1. Wet oxidation (persulfate) - non-dispersive infrared detection (NDIR)
In this method, the sample to be tested is treated with phosphoric acid before oxidation to remove inorganic carbon, and then the TOC concentration is measured. Most of the modern TOC continuous analyzers are wet oxidation. Wet oxidation is not sufficient for the oxidation of complex water bodies (eg: humic acid, high molecular weight compounds, etc.), so it is not suitable for water bodies with high TOC content, but it is possible for conventional water bodies such as surface water.
2. High temperature catalytic combustion oxidation - non-dispersive infrared detection (NDIR)
The application time of high-temperature catalytic combustion oxidation is much later than that of wet oxidation, but because the high-temperature combustion is relatively thorough, it can be applied to water bodies such as rivers, seawater and industrial wastewater with heavy pollution.
3. UV Oxidation - Non-Dispersive Infrared Detection (NDIR)
The method is the same as that of wet oxidation, but the principle of ultraviolet light (185nm) irradiation is used to remove inorganic carbon before the sample enters the ultraviolet reactor, and more accurate results are obtained. The UV oxidation method is not suitable for high-content TOC such as granular organics, drugs, and proteins, but it can be used in water bodies such as raw water and industrial water.
4. Ultraviolet (UV)-Wet (Persulfate) Oxidation-Non-Dispersive Infrared Detection (NDIR)
This method is the synergistic effect of UV oxidation and wet oxidation, complementing and promoting each other, and the oxidative degradation effect is better than any one of them. As UV oxidation cannot be used in water with high content of TOC, the synergy of the two can measure water with heavy pollution. It has high popularity and mature technology because of its strong applicability and wide measurable range.
5. Resistance method
This method is a technology that has been applied in recent years. Its principle is to measure the difference in resistivity of the sample before and after ultraviolet oxidation under the premise of temperature compensation. However, this method has strict requirements on the source of the water body to be measured, only relatively clean industrial water and pure water can be used, and the application direction is single.
6. Ultraviolet method
The detection and analysis of TOC by UV absorption spectroscopy can be traced back to 1972. Dobbs et al. studied the linear relationship between the UV absorbance value (A) at 254 nm and the TOC in the secondary effluent of urban sewage treatment and river water. After decades of development, the application of this method has developed rapidly due to its advantages of fast, non-contact measurement, good repeatability, and low maintenance.
7. Conductivity method
The main device involved in this method is a conductivity cell, which consists of a reference electrode, a measuring electrode, a gas-liquid separator, an ion exchange resin, a reaction coil, and a NaOH conductivity liquid. The advantages of conductivity cells are low price and easy popularization, but poor stability.
8. Ozone oxidation method
Taking advantage of the strong oxidizing property of ozone and using ozone oxidation as the detection technology of TOC, it has fast reaction speed, no secondary pollution, and high application value. Therefore, the application prospect of this method is very promising.
9. Ultrasonic cavitation sonoluminescence method
Sonochemistry has become a booming research field. The research of sonoluminescence has been involved in the field of environmental protection. Relevant scholars in my country have done a lot of work in basic research and applied research. This unique method has been recognized by experts. . It has the advantages of no secondary pollution, no need to add reagents, and simple equipment.
10. Supercritical water oxidation
Suitable for high salinity applications, Supercritical Water Oxidation (SCWO) technology was originally used to treat large volumes of wastewater, sludge and contaminated soil. Now used in commercial laboratory TOC analyzers, when the temperature and pressure of the injection water are raised above the critical point of water (375°C and 3,200psi), the organic waste is rapidly and completely oxidized by the oxidant in the water. The properties of supercritical water can make organic carbon oxidized to carbon dioxide extremely efficiently and quickly, even if there are chlorides and other inorganic substances that can cause negative interference when using non-supercritical oxidation methods.