Modeling Nonionic Polyacrylamide Flocculation Using Population Balances

Nonionic polyacrylamide is widely used as a flocculant in wastewater treatment, but current knowledge is limited to empirical observations on how they work. A population balance model for flocculation of particle suspension by nonionic polyacrylamide under quiescent flow condition was presented. The model takes particles aggregation, flocs breakage and flocs restructure into account. It was found that the process of flocculation is a dynamic and nonlinear process in which particles, micro-flocs and macro-flocs are constantly seeking equilibrium through aggregation and breakage. The size of micro-flocs and macro-flocs was obtained respectively in the flocculation of sediment and nonionic polyacrylamide. Moreover, bridging effect of nonionic polyacrylamide is the main reason for the faster increase of settling velocity. When the experimental results from literature were tested, the model which combined with population balance equations and computational fluid dynamics predicted the experimental behavior of flocculation both adequately and directly in three dimensions. The proposed model is the first time to reproduce the process of flocculation in three dimensions, and the model is more rational and general to predict the process of flocculation in wastewater treatment.

關鍵字

Aggregation ； Breakage ； Micro-flocs ； Macro-flocs ； CFD ； Bridging effect

並列摘要

非離子聚丙烯酰胺廣泛應用於水處理中。然而在實際應用過程中，側重於經驗性的方法。本文結合群體平衡理論對非離子聚丙烯酰胺在靜水中的絮凝過程進行了有效的計算模擬。該理論模型考慮到了絮凝過程中顆粒或絮凝體之間的絮凝、分裂和重組等因素。結果表明：絮凝的過程是顆粒、絮凝體和絮凝團之間通過絮凝和分裂的方式不斷尋求平衡的動態非線性過程。結合之前的試驗結果，絮凝體和絮凝團的有效範圍得以確認；分析認為基於非離子聚丙烯酰胺的橋聯機理是絮凝體（團）沈速不斷遞增的主要原因。群體平衡模型結合計算流體動力學的方法首次在三維尺度上有效的再現絮凝的過程。同時，相對於其他計算方法，該方法是壹種更加實用和通用的方法。

並列關鍵字

絮凝；分裂；絮凝體；絮凝團； CFD ；橋聯作用

國際替代計量

Modeling Nonionic Polyacrylamide Flocculation Using Population Balances

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