Department of Civil, Construction, and Environmental Engineering, North Carolina State University, Raleigh, NC 27695, United States.
Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, NC 27695, United States.
Water Res. 2016 Jan 1;88:786-795. doi: 10.1016/j.watres.2015.11.009. Epub 2015 Nov 10.
Fat, oil, and grease (FOG) deposits formed in sanitary sewers are calcium-based saponified solids that are responsible for a significant number of nationwide sanitary sewer overflows (SSOs) across United States. In the current study, the kinetics of lab-based saponified solids were determined to understand the kinetics of FOG deposit formation in sewers for two types of fat (Canola and Beef Tallow) and two types of calcium sources (calcium chloride and calcium sulfate) under three pH (7 ± 0.5, 10 ± 0.5, and ≈14) and two temperature conditions (22 ± 0.5 and 45 ± 0.5 °C). The results of this study displayed quick reactions of a fraction of fats with calcium ions to form calcium based saponified solids. Results further showed that increased palmitic fatty acid content in source fats, the magnitude of the pH, and temperature significantly affect the FOG deposit formation and saponification rates. The experimental data of the kinetics were compared with two empirical models: a) Cotte saponification model and b) Foubert crystallization model and a mass-action based mechanistic model that included alkali driven hydrolysis of triglycerides. Results showed that the mass action based mechanistic model was able to predict changes in the rate of formation of saponified solids under the different experimental conditions compared to both empirical models. The mass-action based saponification model also revealed that the hydrolysis of Beef Tallow was slower compared to liquid Canola fat resulting in smaller quantities of saponified solids. This mechanistic saponification model, with its ability to track the saponified solids chemical precursors, may provide an initial framework to predict the spatial formation of FOG deposits in municipal sewers using system wide sewer collection modeling software.
脂肪、油和油脂（FOG）沉积物在卫生下水道中形成，是基于钙的皂化固体，是美国全国范围内大量卫生下水道溢流（SSO）的原因。在当前的研究中，确定了实验室皂化固体的动力学，以了解两种脂肪（菜籽油和牛脂）和两种钙源（氯化钙和硫酸钙）在三种 pH 值（7 ± 0.5、10 ± 0.5 和 ≈14）和两种温度条件（22 ± 0.5 和 45 ± 0.5°C）下在下水道中形成 FOG 沉积物的动力学。本研究的结果显示，脂肪与钙离子的一部分快速反应形成基于钙的皂化固体。结果进一步表明，源脂肪中棕榈酸脂肪酸含量增加、pH 值和温度幅度显著影响 FOG 沉积物形成和皂化速率。动力学的实验数据与两个经验模型进行了比较：a）Cotte 皂化模型和 b）Foubert 结晶模型以及包括碱驱动三酰基甘油水解的基于质量作用的机械模型。结果表明，与两个经验模型相比，基于质量作用的机械模型能够预测不同实验条件下皂化固体形成速率的变化。基于质量作用的皂化模型还表明，与液态菜籽油相比，牛脂的水解速度较慢，导致皂化固体的量较小。这种基于机械作用的皂化模型，由于其能够跟踪皂化固体的化学前体，可以为使用全系统下水道收集建模软件预测市政下水道中 FOG 沉积物的空间形成提供初始框架。
