Page 23 - Materials Chemistry, Second Edition

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Sustainable Industrial Design and Waste Management
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Physical treatment: Physical processes for waste treatment include screen-
ing, sedimentation and clarification, centrifugation, flotation, filtration, sorp-
tion, evaporation and distillation, air or steam stripping, membrane-based
filtration processes, etc. These processes are mostly applied to liquid haz-
ardous wastes, and involve the separation of suspended or colloidal solids
from the liquid phase. The selection of the technology depends mainly on
the concentration and characteristics of the suspended solids relative to the
liquid phase. Physical processes segregate the waste from one form to another,
reduce the volume, and concentrate the solids to facilitate further treatment
or further actions. Whenever a waste containing liquids and solids is to be
treated, physical separation of the solids from the liquid should be considered
first because it is generally cost-effective to treat a low volume, high con-
centration waste. Usually physical treatment is used in combination with
other treatment technologies for optimum waste treatment and disposal.

Chemical treatment: Chemical treatment involves the use of chemical reac-
tions to transform harmful waste into less harmful, or non-harmful waste, or
make it less mobile in the environment. Many different types of chemical
treatment processes are used in waste management such as neutralization,
precipitation, coagulation, flocculation, oxidation, reduction, etc. Chemical
treatment can have some advantages such as volume reduction and promot-
ing resource recovery from wastes. Because it can be employed for resource
recovery, and to produce useful byproducts and environmentally acceptable
residues, chemical treatment should be considered before sending an untreated
hazardous waste to an off-site landfill for disposal. Also, since liquid wastes
should not be disposed of in a landfill without prior treatment, chemical treat-
ment is often used to make it either non-hazardous, or at least chemically
convert it to a solid or semi-solid, which makes the contaminants chemically
stable and not very mobile in the landfill environment.

Biological treatment: Biological treatment can be used for organic liquid
wastes or organic solid wastes such as municipal wastewater, landfill
leachate, contaminated soil, etc. Biological treatment may be categorized,
according to the oxygen utilization, into aerobic and anaerobic processes. In
the aerobic process, oxygen is required to decompose organic matter as the
aerobic bacteria needs to grow and multiply. The anaerobic process uses
anaerobic bacteria, in an oxygen deficient atmosphere, to decompose organic
matter. Aerobic organisms are most commonly used to treat industrial and
municipal wastewater. Anaerobic systems are usually used for the treatment
of concentrated organic waste or organic sludges. Technologies have been
developed in which anaerobic bacteria can be used to treat complex toxic
organics such as solvent contaminated groundwater. Aerobic bacteria is used
commonly for the treatment of petroleum contaminated soils and sludge.
Sustainable treatment: Sustainable treatment is a new term and is defined as
“the type of treatment or combination of different types of treatments able