Sewage advanced treatment and reuse

The common methods for advanced treatment of sewage are as follows:

1.Activated carbon adsorption

Activated carbon is a kind of porous material, and it is easy to control automatically, and is adaptable to the change of water, water and water temperature. So active carbon adsorption is a kind of deep treatment technology with broad application prospect. Activated carbon has a very obvious removal effect on organic matter with molecular weight of 500~3000. The removal rate is generally 70% ~ 86.7%. It can effectively remove olfactory, chromaticity, heavy metals, disinfection byproducts, chlorinated organic compounds, pesticides and radioactive organic compounds.

Commonly used activated carbon mainly consists of three main categories: powdered activated carbon (PAC), granular activated carbon (GAC) and bioactive carbon (BAC). In recent years, many researches on PAC have been carried out abroad, and the adsorption capacity of various specific pollutants has been thoroughly studied. According to the degree of water pollution, in the water treatment system, adding powder activated carbon to remove the COD in the water, the chromaticity of the filtered water can be reduced by 1~2 degrees, and the odor is reduced to 0 degrees. GAC has been widely used in foreign water treatment, and the treatment effect is more stable. Among the 64 organic indexes of the USEPA standard of drinking water, 51 items are listed as the most effective technology for GAC.

The disadvantage of the GAC process is the high cost of infrastructure and operation, and the easy production of carcinogens such as nitrite. How to further reduce infrastructure investment and operating costs and reduce the cost of activated carbon regeneration will become the focus of future research. BAC can play a synergistic role in biochemical and physicochemical treatment, thereby prolonging the working cycle of activated carbon, greatly improving treatment efficiency and improving effluent quality. The shortcoming is that the activated carbon micropores are easily blocked, and the pH of the influent water quality is narrow, and the impact load is poor. At present, the European BAC technology has been developed to more than 70 water plants, the most widely used is the advanced treatment of water.

2. Membrane separation method

Membrane separation technology is a new type of fluid separation unit operation technology represented by polymer separation membrane. Its biggest feature is that there is no phase change in the process of separation. A high separation effect can be obtained by only a certain pressure as the driving force. It is a very energy saving technology.

Microfiltration can remove bacteria, viruses and parasites, and also reduce the phosphate content in water.

Ultrafiltration is used to remove macromolecules, and the removal rate of COD and BOD for two stage effluent is more than 50%.

The reverse osmosis is used to reduce the salinity and remove the total dissolved solids. The desalination rate of two grade effluent is over 90%, the removal rate of COD and BOD is about 85%, and the removal rate of bacteria is more than 90%.

Nanofiltration is between reverse osmosis and ultrafiltration, and its operating pressure is usually 0.5 ~ 1.0MPa. A remarkable characteristic of nanofiltration membrane is ion selectivity. The removal rate of two valence ions is up to 95%, and the removal rate of monovalent ions is low, 40% ~ 80%. Pan Qiaoming and others adopted membrane bioreactor and nanofiltration membrane integrated technology to treat molasses alcohol wastewater, and the effluent COD was less than 100mg/L, and the reuse rate of wastewater was more than 80%.

The application of membrane technology in the field of advanced treatment in China is still far from the advanced level in the world. Future research focuses on the development and manufacture of high strength, long life, anti pollution, high throughput membrane materials, focusing on membrane pollution, concentration polarization and cleaning and other key problems.

3. Advanced oxidation method

The high concentration of organic pollutants and toxic and harmful pollutants discharged from industrial production are many kinds and harmful, some of them are difficult to biodegrade and have the effect of inhibiting and poisoning the biochemical reactions. The advanced oxidation method produces highly active free radicals (such as OH, etc.) in the reaction, which makes the organic pollutants difficult to degrade into easy to degrade small molecular substances, even directly produce CO2 and H2O, so as to achieve the purpose of harmless.

4. Wet oxidation

Wet oxidation (WAO) is used in high temperature (150~350) and high pressure (0.5 ~ 20MPa) to use O2 or air as oxidant to oxidize organic or inorganic substances in water to achieve the purpose of removing pollutants. The final product is CO2 and H2O.

Wet catalytic oxidation (CWAO) is a suitable catalyst in the traditional wet oxidation process to enable the oxidation reaction to be completed in a more mild condition and in a shorter time, which can also reduce the corrosion of the equipment and reduce the cost of operation. At present, a continuous flow CWAO industrial experimental facility built in Kunming has already shown better economic performance.

The catalysts for wet catalytic oxidation are generally divided into 3 types: metal salts, oxides and composite oxides. At present, the most frequently used catalysts for economic consideration are transition metal oxides such as Cu, Fe, Ni, Co, Mn and their salts. The use of solid catalyst can also avoid the loss of catalyst, the two pollution and the waste of funds.

5. Supercritical water oxidation

Supercritical water oxidation raises the temperature and pressure above the critical point of water, and the water in this state is called supercritical water.

The density, permittivity, viscosity, diffusivity, conductivity and solvent chemistry of the water are different from those of ordinary water. The higher reaction temperature (400~600 C) and pressure also accelerate the reaction rate, which can achieve high destruction efficiency for organic matter in a few seconds.

For the first time in Texas, Harrington used large scale supercritical water oxidation to treat sludge, with a daily capacity of 9.8t. The system has proved that the removal rate of COD is more than 99.9%, and the organic components in the sludge are all converted into CO2, H2O and other harmless substances, and the operation cost is low.

6. Photochemical catalytic oxidation

At present, the photochemical catalytic oxidation method is mainly divided into Fenton reagent method, Fenton like reagent method and TiO2 oxidation method.

Fenton reagent method was discovered by Fenton in twentieth Century. Now, as a meaningful research method in the field of wastewater treatment, it has been re emphasized.

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Sewage advanced treatment and reuse