Waste is the inevitable outcome of human society. With the rapid economic growth, urban garbage seriously pollutes the environment. The disposal of municipal waste has got attention. But medical waste is different from the ordinary urban waste, because of it contains a large number of bacteria, viruses and chemical agents. Random treatment of medical waste is extremely serious threat environment and human health. In order to guarantee the health of people, it is necessary to choose the effective solutions for processing medical waste.

At present, disposal methods of hospital waste include sanitary landfill, electromagnetic wave sterilization, pressure steam sterilization, high-temperature incineration, chemical disinfection pyrolysis. This article analyzes the disposal methods of method waste on influencing parameter, advantages and disadvantages.

Sanitary Landfill

Sanitary landfill is the ultimate disposal of medical waste; the principle is to fill waste in the ground. Medical waste is decomposed into harmless substances through the decomposition of microbial for a long time. If there are no anti-seepage measures when using landfill method, a variety of toxic substances, pathogens, radioactive substances will penetrate into soil along with rain. Therefore, this disposal method need select site scientifically. Impermeable layer shall be laid with clay and high-density polyethylene. Collecting and output pipelines shall be installed for landfill gas. So the landfill treatment must be very careful, medical waste must be pretreated according to the relevant standards.

Influence parameters: This method need that site of geological conditions shall meet with standards according to characteristics of medical waste. Scale of site shall be established with the corresponding civil technology according with soil and climate.

Advantages and disadvantages: The advantages of landfill are simple process, small investment, and it can process a large amount of medical waste. But it has many disadvantages such as: medical waste shall be disinfected before filling; site needs a large investment and area; medical waste will produce a large amount of harmful gases and volatile organic compound including methane, ammonia, hydrogen sulfide gas, nitrogen, carbon monoxide, oxygen and hydrogen. Soil and underground water shall be monitored in the long term.

Electromagnetic Wave Sterilization

Electromagnetic wave sterilization includes microwave and radio wave. Microwave sterilization uses 2450MHz high-frequency electromagnetic waves, and radio wave uses 10MHz low-frequency electromagnetic waves. The penetration of radio waves is stronger than the microwave. Electromagnetic wave can be absorbed by water, fat and protein. Medical waste treated can be filled under the ground. This method has application examples in United States, Australia, Germany and Philippines.

Influence parameters of this method are output power and the actual field strength, nature and moisture of waste.

Advantages and disadvantages: The advantages of this method are such as: obvious reducing volume of waste, complete closed system, lower pollution, fully automatic type and easy operation. The disadvantages are high investment and operation cost, poor weight loss of waste; and there will be odor. It is not suitable for blood and hazardous chemical waste.

Pressure Steam Sterilization

The principle of this method is that pressure steam will penetrate the inside of the medical waste sorted and crushed under the condition of 100KPa, 121Cc. And protein of microorganism in medical waste will be killed. Hospital waste processed is sent to sanitary landfill or incinerate. This method is also suitable for disinfection of work clothes, syringe, surgical dressing and microbial media; but it is not suitable for the pathological waste.

Influence parameters: The main parameters of this method are temperature, steam quality and time of action; and size of waste will affect the penetration of steam; processing period affects the thoroughness of sterilization; air in the container cannot be completely removed will affect the temperature of sterilization.

Advantages and disadvantages: This method has advantages of low investment cost and operating cost, easy testing, low risk, good effect and a wide range of medical wastes. The disadvantages are such as: volume and appearance of the waste does not change basically; air pollutant may be discharged; it is easy to produce odor; formaldehyde, phenol and mercury cannot be processed.

High-temperature Incineration

Medical waste is mainly composed of organic hydrocarbons, containing more combustible components and a high calorific value. Incineration is a deep oxidation chemical process. Under the action of high temperature flame, medical wastes in the incineration plant are transformed into residue and gas through drying, igniting and incineration. Infection sources and hazardous substances of medical waste can be effectively destroyed during the incineration process.

Influence parameters: Incineration plant must have appropriate turbulence and mixing, keeping the current moisture content of the medical waste. The influence parameters also contain loading status, temperature and residence time, maintenance of combustion chamber.

Advantages and disadvantages: The advantages of incineration are the follows: volume and weight of waste reduce significantly. It is fit for large-scale medical waste disposal. It is stable operation and excellent effect of sterilization and pollutant. Potential heat energy can be recycled. But it has many disadvantages such as: high costs, serious air pollution, easy to produce dioxins, polycyclic aromatic compounds and other harmful gases such as hydrogen chloride and sulfur dioxide. This system need to be required with a sound exhaust gas purification system.

Chemical Disinfection

Chemical disinfection is that medical waste crushed will be mixed with a certain concentration of disinfectant; they have enough contact area and time. The organic matter is decomposed and microbe is killed during the disinfection process. This method is suitable for liquid medical waste and pathology of waste; and it has been gradually used for medical waste which cannot be disinfected by heating or humidifying.

The influence parameters of chemical disinfection are concentration and temperature of disinfectants; disinfectants shall be used according to nature of hospital waste; and parameters also include mixing times of waste and agent, fluid recycling, etc.

Advantages and disadvantages: The advantages of chemical disinfection are simple operation process, good deodorant effect, low investment and operation; waste reduction rate is high, it will not produce waste water and gas. The disadvantages are such as: dry waste needs good crushing machine and testing of PH value; wet waste treatment will produce waste water and gas, most of the disinfectant is harmful to humans. It is not suitable for chemical waste, radioactive waste, volaticle and semi-volatile organic compounds.

Pyrolysis Technology

Pyrolysis is to convert organic components with large molecular weight into flammable gas, liquid fuel and carbon black, under the conditions of oxygen-free or oxygen-poor when temperature is 600 to 900 celsius. Gas produced from pyrolysis mainly contains dydrogen, methane, carbon monoxide, carbon dioxide, hydrocarbons, and other volatile organic compounds.

The influence factors of medical waste pyrolysis are temperature and reaction time. Pyrolysis efficiency can be affected by humidity and size of medical waste. Pyrolysis mode is determined by the material molecular structure.

Advantages and disadvantages: The advantages of medical waste pyrolysis are as follows: it can completely process waste. Combustible gas can be used as fuel for heating pyrolysis furnace; the operating cost is much lower than conventional incineration. In addition, pyrolysis requires a smaller air coefficient, so amount of flue gas produced is significant reduction. The required purification device for flue gas is smaller, so the overall cost is smaller than the conventional incineration.

Pyrolysis of medical waste produces less harmful substances. Due to the traditional incineration is oxygen-enriched combustion, so it is easy to produce dioxins. Pyrolysis is processed in the terms of anoxic and acidic gases without chlorine, which reduces the production of dioxins. Range of application of pyrolsyis is very wide. And medical waste does not require pretreatment and classification, waste is sent into the reactor directly, so pyrolysis method can treat any kind of medical waste.

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