基于磷酸铵镁生成与利用的湿地填料磷回收机理研究

Change from "phosphorus removal" to "phosphorus recovers" is a promising solution for phosphorus polluted wastewater treatment and source reuse. Phosphorus recover through struvite precipitation has great shortcomings of artificial addition of magnesium contained chemical regent, hard to accumulation and expensive to operate. Generation, retention and accumulation of struvite within magnesium contained wetland media can not only solve above problems, but also bring a new approach for utilizing the low quality phosphorus saturated wetlands media as reliable fertilizer . In the present study, industrial magnesium slag is chosen as constructed wetland media to study the struvite generation, accumulation and utilization: (1)Based on determining the physical and chemical characteristics and key chemical composition, theoretical struvite precipitation mode for magnesium slag has been developed after studying the magnesium ion releasing mechanism and key process impacting on struvite precipitation; (2)Under the theoretical mode, interaction and function mechanism between phosphorus adsorption and struvite precipitation on magnesium slag were studied, and then recommended a phosphorus removal and recover optimal mode for magnesium slag under the combination of phosphorus adsorption and struvite precipitation; (3)Under the optimal mode, phosphorus storage and bioavailable phosphorus fraction contents were measured, and which was then employed to evaluate the plant growth adaptability and phosphorus recover efficiency in the pot experiments. Initiation of this study will help to reveal the struvite precipitation behaviour and accumulation mechanism within constructed wetland media, and theoretically guide the engineering practices for phosphorus recover from phosphorus saturated struvite accumulated wetland media.

"磷去除"转为"磷回收"是含磷污水处理与资源化的必由之路。磷酸铵镁沉淀磷回收过度依赖化学药剂镁源且沉淀富集难、成本高。利用含镁湿地填料生成、滞留和富集磷酸铵镁可有效解决上述难题，还是破解传统磷饱和湿地填料因含磷量低难用作磷肥的新思路。 课题以工业镁矿渣为湿地填料，开展磷酸铵镁生成、富集及利用研究：（1）基于镁矿渣理化性质和关键化学成分测定，研究镁离子释出机制和磷酸铵镁生成关键过程及影响因素，提出镁矿渣磷酸铵镁生成理想模式；（2）在理想模式下，研究磷吸附与磷酸铵镁生成间的相互影响和作用机理，提出磷吸附与磷酸铵镁生成协同下镁矿渣磷去除和回收的优化模式； （3）在优化模式下，研究磷饱和镁矿渣的磷赋存量和生物可利用磷组分含量，基于盆栽试验评价磷饱和镁矿渣的植物生长适宜性及磷吸收有效性。 课题的开展有助于辨识湿地填料的磷酸铵镁生成行为和富集规律；进而为基于磷酸铵镁生成和富集的湿地磷回收提供理论指导。

“磷去除”转为“磷回收”是含磷污水处理与资源化的必由之路。利用含镁湿地填料生成、滞留和富集磷酸铵镁（MAP）是破解传统湿地管理和污染治理问题的新思路。以工业镁矿渣（MSP）为湿地填料，开展MAP生成、富集及利用研究，主要结论如下：.（1）分析了MSP酸溶释出镁离子的特征及影响因素。随着浸出时间的延长，浸出液中镁离子浓度逐渐增加，浸提5h后MSP中镁离子达到浸出平衡；浸出溶液中镁离子的浓度随着浸提液中盐酸浓度的降低而逐渐下降。增大浸出液中MSP浓度，镁离子的浸提效率反而降低。当浸提盐酸浓度为1mol/L，浸出液中MSP浓度为5g/L时，镁离子的浸出量达到最大值（117.70mg/kg）。浸提后MSP粒径减小，比表面积增大，其矿物晶格受到破坏，其对溶液中的磷吸附能力得到强化。浸出液中的镁离子理论磷回收潜力为810mg P/kg。.（2）HCl浸提后，MSP表面特性的改善导致其对磷酸盐的吸附容量增加188.96mg/kg。比较而言，D–R模型能更好的描述等温吸附过程，拟合系数超过0.94。浸提后吸附自由能减少了9.75%。HCl浸提液中96%的Mg2+来自于MSP中酸可溶态镁（可交换态和碳酸盐结合态），能够为MAP沉淀反应提供可靠的镁源。在最佳实验条件下（pH值为10.0，NH4+和PO43−的摩尔比为1:1时）其对PO43−的去除率可达53.63%。在HCl浸提MSP混合体系中MAP沉淀及吸附可以同步发生。与吸附过程相比，MAP沉淀是溶液中PO43−最主要的去除方式，其贡献达63.19%。.（3）HCl处理MSP对磷酸盐的吸附能力较强，在填料饱和实验开始8天后，去除率就由75%降低至50%以下。过填料饱和及浸提液沉淀制备得到的产品中含有MAP沉淀，产物中Mg含量为9.21%，P2O5含量为32.64%。饱和吸附及混合沉淀处理显著改善了MSP的磷形态特征。理论上饱和填料+混合沉淀易于被作物直接吸收利用的生物可利用性磷高达35.54%；.（4）盆栽实验表明，饱和填料+混合沉淀处理组各项生长指标显著高于卡美拉和红壤土处理，具有为小白菜生长提供元素的功能，肥效显著，在实验条件下饱和填料+混合沉淀用作肥料时重金属累积风险较低。