in view of the present situation of effluent disinfection in municipal sewage treatment plants in china, the principle and equipment composition of ultraviolet disinfection, liquid chlorine disinfection, ozone disinfection and other sewage disinfection processes and their respective characteristics are introduced respectively, and these disinfection processes are compared comprehensively. the application scope of each process is pointed out to guide the relevant personnel to be reasonable. choose to improve the disinfection efficiency of sewage.
after secondary treatment, the water quality of municipal sewage has been improved and the bacterial content has been greatly reduced. however, the absolute amount of bacteria is still considerable and pathogenic bacteria may exist. after removing these microorganisms, the wastewater can be safely discharged into the water body or recycled. with the continuous improvement of residents'requirements for quality of life, the impact of secondary effluent from sewage treatment plants on urban water has aroused more attention to health and safety issues. disinfection is one of the basic methods to inactivate these pathogenic organisms, so the tail water disinfection of sewage treatment plants has become an important process in sewage treatment, water treatment professionals are constantly exploring the best method of sewage disinfection.
1 several disinfection methods
1.1 physical disinfection method ultraviolet disinfection
1.1.1 uv disinfection principle
ultraviolet disinfection is a physical method of disinfection, ultraviolet disinfection is not to kill microorganisms, but to remove their reproductive capacity for inactivation. the principle of ultraviolet disinfection is to use ultraviolet light to destroy the genetic material of microorganisms nucleic acid (dna or rna), so that it can not divide and replicate. in addition, ultraviolet radiation can also cause damage to other microbial structures. ultraviolet light is an invisible light with a wavelength of 136nm~400nm. near 260 nm in this band has been proved to be the most efficient sterilization, and the maximum output power of the uv lamp is 253.7 nm. the output of this wavelength has accounted for 90% of the ultraviolet energy and 30% of the total energy in the world's top ultraviolet lamp. because of the existence of high intensity and high efficiency ultraviolet c band, ultraviolet technology has become a competitive technology in the field of water disinfection.
the structure of 1.1.2 uv disinfector
1) open structure. the water disinfected in the open uv disinfector flows through the uv disinfector under gravity and kills microorganisms in the water.
2) closed structure. the sealed uv disinfector is a pressurized type. the disinfected water is sealed with a metal cylinder and a ultraviolet lamp with a quartz sleeve.
1.2 chemical disinfection methods
1.2.1 liquid chlorine disinfection
1) the principle of liquid chlorine disinfection. when the liquid chlorine or hypochlorite (naclo) solution was added to the water for disinfection, the following reactions were observed in the water:
hoc and locl- are called effective free chlorine, among which hocl is the best disinfectant. when discharged into the water, chlorine reacts with ammonia and organic nitrogen in the water to form inorganic and organic chloramines, which are called chlorine compounds. total residual chlorine refers to the sum of effective free chlorine and effective chlorine. the disinfection effect of chlorine is affected by contact time, dosage, water quality (nitrogen compound concentration, ss concentration), temperature, ph and control system.
2) chlorination system. the commonly used chlorination systems include chlorination machines, contact tanks, mixing equipment and chlorine bottles, as shown in figure 1.
1.2.2 ozone disinfection
1) the principle of ozone disinfection. ozone (o3) is an isomorphic oxygen (o2). pure o3 is blue gas at room temperature and atmospheric pressure. ozone has strong oxidation capacity (second only to fluorine) and can oxidize most of the organic matter. ozone sterilization is a physical, chemical and biological reaction. ozone sterilization has the following three functions:
a. ozone can oxidize and decompose enzymes necessary for the oxidation of glucose in bacteria, killing bacteria and killing them. b. directly interact with bacteria and viruses, destroy their cell walls, dna and rna, bacterial metabolism is destroyed, resulting in death (dna-ribonucleic acid; rna-deoxyribonucleic acid). a virus is a large molecule wrapped by protein in a nucleic acid, and the virus contains only one nucleic acid. c. penetrate the cell membrane tissue, invade the lipoprotein acting on the outer membrane and the lipopolysaccharide inside the cell membrane, cause the bacteria to have permeability distortion, dissolve and die. therefore, o3 can kill algae and bactericide, and it can also inactivate viruses, spores and other microorganisms with strong vitality.
2) ozone treatment process for sewage. ozone oxidation is strong and unstable, and it can not be stored. therefore, it should be produced locally as needed. generally, the preparation of ozone consists of ultraviolet radiation, electrochemical method and corona discharge. at present, the corona discharge method dominates the preparation of ozone. the ozone gas prepared by the ozone generator is transported to the sealed ozone contact tank through a pipeline and reacts with the treated sewage. after the reacted gas is collected from the top of the pool, it leaves the contact pool through the collector and enters the tail gas ozone decomposer where the remaining ozone gas is decomposed into oxygen and discharged into the atmosphere (see figure 2).
1.2.3 chlorine dioxide disinfection
chlorine dioxide is 5 times more soluble in water than chlorine and 2.5 times more oxidizable than chlorine. it is a strong oxidant. dissolved in water is safe and is internationally recognized as the only highly effective disinfectant for chlorine disinfection.
chlorine dioxide is unstable in nature and can only be prepared in situ by chlorine dioxide generator. there are mainly two kinds of small chemical chlorine dioxide generators used in water treatment field: compound chlorine dioxide generators using sodium chlorate and hydrochloric acid as raw materials and pure chlorine dioxide generators using sodium chlorite and hydrochloric acid as raw materials.
1) the principle of compound chlorine dioxide generator. compound chlorine dioxide generator is prepared by two oxidation of sodium chlorate and hydrochloric acid.
