2.1.1
The works for this Project in
Sha Tau Kok mainly comprises of the following items and as shown in the Layout
Plan of Figure 2.1a:
a)
Increase the treatment capacity
of Sha Tau Kok Sewage Treatment Works (STKSTW) to 5,000 m3/day at
ADWF by 2021, with suitable allowance to cater for a further increase of
treatment capacity to 10,000 m3/day at ADWF after 2030 in Phase 2;
b)
Construct a temporary sewage
treatment plant (TSTP);
c)
Demolish the existing Sha Tau
Kok Sewage Pumping Station (STKSPS) and decommission the rising main between
STKSPS and STKSTW;
d)
Construct a length of 520m new gravity sewer; and
e)
Abandonment of the existing
submarine outfall and construct a length of 1700m new submarine outfall.
f)
Increase the Treatment Capacity
of STKSTW and Construct a TSTP
2.1.2
The existing STKSTW is located
at Sha Tau Kok Town. It currently provides secondary level treatment to sewage
collected from Sha Tau Kok township (including Yim Liu Ha, Tsoi Yuen Kok and
Sha Tau Kok Tsuen). STKSTW was commissioned in 1989 with a design capacity of
1,660 m3/day at average dry weather flow (ADWF).
2.1.3
The proposed STKSTW expansion will
increase the treatment capacity to 10,000 m3/day with betterment
to the current secondary treatment level. STKSTW will not receive sewage flow
from existing catchment of other sewage treatment works. A Membrane-bioreactor
(MBR) type sewage treatment plant will be adopted.
2.1.4
The MBR process can produce good
quality effluent through a combination of microfiltration membranes and
suspended growth biological reactor. The membranes replace the solids
separation of secondary clarifiers and the polishing of granular filter media
that are found in conventional activated sludge systems.
2.1.5
By eliminating the need for
sludge settling, the MBR process can operate at higher mixed liquor suspended
solids concentration than conventional activated sludge systems. This results
in a plant that is more compact than a conventional plant, requiring a smaller footprint
to produce effluent of similar quality. All the membrane modules will be placed
in MBR tanks, which are covered and installed indoor.
2.1.6
The expansion works will
include construction of new sewage treatment facilities. A temporary sewage
treatment plant (TSTP) is proposed as the interim measure to cope with the
sewage flow in order to isolate the existing STKSTW from the expansion works.
2.1.7
The proposed TSTP will have a
treatment capacity of 2500 m3/day. A Moving Bed Biofilm Reactor
(MBBR) type sewage treatment plant will be adopted. A suitably designed
additional Chemical Enhanced Primary Treatment (CEPT) process using ferric
chloride or alum dosing to the influent will also be effected if necessary.
2.1.8
The MBBR process with secondary
treatment and necessary enhancement can improve the effluent quality standard
compared with the existing STKSTW such that the TSTP can comply with the
discharge license of existing STKSTW.
2.1.9
All the expansion works will be
constructed within the existing site boundary of STKSTW. The proposed general
layout of the STKSTW and TSTP are shown in Figure 2.4 – 2.14 respectively. The
Schematic Process Flow Diagrams are shown in Figure 2.2 and Figure 2.3 for STKSTW and TSTP
respectively. The dimension
of the above-ground structure is 73m (L) x 25m (W). The
respective height of the new structure for the expanded STKSTW and TSTP is
approximately 10m – 19m and 10m above the proposed ground level. The site coverage of the sewage treatment works is 35%. The gross floor
area for the expanded STKSTW and TSTP is approximately 5,700 m2 and
1,550m2 respectively. The breakdown of respective area for the expanded
STKSTW and TSTP are as follow:
|
Area
|
Dimension
|
Height
|
Footprint
|
|
Site extent
|
-
|
-
|
4,950m2
|
|
Above-ground
structure for expanded STKSTW
|
73m
x 25m
|
10m – 19m
|
1740m2
|
|
Above-ground
structure for TSTP
|
47m x 19m
|
10m
|
774m2
|
Demolish
the Existing STKSPS, Decommission the Rising Main between STKSPS and STKSTW,
and Construct New Gravity Sewer
2.1.10
The existing STKSPS is located
at Shun Lung Street. It is currently equipped with three submersible pumps (two
duty and one standby) with the existing pumping capacity of 90L/s.
2.1.11
A sewerage scheme to demolish the
STKSPS after expansion of STKSTW is proposed. The scheme includes construction
of a section of sewer to divert the existing sewage flow from STKSPS to STKSTW which
can isolate STKSPS for demolition.
2.1.12
The proposed scheme consists of
the following:
·
Sewage from STK town will be
diverted to the proposed sewer and conveyed to the expanded STKSTW by gravity.
·
The STKSPS and its rising mains
will be decommissioned.
·
The land will be utilized for
other beneficial purposes.
·
The rising mains will be
grouted and abandoned.
·
No excavation works will be
required for the decommissioning of the rising mains.
Abandonment
of the Existing Submarine Outfall and Construct a New One
2.1.13
The existing outfall is
inadequate to cope with the increased sewage flow in the future. Construction
of a new submarine outfall with larger capacity is necessary to discharge the
treated effluent to Starling Inlet. The alignment of the new submarine outfall
is shown in Figure 2.1b.
2.1.14
The discharge point of the
proposed submarine outfall will be located in the water near Ah Kung Au. The
submarine outfall will be constructed by trenchless method under the seabed of
Starling Inlet. A diffuser (approximate 54m x 22m with 11 risers), which can
help to improve the mixing and dilution efficiency of effluent, will be
constructed on the seabed of Starling Inlet to discharge the treated effluent. It
will be located far away from the water sensitive receivers as identified in
Chapter 5, which are mainly in the inner water. It is not expected to have
excavation/ dredging works for future routine maintenance works during
operation. According to the Aerial Photographs, the proposed discharge location
near Ah Kung Au is part of Starling Inlet from 1969.
Effluent
Reuse
2.1.15
In view of
recent developments in sewage treatment technology, which could produce high
quality effluent, reuse of the treated effluent would also be considered for
Phase 1 and Phase 2 STKSTW to minimize direct effluent discharge.
2.1.16
The
expanded STKSTW will be able to advance treat the secondary effluent after
secondary treatment at sewage treatment works for the production of reclaimed
water for non-potable use within STKSTW. The use of reclaimed water is
primarily for cleansing, toilet flushing and landscape irrigation within
STKSTW. The maximum design flow of the abovementioned use is 50m3/day
which is 0.5% of the ultimate design capacity of STKSTW.
2.1.17
There will be no off-site
effluent reuse. The treated effluent will undergo a chlorination process by
means of sodium hypochlorite with the dosage of 4kg/day before being conveyed
to the point of usage to minimize bacterial growth and contamination during the
transmission. The process for generation of chlorinated treated effluent will
cease when its quantity reaches a pre-set level of 50m3/day. The
flow chart below shows the process train of the advanced treatment:
EFFLUENT AFTER
MBR TREATMENT AT SEWAGE TREATMENT WORKS
|
CHLORINATION
PROCESS BY SODIUM HYPOCHLORITE
|
RECLAIMED WATER
FOR GENERAL HOUSEKEEPING, TOILET FLUSING AND LANDSACPE IRRIGATION
|
PROCESS TRAIN FOR
ADVANCED TREATMENT FOR EFFLUENT REUSE
2.1.18
There are certain effluent reuse standards
that are being practiced in Hong Kong.
The effluent quality standards adopted for the reuse at Ngong Ping STW
(for toilet flushing and controlled irrigation), North District (for toilet
flushing, unrestricted irrigation & water features), Lo Wu Correction
Institution (for toilet flushing) and WSD’s water quality objectives for toilet
flushing have been reviewed to derive the proposed standards for the STKSTW. The
proposed standard is listed in Table 2.1.
Table 2.1 Proposed Reclaimed Water Quality for non-potable uses within
STKSTW
|
Determinand
|
Unit
|
Proposed Reclaimed Water Quality Criteria
for STKSTW *
|
|
pH
|
n/a
|
6-9 (d)
|
|
Turbidity
|
NTU
|
≤ 2 (b-d)
|
|
Total Suspended Solids
|
mg/L
|
≤ 10 (a)
|
|
Biochemical Oxygen Demand (BOD5)
|
mg/L
|
≤10 (a)
|
|
Colour
|
Hazen Unit
|
≤ 20 (a)
|
|
Ammonia Nitrogen
|
mg/L
|
≤ 1 (a)
|
|
Threshold Odour Number
|
T.O.N
|
≤ 100 (a)
|
|
Synthetic Detergents
|
mg/L
|
≤ 5 (a)
|
|
Escherichia
coli
|
cfu/100ml
|
Not Detectable (b-d)
|
|
Dissolved Oxygen
|
mg/L
|
≥ 2 (a)
|
|
Residual Chlorine
|
mg/L
|
≥ 1 (b)(e) (For
cleansing and toilet flushing)
|
|
|
mg/L
|
≤
1 (d) (For landscape irrigation)
|
|
*Note:
The effluent standards are
adopted from:
(a)
Agreement. No. CE 29/2001 – Outlying
Islands Sewerage Stage 1 Phase 1 – Ngong Ping Sewage Treatment Works and
Sewerage Investigation, Design and Construction.
(b)
Agreement No. CE 16/2004
(DS) – Demonstration Scheme on Reclaimed Water Uses in the North District –
Investigation
(c)
Contract No. SS P320 –
Design and Construction of the Redevelopment of Lo Wu Correctional
Institution
(d)
Guideline for Water Reuse,
(2004), USEPA
|
2.1.19
In order to meet the above
effluent reuse standard, sodium hypochlorite will be fed into reclaimed water
storage tank for disinfecting and maintaining a suitable residual chlorine
level on the portion of reclaimed water for reuse. Approximate 50L of sodium
hypochlorite solution would be stored on-site for effluent reuse.
2.1.20
The effluent reuse is adhered
to measures such as setting appropriate water quality requirements which is
presented in Table 2.1 above, prevention of cross-connections with potable
water supplies and avoidance of improper or inadvertent use of reclaimed water.
2.1.21
The reclaimed water pipeline
will be a separate system and will not be connected with the potable water
pipeline system. To avoid cross-connection of the reclaimed water supply to the
potable water supply, the pipes for the reclaimed water will be specially
arranged to differentiate them from that of the potable water pipe, e.g.
clearly labelled with warning signs and notices, colour-coded, and/or using
different pipe size, so that physical connection of the reclaimed water pipes
with the potable water fittings would not be possible.
2.1.22
For ground and facility washing
and landscape irrigation applications, operators will not be allowed to use
high pressure jet to avoid any atomized water to minimize aerosol formation from the reclaimed water.
2.1.23
Usage of reclaimed water will
reduce the quantity of potable water consumed in the existing DSD sewage
treatment works. This is considered to be the benefits or positive impacts of
the Project. The promotion of the use of reclaimed water in appropriate
circumstances to enable conservation of potable water will contribute to a
green and sustainable environment in Hong Kong.
2.2
Need of the Project
2.2.1
The need of the Project is to
meet the sewage treatment demand of the future population for supporting the
planned growth and development within the Sha Tau Kok area.
Existing Conditions
2.2.2
The existing STKSTW is
inadequate to cope with the population growth and future development within the
catchment.
2.2.3
The existing submarine outfall is
inadequate to cope with the increased sewage flow in the future.
2.2.4
The existing submarine outfall is
discharging treated effluent near-shore of Starling Inlet.
Purpose of the Project
2.2.5
The Project is to increase the
capacity of STKSTW to cope with the forecast increase in sewage flow upon
completion of sewerage under project “North District sewerage, stage 2 part 2 A
– Pak Hok Lam trunk sewer and Sha Tau Kok village sewerage” in Sha Tau Kok
areas, extensions of village sewerage in the areas planned by EPD, and the
proposed housing developments in Sha Tau Kok Town.
2.2.6
A new submarine outfall is
required for the Project to provide enough capacity for discharging the
increased sewage flow to Starling Inlet.
Scope
of the Project
2.2.7
The scope of the Project
includes the following:
a)
Increase the treatment capacity
of Sha Tau Kok Sewage Treatment Works (STKSTW) to 5,000 m3/day at
ADWF by 2021, with suitable allowance to cater for a further increase of
treatment capacity to 10,000 m3/day at ADWF after 2030 in Phase 2
b)
Construct a temporary sewage
treatment plant (TSTP);
c)
Demolish the existing Sha Tau
Kok Sewage Pumping Station (STKSPS) and decommission the rising main between
STKSPS and STKSTW;
d)
Construct a length of 520m new
gravity sewer; and
e)
Abandonment of the existing submarine
outfall and construct a length of 1700m new submarine outfall.
Environmental
Benefits of the Project
2.2.8
The environmental benefits of
the Project include the following:
a)
Improve treatment to produce
effluent with better quality
b)
Provide more treatment capacity
within the existing plant site
c)
Enclose the treatment
facilities and provide odour treatment to improve air quality
d)
Incorporate environmental
enhancements in the new treatment facilities, including renewable energy,
energy-efficient electrical and mechanical equipment, greening, and water
saving measures, etc.
e)
Locate the discharge point of
the new submarine outfall away from sensitive receivers, including the fish
culture zones and the identified species of conservation importance
Without
Project
2.3.1
The existing capacity of STKSTW
is expected to be fully committed in early 2019 based on the flow-build-up
derived from the latest planning data and village sewerage programme.
2.3.2
The existing STKSTW will suffer
from insufficient capacity to cope with the increase in sewage flow and loads
in the future, and consequently deteriorate the coastal water quality. Sewage
collected from the villages sewerage system will not receive treatment before
discharge since STKSTW do not have sufficient capacity to cope with the sewage
flow from the extended villages.
With
Project
2.3.3
STKSTW will have sufficient
capacity to cope with the increased sewage flow in the future for the existing
catchment and sewage collected from the extensions of different villages
sewerage projects. The proposed effluent quality is shown in the following
table:
Table 2.2a Proposed Effluent Quality
|
Parameter
|
Proposed
Effluent Quality
|
|
95% tile
|
Upper Limit
|
|
BOD5
(mg/L)
|
20
|
40
|
|
Suspended
Solids (mg/L)
|
30
|
60
|
|
Total
Nitrogen (mg/L)
|
12
|
24
|
|
E.
Coli (count/100mL)
|
1,500
|
100
(Note 1)
|
|
Note:
1. The upper limit is in monthly geometric
mean.
|
2.4.1
The purpose of this section is
to present the comparison of engineering and environmental benefits and
drawbacks of possible sewage treatment options. The selection of the preferred
option will consider avoiding the adverse environmental impacts to a maximum
practicable extent.
2.4.2
The existing STKSTW provides a
secondary level treatment. The existing discharge standard is shown below:
Table
2.1b STKSTW Existing
Discharge Standard
|
Parameter
|
95% -tile
|
Upper limit
|
|
Suspended Solids (mg/L)
|
30
|
60
|
|
BOD5 (mg/L)
|
20
|
40
|
|
E.Coli
(count/100mL)
|
1,500
|
100 (Note
1)
|
|
Note:
1. The upper limit is in monthly geometric
mean.
|
2.4.3
Secondary treatment level has
been considered for STKSTW, which is capable of removing biodegradable organic
matter, suspended solids and total nitrogen for compliance with the Water
Quality Objectives of Mirs Bay Water Control Zone. The
treatment method can fulfil the Project requirements without causing adverse
water quality and ecological impact.
2.4.4
Different options of secondary
treatment have been considered and presented in Section 2.5.13. All
these options are capable of meeting the Water Quality Objectives of Mirs Bay
Water Control Zone.
2.5.1
The consideration of
alternatives of the Project in conjunction with the existing STKSTW include the
following:
·
Options of Expansion Scheme
·
Options of Treatment Process
·
Disinfection Options
·
Sludge Treatment and Disposal
·
Consideration of Demolition of
the STKSPS
·
Consideration of New Sewer
Alignment
·
Consideration of new submarine Outfall
Alignment
·
Consideration of Abandonment of
the Existing Outfall
2.5.2
The alternatives were developed to consider alternative treatment level,
processes, design and internal layouts, alternative locations for the new
treatment facilities and submarine outfall alignment, alternative phased
installation for different flow projections, alternative designs to avoid or
minimize emergency discharges and alternative scale/size of the above-ground
structures, with a view to avoiding or reducing air quality, noise, water quality,
ecological, fisheries, landscape and visual and cultural heritage impacts
during construction and operation of the Project. The considerations covered by the
alternatives are summarized in the following table.
Table
2.2 Summary of the
Considerations Covered by the Alternatives
|
Considerations
|
Options of Expansion Scheme
|
Consideration of Decommission of TSTP
|
Options of Treatment Process
|
Disinfection Options
|
Sludge Treatment and Disposal
|
Consideration of Alternative Internal layouts
|
Consideration of Demolition of the STKSPS
|
Consideration of New Sewer Alignment
|
Consideration of Outfall Alignment
|
Consideration of Abandonment of the Existing
Outfall
|
Consideration of
Phased installation
|
Consideration of minimizing emergency discharges
|
Consideration of Alternative Construction Methods
and Sequence of Works
|
|
Alternative Treatment Level
|
|
|
ü
|
ü
|
|
|
|
|
ü
|
|
|
|
|
|
Alternative Treatment Processes
|
|
|
|
ü
|
ü
|
|
|
|
|
|
|
|
|
|
Alternative Design and Internal Layouts
|
|
|
ü
|
|
ü
|
ü
|
|
|
|
|
|
|
|
|
Alternative Locations for the New Treatment
Facilities
|
ü
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Alternative Submarine Outfall Alignment
|
|
|
|
|
|
|
|
|
ü
|
ü
|
|
|
|
|
Alternative Phased Installation for Different
Flow Projections
|
|
|
|
|
|
|
|
|
|
|
ü
|
|
|
|
Alternative Designs to Avoid or Minimize
Emergency Discharges
|
|
|
|
|
|
|
|
|
|
|
|
ü
|
|
|
Alternative Scale/Size of the Above-Ground
Structures
|
|
|
ü
|
|
ü
|
|
|
|
|
|
|
|
|
|
Other Considerations
|
|
ü
|
|
|
|
|
ü
|
ü
|
|
ü
|
|
|
ü
|
2.5.3
Comparisons of the environmental benefits and dis-benefits of
alternative development options are summarized and presented for the
alternative evaluation. The recommended
preferred options are selected to avoid adverse environmental impacts.
Options
of Expansion Scheme
2.5.4
Based on the programme and cost
of construction, land requirement and environmental issues, three options are
considered suitable for the expansion of STKSTW. These options for expansion
scheme are shown in Figure 2.18 – 2.20.
a)
Option 1 – Offsite Temporary
Sewage Treatment Plant (TSTP)
An
offsite TSTP with a capacity of 2500m3/day ADWF will be constructed to
maintain the sewage treatment operation during upgrading works of existing
STKSTW.
Existing
STKSTW will be expanded in the existing site after the TSTP is commissioned.
The
TSTP will be decommissioned upon commissioning of the Phase 1 expansion.
b)
Option2 – Onsite Temporary
Sewage Treatment Plant (TSTP)
An onsite
TSTP with a capacity of 2500m3/day will be deployed at the
south-eastern corner of the existing site to maintain sewage treatment
operation before decommissioning STKSTW for construction.
The TSTP will
be decommissioned upon commissioning of the Phase 1 expansion.
c)
Option 3 – Utilize the area of
existing Police Operation Base (POB)
The
existing POB will be relocated to a new site.
A new STW
with a capacity of 5000m3/day
ADWF will be built at POB site such that the existing STKSTW can be maintained
until commissioning of the Phase 1 expansion in the POB site.
The
commission time of Phase 1 expansion will be delayed as time is needed to
relocate the POB.
An onsite
TSTP will still be deployed as the existing STKSTW could not meet the project
sewage flow after 2019.
2.5.5
The options have been assessed
based on the evaluation criteria of cost, programme, land requirement, public
acceptance and environmental considerations. For the environmental considerations, the environmental benefits and
dis-benefits were compared. The findings
of the assessment are summarized in Table 2.3 and Table 2.4.
2.5.6
Option 2 is found to be the preferred
option. The major environmental benefits of this option are that the expansion
works will be carried out in the existing STKSTW and relocation of the police
operation base is not necessary. The cost, programme, and public acceptance of
this option are also considered comparatively favourable.
Table 2.3 Evaluation of
Alternative Expansion Schemes
|
Item
|
Options
|
|
1
|
2
|
3
|
|
Offsite TSTP
|
Onsite TSTP
|
Offsite Expansion
|
|
Environmental Considerations
|
2
|
3
|
1
|
|
*Note: “3” indicates the most preferable option and
“1” indicates the least preferable option.
|
Consideration
of Decommission of TSTP
2.5.7
The TSTP
is necessary to maintain sewage treatment service during the construction of
STKSTW which is anticipated to be completed by 2021. Upon completion of the
expansion works of STKSTW, the TSTP is recommended to be decommissioned.
2.5.8
To save
construction time and cost, TSTP would adopt MBBR process as mentioned in Section
2.1.7 as MBBR is relatively operation and maintenance
friendly with less energy consumption. It would
also be constructed aboveground and would adopt packaged units such as packaged
pre-treatment unit with supporting facilities which enable it to be completed by
2019.
2.5.9
An
alternative has been considered that the TSTP is constructed based on permanent
plant standards such that its service life can last longer. As the site is
congested, only the southern side of site is free to construct TSTP. As it is
close to the existing sea wall, deep excavation is considered at high risk and
difficult. Hence, in sake of safety, it is not recommended to construct a permanent
plant at southern side of site.
2.5.10
As
mentioned in Section 2.1.8, the effluent standard of TSTP would be better than
the existing STKSTW and can comply with the discharge license of existing
STKSTW.
2.5.11
TSTP is
recommended to be decommissioned after the expanding works of STKSTW completed
as the expanded STKSTW would have better effluent quality than TSTP which could
generally improve the water quality of Starling Inlet. In addition, as TSTP is
considered as a temporary structure, it could not blend in with the surrounding
and would obstruct the original landscape proposal at the area which is part of
the mitigation measures in operation phase to mitigate the visual impact of the
expanded STKSTW.
2.5.12
As the E&M
equipment design life is usually 15 years, the decommissioned E&M equipment
is recommended to be reused either by the Contractor or DSD for other similar
project as far as practicable.
Options
of Treatment Process
·
Membrane Bioreactor (MBR) - a mechanically
intensive process with excellent solids, BOD and coliform removal;
·
Moving Bed Bioreactor in
combination with Dissolved Air Floatation (MBBR+DAF) - a high-rate variation of
the conventional aeration plant process; and
·
Sequencing Batch Reactor with
filtration (SBR + Filtration) - a flexible and less mechanically-intensive process.
2.5.14
During operation and
maintenance, all 3 process options will require regular cleansing and use of
chemicals. A number of chemicals such as
calcium carbonate, lime, citric acid, sodium hypochloride and sugar will be required.
The sewage after cleansing will be diverted back to the treatment process tanks
for treatment before discharging through the outfall. All used chemicals will
also be neutralized and treated appropriately to stabilize the pH before discharging
through the outfall. Therefore, no environmental dis-benefit is anticipated.
2.5.15
The advantages and
disadvantages of the 3 process options are compared in Table 2.5.
Table 2.5 Comparison for
Three Processes
|
Options
|
Environmental Benefits
|
Environmental Dis-benefits
|
|
MBR
|
·
Smallest footprint required and hence limits
the extent for creating environmental impacts.
·
Provide the best effluent quality within a
small footprint.
·
Produce the least amount of sludge amongst the
options
|
·
Highest power consumption among the 3
processes.
|
|
MBBR
|
-
|
·
Require larger footprint for meeting the
discharge standard which will create additional environmental impacts and
public nuisance.
|
|
SBR
|
-
|
·
Require larger footprint for meeting the
discharge standard which will create additional environmental impacts and
public nuisance.
|
2.5.16
MBR process is preferred for
the expansion of STKSTW taking into consideration the lower life cycle cost,
effluent quality, process reliability, compact footprint, and process
full-scale application experiences in Hong Kong.
2.5.17
Higher level of treatment
process is not considered as effluent provided by MBR process can already meet
the WQO standard. Adopting higher level treatment is considered not cost
effective and will delay the construction programme. In addition, taking into
the consideration of land requirement, compact process is considered more
suitable for this project.
Disinfection
Options
2.5.18
The water quality impact
assessment results as presented in Section 5 showed that the discharge of
effluent from the expanded STKSTW after biological treatment by MBR will not
cause any adverse water quality impact and will comply with the Water Quality
Objectives of Mirs Bay Water Control Zone.
Under normal operation, the membranes are able to remove E. Coli and
other bacteria from the treated effluent before discharge to the outfall.
Sludge
Treatment and Disposal
2.5.19
Sludge digestion is used for
energy recovery and to reduce the mass of sludge solids in sewage treatment. The
major part of the energy recovery and solids destruction comes from primary
sludge. The waste activated sludge (WAS)
solids from the secondary biological treatment (in MBR, MBBR and SBR) remain
largely constant throughout the digestion unless extensive pre-treatment, such
as thermal hydrolysis, is applied.
2.5.20
It is considered inefficient to
provide sludge digestion since the required pre-treatment cannot be efficiently
provided for this plant size.
2.5.21
Based on above evaluation, it
is recommended not to include sludge digestion at the expanded STKSTW. This will allow the new treatment facilities to
fit within the limited footprint available; reduce capital and operational cost
of the expanded STKSTW; and retain the heating/energy value in the sludge. When
the sludge is dewatered and transported to the Sludge Treatment Facility (STF),
the heating/energy value in the sludge will help the incineration process achieve
autogenous combustion i.e. continuous incineration without the additional use
of external fuel.
2.5.22
There is an existing
administrative requirement imposed by EPD to have a minimum of 30% dry solids
content of dewatered sludge cake for disposal at the strategic landfills or
further treatment at the STF. Filter presses will be provided at the expanded
STKSTW to dewater the sludge to achieve a minimum of 30% dry solid content in the
dewatered sludge.
2.5.23
Based on the preliminary
estimation, 1.7m3/day, 3.5m3/day and 7m3/day
of dewatered sludge will be produced for TSTP, phase 1 expanded STKSTW and
phase 2 expanded STKSTW respectively. The dewatered sludge is recommended to
transport to STF at Tuen Mun for disposal or further treatment.
2.5.24
A preliminary layout plan for the
expanded STKSTW and TSTP with the recommended treatment options are shown in Figure 2.4a – 2.12 and 2.13 – 2.14 respectively. The layout minimizes the
impact on landscape and visual aspects by providing greening and tree planting
area as shown in Figure 2.4a and Figure 2.4b for construction stage and
operation stage respectively. Structures for the expanded STKSTW and TSTP will adopt
a low-rise design to minimize their height as far as practicable and minimize
the obstructive effect. The respective height of the new structure for the
expanded STKSTW and TSTP is approximately 10m – 19m and 10m above the proposed
ground level. In addition, the process flow diagrams are shown in Figure 2.2 and 2.3 for the expanded STKSTW
and TSTP respectively.
Consideration
of Alternative Internal Layouts
2.5.25
An
alternative internal layout has been considered and is shown in Figure
2.24 and Figure
2.25. The underground tanks are
proposed to place above ground at the southern side of the site which can
facilitate the operation and maintenance works during operation phase. However,
in view of the above ground tanks, the alternative layout will have greater
visual impact compared to the proposed scheme as shown in Figure
2.4a- 2.12. In
addition, as the above ground tanks will occupy the southern side of site which
will be in conflict with the TSTP. The TSTP has to be constructed offsite and
the environmental dis-benefits of the offsite TSTP expansion scheme has been
illustrated in Section 2.5.4. Hence, this alternative internal layout is not
recommended.
Consideration
of Demolition of the Sha Tau Kok Sewage Pumping Station
2.5.26
The existing STKSPS is
currently delivering all the sewage from the existing STKSTW catchment to the
inlet of STKSTW. A sewerage scheme which will demolish the STKSPS after
expansion of STKSTW is proposed. The scheme includes provision of a new sewer
along Shun Hing Street and the access road leading to STKSTW.
2.5.27
The proposed sewer will connect
to a section of sewer to be completed in 2016 for discharging to the expanded
STKSTW by gravity.
2.5.28
Under the proposed scheme,
sewage from STK town will be diverted to the new sewer and conveyed to the
expanded STKSTW by gravity. The STKSPS will be demolished and its rising mains will
be decommissioned and the land will be released to Lands Department.
2.5.29
Alternatively, the STKSPS will
be upgraded to accommodate the increased sewage flow. In addition to increase the pumping capacity,
the upgrade of STKSPS will include the following considerations:
a)
The aesthetic design of the existing STKSPS will
need to be enhanced according to Guidelines on Aesthetic Design of Pumping
Station Buildings;
b)
Upgrading the existing STKSPS will be
classified as a designated project which require an environmental permit under item F.3(b)(i), Part I of
Schedule 2 of the Environmental Impact Assessment Ordinance (EIAO), as the proposed sewage
pumping station has an installed capacity (average dry weather flow) of more
than 2,000 m3 per day and its boundary is less than 150 m from an
existing residential area.
c)
Stringent requirement for odour, water, noise
impacts, etc. resulting from the upgrading works will need to be met according
to Technical Memorandum of EIAO; and
d)
Construction works at the current site of
STKSPS will likely arouse public objection since the site is located near Sha
Tau Kok Chuen.
2.5.30
The environmental benefits and dis-benefits of the two options are
summarized in the following table.
Table 2.6 Environmental Benefits and Dis-benefits for the STKSPS Options
|
Options
|
Environmental Benefits
|
Environmental Dis-benefits
|
|
Demolish
the existing STKSPS
|
·
Limit the footprint for the construction works
to the existing STKSTW site. This is far from residential area and
comparatively less environmental impacts will be created.
·
Odour, noise and visual impacts to surrounding
sensitive receivers can be removed.
|
·
Minor dust and noise issues are anticipated
during the short demolishing period.
|
|
Upgrade
the existing STKSPS
|
-
|
·
Construction works at the current site of
STKSPS will arouse public objection since the site is located near Sha Tau
Kok Chuen due to higher significance of impacts on air quality, noise,
landscape and visual condition.
|
2.5.31
In addition to the
environmental dis-benefits, the STKSPS upgrading works will increase the cost
of construction and delay the programme for the Project.
2.5.32
It is considered that
demolishing of the existing STKSPS and replacing it by gravity sewer is the
preferred option.
Consideration
of New Sewer Alignment
2.5.33
There are 2 options for the
construction of the new sewer.
a)
The first option is to lay the new
sewer along the existing rising main on the Sha Tau Kok Road – Shek Chung Au
section.
b)
The second option is to lay the
new sewer along Shun Hing Street and passing the outside of the southern boundary
of the Sha Tau Kok Recreation Ground to the STKSTW.
2.5.34
Two options for the alignment
of the gravity system are shown in Figure 2.16.
2.5.35
The environmental benefits and
dis-benefits of the sewer alignment options are summarized in the following
table.
Table 2.7 Environmental Benefits and Dis-benefits for the Alternative
Sewer Alignments
|
Options
|
Environmental Benefits
|
Environmental Dis-benefits
|
|
Sha Tau Kok
Road
|
·
Excavation occurs once during construction of
the proposed sewer system and decommission of the existing rising main.
|
·
Numbers of sensitive receivers immediately
affected (Sha Tau Kok Chuen, Sha Tau Kok Recreation Ground and residential
buildings along Sha Tau Kok Road) during construction and maintenance.
|
|
Shun Hing Street
|
·
Fewer sensitive receivers are immediately
affected (Sha Tau Kok Chuen and Sha Tau Kok Recreation Ground) during
construction and maintenance in comparison to the other option.
|
-
|
2.5.36
Shun Hing Street Option is the
preferred option since it will affect fewer environmental sensitive receivers.
2.5.37
Significant traffic impact and
interface issue is anticipated if the sewer is to be constructed along Sha Tau
Kok Road – Shek Chung Au as it is the only access for Sha Tau Kok Chuen and
most of the utilities are laid under Sha Tau Kok Road – Shek Chung Au.
Consideration
of Outfall Alignment
Maintain
the Existing Discharge Location
·
Revise the diffuser design such
as discharge orientation, increase the number of discharge ports, adjust the
discharge velocity, etc.
·
Review the effluent discharge
qualities
2.5.41
The mariculturists’ strong
objection to the proposed outfall alignment could be a major risk to the
project since public consultation is of paramount importance to the successful
implementation of the Project.
2.5.42
In addition to the mariculturists
’ strong objection, there is a lack of strong evidence that the WQO could be
met with certainty. Maintaining the existing discharge location is considered
not feasible. An alternative outfall
alignment and design is proposed.
Proposed
Outfall Alignment
2.5.43
The proposed outfall alignment
from Starling Inlet to the water near Ah Kung Au is shown in Figure 2.15.
2.5.44
The considerations taken for
the proposed new outfall alignment include the following:
b)
Gain public acceptance
c)
Optimize the length of the
outfall
2.5.45
With reference to the latest
Nautical Chart of 2012 at Starling Inlet, the water depth near Ah Kung Au is
about 5m (during low tide) which is more favourable for effluent mixing and
enhance the near-field modelling result. Apart from the water depth, the
current velocity is generally stronger than that of the original proposed
outfall location which will also favour mixing and dilution of effluent. The Ah
Kung Au discharge location will minimize environmental impact and meet the WQO.
2.5.46
A near-field modelling with
CORMIX was carried out. The overall trend is that the initial dilution is
better performed offshore than inshore, which allows the possibility of meeting
the WQO. In order to obtain more
accurate modelling results, the proposed effluent quality has been fine-tuned (as
illustrated in Table 2.) for further modelling. The proposed effluent
quality will not affect the footprint of STKSTW and have minimal impact to the
process design.
2.5.47
The Horizontal Direction
Drilling (HDD) method will be implemented to construct the submarine outfall
beneath the Starling Inlet (Approximate 90m below the seabed level). A
cofferdam at the receiving pit of the outfall will be constructed and the
receiving pit will be dried. Then, the marine deposit will be removed from the
cofferdam and pre-reaming will be carried out in order to install the pipeline
and diffuser. The receiving pit will then be backfilled to the original seabed
level and the cofferdam will be removed. In accordance with the construction sequence
described, the HDD method will not disturb the surrounding sediments. A simple
cross section illustrates the HDD method is shown in Figure 2.17.
2.5.49
The proposed outfall alignment was
estimated to be about 2.0km long. Based on the near-field model results, the
proposed outfall alignment was optimized to about 1.7km long. Further reduction
is not recommended due to the decreasing water depth and the decreasing
distances to the nearby sensitive receivers.
Table
2.8 Environmental Benefits and Dis-benefits for Alternative Outfall
Alignment
|
Options
|
Environmental Benefits
|
Environmental Dis-benefits
|
|
Maintain
Existing Discharge Location
|
·
Outfall alignment is short
·
Less mud will be dredged from the sea-bed.
|
·
Located near the Sha Tau Kok Fish Culture Zone
which could create fisheries impact
and concern to mariculturists
·
May not be able to achieve the Water Quality
Objectives of Mirs Bay Water Control Zone
|
|
Discharge at Ah Kung Au
|
·
Improve water quality at Starling Inlet.
·
Can achieve the Water Quality Objectives of
Mirs Bay Water Control Zone
·
Located further away from Sha Tau Kok Fish
Culture Zone
|
·
Outfall Alignment is long
·
More soil will be dredged or excavated from
the sea-bed.
·
Reaming of rock underneath the sea-bed will be
required.
|
Temporary
Sewage Treatment Plant
2.5.50
Effluent from the TSTP will be
discharged through the existing outfall. According to the preliminary
construction programme, the new outfall and the TSTP will be completed by Year
2020 and Year 2018 respectively. Calculations show that the existing outfall will
be able to cope with the maximum projected flow from the TSTP, during
construction of the permanent STKSTW.
Consideration
of Abandonment of the Existing Outfall
2.5.51
Following the operation of the
expanded STKSTW, the existing outfall will cease operation. The existing
outfall will be abandoned by grouting or foam concreting. Prior to the grouting
/ foam concreting of the existing outfall, the outlet of the outfall would be
isolated from the sea level (such as temporarily extent the outfall above sea
level) and pump out the sea water inside the pipe. The grouting / foam
concreting would be performed by tremie pipe in order to avoid leakage of
concrete to the sea. The temporary works on the outlet of the outfall would not
be demolished until the concrete inside the outfall settled.
2.5.52
The arrangement will avoid the
needs of dredging and backfilling such that the seabed and aquatic ecosystem will
not be disturbed. The increase in turbidity of the surrounding water body is
minimised for the abandonment operation.
2.5.53
The environmental impact of this
arrangement is insignificant in comparison with the demolition and removal
option.
Consideration of Phased Installation for Expanded STKSTW
2.5.54
Based on the Sha Tau Kok Sewage
Treatment Works Expansion – Feasibility Study, the forecasted sewage treatment
capacity of STKSTW shall be increased to cope with the increased sewage flow
due to population growth and expansion of sewage catchment of STKSTW by
different sewerage projects.
2.5.55
As mentioned in paragraph
2.5.6, the civil and structural works will be built to Phase 2 capacity (10,000
m3/day at ADWF) by 2021.
2.5.56
The following options on phased
installation have been considered:
Installation
of sewage treatment facilities in one single phase
2.5.57
The sewage treatment facilities
will be installed in one single stage with a treatment capacity of 10,000 m3/day
at ADWF by 2021. Some of the sewage treatment facilities will be left idle since
there is not enough sewage flow at early stage. The operation & maintenance
cost will increase since extra maintenance will need to be taken for the units
installed.
Phased
installation of sewage treatment facilities
2.5.58
The sewage treatment facilities
will be installed in phases. According to the latest flow-buildup, sewage flow
would not reach 10,000m3/day until 2030. As such, it is proposed to
install the sewage treatment facilities in phases. When phase 1 expansion
completes, sewage treatment facilities with a treatment capacity of 5,000m3/day
will be installed first to cope with the increased sewage flow. Continuous
monitoring of the sewage flow will be carried out in order to plan for the
increase in treatment capacity for phase 2 expansion.
Table
2.9 Environmental Benefits and Dis-benefits for Phased Installation
|
Options
|
Environmental Benefits
|
Environmental Dis-benefits
|
|
Installation
of Sewage Treatment Facilities in One Single Phase
|
·
Completing all works in one single phase would
minimize nuisance to the public.
|
·
Idle equipment will still require energy to
maintain which increase energy consumption
|
|
Phased Installation of Sewage Treatment Facilities
|
·
Reduce the amount of idle equipment which
increase energy efficiency
·
Reduce use of chemicals required for the
maintenance of the idle equipment
|
·
May have nuisance to the public during
installation of facilities in Phase 2.
|
Consideration of Minimizing Emergency Discharge
2.5.59
In the event of emergency, such
as power outage, it is essential to provide measures to prevent flooding of the
sewage treatment works and direct discharge of sewage into nearby watercourse.
2.5.60
One option to avoid emergency
discharge is to export the sewage to the nearest STW. However, as the sewerage
system to STKSTW is by gravity, a pumping station would be required to divert
the sewerage to nearest STW which is Shek Wu Hui STW. As Shek Wu Hui STW is
about 11km away from STKSTW, it required a long sewer pipe and numbers of
pumping station which may induce other environmental impact during
construction. Hence, this option is not preferable,
2.5.61
In order to minimize
the risk of emergency discharge of untreated or partially-treated sewage into
the marine water of Starling Inlet, a number of precautionary measures have been taken into account in the
design of the expanded STKSTW. These
measures include:
·
Provision of dual power supply;
·
Provision of standby equipment for all treatment
units; and
· Provision of onsite storage of raw sewage up to 6 hours.
Dual power supply to eliminate the risk of power failure
2.5.62
The electrical
system of the STKSTW is proposed to receive two incoming supplies. Such dual supply configuration is to achieve
a reliable power supply for continuous operation of the pumps and auxiliary
equipment. Also, the arrangement for the
two power sources to be fed by two different ring circuits is desirable.
Provision of standby equipment for all
treatment units
2.5.63
Standby sewage treatment units will be provided in case of individual
equipment breakdown. Extra on-line sewage treatment units will be provided as
standby or on-shelf standby.
Provision of onsite storage of
raw sewage
2.5.64
A total storage capacity of 6-hour ADWF (2500 m3) will be
provided in case of failure of the sewage treatment works or power failure as
it is expected that the plant operation could normally be resumed within 6
hours based on detailed assessment on the emergency response procedure of
STKSTW and TSTP. The proposed emergency response plan is shown in Annex 2A. The emergency storage in STW will hold the untreated sewage. In case
overflow of the emergency storage occurs at the STW, a safety outlet will
function to divert excess incoming flows directly into Starling Inlet to
protect the STW from flooding. The location of safety outlet of STKSTW is shown
in Figure 2.4b. For TSTP, the safety outlet will be the existing outfall of STKSTW. The
detailed design will investigate and incorporate all practicable precautionary
measures to minimize the likelihood of such an event.
Table
2.10 Environmental Benefits and Dis-benefits for Emergency Measures
to Prevent Emergency Discharge
|
Options
|
Environmental Benefits
|
Environmental Dis-benefits
|
|
Dual Power
Supply
|
·
Minimize the risk of power outage hence a more
reliable STW
|
-
|
|
Provision of Standby Equipment
|
·
Minimize the risk of individual equipment
failure affecting the sewage treatment process
|
·
Standby equipment will require extra energy
for maintenance.
·
Extra material, such as lubricant, will be
needed for maintenance of the standby equipment
|
|
Provision of onsite storage of raw sewage
|
·
Reduce risk of sewage overflow and flooding of
the sewage treatment works
|
·
Largest footprint, due to construction of
additional tanks for onsite storage. This will create additional
environmental impacts and public nuisance.
·
Surplus C&D material.
|
|
|
|
|
2.5.65
As a result, precautionary measures such as routine/
regular checking of equipment, provision of dual power supply and backup generator, provision of
standby equipment for sewage treatment, 24-hour monitoring on the operation of STKSTW,
installing remote control and monitoring system (SCADA) to allow off-site
monitoring and provision of 6-hour emergency storage will be provided. According
to the emergency response plan in Annex 2A, the plant operation could normally be resumed within 6 hours. Hence, with
the implementation of above preventive measures, the possibility of sewage
overflow from STKSTW will be extremely low. Although emergency discharge has
never been happened in STKSTW since it is commissioned in 1989, safety outlet
will still be provided to the storage tanks to prevent flooding of the STKSTW
in case emergency discharge is required.
2.6.1
Alternative construction
methods and sequence of works have been considered for the construction of the
expanded STKSTW and the new outfall.
Construction of the Expanded STKSTW
2.6.2
The new structures for expanded
STKSTW will be constructed mostly with reinforced concrete for the benefits of
durability and ease of maintenance.
2.6.3
Reinforced concrete
construction is required for the water-retaining treatment tanks within the
expanded STKSTW.
2.6.4
Steel construction typically
takes less time. This alternative construction method cannot be widely adopted because
of the water retaining requirement within the new structure within the expanded
STKSTW. To facilitate the construction programme and minimize the environmental
impacts during construction, steel construction will be adopted locally in the
above-ground portion of the new structures where considered feasible and
practical. Constructing the expanded STKSTW completely above-ground is
feasible. As this will reduce the
excavation volume, the construction duration will be shortened. However, the elevated structure will not only
require more pumping which consumes more energy from lifting the water to higher
elevation but also cause adverse visual impact. Therefore, a completely
above-ground design is not adopted.
2.6.5
The expanded STKSTW will be
designed to a multi-level structure to minimise the footprint and fit within
the existing site. The water retaining
treatment tanks will be constructed below ground to minimize pumping and energy
consumption. As a whole, a low-rise design will be adopted to minimize the
visual impact.
2.6.6
The environmental benefits and
dis-benefits of the alternative STKSTW construction methods are summarized in
the table below.
Table
2.11 Environmental Benefits and Dis-benefits for Alternative STKSTW
Construction Methods
|
Options
|
Environmental Benefits
|
Environmental Dis-benefits
|
|
Reinforced
Concrete Construction
|
·
Considered most favorable for durability and
ease of maintenance
|
·
Longer construction period
|
|
Steel Construction
|
·
Shorter construction period
|
·
Not feasible or practical for the water
retaining treatment tanks
|
|
Above-ground Construction
|
·
Shorter construction period
|
·
Require more pumping and higher energy
consumption
·
More obtrusive visually and aesthetically
|
|
Combination of Above –ground and below-ground
Construction
|
·
Minimize pumping and energy consumption
·
Less visible
·
Public acceptance
|
·
Longer construction period
|
2.6.7
The alternative sequence of
works are previously considered and discussed under the alternative expansion
schemes.
Construction
of the New Outfall
2.6.8
Trenchless construction
techniques are proposed for the construction of the submarine outfall beneath
the Starling Inlet. It is identified that trenchless technique by Tunnel Boring
Machine (TBM), by Horizontal Direction Drilling (HDD) and dredging are feasible
in the construction of the submarine outfall. But as discussed below, the
trenchless technique by HDD is more suitable for the construction of submarine
outfall.
2.6.9
TBM method for the construction
of the submarine outfall is considered technically feasible in Sha Tau Kok. The
major concern for TBM method is that the heavy TBM equipment which will generate
transport logistics problem within the existing STKSTW footprint. Furthermore, TBM
method requires large working area in order to house the slurry tank and
electricity generator which is infeasible due to limited site area.
2.6.10
Dredging method requires the
excavation of the soil at the sea-bed of the Starling Inlet. After dredging,
the submarine outfall will be laid on the rock and backfilled by soil. This
method will create disturbance to aquatic ecosystem since the bottom sediments
will be disturbed and release toxic chemicals which will contaminate the
aquatic organism. The increase in turbidity during dredging will also create
ecological impact to the marine life
2.6.11
Horizontal Directional Drilling
(HDD) involves drilling a pilot hole, typically 100 to 150mm in diameter, and
then progressively enlarging the hole, using reaming tools in increments of 200
to 300 mm, until the required diameter is achieved (1.3 to 1.5 times the outer
diameter of the pipe). Drilling fluid (bentonite and/or polymer) is used to
remove the cuttings from the bore and in soft ground to stabilize the hole
during construction. Reaming is either done in the reverse direction to the
pilot boring or in the same direction (forward reaming). Once the reamed hole
has been fully formed, the pipeline is pulled and/or pushed into the reamed
hole. The suitability of HDD for this project is largely dependent on the
geotechnical conditions and the identification of suitable sites for launching
and reception of the drill and the pipe.
2.6.12
Table 2.12 provides the environmental benefits and dis-benefits of the three options
of construction methods for the submarine outfall.
Table 2.12 Environmental
Benefits and Dis-benefits for Alternative Outfall Construction Methods
|
Options
|
Environmental Benefits
|
Environmental Dis-benefits
|
|
Trenchless
Technique by TBM
|
·
No significant impact to marine ecology,
landscape and visual quality in comparison to the dredging method. Approximately
7,500m3 sediment will be removed
|
·
There is no sufficient space for slurry tank
and power generator within the STKSTW. A temporary worksite is required which
creates a larger footprint is needed and hence more environmental impact is
anticipated.
|
|
Trenchless Technique by HDD
|
·
No significant impact to marine ecology,
landscape and visual quality in comparison to the dredging method.
Approximately 3,040m3 sediment will be removed.
|
·
Require treatment prior to discharge of the
drilling fluid.
|
|
Dredging
|
·
Construction period and impact duration may be
shorter than the trenchless methods.
|
·
Causes water quality issues with a larger
extent of impact area. The sediments of the seabed will be disturbed, toxic
substances from the sediments will be released, and turbidity will increase. Approximately
40,000m3 sediment will be removed by dredging method.
·
Disturbance of the marine ecology, landscape
and visual quality.
·
Potential impact to Sha Tau Kok Fish Culture
Zone.
|
Sequence
of Works
2.6.13
As the proposed gravity sewer
overlap with Shun Hing Road, it shall be constructed in segments (approximately
20m – 30m per workfront) with limited number of concurrent workfronts to
minimize disturbance to the local public and road users. In view of the potential
noise impact, a total of not more than two workfronts working simultaneously
would remarkably reduce the construction noise to the surrounding but at the
same time be able to deliver the Project as per programme.
2.6.14
A comparison on sequence of
works is presented in Table 2.13.
Table 2.13 Environmental Benefits and Dis-benefits for Alternative Works
Sequence
|
Options
|
Environmental Benefits
|
Environmental Dis-benefits
|
|
Single
Workfront
|
·
Surface works limited to the single workfront,
and hence minimize the disturbance to the local public and road users.
·
Less PMEs is required
|
·
Nearby Sensitive receivers will be subjected
to longer period of environmental disturbance.
·
Longer overall project construction period
with longer duration of environmental impacts.
|
|
Multiple workfronts
|
·
Reduce the overall duration of construction
works and thus reduce the duration of potential environmental impacts to
nearby sensitive receivers.
|
·
More PME will be involved and this would cause
relatively heavier noise and dust impacts.
|
2.6.15
Temporary Sewage Treatment
Plant will be constructed by erection of temporary steel structure. The
foundation of the expanded STKSTW will first be constructed and followed by
erection of falsework and formwork for superstructure and concreting. No viable
alternative is considered.
2.7.1
After assessing the expansion
schemes in respect of their cost, programme, land requirement, public acceptance
and environmental consideration, Option 2A is recommended for the expansion
scheme of STKSTW. An expanded STKSTW will be built within the existing site of
STKSTW and a TSTP will be built to cope with the sewage flow during the
construction of the expanded STKSTW.
2.7.2
It is unavoidable to construct
TSTP to temporary treat the sewage flow during the construction of the expanded
STKSTW. It would be decommissioned after the expanded STKSTW operated. The
materials of the TSTP could be reused if there are projects necessary.
2.7.3
The treatment process selected
for the expanded STKSTW will be the MBR Process as it can provide the best
effluent quality within a small footprint. Smaller footprint can also limit the
extent for creating environmental impacts.
2.7.4
The STKSPS will be demolished
instead of upgrading it. The sewage in the Sha Tau Kok Town will be collected and
conveyed to STKSTW by gravity. Extra upgrading works for the STKSPS will
further increase the cost of construction and delay the programme for the Project.
Therefore it is considered that demolishing of the existing STKSPS and
replacing it by gravity sewer will be a more favourable option in terms of cost
and programme. The gravity sewer will be constructed along Shun Hing Street to
connect the existing sewerage network and convey to the expanded STKSTW.
2.7.5
The new outfall will extend
from Starling Inlet to Ah Kung Au to move the discharge point away from the
sensitive receivers as far as practicable and to ensure the effluent can comply
with the WQO.
2.7.6
The existing outfall will be
abandoned in place by grouting or foam concreting to minimize impacts to the
surrounding waters.
2.7.7
The expanded STKSTW will be a
multi-level building which consists of a partially below-grade reinforced
concrete structure to facilitate maintenance, minimize energy consumption and visual
impacts.
2.7.8
For the submarine outfall, the
trenchless technique of HDD is recommended because it creates the least
environmental impact to the marine ecosystem. In consideration to the length of
the submarine outfall and the placement of the whole section of the pipe under
the sea, Horizontal Directional Drilling (HDD) is the most suitable trenchless
method. The other trenchless methods are greatly constrained by the length and
site condition.
2.7.9
The civil works for the
construction will be carried in single phase and phased installation will be
carried out for E&M works and sewage treatment facilities.
2.7.10
To minimize the emergency
discharge of raw sewage, precautionary measures such as routine/ regular
checking of equipment, provision of dual power supply, provision of standby equipment for sewage treatment, 24-hour monitoring on
the operation of STKSTW, installing remote control and monitoring system
(SCADA) to allow off-site monitoring and provision of
an on-site 6 hours ADWF storage. With the implementation of above preventive
measures, the possibility of sewage overflow from STKSTW will be extreme low.
However, safety outlets will be provided to prevent flooding of the STKSTW.
2.7.11
The gravity sewer along Shun
Hing Road will be constructed in segments (approximately 20m to 30m per
workfront) with limited number of concurrent workfront to minimize disturbance
to the local public and road users. The expansion of the Sha Tau Kok Sewage Treatment
Works will be limited in the extent of the existing STKSTW.
2.8.1
The proposed site
for the modification/upgrading of sewage treatment works
(STW) and expansion of STW falls within an area zoned “Government,
Institution or Community” (“G/IC”) on the approved Sha Tau Kok Outline Zoning
Plan (OZP) No. S/NE-STK/2. According to the Notes of the OZP, ‘sewage treatment
plant’ is a Column 2 use and requires planning permission from the Town
Planning Board (TPB). As regards the existing STW, according to the covering
Notes, no action is required to make use of any land or building which was in
existence immediately before the first publication in the draft development
permission area plan. However, any material change of such use or any other
development (except minor alteration and/or modification to the development of
the land or building in respect of such use which is always permitted) must
always be permitted in terms of the Plan or in accordance with a permission
granted by the TPB. As the expansion works will include construction of new
temporary sewage treatment plant to handle the interim flow as well as the
demolition of the existing sewage treatment plant and construction of a new one
to increase the treatment capacity from 1,660m3/day to 10,000m3/day.
In this connection, the proposed sewage treatment works require planning
permission from the TPB.
2.8.2
The tentative implementation
schedule for the Project is presented below:
Table
2.14 Key Dates of Implementation Programme
|
Item
|
Date
|
|
Approval of Application for Permission under Section 16
of the Town Planning Ordinance
|
Nov 2016
|
|
Tender Gazette
|
Jan 2017
|
|
Commencement of Construction
|
May 2017
|
|
Completion of Construction
|
Dec 2022
|
2.9.1
Public consultation started as
early as in 2012 and consists of various meeting, discussion and site visit. Consultations
had been conducted with Sha Tau Kok Rural Committee and mariculturists regarding the proposed works
under this Project. Three consultation meetings had been arranged in 2014. Referring
to Section 2.5.48 above, the outfall location leading to
potential deterioration of water quality affecting the nearby fish culture zone
is the major concern. 5 consultation
meetings were carried out in 2015 to gather the views from STKRC and mariculturists on the proposed alignment of
the submarine outfall. The public also concerns about the visual impact of the
STKSTW and TSTP, particular on their height with “fung shui” issue to their
villages. In the design of STKSTW, two basements were proposed in order to
minimize the height of plant aboveground such that the visual impact is
mitigated. STKRC and North District Council finally endorsed the design. The
summary of the consultation meeting is summarized in Table 2.16.
Table
2.16 Summary of the consultant/meeting events
|
Date
|
Consultations
/ Meeting Events
|
|
28
Nov 2012
|
Consultation
with Sha Tau Kok District Rural Committee (STKRC)
|
|
28
Nov 2012
|
Consultation
with Sha Tau Kok District councilors
|
|
20
Dec 2012
|
Meeting
with STKRC
|
|
2
Feb 2013
|
Visiting
Sai Kung Sewage Treatment Works with STKRC
|
|
24
Apr 2014
|
Meeting
with STKRC
|
|
7
Aug 2014
|
Consultation
with STKRC and fishers Representative
|
|
23
Jun 2015
|
Consultation
with Sha Tau Kok District councilors
|
|
15
Jul 2015
|
Consultation
with STKRC and fishers Representative
|
|
20
Jul 2015
|
North
District Council – The 22nd Meeting of the District Minor Works
& Environmental Improvement Committee
|
|
19
Aug 2015
|
Meeting
with STKRC & Sha Tau Kok District councilors
|
|
24
Aug 2015
|
Consultation
with Sha Tau Kok Tam Shui Hang villagers
|
|
24
Aug 2015
|
Consultation
with Sha Tau Kok Town residents and fishers
|
|
14
Sep 2015
|
North District Council – The 23rd
Meeting of the District Minor Works & Environmental Improvement Committee
|
Table 2.17 Summary of
Project Interfaces of STKSTW
|
Item
|
Details
|
|
1
|
Project
Title
|
Sediment
Removal at Sha Tau Kok Fish Culture Zone, Boat Shelter and Approach Channel
|
|
Works Department
|
Civil Engineering Office, CEDD
|
|
Description of Works
|
To remove the sediments at the Sha Tau Kok
Fish Culture Zone, as well as to carry out maintenance dredging at Sha Tau
Kok Boat Shelter and Approach Channel.
|
|
Programme
|
Commencement
Date: 2017 tentatively
Completion
Date: 2018
|
|
2
|
Project Title
|
Drainage Improvement Works at North
District, including various drainage improvement measures in Sha Tau Kok.
|
|
Works
Department
|
Drainage
Projects Division, DSD
|
|
Description
of Works
|
To
carry out drainage improvement works in Sha Tau Kok Town area, including various
drainage improvement measures.
|
|
Programme
|
Commencement
Date: 2018
Completion
Date: 2022
|
|
3
|
Project Title
|
Public Rental Housing Estate at Sha Tau
Kok
|
|
Works
Department
|
Hong
Kong Housing Society
|
|
Description
of Works
|
To
construct public housing blocks which can accommodate a maximum population of
800 people.
|
|
Programme
|
Commencement
Date: December 2014
Completion
Date: End 2016
|
Drainage
Improvement Works at North District, including various drainage improvement
measures in Sha Tau Kok
2.10.2
According to the drawings
provided by Drainage Projects Division of DSD, an approximate 1m diameter
covered drainage pipe is proposed to be constructed along the access road to
STKSTW. A twin 1350 mm diameter drainage pipes is proposed to be constructed along
Sha Tau Kok Road – Shek Chung Au. There will be minor interface between the
drainage pipes by Drainage Projects Division and the proposed gravity sewer.
Liaison will be done with Drainage Projects Division to determine the alignment
of the proposed gravity sewer
Public Rental Housing
Estate at Sha Tau Kok
2.10.3
According to Hong Kong Housing
Society, the construction of the project will be completed by end of 2016 with
immediate population. It is assumed that during the commencement of the
construction for the expansion of STKSTW, the main construction works for the
public rental housing estate development, such as piling and excavation works
will be completed and there will be no potential project interface.
Sediment Removal at Sha Tau Kok
Fish Culture Zone, Boat Shelter and Approach Channel
2.10.4
The proponent (CEDD) of
“Sediment Removal at Shat Tau Kok Fish Culture Zone” has been consulted to
obtain the latest programme. The CEDD’s sediment removal project would be
conducted from the first half of 2017 to the first half of 2018 to remove
sediment from the STKFCZ, STK boat shelter and approach channel, as well as the
dredging area between the island and the shore.
The programme overlaps with the marine construction of cofferdam at the
location of outfall diffuser for this Project which would be conducted in 2017
for 3 months. There will be a minor interface issue between construction of
cofferdam and dredging for sediment removal along the approach channel. No
adverse cumulative environmental impact was anticipated and details were
presented in the following chapters. DSD will liaise with CEDD to avoid
concurrent works being undertaken in the vicinity of the proposed diffuser.