Nuclear wastewater refers to the wastewater generated by nuclear power plants in normal daily activities, mainly including cooling system wastewater, nuclear fuel reprocessing wastewater, auxiliary facility wastewater, etc. Radioactive substances mainly include tritium, uranium, plutonium, thorium, and radium. Since these radioactive wastewater will directly or indirectly affect human health and life, they need to be treated before they can be discharged. At present, the main nuclear wastewater treatment methods are as follows:
1. Chemical Precipitation
Chemical flocculation precipitation is to add a precipitant to the nuclear wastewater, so that the precipitant (such as iron salt, aluminum salt, soda, phosphate, etc.) reacts with the radionuclides in the nuclear wastewater to become an insoluble precipitate. It reduce the content of radionuclides in nuclear wastewater, so as to achieve the effect of nuclear wastewater purification.
2. Membrane Separation
Membrane separation is a technology that achieves solid-liquid separation, purification, and concentration by physically intercepting pollutants. It is distinguished by the pore size of the membrane, which is usually divided into microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. In order to achieve high efficiency and low cost, they are usually used in combination according to different liquid types or in combination with other processes.
The microfiltration membrane has a larger pore size, so it is usually used to intercept pollutants with larger diameters. When treating nuclear wastewater, it is generally used after the chemical flocculation and sedimentation process to remove large particle sediments formed after flocculation and sedimentation, and protect the downstream ultrafiltration, nanofiltration, reverse osmosis and other filtration systems.
Ultrafiltration membranes are usually used to intercept pollutants such as colloids, and suspended solids in liquids, and generally only allow soluble compounds to pass through. In the nuclear wastewater treatment process, the ultrafiltration process can be selected according to different unclear wastewater projects. It is generally used after the microfiltration process as a pretreatment for nanofiltration or reverse osmosis filtration systems.
Nanofiltration membranes can intercept multivalent ions and only allow certain low-valent ions and solvent molecules to pass through. The reverse osmosis membrane can intercept various inorganic ions. Both nanofiltration membranes and reverse osmosis membranes can remove radioactive ions in nuclear wastewater. Appropriate filtration processes should be selected based on the content and type of radioactive ions in nuclear wastewater to achieve the purpose of cost-effectively reducing the content of radioactive ions in nuclear wastewater.
3. Ion Exchange
Ion exchange is to use the cations or anions on the ion exchanger to exchange with the radioactive ions in the nuclear wastewater, remove the radioactive cations or anions in the unclear wastewater, and reduce the content of radioactive substances in the nuclear wastewater, so that the treated nuclear wastewater can meet the discharge standards.
4. Concentration by Evaporation
Evaporation and concentration is to heat the radioactive nuclear wastewater, so that the water in the nuclear wastewater evaporates to form water vapor to be discharged to obtain a higher concentration of radioactive nuclear wastewater, and then solidity the radioactive nuclear wastewater to achieve the purpose of treating nuclear wastewater.
Adsorption technology mainly relies on the adsorption of adsorbents to treat radioactive nuclear wastewater. Adsorbents are generally divided into biomass adsorption materials, inorganic adsorption materials and synthetic polymer materials. They can reduce the content of radionuclides in nuclear wastewater, thereby achieving the effect of purifying nuclear wastewater.
Radioactive nuclear wastewater can also use biotechnology to remove radionuclides in nuclear wastewater. Biotechnology usually uses microbial cells or plants to remove radionuclides in nuclear wastewater through transformation, adsorption, accumulation, sedimentation, and volume expansion mechanisms, thereby reducing the content of radionuclides and making nuclear wastewater meet discharge standards.