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Medical wastewater treatment process and principles

Medical sewage treatment is mainly aimed at sewage discharged from hospital clinics, laboratories, wards, laundry rooms, X - ray photography rooms and operating rooms. Its sewage source and composition are very complex. Hospital sewage contains a large number of pathogenic bacteria, viruses and chemicals, which are characterized by space pollution, acute infection and latent infection.
Hazards of medical wastewater:
Medical waste water has attracted public attention for many times. The discharge of medical waste water has caused great harm to water resources and has become a " source" of harm to public health. Only a handful of hospitals in some areas can truly meet the national emission standards. At present, the law is not standardized and the awareness of environmental protection is weak, resulting in the direct discharge of medical expenses and the " high pollution and low treatment" existing in major hospitals.
However, at present, major hospitals do not properly dispose of medical waste water with serious harm, ignoring the vicious water pollution incident that may be caused by virus infection in the waste water. At the same time, the relevant national legislation also needs to be followed up in time to make more explicit provisions on the treatment of medical expenses and water, and environmental protection departments at all levels should also strengthen management and popularize environmental awareness. Compared with industrial waste water, medical waste water has greater impact on the environment and greater harm. During the operation of the hospital, wastewater with direct or indirect infectivity, toxicity and other hazards will inevitably be produced. The source of these wastewater determines its composition complexity and involves various biological, chemical or radioactive pollution. Medical wastewater contains not only a large number of pathogens such as bacteria, viruses and eggs, but also chemical agents and radioisotopes, which have several characteristics of space pollution, acute infection and latent infection. If medical sewage containing pathogenic microorganisms is discharged directly into urban sewers without harmless treatment such as disinfection and inactivation, it will often cause water and soil pollution, and will seriously cause various diseases or cause outbreaks of waterborne infectious diseases.
Principles of Medical Wastewater Treatment and Process Treatment
1, the whole process control principle. To control the whole process of hospital sewage generation, treatment and discharge.
2. Principle of reduction. Strict hospital internal health and safety management system, strict control and separation at the source of sewage and dirt, hospital domestic sewage and ward sewage are collected separately, i.e. source control and clean-up diversion. It is strictly prohibited to dispose of hospital sewage and dirt into sewers at will.
3. Principle of local treatment. In order to prevent the pollution and harm in the process of hospital sewage transportation, local treatment must be carried out in the hospital.
4. Guiding principles of classification. According to the hospital nature, scale, sewage discharge destination and regional differences, the hospital sewage treatment is classified and guided.
5. The principle of combining compliance with risk control. Comprehensive consideration should be given to the basic requirements for sewage discharge in general hospitals and infectious disease hospitals, while strengthening the awareness of risk control and improving the ability to deal with emergencies from the aspects of technology, engineering construction and supervision and management.
6. Principles of Ecological Security. Effectively remove toxic and harmful substances from sewage, reduce the generation of disinfection by-products in the treatment process, control excessive residual chlorine in the effluent, and protect the ecological environment.
Treatment process
The secondary biochemical treatment processes for hospital sewage treatment include activated sludge process, biofilm process, etc. How to treat medical sewage has a better effect. Different treatment processes need to be selected according to the treatment target. Here we introduce several different treatment processes:
Grille well
The sewage contains a large amount of suspended solids and floaters. The role of the grid is to intercept and remove the above-mentioned substances and to protect the water pump and subsequent treatment units. The grid well is located directly above the lifting well and is built with a steel concrete structure and an adjusting pool. A grid is built above the grid well to prevent the grid slag from spreading viruses. In order to coordinate the surrounding environment, the outside of the grid well can be beautified. Operators can disinfect, clean and transport the grid slag regularly and burn it off as medical waste. In order to reduce the labor intensity of operators, improve the working environment and ensure the effect of sewage deslagging, a mechanical grille and a basket - lifting grille are installed in the grille well. The mechanical grille and basket - lifting grille are made of stainless steel material and have corrosion resistance. The mechanical grille automatically cleans the grille slag from the sewage. It is easy to manage, has few failures and has low maintenance rate.
regulating reservoir
Adjust the quality and quantity of sewage. The regulating pool adopts an underground closed steel concrete structure and is built together with other processing units to save capital construction investment. The top of the pool is covered with soil. In order to facilitate inspection and maintenance, the corner of the regulating pool is provided with inspection holes to regularly maintain the regulating pool. The adjusting tank is equipped with a submersible mixer to stir regularly to prevent suspended particles from settling.
Flocculation sedimentation tank
It is used to remove suspended pollutants in sewage, reduce the interference of suspended substances to disinfectants, save the amount of disinfectants, and provide a good environment for on-line automatic monitoring of residual chlorine. In order to reduce the occupied area, vertical sedimentation tank and buried reinforced concrete structure are adopted, which are built together with other processing units. The top of the tank is covered with soil. In order to facilitate inspection and maintenance, inspection holes are provided at the corners of the flocculation sedimentation tank, which can be regularly maintained. Sludge is deposited in the sludge bucket and discharged into the sludge concentration tank through the sludge pipe regularly by the sludge pump, and the effluent flows into the disinfection contact tank from the sludge pipe.
Disinfection contact pool
The effluent from the sedimentation tank enters the disinfection contact tank to maintain a certain contact residence time between the sewage and the disinfectant to ensure that the disinfectant effectively kills bacteria in the water and discharges the effluent to the municipal pipe network. According to the " Discharge Standard for Water Pollutants in Medical Institutions" ( GB 18466 - 2005 ), the contact time of sewage in infectious disease hospitals should not be less than 1.5 hours, and that of sewage in general hospitals should not be less than 1.0 hours. A hospital in Beijing is a general hospital with infectious diseases, so the hydraulic retention time of the contact pool is 1.5 hours. By adopting the buried reinforced concrete structure, it is built together with other processing units to save capital investment, and the top of the pool is covered with soil. For inspection and maintenance convenience, inspection holes are provided at the corners that contact the oxidation pool, so that the adjustment pool can be maintained on a regular basis. A diversion wall is arranged in the contact tank to avoid short flow, and an automatic residual chlorine monitoring device is arranged at the outlet of the contact tank so as to adjust the dosage of disinfectant in time.
Sludge storage tank
Collect and store sludge produced by flocculation sedimentation tank, regularly add lime into the tank to disinfect the sludge, dehydrate the sludge, transport the dry sludge out, and return the filtrate to the regulating tank. By adopting the buried reinforced concrete structure, it is built together with other processing units to save capital investment, and the top of the tank is covered with soil. In order to facilitate inspection and maintenance, inspection holes are provided at the corners of the sludge storage tank so that the adjustment tank can be maintained on a regular basis. A submersible mixer is arranged in the sludge storage tank to facilitate stirring during sludge dosing and disinfection.
In view of the problem of disinfection treatment of medical sewage, we briefly introduce several treatment methods:
1. Ozone treatment process
Ozone is an unstable gas with special pungent smell. At normal temperature, ozone is blue gas and is one of the strongest known oxidants.
Ozone treatment can kill bacterial propagules and spores, viruses, fungi, etc. and can destroy the toxin of endophytic bacteria, which is the best treatment process for disinfection at present. After ozone treatment, the bacteria removal rate in water is 99.985 % - 99.998 %, organic matter removal rate is 40 %, chroma removal rate is 77 %, nitrite removal rate is 79.5 %, and protein-like ammonia removal rate is 11.9 %. However, the disadvantage is that the operation cost is more expensive than the traditional use of liquid chlorine for disinfection.
2. Chlorine disinfection process
Liquid chlorine, as the most common disinfectant at present, is widely used in various fields and is the most widely used water treatment and disinfection method so far. Its main characteristics are wide and reliable sources of liquid chlorine in industrial products bottled, low investment and operation cost of disposable equipment for chlorine disinfection, relatively stable disinfection effect and relatively mature design experience, so it is widely used. The deficiency lies in the fact that after nearly 20 years of application, people find: on the one hand, chlorine is a toxic gas, so they must be very careful during transportation and use to prevent chlorine leakage; On the other hand, using chlorine to treat organic wastewater, especially humic acid-containing water, can generate halogenated hydrocarbons ( trihalomethane, chlorinated hydrocarbons, etc. ), which are extremely destructive and carcinogenic to human tissues. In addition, liquid chlorine disinfection is not effective for some viruses and spores. With the passage of time, viruses in water are more resistant to chlorination disinfection. Therefore, in the western developed countries, the liquid chlorine treatment of medical sewage is gradually being replaced by chlorine dioxide or sodium hypochlorite.
3. Sodium hypochlorite treatment process
At present, there are two ways to treat hospital sewage with sodium hypochlorite. One is to treat medical sewage by adding bleaching powder ( sodium hypochlorite ) or bleaching essence ( calcium hypochlorite ) tablets. The method is low in cost, simple and easy to implement, and is more suitable for the treatment of medical sewage in rural township hospitals and community health centers with relatively small number of patients, relatively simple waste water components and less production. However, it is difficult to ensure the accuracy of the dosing agent due to manual dosing of bleaching powder or bleaching essence. The other is to use automatic sodium hypochlorite generator equipment to treat medical sewage. On the one hand, the sodium hypochlorite generation equipment can be continuously operated, so that on the one hand, automatic metering and dosing of disinfection agents can be realized according to the type and quantity of pollutants in sewage, and the treatment effect is relatively stable. However, its main disadvantages are high operating cost due to salt consumption and power consumption, and easy corrosion of equipment. Due to the high operating cost of sodium hypochlorite treatment method and the need for specialized technical personnel to manage and maintain the equipment, this method is more suitable for sewage treatment in general hospitals with a large number of patients above the prefecture level, a large amount of waste water produced and a complex composition.

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