Disinfection Technology
5.1 Common Disinfection Techniques for Hospital Wastewater
Disinfection of hospital wastewater is an important process for hospital wastewater treatment, which aims to kill various pathogenic bacteria in the wastewater. Hospital sewage disinfection commonly used disinfection processes are chlorine disinfection (such as chlorine, chlorine dioxide, sodium hypochlorite), oxidant disinfection (such as ozone, peroxyacetic acid), radiation disinfection (such as ultraviolet light, γ-ray). Table 5-1 summarizes and compares the advantages and disadvantages of the commonly used chlorine disinfection, ozone disinfection, chlorine dioxide disinfection, sodium hypochlorite disinfection, and ultraviolet disinfection methods.
Table 5-1 Comparison of Commonly Used Disinfection Methods
5.2 Liquid Chlorine Disinfection Systems
Liquid chlorine disinfection is one of the most commonly used methods for hospital wastewater disinfection. Chlorine (Cl2) is a strong oxidizing agent and a broad-spectrum bactericide, which can effectively kill bacteria and viruses in sewage, and has a continuous disinfection effect. Chlorine disinfection has the advantages of easy to obtain, low cost; simple process, mature technology; simple operation, accurate dosage; do not need huge equipment and so on. However, chlorine gas is toxic, corrosive, operation, management has a certain degree of danger.
Chlorine gas is a pressurized liquefied gas, which is generally shipped in tank bottles, tankers, tank cars, barges and other pressure vessels.
Liquid chlorine disinfection system is mainly composed of chlorine storage cylinders, chlorine machine, water ejector, solenoid valve, chlorination pipeline and chlorination room and liquid chlorine storage room.
5.2.1 Chlorine bottle
(1) In general, it is appropriate to use a small capacity chlorine bottle. Chlorine bottles should be used for a period of not more than 3 months.
(2) The maximum amount of chlorine discharged from each chlorine bottle per unit of time should be in accordance with the following:
Chlorine bottles with a volume of 40 liters: 750g/h; 500kg chlorine bottles: 3,000g/h.
5.2.2 Chlorine machine
Hospital sewage disinfection using liquid chlorine, must be used to vacuum chlorine machine and chlorine injection tube outlet submerged in the sewage.
Chlorine to the sewage is thrown through the chlorinator water injector to complete, the water injector requires tap water has 0.2MPa pressure, in the water injector to form a negative pressure, the chlorine gas will be sucked in and mixed, and then chlorine water thrown to the chlorination point.
There are two typical hospital wastewater treatment process chlorination methods: siphon fixed-ratio chlorination and elevated automatic fixed-ratio chlorination.
(1) when the hospital sewage station collector pipe is higher than the station outside the public **** sewage pipe or water level of the body of water (usually need to have a 600mm difference in height), can be used siphon fixed-ratio chlorination disinfection system.
(2) When the sewage needs to be lifted to be discharged out of the station, the lifting type automatic fixed-ratio chlorination is used, and the disinfection dosing equipment and the lifting pump are operated synchronously, and the sewage pumps are automatically started by the water level of the catchment basin, and at the same time, the dosing system is controlled to be operated synchronously.
5.2.3 Chlorination system pipe
(1) the pipeline should be used to convey chlorine copper pipe; chlorine solution pipeline should be used to convey hard PVC pipe, valves using plastic diaphragm valves.
(2) The pipeline of chlorination system should be equipped with corrosion-resistant pressure gauge, and the water injector should be equipped with ordinary pressure gauge on the feed pipe.
(3)The pipeline of chlorination system should be installed openly, the buried pipeline should be located in the pipe trench, and the pipeline should have certain support and slope.
5.2.4 Chlorination room and liquid chlorine storage room
The use of liquid chlorine disinfection should be equipped with liquid chlorine storage room and chlorination room.
(1) chlorination room
Hospital sewage chlorination room location selection should be based on the overall planning of the hospital, the location of the discharge outlet, environmental health requirements, wind direction and maintenance management and transportation and other factors to determine.
Chlorination room is mainly placed in the chlorinator and other chlorination equipment in addition to chlorine bottles. Chlorination room should have the necessary measurement, safety and alarm devices. Chlorination room door to the outside, the use of explosion-proof lighting and other explosion-proof motors and appliances, with an exhaust fan, the number of air changes according to 12 times / hour design. Exhaust fan is located in the chlorination room at a low place, and consider the outdoor environment, to be far away from the personnel activities. Chlorination room indoor electrical, piping, 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 injection site. Liquid chlorine storage room must have lifting equipment (the use of 40kg vials can not install lifting equipment) and scales.
Liquid chlorine storage room should be set up to accommodate chlorine bottles of the pool, the pool should be maintained at a certain level, once the chlorine bottle leakage, chlorine bottles should be quickly pushed to the pool.
Liquid chlorine storage room directly to the outdoor door should be open to the outside, should be set up to exhaust equipment, the vent is located in the room 400mm from the ground. Lighting using explosion-proof lamps, set up safety and chlorine alarm devices.
5.2.5 Scope of application
1, liquid chlorine disinfection should not be used in densely populated areas of hospitals and small-scale hospital sewage disinfection. Can be used away from populated areas of larger (> 1000 beds) and higher management level of hospital sewage treatment system.
2, chlorine disinfection due to high chlorine residual will cause the death of aquatic organisms in surface water, so when the hospital sewage discharged to the surface water should be taken to dechlorination measures or careful use of chlorine disinfection.
5.2.6 Operation Management
1, it is strictly prohibited without chlorine machine directly into the sewage chlorine.
2, liquid chlorine packed in tankers and cylinders. Chlorine packaging: bottle filling weight shall not be greater than 1.25kg / L, tanker filling weight shall not be greater than 1.20kg / L.
3, in the operation room or chlorination room should be placed at the entrance to the convenient use of toolboxes and have a clear sign of the maintenance tools, medicines and gas masks and so on.
4, chlorine bottles placed on the scale or chlorine display, small bottles should be placed vertically, large cylinders are lying and fixed, do not make it roll.
5, parallel chlorine bottles should be set up a spare bottle, through automatic or manual switching device to replace the new chlorine bottle.
6, chlorine bottles and chlorine machine to avoid heating, sunlight and open flame. In order to ensure the normal supply of chlorine, chlorine bottles between the room temperature should be maintained at a medium temperature (15 ℃).
7, liquid chlorine transportation, storage and so on according to GB11984 implementation.
5.3 Chlorine dioxide disinfection
Chlorine dioxide has the function of efficient oxidizer, disinfectant and bleach. As a strengthened oxidant, it oxidizes the product without organic chlorides; as a disinfectant, it has a broad-spectrum disinfection effect.
Chlorine dioxide must be prepared on site. On-site preparation of chlorine dioxide is mainly chemical and electrolytic methods.
1, chemical preparation of chlorine dioxide disinfection process is sodium chlorate, sodium chlorite, sodium hypochlorite and hydrochloric acid and other raw materials, chemical reaction occurs through the reactor to produce chlorine dioxide gas, and then mixed by the water injector to form a chlorine dioxide aqueous solution, and then added to the sewage being disinfected into the disinfection of the disinfectant contact pool disinfection.
2, electrolysis preparation of chlorine dioxide disinfection process is saturated brine as raw material through electrolysis to produce chlorine dioxide, chlorine, hydrogen peroxide, ozone gas mixture for disinfection. The synergistic effect of the gas mixture has a broad-spectrum bactericidal ability, and its disinfection effect is much stronger than any single disinfectant.
5.3.1 Engineering Design
1, chemical preparation of chlorine dioxide disinfection process
(1) Chlorine dioxide disinfection system design and generator selection should be based on the water quality of hospital sewage water quality and treatment requirements to determine, and to consider standby.
(2) Because the raw materials are strong oxidizing or acidic chemicals, the storage room must be considered separate and safe storage; the storage capacity is 10 to 30 days of dosage.
(3) Chlorine dioxide solution concentration should be less than 0.4%, and its dosage should be fixed ratio with the sewage or automatic control with residual chlorine.
(4) Chlorine dioxide monitoring alarm and ventilation equipment should be designed.
2, electrolytic preparation of chlorine dioxide disinfection process
(1) electrolytic preparation of chlorine dioxide equipment mainly consists of electrolytic tanks, power supply, water pumps and water jets. Electrolysis tank using 6V or 12V DC power supply.
(2)Electrolysis method of chlorine dioxide equipment salt dissolution device is generally integrated with the generator, but because of the chlorine dioxide for the mixing of disinfection gas, in order to be able to set the ratio of chlorine cast, must be set up solution box.
(3) chlorine dioxide is brought out by the water injector and dissolved in water, so the equipment must have enough pressure between the tap water, such as water pressure is not enough 0.2MPa, need to add a pipeline pump.
(4) Attention should be paid to the design of the equipment hydrogen exhaust pipe, timely exclusion of explosive gases generated during the operation of the equipment.
5.3.2 Scope of application
1, chlorine dioxide disinfection is not suitable for densely populated areas and large-scale hospital sewage disinfection. Can be used away from populated areas, smaller hospital sewage treatment system.
2, due to chlorine dioxide in the air and water concentration reaches a certain level will explode, so the method is suitable for a higher level of management of hospital sewage treatment system.
3, the chemical method is suitable for size >500 beds of hospital sewage treatment disinfection system.
4, chlorine dioxide disinfection due to high chlorine residual will cause the death of aquatic organisms within the surface water, so when the hospital sewage discharged to the surface water should take dechlorination measures or careful use of chlorine dioxide disinfection.
5.3.3 Operation Management
1, chlorine dioxide activation solution is unstable, should be used now.
2, when preparing the solution, avoid mixing with alkali or organic matter.
3, dosage according to the actual water quality and water experiment to determine.
5.4 Sodium hypochlorite disinfection
Sodium hypochlorite disinfection is the use of commercial sodium hypochlorite solution or on-site preparation of sodium hypochlorite solution as a disinfectant, the use of hypochlorous acid produced by the dissolution of the water has a good effect on the killing of pathogenic bacteria in the sewage disinfection.
1, sodium hypochlorite generator
Use of electrolysis of salt water (or sea water) to produce sodium hypochlorite solution. The advantages of this generator is a simple structure, high degree of automation, low power consumption, salt consumption is small, the production of sodium hypochlorite up to 10 ~ 12% (effective chlorine content). The disadvantage is that it is easy to form calcium and magnesium deposits on the electrode surface, and it is necessary to clean the electrode frequently.
Commercial sodium hypochlorite solution effective chlorine content of 10% to 12%, sodium hypochlorite is a light yellow transparent liquid, with the same special odor as chlorine.
2, bleach and bleach disinfection
Bleach (Ca (OCL) 2) is a white powder, with a strong odor, chemically unstable, easy to decompose and fail, can make most of the organic color oxidation discoloration or bleaching.
Bleach extract is a more pure calcium hypochlorite, effective chlorine content of 65% to 70%, is a more stable chlorinating agent, sealed well when the long-term preservation (about 1 year). Bleach for hospital sewage disinfection can be used directly to add powder to hospital sewage, can be used for dry dosing method, but also can be dissolved in water, made of bleach solution added to the sewage, called wet dosing. There is also a way to make bleach into tablets with a disinfectant machine to add.
5.4.1 engineering design
1, supporting buildings and equipment
The use of sodium hypochlorite generator disinfection of sewage treatment stations 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. Salt preparation room and sodium hypochlorite generator equipment room should be divided into two rooms.
2, the main process parameters
(1) according to the water quality and quantity of sewage water, treatment level calculation of chlorine, according to the chlorine dose selection of sodium hypochlorite generator model and number of units, and then calculate the amount of salt, salt storage.
(2) sewage volume is calculated according to the highest daily sewage volume, salt water pool is designed according to 12 ~ 24h.
(3) sodium hypochlorite solution storage tank is designed according to 8 to 16h.
3, sodium hypochlorite casting
Sodium hypochlorite generated by the sodium hypochlorite generator sodium hypochlorite solution stored in the tank, can be used siphon automatic casting or sewage pumps and sewage pumps linkage casting, will be the solution through the casting pipe, solenoid valves, flowmeter will be the solution cast into the sewage tank or sewage pipe.
4, bleaching powder dosing
(1) bleaching powder wet dosing system needs to be set up to dissolve the drug tank and dosing tank.
(2)Dissolving tank and dosing tank is generally made of plastic, dissolving tank needs to be equipped with agitators, generally set up 2, dosing tank can be set up 1, the slag is discharged into the sewer, the size of dissolving tank and dosing tank according to the treatment of sewage and dosing calculation to determine the amount of drug.
5.4.2 Scope of application
1, sodium hypochlorite disinfection is not suitable for disinfection of sewage in densely populated areas and large-scale hospitals. Can be used away from populated areas, smaller hospital sewage treatment system.
2, bleach, bleach is suitable for scale & lt; 300 beds of economically underdeveloped areas of hospital sewage disinfection system.
3, electrolysis sodium hypochlorite generator is suitable for the higher level of management of hospital sewage treatment disinfection system.
4, chlorine dioxide disinfection due to high chlorine residual will cause the death of aquatic organisms within the surface water, so when the hospital sewage discharged to the surface water should be taken to dechlorination measures or careful use of chlorine disinfection.
5.4.3 Operation Management
1, sodium hypochlorite solution storage tank should be corrosion-resistant, can be made of polyvinyl chloride plate or fiberglass.
2, in the use of sodium hypochlorite solution disinfection, must pay attention to the preservation conditions, and often analyze the effective chlorine content, in order to grasp the attenuation of the effective chlorine, to determine the optimal amount of delivery each time and the delivery cycle, to reduce the loss of chlorine.
3, commercial sodium hypochlorite should be stored at about 21 ℃ to avoid light.
4, bleaching powder should be stored in dry, cool and ventilated warehouses, to prevent sun and rain, should be away from fire and heat sources, not with organic matter, acids and reducing agents **** storage.
5, bleaching powder into the dissolving tank, add water to formulate the effective chlorine content of 1% to 5% of the solution, static clarification, the use of supernatant cast. Prepare 1 to 2 times a day.
5.5 Chlorine disinfection contact pool
1, hospital wastewater disinfection according to the mode of operation can be divided into continuous disinfection and intermittent disinfection two ways.
2, contact disinfection pool volume should meet the contact time and sludge deposition requirements. Infectious disease hospital sewage contact time should not be less than 1.5 hours, general hospital sewage contact time should not be less than 1.0 hours.
3, continuous disinfection of the contact pool effective volume for the sewage part of the volume and the sludge part of the volume and the sum.
4, intermittent disinfection, the total effective volume of the contact pool should be based on the work shift, disinfection cycle to determine the general desirability of regulating the pool volume 1/2.
5, contact disinfection pool is generally divided into two compartments, each compartment of the total volume of half. Pool should be set up to guide the wall (plate), to avoid short flow. Guide wall (plate) of the net distance should be determined according to the amount of water and maintenance space requirements, generally 600 ~ 700mm. contact pool length and width ratio should not be less than 20:1. contact pool should be set at the exit of the sampling port.
6, the design should be selected according to the design of the actual operation of the treatment process, according to the most unfavorable combination of circumstances, calibration of the actual contact time to meet the design requirements.
5.6 Chlorine disinfection design points
When the sewage chlorine disinfection process, the design of chlorine can be determined according to the following data:
1, liquid chlorine disinfection system with reference to the "Design Code for Outdoor Drainage," GBJ14-87 relevant chapters of the design.
2, to strengthen the treatment effect of the primary treatment effluent design chlorination in terms of effective chlorine, generally 30-50 mg / L.
3, secondary treatment effluent design reference chlorine is generally 10-15 mg (effective chlorine) / L.
4, when the sewage is disinfected by other methods, the design of its dosage should be determined according to the specific water quality.
5, dosing equipment for at least 2 sets, 1 with a spare.
6, chlorine dosage for reference, the operation should be based on the amount of chlorine and the actual water quality and water experiment to determine the dosage.
5.7 Ozone disinfection
Ozone, the molecular formula for O3, has a special irritating odor, is internationally recognized as a green sterilization disinfectant. Ozone in the water to produce a strong oxidizing capacity of monoatomic oxygen (O) and hydroxyl (OH), hydroxyl (OH) on a variety of disease-causing microorganisms have a strong killing effect, monoatomic oxygen (O) has a strong oxidizing capacity of a variety of viruses, bacteria have a strong killing ability.
Ozone disinfection has a fast response, less investment; adaptability, in the pH5.6 ~ 9.8, water temperature 0 ~ 37 ℃ range, ozone disinfection performance is stable; no secondary pollution; can improve the physical and sensory properties of water, decolorization and deodorization and deodorization effect. But the shortcomings are no continuous disinfection, only on-site production and use, ozone disinfection method of equipment costs are higher, more power consumption.
The ozone preparation method has a corona discharge method, ultraviolet method, chemical method and radiation method, etc., the project generally use corona discharge method.
5.7.1 engineering design
1, hospital sewage ozone treatment station should be set up air compressor room, ozone generator equipment room and operation room. Air compressor room to place air compressor, air compressor should be shockproof and prevent noise. Ozone generator room should be left with equipment maintenance space. Ozone contact tower in cold areas should be located indoors, exhaust gas treatment is set up after the exhaust pipe to the outdoors.
2, hospital sewage disinfection of the main process parameters shown in Table 5-2.
Table 5-2 hospital sewage ozone disinfection of the main process parameters
3, in the selection of ozone generator, according to the quality of sewage water and treatment process to determine the amount of ozone dosage, and then according to the amount of ozone dosage and unit time to determine the amount of ozone used to use the amount of ozone used to select the number of units of ozone generators and models per hour.
4, ozone and sewage contact generally use the bubble method, the smaller the bubble dispersion, the higher the ozone utilization rate, the better the disinfection effect. Therefore, to choose a good gas-water mixing effect of the ozone inlet device.
5, ozone system equipment and piping should be done to prevent corrosion and sealing.
6, ozone equipment room should be set up ventilation equipment, ventilator should be installed near the ground.
7, at the end of the process must be set up tail gas treatment or tail gas recycling device, the ozone exhaust after the reaction must be decomposed and destroyed or recycled to meet the emission standards.
5.7.2 Scope of application
1, the use of secondary treatment of hospital wastewater is best to use ozone disinfection, so that you can reduce the amount of ozone dosage, reduce the equipment investment costs and operating costs.
2, higher investment and operating costs, applicable to higher management level of infectious disease hospitals and general hospital sewage treatment.
5.7.3 Operation Management
1, ozone is toxic to humans, the national provisions of the permissible concentration of 0.2mg/m3 in the atmosphere.
2, ozone is a strong oxidizing agent, the higher the concentration of the damage to contact with the goods more serious, the use of attention should be paid.
3, in the use of ozone sterilization should be controlled to affect the effect of factors, including temperature, relative humidity, organic matter, pH, turbidity of water, water color, etc..
4, in the process of ozone production, to avoid the discharge electrode wet and cause circuit breakage.
5, ozone production is affected by voltage, air intake and air intake pressure.
6, ozone dosage and the amount of residual ozone in the disinfection plays an important role, the use of attention should be paid to control.
5.8 Ultraviolet disinfection
Disinfection of the use of ultraviolet light is C-wave ultraviolet, its wavelength range is 200 ~ 275nm, the strongest bactericidal effect of the band is 250 ~ 270nm. ultraviolet disinfection technology is the use of specially designed high-power, high-intensity and long-life C-band ultraviolet light generator produced by strong ultraviolet irradiation of running water, so that a variety of water bacteria, viruses, parasites, water, water and water. UV technology is the use of specially designed high-power, high-intensity and long-life C-band ultraviolet light generator device to produce strong ultraviolet light irradiation of flowing water, so that all kinds of bacteria, viruses, parasites, algae and other pathogens in the water are subjected to a certain dose of UV light radiation, the DNA structure of its cellular tissues are damaged and inactivated, so as to kill bacteria, viruses, and other pathogens in the water to achieve the purpose of disinfection and sterilization and purification. Ultraviolet sterilization speed, good effect, does not produce any secondary pollution, belongs to the international new generation of disinfection technology. However, it requires a low concentration of suspended solids in the water to ensure good light transmission.
5.8.1 Engineering
1, the use of ultraviolet disinfection requires the treatment of suspended solids in the water concentration & lt; 10mg / L, under these conditions the recommended irradiation intensity of 25-30μW/cm2, irradiation time & gt; 10s.
2, ultraviolet disinfection system can be used open channel type or closed type. Relatively speaking, the open channel type is easier to monitor and maintain than the closed type, the resistance to water flow is also small.
3, ultraviolet system should also include cleaning facilities. Hospital sewage should be used to set up automatic cleaning device.
4, ultraviolet system for hospital sewage treatment process emissions of gas disinfection, the use of circulating ultraviolet air disinfection device.
5, ultraviolet lamps should be professionally recycled.
5.8.2 Scope of application
1, the effluent concentration of suspended solids less than 10mg / L of sewage treatment system can be used in ultraviolet disinfection;
2, in the case of special requirements, such as discharged into certain waters with special requirements, the ultraviolet disinfection can be used;
5.8.3 Operation and management
1, shall not make the ultraviolet light source irradiation to people, and pay attention to eye protection, so as not to cause injury.
2, in the process of use, pay special attention to the irradiance value of the ultraviolet lamp to determine.
3, the use of ultraviolet lamps, the irradiance of the new lamp shall not be less than 90 uw/cm2, the use of ultraviolet irradiance shall not be less than 70 uw/cm2, where less than 70 uw/cm2 should be replaced in a timely manner lamp.
4, the optimal temperature range of ultraviolet disinfection is 20 ~ 40 ℃, the temperature is too high or too low will affect the disinfection effect.
5, in the process of use, should keep the surface of the ultraviolet lamp clean, generally every two weeks with an alcohol cotton ball wipe, found that the surface of the lamp with dust, oil, should be wiped at any time.