Hospital sewage disinfection technology

Common disinfection techniques for hospital sewage

Hospital sewage disinfection is an important process of hospital sewage treatment, and its purpose is to kill various pathogenic bacteria in sewage. Common disinfection processes for hospital sewage disinfection include chlorine disinfection (such as chlorine, chlorine dioxide, and sodium hypochlorite), oxidant disinfection (such as ozone, peracetic acid), and radiation disinfection (such as ultraviolet light and gamma rays). Table 1 summarizes and compares the advantages and disadvantages of commonly used chlorine disinfection, ozone disinfection, chlorine dioxide disinfection, sodium hypochlorite disinfection and ultraviolet disinfection methods.

advantageDisadvantagesDisinfection effect
chlorine(Cl2)Has continuous disinfection; simple process and mature technology; simple operation and accurate dosage.It produces organic chlorides (THMs) with carcinogenic and teratogenic effects; the treated water has a smell of chlorine or chlorophenol; the chlorine gas is highly corrosive; and the operation management has certain risks.Can effectively sterilize, but the effect of killing viruses is poor.
Sodium hypochlorite (NaOCl)Non-toxic, non-hazardous operation and management.Produce organic chlorides (THMs) with carcinogenic and teratogenic effects; increase the pH of water.The same as Cl2 sterilization effect.
Chlorine dioxide (ClO2)It has strong oxidation and does not produce organic chlorides (THMs); it is simple and convenient to put in; it is not affected by pH.ClO2 operation and management have certain risks; they can only be produced and used locally; the preparation equipment is complicated; and the operation management requirements are high.It has better sterilization effect than Cl2.
Ozone (O3)It has strong oxidizing ability and short contact time; it does not produce organic chloride; it is not affected by pH; it can increase dissolved oxygen in water.The operation and management of ozone have certain risks; the operation is complicated; the production rate of ozone is low; the power consumption is large; the capital investment is large; the operating cost is high.The effects of sterilization and virus killing are very good.
UltravioletNo harmful residual substances; no odor; simple operation and easy automation; low operation management and maintenance costs.High power consumption; UV lamps and quartz sleeves need to be replaced regularly; high water quality requirements for treated water; no subsequent sterilization.The effect is good, but there are requirements for the concentration of suspended matter.

Liquid chlorine disinfection system

Liquid chlorine disinfection is one of the most commonly used methods in hospital sewage disinfection. Chlorine (Cl2) is a strong oxidant and broad-spectrum fungicide, which can effectively kill bacteria and viruses in sewage, and has a continuous disinfection effect. Chlorine disinfection has the advantages of easy availability of chemicals and low cost; simple process and mature technology; simple operation and accurate dosage; no need for huge equipment. However, chlorine gas is poisonous and corrosive, and there are certain risks in operation and management.

Chlorine gas is a liquefied gas under pressure. It is generally shipped with pressure vessels such as tanks, tankers, tankers, and barges.

Liquid chlorine disinfection system is mainly composed of chlorine storage cylinder, chlorination machine, water injector, solenoid valve, chlorination pipeline, chlorination room and liquid chlorine storage room.

1. Chlorine bottle

  1. In general, a small-capacity chlorine bottle should be used. The one-time use period of chlorine bottles should not exceed 3 months.
  2. The maximum amount of chlorine gas discharged from each chlorine bottle per unit time should meet the following requirements:

Chlorine bottle with a volume of 40 liters: 750g / h; Chlorine bottle with 500kg: 3000g / h.

2. Chlorination machine

When the hospital sewage is disinfected with liquid chlorine, a vacuum chlorination machine must be used, and the outlet of the chlorine pipe is submerged in the sewage.

The addition of chlorine gas to the sewage is completed by the water injector of the chlorination machine. The water injector requires 0.2MPa pressure in the tap water. A negative pressure is formed in the water injector. The chlorine gas is sucked and mixed, and then the chlorine water is added to the chlorination point.

Typical hospital sewage treatment process has two kinds of chlorination methods: siphon-type constant ratio chlorination and lifting type automatic constant ratio chlorination.

  1. When the water collection pipe in the hospital sewage station is higher than the public sewage pipe or water level outside the station (usually a height difference of 600mm is required), a siphon fixed-chlorination disinfection system can be used.
  2. When the sewage needs to be lifted before it can be discharged out of the station, the lift-type automatic constant ratio chlorination is used. The disinfection and dosing equipment and the lift pump are operated synchronously. The sewage pump is automatically started by the water level of the collection tank, and the dosing system is also controlled to run synchronously.

3. Chlorination system pipes

  1. Copper pipes should be used for the delivery of chlorine gas; hard polyvinyl chloride pipes should be used for the delivery of chlorine solution, and plastic diaphragm valves should be used for the valves.
  2. The pipeline of the chlorination system should be equipped with a corrosion-resistant pressure gauge, and the ordinary pressure gauge should be installed on the water supply pipe of the water ejector.
  3. The pipeline of the chlorination system should be installed directly, the buried pipeline should be set in the trench, and the pipeline should have a certain support and slope.

4. Chlorination room and liquid chlorine storage room

When using liquid chlorine for disinfection, a liquid chlorine storage room and a chlorine addition room should be provided.

  1. Chlorination room
    The choice of the location of the hospital sewage chlorination room should be determined according to factors such as the overall plan of the hospital, the location of the discharge outlet, environmental sanitation requirements, wind direction, maintenance management and transportation.
    The chlorination room is mainly equipped with chlorination equipment other than chlorine bottles, such as chlorination equipment. There should be necessary measurement, safety and alarm devices in the chlorination room. The door of the chlorination room opens outwards, uses explosion-proof lamp lighting and other explosion-proof motor appliances, and has an exhaust fan. The frequency of ventilation is designed according to 12 times / hour. The exhaust fan is located at a low place in the chlorination room, and considering the outdoor environment, it should be far away from the personnel activity place. Chlorine room indoor electrical, pipeline, ground, etc. should be considered to prevent chlorine corrosion.
  2. Liquid chlorine storage room
    Liquid chlorine storage room should be as close as possible to the place of addition. Liquid chlorine storage room must have lifting equipment (use 40kg vial can be installed without lifting equipment) and scales.
    The liquid chlorine storage room should be equipped with a pool that can contain chlorine bottles. The pool should maintain a certain water level. Once the chlorine bottle leaks, the chlorine bottle should be quickly pushed into the pool.
    The door of the liquid chlorine storage room that leads directly to the outside should be opened outwards, and exhaust equipment should be provided, and the vent should be located 400mm from the ground of the room. Explosion-proof lamps are used for lighting, and safety and chlorine alarm devices are installed.

5. Scope of application

  1. Liquid chlorine disinfection should not be used for sewage disinfection in hospitals and small-scale hospitals in densely populated areas. It can be used in hospital sewage treatment system with large scale (> 1000 beds) and high management level far away from population settlement.
  2. Chlorine disinfection Because the residual chlorine is too high, it will cause the death of aquatic organisms in the surface water. Therefore, when the hospital sewage is discharged to the surface water, dechlorination measures or chlorine disinfection should be used with caution.

6. Operation management

  1. It is strictly forbidden to directly add chlorine gas to the sewage without a chlorine adding machine.
  2. Liquid chlorine is packed by tank truck and cylinder. Chlorine packaging volume: the bottled filling weight should not be greater than 1.25kg / L, and the tank truck filling weight should not be greater than 1.20kg / L.
  3. Toolboxes, maintenance tools, medicines and gas masks that are easy to use and have obvious signs should be placed at the entrance of the operation room or chlorination room.
  4. The chlorine bottle should be placed on the scale or the chlorine indicator. The small bottle should be placed upright and the large steel bottle should be placed horizontally and fixed. It should not be allowed to roll.
  5. The parallel chlorine bottles should be equipped with spare bottles, and the new chlorine bottles should be replaced by automatic or manual switching devices.
  6. Chlorine bottles and chlorination machines should avoid heating, sunlight and open flames. In order to ensure the normal supply of chlorine, the indoor temperature of the chlorine bottles should be kept at a medium temperature (15 ° C).
  7. Liquid chlorine transportation and storage shall be carried out according to GB11984.

Chlorine dioxide disinfection

Chlorine dioxide has the functions of high-efficiency oxidant, disinfectant and bleach. As an enhanced oxidant, the products it oxidizes contain no organic chlorides; as a disinfectant, it has a broad-spectrum disinfection effect.

Chlorine dioxide must be prepared on site. The methods of preparing chlorine dioxide on site are mainly chemical method and electrolytic method.

  1. The disinfection process of preparing chlorine dioxide by chemical method uses sodium chlorate, sodium chlorite, sodium hypochlorite and hydrochloric acid as raw materials. The chemical reaction occurs in the reactor to produce chlorine dioxide gas, which is then mixed by a water jet to form chlorine dioxide The aqueous solution is then added to the disinfected sewage into the disinfection contact tank for disinfection.
  2.  The electrolysis method for preparing chlorine dioxide disinfection process is a mixture of chlorine dioxide, chlorine gas, hydrogen peroxide, and ozone produced by electrolysis of saturated saline as raw materials for disinfection. The synergistic effect of the mixed gas has a broad-spectrum sterilization ability, and its disinfection effect is far stronger than any single disinfectant.

1. Engineering design

  1. Chemical preparation of chlorine dioxide disinfection process
    (1) Chlorine dioxide disinfection system design and generator selection should be determined according to the water quality and treatment requirements of hospital sewage, and considered for standby.
    (2) Because the raw materials are strong oxidizing or strong acid chemicals, separate and safe storage must be considered in the storage room; the storage capacity is 10 to 30 days.
    (3) The concentration of chlorine dioxide solution should be less than 0.4%, and its dosage should be proportional to the sewage or automatically controlled by the amount of residual chlorine.
    (4) Chlorine dioxide monitoring alarm and ventilation equipment should be designed.
  2. Electrolytic preparation of chlorine dioxide disinfection process
    (1) Electrolytic method for preparing chlorine dioxide equipment is mainly composed of electrolytic cell, power supply, water pump and water ejector. Two 6V or 12V DC power supplies are used for the electrolytic cell.
    (2) The salt-dissolving device of the equipment for preparing chlorine dioxide by electrolytic method is generally integrated with the generator. However, because the chlorine dioxide is a mixed sterilizing gas, a solution tank must be installed in order to be able to cast chlorine in a fixed ratio.
    (3) Chlorine dioxide is taken out by the water injector and dissolved in water, so there must be enough pressure tap water between the equipment, if the water pressure is not enough 0.2MPa, it is necessary to install a pipeline pump.
    (4) Attention should be paid to the design of the hydrogen discharge pipe of the equipment, and the explosive gas generated during the operation of the equipment should be eliminated in time.

2. Scope of application

  1. Chlorine dioxide disinfection should not be used for sewage disinfection in densely populated areas and large-scale hospitals. The utility model can be used in a small-scale hospital sewage treatment system far away from a populated area.
  2. Since the concentration of chlorine dioxide in the air and water reaches a certain level, it will explode, so this law is applicable to hospital sewage treatment systems with high management levels.
  3. The chemical method is applicable to hospital sewage treatment and disinfection systems with a scale of> 500 beds.
  4. Chlorine dioxide disinfection Because the residual chlorine is too high, it will cause the death of aquatic organisms in surface water. Therefore, when hospital sewage is discharged to surface water, dechlorination measures should be taken or disinfection with chlorine dioxide should be used with caution.

3. Operation management

  1. Chlorine dioxide activating solution is unstable and should be used now.
  2. When preparing the solution, avoid mixing with alkali or organic matter.
  3. The dosage is determined according to the actual water quality and quantity experiment.

Sodium hypochlorite disinfection

Sodium hypochlorite disinfection is the use of commercial sodium hypochlorite solution or sodium hypochlorite solution prepared on site as a disinfectant. The hypochlorous acid generated after its dissolution has a good killing effect on pathogenic bacteria in water and disinfects sewage.

  1. Sodium hypochlorite generator
    Using electrolytic salt water (or seawater) to prepare an aqueous solution of sodium hypochlorite. The advantages of this generator are simple structure, high degree of automation, low power consumption and low salt consumption. The production of sodium hypochlorite can reach 10-12% (effective chlorine content). The disadvantage is that calcium and magnesium deposits are easily formed on the electrode surface, and the electrode needs to be cleaned frequently.
    Commercial sodium hypochlorite solution has an effective chlorine content of 10% to 12%. Sodium hypochlorite is a light yellow transparent liquid with the same special smell as chlorine gas.
  2. Bleaching powder and bleaching powder fine disinfection
    Bleaching powder (Ca (OCL) 2) is white powder, with strong odor, unstable chemical properties, easy to decompose and fail, and can make most organic colors oxidatively fade or bleach.
    Bleaching powder is relatively pure calcium hypochlorite with an effective chlorine content of 65% to 70%. It is a relatively stable chlorinating agent and can be stored for a long time (about 1 year) when it is well sealed. Bleaching powder is used for disinfection of hospital sewage. Powder can be directly added to hospital sewage. It can be used for dry addition, or it can be dissolved in water to make a solution to be added to sewage. plus. Another method is to add bleaching powder into tablets and add them with a sterilizer.

1. Engineering design

  1. Supporting buildings and equipment
    Sewage treatment stations using sodium hypochlorite generator disinfection should be arranged according to the model of sodium hypochlorite generator and its ancillary equipment requirements. General requirements require a dedicated salt preparation room and sodium hypochlorite generator equipment room. The salt preparation room and the sodium hypochlorite generator equipment room should be divided into two rooms.
  2. Main process parameters
    (1) Calculate the amount of chlorine input according to the water quality and treatment level of the sewage, select the model and number of sodium hypochlorite generators according to the amount of chlorine input, and then calculate the salt consumption and salt storage.
    (2) The sewage volume is calculated according to the highest daily sewage volume, and the salt water pool is designed for 12 ~ 24h.
    (3) The storage tank of sodium hypochlorite solution is designed for 8 ~ 16h.
  3. Dosing of sodium hypochlorite
    The sodium hypochlorite solution generated by the sodium hypochlorite generator is stored in the storage tank, and can be added by siphon type automatic injection or linked with the sewage pump. The solution is added to the sewage tank or through the addition tube, solenoid valve, flow meter Sewage pipe.
  4. Adding bleaching powder
    (1) The wet dosing system for bleaching powder needs to be equipped with a dissolving tank and a dosing tank.
    (2) The drug dissolving tank and the distributing tank are generally made of plastic. The drug dissolving tank needs to be equipped with a stirrer. Generally, there are 2 distributing tanks and 1 distributing tank. The size is calculated and determined according to the amount of treated sewage and the amount of medicine injected.

2. Scope of application

  1. Sodium hypochlorite disinfection should not be used for sewage disinfection in densely populated areas and large-scale hospitals. The utility model can be used in a small-scale hospital sewage treatment system far away from a populated area.
  2. Bleaching powder and bleaching powder are suitable for hospital sewage treatment and disinfection systems in economically underdeveloped areas with a size of less than 300 beds.
  3. Electrolytic sodium hypochlorite generator is suitable for hospital sewage treatment and disinfection system with high management level.
  4. Chlorine dioxide disinfection. Too much residual chlorine will cause the death of aquatic organisms in surface water. Therefore, when hospital sewage is discharged to surface water, dechlorination measures or chlorine disinfection should be used with caution.

3. Operation management

  1. The storage tank of sodium hypochlorite solution should be anti-corrosion and can be made of polyvinyl chloride plate or glass steel.
  2. When using sodium hypochlorite solution for disinfection, you must pay attention to the storage conditions, often analyze and test the effective chlorine content in order to grasp the attenuation of available chlorine, determine the best delivery volume and delivery cycle for each time, and reduce the loss of chlorine.
  3. Commercial sodium hypochlorite should be stored away from light at about 21 ℃.
  4. The bleaching powder should be stored in a dry, cool and ventilated warehouse to prevent the sun and rain, and should be away from fire and heat sources, and should not coexist with organic matter, acids and reducing agents.
  5. Put the bleaching powder into the dissolving tank, add water to make a solution with an effective chlorine content of 1% to 5%, still clarify, use supernatant to add. 1 to 2 times a day.

Chlorine disinfection contact pool

  1. Hospital sewage disinfection can be divided into continuous disinfection and intermittent disinfection according to the operation mode.
  2. The volume of the contact disinfection tank should meet the requirements of contact time and sludge deposition. The infectious disease hospital sewage contact time should not be less than 1.5 hours, and the general hospital sewage contact time should not be less than 1.0 hour.
  3. The effective volume of the continuous disinfection contact tank is the sum of the volume of sewage and the volume of sludge.
  4. During intermittent disinfection, the total effective volume of the contact tank should be determined according to the work shift and disinfection cycle, and generally should be 1/2 of the volume of the adjustment tank.
  5. The contact disinfection tank is generally divided into two compartments, and the volume of each compartment is half of the total volume. A diversion wall (board) should be installed in the pool to avoid short flow. The clear distance of the diversion wall (board) should be determined according to the water volume and maintenance space requirements, generally 600 ~ 700mm. The length and width ratio of the contact pool should not be less than 20: 1. A sampling port should be provided at the exit of the contact pool.
  6. During the design, the actual operating conditions of the treatment process selected by the design should be combined according to the most unfavorable conditions, and the actual contact time should be checked to meet the design requirements.

Design points for chlorine disinfection

When the sewage adopts the chlorine disinfection process, its design chlorine addition can be determined according to the following data:

  1. The liquid chlorine disinfection system is designed according to the relevant chapters of “Outdoor Drainage Design Code” GBJ14-87.
  2. The design of the primary treatment effluent to enhance the treatment effect is based on available chlorine, generally 30-50mg / L.
  3. The design reference of secondary treatment effluent is usually 10-15 mg (available chlorine) / L.
  4. When the sewage is sterilized by other methods, the designed dosage shall be determined according to the specific water quality.
  5. At least 2 sets of dosing equipment, one for each use and one for use.
  6. The dosage of chlorine is the reference value, and the dosage should be determined according to the experiment of residual chlorine and actual water quality and water quantity during operation.

Ozone, with the molecular formula of O3, has a special pungent odor, and is an internationally recognized green environmental protection sterilization disinfectant. Ozone produces monoatomic oxygen (O) and hydroxyl (OH) with strong oxidizing ability in water. Hydroxy (OH) has a strong killing effect on various pathogenic microorganisms. Monoatomic oxygen (O) has strong oxidizing ability, It has a strong ability to kill various viruses and bacteria.

Ozone disinfection has quick response, low dosage; strong adaptability, stable ozone disinfection performance in the range of pH 5.6 ~ 9.8, water temperature 0 ~ 37 ℃; no secondary pollution; can improve the physical and sensory properties of the water, with decolorization And to smell and taste. But the shortcomings are that there is no continuous disinfection function, only on-site production and use, the cost of ozone disinfection equipment is relatively high, and the power consumption is relatively large.

Ozone preparation methods include corona discharge method, ultraviolet method, chemical method and radiation method, etc. The corona discharge method is generally used in engineering.

1. Engineering Design

  1. Hospital sewage ozone treatment station should be equipped with air compressor room, ozone generator equipment room and operation room. An air compressor is installed in the air compressor room, and the air compressor should be shock-proof and noise-proof. There should be room for equipment maintenance between the ozone generators. Ozone contact towers should be installed indoors in cold areas, and exhaust pipes should be installed to discharge the exhaust after treatment.
  2. The main process parameters of hospital sewage disinfection are shown in Table 2.
  3. When choosing an ozone generator, determine the amount of ozone added according to the sewage water quality and treatment process, and then determine the amount of ozone used according to the amount of ozone added and the amount of water treated per unit time. model.
  4. The contact method of ozone and sewage generally adopts the bubbling method. The smaller the bubble dispersion, the higher the ozone utilization rate and the better the disinfection effect. Therefore, it is necessary to choose an ozone air intake device with good gas-water mixing effect.
  5. The pipelines of the ozone system equipment should be anti-corrosive and sealed.
  6. Ventilation equipment should be installed in the ozone equipment room, and the ventilator should be installed near the ground.
  7. The tail gas treatment or tail gas recovery device must be installed at the end of the process. The ozone tail gas discharged after the reaction must be decomposed and destroyed or recycled to meet the emission standard.
ItemPrimary treatment effluentSecondary treatment effluent
Ozone dosage / mg · L-130 ~ 5010 ~ 20
Contact time / min305 ~ 15
Coliform removal rate /%99.9999.99

The main process parameters of ozone disinfection of hospital sewage

2. Scope of application

  1. It is better to use ozone disinfection for hospital sewage with secondary treatment, which can reduce the amount of ozone added, reduce equipment investment costs and operating costs.
  2. The investment and operating costs are high, which is suitable for sewage treatment in infectious disease hospitals and general hospitals with high management level.

3. Operation management

  1. Ozone is toxic to people, and the national regulations allow the concentration in the atmosphere to be 0.2mg / m3.
  2. Ozone is a strong oxidant. The higher the concentration, the more damage it will cause to the contacted items. Please pay attention when using it.
  3. The factors that affect the sterilization of ozone should be controlled during use, including temperature, relative humidity, organic matter, pH, water turbidity, water color, etc.
  4. In the process of ozone production, avoid the discharge electrode from being wet and causing a disconnection.
  5. The output of ozone is affected by the voltage, intake air volume and intake air pressure.
  6. The amount of ozone added and the amount of residual ozone play an important role in disinfection, and should be controlled during use.

Ultraviolet rays used for disinfection are C-wave ultraviolet rays, whose wavelength range is 200 ~ 275nm, and the most sterilizing band is 250 ~ 270nm. Ultraviolet disinfection technology utilizes specially designed high-power, high-intensity and long-life C-band ultraviolet light generating equipment to irradiate flowing water, so that various bacteria, viruses, parasites, algae and other pathogens in the water receive a certain dose After being irradiated with ultraviolet C light, the DNA structure in the cell tissue is destroyed and loses its activity, thereby killing bacteria, viruses and other pathogens in the water, so as to achieve the purpose of disinfection and sterilization and purification. Ultraviolet sterilization has a fast speed and good effect without any secondary pollution. It belongs to a new generation of disinfection technology in the world. But the concentration of suspended matter in water is required to be low to ensure good light transmittance.

1. Engineering Design

  1. When using ultraviolet disinfection, the concentration of suspended matter in the treated water is required to be <10mg / L. Under this condition, the recommended irradiation intensity is 25-30μW / cm2, and the irradiation time is> 10s.
  2. The ultraviolet disinfection system can adopt open channel type or closed type. Relatively speaking, the open channel type is easier to monitor and maintain than the closed type, and has less resistance to water flow.
  3. The ultraviolet system should also include cleaning facilities. Hospital sewage should be equipped with automatic cleaning devices.
  4. When the ultraviolet system is used to disinfect the gas discharged in the process of hospital sewage treatment, a circulating ultraviolet air disinfection device is used.
  5. The UV lamps should be professionally recycled.

2. Scope of application

  1. Ultraviolet disinfection method can be used for sewage treatment system with effluent suspended matter concentration less than 10mg / L;
  2. In the case of special requirements, such as when discharged into certain waters with special requirements, ultraviolet disinfection can be used;

3. Operation management

  1. Do not expose the ultraviolet light source to people, and pay attention to the protection of eyes to avoid damage.
  2. During use, pay special attention to the measurement of the irradiance value of the ultraviolet lamp.
  3. For the ultraviolet lamp used, the irradiation intensity of the new lamp should not be less than 90uw / ​​cm2, and the irradiation intensity of the ultraviolet light in use should not be less than 70 uw / cm2. Those who are below 70 uw / cm2 should replace the lamp in time.
  4. The most suitable temperature range for UV disinfection is 20 ~ 40 ℃, if the temperature is too high or too low, it will affect the disinfection effect.
  5. During use, the surface of the ultraviolet lamp should be kept clean. Generally, wipe it with an alcohol cotton ball every two weeks. If there is dust or oil on the surface of the lamp, wipe it at any time.

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