碱渣固化污泥材料用作填埋场临时覆盖层的性能研究

Temporary covers are the important parts in landfill. The unclear understanding of the performance of temporary covers might inhibit the standardization of sanitary landfill, which will lead to a risk of pollution of air, soil and groundwater around landfill. Based on the concept of treat waste by waste, the project will focus on the mechanism of solidification/stabilization of sludge with soda residue, and then the application as the temporary covers. Firstly, with soda residue as the main agent, the mechanical properties, leaching toxicity, and microstructure of the solidified municipal sludge will be studied, and the mechanism of solidification/stabilization will be revealed. Secondly, the hydraulic standards for temporary cover materials will be determined based on analysis of transport of water and pollutants in landfill unit. The long-term performance of the solidified sludge, under the effects of continuous rainfall, dry-wet cycles, freeze-thaw cycles, and high temperature and leachate environment, will be studied. Thirdly, a series of landfill model tests will be carried out to clear the mechanism of temporary covers on the properties of waste, leachate, and landfill gas. And then the design method of temporary cover material to accelerate stabilization of landfill will be proposed. The aim of the project is to provide key theoretical basis for promoting the safe disposal and resource utilization of municipal sludge and soda residue, accelerating the stabilization and reducing the pollution of landfill.

临时覆盖层是填埋场重要的组成部分，其性能认识不清严重影响卫生填埋工序的规范化，导致填埋场周围空气、土壤和地下水存在污染风险。本项目基于“以废治废”的思想，对碱渣固化/稳定化污泥的机理进行研究，重点探讨固化污泥用作临时覆盖材料的工作机理。以碱渣为主要固化剂对市政污泥进行固化处理，研究固化污泥力学性质、浸出毒性、微细观结构等变化规律，揭示碱渣对污泥的固化/稳定化机理；在水分和污染物运移计算基础上确定临时覆盖材料渗透性能标准，分别针对中间覆盖和日覆盖层所处的连续降雨、干湿循环、冻融循环及高温和高腐蚀等环境，研究碱渣固化污泥长期性能的变化规律及其机理；开展垃圾填埋模型试验，研究临时覆盖层对垃圾、渗滤液和填埋气性质的影响规律，确定有利于填埋场稳定化的临时覆盖材料设计方法，从而为促进市政污泥的安全与有效处置、实现碱渣和污泥等废弃物的资源化利用、加快填埋场稳定化并减小填埋场二次污染提供科学依据。

为研究碱渣固化/稳定化市政污泥用作填埋场临时覆盖层的性质，开展碱渣对市政污泥的固化/稳定化机理研究、填埋场复杂环境下碱渣固化污泥性质、碱渣固化污泥对填埋场固、液、气性质的影响研究。主要结论有：（1）以生石灰干化、碱渣和矿渣固化后，市政污泥养护7d时无侧限抗压强度超过50kPa，渗透系数在10-7cm/s数量级，重金属浸出浓度低于危险废物限值，浸水条件下强度呈增大趋势，可用作填埋场覆盖材料。（2）随着干湿循环次数的增加，水化反应持续进行，钙钒石、水铝钙石和水化硅酸钙等增多，孔隙体积减小，强度呈增大趋势，7次循环后固化污泥的强度为循环前的1.16~1.45倍，表现出良好的干湿耐久性。（3）第1次冻融循环后固化污泥的强度增大，后续循环导致强度有所降低，但10次循环后固化污泥的强度为循环前的1.11~1.54倍。水化产物的胶结作用强于冻融循环的劣化作用，固化污泥表现出良好的冻融耐久性。（4）在填埋场渗滤液长期浸泡作用下，固化污泥强度随浸泡时间的增加而增大，但当碱渣掺量过多对强度不利，浸泡210d后强度降低；碱渣对污泥和渗滤液中铬、铜、铅、砷等污染物具有稳定化作用。（5）在填埋场高温环境下，固化污泥的强度随温度增加先增大后减小，渗透系数和压缩系数则先减小后增大。40°C时有利于水化硅酸钙形成，此时固化污泥强度最大、渗透性和压缩性最小。（6）碱渣固化污泥用作填埋场临时覆盖层时，可为填埋场内部提供养分，有助于调节渗滤液pH值、保持环境稳定，并在一定程度上加速固体垃圾降解。（7）渗滤液回灌对固化污泥临时覆盖层具有一定的腐蚀作用，随着运行时间的增加，固化污泥强度先增大后减小至趋于稳定，而无回灌条件下强度增大并趋于稳定。通过本项目研究，确定了碱渣固化市政污泥用作填埋场临时覆盖层的固化方案，明确了填埋场复杂环境下碱渣固化污泥性质的变化特征、临时覆盖层与填埋场垃圾和渗滤液的相互作用规律，为碱渣和污泥等固体废弃物的资源化利用、加强填埋场安全可靠性提供了理论支撑。