污泥水热法脱水预处理过程耦合重金属化学浸提脱除和迁移机理研究

Incineration can quickly reduce the volume and mass of sewage sludge and realize harmless for environment. However, high content of water in sludge increases the external heat consumption and heavy metal causes the secondary pollution during combustion. Sludge dewatering and heavy metal removal are the key difficulties for clean energy utilization of sludge. This project points out an innovative idea of source adjustment of fuel for pollution control as ‘initial mechanical dewatering + a pretreatment of chemical extraction combined with thermal hydrolysis + secondary mechanical dewatering’: the initial mechanical dewatering significantly reduces the mass for following pretreatment to decrease the external energy requirement, the combination of chemical extraction and thermal hydrolysis increases the free water percentage and promotes the conversion of insoluble metal to soluble species, at the end, water and heavy metal are together removed from solid-phase sludge by secondary filter press. This project is plan to carry out the following work: measure the improvement of fuel characteristics of dewatered sludge and detect the removal efficiency of heavy metal; analyze the speciation of residual metal and the toxic leaching, analyzing the correlation between speciation and toxic; research the selective effect of different parameters on heavy metal removal, and extract the directional transfer of specific heavy metal; explore the mechanism of heavy metal removal, basing on chemical kinetics and principal component analysis. The objectives of this study include: establish the parameters of optimal condition for deep dewatering simultaneous with effective heavy metal removal; get the speciation distribution of residual heavy metal in dewatered sludge and the characteristics of toxic leaching, and demonstrate the correlated model between metal speciation and leaching ratio; establish the kinetics model of metal transfer and clarify the mechanism, and understand the enhancing method of directional transfer of specific metal. This work can provide theoretical basis for the development of new applied technology, having important scientific value and broad application potential.

焚烧能快速实现污泥减容、减量和无害化，但污泥高水分和富含重金属使焚烧能耗高并排放重金属，是污泥能源化清洁利用的关键瓶颈。项目提出“一次机械脱水+水热法耦合化学浸提法预处理+二次机械脱水”的源头调质控污新思路：一次机械脱水减少污泥预处理量，耦合水热法增加自由水含量并促进不可溶重金属向可溶态转化，二次压滤后实现脱水和重金属脱除协同。研究污泥燃料提质效果和重金属去除效率；测量污泥中残留重金属赋存形态和浸出毒性，分析两者的相关性；分析耦合法各参数对重金属脱除的选择性，解析定向迁移规律；基于主成分分析和反应动力学研究重金属迁移机理。研究得到深度脱水和重金属高效去除协同的最优工况参数；掌握污泥中残留重金属形态和毒性浸出特性及关联模型；构建重金属动力学迁移模型，阐明重金属迁移机理，了解目标重金属定向迁移强化法。该研究将为发展相关应用技术提供理论基础，具有重要的科学价值和广阔的应用潜力。

污泥无序处理对我国环境保护和粮食安全（重金属超标污染）构成巨大威胁。焚烧技术能够快速实现减容、减量及能量回收，但污泥高含水和富含重金属对燃烧组织和污染控制造成巨大困难，是污泥能源化清洁利用的关键瓶颈。为有效降低污泥焚烧处置能耗和减少重金属排放污染，提出“污泥水热法脱水预处理过程耦合重金属化学浸提脱除和迁移机理研究”，通过源头调质实现燃料品质提升和控污。.项目主要开展了研究内容：1）水热温度、初始气氛和压力、添加剂等对污泥水热脱水及燃料特性的影响和作用；2）污泥水热过程重金属固液相分布及固相中重金属的赋存形态；3）干燥污泥复杂气氛（N2-O2-CO2-H2O）下高温气化特性；4）污泥气化/热解固相产物对重金属吸附能力；5）水热温度提高到超临界状态下污泥分解生成可燃气规律。. 通过研究得到：1）对于原始污泥，水热温度定在140℃就显示了良好的改善作用，而对机械脱水污泥水热温度需要更高（180℃），同时水热时间在15min后残留污泥变化不大；2）通过对NaCl、CaCl2、Ca(OH)2和FeCl3对水热脱水效果比较得到FeCl3具有最显著作用。3）初始压力对水热反应起到了促进效果，增强了水热效果，改善了污泥机械脱水性；不同初始气氛对脱水改善效果不同，Air对水热污泥脱水作用稍强；4）污泥水热过程对水中重金属具有很强的吸附作用，可以利用该特性开展污泥和含重金属飞灰协同处理；5）一定含量的CO2（20%~30%）可促进污泥气化，提高气化效率、可燃气产率以及气体热值等；6）污泥超临界水气化过程温度、反应釜压力和污泥浓度均对合成气组成及产量存在影响，升高温度和降低浓度有利于气化反应，高压力抑制了气化反应，但是升高温度和降低污泥浓度均会提高技术成本，需进一步优化反应温度和浓度。. 本项目的研究对认识污泥水热处理过程脱水性和燃料特性的认识具有重要意义，不仅了解了水热处理的优势，同时也更清晰认识到处理效果的有限性；提出进一步研究低温超临界水热条件下污泥气化/碳化特性研究。