Liu Jialiang, Ma Haikuan, Yuan Guang, Wang Zhaoyu, Ma Ran, Zhang Shuwei, Cao Xuan, Wang Yang, Liu Yan
Institute of Oceanographic Instrumentation, Qilu University of Technology (Shandong Academy of Sciences), 37 Miaoling Road, Qingdao 266100, China.
College of Information Science and Engineering, Ocean University of China, 238 Songling Road, Qingdao 266100, China.
Rev Sci Instrum. 2023 Jun 1;94(6). doi: 10.1063/5.0136099.
Chemical oxygen demand (COD) is an important indicator for monitoring the quality of seawater. The COD of seawater reflects the levels of organic pollutants in the water. Methods that are commonly used to measure the COD of seawater have high accuracy, good repeatability, and low costs. However, using them for the in situ real-time monitoring of the COD of seawater is unfavorable because they require complex procedures and a long measurement time and may cause pollution to the environment. This paper reports on an optical sensor that accurately determines the COD of seawater in situ. The COD determination is based on the absorption of ultraviolet and visible lights with different wavelengths by organic matter in the water. Single-point LEDs emitting lights with different wavelengths (254, 265, 280, and 546 nm) were used as sources of excitation lights, and photodiodes were used as receiving devices. The optical system, circuit system, and mechanical structure of the sensor were efficiently integrated. The inversion of the COD of seawater was obtained after turbidity correction using the multiple linear regression algorithm. The maximum measurement error, detection limit, and repeatability of the sensor were 5%, 0.05 mg/l, and 0.62%, respectively. Moreover, the R2 values for correlations between COD values and absorbance values measured at three wavelengths (254, 265, and 280 nm) were above 0.99. Overall, the sensor is suitable for the in situ real-time monitoring of the COD of seawater. It requires a short measurement time and generates no pollution.
化学需氧量（COD）是监测海水水质的一项重要指标。海水的化学需氧量反映了水中有机污染物的含量水平。常用的测量海水化学需氧量的方法具有高精度、良好的重复性和低成本的特点。然而，使用这些方法对海水化学需氧量进行现场实时监测并不理想，因为它们需要复杂的程序和较长的测量时间，并且可能对环境造成污染。本文报道了一种能现场准确测定海水化学需氧量的光学传感器。化学需氧量的测定基于水中有机物对不同波长紫外光和可见光的吸收。发射不同波长（254、265、280和546纳米）光的单点发光二极管被用作激发光源，光电二极管被用作接收装置。该传感器的光学系统、电路系统和机械结构得到了有效整合。使用多元线性回归算法进行浊度校正后，得到了海水化学需氧量的反演值。该传感器的最大测量误差、检测限和重复性分别为5%、0.05毫克/升和0.62%。此外，在三个波长（254、265和280纳米）处测量的化学需氧量值与吸光度值之间的相关系数R2值均高于0.99。总体而言，该传感器适用于海水化学需氧量的现场实时监测。它测量时间短且不会产生污染。
