1 Introduction to the characteristics of hospital sewage
The pollutants contained in hospital sewage are quite special, including medicines, disinfectants, diagnostic reagents, detergents and other ingredients, pathogenic microorganisms, parasite eggs and other parasites, and viruses like roundworm eggs. In addition, if the hospital has an isotope consultation room, there will be radioactive substances in the sewage of the hospital. Compared with other types of sewage, it has a small amount of pollution, but it has a stronger pollution power. If it is discharged directly without treatment, it will cause water pollution and may spread a large number of diseases.
2 Select the disinfection method
There are four main ways to disinfect hospital sewage: first, bleaching powder, which has a large dosage, uneven mixing, and contains more impurities, and the disinfection effect is not ideal, so it is basically no longer used; second, liquid chlorine, its The disinfection ability is strong, the price is relatively cheap, and it is widely used in tap water and hospital disinfection. However, the preparation of chlorine is inconvenient, liquid chlorine cylinders are easy to leak, and there are great safety risks. Therefore, many hospitals plan to eliminate this method; third, using sodium hypochlorite generators, this equipment has a short life and a high failure rate. The cost is high, and the disinfection ability is not strong, so it is gradually replaced; fourth, the use of ozone, which is a strong oxidant, has a better use effect. However, it costs more, requires a large investment, and is difficult to maintain. The hospital uses relatively more less.
3 Application of chlorine dioxide in hospital sewage treatment
3.1 Characteristics of chlorine dioxide
The color of chlorine dioxide is yellow-green to red, and its existence state is gas. Its smell is more irritating than chlorine. The solubility of chlorine dioxide in water is linearly related to the reciprocal of water temperature, and the maximum solubility is 2900g/L. When it is concentrated and pressurized, it is relatively unstable and cannot be stored under pressurization. In chlorine dioxide, chlorine exists in a positive tetravalent state. Its available chlorine content is 2.63 times that of chlorine gas, and its activity is 2.5 times that of chlorine gas. Under different conditions, the reaction formula of chlorine dioxide is different.
Under acidic conditions, chlorine dioxide is highly oxidizing, and the reaction formula is:
Under water treatment conditions, its reaction formula is:
3.2 Disinfection of chlorine dioxide
Chlorine dioxide began to be used in the 1940s and was used for the bleaching of pulp. Many companies in Europe and the United States use chlorine dioxide to treat drinking water and wastewater. my country began to strengthen the research on chlorine dioxide in the 1980s and has made remarkable achievements up to now.
Tests have proved that chlorine dioxide can kill microorganisms, such as bacterial propagules, fungi, viruses, etc. It can destroy trace organic pollutants in water, such as cyanide, hydrogen sulfide, organic sulfide, etc. In addition, it can oxidize metal ions in a reduced state in water. Since chlorine dioxide is less affected by pH, it can kill algae and reduce the color, odor and turbidity of the aqueous solution. Its effect is five times that of sodium hypochlorite. In sewage treatment, it does not form organic halides, and has a better effect on hospital sewage treatment.
The disinfection effect of chlorine dioxide on viruses is higher than that of ozone and liquid chlorine. It reacts quickly with sewage, and the contact time is one-half to one-fourth of chlorine, from one hour to half an hour. In addition, the area of the contact pool can be reduced to half, which greatly saves investment costs.
3.3 The difference between chlorine dioxide and chlorine disinfection
According to the effectiveness of common disinfectants, ozone is the first, chlorine dioxide is second, chlorine is third, and chloramine is the last. Chloramine is the first in water stability, chlorine dioxide is second, and chlorine is third. Ozone last. From the above arrangement, we can see that the bactericidal ability of chlorine dioxide and the stability in water are better than chlorine. In addition, pH rarely affects the disinfection ability of chlorine dioxide, and water pollution has a relatively small influence on its disinfection effect.
"Chlorine dioxide does not react with some compounds in water, such as ammonia, nitrogen, alcohols, esters, etc.). In contrast, chlorine reacts with ammonia in water to produce monochloramine, dichloramine and trichloramine, which will significantly reduce the free chlorine content and disinfection effect. Chlorine dioxide oxidizes organic matter in sewage mainly by oxidation reaction. After oxidation, organic matter can be degraded into products containing oxygen groups without chlorinated products. Chlorine or chlorination will form chlorinated derivatives of chloroform. These chemicals have carcinogenic effects and are difficult to degrade in nature. Chlorine dioxide can also oxidize and decompose griseofulvin and humic acid, and the degradation products will not appear in the form of chloroform, which is unmatched by traditional chlorination disinfection methods.
3.4 Preparation of chlorine dioxide
Chlorine dioxide is active and unstable, which makes its application limited by certain conditions. The traditional method is on-site preparation, and on-site preparation methods include diaphragm electrolysis and chemical methods. The general principle of preparing chlorine dioxide by chemical method is to use chlorine gas or sodium hypochlorite as raw materials, and chemically react with chlorous acid solution in the generator to obtain chlorine dioxide solution. It can also use sodium chlorite and hydrochloric acid to generate chlorine dioxide. The reaction inside the vessel is obtained. At this stage, there are already many domestic companies producing chemical chlorine dioxide generators. The main components of the chemical chlorine dioxide generator are the reaction system, the absorption system, the raw material supply system and the control system. During work, the reaction raw materials are sent to the reaction system through quantitative transportation, the catalyst is used to generate chlorine dioxide gas, which is absorbed by the absorption system to form a certain concentration of chlorine dioxide solution, and finally put into the sewage to be treated.
It is confirmed by research that the addition of special stabilizers can produce stable chlorine dioxide. The chlorine dioxide content in the stable chlorine dioxide liquid is 2%-10%, and the chlorine dioxide content in the solid product is 28%-40%. In experiments and practical applications, stable chlorine dioxide becomes active due to activation under acidic conditions, and the new ecological oxygen and hypochlorous acid molecules it releases can double-oxidize microorganisms. Compared with a single sodium hypochlorite disinfection method, its oxidizing ability is stronger. When the ratio of the amount of stable chlorine dioxide solution to hydrochloric acid is 1, the chlorine dioxide can be activated. The activation is carried out for 10-15 minutes and diluted with water, and the activation effect is best at this time. The activated chlorine dioxide solution should be placed in a dark container with a lid, and the expiration date is two weeks. The stable-state chlorine dioxide or chlorine dioxide generator does not consume electricity during commercial use, which is beneficial to the effective promotion of chlorine dioxide.
3.5 Treatment of hospital sewage
At this stage, most domestic hospitals use primary treatment plus chlorination disinfection for sewage treatment. Taking the author’s hospital as an example, the process of the treatment process is roughly as follows: fecal waste water → septic tank → other sewage → grille → regulating tank.
This kind of disinfection technology has disadvantages. It has high anti-corrosion requirements for the sodium hypochlorite generator, high power consumption, and the prepared sodium hypochlorite solution is very unstable. If it is improperly stored, it is particularly easy to decompose. After the disinfection work is completed, the residual chlorine content in the sewage can easily exceed the standard , The indicators of other pollutants did not meet the prescribed standards.
If chlorine dioxide is used instead of sodium hypochlorite to treat hospital sewage, the treatment process and flow are basically unchanged. To ensure that the treated water quality can meet the national standard, it is necessary to perform a first-level flocculation sedimentation treatment after the adjustment tank, to uniformly treat the water quality, and to put in flocculants, which can absorb, precipitate and separate some organic matter and suspended matter in the sewage. The oxidation reaction of upper chlorine dioxide can greatly remove COD, BOD, virus and SS in sewage, reaching the national standard. If the sodium hypochlorite disinfection method is used, its oxidizing ability is relatively weak, and the COD removal effect is not ideal.
The process of chlorine dioxide treatment of sewage is: hospital comprehensive sewage → grille → water quality adjustment → flocculation and sedimentation → chlorine dioxide contact disinfection → discharge up to standard
Through the above process, the virus and other microorganisms in the hospital sewage treatment are killed, and the discharge can reach the national standard.
3.6 Problems and countermeasures in sewage treatment
Using chlorine dioxide for disinfection, the by-products in the water are chlorite and a lower concentration of chlorate. Among the easily visible carcinogens listed by the International Cancer Institute, chlorite is among them. The prescribed content standard of chlorite in drinking water is 200μg/L; according to the toxic sensory characteristics, chlorite is classified as a level 3 danger. During sewage treatment, the amount of chlorite and chlorate produced is related to the total organic carbon content in the water. It can be seen that the dosage of chlorine dioxide must be effectively controlled during sewage treatment. In addition, in the process of treating sewage, biochemical treatment is required before disinfection treatment in order to effectively control the pollutants in the water, thereby reducing the content of pollutants.