2
PROJECT DESCRIPTION
2.1
Need for the Project
2.1.1.1
Over the past few decades, the Government completed
many sewage collection, treatment and disposal projects in order to improve the
water quality of Hong Kong waters. The
most important project is the Harbour Area Treatment
Scheme (HATS) Stage 1. The Government is currently implementing HATS Stage 2A
to convey more sewage to Stonecutters Island Sewage Treatment Works (SCISTW)
for chemically enhanced primary treatment (CEPT).
2.1.1.2
While the water quality of Hong
Kong waters continues to be improved, more sewage sludge, which is
the waste generated after the sewage treatment process, will need to be
handled. Currently, about 813 wet tonnes of
sludge is generated from 11 sewage treatment works (STWs)
in Hong Kong. The type and estimated amount of
sludge generated from these are listed in Table 2.1.
Table 2.1
Current and Future Sludge Generation from 11 Sewage Treatment
Works in Hong Kong
|
|
Sewage Treatment Works
|
Sludge Type
|
Estimated Sludge Generation (1)
wet tonne/day
(%)
|
|
Current
|
Future
|
|
1
|
Stonecutters Island STW
|
Undigested CEPT Sludge
|
593 (73%)
|
1,750 (87.5%)
|
|
2
|
Pillar Point STW
|
|
3
|
San Wai STW
|
|
4
|
Sham Tseng STW
|
|
5
|
Siu Ho Wan STW
|
|
6
|
Sai Kung STW
|
Digested Primary &
Secondary Sludge
|
220 (27%)
|
250 (12.5%)
|
|
7
|
Shatin STW
|
|
8
|
Shek Wu Hui
STW
|
|
9
|
Tai Po
STW
|
|
10
|
Yuen Long STW
|
|
11
|
Stanley STW
|
Undigested Secondary Sludge
|
|
TOTAL
|
813 (100%)
|
2,000 (100%)
|
Notes:
(1)
Based on a solids content of 30% for the dewatered sludge
2.1.1.3
At present, landfilling is
the only disposal means of dewatered sewage sludge in Hong Kong. However, this
current practice is considered not sustainable as sludge takes up precious
space of the existing landfills, which are anticipated to reach their
capacities in early to mid 2010 decade.
2.1.1.4
Due to its high water content, dewatered sludge has to
be co-disposed with municipal solid waste (MSW) and construction waste in a
ratio of 1:10. Excessive disposal of sludge would lead to slope failure
at landfills, thereby causing serve disruption to operation or even closure of
landfills. However, this disposal ratio would be difficult to be achieved
due to the decrease in MSW with the implementation of various waste management
measures in accordance with “A Policy Framework for the Management of
Municipal Solid Waste (2005-2014)”, and the increase in sludge production
after the commissioning of HATS Stage 2A and expansions of some existing sewage
treatment works (STWs).
2.1.1.5
Disposal of biodegradable waste including sewage sludge
at landfill is not in line with international trend as it produces more
greenhouse gases. Thus, the current practice is not considered as a
sustainable disposal means of dewatered sewage sludge.
2.1.1.6
Therefore, a sustainable alternative for sludge
disposal is crucially needed.
2.1.1.7
If a sustainable alternative for sludge disposal is not
sought (i.e. scenario without the Project), dewatered sludge would continue to
be disposed of at landfills, placing burden on the limited landfill capacity in
Hong Kong and shortening the life of the landfills in a rapid rate. With
the increase in the amount of sludge and decrease in the amount of MSW to be
disposed of at landfills, the stability of the landfills would be jeopardized,
thereby causing serve disruption to operation or even closure of
landfills.
2.1.1.8
With the proposed STF, the amount of waste to be
disposed of at landfills will substantially decrease as the volume of waste
generated after the sludge treatment process would only be about 10% of the
original volume. The landfill life can be extended. Besides, the
production of greenhouse gases due to disposal of sewage sludge will be
reduced.
2.2
Selection
of Suitable Sludge Treatment Technology
2.2.1
Consideration of Different
Technologies for Sludge Treatment
2.2.1.1
A review of international sludge management practices
was carried out. The key findings of the review are summarized below:-
(i)
There is an increasing application of incineration for
treating sewage sludge before final disposal. This method is most widely
used in Japan, where there is also an increasing extent of further treatment on
the incineration ash to minimize land requirement for final disposal. The
significant use of incineration in Japan is primarily driven by the scarcity of
land available for sludge/ash disposal. There is also apparent increasing trend
in using incineration in the U.S., France, Germany, Luxembourg, the Netherlands,
and the UK. Moreover, for new incineration installations, the use of fluidized
bed systems becomes prevalent. Use of co-incineration of sewage sludge with MSW
is however limited.
(ii)
In the U.S., there is a decreasing concern on dioxin
emission from fluidized bed incinerators. In December 1999, USEPA announced in
the Federal Register that, based on the results of risk assessment, it was
proposing not to include dioxins emission limits for sludge incinerators. USEPA
based its decision on the fact that the 254 sludge incinerators emit a combined
total of 6 grams TEQ (dioxins)/year out of the 2,745 grams TEQ (dioxins)/year,
which was only about 0.2%, of the total released to the atmosphere in the
U.S.. In addition, USEPA determined that the highest associated risk
factor was low. There are still however regulations governing the dioxin
emissions in Japan and EU.
(iii)
The main method for ultimate sludge disposal is land
application in Singapore, the US and European countries. In these
countries, the most common methods are sludge stabilization and dewatering.
Sludge drying is also increasingly used with land application particularly when
there is a market for the dried/palletized products.
(iv)
Direct sludge disposal to sanitary landfill is
decreasing and this trend seems to continue because of the capacity constraints
of available sanitary landfills in most countries. This is also supported from
environmentalist viewpoints due to the possible associated greenhouse effects.
2.2.1.2
Based on the review, fluidized bed incineration and
heat drying were shortlisted for further evaluation because they were proven
technologies and applied widely for bulk volume reduction before disposal at
landfills in order to sustain the landfill life.
2.2.2
Option Evaluation Criteria
2.2.2.1
The proposed criteria used to evaluate the shortlisted
sludge treatment technologies for the STF are grouped into the following three
main areas:-
(i)
Environment
w
Waste reduction
w
Potential for reuse
w
Human health impacts
w
Air quality impacts
w
Water quality impacts
w
Noise impacts
w
Ecological impacts
w
Landscape and visual impacts
(ii)
Engineering
w
Process performance
w
Operation and maintenance
w
Operational flexibility
w
Operational security
w
Land requirement
(iii)
Financial Analysis
2.2.3
Evaluation of Shortlisted Sludge
Treatment Options
2.2.3.1
Table 2.2 shows the
results of the evaluation of the fluidized bed incineration and heat drying.
Table 2.2
Evaluation of Shortlisted Sludge Treatment Technologies
|
Evaluation Criteria
|
Incineration
|
Heat Drying
|
Remarks
|
|
Environmental Acceptance
|
|
Waste Reduction
|
***
|
*
|
The
end volume requiring landfilling after heat drying
is about 2 times more than incineration.
|
|
Potential for Reuse
|
***
|
*
|
Potential
markets for salty dried pellets (which can be used as fertilizers) produced
from heat drying are limited, while incineration can produce extra energy for
reuse.
|
|
Human Health Impacts
|
**
|
***
|
No
adverse impact is expected from both incineration and heat drying based on
the preliminary findings. However, as heat drying produces less air
pollutants, heat drying has a higher score in both human health and air
quality impacts.
|
|
Air Quality Impacts
|
**
|
***
|
|
Water Quality Impacts
|
**
|
**
|
|
Noise Impacts
|
**
|
**
|
|
Ecological Impacts
|
**
|
**
|
|
Landscape and Visual Impacts
|
**
|
**
|
|
Engineering Feasibility
|
|
Process Performance
|
**
|
***
|
Process
performance for both incineration and heat drying are acceptable. However,
incineration has a higher potential down-time. It is also more complex,
and requires close operation control and significant maintenance expertise
for proper operation.
|
|
Operation and Maintenance
|
**
|
***
|
|
Operational Flexibility
|
*
|
**
|
Heat
drying can adapt more readily to changes in calorific value than
incineration.
|
|
Operational Security
|
***
|
*
|
Heat
drying has a potential dust explosion risk.
|
|
Land Requirement
|
*
|
**
|
Incineration
requires a larger footprint than heat drying.
|
|
Financial Aspect
|
|
Life cycle cost
|
***
|
*
|
Heat
drying has a higher life cycle cost due to its higher consumption of fuel and
power.
|
Note:
* Less
Preferable **
Preferable *** Highly
Preferable
2.2.3.2
Although the heat drying technology is marginally
better than the incineration technology on the issues of maintainability, land
requirement and process performance, heat drying has a higher lifecycle cost
and operation and maintenance (O&M) cost since the drying process requires
more energy. The fuel and power costs contribute about 80% of the total
O&M costs for the heat drying option, and no energy can be reused from the
drying process. In contrast, the O&M costs for the incineration option are
only 23% of that of heat drying, mainly resulted from savings in fuel and
energy. Besides, the energy from the incineration process can be reused. Although
the incineration technology involves a higher capital cost, the capital cost
can be offset by the significantly low O&M costs. In view of its low
life cycle cost, the incineration technology is more favorable. Besides, the
volume of the end product after incineration is significantly lower than that
after heat drying. About 85% of the landfill space would be saved if the
incineration technology is adopted. This would help to sustain the landfill
life, which is the driving force of this Project.
2.2.4
Recommended Sludge Treatment Option
2.2.4.1
Based on the results of the evaluation of the
shortlisted sludge treatment options, it was concluded that fluidized bed incineration
would be the most preferable option and would be adopted for the STF.
2.2.4.2
The recommended sludge treatment technology for the STF
consists of the following process trains:-
·
Sludge
receiving, storage and feeding system;
·
Fluidized
bed incinerators;
·
Waste heat
recovery and power generation system;
·
Flue gas
treatment system;
·
Ash storage
and handling system;
·
Residues
storage and handling system;
·
Fluidized
bed sand storage and handling system; and
·
Reagent reception and
storage system.
2.3
Site Selection
2.3.1
Consideration of Alternative Site
Locations
2.3.1.1
A preliminary site
search exercise was conducted under a separate study to identify the potential
sites for the development of STF. An initial list of
potential sites was first compiled according to the following site search
criteria:-
·
Availability
of the site;
·
Site area
requirement;
·
Preference
for site access by marine and road;
·
Establishment
of berthing facility to accommodate an 80m long container vessel;
·
Preference
for 200m buffer zone with no residential development;
·
No height
restrictions within 110m; and
·
Preference for a site
close to an existing landfill, public facilities and accessible by direct road
link from major STWs.
2.3.1.2
Concerned government parties were invited to comment on
the initial list of potential sites and to advise a shortlist of potential
sites for further assessment based on the following exclusionary criteria:-
·
Areas of
topographically confined air sheds;
·
Sites
within country parks;
·
Sites of
special scientific interest;
·
Sites
within residential areas or densely populated areas;
·
Sites close
to urban areas dominated by high-rise developments;
·
Sites
within the eastern part of the Hong Kong SAR landmass;
·
Sites
excluded by previous studies (provided that the justifications are still valid
under the current exercise);
·
Identical
sites already considered by other studies; and
·
Sites with conflicts to
planning intention or incompatible with nearby land uses.
2.3.1.3
Based on the review,
nine potential sites were shortlisted for further
evaluation (the locations of nine potential sites are shown in Figure 2.1):
·
Site 1 –
Quarry Site, Lamma Island;
·
Site 2 – Shek Kwu Chau;
·
Site 3 – Ha
Pak Nai;
·
Site 4 – Tuen Mun Port;
·
Site 5 –
Stonecutters Island;
·
Site 6 – West
Lamma Island (Ha Mei Wan);
·
Site 7 –
Siu Ho Wan;
·
Site 8 –
Tit Cham Chau; and
·
Site 9 – Nim Wan.
2.3.2
Site Selection Criteria
2.3.2.1
The proposed criteria used to select the most
appropriate site for the STF are grouped into the following 5 main areas:
(i)
Environmental Comparative
w
Air Quality
w
Noise
w
Water Quality
w
Marine Ecology and Fisheries
w
Terrestrial Ecology
w
Landscape and Visual
(ii)
Engineering Feasibility
w
Ease of Construction
w
Geotechnical Conditions
w
Water Supply
w
Power Supply
w
Wastewater Treatment
(iii)
Operational Convenience
(iv)
Financial Assessment
(v)
Strategic and Planning Issues
2.3.3
Evaluation of Shortlisted Sites
Site 1 -
Quarry Site, Lamma Island
2.3.3.2
This site is located in a small reclamation area next to the quarry site at
the entrance to Sok Kwu
Wan, Lamma Island. Sok
Kwu Wan is a popular tourist spot, with various
indigenous villages in close proximity. Tidal current speeds at the site
are relatively low and no large thermal plume is expected from cooling water
being discharged from the STF when water cooling is adopted. According to
the study on “Outlying Island Sewerage Scheme Stage I and II Pack J — Sok Kwu Wan Sewage Treatment and
Disposal Facilities”, 13 coral species were recorded in Sok
Kwu Wan. The intertidal soft shore habitats in the
vicinity of the site are expected to be of low to moderate ecological value.
2.3.3.3
The STF in this location would likely be acceptable in
terms of environmental impacts, except landscape and visual impact which would
be a concern. However, this site is accorded a lower priority as
reclamation would be required for siting of the STF.
2.3.3.4
New submarine water supply line, electricity supply
line and on-site wastewater treatment works would also be required.
Moreover, in this option, marine transportation is the sole means for the
delivery of sludge, process chemicals and ash. As a result, this option is of
low ranking for both the engineering feasibility and operational convenience.
2.3.3.5
Furthermore, the overall planning intention for Lamma Island is to conserve the natural landscape and rural
character and to enhance the island as a leisure destination. Therefore, the
proposed development of the STF is considered violating the planning intension.
Site 2 - Shek Kwu Chau
2.3.3.6
This site is located in a reclaimed area on the
southern side of Shek Kwu
Chau. This site is subject to strong stratification in wet season and
reasonable dispersion due to the tidal currents.
2.3.3.7
The habitat is polychaete
dominated in this site. However, the benthic assemblages can be classified as
being of low ecological importance. The island is surrounded by the huge Shek Kwu Chau AFCD fishing zone,
and is deemed as of high importance in terms of fisheries resources. Shek Kwu Chau is sparsely
inhabited except that it has been granted for use by the Society for the Aid
and Rehabilitation of Drug Addicts (SARDA). Apart from the settlement of
SARDA, the closest air and noise sensitive receivers (ASRs and NSRs) are the village type developments located at about
170m to the north of the site.
2.3.3.8
The development of the STF at this site is not likely
to cause adverse impacts on water quality, terrestrial ecological and marine
ecological & fisheries. However, air and noise impacts would be
anticipated. Also, moderate landscape and visual impact would be expected
due to the loss of local natural coastline. The proposed stack at the STF
will cause disturbance to the vegetation and intrusion to the open views of the
residents from SARDA.
2.3.3.9
Since reclamation is required for siting,
it is in a lower priority compared to other sites. Also, new submarine water
supply line, electricity supply line and wastewater treatment works would also
be required. In addition, marine transportation is the sole means for the
delivery of sludge, process chemicals and ash for this site, and thus resulted
in its low ranking for both the engineering feasibility and operational
convenience.
2.3.3.10
The principal planning intention for Shek Kwu Chau is for landscape
and coastal protection. As such, the development of the STF would be
inconsistent with the planning intention.
Site 3 - Ha
Pak Nai
2.3.3.11
The proposed STF in Ha Pak Nai
is located within outer Deep Bay adjacent to the east of the existing West New
Territories (WENT) Landfill. The tidal currents in this area are low and
little dispersion of the cooling water discharges would be expected when water
cooling is adopted. The proposed site is relatively flat and mainly
consists of agricultural land, fish ponds, rural settlements and farm
buildings. The seagrass, mangrove and mudflat
habitat of Ha Pak Nai are considered to be of high
conservation value. The development of STF would probably require the
relocation of population, including the agricultural and fishery users.
2.3.3.12
The development of the STF at Ha Pak Nai is likely to result in adverse water quality,
ecological and fisheries impacts due to the cooling water discharges if water
cooling is adopted. Loss of fishponds at Ha Pak Nai
will be expected due to the development of the proposed STF. Moreover, it will
cause direct loss of habitats and indirect impacts to wildlife due to land
utilization and human activities, resulting in “moderate to high” ecological
impact. Furthermore, it will cause landscape and visual impact to the
local residents in Ha Pak Nai.
2.3.3.13
It is noted that extensions of water supply and
electricity supply line would be required for the construction and operation of
the STF at Ha Pak Nai. A dedicated wastewater
treatment works would also be required. In view of the above, this site
is at moderate ranking in both engineering feasibility and operational
convenience aspects.
2.3.3.14
From the strategic and planning point of view, Ha Pak Nai is designated for coastal protection and agricultural
and therefore, the development of the STF thereat would be inconsistent with
the planning intention.
Site 4 - Tuen Mun Port
2.3.3.15
This site is located in the reclaimed area in the
future planned Tuen Mun
Port Development Area. Owing to the high tidal current, significant salinity
stratification is expected around this site, in particular in wet season.
Moreover, the presence of protected Indo-Pacific Hump-backed Dolphin in the
nearby coastal waters is one of the major concerns for assessing suitability of
this site for the development of the STF. Furthermore, the topography of the surrounding
area consists of mountain ridges, spurs and coastal plains. Also, about 500m to
the east of the proposed site is the Lung Kwu Sheung Tan, where village type developments are found.
2.3.3.16
In general, this site is likely to be acceptable in
terms of environmental impacts with the implementation of the relevant
mitigation measures.
2.3.3.17
From the engineering point of view, reclamation and the
extension of water supply and electricity supply line would be required, and
resulting in its low ranking for developing the STF at this site.
Nevertheless, this site can be accessed by both road and marine
transportations, and hence ranked top in the operation convenience aspect.
2.3.3.18
In the consideration of the emerging needs for port
development in Hong Kong, the development planning for Tuen
Mun Port is uncertain and thus subsequently poses
high uncertainty for the development of the STF at this site.
Site 5 -
Stonecutters Island
2.3.3.19
This site is located in the Stonecutter Island.
Currently, part of the site is occupied by the SCISTW.
2.3.3.20
Adverse environmental impacts are not likely to be
resulted from the development of the STF at Stonecutters Island.
Moreover, in view of the close proximity of the SCISTW, it is expected that no
difficulties would be encountered for the supply of water and power, as well as
the wastewater disposal at this site. Furthermore, this site is ranked
high as it can be accessed by both road and marine transportations.
Despite the above, difficulties are anticipated for the construction of the STF
in close proximity of the existing SCISTW without disturbing its normal
operation.
2.3.3.21
Regardless the likely acceptable environmental impacts,
engineering feasibility and operation convenience, the major drawback of this
site is that there would be inadequate area for the development of the STF at
this proposed site.
2.3.3.22
The site has now been reserved for the development of
the HATS 2A project and is effectively not available.
Site 6 - West Lamma Island
2.3.3.23
This site is located in the southwest of the existing Hongkong Electric Co. Ltd. (HEC), Lamma
Power Station. It is an existing Government seabed where reclamation
would be required. The tidal currents in the vicinity of the discharge
point are likely to be low and thus significant dilution of the thermal plumes
is not expected. The use of the area as a spawning and nursery ground by
commercial fish species makes the waters surrounding the proposed STF have been
deemed to be of high importance to the Hong Kong fishery. The nearest
population centre is approximately 1.5km to the north of the proposed site.
2.3.3.24
The development of the STF at West Lamma
Island would unlikely result in unacceptable air quality and ecology impacts,
however, measures would be required to mitigate the impacts associated with
noise, water, marine ecological & fisheries and landscape & visual
aspects.
2.3.3.25
Similar to other sites which require reclamation, new
submarine water supply line would be required for the STF at West Lamma Island. Also, this site would only be accessed
by means of marine transportation and this fact results in low ranking for both
the engineering feasibility and operational convenience aspects.
Site 7 - Siu
Ho Wan
2.3.3.26
This site is located in Siu Ho Wan, adjacent to the
existing Siu Ho Wan Water Treatment Works (WTW) and the North Lantau Expressway. Air and noise sensitive receivers have
not been identified in the vicinity of the proposed site.
2.3.3.27
This site is subject to height restriction due to its
close proximity of Chek Lap Kok
Airport, i.e. the proposed stack height at the STF site should be less than
120m while the buildings’ height would not be higher than 20m.
2.3.3.28
The development of the STF at Siu Ho Wan would likely
result in unacceptable air quality impacts even with the implementation of
mitigation measures. Apart from the air quality, other adverse
environmental impacts would not be anticipated.
2.3.3.29
As mentioned above, the proposed site is located close
to the existing Siu Ho Wan WTW and Siu Ho Wan STW, water and power would
therefore be supplied without any difficulties. However, this site is far
away from the other STWs and thus increases the
inconvenience of sludge transportation. Hence, it is in the middle rank for
operation convenience aspect.
2.3.3.30
The proposed site area is planned for major
recreational and tourism related development and the development of the STF
will violate the planning intension.
Site 8 - Tit
Cham Chau
2.3.3.31
This site is located at the southern-most tip of the
proposed reclamation at Tseung Kwan O Area 137.
The closest developments are the SENT Landfill and the Tseung
Kwan O Industrial Estate, which are located to the northeast and north,
respectively. The closest residential areas locate about 3km to the north of
the site. The tidal current at this site is relatively low and no significant
dispersion of the cooling water discharges would be expected.
2.3.3.32
In general, with the implementation of the mitigation
measures, adverse environmental impacts are not anticipated for developing the
STF at Tit Cham Chau.
2.3.3.33
Extension of the existing water supply line would be
required for the development of the STF. Both marine and road transportations
would be available for this site, making this site to be of upper rank for both
engineering feasibility and operation convenience aspects.
2.3.3.34
Currently, Tit Cham Chau is the only vacant area
designated for the use by Potentially Hazardous Industries (PHI) and it is
unlikely for the Government to release the site for development of the STF.
Site 9 - Nim Wan
2.3.3.35
This site is located adjacent to the Black Point Power
Station and WENT landfill in Nim Wan. The site
is currently use for storage of pulverised fuel ash
(PFA), a by-product of the coal-burning. The site is remote from residential
areas.
2.3.3.36
The development of the STF in Nim
Wan would unlikely result in unacceptable water quality impact, marine
ecological & fisheries impact, terrestrial ecological impact and landscape
& visual impact. However, mitigation measures would likely be required to
alleviate the potential air quality and noise impacts associated with STF at
this location.
2.3.3.37
In view of the remoteness of the site, extension of
water supply line and construction of on-site wastewater treatment works would
be required for the development of the STF in this site. The site is
accessible by means of road and marine transportations resulting in its middle
rank for both engineering feasibility and operation convenience aspects.
2.3.3.38
At present, this site has no land use designation and
no major strategic consideration regarding this area.
2.3.3.39
The 9 shortlisted sites were evaluated based on the
criteria listed in Section 2.3.2. The results of the evaluation
are summarized in Table 2.3.
Table 2.3
Summary of Assessment Results for Site Selection
|
Potential Site
|
Environmental Impact
|
Engineering Feasibility
|
Operational Convenience
|
Economic Issues
|
Strategic and Planning Issues
|
|
Quarry Site
|
**
|
*
|
*
|
***
|
**
|
|
Shek Kwu
Chau
|
**
|
*
|
*
|
*
|
*
|
|
Ha Pak Nai
|
*
|
**
|
**
|
**
|
*
|
|
Tuen Mun
Port
|
***
|
**
|
***
|
**
|
***
|
|
Stonecutters Island
|
***
|
***
|
***
|
***
|
*
|
|
Ha Mei Wan
|
**
|
*
|
*
|
*
|
***
|
|
Siu Ho Wan
|
**
|
***
|
**
|
**
|
**
|
|
Tit Cham Chau
|
***
|
***
|
***
|
**
|
**
|
|
Nim Wan
|
***
|
***
|
**
|
***
|
***
|
Note:
* Less
Preferable
** Preferable *** Highly
Preferable
2.3.3.40
The results of the assessment indicated that the potential
sites in Tuen Mun Port,
Stonecutters Island, Tit Cham Chau and Nim Wan would
be more favorable in view of their relatively low environmental impacts.
2.3.3.41
However, the potential sites in Tuen
Mun Port and Stonecutters Islands are not available
for the STF development as the development of Tuen Mun Port is not proceeded as planned, and the proposed site
area in the Stonecutters Island is reserved for development of HATS Stage 2A
project.
2.3.3.42
It would be unlikely for the Government to release the
site in Tim Cham Chau for development of the STF since Tim Cham Chau is the
only available site designated for PHI in Hong Kong.
2.3.3.43
Among the four preferred options, Nim
Wan is the only available site suitable for STF.
2.3.4
Recommended Site
2.3.4.1
Based on the results of the evaluation, the STF is proposed to be located in the
pulverized fuel ash lagoon (PFA) area in Tsang Tsui
near Nim Wan, adjacent to the WENT Landfill and to
the northeast of the Black Point Power Station.
2.3.4.2
The existing PFA area was constructed in the mid- to
late 1980’s through the reclamation of coastal areas adjacent to Nim Wan, and were divided by bunds into the East, Middle
and West Lagoons. Since 1989, the lagoons have been used for the storage of
PFA, a by-product of the coal-burning. PFA is a fine, grey powder formed from
the rock particles contained within coal, consisting mainly of silica, alumina
and iron oxide. Surplus PFA is mixed with sea water and pumped as a
slurry for storage in the lagoons.
2.3.4.3
The existing PFA area is granted to Castle Peak Power
Company Limited. The Middle and West Ash Lagoons are still used for the storage
of PFA. In 1997, CLP began to use the Middle Lagoon as part of its water
collection and conservation system. Freshwater discharged from various
systems within the Castle Peak Power Station, together with rainwater from the
site, are fed into the lagoon for storage through a system of pipes. The
water can then be pumped back into the power station as and when it is needed.
2.3.4.4
The proposed site for
STF is located in the northern part of the East Lagoon. The open water of
Deep Bay is located to north of the proposed site. The STF site will be
accessed through a temporary vehicular bridge spanning across the existing
channel between the existing WENT Landfill site and the lagoon area. Alternative temporary and permanent access to the STF site to suit
the phased development of the WENT Landfill Extension project will be
investigated and proposed under the WENT Landfill Extension project.
2.3.4.5
The project area boundary of the STF is shown in Figure 2.2. It is estimated
that the STF, including its ancillary and supporting facilities will occupy an
area of approximately 7 hectares.
2.4
Scope of
the Project
2.4.1
Introduction
2.4.1.1
The Project will include the three phases:-
·
Decommissioning
of PFA Lagoon;
·
Construction
of the STF; and
·
Operation of the STF.
2.4.1.2
The scopes of works in different phases of the Project
are provided in the following sections.
2.4.1.3
Design-Build-Operate (DBO) contract arrangement will be
adopted for the Project. A reference design for the STF has been
prepared, and the contractor will be responsible for the detailed design,
construction and operation of the STF.
2.4.2
Decommissioning of PFA Lagoon
2.4.2.1
Based on the requirement of EIA Study Brief,
decommissioning of the East Lagoon prior to the construction of the STF should
be assessed. After the preliminary assessment, there will be no existing
facility to be removed or demolished. In addition, as the finish ground level
of STF will be elevated to a level higher than the average ground level of the
existing East Lagoon, no disposal of PFA will be required during the
construction phase.
2.4.2.2
The decommissioning works will be minimal, and no
potential environmental issues associated with the decommissioning of the East
Lagoon are envisaged.
2.4.3
Construction of STF
2.4.3.1
The construction of the STF will include the following
stages:-
·
Site
drainage;
·
Site
formation;
·
Foundation
piling;
·
Civil works
(including construction of a vehicular bridge);
·
Mechanical
& electrical plant installation;
·
Buildings
and STF ancillaries;
·
Roads,
utilities, services and landscaping;
·
Field/ancillary
instrumentation and control works;
·
Power
generation; and
·
Power transmission
within the STF site.
2.4.3.2
The major proposed buildings and facilities in the STF
site are listed below:-
·
Delivery
Bays;
·
Incinerators and Air Control Equipment;
·
Flue Gas Residuals Silos, Ash Silos and Loading Area;
·
Chemical/ Fuel Storage and Feeding;
·
Stack;
·
Maintenance Workshop;
·
Utility Yard;
·
Desalination Plant, Seawater Pumping Station and Storage Tank;
·
Sewage
Treatment Works and Sewage Holding Tank;
·
Administration
Building / Laboratory / Visitor and Education Centre;
·
Car Park;
and
·
Truck Parking Area.
2.4.3.3
A reference design of the STF has been prepared. The
preliminary layout plan of the proposed buildings and facilities in the STF
site and the preliminary layout of the incinerator system are shown in Figure 2.3 and Figure 2.4.
2.4.3.4
In the reference
design, six numbers of incineration units were
provided, each with a design capacity of 120 dry tonnes/day.
This option will produce excess heat of approximately 60 tonnes
of steam per hour which would be used in steam turbines to produce electricity
for use on-site.
2.4.3.5
The design of the incineration facility will meet the
requirements of the latest best practicable means (BPM) for incinerators
and the target emission limits as shown in Table 2.4, which in turn are
based upon the latest standards established in Europe.
A combustion zone operating at 850ºC with a residence time of 2 seconds is
recommended in the BPM. Under such high temperatures and long residence
time, a very high percentage of organic compounds and odorous substances
present in the combustion gases will be destroyed. Other measures, which
are recommended in the BPM to render the emissions harmless, include the
following:-
(i)
An efflux velocity higher than 15 m/s under full load
conditions;
(ii)
An exit temperature higher than 80oC under
full load conditions (based on the preliminary design, the discharge
temperature of flue gas would be 190 oC); and
(iii)
An oxygen content at the combustion chamber at least
6%.
2.4.3.6
The target air emission limits shown in Table 2.4 are
restrictive. However, air quality concerns can be addressed using the following
state-of-the-art equipment:-
(i)
Primary bag filtration for coarse particulates removal;
(ii)
Injection of sodium bicarbonate for acids pollutants
removal;
(iii) Injection of activated carbon for mercury organic micro-pollutants
removal;
(iv) Secondary bag filtration for removal fine particulates;
(v)
Electrostatic precipitation for removal of fly ash and
coarse particulates; and
(vi)
Wet/ Dry Scrubbing for removal of fly ash.
Table 2.4 Target Air Emission Limits
|
Air Pollutant
|
Target Emission Limits (mg/m3) (1)
|
|
Daily
|
Half - Hourly
|
|
Particulates (4)
|
10
|
30
|
|
Organic Compounds
|
10
|
20
|
|
Hydrogen Chloride (HCl)
|
10
|
60
|
|
Hydrogen Fluoride (HF)
|
1
|
4
|
|
Sulphur Dioxide (SO2)
|
50
|
200
|
|
Carbon Monoxide (CO)
|
50
|
100
|
|
Nitrogen Oxides (NOX)
as Nitrogen Dioxide (NO2)
|
200
|
400
|
|
Mercury
|
0.05 (2)
|
-
|
|
Total Cadmium & Thallium
|
0.05 (2)
|
-
|
|
Total Heavy Metals
|
0.5 (2)
|
-
|
|
Dioxins & Furans (3)
|
1´10-7
|
-
|
Notes :
(1) Emission limits
are reference to 0oC and 101.325 kPa, dry
and 11% oxygen content conditions.
(2) Average values
over a sampling period of a minimum of 30 minutes and a maximum of 8 hours,
including Sb, As, Pb, Co,
Cr, Cu, Mn, V and Ni.
(3) The unit is I-TEQ
(The emission limit is equal to 0.1 ng I-TEQ m-3),
according to the BPM 12/1, the averaging time for dioxin is 6 to 8 hours.
(4) The particulate
emission limit is assumed to be RSP.
2.4.3.7
The burning of auto-thermic sludge
in the incinerators will produce excess thermal energy, which can be used to
generate electricity. Incineration with energy recovery is thus recommended for
the STF. Energy generated from the incineration process will be used for
internal reuse and other ancillary facilities within the STF site to offset the
power cost from retail. As the surplus power is anticipated to be minimal
and it would be unlikely for CLP to purchase the surplus power, the surplus
power would not be sold. Therefore, no power transmission line will be
constructed outside the STF site.
2.4.3.8
Water used by the STF will be supplied by an on-site
desalination plant. Besides, all wastewater generated from the operation of the
STF, such as washdown water generated from the sludge
treatment activities and domestic wastewater generated by plant personnel, will
be treated at an on-site wastewater treatment plant and reused in the
STF. The wastewater treatment plant will be enclosed inside a building
and a ventilation system with deodorizers will be installed for the sludge
dewatering facilities.
2.4.4
Operation of STF
2.4.4.1
The STF will be operated in 24-hour basis daily, while
the reception of sludge will be limited from 8 am to 8 pm, tentatively.
2.4.4.2
Currently, dewatered sludge is transported from the STWs to the WENT Landfill for disposal by a combination of
marine and road transportation. The current operational practice for
transporting dewatered sludge from the STWs will
continue during the operation of the STF. For the STWs
with marine berthing/loading facilities (i.e. SCISTW and Siu Ho Wan STW),
dewatered sludge will be delivered by marine transport to the pier at WENT
Landfill and then transported to the STF by truck. Marine transportation
would cause less traffic impact, particularly in Tuen
Mun area and along Nim Wan
Road. Apart from the traffic concern, marine transport can minimize potential
noise impact, odour emission, and human health risk
associated with road transportation. For the STWs
without marine berthing/loading facilities, the dewatered sewage sludge will be
delivered by road transport in water tight containers or skips, or in
truck-mounted containers to the STF.
2.5
Consideration of Alternative
Sequences of Construction
2.5.1.1
Alternative sequences of construction, including concurrent
construction sequence and phased construction sequence, were considered.
2.5.1.2
Concurrent construction sequence involves various
construction activities occurring at the same time. The environmental benefit of this construction
sequence would be the reduction of the construction
period and hence the duration of impact due to the construction. However,
the magnitude of the overall environmental impact could be significant.
2.5.1.3
Phased construction sequence involves construction
activities being carried out one followed by another. This construction sequence would help reducing the magnitude of the overall impacts, but the construction period would be
longer.
2.5.1.4
As the two approaches have their environmental benefits
and dis-benefits, a balancing approach which involves
a combination of concurrent and phased construction sequences in different
stages of the construction will be adopted to alleviate the potential
environmental impact and to meet the target commission date. For
instance, the phased construction sequence would be adopted to avoid
construction activities which would induce considerable noise (e.g. pilling
works) to be carried out at the same time.
2.6
Consideration of Alternative
Construction Methods
2.6.1.1
To minimize the potential environmental impacts,
alternative construction methods were considered. For the piling works,
percussive piles and socketted H-piles were
considered. Percussive piles would cause substantial noise and vibration
impacts, whereas the noise and vibration impacts due to the construction of socketted H-piles would be significantly
lower. Considering the environmental benefits and
dis-benefits of the alternative piling methods, socketted H-piles is recommended for this project to
minimize the potential noise impact during the construction.
2.7
Construction Programme
2.7.1.1
The construction of the STF will commence in early
2010. The STF is tentatively scheduled for commissioning by end 2012 and
will have a design life of 20 years. The tentative project programme is shown in Table 2.5.
Table 2.5
Construction Programme
|
Description
|
Date
|
|
Award of Contract
|
March 2010
|
|
Site Establishment and Temporary Works Preparation
|
March – June 2010
|
|
Construction of STF and Ancillary Facilities
|
June 2010 – March 2011
|
|
Testing and Commissioning
|
Feb – Oct 2012
|
2.8
Interactions with Other Projects
2.8.1.1
The following projects may have potential interaction
with this Project:-
WENT Landfill Extension
2.8.1.2
The engineering feasibility and EIA Study for the WENT
Landfill Extensions is being carried out by the EPD.
2.8.1.3
The proposed WENT Landfill Extension would occupy the
remaining area of the East, Middle and West Ash Lagoons, adjacent to the
proposed STF site. The preliminary site boundary of the proposed WENT
Landfill Extension is shown on Figure
2.5. The site formation of the WENT Landfill Extension is
tentatively scheduled to commence in 2016/17.
2.8.1.4
As the construction of the STF at the proposed site at
the East Ash Lagoon is scheduled for completion in 2012, the construction works
for the STF would not be concurrent with the proposed WENT Landfill
Extension. If the WENT Landfill Extension proceeds as planned, the
proposed landfill extension would occupy the remaining area of the whole ash
lagoon area in the future. The STF site will be accessed through a temporary
vehicular bridge spanning across the existing channel between the existing WENT
Landfill site and the lagoon area. Alternative temporary and permanent access
to the STF site to suit the phased development of the WENT Landfill Extension
project will be investigated and proposed under the WENT Landfill Extension
project.
Integrated Waste
Management Facilities (IWMF)
2.8.1.5
In order to deal with the serious and imminent waste
problem, the Government proposes to develop the IWMF to substantially reduce
the volume of unavoidable waste, thereby extending the life span of the
existing landfills and their extension. A comprehensive site search
exercise has been carried out to identify potential sites in Hong Kong suitable
for the development of the Phase 1 of the IWMF. The result of this
exercise concluded that the sites at (i) the Middle
Lagoon of Tsang Tsui Ash Lagoons and (ii) Shek Kwu Chau are suitable for
consideration.
2.8.1.6
It is understood that detailed engineering and EIA
studies for the two potential sites will commence by the end of 2008 in
accordance with EIA Study Brief No. ESB-184/2008 to ascertain their ultimate
suitability and to assist in the decision on the final choice of site. As
the studies are yet to be commenced, and the ultimate suitability of the Tsang Tsui Ash Lagoons site and the decision on the final choice
of site are yet to be ascertained, there is no relevant information available
at the moment for any meaningful assessment under this EIA Study. It is
however certain that in the EIA study of the IWMF, the cumulative environmental
impacts associated with the IWMF and other concurrent projects, including but
not limited to the STF, will be examined in accordance with the EIAO-TM
requirements before the ultimate suitability of the site can be ascertained and
the decision on the final choice of site can be made.
Tuen Mun – Chap Lap Kok Link and Tuen Mun Western
Bypass
2.8.1.7
The Highways Department (HyD)
has just commissioned consultant studies for the investigation and preliminary
design of the Tuen Mun – Chek Lap Kok Link and Tuen Mun Western Bypass since May
and July 2008 respectively.
2.8.1.8
The proposed Tuen Mun – Chek Lap Kok Link is a dual two-lane highway approximately 9 km long
connecting the Tuen Mun
Western Bypass at the southern coast of Tuen Mun Area 40 in the north, with the Airport and North Lantau in the south, whereas the proposed Tuen Mun Western Bypass is a dual
two-lane highway approximately 8.5 km long connecting the Kong Sham Western
Highway in the north and the Tuen Mun
– Chek Lap Kok Link in the
south.
2.8.1.9
As the studies have just been commenced and the
alignments are yet to be finalized, there is no relevant information available
at the moment for any meaningful assessment under this EIA Study. In
addition, for these two proposals, the traffic related emissions will be mostly
generated near the ground and the impacts would therefore be very much
localized. Given that these two proposals will be at least a few
kilometers from the STF site, there would be minimal cumulative impacts with
the stack emissions from the STF and other major emission sources considered in
this EIA. It is understood that the cumulative environmental impacts
associated with these two proposals and other concurrent projects, including
but not limited to the STF, will be examined in accordance with the EIA Study
Brief No. ESB-174/2007 and ESB-175/2007 respectively under relevant EIA studies
for these two highway projects.
2.9
Assessment Areas of the EIA Study
2.9.1.1
The assessment areas for the purpose of this EIA Study,
as specified in the Brief, are specified in Table 2.6 below.
Table 2.6
Areas Covered by the EIA Study
|
Type of Impact Assessment
|
Assessment Area
|
|
Air quality
|
Existing, planned and committed air sensitive
receivers in North-West New Territories including Ngau
Hom Sha, Tin Shui Wai, Ha Pak Nai, Sheung Pak Nai, Tuen Mun Area 38, Lung Kwu Sheung Tan, Lung Kwu Tan, Tuen Mun City Center, Butterfly Beach area, Pak Long and
premises of Castle Peak Power Company Limited, etc. Emission Sources
including Green Island Cement Plant, EcoPark, Shiu
Wing Steel Mill, WENT Landfill and Extension, Black Point and Castle Peak
Power Plants will be included.
|
|
Water quality
|
Area within 300m of the site boundary, and all
relevant water sensitive receivers downstream of emergency bypass (if any)
from the proposed sewage treatment works, including existing cooling water
system of the Black Point Power Station
|
|
Ecology
|
Areas within 500m from the site boundary
|
|
Noise
|
Area within the site boundary, and the
representative noise sensitive receivers along and within 300m of Lung Kwu Tan Road
|
|
Landscape
|
Area within 500m from the site boundary
|
|
Visual
|
Zone of visual influence defined by the visual
envelope of the Project
|