After reading this article you will learn about:- 1. Definition of Hazardous Waste 2. Classification of Hazardous Waste 3. Management.
Definition of Hazardous Waste:
One of the primary difficulties encountered by the government and industries engaged in hazardous waste control programs is to realistically define hazardous waste. Within different jurisdiction there have been multiply levels of sophistication in identifying hazardous waste.
Definition of Hazardous Waste in Indian Context:
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Previous definition:
“Any solid waste, other than radioactive wastes, which by reasons of physical and/or chemical or reactive or toxic, explosive, corrosive or other characteristics causing danger or likely to cause danger to health or environment whether alone or when coming in contact with other waste or environment.”
New definition:
1. Waste substances, which are generated in the process included in column 2 of Schedule-1 and consist of wholly or partly of the waste substances referred to in column-3 of the same schedule. (as many as 42 types of processes and corresponding wastes have been identified).
2. Waste substances which consists wholly or partly of substances indicated in Schedule-2 unless the concentration of the substances is less than the limit indicated in the same schedule: and (wastes are categorized in five categories Class A, B, C, D & E depending on concentration limits, Class E does not have any concentration limit).
3. Waste substances indicated in Part-A of the Schedule-3 unless they do not possess any of the hazardous characteristics in Part- B of the same Schedule. (Part-A of Schedule-3 consists Lists A & B of the wastes to be applicable only for imports and exports. Part-B presents a list of hazardous characteristics).
Classification of Hazardous Waste:
It is important to have a clear understanding of the nature of materials involved to discuss the techniques for its management. The understanding is not limited to the physical state or composition but also to a complete scheme of characterization that includes all information necessary for disposal or recycling after treatment.
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A means of characterizing the waste is needed by the producer, disposer and the recycle. Practically, producer often does not have sufficient information, support, motivation or incentives to carry out treatment and/or disposal of hazardous waste and hence greater responsibility lies with the disposal contractor, if appointed for secured landfill out-side the company premises.
In order to help the producer, disposer and recycle in the identification of hazardous waste, United State Environment Protection Agency describe the testing of solid wastes for various hazard parameters such as corrosively, reactivity, ignitability as well as toxicity to designate the waste as hazardous (Table-1).
Management of Hazardous Waste:
Any sort of hazardous waste finds its management in either of the following ways:
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1. Waste minimization.
2. Waste treatment.
3. Waste disposal.
1. Waste Minimization, Reuse/Recovery:
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The green productivity concept always supports and encourages waste minimization for Cleaner production. The fact that reduction is better than management is a vital factor in making any strategy at the time of commissioning of any industrial project. More often this aspect is overlooked by other measures of material productivity like, manpower deployment, labor productivity and energy consumption and project out-put.
In-fact, waste reduction is a way of improving profitability and competitiveness. It not only minimize the need of abiding by pollution control regulations that force to spend more and more money for rather smaller increments of environmental protection but also reduces risks associated with the generation of such wastes. Waste -reuse or recycle is usually the step before pollution control but the economic limitations have to be taken into account.
Following are the various approaches to waste minimization and its reuse:
1. Alternative usage of waste products.
2. Modifying production process.
3. Altering primary source of waste generator by improving process technology and equipment.
4. Improving plant operations such as better house-keeping, improved material handling, and equipment maintenance, automating process equipment, better monitoring and improved waste tracking.
5. Optimising process conditions.
6. Introducing substitute raw materials which have a lesser potential of generating hazardous waste.
7. Redesigning or reformulating end products.
8. Segregating usable wastes and waste.
9. Segregating waste and hazardous waste.
10. Transferring the waste to another industry that can utilize it.
11. Reprocessing waste to recover energy or material.
12. Recycling potential waste or portion of it to the generator site.
2. Waste Treatment:
All the waste products whether from manufacturing process or treatment facility must be treated for the impurities hazardous to the nature to render them harmless to the environment.
The various treatment procedures can be classified as:
1. Physical.
2. Chemical.
3. Biological.
4. Thermal.
Usually a combination of the techniques is employed, to developed the most cost-effective and environmentally acceptable solution. Description of each one of the treatment processes is not the scope of this paper and hence only an overview is given here to have an understanding of these processes.
1. Physical Treatment:
Physical treatment of hazardous waste includes a number of separation processes commonly used in industry. It is of first importance where waste containing liquids and solids are separated to reduce cost.
2. Chemical Treatment:
These procedures involve the use of chemical reactions with the help of various chemicals to convert hazardous waste into less hazardous substances. The chemical treatment produces useful by- products and some-times residual effluent that are environmentally acceptable. Chemical reactions, either reduce the volume of the waste or convert the wastes to a less hazardous form.
3. Biological Treatment:
Biological treatment is an effective, efficient and cost- effective way to treat7remove hazardous substances from wastewater through biological agents. Hazardous waste materials are toxic to some of the microorganism. But a substance, which is toxic to one group of organism, may act as valuable source of food for another group.
Bio-treatment is required in ideal conditions for better growth of bio-agents and hence is a limitation factor also. Biological systems can lower the cost of downstream processes by reducing organic load if they are supplemented by other physical or chemical treatment steps.
4. Thermal Treatment:
Components of most hazardous wastes are carbon, hydrogen, oxygen, halogens, sulphur, nitrogen and heavy metals. Due consideration should be given to these constituents while applying incineration technology to the thermal destruction of hazardous waste.
In incineration, in general, waste is destroyed or reduced to CO2, H2O and other inorganic substances and these substances are harmless. The only limitation with this treatment process is generation of effluent or emission which is rather secondary pollution. Various treatment options for hazardous wastes are summarized in Table-3.
Various physical, chemical and biological treatment processes are depicted below:
3. Waste Disposal:
This is an ultimate option with every industry. Depending upon the characteristics of the wastes, two types of disposal methods can be used for hazardous wastes.
The predominant method for hazardous wastes disposal after treatment and reuse are:
1. Landfill.
2. Incineration.
Landfill:
Landfills are necessary because one cannot totally eliminate generation of hazardous waste and treatment technologies produce residues.
Landfills involve:
1. Low permeability soil linear and/or synthetic linear to prevent seepage of leachate to underground strata.
2. Drainage layer for leachate collection with leak detection system.
3. Diversion of surface run-of to avoid further pollution.
4. Impermeable cover.
5. Groundwater monitoring wells.
Issues with secure landfills:
Landfill options are highly risky options if not taken care. There is always threat of subsurface pollution.
The other considerations are as follows:
i. Only solid wastes are landfilled. Liquid wastes are solidified before being placed in a secure landfill.
ii. Landfill slope stability-subsidence of the cells is taken into account.
iii. Proper segregation and tracking of wastes is necessary to know where the waste has been placed in the compartment.
iv. Record keeping is must.
v. Maintenance of landfill cover integrity and monitoring of ground water. Various disposal options for hazardous wastes are summarized in Table 4.
