HAZARDOUS WASTE TREATMENT - Environmentally Conscious Materials Handling - page 175

that influent contaminant concentration is detected in the effluent coming off the
carbon column (Eckenfelder 2000). Contaminant concentration in the effluent
will increase after breakthrough. However, if one runs the carbon columns in
the series, the carbon bed in the first column is fully utilized before reaching
the second column, and not much of the contaminant will be released to the
environment.
The major design considerations include flow rate and headloss, nature and
amount of organic compounds present, empty bed contact time required, filtration
rate, and carbon regeneration frequency and methods. It is feasible to regenerate
spent carbon for economic reasons. Different modes of regeneration include ther-
mal methods, solvent extraction, acid or base treatment, and chemical oxidation.
When determining the suitability of using GAC for specific hazardous waste, the
change in capacity of carbon through consecutive regeneration cycles should be
taken into consideration (Eckenfelder 2000).

2.3 Oxidation

2.3.1 Chemical Oxidation
The objective of chemical oxidation is to detoxify waste by adding an oxidiz-
ing agent and to chemically transform waste components to compounds such as
carbon dioxide and water. It is a well-established technology capable of treating
a wide range of liquid hazardous waste that include organic compounds such as
pesticides, phenols, detergents, chlorinated VOCs, phenolic waste, wastes with
low organic content, and cyanide. The chemicals that are reduced are the con-
taminants.
Oxidation-reduction reactions occur in pairs to form an overall REDOX reac-
tion. Oxidizing agents are nonspecific and will react with any reducing agents
present in the waste stream.
Hazardous waste treatment by chemical oxidation involves mixing two liq-
uid streams—the waste and the treatment chemical—or contacting the aqueous
solution with gas. The mixing reactors can be in batch, completely mixed, or
plug flow mode. Mixing can be provided by mechanical agitation, introducing
air through the reactor.
The oxidizing chemicals have the following properties:
• Ozone . Ozone is a very powerful oxidant. It is unstable and dissociates
into side reactions rapidly. Its high free energy indicates that the oxidation
reaction may proceed to completion. Ozone dissociates to oxygen very
rapidly and must be generated on site.
• Hydrogen peroxide . Hydrogen peroxide is effective in oxidizing toxic haz-
ardous wastes and cyanide-bearing wastes. Hydrogen peroxide generates
hydroxyl radicals ( OH) in the presence of a catalyst such as iron. The

radical reacts with organics and reduced compounds to produce a reac-
tive organic radical (

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R). The organic radical reacts again with peroxide to