Hospital Wastewater Treatment Process
1. The characteristics of hospital sewage
Hospital waste water contains some special pollutants, such as drugs, disinfectants, diagnostic agents, detergents, and a large number of pathogenic microorganisms, parasite eggs and various viruses (such as roundworm eggs, hepatitis virus, tuberculosis and dysentery) . In addition, there are radioactive substances such as radium 226, phosphorus, gold 198, and iodine 131 in the sewage of hospitals with isotope clinics. Compared with industrial wastewater and domestic sewage, it has the characteristics of small water volume and strong pollution. If it is not properly treated and discharged, it will inevitably pollute the water source and spread diseases.
2. Traditional hospital sewage treatment methods
2.1 Biological oxidation method
Biological oxidation process, also known as activated sludge process, is the most commonly used traditional treatment method for various sewage treatment. Using blast aeration, mechanical aeration, etc., a large number of filamentous bacteria and fungi in the sewage can be multiplied. These microorganisms have the ability to adsorb and oxidize harmful substances in the sewage, thereby reducing the COD and BOD of the sewage, so that the sewage can be purified. Some hospital sewage treatment plant also use both anaerobic and aerobic methods. That is, in the anaerobic process, anaerobic microorganisms multiply, nitrify and adsorb harmful substances in water. The disadvantage is that a large amount of activated sludge will be produced, and the sludge must be treated, which lengthens the treatment process, increases engineering costs, and causes secondary air pollution during the aeration process. There are many domestic examples in this regard, and the Fifth Hospital of Daqing City is one of them (rotary aeration method).
Commonly used biological oxidation methods include biological contact oxidation method, biological turntable method, tower biological filter method, jet aeration method and oxidation ditch method.
2.2 Chemical Agent Process
The chemical agent method is to put an appropriate amount of chemical agent into the sewage to oxidize the harmful substances in the sewage to achieve aggregation, adsorption and precipitation. This method has been gradually developed in the past 30 years after the traditional biochemical method.
- Liquid chlorine: Because of its strong disinfection ability and cheap price, liquid chlorine is widely used in the disinfection of tap water and hospital sewage. However, chlorine is a yellow toxic gas with a pungent odor. It cannot be produced anytime and anywhere. Special storage equipment and chlorination equipment must be provided. Liquid chlorine dosing equipment has a complex structure, is easy to be corroded, and is highly dangerous, so it is restricted to use in cities or areas with overly concentrated populations.
- Sodium hypochlorite solution: Sodium hypochlorite is one of the most primitive disinfection treatment methods. The method has the advantages of convenient raw material source, stable product, convenient transportation, low equipment investment, low operating cost, convenient management, safety and reliability, no sludge due to disinfectant, and wider application. However, sodium hypochlorite has a weak disinfection ability and waste residues during the treatment process, which are gradually being replaced by other products.
- Ozone method: Ozone is a strong oxidant. Adding a proper amount of ozone to the sewage will oxidize microorganisms and various metal ions in the water. Using this method to treat hospital sewage is more thorough, with less secondary pollution. The disadvantage is that there are a lot of supporting equipment, a large one-time investment, a large amount of equipment maintenance, and a large amount of electricity consumption, which increases the annual operating cost.
3. The current better approaches
3.1 CASS process biochemical treatment
3.1.1 Features of CASS process
The CASS pool has been reduced in volume but improved in effects through technological innovation and optimized design. This method continuously feeds water but does not aerate. The concentration of organic matter is very high, and it is in anoxic and anaerobic state, which inhibits the growth of aerobic bacteria and prevents the sludge from expanding. The main reaction zone is divided into two parts, anoxic and aerobic, and aeration, precipitation and water skimming are carried out periodically. No water enters in the sedimentation stage, which eliminates possible hydraulic interference and improves the sludge characteristics and effluent quality. It has stronger adaptability and better treatment effect in hospital sewage with large changes in water quality and quantity, whose composition is very complex, containing a variety of bacteria, viruses, parasite eggs and some harmful substances. It is really an ideal hospital sewage biochemical treatment method:
- The project construction cost is low. CASS biodegradation, sludge sedimentation and waste water discharge are all carried out in the same tank, without the need for adjustment tanks, secondary sedimentation tanks and sludge return equipment, which can greatly save investment, reduce land use and reduce operating costs. Generally, the construction cost can be saved by 10% to 25%, and the floor space can be reduced by 20% to 35%.
- Saving operating costs. Due to periodic aeration, the concentration of dissolved oxygen in the tank decreases during the precipitation and drainage stages. During aeration, the oxygen concentration gradient is large, the transfer efficiency is high, the energy saving effect is significant, and the operating cost can be saved by 10%-25%.
- High organic matter removal rate and nice effluent quality. CASS method not only can effectively remove various organic pollutants in sewage, but also has good denitrification and phosphorus removal functions. With the investment in the secondary treatment to reach the water quality of the tertiary treatment.
- The CASS process can easily achieve aerobic, anoxic and anaerobic conditions in the delayed aeration and periodic cycle. For the treatment of hospital sewage, it is necessary to consider the virus and pathogenic bacteria in the sewage, so it cannot be treated by ordinary sewage purification tanks. It is necessary to use anaerobic and facultative combined way, and a series of physical, chemical, and biological principles are used to precipitate, decompose, swallow, and kill organic matter, germs, and viruses in infectious disease sewage. The CASS method can meet this requirement well.
- The CASS method adopts delayed aeration, so that the sludge yield is low, the dehydration is good, and it is easy to handle, and reduces the sludge treatment cost. The new type of underwater aeration equipment replaces the traditional blast aeration method. It is flexible to use, the system is very simple, and there is no noise pollution.
- Management unit, reliable operation. Sewage treatment plants have fewer types and quantities of equipment, and relatively simple control systems. They use a floating type of special water skimming device that can automatically lift and a special decanter to drain water during the water intake process, and the lifting of the seepage device is automatic to ensure stable water output.
3.2 Chlorine dioxide disinfection
3.2.1 The characteristics of chlorine dioxide disinfection
Chlorine dioxide is a high-efficiency, broad-spectrum, safe, fast, multi-functional, long-lasting, convenient storage and use of sterilization and disinfectant. The United Nations World Health Organization (WHO) lists it as a safe disinfectant (A1) level , The US Environmental Protection Agency (EPA) and the US Food and Drug Administration (FDA) approved it to be used in hospitals, food processing and other departments.
Commercial chlorine dioxide products produced at home and abroad are mainly stable chlorine dioxide solutions, and there are also a small number of solid chlorine dioxide products such as slow-release groups, colloidal particles, and microencapsulated powders. In recent years, the chlorine dioxide method is very popular in the domestic sewage treatment industry, and it has a good effect in hospital sewage treatment.
Advantages of chemical chlorine dioxide disinfection used to treat hospital sewage:
- ClO2 can kill all microorganisms, including bacterial propagules, cell spores, fungi, mycobacteria and viruses. It can effectively destroy trace organic pollutants in water, such as benzopyrene anthraquinone, chloroform, carbon tetrachloride, phenol, chlorophenol, cyanide, hydrogen sulfide and organic sulfide. It can well oxidize some reduced metal ions in water such as Fe2+, Mn2+, Ni2+, etc. It is less affected by pH and has a killing effect on algae. It can also reduce the color, turbidity and odor of the aqueous solution. Its effect is 5 times that of sodium hypochlorite. It does not form significant organic halides in sewage treatment, making it an ideal choice for hospital waste water treatment.
- Chlorine dioxide is more effective in disinfecting viruses than ozone and liquid chlorine, and reacts quickly with sewage. The contact time is 1/2-1/4 of chlorine, which can be shortened from 1h to 0.5h, and the contact pool can be reduced to half of the original. Greatly save investment.
3.2.2 Treatment effect
Jiangsu Cancer Hospital is a tertiary A-level specialist hospital with more than 600 beds. The daily discharge of sewage is about 500t. Use a chemical chlorine dioxide generator to treat hospital sewage. The use of chlorine dioxide generator does not require biochemical treatment, so that the number of bacteria, COD and other indicators can meet the emission standards, which greatly saves the investment in hospital sewage treatment facilities and daily operating costs. The treated hospital sewage fully meets the discharge standards.
To determine the hospital sewage treatment process, not only must achieve the purpose of disinfection and sterilization, but also consider the water quality requirements for the discharge of sewage and the division of environmental functional zones of receiving waters. Hospital sewage should comply with the 'Water Pollutant Discharge Standards for Medical Institutions' (GB18466-2005), which puts forward higher requirements for hospital sewage treatment. According to standards and related requirements, the use of chemical chlorine dioxide disinfection or CASS process to treat hospital sewage can well adapt to this change. Compared with the corresponding treatment method, it has good effect, low investment, convenient management and low operating cost. , The technology is advanced and practical, and it is very competitive in technology and economy. It is the preferred method of integrating social, economic, environmental and ecological benefits in the current hospital sewage treatment.