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

调理和脱水过程中凝胶状行为的化学、流变学和物理探索

• 批准号: 0229293
• 负责人: Steven Dentel
• 金额: $ 20.99万
• 依托单位: University of Delaware
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-07-01 至 2006-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0229293&HistoricalAwards=false
• 关键词: Chemical; Rheological; Physical; Exploration; Gel

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.

0229293 登特尔 美国每年产生超过700万干吨的废水固体，这些材料的调节、脱水和处理或再利用的成本每年可能超过10亿美元。改进调节和脱水工艺将降低这些成本，并增加可行的再利用选择。 然而，生物固体性质的物理和化学起源还没有得到很好的理解，因此不可能清楚地定义化学品可以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束缚的刚性球形颗粒，但这种模型未能描述生物固体行为的某些关键方面。因此，用于调节的化学品类型和剂量的选择是通过试验和错误来进行的，并且脱水过程是根据经验设计、选择和操作的。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，一个完全不同的范例已被证明是富有成效的，在描述污泥调理和脱水的某些方面。污泥通常被描述为刚性颗粒的浓缩悬浮液，其絮凝作用与水处理中的混凝作用非常相似，最近的报告建议将污泥描述为凝胶。此类系统的行为已在聚合物化学等其他领域完成，因此可以使用基本方法。特别是，凝胶的依数性已被证明可以解释污泥行为的某些方面，如过滤和干燥。使用这些概念的一个优点是，它们是在分子和热力学原理的基础上，因此可能会被链接到基本原则时，描述化学调理processes.This建议提出了四个假设，测试凝胶模型可能有助于了解污泥行为的程度。这些假设是基于悬浮行为的可测量的后果，这将取决于依数性是否支配材料的响应，或者是否必须调用更多的基于结构的属性。 凝胶模拟最重要的缺点可能是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至关重要。没有明显的方法可以用依数模型来解释这一点（尽管将评估聚合物断裂作为间接因素的影响）。然而，即使是最新的分析模型的泥浆过滤不考虑剪切效应作为一个定量的影响污泥的正常应力的反应。除了测试凝胶或依数模型用于描述污泥的功效之外，还建议使用流变和动态过滤装置来实验表征过滤期间的剪切效应。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脱水过程应用中的重要领域。 提出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，并将其用于合成污泥和取样污泥。拟议的研究应该提高我们对污泥性质的理解，以及污泥如此顽强地保持水分的具体原因。通过对生物污泥的凝胶与颗粒/结构描述的考虑和可能的合成，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，这将导致在废水处理设施中更好地应用这些做法。