1.Advanced oxidation methods (AOPs)
AOPs mainly include O3 / UV (ultraviolet) method, UV / solid phase catalyst method, H2O2 / UV method, H2O2 / Fe2 + method, O3 / H2O2 method and so on. The principle is that -OH is produced in the reaction with extremely strong oxidizing capacity; -OH can oxidize organic pollutants in water without selective, making it completely mineralized into CO2 and H2O. AOPs has advanced technical and economic indicators, is non-toxic, and has no pollution. It is a typical green water treatment technology. Among them, the photocatalytic oxidation method is the most economical and has become a research hotspot.
As the fixation of photocatalysts has not been well solved, suspended phase catalysts have the disadvantages of being easily deactivated, easy to aggregate and difficult to recover. Photocatalytic reactors suitable for industrial applications need to be developed urgently.
2. Electrocatalytic oxidation method
The electrocatalytic oxidation method uses the catalytic action of special electrode materials during electrolysis to generate -OH, which completely oxidizes organic pollutants to CO2 and H2O. This method has good treatment effect, fast speed, small footprint, no pollution during implementation, simple post-treatment, and no secondary pollution, and it is a green water treatment technology. In practical applications, it is necessary to solve the problems of effectively suppressing side reactions such as hydrogen evolution and oxygen evolution, improving current efficiency, improving packing, and power supply methods.
3.Supercritical water oxidation method (SCWO)
The principle of SCWO is to use supercritical water as the reaction medium, and in the presence of oxidants (such as oxygen, hydrogen peroxide, etc.), undergo the free radical reaction at high temperature and pressure to oxidize and decompose organic substances into CO and so on.
In the supercritical state, the density of water is close to that of liquid and the viscosity is close to that of gas. It has a strong penetrating ability similar to gas and a large density and solubility similar to liquid. It can interact with non-polar substances (such as hydrocarbons), Organic substances and gases (such as air and oxygen) are completely mutually soluble, which avoids the resistance of interphase mass transfer and increases the degradation rate of pollutants.
Compared with the incineration method and wet air oxidation method, SCWO has the advantages of no catalyst, short residence time, high removal efficiency, cleanliness, and broad spectrum. It can be used for chemical, pharmaceutical, food, military and nuclear industry wastewater treatment, and municipal wastewater treatment. SCWO has many technical difficulties, such as research and development of broad-spectrum catalysts, effective control of high temperature and pressure, solving the problem of solid particles blocking equipment, inhibiting scaling, and recovering thermal energy with maximum efficiency. The lack of in-depth research on its thermodynamics and dynamics makes engineering design and process development difficult.
4. Ultrasonic degradation technology
The principle of ultrasonic degradation of organic pollutants is that when the acoustic energy is sufficiently strong, the attractiveness between the molecules in the liquid phase is broken in the loose half-cycle, forming a cavitation nucleus with a lifetime of 0.1 μs, which is exploding. The instantaneous time can produce a local high temperature and high pressure environment of about 4 000 K and 100 MPa, and a jet with a strong impact force at a speed of about 110 m / s. This condition is sufficient to cause all organic substances to undergo chemical bond rupture, pyrolysis or free radical reactions in the cavitation bubbles to degrade organic pollutants in the wastewater.
At present, the research on ultrasonic degradation technology is still in the exploratory stage, and many problems need to be solved, such as the enhanced approach to organic degradation, the degradation mechanism, the rational design of the reactor, the development of high-frequency ultrasonic generators, the quantitative description of the reaction process, and cavitation. Study on bubble interface characteristics, continuous processing technology development, pollutant degradation characteristics in multi-phase systems, and avoidance of toxic intermediates.
5. Membrane treatment technology
Most membrane separation processes have no phase change and can be operated at normal temperature. They have the advantages of low energy consumption, high efficiency, simple process, small investment and light pollution, and have developed rapidly in water treatment applications. It includes microfiltration (MF), ultrafiltration (UF), dialysis (D), electrodialysis (ED), nanofiltration (NF) and reverse osmosis (RO), pervaporation (PV), liquid membrane (LM) and so on. Among them, RO and NF technologies are particularly noticeable.
Large-scale applications of RO technology are mainly brackish water and seawater desalination and mixtures that are difficult to handle by other methods. In order to further improve the reliability of the membrane, the adsorption mechanism of the membrane, better membrane materials and optimization of the surface structure of the membrane need to be studied in order to improve the water flux, selectivity, high temperature resistance and oxidation resistance of the membrane.