Chemical, Rheological, and Physical Exploration of Gel-Like Behavior in Conditioning and Dewatering Processes

0229293 Dentel美国每年产生700多万吨干固体废水，这些材料的调理、脱水和处置或再利用的成本每年可能超过10亿美元。改善调理和脱水过程将减少这些费用，并增加可供再利用的可行选择的数量。然而，生物固体性质的物理和化学起源还不是很清楚，因此不可能清楚地定义化学物质可以改善生物污泥脱水性能的机制。例如，最常见的材料性质模型是刚性球形颗粒被线性聚合物链束缚的模型，但该模型未能描述生物固体行为的一些关键方面。因此，调理的化学类型和剂量的选择是通过试错进行的，脱水过程是通过经验设计、选择和操作的。我们不太可能接近最佳利用这些过程，其后果是经济和环境代价高昂的。最近，一个完全不同的范例已经被证明在描述污泥调节和脱水的某些方面是卓有成效的。污泥通常被描述为刚性颗粒的浓缩悬浮液，在水处理混凝中很像是絮凝的，最近的报告建议将污泥描述为凝胶。这类体系的行为已经在其他领域完成，如聚合物化学，因此基本方法是可用的。特别是，凝胶的综合性能已被证明在过滤和干燥等重要方面解释了污泥行为的某些方面。使用这些概念的一个优点是它们以分子和热力学原理为基础，因此在描述化学调节过程时可以与基本原理相联系。这项建议提出了四个假设，以测试凝胶模型在多大程度上可以帮助理解污泥的行为。这些假设是基于悬浮行为的可测量结果，这将取决于材料的响应是由综合性质决定的，还是必须引用更多基于结构的性质。凝胶类比的最大缺点可能是在过滤过程中的剪切力的作用，这是带式压滤机和离心机成功脱水的关键。没有明显的综合模型可以解释这一点(尽管聚合物断裂作为间接因素的影响将被评估)。然而，即使是最新的泥浆过滤分析模型也没有将剪切效应视为对污泥对正常应力的反应的定量影响。除了测试凝胶或综合模型描述污泥的有效性外，还建议使用流变仪和动态过滤设备来实验表征过滤过程中的剪切效应。这些实验不仅将界定污泥行为的凝胶状方面，而且将结构模型扩展到对脱水过程应用非常重要的领域。建议的实验方法是将经典的污泥描述方法(如固体、电泳、粒度分析、过滤试验)与其他描述凝胶行为的方法(如流变学、电导率、溶胀、电荷密度/滴定)相结合，并将其用于合成和样品污泥。这项拟议的研究应该会提高我们对污泥性质的理解，以及它如此顽强地保持水分的具体原因。通过考虑和可能合成生物污泥的凝胶与颗粒/结构描述，可能会出现对污泥流动、浓缩、过滤甚至干燥的改进和定量描述。最终，这将导致这些做法在废水处理设施中得到更好的应用。

0229293 Dentel With over seven million dry tons of wastewater solids generated annually in the U.S., the costs of conditioning, dewatering, and disposal or reuse of these materials may cost in excess of $1 billion per year. Improvements in the conditioning and dewatering processes would reduce these costs and increase the number of feasible options for reuse. The physical and chemical origins of biosolids properties are not well understood, however, and thus it is not possible to clearly define the mechanisms through which chemicals may improve biological sludge dewaterability. The most common model of material properties invoked, for example, is that of rigid spherical particles bound by chains of linear polymers, but this model fails to describe some crucial aspects of biosolids behavior. Consequently, the selection of chemical types and doses for conditioning are by trial and error, and dewatering processes are empirically designed, selected, and operated. It is unlikely that we come close to optimum use of these processes, and the consequences are economically and environmentally costly. Recently, a quite different paradigm has been shown to be fruitful in describing some aspects of sludge conditioning and dewatering. Where sludges have typically been described as concentrated suspensions of rigid particles that are flocculated much as in water treatment coagulation, recent reports suggest the description of sludges as gels. Behavior of such systems has been accomplished in other fields such as polymer chemistry, and thus fundamental approaches are available. In particular, colligative properties of gels have been shown to explain certain aspects of sludge behavior in important respects like filtration and drying. An advantage of using these concepts is that they are grounded in molecular and thermodynamic principles, and thus may be linked to fundamental principles when describing chemical conditioning processes.This proposal presents four hypotheses that test the extent to which a gel model may assist in understanding sludge behavior. The hypotheses are based on measurable consequences of suspension behavior that will depend on whether colligative properties govern the material's response, or whether more structurally based properties must be invoked. Perhaps the most important shortcoming of a gel analogy is in the role of shear stress during filtration, which is essential in successful dewatering by belt filter presses and centrifuges. There is no obvious means by which a colligative model may account for this (although the effects of polymer breakage as an indirect factor will be assessed). However, even the newest analytical models of slurry filtration do not consider shear effects as a quantitative influence on a sludge's response to normal stresses. Beyond testing the efficacy of a gel or colligative model for describing sludges, it is also proposed to experimentally characterize shear effects during filtration, using rheometric and dynamic filtration devices. The experiments will not only delimit the gel-like aspects of sludge behavior, but extend the structural models into realms that are important in dewatering process applications. The experimental approach proposed is to combine methods classically used for sludge description (e.g. solids, electrophoresis, particle size analysis, filtration tests) with others that will describe gel behavior (e.g. rheometry, conductivity, swelling, charge density/titration) and use them on both synthetic and sampled sludges. The proposed research should improve our understanding of the nature of sludge and the specific reasons that it retains water so tenaciously. Through a consideration and possible synthesis of gel vs. particulate/structural descriptions of biological sludges, improved and quantitative descriptions of sludge flow, thickening, filtration, and even drying are likely to emerge. Ultimately, this will lead to sounder application of these practices in wastewater treatment facilities.