Six kinds of sewage treatment technology

1. Physical law

Physical sewage treatment is the use of physical action to separate the main suspended pollutants in sewage, and the chemical properties of the water are not changed in the treatment process.

(1) Precipitation (gravity separation) sewage into the pool due to the reduced flow rate, the solid material in the sewage is precipitated under the action of neutrality, and the solid material is separated from the water, this process has a good separation effect, simple and easy to operate, and is widely used, such as the sedimentation tank and sedimentation tank of the sewage treatment plant. The sedimentation tank is mainly used to remove the dense solid particles in the sewage, and the sedimentation tank is mainly used to remove a large number of granular suspended solids in the sewage.

(2) Screening (interception) The use of screening media to intercept suspended matter in sewage. The equipment belonging to the sand filtration treatment is the grating, micro filter, sand filter, vacuum filter, filter press (the latter two are mainly used for sludge dehydration) and so on.

(3) Air flotation (floating) For some fine particles whose relative density is close to water, it is difficult to sink or float in water due to their own weight, air flotation devices can be used. This method will be the air into the sewage, and make it in the situation of tiny bubbles precipitated from the water, sewage density is close to the water of small particles of pollution impurities (such as emulsified oil) adhere to the bubble, and with the bubble to the surface, the formation of foam scum and remove. According to the different ways of air injection, air flotation equipment has pressure dissolved steam gas flotation, impeller gas flotation and jet gas flotation. In order to improve the effect of air flotation, sometimes it is necessary to add coagulant to the sewage.

(4) Centrifugal and swirl separation makes the sewage containing suspended solids or emulsified oil, because the quality of suspended solids and wastewater is different, the centrifugal force is different, the mass of suspended solids is thrown to the outside of the sewage, so that the suspended solids and sewage can be discharged through their respective discharge outlets outside the equipment, so that the sewage can be purified.

2. Chemical method

The chemical treatment of sewage is to add chemicals to sewage, use chemical reactions to separate and recycle pollutants in sewage, or convert them into harmless substances. There are the following chemical treatment methods.

(1) Coagulation method Coagulation method is to add a certain amount of chemicals to the sewage, through the reaction process of destabilization, bridging, etc., so that the pollutants in the sewage condense and settle. The colloidal pollutants in the water are usually negatively charged, and the colloidal particles repel each other to form a stable mixture. If the electrolyte with the opposite charge in the water (coagulant) can change the colloidal particles in the sewage to be electrically neutral, and condense into large particles under the action of molecular gravity.

(2) Neutralization method The process of eliminating excess acid and alkali in sewage by chemical methods so that its pH value reaches about neutral is called neutralization method. Alkali is used as a neutralizer in the treatment of acid-containing sewage, and acid is used as a neutralizer in the treatment of alkali-containing sewage, and CO2 can also be blown into the flue gas for neutralization. Acid and base refer to inorganic acid and inorganic base, generally in accordance with the principle of "waste to waste", can also be neutralized by chemicals, can be carried out continuously, can also be intermittent.

(3) The organic matter and inorganic matter in the dissolved state of the sewage by the REDOX method, after the addition of oxidants and reducing agents, oxidation and reduction occur due to the migration of electrons to form harmless substances. Commonly used oxidants are oxygen in the air, pure oxygen, bleaching powder, ozone, chlorine, etc. Oxidation method is mostly used to treat cyanogen containing phenol wastewater. The commonly used reducing agents are iron filings, ferrous sulfate, sodium bisulfite, etc. The reduction method is mostly used to treat wastewater containing chromium and mercury.

(4) The electrolysis method inserts an electrode in the waste water and passes a current to accept electrons on the cathode plate. In the electrolysis of water, oxygen is produced on the anode and hydrogen is produced on the cathode. The above comprehensive process causes oxidation on the anode and reduction on the cathode. At present, electrolysis is mainly used to treat wastewater containing chromium and cyanide.

(5) Sewage water adsorption treatment is mainly the use of solid material surface adsorption of pollutants in sewage, adsorption can be divided into physical adsorption and biological adsorption. Physical adsorption is produced between the adsorbent and the adsorbent under the action of molecular forces, does not produce chemical changes, and the chemical adsorption law makes the adsorbent and the adsorbent adsorbent under the action of chemical bond forces, so the chemical adsorption selectivity is strong. In addition, biological adsorption can also be produced under biological action. The adsorbents commonly used in sewage treatment are activated carbon, sulfonated coal, diatomite, coke and so on.