Figure 2: Overview of scheduled waste generation
plant. The wastewater shall be treated prior its
discharge to the water bodies. The wastewater
treatment generates sludge. Air pollutant shall be
captured prior to being emitted to the atmosphere.
Depending on methods and technologies of air
pollution control system, either ash or sludge
will be generated after the treatment. The ash
and sludge generated from the pollution control
system are SW.
The safe and economical disposal of sludge
has always been of major concern. One of the
options for sludge disposal is incineration prior to
landfilling. Incineration converts sludge into ash
as well as drastically reducing the volume and
mass of residual solids materials for landfilling.
However, industries face huge problems of sludge
disposal due to its high disposal cost. Sludge from
wastewater treatment plant (WWTP) contains high
water content, up to 90% wet basis in certain
cases. In this case, the industries could save up
to 90% of the disposal costs by removing this
water. The conventional drying methods such as
mechanical dewatering (belt filter press/decanter),
and convective drying are ineffective and requires
large space. Thus, new treatment technology has
to be developed to achieve effective drying.
SCHEDULED WASTE RECOVERY
TECHNOLOGY
Microwave Drying
Microwave is an electromagnetic wave covering
a frequency range of 300MHz - 300GHz. For
heating purpose, the operation frequency used
falls within 915-2450MHz. Microwave interacts
with dielectric materials such as water and
gives up energy to increase the materials
temperature. Water is a major polar component
in sludge materials. During microwave drying,
vibrations of water molecules take place in an
alternating electric field (Figure 3). The increased
kinetic energy in water molecules weakens the
attraction between the water molecular and
other substances in the sludge, thereby aiding
the migration of water molecules to the surface.
This special mechanism is termed as volumetric
heating (where the heating take place at all
points within the material), with higher thermal
efficiency and shorter drying time compared
to the commercial conductive drying (heat
movement from exterior into the material), which
suffers from heat transfer co-efficient of the
material.
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