钙(Ca-P)结晶磷回收效果易受共存杂质CO32-碱度影响,为探明CO32-碱度对Ca-P结晶磷回收的影响,综合运用电位滴定实验和烧杯实验,全面分析了不同CO32-碱度下Ca-P结晶体系pH值、电导率、碱度和Ca形态变化,并结合磷回收动力学过程和结晶产物XRD结果,探讨了CO32-碱度的影响机制.结果表明,当结晶反应时间足够长时,Ca-P结晶磷回收效果受CO32-碱度影响较小,而是主要决定于Ca-P结晶产物自身热力学性质.实验条件下,结晶反应时间为7200s时,各实验组和空白组磷回收率均为40%左右. CO32-碱度改变了Ca-P结晶磷回收动力学过程,低CO32-碱度时以提供碱度促进Ca-P结晶为主,高CO32-碱度时则通过碳酸钙(Ca-C)结晶消耗游离态Ca2+迟滞Ca-P结晶.受热力学特性驱动, Ca-C离子簇和晶体将溶解释放游离态Ca供Ca-P持续结晶.研究成果为消除CO32-碱度对污水Ca-P结晶磷回收效果的影响提供了直接理论依据.
Abstract
The phosphorus recovery efficiency through calcium phosphate (Ca-P) crystallization in wastewater demonstrates significant susceptibility to carbonate alkalinity (CO32–), a predominant coexisting impurity in wastewater. To elucidate the influence of CO32- alkalinity on phosphorus recovery of Ca-P crystallization, the variation of pH, conductivity, alkalinity, and Ca morphology in Ca-P crystalline systems with difference CO32– alkalinity levels were systematically analyzed by integrated potentiometric titration and jar testing. Meanwhile, the influence mechanism of CO32– alkalinity was explored based on the kinetics of phosphorus recovery and XRD results of crystallization products. The results indicate that, provided crystallization reaction time long enough, phosphorus recovery efficiency was less affected by CO32– alkalinity, but mainly determined by the thermodynamic properties of Ca-P crystallization product itself. Under extended reaction durations (7200s), phosphorus recovery efficiencies stabilized at around 40% across all experimental and control groups. CO32– alkalinity changed the kinetics of Ca-P crystallization. CO32– alkalinity with low level promoted Ca-P crystallization by providing alkalinity, compared to delay of Ca-P crystallization by consuming free Ca2+ through calcium carbonate (Ca-C) crystallization while at high level. Driven by thermodynamic properties, Ca-C ion clusters and crystals would dissolve and release free Ca for continuous crystallization of Ca-P. The research results provide a direct theoretical basis for eliminating the influence of CO32– alkalinity on the phosphorus recovery efficiency of Ca-P crystalline from wastewater.
关键词
Ca-P结晶 /
磷回收 /
CO32-碱度 /
电位滴定 /
Ca-C结晶
Key words
Ca-P crystallization /
phosphorous recovery /
CO32– alkalinity /
potentiometric titration /
Ca-C crystallization
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基金
水利部重大科技项目(SKS-2022079);大学生创新创业训练计划项目(S202310536060);郴州国家可持续发展议程创新示范区建设省级专项(2022sfq51)
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