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Experimental and modeling studies for optimizing flocculant-aided sediment retention ponds.

機譯：優(yōu)化絮凝劑沉淀池的實驗和模型研究。

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摘要

Attempts to control sediment-containing runoff and associated water quality problems have involved the establishment of many small to medium sediment retention ponds and the injection of nonionic and anionic polyacrylamide (PAM) flocculants to enhance colloid removal. However, to date use has been driven more by practicing engineers and trial-and-error approaches than by logical and consistent design approaches. Therefore, the purpose of this research was to optimize colloidal clay removal in PAM-aided sediment retention ponds by applying experimental and theoretical methodologies.;Initially, simple measurement techniques for the molecular weight (MW) and charge density (CD) of various PAMs were tested and their characteristic behaviors in aqueous solution were investigated for use in subsequent optimization tasks. A simple intrinsic viscosity measurement technique and acid-base titration method showed their capabilities as the most plausible substitutes of state-of-the-art techniques in measuring MW and CD, respectively. Also, a cylindrical shape for PAM conformation in aqueous solution was shown to be the best assumption for predicting the characteristic behavior of PAM molecules.;In adsorption and flocculation experiments with nonionic PAMs and negatively-charged kaolinite clay particles, adsorption capacities of PAMs on kaolinite were found to increase with increasing PAM MW up to a certain size (∼ 18 M g/mol) but then decrease beyond this size due to entanglements between PAM molecules. Flocculation efficiency with nonionic PAM also increased with increasing MW up to a point due to its nonequilibrium kaolinite flocculation but eventually decreased by entanglements between PAM molecules. In parallel experiments with anionic PAMs and negatively-charged kaolinite particles, adsorption capacities were found to be inversely proportional to the PAM CDs, while flocculation efficiencies were directly proportional to the PAM MWs. Along with the effects of PAM MW and CD, the presence of divalent cations such as Ca2+ and Mg2+ enhanced adsorption and flocculation due to cationic bridging and/or charge screening between PAM and kaolinite (PAM-- --+M+---Kaolinite). However, concurring steric stabilization was also found to counteract flocculation due to the conformational compaction of adsorbed PAMs by the cationic bridging between pre-adsorbed PAM molecules (PAM---- +M+---PAM). In short, PAM and solution characteristics, including change density (CD), molecular weight (MW) of PAM, and cationic species in the solution, were found to make critical effects on adsorption and flocculation and thus to be the controlling parameters in optimizing PAM applications as soil stabilizers or flocculants. In a model-based optimization of PAM-aided sediment retention ponds, the applicability of utilizing multi-dimensional Discretized Population Balance Equations combined with a Computational Fluid Dynamics (CFD-DPBE model) was demonstrated in a series of simulation tasks with a model retention pond. The CFD-DPBE model was demonstrated to be a valuable simulation tool for natural and engineering flocculation and sedimentation systems as well as flocculant-aided sediment retention ponds.
機譯：試圖控制含沉積物的徑流和相關的水質(zhì)問題的嘗試涉及建立許多中小型沉積物保留池，以及注入非離子和陰離子聚丙烯酰胺（PAM）絮凝劑以增強膠體去除能力。但是，到目前為止，使用更多地是由實踐工程師和反復試驗的方法推動的，而不是邏輯和一致的設計方法。因此，本研究的目的是通過應用實驗和理論方法來優(yōu)化PAM輔助沉積池中膠體粘土的去除。首先，對各種PAM的分子量（MW）和電荷密度（CD）進行簡單測量的方法是對其進行了測試，并研究了其在水溶液中的特征行為，以用于后續(xù)的優(yōu)化任務。一種簡單的特性粘度測量技術和酸堿滴定法顯示了它們分別作為測量MW和CD的最新技術的最合理替代品的能力。此外，在水溶液中呈PAM構型的圓柱形狀是預測PAM分子特征行為的最佳假設。;在非離子PAM和帶負電的高嶺石粘土顆粒的吸附和絮凝實驗中，PAM在高嶺石上的吸附能力據(jù)發(fā)現(xiàn)，隨著PAM MW的增加，達到一定大?。?18 M g / mol）時會增加，但隨后由于PAM分子之間的纏結而減小到超過該大小。由于非平衡高嶺石的絮凝作用，非離子型PAM的絮凝效率也隨著MW的增加而增加，但最終由于PAM分子之間的纏結而降低。在使用陰離子PAM和帶負電的高嶺石顆粒的平行實驗中，發(fā)現(xiàn)吸附能力與PAM CD成反比，而絮凝效率與PAM MW成正比。除了PAM MW和CD的影響外，由于PAM和高嶺石之間的陽離子橋接和/或電荷篩選（PAM---+ M +-Kaolinite），Ca2 +和Mg2 +等二價陽離子的存在增強了吸附和絮凝作用。 。然而，由于預先吸附的PAM分子（PAM ---- + M + --- PAM）之間的陽離子橋連，由于吸附的PAM的構象緊密性，同時存在的空間穩(wěn)定作用也被抵消。簡而言之，發(fā)現(xiàn)PAM和溶液特性（包括PAM的變化密度（CD），分子量（MW）和溶液中的陽離子種類）對吸附和絮凝產(chǎn)生關鍵影響，因此是優(yōu)化PAM的控制參數(shù)。用作土壤穩(wěn)定劑或絮凝劑。在基于模型的PAM輔助沉積池的優(yōu)化中，在模型保持池的一系列模擬任務中證明了將多維離散種群平衡方程與計算流體動力學（CFD-DPBE模型）相結合的適用性。 CFD-DPBE模型被證明是用于自然和工程絮凝和沉降系統(tǒng)以及絮凝劑輔助沉積池的有價值的仿真工具。

著錄項

  • 作者

    Lee, Byung Joon.;

  • 作者單位

    Clemson University.;

  • 授予單位 Clemson University.;
  • 學科 Agriculture Soil Science.;Engineering Sanitary and Municipal.;Engineering Environmental.
  • 學位 Ph.D.
  • 年度 2008
  • 頁碼 267 p.
  • 總頁數(shù) 267
  • 原文格式 PDF
  • 正文語種 eng
  • 中圖分類 土壤學;建筑科學;環(huán)境污染及其防治;
  • 關鍵詞

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