Biological pretreatment is to remove ammonia nitrogen and some organic matter by biological action.
The biological pretreatment technology of micro-polluted water source has been studied and applied for more than 30 years, and has been widely recognized by people.
As the pretreatment of micro-polluted water source, the main advantages of biological treatment are: the removal of nh3-n, no2-n, AOC, the removal of organic matter, chroma, smell, TOC, turbidity has a certain effect.
The disadvantage is that it occupies a large area and the treatment effect is greatly affected by the water quality and temperature of the water source.
Application of preoxidation technology
Prechlorination, preozonation, permanganate and chlorine dioxide are mainly used.
Prechlorination has been widely used in China, which is used to remove algae and degrade organic matter, and the cost is low. However, the disinfection by-products generated by chlorine and organic matter in water are very harmful to human body, so the use of pre-treatment in micro-polluted water sources should be phased out.
Preozonation is mainly used to remove iron and manganese from groundwater, to remove chroma and smell, and to degrade polymer organic compounds in water. It is also used to improve flocculation and clarification.
In the application of pre-ozone engineering, its main purpose is to assist coagulation. If necessary, it is considered to strengthen the removal of algae, chroma and organic pollutants. The ozone input is generally 0.2 ~ 2.0mg/L.
Ozone pretreatment can control the production of disinfection by-products by changing the physical and chemical properties of organics in water and reducing the chlorination activity of organics in water.
However, it should be noted that when the raw water contains relatively high concentration of bromide ions or when excessive ozone is added, the ozone pre-oxidation makes bromide ions convert to bromate ions, and makes the concentration of bromotrihalomethane, bromoacetic acid and so on in the water increase.
The pre-ozone process covers less land, the process effect is not affected by the season, temperature and other factors, the effect is stable.
However, ozone needs to be prepared in site and the operation cost is high.
Potassium permanganate is a strong oxidant, which can selectively interact with organic pollution in water and destroy unsaturated functional groups of organic matter. It has been used to remove smell and chroma in water since 1960s with good effect.
In recent years, the permanganate compound agent has been developed, which has the remarkable efficacy of oxidation to help coagulation, algae removal, odor removal, and removal of trace organic pollutants in surface water, and can also reduce the formation potential of trihalomethane.
The intermediate state and new ecological components of permanganate compound in the process of oxidation can enhance the removal of trace organic pollutants in water.
In addition, the new ecological manganese dioxide has adsorption effect on a variety of trace organic and inorganic pollutants in water, which can improve the removal effect of a variety of organic pollutants and heavy metals in water.
Chlorine dioxide preoxidation
The application of chlorine dioxide preoxidation is still relatively few, but the chlorine dioxide preoxidation has a better removal effect on aromatic hydrocarbon compounds, can control the formation of THMs, reduce the formation of total organic halogen, and has a good decolorization effect on colored substances in water.
The organic by-products formed by chlorine dioxide preoxidation are less and less toxic, while the inorganic by-products mainly include chlorite and chlorate.
Have research report, the adverse effect of salt of chlorite and chlorate salt basically lies in its strong oxidation sex and toxic action to human body nervous system, long-term drinking can cause anaemia to wait.
At present, the research of this aspect needs to be further deepened.