Reverse osmosis
Reverse osmosis, also known as RO, is a membrane separation operation driven by pressure difference to separate solvent from solution. Because it is opposite to the direction of natural infiltration, it is called reverse osmosis. According to the different Osmotic pressure of various materials, the reverse osmosis pressure greater than Osmotic pressure, i.e. Anti-Infiltration Act, can be used to achieve the purpose of separation, extraction, purification and concentration.
Reverse osmosis principle
Apply pressure to the feed liquid on one side of the membrane. When the pressure exceeds its Osmotic pressure, the solvent will reverse osmosis against the direction of natural osmosis. Thus, a penetrating solvent, i.e. a permeate, is obtained on the low-pressure side of the membrane; The high-pressure side obtains a concentrated solution, which is the concentrated solution. If seawater is treated with reverse osmosis, fresh water is obtained on the low-pressure side of the membrane and brine is obtained on the high-pressure side.
The main components of reverse osmosis
The reverse osmosis water treatment equipment mainly consists of membrane components, pressure vessels, mechanical filters, metering pumps, pipelines, control systems, etc.
Membrane components are the core components of reverse osmosis water treatment equipment, mainly composed of reverse osmosis membranes. Among them, the membrane is divided into two parts: the high-pressure side and the low-pressure side. The high-pressure side is usually a hollow membrane tube with a membrane inside, while the low-pressure side is a pure water pipe or solution tube. The main function of the membrane is to filter impurities and ions in water, achieving water purification and desalination.
Pressure vessel is a device that supports membrane components, and its main function is to provide the high pressure required for the reverse osmosis process. Common pressure vessel materials include fiberglass, carbon steel, etc. Pressure vessels generally have a certain number of membrane components inside for reverse osmosis processes.
Mechanical filters are equipment for pre-treatment of raw water, mainly used to remove suspended solids, sediment and other large particle impurities in the water, and prevent these impurities from causing membrane blockage and damage. The filter material for mechanical filters can be quartz sand, quartz balls, activated carbon, etc.
The metering pump is a device used to send raw water into the reverse osmosis equipment, and its main function is to control the flow rate and stable pressure of the raw water. Its role in reverse osmosis water treatment equipment is very important, as only stable inlet conditions can reverse osmosis equipment operate normally.
The pipeline is an important part used to connect various components, and its main function is to transport incoming and outgoing water, reverse osmosis liquid, and waste liquid to corresponding positions.
The control system is the intelligent core of reverse osmosis water treatment equipment, which realizes the automation and continuous operation of the equipment. Mainly including PLC program controllers, touch screens, flow meters, etc. Through the control system, operators can monitor the operation status of the equipment in real-time, adjust the parameters between various components, and promptly identify problems to ensure the normal operation of the equipment.
Reverse osmosis applications
Desalination of seawater and brackish water
Since the 1960s, reverse osmosis desalination has become an important way to obtain drinking water and an effective method to solve the shortage of freshwater resources. Reverse osmosis desalination technology is mainly applied in two aspects: seawater desalination and desalination of brackish water.
Preparation of pure water and Ultrapure water
The reverse osmosis+mixed bed water treatment technology has improved the original full ion exchange water production process. During operation, water production has increased, water quality has improved, and water production costs have been significantly reduced. In addition, many researchers have conducted experimental research on the reverse osmosis+electrodeionization method for producing pure water, achieving the expected results and confirming the feasibility of the reverse osmosis+electrodeionization method for producing high-purity water.
Industrial wastewater treatment
Industrial wastewater treatment is one of the most widely used fields of reverse osmosis technology except desalination and pure water preparation. Industrial wastewater treatment has multiple meanings, such as reducing production costs, protecting the environment, and realizing wastewater recycling. Due to the high requirements for influent water in reverse osmosis membranes, the use of reverse osmosis technology for advanced treatment of wastewater often requires the combination of pre-treatment processes such as sedimentation, coagulation, microfiltration, ultrafiltration, activated carbon absorption, and pH regulation.
Heavy metal wastewater treatment
Reverse osmosis technology has been applied early in the treatment of heavy metal wastewater, and extensive research has been conducted both domestically and internationally. As early as the 1970s, reverse osmosis technology had been applied in the treatment of electroplating wastewater, mainly for large-scale treatment of nickel, chromium, zinc rinsing water and mixed heavy metal wastewater.
Printing and dyeing wastewater treatment
Printing and dyeing textile wastewater not only has high chromaticity and large water content, but also has very complex components. The wastewater contains dyes, slurries, oil agents, additives, acid and alkali, fiber impurities, and inorganic salts. The dye structure also contains many highly toxic substances, such as nitro and amine compounds, as well as heavy metal elements such as copper, chromium, zinc, and arsenic. If discharged directly without treatment, it will inevitably cause serious pollution to the environment.
Circulating wastewater treatment in power plants
The circulating cooling water system of the power plant consumes a large amount of water, accounting for 80% of the water used in pure Fossil fuel power station and more than 50% of the water used in thermal power plant. Recycle and treat the circulating discharge water. The produced water as the source of circulating make-up water or boiler make-up water system can not only prevent environmental pollution, but also effectively save water resources and reduce production costs.
Chemical wastewater treatment
During the production process of K2CO3 using ion exchange method, a large amount of NH4Cl wastewater will be generated. In order to save water and completely solve the problem of NH4Cl wastewater discharge, Zhang Jizhen adopted a combination of ion exchange, reverse osmosis membrane separation, and low-temperature multi-effect flash evaporation to further concentrate and recover low concentration NH4Cl wastewater, so that the wastewater can be converted from standard discharge to full recycling and utilization, achieving zero discharge.