Takács I, Murthy S, Smith S, McGrath M
EnviroSim Associates, 7 Innovation Drive, Suite 205, Flamborough, ON L9H 7H9, Canada.
Water Sci Technol. 2006;53(12):21-8. doi: 10.2166/wst.2006.402.
Chemical phosphorus removal using metal (iron and aluminium) salts is frequently used to control effluent soluble phosphorus levels in wastewater treatment plants. In the Washington DC area effluent phosphorus requirements are extremely stringent to protect the Chesapeake Bay. Full-scale data from two plants in the area were analysed to establish phosphate behaviour in the presence of iron. Titration experiments and mathematical modelling were performed to determine the role of ferric phosphate and hydroxide precipitation and other mechanisms that may potentially be involved in phosphorus removal. Iron addition is described in the model using a chemical equilibrium approach extended with surface charges and adsorption. The model verifies key observations from full-scale data: (a) extremely low orthophosphate levels can be achieved over a wide range of pH values, (b) a mixture of ferric phosphate and ferric hydroxide precipitate is forming with the hydroxide acting as sorbent, (c) molar ratios of Fe/P (iron dosed to phosphate removed) vary widely (1.0-3.9) based on the technology used and residual phosphate levels. The model will be a useful tool for engineers to optimise preliminary, simultaneous and tertiary P removal, both for design and plant operation.
使用金属（铁和铝）盐进行化学除磷常用于控制污水处理厂废水中的溶解性磷水平。在华盛顿特区地区，为保护切萨皮克湾，对废水排放中的磷要求极为严格。分析了该地区两家工厂的实际运行数据，以确定铁存在时磷酸盐的行为。进行了滴定实验和数学建模，以确定磷酸铁和氢氧化铁沉淀的作用以及其他可能参与除磷的机制。在模型中，使用基于表面电荷和吸附扩展的化学平衡方法来描述铁的添加。该模型验证了实际运行数据中的关键观察结果：（a）在广泛的pH值范围内可实现极低的正磷酸盐水平；（b）形成了磷酸铁和氢氧化铁沉淀的混合物，其中氢氧化铁起吸附剂的作用；（c）基于所使用的技术和残留磷酸盐水平，铁与磷的摩尔比（投加的铁与去除的磷酸盐之比）变化很大（1.0 - 3.9）。该模型将成为工程师优化一级、同步和三级除磷过程的有用工具，无论是在设计还是工厂运行方面。
