By introducing the optic bag system, food waste will be packed
in an optic bag (e.g. a bag in green colour), while the residual MSW
will be packed in a common plastic bag or a pre-paid designated
bag if MSW charging scheme is implemented by the Hong Kong
Special Administration Region (HKSAR) Government. The optic
bag comes in two sizes, which are 10 l size with 270 mm
width 130 mm depth 480 mm height and 30 l size with
300 mm width 220 mm depth 640 mm height (Mepex, 2014).
All the packed wastes will still be disposed of at the existing collection
bins or rubbish chutes. By doing so, it will avoid the need for
the households and C&I sectors to reconfigure the waste storage
space in their properties. All the wastes will then be collected by
the refuse collection vehicles and transported to the respective
refuse transfer stations in Hong Kong. As such, no changes to collection
routines are required. It is observed that the optic bag is
comparatively thicker than the common plastic bag used in Hong
Kong. In Oslo, Norway, the optic bag remains intact in the optical
sorting plant after it is transported via refuse transfer vehicles.
The refuse transfer vehicles used in Oslo are of similar configuration
(i.e. with rear compactor) to those in Hong Kong. Hence,
it is believed that the optic bag will not be damaged when it arrives
at the refuse transfer stations in Hong Kong.
Upon arrival at the refuse transfer stations, all the waste bags
will be unloaded into a receiving pit. At this point, the optic bags
have yet to be separated from the other bags. All the bags will then
be sent to a main conveyor belt, in which an optic sensor technology
will be used to sort the bags. The green colour of the optic bag
allows the optical camera in the sorting plant to identify and sort
the optic bag from the other plastic bags automatically. When an
optic bag of green colour (i.e. food waste) is detected, a signal will
be sent to push the green bag off the main conveyor belt to a second
belt. An Enviflex system (i.e. an automatic bag-opener and
breaker of food waste) can be employed to separate the collected
food waste from the optic bag. In the system, a hydraulically driven
roller will be used to open the optic bag. The optic bag will be
pulled in a long strip and the food waste will be broken into pieces
of approximately 35–50 mm. The food waste and the optic bag will
then be screened for separation. Finally, the food waste will be
compacted and containerized in purposely built containers and
then transported to various food waste recycling facilities for further
treatment. Meanwhile, the other residual MSWs such as plastics
and papers, which are packed in common plastic bags, will be
sent to a proposed advanced incineration facility. After combustion,
the heat generated will be used in a steam turbine for
generating electricity.
T