In
response to clause 3.3 of the EIA Study Brief, the Project Proponent has explored
different construction methods and operation arrangements for the Projects in a
view to avoid or minimize adverse environmental impacts. This section summarizes the alternatives that
have been considered during the planning and design stages and the rational for
choosing the preferred options.
The proposed biodiesel plant will be
located at the
During the project planning and design
stage, two construction methods for the jetty were considered. The first option (Option 1) (see Figure 2.2b)
is to construct a vertical seawall with concrete blocks. Standard concrete seawall blocks will be
placed by crane on compacted rockfill foundation and
the space between the concrete block seawall and the land will be filled with
compacted granular fill. The area
reclaimed will be paved with concrete or bitumen macadam. In this option, the reclamation will obstruct
the water flow in the area and thus may affect the flow regimes during the
operational phase. The habitat and
marine organisms on the existing seawall will be directly impacted as a result
of the construction of the jetty.
Another option considered is construction
of a piled deck jetty (Option 2) (see Figure 2.2c). The jetty will be in form of a reinforced
concrete deck supported by marine piles (about 1m diameter each). The piles will be installed using drilling
rig and hence will have minimal impact on the existing seawalls. No dredging works or reclamation will be
required. Although there may be
localised effects due to physical resistance of the piles, the water flows
through the piled structure and the bathymetry will generally be
maintained. It is not expected that the
piles will cause adverse impacts to the water flow regime at the jetty during
operation phase. Unlike Option 1, this
option will only affect the areas where the piles will be placed and hence the
potential impacts to marine ecology will be very much reduced and minimal. The piles will also serve as artificial
habitat for the settlement and re-colonisation of marine assemblages. Therefore, Option 2 (ie
a piled deck jetty) is selected for detailed engineering design and adopted for
EIA Study.
A tank farm will be constructed within the
biodiesel plant for storage of feedstock and products. With respect to the nature of the materials
to be stored, concrete tanks are more susceptible for cracks and hence have a
higher change of leakage. For storage
of similar materials, steel tanks are commonly used. Steel tank offers better mechanical,
technical and safety standards. In
addition, the concrete tanks will have to be constructed on-site and will
generate more construction waste and have a higher potential to cause dust and
noise impacts. The storage tanks will
therefore be constructed with structural steel.
The tanks will be prefabricated off-site
and delivered to the site for installation.
To ensure the integrity of the tanks, the tanks will be installed on a
reinforced concrete platform which will be supported by a thick layer of
granular fill to allow for settlement during full load. This will minimize the potential leakage from
the tanks. The tank farm area will be bunded (at least 110% of the volume of the largest tank) to
contain ay spillage or leakage from the tanks.
Most of the pipelines for conveying raw
materials, semi-products and end-products within the Site are overhead
pipelines installed on the pipe bridges.
Overhead pipelines are preferred to underground pipelines as any leakage
of the pipelines can be easily detected by visual inspection. The potential for land contamination can be
minimized if leakage occurred. All
pipelines on the pipe bridges are welded and the connections (such as flanges
and values) will be placed within or above a bunded
area to minimize the environmental impacts if leakage occurred at the
joints.
The minimum height of all pipe bridges is
4.5m above ground level to prevent them from collision by vehicles. Height check and control will be implemented
at the site entrance to ensure no vehicle taller than 4.5m will enter to the
pipe bridges areas. The columns of the
pipe bridges will be protected by a concrete wall.
The biodiesel manufacturing process
adopted for the plant has taken accounted of the best available technology
(BAT) for the multiple feedstock processes.
Material recycling and waste minimization have been carefully considered
in the design of the production processes which allow better material
utilization and minimize the generation of solid waste and wastewater. The adopted technology has the following
characteristics:
·
Generate saleable by-product:
All by-products are saleable. The
main by-products are glycerine and potassium sulphate which can be sold for
chemical, pharmaceutical and other industrial applications. This will avoid the need to dispose the
by-products generated from the processes.
·
Offer a high material-to-product
conversion: During the processes, sub-standard products
will be recycled back into the system at various stages. This will minimise the generation of chemical
waste and wastewater from the plant.
·
Minimize energy use:
The main biodiesel production line is a semi-continuous process which is
operated at atmospheric pressure and room temperature. This minimizes the energy consumption of the
plant. In addition, the bioheating oil (which is a lower grade biodiesel) and
biogas generated from the biodiesel production process and wastewater treatment
plant, respectively will be reused on-site as a fuel
for the boilers. This minimizes the use
of petroleum based fuel (eg diesel or Town Gas).
·
Choose the most suitable raw materials:
The raw materials used for the manufacturing processes are chosen to
minimize the potential environmental, health and safety impacts. Table
2.3a summarizes the rationales for choosing raw materials to be used for
the biodiesel production processes.
Table 2.3a Raw
Materials to be used for the Biodiesel Production Processes
|
Function in the Production Line |
Raw Materials |
Other Potential Materials |
Rationale |
|
Strong
acid to be added to carboxylic acids
in the fat to minimize reaction time |
Sulphuric Acid |
Other strong
acids |
A saleable
by-product potassium sulphate (a raw material for agricultural fertilisers)
will be produced and thus minimized waste generation |
|
Simple alcohol
to replace glycerol in the feedstock during the transesterification
process |
Methanol |
Other simple
alcohol (eg ethanol) |
To produce a
saleable product, fatty acid methyl ester.
Methanol has been attributed a harmfulness ranking of “low” and has a
lower photochemical ozone creation potential (POCP) of 21 comparing with that
of ethanol (45) |
|
Acid to be used
in the washing steps |
Phosphoric Acid |
Other acids (eg sulphuric acid) |
To reduce the
input of sulphur-based materials and hence minimise the risk of sulphur being
added to the biodiesel. Phosphoric acid
is more effective than other acids in removal of impurities. |
|
Alkaline
catalyst for various stages of process |
Potassium
Hydroxide |
Other alkaline
catalyst (eg sodium hydroxide) |
To produce a saleable
product, potassium sulphate (a solid which is easy to handle). The use of sodium hydroxide will produce
sodium sulphate which is highly soluble.
It will be discharged into liquid waste stream and cannot be reused |
Various VOC recovery and abatement
technologies listed in the European Commission’s Integrated Pollution
Prevention and Control (IPPC) have been reviewed. Wherever possible, the VOCs
recovered will be re-used within process.
The VOC recovery technologies considered during the design stage are
listed in Table 2.3b.
Table 2.3b VOC
Recovery Technologies
|
Technique |
|
Recycling Potential |
|
Condensation |
To condense the VOCs
by increasing the pressure or reduce temperature |
Condensate can be reused in the system |
|
Absorption |
Remove VOCs
from a gas stream by mass transfer into a scrubbing liquor |
Resulting a mixture which can recycled |
|
Adsorption |
Remove VOCs from
a gas stream by passing the gas through a solid medium |
Typically for final polishing of the
exhaust gas. The VOCs
cannot be recovered for recycling |
|
Thermal Oxidation |
Complete thermal breakdown of VOCs will lead to the formation of carbon and water. This
can be combined with existing combustion units such as boilers or biogas
flares |
Do not enable recycling |
Condensation is chosen to recycle the
majority of the spent methanol. Methanol
from the process exhaust emissions will be recovered for reuse using condensers
and a wet scrubber which will use water as the scrubbing medium. The spent scrubber water will be recycled and
the methanol will be separated in the demethanolisation/
dewatering column. The methanol will be
reused in the production processes.
Although the VOCs arising from feedstock
pre-treatment and storage tanks are expected to be low ([1]), the exhaust air or vent gas from the
pre-treatment and storage tanks which will be removed by a two-bed carbon
filter adsorption system. The potential
VOC emission from the plant will therefore be negligible. During the
loading of the methanol tank, the vent gas will be recovered/ recycled back to
the tanker so that the vent gas will not be discharge to the atmosphere.
In order to minimize potential odour
nuisance, all the GTW and WCO will be unloaded at the designated stations via
flexible hoses or pipelines in a closed system arrangement. The GTW screening room and screenings
storage room will be provided with ventilation at all time (except during
maintenance period) to maintain a slight negative pressure to prevent odour
emissions to the atmosphere. The exhaust
air will be scrubbed. Instead of
discharging to the atmosphere, the scrubbed air will be used as part of the
ventilation air for the enclosed wastewater treatment tanks and air supply for
the aeration tanks. This will further
minimise the discharge of odorous air to the atmosphere (please refer to Section 3.2.2 for further details).
All processing vessels and tanks in the
biodiesel plant, including wastewater treatment tanks, will be enclosed to
prevent odour emissions ([2]).
The vent gas will be scrubbed prior to discharge to the atmosphere
(please refer to Section 3.2.2 for
further details).
The surplus sludge from the sludge
thickener will be dewatered to at least 30% dry solids (about 1.3 tpd) using a belt press in the Sludge Dewatering Room. The dewatered sludge will be stored in
container inside the Sludge Room. The
roller door of the Sludge Room will be closed except for removal of the sludge
container for disposal. The Sludge Dewatering
Room and Sludge Room will be provided with a ventilation system and the exhaust
air will be scrubbed (by the final scrubber, see Figure 4.4a) prior to discharge to the atmosphere. A slight negative pressure will be
maintained at all times when the sludge dewatering process is carrying out and
sludge is being stored in the Sludge Room.
The sludge container will be properly covered with metal flip doors or
tarpaulin before the roller door of the Sludge Room is opened.
Source reduction
and segregation are adopted in the design of the wastewater management system
to minimize the needs for treatment.
Source reduction measures include recycling of the biodiesel wash water
through the process and careful control of the process and utilities. In addition, containment bund will be
provided for the material storage tanks and good housekeeping will avoid/
minimize the potential for land contamination and surface water contamination.
The Site will be
provided with separate surface water and foul water drainage systems to prevent
untreated sewage/ potentially contaminated stormwater runoff from discharge into
the sea (see Figure 3.2h). The proposed drainage system consists of
three separate sub-systems:
·
Wastewater from the process, utilities and high-risk
yard areas (ie tank farm and GTW reception area);
·
Surface
water runoff from low risk areas (ie non process
area); and
·
Surface
water runoff from roofs.
The wastewater collected from the process
and high-risk yard areas will be collected and treated at the on-site
wastewater treatment plant to meet the statutory requirements for discharge to
foul sewer. In order to prevent
contaminated surface runoff from discharge off-site, surface runoff of the bunded area will pass through an oil interceptor before
discharge to the stormwater drainage system of the
TKOIE.
Wastewater
generated from feedstock pre-treatment and glycerine dewatering processes will contain trace amount
of oils and fats and have a high COD concentration. The wastewater will be treated at the on-site
wastewater treatment plant prior to discharge to the foul sewer leading to the
TKO Sewage Treatment Plant. Different treatment
methods have been considered in the planning and design stages and they are
described below.
Pre-treatment options including grit
separation, sedimentation (including coagulation and flocculation), air
flotation, filtration and membrane filtration have been considered. Three pre-treatment techniques, including
the dissolved air flotation (DAF), settlement after chemical treatment and
membrane filtration, can achieve more than 80% fat/oil removal efficiency and
therefore they are further studied. Table 2.3c compares these
technologies. Oil-water separator and
DAF with prior equalisation and pH adjustment are selected for the design of
the on-site wastewater treatment plant.
Table 2.3c A
Comparison of Potential Wastewater Pre-Treatment Technologies
|
Technique |
Advantages / Disadvantages |
|
Dissolved Air Flotation (DAF) |
·
Ideally
suited to treat wastewaters containing high concentrations of fats and oils ·
Can
reduce COD/BOD concentrations by more than 80% |
|
Settlement / Sedimentation |
·
Much
larger footprint than DAF or membrane filtration ·
The
process is not induced / controlled by a physical separation process ·
Settlement
tank requires a large open area and also have a higher potential for odour
emissions |
|
Membrane Filtration |
·
Fats
have a high potential to block the membrane which will lead to a rapid tail
off of removal efficiency |
After pre-treatment (ie
DAF process), the wastewater will be conveyed to the biological treatment
processes to further reduce the organic loading. An anaerobic treatment process, Internal
Circulation (IC) reactor (utilising the upflow anaerobic
sludge blanket (UASB) technology), will be used to further reduce the organic loading of the
wastewater. The wastewater will then be
treated by an activated sludge treatment process to reduce the remaining COD
from the anaerobic digestion. These
treatment technologies were chosen because of their high removal efficiency for
organic matters in the wastewater. A
combination of the IC reactor and an activated sludge treatment process has
been widely used to treat wastewater with high COD/BOD (such as fermentation,
paper and pulp, brewery and food etc).
PFAD and methanol will be received from
barges via the on-site jetty. Biodiesel
will be pumped from the storage tanks to the barge. Different transfer methods, such as drums and
ISO tankers, hose pipe, etc were considered for the transfer of materials from
the jetty to the tank farm to minimize the risk of spillage and hence water
pollution and land contamination. Dry coupling will
be used to connect the loading/unloading pipes to prevent leakage of the
material at the joints. This technology
has been used in a number of existing biodiesel plants in
Barge with well insulated
compartments will be used to
minimise energy required to heat up the PFAD and maintains the material in
liquid during transfer. The PFAD will be pumped to the
storage tank through a coiled heat pipeline.
ISO Tanker barge can also be used as the heating coils can be put into the tanker
if heating is required. ISO tanker barge has been used for transfer
of oil at the Shell Oil Terminal in Tsing Yi. The bulk transfer of feedstock (PFAD and
methanol) by barge will also minimise the traffic associated with delivery of
the materials by road.
Other precautionary measures such
as loading/unloading of materials at a bunded area and on-site drainage
system will also minimise the risk of water pollution
(see Section 6).
The tank farm is the main area for on-site
storage of raw materials and products.
All tanks and pumps are designed to fulfil both local and international
standards for mechanical, technical and safety requirements.
The layout of the tanks has been designed
to comply with local fire protection requirements. The methanol storage tank will be placed in
a separate bunded area. It will be located more than 15m from other
dangerous goods tanks (such as the biodiesel storage tanks) and away from the
site boundary in order to minimise the potential risk to off-site population. The other storage tanks for the dangerous
goods are located at least 10m from site boundary so that there will be
sufficient buffer zone to minimize potential risk to off-site population.
The Project Proponent has explored various
construction methods and operation arrangements for the Project in a view to
avoid or minimise adverse environmental impacts. Practicable means to prevent marine pollution
and hazardous incidents arising from transfer of PFAD and methanol from the
jetty to storage tanks and biodiesel from the storage tank to the jetty have
been considered in the design. The
design and operation of the biodiesel plant have taken account of the best
available technology to minimise potential environmental pollution and risk to
the public.