亚铁盐与高铁盐除磷工艺的对比研究

摘要

亚铁盐和高铁盐是目前最为常用的化学除磷混凝剂。为选用和优化铁盐除磷工艺提供理论依据和技术参数，采用多角度理论分析与响应曲面实证试验的方法，分别从热力学、计量学、铁盐除磷过程、铁盐除磷成本等方面，系统比较了亚铁盐和高铁盐除磷工艺的性能。理论分析表明，相对于亚铁盐，高铁盐除磷更为有效，且除磷剂消耗量较少，出水磷浓度较低，但高铁盐除磷的致酸性较强，废水达标排放的需碱量较大。实证试验表明，铁磷比和 pH 是高铁盐和亚铁盐除磷反应的显著影响因素，铁磷比、pH和快速搅拌速度之间的复合作用差异显著，操作中宜促进协同作用，抑制拮抗作用；相对于亚铁盐，高铁盐的除磷效率较高，出水磷浓度较低，除磷剂消耗量较少，但除磷成本较高。基于理论分析与实证结果，研究认为以亚铁-高铁混合物作为混凝剂，或将亚铁盐部分或全部转化为高铁盐，可综合亚铁盐除磷工艺与高铁盐除磷工艺两者的优势，提高除磷剂的有效性和经济性。%　　Ferric salts and ferrous salts are common precipitators used for chemical phosphorus removal technology. In order to provide theoretical basis and suitable technical parameters for the selecting and optimizing the technic of phosphorus removal by iron salts, theoretical analysis and practical experiments were conducted. Herein the phosphorus removal processes were compared in respect of thermodynamics, stoichiometry, process characteristics and operation cost. The results of theoretical analysis show that, compared to ferrous salt, the reaction between ferric salt and phosphate is more favorable, the dose of precipitant required is less and the residual phosphorus concentration is lower. However, phosphorus removal with ferric salt leads to a low pH, which implies that more alkali for aftertreatment is needed to meet the discharge standard. The results of practical experiments show that, the effects of iron/phosphorus ratio and pH are significant on phosphorus removal for both ferric salt and ferrous salt, but the combined effects of factors (Fe/P, pH, FMS–Flash Mixing Speed) are obviously different from one another. During the wastewater treatment, the synergic action of the above operation parameters should be fully used, while the antagonistic action of operation parameters should be carefully avoided. Compared with ferrous salt, the phosphorus removal with ferric salt is more efficient with less precipitant requirement and lower residual phosphorus concentration, but higher cost. Based on the theoretical analysis and practical experiment, the mixture of ferric salt and ferrous salt is recommended as an alternative precipitant, or ferrous salt is suggested to be partially or completely oxidized into ferric salt for phosphorus removal, which could combine the advantages of both the two technologies.