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

在美国，每年产生的废水固体超过700万吨，处理、脱水和处理或再利用这些材料的成本每年可能超过10亿美元。调节和脱水过程的改进将降低这些成本，并增加可重复使用的可行选择的数量。然而，生物固体特性的物理和化学起源尚未得到很好的理解，因此不可能明确定义化学物质可能改善生物污泥脱水性的机制。例如，最常见的材料特性模型是由线性聚合物链结合的刚性球形颗粒，但该模型未能描述生物固体行为的某些关键方面。因此，选择化学类型和剂量的条件是通过试验和错误，脱水过程是经验设计，选择和操作。我们不太可能接近这些过程的最佳利用，其后果是经济和环境代价高昂。最近，一种完全不同的范式在描述污泥调节和脱水的某些方面已被证明是富有成效的。污泥通常被描述为絮凝的刚性颗粒的浓缩悬浮液，就像水处理中的絮凝一样，最近的报告建议将污泥描述为凝胶。这种体系的行为已经在聚合物化学等其他领域完成，因此基本方法是可用的。特别是，凝胶的依数性质已被证明可以解释污泥行为的某些方面，如过滤和干燥等重要方面。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联系起来。本提案提出了四个假设，以测试凝胶模型在多大程度上有助于理解污泥行为。这些假设是基于悬浮行为的可测量结果，这将取决于是否依数特性控制材料的响应，或者是否必须调用更多基于结构的特性。也许凝胶类比最重要的缺点是在过滤过程中剪切应力的作用，这对于带式压滤机和离心机成功脱水是必不可少的。没有明显的方法可以通过一个综合模型来解释这一点（尽管聚合物断裂作为一个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考虑剪切效应对污泥对正应力响应的定量影响。除了测试用于描述污泥的凝胶或累加模型的有效性之外，还建议使用流变学和动态过滤装置实验表征过滤过程中的剪切效应。这些实验不仅将划定污泥行为的凝胶样方面，而且将结构模型扩展到脱水过程应用中重要的领域。提出的实验方法是将污泥描述的经典方法（如固体、电泳、粒度分析、过滤测试）与描述凝胶行为的其他方法（如流变学、电导率、膨胀、电荷密度/滴定）结合起来，并将它们用于合成污泥和取样污泥。拟议的研究应该提高我们对污泥的性质和它如此顽强地保留水分的具体原因的理解。通过对生物污泥的凝胶与颗粒/结构描述的考虑和可能的综合，可能会出现对污泥流动、增稠、过滤甚至干燥的改进和定量描述。最终，这将导致在废水处理设施中更合理地应用这些做法。

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.