Centro de Investigación y Desarrollo en Criotecnología de Alimentos, CONICET La Plata, UNLP 47 y 116 B1900AJJ, La Plata, Argentina.
J Hazard Mater. 2010 May 15;177(1-3):199-208. doi: 10.1016/j.jhazmat.2009.12.018. Epub 2009 Dec 11.
The objectives of this work were: (a) to analyze the effect of alkalinity, pH and initial Fe:P molar ratio (Fe(0):P(0)) on the precipitation of orthophosphate using ferric chloride in the presence of activated sludge in order to represent conditions of simultaneous precipitation, and in exhausted wastewater to simulate conditions of post-precipitation, (b) to compare the experimental results with predictions obtained from a chemical equilibrium model, and (c) to propose a mechanistic model to determine the dose of coagulant required to achieve a given orthophosphate removal degree at constant pH. Results showed that the presence of biomass did not affect the orthophosphate precipitation; however, addition of ferric chloride caused a drop of pH to values not compatible with the normal activity of activated sludges. For this reason, the wastewater was supplemented with NaHCO(3); when 1gL(-1) NaHCO(3) was added, orthophosphate removals higher than 97% and pH above 6.2 were obtained using Fe(0):P(0)=1.9. Precipitation assays at constant pH showed that Fe(III) hydrolysis and FePO(4) precipitation reaction compete with each other. Calculations using a chemical equilibrium model (CHEAQS) predicted that ferric phosphate precipitation should not take place if pH is higher than about 7.8. However, experimental results showed that ferric phosphate precipitation occurred even at pH 9. For this reason, a mechanistic model was proposed to predict orthophosphate concentrations as a function of Fe(0):P(0) at constant pH. The model can be applied to calculate the minimum Fe(III) concentration required to achieve a given discharge limit for orthophosphate as a function of its initial concentration and pH.
(a) 分析在活性污泥存在下使用三氯化铁沉淀正磷酸盐时碱度、pH 和初始 Fe:P 摩尔比 (Fe(0):P(0)) 的影响，以代表同时沉淀的条件，以及在耗尽废水中模拟后沉淀的条件；(b) 将实验结果与化学平衡模型的预测进行比较；以及 (c) 提出一个用于确定在恒定 pH 下达到给定正磷酸盐去除程度所需的混凝剂剂量的机理模型。结果表明，生物量的存在并不影响正磷酸盐的沉淀；然而，添加三氯化铁会导致 pH 下降到不适合活性污泥正常活动的水平。因此，废水被补充了 NaHCO(3)；当添加 1gL(-1) NaHCO(3)时，使用 Fe(0):P(0)=1.9 可以获得高于 97%的正磷酸盐去除率和 pH 高于 6.2。在恒定 pH 下进行的沉淀实验表明，Fe(III)水解和 FePO(4)沉淀反应相互竞争。使用化学平衡模型 (CHEAQS) 的计算预测，如果 pH 高于约 7.8，则不应发生铁磷酸盐沉淀。然而，实验结果表明，即使在 pH 为 9 时也发生了铁磷酸盐沉淀。为此，提出了一个机理模型来预测在恒定 pH 下作为 Fe(0):P(0)函数的正磷酸盐浓度。该模型可用于计算在给定的正磷酸盐初始浓度和 pH 下达到给定排放限值所需的最小 Fe(III)浓度。
