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Supercritical fluid technology for wastewater treatment

Summary

The experimental results show that the adsorbent GDx-301 can be used to adsorb organic matter in water and then extract and desorb with supercritical CO2 fluid, so that the organic matter in the wastewater can be enriched and removed.

Supercritical fluid technology for wastewater treatment

The effect is obvious, and supercritical CO2 can be used quickly and effectively at lower temperature. Desorption of organic matter.

The supercritical CO2 fluid was used to study the dichlorvos wastewater. At a temperature of 60 °C and a pressure of 25 MPa, the DDW removal rate in the sample reached 100%.

The cyanide-containing wastewater was studied. It was found that when the pressure was 10-15 MPa, the temperature was 30-50 degrees Celsius, and the extraction time was 20-30 minutes, the cyanide removal rate in the wastewater was close to 70%.

Supercritical Water Oxidation

A liquid whose temperature and pressure are above a critical point is called a supercritical fluid (SCF). The application of supercritical fluid technology to environmental protection is a new research direction.

Due to its energy saving and high efficiency, it is favored by environmental protection experts at home and abroad.

Advanced industrial countries are competing for development and have made breakthroughs in the treatment of three wastes.

Some developed countries in Europe and the United States have already realized industrialization of supercritical fluid technology. China has little research on supercritical fluids and is still in the experimental stage.

At present, supercritical fluid technology has been applied to the treatment of high concentration refractory organic wastewater, including supercritical extraction (SEF) and supercritical water oxidation (SCOW).

Properties of supercritical fluids

The supercritical co2 fluid is a non-agglomerating gas that does not liquefy even if the pressure is increased due to the disappearance of the boundary between the liquid and the gas. Supercritical fluids combine the physical properties of liquids and gases. It is basically still in a gaseous state, but unlike a normal gas, it is a dense gaseous state.

Its density is two orders of magnitude larger than that of a normal gas, and is similar to a liquid. It has a lower viscosity than liquid, but it spreads faster than liquid (about two orders of magnitude), so it has better fluidity and transfer properties.

Its dielectric constant changes drastically with changes in pressure (eg, an increase in dielectric constant favors the dissolution of some highly polar materials).

In addition, this physical property changes depending on the pressure and temperature. Because water and co2 are stable in nature and non-toxic, odorless, colorless, and non-corrosive, they are the most commonly used supercritical fluids.

Supercritical co2 fluid extraction

The critical temperature of supercritical co2 fluid is 31.26 °C, the critical pressure is 72.9 atm, it has strong solubility and low viscosity, can extract and separate a certain substance, has high separation efficiency, can be carried out at a lower temperature, It is suitable for separating heat sensitive and oxidizable substances.

Supercritical co2 fluid technology for the treatment of organic wastewater. In the aspect of pesticide wastewater treatment:

The supercritical CO2 fluid was used to study the dichlorvos wastewater. At a temperature of 60 °C and a pressure of 25 MPa, the DDW removal rate in the sample reached 100%.

The cyanide-containing wastewater was studied. It was found that when the pressure was 10-15 MPa, the temperature was 30-50 degrees Celsius, and the extraction time was 20-30 minutes, the cyanide removal rate in the wastewater was close to 70%.

Supercritical CO2 extraction combined with adsorption method for the treatment of high concentration organic wastewater is a more effective treatment.

The method of enriching organic pollutants in water by solid phase adsorption combined with supercritical CO2 method was studied. The extraction and desorption conditions were selected as 22.0MPa and 60 degrees Celsius, with 0.5ml methanol as modifier, static extraction for 5min and 15.0ml supercritical.

The CO2 fluid was dynamically extracted for 30 min, and the best solvent for extraction was ethanol. The experimental results show that the adsorbent GDx-301 can be used to adsorb organic matter in water and then extract and desorb with supercritical CO2 fluid, so that the organic matter in the wastewater can be enriched and removed.

The effect is obvious, and supercritical CO2 can be used quickly and effectively at lower temperature desorption of organic matter.

Supercritical water oxidation technology

When the temperature of the water exceeds 374 degrees Celsius and the pressure exceeds 22 MPa, it is in a supercritical state.

The properties of supercritical water are similar to those of non-polar compressed gases, and its solvent properties are similar to those of low-polar organics, so it is completely miscible with non-polar (or weakly polar) organics and can also interact with O2, CO2, N2. H2 and the like are completely mutually soluble, but the solubility of inorganic substances, particularly inorganic salts, in supercritical water is very low.

At the same time, supercritical water has an easily changeable density, a low surface tension, a low viscosity and a high diffusion coefficient. Supercritical Water Ox idation (SCWO) refers to the oxidation of organic matter in water when the temperature and pressure are higher than the critical temperature of water (374 degrees Celsius) and the critical pressure (22 MPa).

When the organic matter and oxygen are simultaneously dissolved in the supercritical water, the oxidation reaction is completed rapidly (about several tens of seconds to several minutes). Supercritical water oxidation is an ideal method for thoroughly degrading toxic waste water without toxic by-products.

Application

Sulfur-containing wastewater

Treatment of sulfur-containing wastewater can be processed at one time, without additional treatment. The supercritical water oxidation technology was used to treat sulfur-containing wastewater. Under the conditions of temperature 723.2K, pressure 26 MPa, oxygen-sulfur ratio 3.47, and reaction time 17 s, S2- could be completely oxidized to SO42- and removed.

Acrylonitrile wastewater

Treatment of acrylonitrile wastewater, can effectively treat high cyanide acrylonitrile wastewater in a short time, COD removal rate is extremely high, no secondary pollution.

Supercritical fluid technology for wastewater treatment

The related experimental research on acrylonitrile wastewater was carried out. When the reaction temperature was 500 ° C and the pressure was 25 MPa, the COD removal rate was 98.8%, the temperature reached 618 ° C, and the COD removal rate was 99.9% when the pressure was 25-28 MPa.

Therefore, the temperature is increased, the removal rate is increased, and the first-level emission standard can be achieved when the temperature reaches 600 degrees Celsius or higher.

Oily wastewater

Treatment of oily wastewater. The oily wastewater was tested by supercritical water oxidation. Under suitable conditions of temperature, pressure and reaction time, the COD removal rate was 99.9%.

In addition, the supercritical water oxidation method can also be used to treat high concentration pharmaceutical wastewater, alcohol wastewater, aromatic organic wastewater, and the like.

The supercritical water oxidation technology has high treatment efficiency, low processing cost, economical and technical feasibility, and has broad development prospects.

Conclusion

Supercritical co2 fluid have broad prospects for wastewater treatment.

Supercritical water oxidation technology treatment of organic wastewater can completely oxidize organic matter to co2, water, nitrogen and the like.

The application of this technology has a very broad prospect. Considerable progress in this respect, and our country (China) is still in the experimental research stage, which requires us to strive for innovation, on the one hand, drawing on international experience, on the other hand, independent research, and strive to realize this technology as Soon as possible Industrial application.