School of Environmental Science and Engineering, Huazhong University of Science and Technology (HUST), Key Laboratory of Water and Wastewater Treatment, MOHURD, Wuhan 430074, China.
Department of Environmental Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
J Environ Sci (China). 2022 Dec;122:72-82. doi: 10.1016/j.jes.2021.10.001. Epub 2022 Feb 1.
Volatile fatty acids (VFAs), which are largely generated during the anaerobic acidification process, are considered to be reliable indicators of the stable process operation. However, the common methods for monitoring VFAs are offline, and they are typically manual requiring time-consuming, costly and complex instruments. This study aims to develop a novel online analyzer for automatic measuring VFAs, which was based on the 5-pH point titration, embedded with a proportional-integral-derivative (PID) feedback control system. The results show that it can achieve accurate and rapid monitoring of VFAs ranging between 0-400 mg/L (<9 min/sample) but simultaneously faces the problems of overtitration and interference of complex characteristics of wastewater. In order to improve its accuracy and stability, the effects of three general coefficients (KK, and K) of PID on the titration were investigated, and the optimal values of K, K, and K were found to be 1.5, 1.0, and -1.0~0.5, respectively. Besides, the initial titration speed was set at 0.06 mL/min, equal to the minimum speed of the peristaltic pump, and the dichotomy approach was integrated into the PID feedback controller. Owing to the above improvements, the relative mean deviation and standard deviation of measuring VFAs in both synthetic and real wastewaters were mostly lower than 5.0% and 5.0 mg/L, proving the online analyzer is rapid, accurate and reliable.
挥发性脂肪酸（VFAs）主要在厌氧酸化过程中产生，被认为是稳定工艺运行的可靠指标。然而，监测 VFAs 的常用方法是离线的，通常需要耗时、昂贵且复杂的仪器进行手动操作。本研究旨在开发一种新颖的在线分析仪，用于自动测量 VFAs，该分析仪基于 5 点 pH 滴定法，并嵌入了比例-积分-微分（PID）反馈控制系统。结果表明，它可以实现 0-400mg/L 范围内 VFAs 的准确快速监测（<9min/样本），但同时面临着滴定过度和废水复杂特性干扰的问题。为了提高其准确性和稳定性，研究了 PID 的三个通用系数（KK 和 K）对滴定的影响，发现 K、K 和 K 的最佳值分别为 1.5、1.0 和-1.0~0.5。此外，初始滴定速度设置为 0.06mL/min，与蠕动泵的最小速度相等，并将二分法集成到 PID 反馈控制器中。由于上述改进，在线分析仪在合成和实际废水中测量 VFAs 的相对平均偏差和标准偏差大多低于 5.0%和 5.0mg/L，证明其快速、准确、可靠。
