Hazardous wastes are materials which are discarded after use from e- products, vehicles, clinical and medical products, fuel products (e.g. oil), gas exploration and extraction. Scientific research indicates that these include materials such as industrial solvents, waste oils, industrial sludges and chemical wastes.
Household, small businesses, farms, and the healthcare and construction sectors also generate quantities of hazardous waste including batteries, electrical equipment, healthcare risk waste, solvent based paint and varnish waste, sheep dip, and fluorescent lamps (Bauer and Herrmann, 1997).
Hazardous waste not only poses risks to the surrounding air, water, and soil, but also do harm to the ecological environment and human health through diversified channels (Li et al., 2015). This unit focuses on the best processes for the management of hazardous waste in the environment.
Hazardous Waste Management
Hazardous waste management consists of several functional elements, which are discussed below.
Hazardous wastes are generated in limited amounts in a community and information on the quantities of hazardous waste generated within a community and in various industries is often scanty.
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Hazardous waste generation outside the industry is irregular and very less in amount, rendering the waste generation parameter meaningless.
The only practical means to overcome these limitations is to conduct a detailed inventory and measurement studies at each potential source in a community. As a first step in developing a community inventory, potential sources of hazardous waste are to be identified.
The total annual quantity of hazardous waste at any given source in a community must be established through data inventory completed during onsite visits. The list of hazardous waste generation sources is presented in the table below.
b) Waste Categories and their Sources
|Biomedical research facilities, colleges and university laboratories, offices, hospitals, nuclear power plants, etc.
|Agricultural chemical companies, battery shops, college and university laboratories, construction companies, electric utilities, hospitals and clinics, industrial cooling towers, newspaper and photographic solutions, nuclear power plants, pest control agencies, photographic processing facilities, plating shops, service stations, etc.
|Biomedical research facilities, drug companies, hospitals, medical clinics, etc.
|Dry cleaners, petroleum reclamation plants, petroleum refining and processing facilities, service stations, tanker truck cleaning stations, etc.
|Construction companies, dry cleaners, ammunition production facilities, etc.
The spillage of containerized hazardous waste must also be considered an important source in addition to the sources listed.
The quantities of hazardous wastes that are involved in spillage are usually not known. The occurrence of spillage cannot be predicted and hence, the potential threat to human health and environment is greater than that from routinely generated hazardous waste.
c) Storage and Collection
Onsite storage practices are a function of the types and amounts of hazardous wastes generated and the period over which generation occurs.
Usually, when large quantities are generated, special facilities are used that have sufficient capacity to hold wastes accumulated over a period of several days.
If only a small amount is generated, the waste can be containerized, and limited quantity may be stored. Containers and facilities used in hazardous waste storage and handling are selected on the basis of waste characteristics.
For example, corrosive acids or caustic solutions are stored in fibre glass or glass-lined containers to prevent deterioration of metals in the container. Great care must be exercised to avoid storing incompatible wastes in the same container or location.
The waste generator, or a specialized hauler, generally collects the hazardous waste for delivery to a treatment or disposal site. The loading of collection vehicles is completed in either of the following ways:
Wastes stored in large-capacity tanks are either drained or pumped into collection vehicles;
Wastes stored in sealed drums or sealed containers are loaded by hand or by mechanical equipment onto flatbed trucks.
The stored containers are transported unopened to the treatment and disposal facility. In order to avoid accidents and the possible loss of life, two collectors should be assigned when hazardous wastes are to be collected.
The equipment used for collection varies with the waste characteristics, and the typical collection equipment are listed in the table below:
d) Equipment for Collection of Hazardous Waste
|Collection equipment and accessories
|Various types of trucks and railroad equipment depending on characteristics of wastes; special marking to show safety hazard; heavy loading equipment to handle concrete-encased lead containers.
|Flatbed trucks for wastes stored in drums; tractor-trailer tank truck combination for large volumes of wastes; railroad tank cars; special interior linings such as glass, fiber glass or rubber.
|Standard packers’ collection truck with some special precautions to prevent contact between wastes and the collector; flatbed trucks for wastes stored in drums.
|Same as those for toxic chemicals, with special colourings and safety warning printed on vehicles.
|Same as those for toxic chemicals with some restriction on transport routes, especially residential areas.
It should be noted that for short-haul distances, drum storage and collection with a flatbed truck is often used. The larger tank trucks, trailers and railroad tank cars are as hauling distances increase.
e) Transfer and transport
Typically, hazardous wastes are not compacted (i.e., mechanical volume reduction) or delivered by numerous community residents.
Instead, liquid hazardous wastes are generally pumped from collection vehicles and sludge or solids are reloaded without removal from the collection containers for transport to processing and disposal facilities.
It is unusual to find a hazardous waste transfer facility, where wastes are simply transferred to larger transport vehicles. Some processing and storage facilities are often part of the material handling sequence at a transfer station.
For example, neutralization of corrosive wastes might result in the use of a lower-cost holding tank on transport vehicles. However, great care must be exercised to avoid the danger of mixing incompatible wastes.
Processing of hazardous waste is done for purposes of recovering useful materials and preparing the wastes for disposal.
Processing can be accomplished on-site or off-site. The variables affecting the selection of processing site include the characteristics of wastes, the quantity of wastes, the technical, economic and environmental aspects of available on-site treatment processes and the availability of the nearest off-site treatment facility (e.g., haul distance, fees, and exclusions).
The treatment of hazardous waste can be accomplished by physical, chemical, thermal or biological means.
Irrespective of their form (i.e., solid, liquid, or gas), most hazardous waste is disposed off either near the surface or by deep burial. The various hazardous waste disposal methods are given in the table below:
|Types of wastes
|Forms of waste
|Deep well injection
Functions: Di=disposal; St=storage;*Wastetypes:1=inorganic chemical without heavy metals; 2=inorganic chemical with heavy metal;3=organic chemical without heavy metal; 4= organic chemical with heavy metal; 5= radiological; 6=biological; 7=flammable and 8=explosive. #Wasteform: S=solid; L=liquid and G=gas.
Although controlled landfill methods have been proved adequate for disposing of municipal solid waste and limited amounts of hazardous waste, they are not suitable enough for the disposal of a large quantity of hazardous waste because of the following reasons:
Possible percolation of toxic liquid waste to the groundwater;
Dissolution of solids followed by leaching and percolation to the groundwater;
Dissolution of solid hazardous wastes by acid leachate from solid, followed by leaching and percolation to the groundwater;
Potential for undesirable reactions in the landfill that may lead to the development of explosive or toxic gases;
Volatilization of hazardous waste leading to the release of toxic or explosive vapours to the atmosphere; and
Corrosion of containers with hazardous wastes.
In general, disposal sites for hazardous wastes should be separate from those for municipal solid wastes. As hazardous wastes can exist in the form of liquids, sludges, solids and dusts, a correct approach for co-disposal for each of the hazardous wastes should be determined.
To preclude the co-disposal of incompatible wastes, separate storage areas within the total landfill site should be designated for various classes of compatible wastes (Phelps etal., 1995).
Liquid wastes are usually stored in a tank near the site and can be introduced into the landfill by means of trenches or lagoons, injection or irrigation. During disposal of lightweight wastes, the disposal area must be kept wet to prevent dust emissions.
Hazardous solid waste characterized by a high degree of impermeability as such must not be disposed of over large areas. When containerized wastes are to be disposed of, precautions must be taken to avoid the rupture of containers during the unloading operation and the placement of incompatible waste in the same location.
To avoid rupturing, the containers are unloaded and placed in position individually. The covering of the containers with earth should be monitored and controlled carefully to ensure that a soil layer exists between each container and the equipment placing the soil does not crush or deform the container.
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While designing a landfill site for hazardous waste, provision should be made to prevent any leachate escaping from landfill site. This requires a clay liner, and in some cases, both clay and impermeable membrane liners are used.
A layer of limestone is placed at the bottom of the landfill to neutralize the pH of leachate. A final soil cover of 25 cm or more should be placed over the liner. The completed site should be monitored continuously, both visually and with sample wells.
In conclusion, from the foregoing, it can be concluded that for effective hazardous waste management, the total annual quantity of hazardous waste at any given source in a community must be established through data inventory completed during onsite visits.
Great care must be exercised to avoid storing incompatible wastes in the same container or location. As hazardous wastes can exist in the form of liquids, sludges, solids and dusts, a correct approach for co-disposal for each of the hazardous wastes should be determined. It is imperative to use the appropriate materials to prevent leachate escaping from landfill site during its design.
Management of hazardous wastes follows the functional elements of solid waste, viz., generation, storage and collection, transfer and transport, processing and disposal;
Processing can be accomplished either on-site or off-site to recover useful materials and to prepare the wastes for disposal;
Regardless of their forms, most hazardous wastes are disposed of either near the surface or by deep burial; and
Controlled landfill methods used for disposing of municipal solid waste are not suitable for the disposal of a large quantity of hazardous waste.