INGENIEUR
Figure 3: Microwave drying
Figure 4 shows a 10kW pilot industrial
continuous microwave dryer in Universiti
Teknologi Malaysia (UTM)’s High Temperature
Processing Laboratory, which contains a conveyor
feeding system and microwave chamber. The
sludge is fed into the microwave chamber by
the feeding system, where volumetric heating
takes place. The research findings indicate that
microwave drying is 30 times more efficient
than conventional convective drying. It took only
a minute for the core temperature in the sludge
material to reach 85°C while 500 minutes is
needed for convective drying to achieve the
same temperature. Microwave heating is more
efficient in sludge drying when compared to the
conventional convective heating method due to
the non-existence of surface limitation, shorter
falling-rate period and significant increase in the
drying process performance.
Energy Recovery
Incineration is a waste treatment process that
involves the combustion of organic substances
contained in waste materials. Incineration and
other high-temperature waste treatment systems
are described as “thermal treatment”. Incineration
of waste materials converts the waste into ash,
flue gas and heat (an exothermic reaction).
Incineration with energy recovery is one of the
several Waste-to-Energy (WtE) technologies. WtE
refers to the process of generating energy in the
Figure 4: Pilot Industrial Continuous Microwave
Dryer (photo taken at UTM’s High Temperature
Processing Laboratory)
form of electricity and/or heat from the primary
treatment of waste, or the processing of waste to
be used as a fuel source. WtE is a form of energy
recovery. According to the zero-emission concept,
dried sludge from WWTP can also be incinerated
as a feedstock for energy recovery prior to disposal
in landfills. Two types of incinerator — rotary-kiln
incinerator and fluidised bed incinerator — are
normally used to incinerate sludge.
Rotary-kiln Incinerator
Rotary-kiln incineration systems are ideal for
processing mixed industrial and HW that include
a combination of solid, sludge, and liquid waste
30 VOL 82 APRIL-JUNE 2020