A new idea of disinfection and sterilization treatment of wastewater under the new environmental protection law

Status of sewage treatment

China's per capita water resources are small and their spatial distribution is unbalanced. With the acceleration of urbanization and industrialization in China, the demand gap of water resources is also increasing. In this context, the sewage treatment industry has become an emerging industry, and is currently in the same important position as the tap water production, water supply, drainage, and water reuse industries. In order to protect the natural water environment, many countries in the world require the effluent of municipal sewage treatment plants to be disinfected before discharge. In June 2000, the former Ministry of Construction, the State Environmental Protection Administration, and the Ministry of Science and Technology jointly issued the "Notice on printing and distributing the Technical Policy on Urban Sewage Treatment and Pollution Prevention", which stipulates: "In order to ensure public health safety and prevent the spread of infectious diseases, urban sewage treatment facilities should be set up disinfection facilities." In the "Discharge Standards for Pollution of Urban Sewage Treatment Plants" (GBl8918-2002) promulgated on December 24, 2002, the microbial index was listed as the basic control index for the first time, and the effluent of sewage treatment plants must be disinfected. It is also required that the maximum allowable discharge concentration of coliform number in sewage treatment plants that implement the secondary standard and the first-level B standard shall not exceed l0 /L, so that the pathological indicators of China's sewage treatment standards are in line with international standards.

Classification of sewage treatment

Domestic sewage

Usually, the sewage treatment of urban domestic sewage can meet the water quality requirements of urban water use only after primary treatment and simple secondary treatment, which can meet the requirements of industrial circulation cooling and household toilet use, and achieve the purpose of water reuse.

Hospital sewage

Hospital sewage is a kind of wastewater produced in the process of diagnosis, treatment and prevention of diseases in hospitals or other medical institutions, with potential infectivity and acute infectivity. It contains a variety of microorganisms and infectious diseases, such as AIDS, hepatitis B, hepatitis C, typhoid fever, dysentery, tuberculosis bacillus and other viruses, are listed as national dangerous pollutants, if not treated directly, the bacteria will spread through water, soil and air, posing a threat to the human body.

Industrial sewage

Industrial sewage such as: farms, food factories, pharmaceutical factories, cosmetics factories and other water due to contain a large number of metal ions, such as mercury, chromium, cadmium, as well as alkali, sulfide and salts and other inorganic substances and show a unique color, pollution is very strong. If industrial wastewater enters the aquatic ecosystem directly, microorganisms can not only reduce the concentration of heavy metals, but also enrich and amplify its effect. According to research, after heavy metals enter the organism, they can accumulate in an organ and cause cumulative poisoning, which ultimately endangers life. Some of the inorganic pollutants in sewage deteriorate the water quality, endanger aquatic life and agriculture; Some make people chronic poisoning, destroy the normal physiological process of the human body, among which heavy metals are the most harmful to the human body, and even carcinogenic.

Common disinfectant for sewage

Disinfection technology is accompanied by the deepening of human understanding of environmental protection and rapid development, the current sewage treatment disinfection methods mainly include ultraviolet disinfection, chlorine disinfection, ozone disinfection, ClO2 disinfection and so on.

1. Chlorine disinfection

The common chlorine disinfection methods include liquid chlorine method and sodium hypochlorite method. Liquid chlorine method is the most popular method in the 1980s, the technology is mature, the price is cheap, the equipment failure rate and cost are significantly lower than the ozone method, but the chlorine gas leakage phenomenon occurs from time to time, and easy to produce secondary pollutants: sodium hypochlorite method is the most used method in the 1990s, equipment investment is less, low operating costs, safe and reliable, easy to manage, reliable for the drug source It is widely used in sewage disinfection, but the disinfection effect is not as strong as chlorine gas.

2. Liquid chlorine

Liquid chlorine is a strong oxidizing agent that was first used to disinfect sewage treatment plants. Because of its strong bactericidal ability, low price and reliable disinfection, it is the most widely used disinfectant at present. The disinfection mechanism of liquid chlorine disinfection method is to use liquid chlorine dissolved in water to produce hypochlorous acid and hydrochloric acid: Cl2+H2O= HCIO+HC1 Hypochlorous acid HCIO diffuses to the surface of the bacteria and penetrates through the cell wall of the bacteria into the cell interior. When HC1O molecules reach the interior of the bacteria, oxidation occurs, destroying the bacterial enzyme system and causing the bacteria to die.