General introduction to disposal techniques

Consideration should be given to eliminating products that can not be used in accordance with the intended use or other authorized use, or reformulated for re-use.

This chapter reviews available disposal techniques and provides guidance for preparing a disposal plan. Disposal methods are divided into three categories (Box 4) and are assessed according to their degree of suitability for the removal of large quantities of obsolete pesticides in developing countries. The main criteria are: ecological rationality of the technology; occupational safety for operators; technical applicability for the destruction of large quantities of obsolete pesticide; adaptation to situations commonly encountered in developing countries; and cost-utility ratio.

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Disposal methods that may be acceptable, depending on the type of product and local conditions, are described in detail. Inappropriate options are briefly described along with the reasons that disqualify them. Promising new techniques are presented quickly.

In general, the applicability of the different disposal techniques depends mainly on the type and amount of product to be removed. A particular technique may be suitable for a certain group of products, but it may be totally inappropriate for another. This means that it is essential to examine the technology in each case in relation to the product.

BOX 4

Summary of methods for disposal of large quantities of obsolete pesticides in developing countries

A. DISPOSAL METHODS THAT MAY BE ACCEPTABLE BY TYPE OF PRODUCT AND LOCAL CONDITIONS

· High temperature incineration;

· Chemical treatment

· Specially equipped landfill (for neutralized materials, incinerator ash and slag);

· Long-term controlled storage.

B. METHODS OF ELIMINATION NOT SUITABLE FOR LARGE QUANTITIES OF PESTICIDES

· Outdoor burning;

· Landfill or landfill;

· Discharge into sewers

· Solar evaporation;

· Cultivation of the land and superficial application;

· Deep well injection;

· Other methods mainly for soil regeneration and groundwater decontamination (including ultraviolet treatment, ozonation, ion exchange, precipitation or flocculation, activated carbon absorption).

C. PROMISING NEW TECHNIQUES

· Pyrolysis by plasma torch;

· Chemical reduction in the gas phase;

· Oxidation process in molten salts;

· Metallurgical treatment process (molten metal method).

Recommendations for the disposal of different products can be found in:

· Treatment and disposal methods for waste chemicals (UNEP / IRPTC, 1985).· International Fact Sheets on Chemical Safety (WHO / IPCS).

It should be noted, however, that the disposal methods recommended in the above documents are often small and are not always suitable for large quantities.

Annex 1 gives general guidance on the methods of incineration suitable for specific groups of pesticides.

Disposal methods that may be acceptable, depending on the type of product and local circumstances

Incineration at high temperature

Operation of incineration

Incineration is a high-temperature thermal oxidation process in which the pesticide molecules are broken down into gases and unburnt solids. Solids are called residues and include ashes and slag. A high chimney leads the gaseous effluents into the air. Chimney gases may contain water, carbon dioxide, acidic or toxic gases and toxic particles, including ash and metal oxides. To reduce pollution, the incinerator may be equipped with a gas cleaning device, such as a gas scrubber and / or electrostatic filters. Solid residues are landfilled.

Hazardous waste incinerators include a main chamber where waste is burned and an afterburner that allows maximum destruction of hazardous organic by-products, maintaining the flue gas at the proper temperature (over 1,100 ° C) for at least two seconds (retention time). As the gas cleaning equipment can not operate at the high temperature of the gases leaving the furnace, the gases in the stack are cooled to temperatures of about 200 ° C.

Properly conducted incineration can, in principle, destroy pesticide waste with a destruction-by-destruction rate of 99.99 percent or higher. For some incinerators, these rates would approach 99.99995 percent. However, the efficiency of incineration depends on many factors, such as: design; process control and maintenance of appropriate values ​​of retention time, temperature and turbulence; the type of incinerated products; and the capacity and efficiency of air pollution control equipment. Improperly used incinerators can create dangerous solid airborne by-products, posing a serious threat to the environment and public health. These by-products are often more toxic than the original product. The potential for the formation of polychlorinated dibenzodioxins and polychlorinated dibenzofurans (often referred to as dioxins and furans), which are extremely toxic and persistent in the environment, is of particular concern. Dioxins and furans are the result of a reaction that occurs during the cooling of stack gases. The factors that influence this reaction are: the temperature of the gas in the chimney; the presence of chlorine and other halogens; and the existence of a catalyst. The risk of dioxin and furan formation can be reduced by the use of an incinerator model in which stack gases are cooled very rapidly (quenching) below the range of temperatures at which dioxins and furans are formed (between 250 ° C and 350 ° C) and which includes a gas scrubber to fix the halogens (eg, a scrubber using sodium hydroxide solution). In addition, special filter systems reduce dioxin and furan emissions. Halogenated pesticides should not be incinerated in the absence of an effective extinguishing and washing system.

Selection of pesticides to incinerate

The ability to properly incinerate a pesticide depends on the type of pesticide, the incinerator model, and the gas cleaning system. Inorganic pesticides can not be incinerated. Organic pesticides containing mercury should not be incinerated. Organic pesticides should be burned at relatively high temperatures (above 1,100 ° C), and the gas should be retained in the flame for at least two seconds. Organic products containing heavy metals, such as tin and lead, may only be incinerated in special cases, under very strict conditions, in facilities reserved for hazardous waste equipped with flue gas cleaning systems that can recover these elements. It is sometimes possible to export products containing heavy metals for recycling. To determine if a specific product may be incinerated, refer to Appendix I, the Material Safety Data Sheet or the documentation listed in Table 3. Otherwise, contact the manufacturer of the product or a reputable incinerator.

For more detailed technical information on the operation and design of incinerators, see The World Bank / WHO / UNEP, Volume III (World Bank / WHO / UNEP, 1989) and Draft technical guidelines on incineration. on land (D10), (UNEP / SCB, 1994C).

The following paragraphs discuss different options for high-temperature incineration, including:

· Large fixed incinerator;
· Low-capacity fixed incinerator
· Mobile incinerator;
· Cement kiln.

Table 3 summarizes the advantages and disadvantages of each of the options as well as the conclusions. Annex I indicates which groups of pesticides can be incinerated in each type of incinerator.

Study of the different incineration options

Large capacity fixed incinerator

High-capacity hazardous waste incinerators are the best method of removing the most obsolete pesticides. They are built specifically to incinerate hazardous waste. These are usually rotary kiln incinerators with an afterburner system and various air pollution control devices. The temperature is maintained between 1100 ° C and 1300 ° C and the retention time in the afterburner is at least two seconds. The kill removal efficiency is between 99.99 and 99.99995 percent. The capacity varies between 0.5 and 7 tons per hour with 24 hours of continuous activity. These incinerators can treat solids and liquids, as well as contaminated soils and materials, containers and conditioned waste. They can handle all kinds of organic pesticides (including organochlorine pesticides), although some incineration companies may refuse, or accept with restrictions, products containing heavy metals such as mercury, or other specific elements such as ‘iodine.

These large incinerators are very expensive (the initial investment is between US $ 10 and 200 million, depending on capacity, stack gas treatment and water treatment characteristics, infrastructure, etc.), and are only profitable if the flow of chemical waste to be incinerated is continuous and substantial. Due to the high level of initial investment and operating costs (which include: large quantities of flushing fluids, transportation of waste to the plant, landfilling of ashes and slag; highly qualified technicians, regular plant maintenance and maintenance, and intensive control procedures, including analytical services), these incinerators are only found in industrialized countries. For the same reasons, the local installation of a large-scale incinerator does not realistically address the problem of obsolete pesticides in developing countries. However, in some industrialized countries there are companies that exploit this type of incinerator and may be allowed to burn obsolete pesticides from less developed countries. The latter can enter into contracts with these companies.

More detailed information on the possible shipment of pesticides to a specialized incinerator in a country accepting waste can be found on page 22.

Incinerator with low capacity

There are a number of low capacity fixed incinerators on the market with various designs and capabilities. The more complete the design, the greater the capacity, the higher the price. The simplest models have only one chamber without afterburners and / or scrubbers. The most advanced models have a master bedroom with an afterburner and scrubber.

Simple models without afterburners and gas cleaners are not suitable for the destruction of large quantities of obsolete pesticides or any amount of waste containing chlorine, phosphorus, sulfur or sulfur. nitrogen. In the absence of these devices, there is a high risk of high atmospheric pollution, especially when organochlorine compounds are incinerated. Many simple models do not reach the required temperature of 1100 ° C, which further increases this risk. They usually have a low capacity, from 10 to 100 kg per hour. It is sometimes necessary to interrupt their operation at regular intervals to open the incineration chamber and remove the ashes.

FIGURE 2. A current high temperature incinerator: Courtesy of Rechem International Ltd, United Kingdom.

More advanced models with a simple purification device cost about US $ 1 million. They can reach the required temperature, but often have a relatively low capacity of 1 to 2 tons per day, which means that it will take up to a year to incinerate a usual amount of 300 tons. Long-term operation results in high operating costs. These incinerators require the permanent supervision of specialists; technicians (expatriates) for maintenance and repairs; a continuous supply of fresh water and large quantities of chemicals for the purification device; safe disposal of ashes and liquids from the gas scrubber; the continuous supply and guarantee of electricity and fuel. The amount of the initial investment of an advanced low-capacity incinerator and the costs of its operation are substantial. In many cases, the cost-utility ratio of these incinerators does not justify their acquisition. Moreover, their use is not practical because of their low capacity, the large quantities of supplies required and the important residues that still need to be eliminated. In most cases, it will be more practical and less expensive to export waste to an industrialized country for treatment in a specialized incinerator. It should also be taken into account that gas cleaning devices are generally less efficient on low capacity than high capacity incinerators, especially after prolonged intensive use, and that

Before using a low-capacity incinerator, it is important to ensure that the model has been tested and approved for the types of pesticides that are to be incinerated. These incinerators are subject to acceptance problems by governments. In Europe, it is difficult and expensive to obtain permission to experiment with a new incinerator model. As a result, European manufacturers sometimes offer small incinerators that have not yet been tested for pesticide incineration, but will be on site before becoming operational. Some governments have been very reluctant to systems that have not been tested in the country of manufacture and have therefore rejected this option.

Hospitals sometimes use low capacity incinerators to incinerate their waste. It is recommended not to use these incinerators for solid pesticides; pesticides containing chlorine, sulfur or nitrogen; those containing metals; or for large amounts of pesticides in general. They should only be considered for relatively small amounts of liquid pesticides, provided that the design, temperature and retention time are adequate; they are equipped with the required purification devices; that the opinion of a specialist has been previously requested; and that national regulations permit such use of hospital incinerators.

Low-capacity incinerators sometimes respond to the problems of particular users, such as local formulation plants, which constantly produce relatively small amounts of low-hazard, non-halogenous wastes (eg packaging and protective equipment). disposable contaminated). These factories must also have the expertise required to operate the incinerator.

Mobile incinerator

There are several models of mobile waste incinerators, from medium to large capacity. The term “mobile” can be confusing because it sometimes takes weeks to mount or dismount such an installation; it would be more accurate to speak of transportable incinerators. These are generally relatively large assemblies including a rotary kiln incinerator and gas cleaning devices. They are mainly used in the United States for on-site cleaning of hazardous waste dumps. They treat large quantities of solid, liquid and semi-liquid wastes and contaminated soils with destruction and emission standards comparable to those of large-capacity fixed incinerators. Mobile incinerators are transported on two or three common trailer trucks, with a gross weight varying between 50 and 80 tons. Prices for mobile incinerators range from US $ 1.5 million to US $ 15 million, depending on capacity and performance. Some companies offer contract mobile incineration services. It can take up to six months for an incinerator to be installed on site (preparation, shipping, transportation in the country, assembly and testing) and the delivery costs can exceed $ 1 million (transportation, assembly, testing, dismantling, transport). Operating costs range from $ 600 to $ 2,000 per tonne depending on the incinerator model and the type of waste. The smaller models have a capacity of 2 to 20 tons per day. US $ 5 million to US $ 15 million, depending on capacity and performance. Some companies offer contract mobile incineration services. It can take up to six months for an incinerator to be installed on site (preparation, shipping, transportation in the country, assembly and testing) and the delivery costs can exceed $ 1 million (transportation, assembly, testing, dismantling, transport). Operating costs range from $ 600 to $ 2,000 per tonne depending on the incinerator model and the type of waste. The smaller models have a capacity of 2 to 20 tons per day. US $ 5 million to US $ 15 million, depending on capacity and performance. Some companies offer contract mobile incineration services. It can take up to six months for an incinerator to be installed on site (preparation, shipping, transportation in the country, assembly and testing) and the delivery costs can exceed $ 1 million (transportation, assembly, testing, dismantling, transport). Operating costs range from $ 600 to $ 2,000 per tonne depending on the incinerator model and the type of waste. The smaller models have a capacity of 2 to 20 tons per day. an incinerator is installed on site (preparation, shipping, transport in the country, assembly and tests) and the costs of provision may exceed 1 million dollars (transport, assembly, testing, dismantling, transport). Operating costs range from $ 600 to $ 2,000 per tonne depending on the incinerator model and the type of waste. The smaller models have a capacity of 2 to 20 tons per day. an incinerator is installed on site (preparation, shipping, transport in the country, assembly and tests) and the costs of provision may exceed 1 million dollars (transport, assembly, testing, dismantling, transport). Operating costs range from $ 600 to $ 2,000 per tonne depending on the incinerator model and the type of waste. The smaller models have a capacity of 2 to 20 tons per day.

These incinerators can achieve a destruction efficiency of 99.999 percent and meet most standards for emissions to the atmosphere. Bringing the incinerator to waste avoids the legal problems posed by the international transport of waste. However, the mobile incinerator does not eliminate the need to transport waste because it is still necessary to bring the pesticides to the incineration site. The transport of a mobile incinerator requires a good road network (roads and bridges must support the weight). Also, weight and height limitations may prohibit the use of an incinerator of this type in some areas. Mobile incinerators, like large-scale incinerators, need to electrical energy, large amounts of water and chemicals for the gas scrubber, and a team of highly skilled technicians. In some cases, the chlorine content of the pesticides to be incinerated is limited to a maximum value. Liquids from the scrubber, ashes and slag must be checked and disposed of properly. As with any potential burn site, an environmental impact study is required. ash and slag must be controlled and disposed of properly. As with any potential burn site, an environmental impact study is required. ash and slag must be controlled and disposed of properly. As with any potential burn site, an environmental impact study is required.

Mobile incineration is a relatively expensive option. The incinerator must be shipped to the site, assembled, tested, dismantled and forwarded. Pesticide stocks must be transported to the site. The mobile incinerator is an option only if the volumes of contaminated products and / or soil to be incinerated are very large (from 1,000 to 5,000 tonnes depending on the model and the waste); and / or if the products to be incinerated come from several countries in the same region. It should be noted that by the end of 1995 no destruction of obsolete pesticides by mobile incinerators had yet been achieved in developing countries. There are professional disposal companies that have mobile incinerators and provide a comprehensive package of services, including the use of

Incineration in a cement kiln

A cement kiln is an oven that rotates slowly to regularly expose limestone, sand and clay at very high temperatures to obtain clinker. Only certain types of furnaces (rotary kilns with electrostatic precipitator and bypass device) can be used for the incineration of pesticides. Pesticides can be burned by mixing them with fuel or by injecting them into the flame. Pesticide injection requires special modifications that can be expensive. If the pesticides have a high calorific value, they can partially replace the fuel. Cement kilns can destroy pesticides because indoor temperatures range from 1400 ° C to 2000 ° C. The retention time of the gas phase is between six and 10 seconds. These ovens can process liquid or semi-liquid waste and save on fuel costs. The acid gases emanating from the organochlorine pesticides are neutralized by the alkaline cement, and the purification device is therefore no longer necessary. The powder formulations are difficult to process, but may be added as slurries or blown into the primary stage furnace. The ash formed will be incorporated into the clinker. This method is not suitable for contaminated soils and large solid items, such as packaging materials. The incineration of deteriorated liquid formulations can cause problems when they contain solid particles (for example, crystals, flakes, corroded metal particles which have become detached from the containers) which could obstruct the device by which the liquid is injected into the oven. The quality of the cement is relatively insensitive to the incineration of small quantities of organic waste, although some contaminants may reduce the quality of the cement. In addition to technical considerations, there are psychological factors that explain why cement manufacturers are reluctant to incinerate pesticides in their plants.

If the process is going well, it seems that the occasional incineration of pesticides poses little risk to the environment. However, the process is not always fully mastered; it can happen that due to incidents the combustion is incomplete and produces polluting emissions. In the long term, the continued use of cement kilns to dispose of hazardous waste can pose environmental problems.

TABLE 3. Executive summary and conclusions concerning the different options for incineration

Technical

Advantages

disadvantages

Conclusion

Large capacity fixed incinerator Big capacity. Can burn large quantities of liquids, solids, semi-liquid residues and thick sludges, as well as conditioned soil and waste. Can operate 24 hours a day; high temperature (1200 ° C); high destruction elimination efficiency up to 99.99995 percent; efficient purification of gases. Can treat chlorinated pesticides without problem. Initial investment and very high operating costs. To be profitable, the waste stream must be continuous and substantial. Developing countries generally do not produce such quantities. Costs make this option unusable in smaller and less developed countries. Local installation of a large-scale incinerator is not a realistic solution to the problem of obsolete pesticides in developing countries.

However, exporting waste to an incinerator of this type in an industrialized country often seems to be the most realistic and best disposal option.

Small capacity fixed incinerator The main advantage of small incinerators is that they can be installed at the place of production of the waste. Simple models without a purification device can not be used to incinerate most pesticides, and in no case large quantities. More sophisticated models with simple purification devices cost about US $ 1 million and still have limited capacity (from 100 kg to 2 tonnes per day). They often can not operate continuously, because it is necessary to remove the ashes from the chamber before incinerating the next batch, and therefore are not suitable for solids. Operating costs are relatively high for the following reasons: low capacity; large volumes of liquids used for gas cleaning; residues that still need to be removed; permanent supervision of a specialist required. The maximum chlorine content of the products is sometimes limited. Are not cost-effective for larger amounts of pesticides. Uncomfortable operation. The ecological rationality of each model must be proven. Many models can not be used to incinerate chlorinated pesticides.

May be suitable for specific users, such as local formulation plants, who continuously produce relatively small amounts of low-hazard, non-chlorinated waste (eg, contaminated equipment and packaging).

Mobile incinerator Mobile units can treat solid and liquid pesticides such as contaminated soils. Destruction elimination yield of up to 99.999 percent; complies with most standards for air emissions. Bringing the incinerator to waste avoids the legal problems associated with the international transport of waste. Because of their weight and height, mobile incinerators can often not be used in some areas. They need electrical power, large amounts of fresh water and chemicals for the purification device, and highly skilled technicians. For some models, the maximum chlorine content of pesticides that can be incinerated is limited. Wastewater, ashes and slag must be properly controlled and disposed of. It is necessary to make preliminary studies of impact on the environment. Mobile incinerators are a relatively expensive option because they require good facilities and infrastructure. They should be considered only when destroying very large volumes of products and / or highly contaminated soils. For quantities less than 1,000 tons, it is cheaper to incinerate pesticides abroad. Even with quantities up to 5,000 tonnes, the cost-effectiveness of a mobile incinerator may not be good.
Cement oven Many countries have cement kilns that, in principle, could be used to destroy pesticide waste. They do not require a purification device in acidic medium. Cost-effective option is potentially attractive: the investment is relatively modest (from $ 100 to $ 150,000 for the introductory system) and saves fuel. Most cement kilns in developing countries are not suitable for this purpose. Models that are can process liquids. They can not process contaminated soils and materials. Incineration of powder formulations is possible but difficult. Liquids containing solid particles (crystals, precipitated emulsions) can create problems.

System malfunctions or incidents in the process can cause toxic emissions. Long-term use to incinerate pesticides can cause environmental problems. The chlorine content of the products to be incinerated can be limited.

Cement kilns can only be used for pesticide disposal if the required technical specifications are met. They should only be used for occasional disposal and not for the long-term incineration of hazardous waste. Given the limited experience available in this area, it is recommended for the time being to use this method only in the case of non-chlorinated liquid formulations of pesticides. When all conditions are met, cement kilns can be a practical, efficient and economical solution.

Note: Annex 1 provides further details on product limitations in the different methods.

While most cement kilns in developing countries are not suitable for waste incineration, many countries have at least one kiln that could in principle be used for this purpose. The cost-effectiveness of this option is potentially interesting, especially for liquids, since a relatively small investment (about US $ 100,000 for a liquid waste introduction device) and US $ 150,000 for a liquid waste device for introducing powder formulations) to adapt the burners, and that savings are made on the fuels.

The incineration of waste (including organic liquids) in cement kilns is increasingly being tested on a commercial scale in OECD countries, but it is rarely used in developing countries for their obsolete pesticides. Until 1995, tests were carried out in Pakistan and Malaysia where modern cement kilns are available. In 1996, it was planned to incinerate relatively large quantities of DNOC in an oven in the United Republic of Tanzania. As these experiments are still limited, it is recommended for the moment to consider this method only for a special case of elimination of pumpable liquid formulations.

Other methods of incineration

Blast furnaces could theoretically be used to burn waste pesticides, but in practice the reduction reactions that occur in these stoves can cause incomplete burning and create pollution.

Incineration at sea on specially constructed vessels is a method that has been used to remove hazardous liquids. For environmental reasons, such as the emission of untreated gases and their absorption in seawater, as well as the risks of serious pollution that may be caused by accidents, the use of this method has been regulated by law. international. This process is no longer used for the disposal of pesticides and other hazardous wastes.

Shipping to a developed country for incineration

In many least developed countries, there are no environmentally sound local options for eliminating pesticides in an efficient and cost-effective manner. Under these conditions, it is necessary to consider exporting them to a country with a large-scale hazardous waste incineration plant.

Exporting is not necessarily an easy option:

· Before shipment, all waste must be repackaged and labeled in accordance with international treaties and recommendations for the international transport of dangerous goods;· International transport of hazardous wastes is governed by the Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal, and by several similar regional conventions (eg the Bamako Convention). The notification procedures prescribed by these conventions must be respected;

· The incineration company must be authorized by its government to import the waste to be incinerated. The difficulty of obtaining these authorizations depends on several factors, including the national cremation capacity at the time of the operation. In overcapacity, it is likely that these authorizations will be more easily granted. A country’s legislation can ban imports of hazardous waste.

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