Comparative Analysis of Medical Waste Disposal Methods

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.

medical waste disposal

 

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.

Medical waste disposal business

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.

hospital biomedical waste management

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.

waste management of hospital

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.

hospital management to oil plant

 

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.

medical waste treatment facility in China

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.

You can clink medical waste to fuel oil pyrolysis technology to learn more, or if you are interested in other waste disposal plant, please contact Kingtiger.

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Urban Waste and Pyrolysis Technology

Municipal solid waste is a major source of pollution. How to efficiently process it is not only effect our environment and economy; more importantly, it will be an important part of recycling of resources in the 21st century. Disposal of waste in green way can save environmental pollution and recycle renewable energy. Waste recycling in green solution is the urgent and basic. Research and development of technology for changing waste to energy complies with the trend of the times. The technology of resource utilization of solid waste has been concerned in many countries.

Urban-solid-waste

Methods and Problems in Treating Urban Solid Waste

  1. Landfill: this method is widely used in the earliest; solid wastes are filled under the ground. Compared to other ways, landfill has many advantages: it can be used for processing all kinds of waste, with mature technology, simple operation, large capacity, as well as low investment and operating costs. It is a major way to treat solid waste. But it has many problems. Waste in landfill has a large number of bacteria, viruses and heavy metal pollution. It also can harm our groundwater for long. Landfill has great potential harm, and it will leave endless troubles for in future.
  2. Composting. Part of solid waste can be used for fertilizer, but this method is only used in small scale, and this fertilizer can cause soil salinization.
  3. Biofermentation gasification technology. This method uses landfill way, waste will be dissolved due to decay in role of biological fungus. It is widely used because of simple operation and low cost. But this method only applies to biomass. End products not only will take up a lot of land, but also can permeate into soil to pollute groundwater and air, such as biogas, residue and leachate, etc.
  4. Oxidation (incineration) technology. At present, incineration is the main way to reduce MSW. Waste incineration power generation plant can dispose parts of waste, and inefficient realize resources recovery. But it also has many disadvantages, such as secondary pollution, high investment and operating cost.
  5. Incomplete oxidation (oxygen-poor) pyrolysis and gasification technology. This plant is very expensive.

Pyrolysis Technology and Application Areas

Pyrolysis refers to chemical process converting a substance (mainly refers to a polymer compound) into several other substances (mainly refers to low monocular weight compound) by thermal energy. The basic factors affecting pyrolysis are temperature, duration of reaction as well as raw materials.

1. Chemical industry

Pyrolysis technology is used for petrochemical industry and coal chemical industry. In the process of petrochemical industry, temperature of pyrolysis is between 700℃ to 800℃, sometimes it can up to above 1000℃. Raw materials are naphtha, kerosene, diesel and heavy oil. In this process, long chain hydrocarbon has been broken into ethylene, propylene and other short-chain hydrocarbon, along with condensation, cyclization and dehydrogenation reactions. Generally, process changing heavy oil into diesel and gasoline is called as the cracking; and processing changing light oil into small molecule olefins and aromatic hydrocarbon is called as the pyrolysis.

2. Sludge treatment

Sludge can be converted into fuel oil, combustible gas and carbon black by pyrolysis technology, between 200℃ to 450℃, due to sludge is mainly composed of fat, protein, carbohydrates and fiber.

3. Organic waste disposal

Some countries began to research pyrolysis technology for organic waste disposal, such as Unite States, Italy, Switzerland, Spain and other countries. In recent years, with energy crisis, more and more people begin to concern on development technology of new energy sources, especially in biomass energy. Agricultural waste, such as straw, rich hull can be changed into biomass energy by this technology. And this pyrolysis technology has reached the commercialization stage.

Fully automatic waste solid pyrolysis system in China
Pyrolysis Plant for Urban Solid Waste

Main Factors of Pyrolysis Technology

Viewing on applications of pyrolysis in various fields, it can be found that there are two factors effecting application and development of pyrolysis technology, internal factors and external factors. Internal factors refer to temperature and humidity of pyrolysis plant. External factors refer to raw materials.

1. Characteristics of materials

Pyrolysis technology refers to organic materials has fission reaction by absorbing heat, based on required temperature and humidity. Quantity of heat and time required are different according to various materials. In general, material with smaller molecular weight like paper can be firstly pyrolyzed; materials with relative large molecular weight like lignine and fatty can be pyrolyzed later. So it is very complex to dispose mixing materials, its reaction will last longer, and end products has a large variability.

Otherwise, there are other factors can affect the process of pyrolysis, such as particle state and humidity, due to they can decide mixability, stirring effect and heat absorption capacity.

2. Pyrolysis time

Residence time of waste will directly decided degree of pyrolysis reaction and type of end products. There is no carbon black at very high reaction rate and temperature, so it is also called as the fast pyrolysis or flash pyrolysis. Generally speaking, the shorter the solid phase reaction residence time, the smaller the proportion of carbon black produced from pyrolysis, the total end production is greater and the reaction is more complete.

3. Temperature of pyrolysis reaction

Temperature is an important factor in process of pyrolysis, it can directly influence distribution and component of end products. Different materials have different pyrolysis temperatures. After many specialists have researched pyrolysis from 300℃ to 800℃, they found that longer time in temperature can produce more carbon black, if pyrolysis stayed in high temperature for loner timer by heating furnace quickly, pyrolysis reactor would more complete, and it can produce more oil gas.

Key Technologies for Solid Waste Pyrolysis

From research of MSW pyrolysis and characteristics, we can found that the key factors to achieve pyrolysis technology on disposal of waste are the control of time and temperature of pyrolysis, material in furnace, utilization and disposal of end products.

Principle of urban waste pyrolysis: reactor is the main place for pyrolyzing organic component of waste. Due to waste has dust, so pyrolysis gas produced will be sent to separator. pyrolysis gas after been separated will be cooled to by pure combustible gas in condenser. Residue will be used as fuel for heating reactor. Hot flue gas will be used as heating fuel after been separated. Solid waste will be sent into reactor for pyrolysis.

Pyrolysis machine for sale
Pyrolysis Reactor Used for Solid Waste Disposal

Pyrolysis technology imitates the forming process of oil, coal and natural gas, to build reverse reaction process. With appropriate temperature, time, activation and reduction environment, larger molecular can be converted into small molecule. With oxygen-free and reducing agent, biomass will be changed into “hydrocarbon” from “carbohydrate”. We will obtain “fuel oil, gas and carbon black” after end products have been collected as physical property.

1. Pretreatment of solid waste

Due to MSW is very complex, waste bricks and metals can’t be pyrolyzed, so it need be firstly sorted by a professional separation machine, if not, process of pyrolysis shall be effected in the following respects. Firstly, pyrolysis effect, because impurity like inorganic substance can consume heating energy. Secondly, mobility of raw materials, part of inorganic substance can reduce service life of pyrolysis reactor due to its chance of molten state. Thirdly, pyrolysis oil produced will have complex ingredient and high viscosity. Pyrolysis can also be affected by particle size and moisture content of waste, because stirring effect can influence heat absorption rate, and different size and moisture will have different stirring effect.

2. Applications and treatment of end product of MSW pyrolysis

Solid waste pyrolysis will produce residue, waste water, combustible gas, pyrolysis oil, as well as carbon black. Residue and waste water produced in pyrolysis shall be processed by professional purification system. Pyrolysis oil can be processed into diesel oil and gasoline by distillation unit. Carbon black also can be milled into superfine carbon black by professional milling plant. End products have the very good market prospect. And there is free of pollution during the whole process.

Features of Waste Pyrolysis

Technological advantages

1. Harmless: free of toxic and harmful substance, zero emission
2. Zero energy consumption: combustible gas can be used as fuel for pyrolysis reactor and power plant.
3. Poly-generation: end products include combustible gas, fuel oil, carbon black, as well as residue for paving.
4. Strong adaptability to environment
5. Small land area
6. High degree of utilization and industrialization
7. Advanced plant
8. Low cost
9. High return

Features of equipment operation:

1. Anisotropy heating in pyrolysis furnace
2. Water in waste will be used after it has been disinfected and distilled.
3. Oxygen insulation can solve the security of pyrolysis plant.
4. Environmental pollution. Anaerobic pyrolysis technology is free of pollution, no chimney. The whole process is in a sealed space, without any odor.

Pollutant Controls in the Process of Pyrolysis

Exhaust gas from pyrolysis will be collected into storage, and then it will be sent into special burner after has been pressurized, with the purpose of remove the CO and other combustible gas. Heat produced will be used as fuel for drying garbage; waste gas will be discharged only when it can meet European standard, after it has been processed by purification system of flue gas and desulfurization and denitrification removal system. The total amount of flue gas from pyrolysis is less than 1/10 of incineration power generation. Total amount of pollutant discharge will be reduced significantly.

Pyrolysis technology for urban waste has advantages of easing the demand for energy resources, solving land occupation of waste, reducing pollution of land and water resources. It can create a considerable economic benefit while protecting our environment.

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