Current practices are moving toward best use technology,
which attempts to reduce the amount of hazardous waste produced in the first
place. Any that is produced is most commonly destroyed or detoxified by a
number of methods with the resulting residues then disposed of. Hazardous
wastes may be treated to minimize their volume and make disposal easier, to
render the waste less toxic or hazardous, or to enhance or facilitate the
recovery and re-use of the waste components of a solution.
Treatments can be classified as physical, chemical,
biological or thermal. Physical treatments are used to separate
solids from liquids through the use of physical forces and mechanical
devices. Chemical treatments are used to neutralize (e.g., by mixing
acids and bases), precipitate, oxidize or reduce chemical components, or to
cause a chemical alteration of a liquid phase to produce a solid, vapour or
altered liquid phase. Biological treatments are used to biodegrade
diluted organic wastes, while thermal treatments are used to cause
the vaporization, oxidation or other destruction of liquid or solid phase
components.
ECO/LOG, Hazardous Waste Management Handbook 1985,
Corpus Information Services Ltd., Don Mills, Ontario, 1984, p. 210-240. Environment Canada, "Economic Profile of the Hazardous
Waste Management Service Industry Subsector in Canada," Fenco Newfoundland
Ltd., July 1988.
Generally, more than one process is used for waste
treatment, with some physical/chemical process often applied first to reduce
the volume of dilute aqueous solutions. No single process is suitable for all
categories of hazardous wastes and frequently several processes are linked in a
series or in a parallel configuration to form a waste-specific treatment. At
present, many of these treatments are well established in industrial
operations, where on-site treatment or partial treatment in order to reduce
bulk for transport is often desirable. Many of the methods for waste treatment
are listed below.
Physical: air stripping carbon adsorption
centrifugation dialysis
distillation evaporation
pond filtration flocculation and precipitation
flotation freeze crystallization
high gradient magnetic separation
liquid-liquid extraction resin adsorption
reverse osmosis sedimentation
steam distillation steam stripping
ultrafiltration Thermal: calcination
incineration molten salt
plasma destruction pyrolysis
supercritical fluid oxidation Chemical: catalysis
chemical dechlorination chlorinolysis
dissolution electrolysis
electrodialysis hydrolysis
ion exchange microwave discharge
neutralization oxidation
ozonation photolysis
reduction Biological: activated sludge
aerated lagoon anaerobic digestion
enzyme treatment trickling filter
Implementation of these treatments appears to be increasing,
together with an increase in the application of the "four-Rs"
(reducing, recovering, reusing and recycling). There is a decrease in the
quantities of high Btu wastes, oily wastes, solvents and dilute watery wastes
being received by waste disposal facilities and an increase in more
concentrated sludges and solids.
Considerable research is underway to develop new processes
for the treatment of hazardous wastes and to refine existing treatments.
Included are: waste solidification studies in Alberta; ultraviolet treatment,
reverse osmosis, ultrafiltration and plasma pyrolysis research in Ontario; and
reverse osmosis, fluidized bed combustion, chemical oxidation and high-rate
filtration and land farming in other parts of the country. A great deal of this
research is being conducted by the private sector through federal contracts.
Currently, a number of technologies are available for
managing, treating and destroying a wide range of hazardous wastes; they
continue to be tested and evaluated. These technologies include low temperature
oxidation (supercritical water), chlorine removal, pyrolysis, extraction and
concentration, vitrification, and biodegradation.
Hazardous wastes make up to 20% of Canada’s waste management
problem. Complementary federal and provincial regulations and cooperative
agreements are in place to control the handling, storage, disposal and
destruction of these wastes in Canada. Full implementation of these control
measures, however, is awaiting decisions by the provinces on the location of
new hazardous waste destruction facilities. In the meantime, existing treatment
and destruction facilities are handling larger amounts of wastes, and new
facilities have been brought on line for the safe elimination of such compounds
as PCBs.
The federal government will take further action to reduce
the generation of hazardous wastes and ensure their safe transportation and
disposal in Canada. These measures will include:
the development of a computerized tracking system to monitor
the movement of hazardous wastes in and out of Canada; this will allow Canadian
industry to participate more easily in international market opportunities to
recycle these products; by 1996, destroying all PCBs under federal jurisdiction and
establishing mobile incinerators in Atlantic Canada, Quebec and Ontario;
by 1996, in co-operation with the provinces, completing
regulations and guidelines for the safe management of hazardous waste streams,
including reduction, re-use, recovery, recycling, transportation, storage and
disposal; and supporting technology aimed at reducing, recycling and
re-using hazardous wastes, or at their safe destruction.
We could avoid many problems by reducing our output of
hazardous waste in the first place. Reduction of all hazardous wastes could be
achieved by: use of more efficient manufacturing processes, use of alternative
compounds, and the re-use as is, or the reprocessing, of waste streams.
Environment Canada estimates that up to one-half of all hazardous wastes are
recyclable. It is the Canadian government’s goal, outlined in the Green Plan,
to reduce the volume of hazardous wastes by 50% of the 1988 amounts by the end
of the century.
Environment Canada policy has been that re-use and recycling
should be encouraged as part of a comprehensive approach to managing hazardous
waste. This general view is supported by international organizations, including
the International Joint Commission (IJC), the European Community, WHO, UNEP and
NATO. The concept and practice of the "four-R’s" are slowly
being incorporated into hazardous waste management schemes by Canadian, British
and European chemical industries. In Ontario, less than 15% of the wastes
managed off-site are being reclaimed or recycled. In Alberta, the volume of
hazardous waste reclaimed or recycled increased by 350% from 1989-1991. One
practice that holds promise for improving the recycling of hazardous wastes is
the transfer of wastes from companies generating them to companies that can use
them in their operations. The federal and provincial governments assist in
matching the needs of potential users with supplies available from the
producers.
In Canada, the largest active hazardous waste exchange
program has been the Canadian Waste Materials Exchange (CWME) operating out of
the Ontario Research Foundation. In 1984, the Ontario Waste Exchange (OWE) was
instituted as a joint project with the Ontario Waste Management Corporation and
the Ontario Research Foundation to increase the effectiveness of the CWME
program. It appears that once the process of exchange has been initiated most waste
is exchanged continuously, at a rate of approximately 200,000 tonnes per year
and an estimated value of $6 million per year.
In 1981, Alberta also launched an active exchange program
called the Alberta Waste Materials Exchange, modelled after the one in Ontario.
Manitoba has a passive waste exchange program in which the province acts as a
coordinator but does not handle wastes directly.
Many hazardous wastes can be captured and detoxified at the
source through simple procedures such as filtration and the addition of
neutralizing with acids to produce a salt and water. Recycling of materials
within an industry (e.g., using closed-loop systems for cyanide recovery in the
electroplating industry and re-purifying solvents) can significantly reduce the
quantities of hazardous waste generated. Additionally, process changes in
industry can significantly reduce the amount of pollutants generated and
at the same time make considerable net savings. An example can be found at Bud
Automotive, Kitchener, where installing a reverse osmosis system has allowed
the reclaiming of industrial oil. Savings were also made through the reduction
in sewage charges, normally proportional to the company’s waste loading. This
company reclaimed its $100,000 expenditure on the reverse osmosis system in six
months.
A 1986 "Report to Congress on Minimization of Hazardous
Waste" said: A survey of 22 industrial processes concluded that if
existing techniques and new waste reduction technologies are fully used,
hazardous wastes could be reduced by one-third or more.The report cited as examples a paper products plant that
saved U.S. $1.8 million a year by recovering vaporized solvent, and a
chemical facility that saved U.S. $72,000 by reprocessing its spent solvent.
In general, it appears that the greatest deterrents to such
innovations have been the cheaper costs of landfills and the improper disposal
methods sanctioned until lately. These made the prospect of recycling seem too
expensive and troublesome.
- Erwin Villagomesa
Reference:http://publications.gc.ca/collections/Collection-R/LoPBdP/BP/bp323-e.htm#D.
Treatment(txt)
It is a good thing that they are able to find ways to make toxic waste useful
TumugonBurahin