Solid waste treatment

Solid waste treatment methods

In Vietnam in the coming years, the trend of solid waste treatment is different between big cities and provinces.

The purpose of waste treatment is to:

Convert waste to a less toxic, more controllable form,
Convert waste into other useful substances,
Reduce volume or mass to store more,
Temporarily held until the right technology.

Depending on the technology applied, processing costs will vary. There is low-cost treatment technology, but secondary pollution is generated during the treatment process. Having modern treatment technology, high operating cost but safe treatment, no odor, no secondary pollution. However, the management of solid waste should be effective, limiting waste generation, reuse and recycling of waste. In solid waste management, the order of priority is arranged as follows:

Reduce emissions,

Currently, in developing countries including ours, solid waste treatment methods are commonly applied as follows:

As for domestic solid waste, a large proportion of organic components are utilized to produce organic fertilizers. However, because the waste classification process is not done synchronously, only a part of domestic waste is bio-composted, the rest is still buried in centralized landfills.

Components that are difficult to biodegrade but are flammable such as shredded paper, rags, plastic, rubber, etc., which are no longer recyclable, can be burned to reduce volume. Construction waste and non-combustible components such as shells, bricks, and ceramics, etc., shall be leveled or buried directly in landfills.

Incineration method:

Incineration is the current popular method in the world for solid waste treatment in general, especially industrial hazardous solid waste and medical hazardous waste in particular. Treatment of exhaust fumes generated from incineration is an issue that needs special attention. Depending on the composition of the exhaust gas, suitable treatment methods can be applied such as chemical methods (precipitation, neutralization, oxidation…), physicochemical methods (absorption, adsorption, electrolysis, etc.) ), mechanical methods (filtration, settling)…

Solid waste incineration is the final treatment stage applied to certain types of waste that cannot be treated by other means. This is the stage of high-temperature oxidation in the presence of oxygen in the air, in which toxic waste is converted into gas and non-combustible components. Exhaust gas generated during incineration is cleaned and released into the atmosphere. Ashes are buried.

The incineration method is widely used in some countries such as Japan, Germany, Switzerland, the Netherlands, Denmark, etc., where the amount of land for waste disposal sites is limited.

Waste treatment by incineration has an important meaning in reducing waste to a minimum for the final treatment stage, which is burying ash and slag. On the other hand, the energy generated in the incineration process can be used for boilers, fireplaces or industries that need heat and power generation. Each incinerator needs to be equipped with an exhaust gas treatment system, in order to control air pollution caused by combustion.

Although incineration requires high treatment costs, it is still commonly used to treat hazardous waste such as medical and industrial waste because these methods treat pollutants relatively thoroughly. infected.

Waste incineration is usually carried out in specialized incinerators at high temperatures, usually from 850 to 1,100oC. The essence of the process is to conduct a combustion reaction, ie the reaction of oxidizing waste with heat and oxygen of the air. The reaction temperature is maintained by adding energy such as electrical energy or the heat released when burning fuels such as gas, diesel, etc.

Currently, in Vietnam, medical hazardous solid waste is mainly treated with small capacity incinerators equipped for each hospital. However, the large central hospitals under the Ministry of Health have well done the collection, classification, transportation and treatment of medical waste. At provincial and district hospitals, the treatment of medical waste depends heavily on the economic conditions of each province. The number of district hospitals equipped with standard incinerators is very small. Therefore, medical waste is usually burned by manual incinerators or buried in hospital grounds.

For industrial hazardous waste treated by the incineration method, it is almost as if the burning principle of medical waste is followed, but the furnace capacity is larger. Currently, industrial parks have not invested in concentrated hazardous solid waste treatment zones. Hazardous solid wastes are usually handled by enterprises under contracts with companies or units that are licensed to transport and treat hazardous solid wastes. In Vietnam, urban environment companies (URENCO for short) are still the leaders in hazardous solid waste treatment. The company researches, designs and manufactures large capacity solid waste incinerators located at several locations, serving the needs of waste treatment in the surrounding area.

Hygienic burial method:

Among the methods of solid waste treatment and destruction in the world in general and in Vietnam in particular, landfilling is the most common and simplest method. This method has been widely applied in most countries around the world. In essence, landfilling is a method of storing waste in an area and covering it with soil.

The landfill method is usually applied to solid waste objects which are municipal waste that is not used for recycling, ash and slag from incinerators, industrial waste. The burial method is also often applied to bury hazardous waste and radioactive waste in specially designed landfills for hazardous waste.

Sanitary landfilling is a method of controlling the decomposition of solids as they are buried and covered with surfaces. Solid waste in landfills will be decomposed by internal biodegradation to produce end products rich in nutrients such as organic acids, nitrogen, ammonium compounds and some gases such as CO2. , CH4.

In the North, Nam Son landfill (Soc Son, Hanoi) is the largest landfill, responsible for garbage treatment for the whole city of Hanoi. The Nam Son landfill receives about 3,000 tons of garbage every day and can increase to 4,000 tons/day in the next two years. Currently, Nam Son beach has filled up 6/9 of the burial cells.

In Ho Chi Minh City, every day, about 6,000 tons of garbage is taken to landfills. However, due to land fund and topography, there are many landfills in Ho Chi Minh City serving the city’s solid waste treatment.

The Go Cat Landfill in Ho Chi Minh City was once the main landfill of Ho Chi Minh City. However, the landfill is now closed because it is full.

Currently, although the Go Cat landfill is closed, the wastewater treatment system, gas recovery system and generator equipment continue to operate.

In addition, Ho Chi Minh City has Phuoc Hiep landfill, belonging to the Northwest Solid Waste Treatment Complex. This landfill covers an area of ​​over 22.8 hectares, with an average garbage treatment capacity of about 3,000 tons/day, built with a total cost of over VND 197 billion. The treatment technology of this landfill is a hygienic landfilling technology, leachate at the landfill will be collected by a system of HDPE pipes and led to a centralized wastewater treatment station, then discharged into the Thay canal. Cai.

Bio-incubation method:

The bio-composting process applies to non-toxic organic matter, first dewatering, then processing until it becomes porous and moist. Humidity and temperature are controlled to keep the material aerobic throughout the incubation period. The process generates its own heat by biochemical oxidation of organic substances. The end products of the decomposition process are CO2, water and stable organic compounds such as lignin, cellulose, fibers, etc.

For small scale (eg livestock farm), organic waste can be applied bio-composting technology in heap. For large scale, it is possible to apply bio-incubation technology on an industrial scale. Temperature, humidity and aeration are strictly controlled for optimum incubation.

In Vietnam, Cau Dien waste processing plant under Hanoi Urban Environment One Member State Company Limited (URENCO) is one of the leading factories in Vietnam in the field of bio-composting. organic waste for composting.

In addition, in the North, there is also Viet Tri waste processing factory, now renamed and developed into a State-owned One-member limited liability company Phu Tho waste treatment and processing also has many years of experience. in the field of bio-incubation.

Solid waste recycling methods:

Recycling has been around for a long time in Vietnam. Recyclable wastes such as metal, plastic and paper are sold by households to scrap collectors, and then transported to craft villages. Waste recycling technology in craft villages is mostly old and outdated, with weak infrastructure and small-scale production leading to serious environmental pollution in some places. Some recycling craft villages are currently facing many pressing environmental problems such as Chi Dao commune (Hung Yen), Minh Khai commune (Hung Yen), paper production village Duong O commune (Bac Ninh)… In general, Recycling activities in Vietnam are not systematically managed but are mainly carried out spontaneously by private establishments.

E-waste is one of the most recycled types of waste in Vietnam. Broken computers, televisions, and locomotives are often sold to a team of waste collectors. These waste products are often separated to collect components, or take the metal and case back to recycling facilities.

However, it is worth mentioning that the recycling technology at these facilities is still too outdated. After usable metals and electronic components are removed and sold or repaired, the remainder is mainly burned or ground and then chemically added to create new products, which are simple products. as simple as bottles, nylon bags with limited quantity.

Plastic recycling is also a potential industry in our country. Currently, Vietnam has more than 2,200 enterprises producing plastic products, about 80-90% of raw materials must be imported while the growth rate of this industry is from 15 to 20% per year. However, at present, the recycling of plastic on an industrial scale has not been really interested in development. Plastic recycling facilities are mainly household-scale establishments, concentrated in craft villages with outdated and manual technology, thus causing serious environmental pollution such as Dong Mau craft village, Yen Dong commune, district. Yen Lac, Vinh Phuc province. The whole village has more than 40 plastic recycling facilities and dozens of households purchasing plastic waste to supply recycling facilities. Every month, the village recycles about 150-200 tons of plastic.

In addition, paper is also a recyclable material, but in Vietnam, the percentage of recovered used paper compared to the total amount of paper consumed is only about 25%, very low compared to other countries in the region because There are many reasons: technology, cost, and the way to legalize production costs for the purchase of domestically collected paper is complicated, causing no progress in domestic paper recovery.

Used paper, after being recovered, is transported to the factory and can be recycled into tissue paper for packaging, tissue paper, newsprint. Small-scale production facilities mainly use locally collected paper to produce low-grade products. In contrast, medium and large-scale establishments mainly use used paper imported from abroad to recycle paper for more advanced products.

Since 2000, many modern and synchronous production lines for pulp from recovered paper have been installed in Vietnam. In 2009, Vietnam put into production a number of new production lines with a total capacity of 190,000 tons/year. In addition, the old lines have been upgraded to the stages of grinding, sieving and separating fibers to bring about higher flour efficiency and better flour quality. The technology of using used paper in Vietnam is making positive changes, contributing to stimulating the development of waste paper collection and the development of the domestic paper industry.

Development trend of solid waste treatment technology:

The amount of solid waste and hazardous waste in Vietnam is increasing rapidly according to the development of the economy in general and the industry in particular, especially in the two key economic regions of the North and the South. However, the problem of collecting, transporting and treating hazardous waste in Vietnam is still inadequate. The number of units capable and licensed to operate in the field of hazardous waste collection, transportation and treatment is small and their capacity and qualifications are still weak, so the rate of hazardous waste treatment is still low. low hazardous waste. Therefore, hazardous waste is often gathered indiscriminately and buried unsatisfactorily.

Currently, our country is in the process of developing and integrating with the world. On the other hand, the information age develops, so scientific and technological achievements are quickly applied. In the field of environmental protection, too, in Vietnam, technologies have been used in the world.

5.1. Trends in solid waste treatment technology in the world

In developed countries, the process of solid waste collection and management is perfected due to the availability of adequate physical and technical foundations, in addition, the people’s awareness of environmental protection is very high. Therefore, the upstream waste separation is very good. On the other hand, waste recycling technologies have been developed and applied popularly in some countries such as the US, Japan, Korea… The environmental industry has been established to solve environmental pollution, recycle waste and bring high economic efficiency.

Economic growth and increased waste always go hand in hand. When living needs are improved, society must provide more products for people. Therefore, production develops, raw materials and natural resources are used by people to create useful products, but in the end will also create waste.

According to statistics, in the US from 1970 to 1998, the amount of solid waste buried and destroyed increased by 37%, the amount of waste per capita increased by 14%. Americans generate 156 million tons of municipal solid waste each year. In Korea, the total amount of solid waste is about 298 million tons/year, of which urban waste is about 58 million tons/year, industrial waste is about 100 million tons/year.

If it is said that the world’s solid waste treatment technology trend in the further future, it can be affirmed that landfill technology will have “no place”, recycling technologies will be deployed and applied depending on the requirements. waste type. In particular, pyrolysis technology will be widely applied, because it allows the most thorough treatment and reduces the volume compared to other methods.

However, in the near future in developed countries where there is already a developed environmental industry and effective recycling technologies are applied, the hygienic burial method accounts for a very low percentage. about 10-15%. In these countries, food processing technology is developed, foods are mainly processed, so the amount of food waste will gradually decrease. On the other hand, in these countries the share of agricultural development is very low. Therefore, the production technology of microbial fertilizers accounts for a very low proportion, only about 1-5% of the waste.

Municipal solid waste, agricultural solid waste, industrial waste tend to be recycled or treated by pyrolysis with the reuse of heat energy in different forms.

The trends in solid waste and hazardous waste management and treatment in countries around the world are as follows:

Focus on thoroughly solving industrial solid waste, for the following reasons:

– Industrial waste causes serious environmental pollution;
– The industry is capable of science and technology;
–The industry is capable of human resources;
–The industry has a department in charge of the environment.

The world moves to no landfill.

Application of advanced technologies, waste recycling.

5.2. Trends in solid waste treatment technology in Vietnam

In Vietnam in the coming years, the trend of solid waste treatment is different between big cities and provinces.

– In big cities, there is a trend of pyrolysis with energy recovery to reduce treatment costs.

– In the provinces, there are two trends in solid waste treatment: sanitary landfill and microbial production.

Within a decade from 2010 to 2020, the trend of urban solid waste treatment in big cities such as Hanoi, Ho Chi Minh City, Hai Phong, Da Nang, Nha Trang … mainly uses thermal methods. manure and recycling methods.

For example, a series of solid waste treatment projects from 2010 to present in Hanoi city have been proposed:

Project of treatment by plasma combustion PJMI 300 tons/day of Thanh Quang Construction and Trading Joint Stock Company (under construction).

Hanoi urban solid waste treatment project at Nam Son Waste Treatment Complex by recycling method of AIC World Progress Joint Stock Company (under construction).

Proposing Xuan Mai urban waste treatment project by recycling technology into diesel oil…

The main reasons big cities need to get rid of the landfill method are lack of space and environmental pollution due to leachate and landfill emissions.

Treatment by pyrolysis: conventional incineration, heat-utilizing incineration, plasma incineration, carbonization method, etc., although the investment and operating costs are high, it will be an alternative measure. alternative to the burial method. Composting and anaerobic digestion can only treat organic components.

Factors affecting the need to apply pyrolysis treatment:

– The need for the recovery of valuable products and energy sources from municipal solid waste.
– The traditional method of incineration causes negative effects.
There are restrictions on burying untreated waste.

Currently, the world has been applying modern technologies in solid waste treatment such as burning garbage to generate electricity, burning plasma at high temperature, recycling waste plastic and waste rubber into fuel oil… Some advanced technologies have also been imported and applied in Vietnam. However, in order to decipher the technology and come to master it, relevant authorities and environmental scientists and technologists need to focus their research on the following issues:

For municipal solid waste:

Research on incineration technology combined with taking advantage of heat energy to generate electricity to use and operate waste treatment systems to reduce treatment costs.

– Research on carbonization technology to form fuel products and environmental pollution treatment materials.

Research on plasma incineration technology to form syngas used to operate waste treatment systems.
– Research on pyrolysis technology to create fuel for use and operation of waste systems.

– Research on the production of effective catalysts for the pyrolysis process to form fuel.

Research on recycling technology of rubber, plastic, metal, paper components…