Li B, Bishop P
Department of Civil and Environmental Engineering, University of Cincinnati, Cincinnati, OH 45221-0071, USA.
Water Sci Technol. 2003;47(11):267-73.
Biodegradation by microorganisms and mass transfer resistance in the micro-environment of activated sludge floc can cause changes in substrate and dissolved oxygen concentrations within the floc and can contribute to stratification of microbial processes inside the flocs. In this study, an integrated model of the microenvironment of the activated sludge floc was developed for floc from wastewaters from several sources and of varying strengths for dynamic simulation of the combined biological processes of COD and nitrogen removal. The model simulation results and measured profiles show the heterogeneous and gradient-governed microenvironment of activated sludge floc under different substrate and bulk oxygen concentrations. The substrate concentration increase zones inside the floc were present in all activated sludge floc from the Miller Brewing Co. wastewater treatment facility (high pollutant strength), with an oxygen penetration depth of only 0.15 mm into the outer layer. The anoxic and substrate concentration increase zones also dominated in the activated sludge floc from the Mill Creek Plant influent (medium pollutant strength), with the outer layer (0.20 mm) participating in the metabolism of the pollutants. The radius of the substrate concentration increase zone inside the sludge floc decreased with pollutant removal along the length of the tank. When the pollutant concentration in the bulk wastewater was low (Muddy Creek Plant), the substrate concentration increase zone disappeared; the whole floc was aerobic and in a high redox status. Our experiments and model analyses demonstrate that the microorganisms' structure-functions inside activated sludge floc change with the bulk substrate concentration and dissolved oxygen concentration.
微生物的生物降解以及活性污泥絮体微环境中的传质阻力，会导致絮体内底物和溶解氧浓度发生变化，并促使絮体内微生物过程出现分层现象。在本研究中，针对来自多个来源、强度各异的废水所形成的活性污泥絮体，构建了一个活性污泥絮体微环境的综合模型，用于动态模拟COD和氮去除的联合生物过程。模型模拟结果和实测剖面显示了在不同底物和整体氧浓度下活性污泥絮体的非均相且受梯度控制的微环境。来自米勒酿酒公司废水处理设施（高污染物强度）的所有活性污泥絮体中均存在絮体内底物浓度增加区，氧渗透到外层的深度仅为0.15毫米。缺氧和底物浓度增加区在米尔溪工厂进水（中等污染物强度）的活性污泥絮体中也占主导地位，外层（0.20毫米）参与污染物的代谢。污泥絮体内底物浓度增加区的半径随着沿池长方向污染物的去除而减小。当整体废水中污染物浓度较低时（泥泞溪工厂），底物浓度增加区消失；整个絮体为好氧状态且处于高氧化还原状态。我们的实验和模型分析表明，活性污泥絮体内微生物的结构功能会随着整体底物浓度和溶解氧浓度而变化。
