Section Title Page
Figures
Figure 6.1 General Layout Plan for BCP
Figure 6.2 General Layout Plan for the Proposed Treatment Process
Figure 6.3 Proposed Landscape at Lower Deck Level Plan for BCP
Figure 6.4 Proposed Landscape at Upper Deck Level Plan for BCP
Appendices
Appendix 6.1 Estimation of Sewage Flow at Existing Site
Appendix 6.2 Estimation of Pollutant Loadings from Existing Site
Appendix 6.3 Estimation of Pollutant Loadings from Proposed Development
Appendix
6.4 Estimation
of Pollutant Loadings Discharge to
Appendix
6.5 Estimation
of Pollutant Loadings Discharge to
This section
presents the assessment of the sewerage and sewage treatment impact associated
with the construction and operation phases of the proposed BCP and associated
facilities, according to section
6.2 Assessment Approach and Methodology
The assessment has
been undertaken in accordance with the criteria and guidelines for evaluating
and assessing impacts on the downstream public sewerage, sewage treatment and
disposal facilities as stated in section
¡
Carry
out the desktop study, water sampling, topography survey and site visit to
collect the relevant information for the assessment.
¡
Investigate
and review the existing/planned sewerage networks and sewage treatment
facilities in the vicinity of the development and determine the sewage flow and
pollutant loading generated from the existing development.
¡
Determine
the potential sewage and pollutant loading arising from the proposed development.
¡
Study
and assess the need and impacts of discharging sewage to the existing/planning
sewerage systems in North East New Territories (NENT).
¡
Investigate
and determine the need and the feasibility of having a separate sewage
treatment plant within the Assessment Area.
¡
Formulate
options to mitigate the sewerage impacts identified and recommend the design,
operation and maintenance requirements for the sewage disposal system.
Desktop study,
topographical survey, water sampling of Deep Bay and site visit have been
undertaken to collect the relevant information for the assessment. The relevant
information collected is summarized below:-
¡
The
existing/planned sewerage facilities layout plan in NENT
¡
The
layout plan for the proposed LT/HYW BCP
¡
The
proposed planning data of the Project
¡
Water
sampling data at
¡
Topographic
survey plan for the proposed Project
6.2.2 Design Standards, Guidelines and Reference
The sewage flow and
pollutant loading generated from the proposed Project are based on the
following standards, guidelines and reference for the sewerage and sewage
treatment design:-
¡
Sewerage
Manual published by Drainage Services Department (DSD)
¡
Guidelines
for the Design of Small Sewage Treatment Plant published by EPD
¡
Review
of North District and
¡
Guidelines
for Estimating Sewage Flows for Sewerage Infrastructure Planning Version 1.0 by
EPD
¡
NENT New
Development Areas (NDAs) – Technical Report on Drainage & Sewerage Impact
Assessment
¡
Final
Report of Planning Study on Liantang/Heung Yuen Wai Cross-boundary Control
Point and its Associated Connecting Road in Hong Kong - Feasibility Study under
Agreement No. CE42/2006 (TP)
¡
Technical
Memorandum – Standards for Effluents
Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters
enacted under the Water Pollution Control Ordinance
6.3 Design Assumptions, Parameters and Criteria
6.3.1 Design Population
The
design population of the proposed LT/HYW BCP and Resite of Chuk Yuen Village is
summarised in Table 6.1 and Table
6.2 respectively.
Table 6.1: Population of the proposed LT/HYW BCP on Hong Kong Side
|
Type |
Daily Vehicles1 |
Daily Passengers1 |
|
Car |
2000 |
30000 |
|
Bus/Coach |
850 |
|
|
Good vehicles |
15000 |
30000 |
|
Staff2 |
- |
500 |
|
Type |
No. |
Kitchen Area (m2) |
|
Canteen3 |
2 |
25 |
Note:
1. All the vehicles and passengers figures are provided by the Shenzhen authority
2. The
total number of staff is based on the data given in the Feasibility Study under Agreement No. CE42/2006 (TP).
3. The area of the canteen kitchen in the proposed LT/HYW BCP is based on the Feasibility Study under Agreement No. CE42/2006 (TP).
Table 6.2: Population of the
Proposed Resite of
|
Development |
Type |
Population |
|
Resite of |
Modern village |
528 |
Note: The
design population of the Village Resite is based on the assumption that there
will be 4 persons per floor, 3 floors in each house and ultimately 44 houses in the Resite.
The number of staff of the proposed
Table 6.3: Staffing of proposed
|
Development |
No. of Staff |
|
|
157 |
|
Note: The no. of
staff is adopted from a similar administration building in another project, namely, Agreement
No. CE 58/2006 (HY) |
|
6.3.2 Design Average Daily Flow
Unit
Flow Factor of Villagers and Staff
To
estimate the average daily flow (ADF), the following global unit flow factors (GUFF)
for villagers and staff have been adopted in accordance with the EPD’s
Guidelines for Estimating Sewage Flows for Sewerage Infrastructure Planning
Version 1.0 and the DSD’s Sewerage Manual respectively:
¡
GUFF of
villagers (modern village) = 0.27 m3/person/day
¡
GUFF of
staff =
Unit
Flow Factor of Passengers
The
GUFF of passengers is estimated based on the Feasibility Study under Agreement
No. CE42/2006 (TP) by adopting the following assumptions:
¡
The flushing
water consumption is
¡
The
sewage flow generated from wash basins is
Assuming
the average processing time for a passenger is about 2 hours, then the GUFF of
passengers, including sewage from both flushing and washing basins, can be
estimated as 0.1 x 2/16 + 0.03 x 2/8 or
Unit
Flow Factor of Canteen
In
accordance with EPD’s Guideline for Design of Small Sewage Treatment Plants,
the GUFF of
6.3.3 Design Pollutant Loadings
The
sewage loadings such as suspended solid (SS), biological oxygen demand (BOD),
nitrite nitrogen (NO2N)+ nitrate nitrogen (NO3N), ammonia
nitrogen (NH3N) and Faecal Coliforms (E. coli) have been identified
for use in this assessment to assess the discharge requirements for the
proposed development.
NO2N
and NO3N are assumed to be in very small amount or zero in raw domestic
wastewater at the beginning and it will be increased with time in a series of bacteria
reaction. Some of the Total Kjeldahl Nitrogen (TKN) will be changed to the form of
NO2N and NO3N and finally discharged into water body (
Unit
Load Factors for Villagers and Staff
The
pollutant loadings of the sewage for villagers and staff are extracted from
Table 4 of the Sewerage Manual Part 1 by DSD as summarised in Table
6.4.
Unit
Load Factors for Passenger
Since
there is no reference data for passenger sewage characteristics, such
characteristics are assumed to be similar to those of the employed population,
but the sewage loading of passengers would be less than that of the employed
population due to the generally shorter time of stay of passengers. To estimate
the unit sewage load factors for passengers, it is assumed that the processing
time of each passenger is about 2 hours while the normal working hour of a
staff is about 8 hours per days. The unit load factors of passengers should
therefore be 1/4 of the unit load factors of staff. However, a factor of 1/3 instead of 1/4 has
been adopted to estimate the unit load factors of passengers to account for the
uncertainties in sewage loadings of passengers. The estimated design unit load
factors of passengers are summarised in Table
6.4.
Unit
Load Factors for Canteens
The
pollutant loading factors of canteens are adopted from the Guideline for Design
of Small Sewage Treatment Plants published by EPD as summarized in Table 6.4.
Table 6.4: Design Unit Load Factors
|
Loading Type |
Unit Load
Factor |
|||
|
|
Villagers1 |
Staff1 |
Passengers2 |
Canteen3 |
|
SS
(kg/day/person) |
0.04 |
0.034 |
0.0113 |
|
|
BOD
(kg/day/person) |
0.042 |
0.034 |
0.0113 |
|
|
TN
(kg/day/person)4 |
0.0085 |
0.0067 |
0.0022 |
- |
|
NH3N
(kg/day/person) |
0.005 |
0.004 |
0.0013 |
- |
|
E. Coli.
(no./day/person) |
4.3x1010 |
3.5x1010 |
1.17 x1010 |
- |
|
Note: 1.
The unit load factors for villagers and staff are based on Table 4 of the
Sewerage Manual Part 1 by DSD. 2.
The unit load factors for passengers are estimated as 1/3 of the unit
load factors for staff. 3.
The unit load factors for canteen are based on the Guideline for
Design of Small Sewage Treatment Plants by EPD. 4. The total nitrogen (TN) is equal to “TKN + nitrite N + nitrate N” whereas TKN is equal to “organic N + NH3N”. As nitrite N and nitrate N are assumed to be in very small amount or zero in raw domestic wastewater at the beginning, TN is taken as equal to TKN in the raw sewage. |
||||
6.3.4 Peaking Factors
Peaking
factors cater for seasonal/diurnal fluctuation and normal amount of
infiltration and inflow. The peaking factors which are functions of equivalent
population should be in accordance with EPD’s Guidelines for Estimating Sewage
Flows for Sewerage Infrastructure Planning Version 1.0 and are shown in Table 6.5.
Table 6.5: Peaking Factor for Sewers
|
|
Peaking Factor (including stormwater allowance) for facility with existing upstream sewerage |
Peaking Factor (excluding stormwater allowance) for facility with existing upstream sewerage |
|
|
<1,000 |
8 |
6 |
|
|
1,000-5,000 |
6 |
5 |
|
|
5,000-10,000 |
5 |
4 |
|
|
10,000-50,000 |
4 |
3 |
|
|
>50,000 |
7.3 x N0.15 or 2.4, whichever is higher |
6 x N0.175 or 1.6, whichever is higher |
|
Note: N is the contributing population in thousands.
6.3.5 Assessment Criteria for the Sewerage Facilities
It
is understood that the site is within a sensitive area where additional
pollutant loadings from the proposed residential development is not allowed to
be discharged to the existing water body from the environmental view point.
Therefore, this “no net increase
in pollutant loading requirement”, particularly for the BOD, SS, Nitrite + Nitrate
Nitrogen, NH3N and E.Coli. in the nearby water body from the
proposed development has been used in assessing the proposals of the sewerage
and sewage treatment facilities.
6.4 Existing Sewerage Conditions
6.4.1 Existing Sewerage and Sewage Treatment Facilities
These existing village sewerage systems have
been designed to collect the sewage flow from these local villages only. It is
considered that the existing systems are unlikely to cope with the additional
flows due to the Project.
6.4.2 Estimated Sewage Flow and Pollutant Loading from the Existing Site
The existing local
villages, Chuk Yuen South and
Table 6.6: Population and
Estimated Sewage Flow from Existing
|
Development |
Type |
Population |
GUFF (m3/person/day) |
ADF (m3/day) |
|
Existing Chuk Yuen
(North) |
Modern village |
378 |
0.24 |
90.72 |
|
Existing Chuk Yuen
(South) |
Modern village |
102 |
0.24 |
24.48 |
|
|
|
|
Total |
115.2 |
Note: The
global unit flow factor (GUFF) for existing Chuk Yuen villagers is in
accordance with Table 2 of Sewerage Manual Part 1, DSD and modern village is
assumed.
Table 6.7: Pollutant Loading of Existing Chuk Yuen Villages
|
Chuk Yuen (North) |
Chuk Yuen (South) |
Total |
||||
|
SS |
15.12 |
kg/day |
4.08 |
kg/day |
19.20 |
kg/day |
|
BOD |
15.88 |
kg/day |
4.28 |
kg/day |
20.16 |
kg/day |
|
TN |
3.21 |
kg/day |
0.87 |
kg/day |
4.08 |
kg/day |
|
NH3N |
1.89 |
kg/day |
0.51 |
kg/day |
2.40 |
kg/day |
|
E. Coli. |
16.25 x1012 |
no/day |
4.39 x1012 |
no/day |
20.64 x1012 |
no/day |
6.4.3 Design Treatment Performance of Existing Systems
It is understood
that the sewage from the existing
Table 6.8: Performance of Septic Tank
|
Loading Type |
|
Design Removal1 |
|
SS |
66% - 75% |
70% |
|
BOD |
40% - 52% |
45% |
|
TN |
20% - 29% |
24% |
|
E. Coli. |
3 log – 4 log |
3 log |
|
Loading Type |
|
Design Increase1 |
|
NH3N2 |
178% - 223% |
200% |
Note:
1.
The design removal and increase percentages of sewage loading are assumed to be the
mid-values of the typical ranges of removal and increase.
2. The amount of NH3N in the effluent of septic tank will be increased after the biological reactions within the septic tank but it will not exceed the amount of TN in the effluent of septic tank as TN=TKN + Nitrate N + Nitrite N and TKN = NH3N + Organic N.
Based on the
performance of Septic Tank, the effluent quality from septic tank in the existing
Chuk Yuen Villages is summarised in Table 6.9 below, which will act as the baseline pollutant loadings
currently discharging to the
Table 6.9: Pollutant Loading Performance of Septic Tank
|
Loading Type |
Before Septic Tank |
After Septic Tank |
||
|
SS |
19.20 |
kg/day |
5.76 |
kg/day |
|
BOD |
20.16 |
kg/day |
11.09 |
kg/day |
|
TN |
4.08 |
kg/day |
3.10 |
kg/day |
|
NH3N |
2.40 |
kg/day |
3.10 |
kg/day |
|
E.Coli. |
20.64 x1012 |
no/day |
20.64 x109 |
no/day |
6.5 Estimated Pollutant Loads due to the Project
6.5.1
Estimated Sewage Flow from the Proposed BCP and
Based
on the design population and sewage unit flow factors as mentioned in Section 6.3, the estimated average dry
weather flows generated from the proposed LT/HYW BCP at
Table 6.10: Estimated Sewage
Flow from Proposed
|
Development |
Type |
Population |
GUFF (m3/person/day) |
ADF (m |
|
Proposed village resite |
Modern village |
528 |
0.27 |
142.56 |
Note: The
GUFF for modern village is based on the EPD’s Guidelines for Estimating Sewage
Flows for Sewage Infrastructure Planning Version 1.0
Table 6.11: Estimated Sewage Flow from the proposed LT/HYW BCP on Hong Kong Side
|
Type |
Daily Vehicles |
Daily Passengers |
GUFF1,2 (m3/person/day) |
Percentage of Using Toilet5 (%) |
ADF (m3/day) |
|
Car |
2000 |
30000 |
0.02 |
10 |
60.00 |
|
Bus/Coach |
850 |
||||
|
Goods vehicles4 |
15000 |
30000 |
0.02 |
10 |
60.00 |
|
Staff |
- |
500 |
0.08 |
100 |
40.00 |
|
Total |
|
60500 |
|
Sub-Total |
160.00 |
|
Type |
No. |
Kitchen Area (m2) |
GUFF3 (m3 per day per m2 of kitchen area) |
ADF (m3/day) |
|
Canteen |
2 |
25 |
0.5 |
25 |
|
|
|
|
Total |
185.00 |
Note:
1.
The
GUFF of passengers is estimated based on the Feasibility Study under Agreement
No. CE42/2006.
2.
The
GUFF of staff is based on the Sewerage Manual by DSD.
3.
The
GUFF of canteen kitchen is based on the Guideline for Design of Small Sewage
Treatment Plants by EPD.
4.
The no.
of passengers for goods vehicles is assumed as 2 persons (i.e. a driver and a
passenger) per vehicle.
5.
The
percentage of passengers using toilets is assumed as 10%, which is referenced
from the design data of Lok Ma Chau sewage treatment system.
As
shown in above table, the 10% of passengers using toilet is adopted based on the
previous design data of sewage treatment system in Lok Ma Chau. Since this percentage of toilet use is a
critical parameter to determine the total sewage flow in the future LT/HYW BCP,
a sensitivity test of using 15% has been carried out and the results are presented
in below Table
6.12 to demonstrate the impact on the sewage flow and pollutant
loadings.
Table 6.12: Estimated Sewage Flow from the proposed LT/HYW BCP on Hong Kong Side (with 15% of passengers using toilet)
|
Type |
Daily
Vehicles |
Daily
Passengers |
GUFF (m3/person/day) |
Percentage
of Using Toilet (%) |
ADF (m3/day) |
|
Car |
2000 |
30000 |
0.02 |
15 |
90.00 |
|
Bus/Coach |
850 |
||||
|
Goods vehicles |
15000 |
30000 |
0.02 |
15 |
90.00 |
|
Staff |
- |
500 |
0.08 |
100 |
40.00 |
|
Total |
|
60500 |
|
Sub-Total |
220.00 |
|
Type |
No. |
Kitchen Area (m2) |
GUFF (m3 per day per m2 of kitchen area) |
ADF (m3/day) |
|
Canteen |
2 |
25 |
0.5 |
25 |
|
|
|
|
Total |
245.00 |
Notes: The percentage of passengers using toilets is taken as 15% for the purpose of sensitivity test.
6.5.2
Estimated Pollutant Loads from the Proposed BCP
and
Estimation
of the pollutant loads arising from the proposed development is detailed in Appendix 6.3. The following Table 6.13 summarizes the pollutant loads arising from the raw sewage of the
proposed development.
Table 6.13: Pollutant Loads
arising from the Raw Sewage of the Proposed Development
|
Parameters |
Loading
from the proposed LT/HYW BCP (10%)1 |
Loading
from the proposed LT/HYW BCP (15%)2 |
Loading
from Chuk Yuen Resite |
Total (10%)1 |
Total (15%)2 |
|
SS (kg/day) |
100.00 |
134.00 |
21.12 |
121.12 |
155.12 |
|
BOD (kg/day) |
100.00 |
134.00 |
22.18 |
122.18 |
156.18 |
|
TN (kg/day) |
16.75 |
23.45 |
4.49 |
21.24 |
27.94 |
|
NH3N
(kg/day) |
10.00 |
14.00 |
2.64 |
12.64 |
16.64 |
|
E. coli
(no./day) |
8.75 x1013 |
12.25 x1013 |
2.27 x1013 |
1..10 x1014 |
1.45x1014 |
|
Note: 1.
The pollutant loadings in these columns are estimated based on 10% of
passengers using toilets, as referenced from the design data of Lok Ma Chau
sewage treatment system. 2. The pollutant loadings in these columns are estimated based on 15% of passengers using toilet for the purpose of sensitivity test. |
|||||
In
order to meet the criteria of no net increase in the pollutant loading
to the nearby water body, mitigation measures are required to be provided. The
proposed schemes for achieving the design requirements are detailed in Section 6.6.
6.5.3
Estimated Pollutant Loads from the Proposed
Apart
from the sewage to be generated by the proposed BCP and Chuk Yuen Village Resite,
sewage will also be generated by the
6.6 Proposed Mitigation Measures
As
discussed above, the proposed BCP and Chuk Yuen Village Resite will definitely
increase the pollutant loading due to the associated sewage discharge. To
achieve the design criteria of no net increase in pollutant loading in the
nearby water body, the following mitigation options have been studied:
¡
Option
1 – Connecting to Shek Wu Hui Sewage Treatment Works (SWHSTW)
¡
Option
2 – Connecting to New Sewage Treatment Works for NDAs at North District
¡
Option
3 – Provision of On-site Sewage Treatment Works at BCP
Any
proposed sewerage and sewage treatment facilities should be capable of
achieving a high level of treatment and delivering disinfected effluent to the
nearby water body.
6.6.1 Option 1 – Connecting to Shek Wu Hui Sewage Treatment Works (SWHSTW)
It
is understood that the SWHSTW is being upgraded from
According
to the collected sewerage information, the existing sewerage systems in the
vicinity of the proposed BCP site are small sewerage systems with a series of
sewage pumping stations for collection of the sewage flow from local villages
in the areas and leachate from NENT Landfill site and for subsequent conveyance
of the collected sewage flow to SWHSTW for treatment and disposal. Apart from the aforementioned small sewerage
system, the existing village systems at some remote village areas are comprised
of septic tank and leach field for on-site natural treatment and disposal.
The
existing village sewerage systems have been designed to collect the sewage flow
from the local villages only. It is
considered that the existing systems are unlikely to cope with the additional
flows due to the proposed Project.
Therefore, upgrading of the village sewerage network and pumping
stations along
As confirmed
by the Authority, the current short-term upgrading works of SWHSTW is
inadequate to cater for the additional flow generated from the proposed LT/HYW BCP
or other new developments such as NDAs, Frontier Closed Area (FCA) in North
District. Thus, this scheme will require a further upgrading / expansion of
SWHSTW if it is to cope with the additional flows from these new developments
in the areas. The exact extents of the
sewerage upgrading works and the expansion of SWHSTW are subject to review and need
to be finalised amongst other projects in the area. As the construction
programme of proposed LT/HYW BCP is very tight (the Project should commence in
2013 and be completed no later than 2018), it would not be prudent to assume
that the SWHSTW would be able to be further expanded / upgraded to cope with the
sewage from the proposed LT/HYW BCP and Chuk Yuen Village Resite. Hence, this option is not recommended.
6.6.2 Option 2 – Connecting to New Sewage Treatment Plant for New Development Areas (NDAs) at North District
Based
on the Revised Technical Report No. 3D on DIA and SIA obtained from NDA
project, it is stated that the recommended scheme of sewage treatment for NDA
is expansion/upgrade of SWHSTW to cater for additional flows from Kwun Tung
North (KTN) and Fanling North (FLN) NDA and construction of a new sewage
treatment works in Ping Che (PC)/Ta Kwu Ling (TKL) to cope with the sewage flow
from PC/TKL NDA, Closed Area and the proposed LT/HYW BCP. However, the reply
from the project proponent of NDA in September 2009 advised that the new sewage
treatment works in PC/TKL would not be able to cater for the sewage generated
from the proposed LT/HYW BCP in terms of the targeted planning programme of the
NDA project. Therefore, this option is most likely not practicable to meet the planned
operation of the proposed LT/HYW BCP in 2018.
6.6.3 Option 3 – On-site Sewage Treatment and Disposal for BCP
Since
both options 1 and 2 are considered as not practicable, in view of the
programme, the option of on-site sewage treatment works is considered. The
proposed on-site sewage treatment works will likely be required to satisfy the
no net increase in pollutant policy in the region.
The
proposed sewage treatment works is to intercept the sewage flows generated from
the proposed LT/HYW BCP as well as Chuk Yuen Village Resite (the existing Chuk
Yuen Village is currently discharging its effluent via septic tanks and leach
field) to satisfy the no net increase requirement.
With
reference to the initial view of sewage treatment works of the proposed LT/HYW
BCP as advised by EPD in August 2009, the proposed local sewage treatment works
is highly recommended. To further reduce the quantity of the effluent
and the associated pollutants discharging into the nearby water body, the possibility of wide reuse of treated
effluent would be explored and considered.
In
order to comply with the policy of no net increase in pollutant loading in
Table 6.14: Comparison of MBR Treatment Performance with Discharge Standards
|
Parameters |
MBR Treatment Performance |
Discharge Standard* |
|
SS |
Below 2 mg/L |
Below 30 mg/L |
|
BOD |
Below 10 mg/L |
Below 20 mg/L |
|
TN |
Below 8 mg/L |
Not specified |
|
NH3N |
Below 1 mg/L |
Below 20 mg/L |
|
E.Coli |
Below 10 CFU/100mL |
Below 1000 CFU/100mL |
|
Residual Chlorine |
|
Below 0.2 mg/L |
* The discharge standards,
except residual chlorine, are extracted from those for the flow rate range of
200 to
Estimation
of the pollutant loads arising from the proposed development after treatment by
the MBR treatment plant is detailed in Appendix 6.4. Tables
6.15 and 6.16 summarize the additional pollutant loads
arising from the treated effluent of the proposed development with 10% and 15%
of passengers using toilet respectively.
Table 6.15: Pollutant Loadings in Treated Effluent (with
10% of passengers using toilet)
|
Parameters |
Treated
Effluent Quality |
Sewage Flow
Rate (m3/day) |
Pollutant
Loadings to Discharge |
|
|
SS |
2 mg/L |
327.56 |
0.66 |
kg/day |
|
BOD |
10 mg/L |
327.56 |
3.28 |
kg/day |
|
TN |
8 mg/L |
327.56 |
2.62 |
kg/day |
|
NH3N |
1 mg/L |
327.56 |
0.33 |
kg/day |
|
E.Coli. |
10 CFU/100
ml |
327.56 |
3.28 x 107
|
no/day |
Table 6.16: Pollutant Loadings in
Treated Effluent (with 15% of passengers using toilet)
|
Parameters |
Treated
Effluent Quality |
Sewage Flow
Rate (m3/day) |
Pollutant
Loadings to Discharge |
|
|
SS |
2 mg/L |
387.56 |
0.78 |
kg/day |
|
BOD |
10 mg/L |
387.56 |
3.88 |
kg/day |
|
TN |
8 mg/L |
387.56 |
3.10 |
kg/day |
|
NH3N |
1 mg/L |
387.56 |
0.39 |
kg/day |
|
E.Coli. |
10 CFU/100
ml |
387.56 |
3.88 x 107
|
no/day |
The treated effluent loadings from the proposed development are compared
with the baseline loadings (i.e., pollutant loadings from the existing Chuk
Yuen villages) in Table 6.17. It can be seen from the table that with the
proposed high level of sewage treatment such as MBR, the treated sewage loadings
discharged from the future development (with either 10% or 15% of passengers
using toilet) will be lower than the baseline pollutant levels. Hence, the requirement of no net increase in
pollutant loading can be achieved.
Table 6.17: Comparison of Pollutant Loadings
|
Parameters |
Baseline
Pollutant Loadings |
Pollutant
Loadings from Proposed Development with MBR Treatment (10%)1 |
Pollutant
Loadings from Proposed Development with MBR Treatment (15%)2 |
|
SS (kg/day) |
5.76 |
0.66 |
0.78 |
|
BOD (kg/day) |
11.09 |
3.28 |
3.88 |
|
TN (kg/day) |
3.10 |
2.62 |
3.10 |
|
NH3N (kg/day) |
3.10 |
0.33 |
0.39 |
|
E.Coli. (no/day) |
20.64 x109 |
3.28 x 107
|
3.88 x 107
|
Note:
1.
The pollutant loadings in the column are estimated based on 10% of passengers
using toilets, as referenced from the design data of Lok Ma Chau sewage
treatment system.
2.
The pollutant loadings in the column are estimated based on 15% of
passengers using toilet for the purpose of sensitivity test.
Nevertheless,
in order to further reduce the quantity of effluent and the associated
pollutants to the nearby water body, reuse of treated effluent has been considered
in this Project. Due to the good
effluent quality from the MBR, the treated effluent can be reused for
irrigation of landscaping area. The possible reuse quantity of treated effluent
is estimated as follows:
For
irrigation, it is assumed that:
¡
The water
consumption rate of irrigation is 6 -10 litres/day/m2 for 120 days
per year.
¡
The
open landscaping area for the proposed BCP site is about 56,400 m2
as shown in the Figures 6.3 and 6.4.
Based
on the above assumptions, it can be estimated that the average amount of water use
for irrigation is 111.25 m3/day. Details of the estimation are given in Appendix 6.5.
After the reuse, the pollutant loadings of the
remaining 216.31 m3/day that will be discharged to the
Table 6.18: Comparison of Sewage Flow and Pollutant Loadings to be discharged after Effluent Reuse (with 10% of Passengers Using Toilets)
|
Parameters |
Baseline Pollutant Loadings |
Pollutant Loadings from Proposed Development after Treatment |
Pollutant Loadings from Proposed Development after Treatment and Reuse |
|
Sewage Flow (m3/day) |
115.2 |
327.56 |
216.31 |
|
SS (kg/day) |
5.76 |
0.66 |
0.43 |
|
BOD (kg/day) |
11.09 |
3.28 |
2.16 |
|
TN (kg/day) |
3.10 |
2.62 |
1.73 |
|
NH3N (kg/day) |
3.10 |
0.33 |
0.22 |
|
E.Coli. (no/day) |
20.64 x109 |
3.28 x 107 |
2.16 x 107 |
While
the estimated total sewage flow from the proposed development and Chuk Yuen
Resite is
Despite
the good quality of MBR treated effluent, the treated effluent for reuse
purpose needs to fulfil the effluent reuse standards on residual chlorine and
E. Coli, as given in Table 6.19.
Table 6.19: Standards for Reuse of MBR Treated Effluent
|
Parameters |
Effluent
Reuse Standards* |
|
Residual Chlorine |
Over 1
mg/L |
|
E.Coli |
Non-detectable |
*The effluent reuse standards for residual chlorine and E.Coli are based
on similar projects with effluent reuse.
In
order to meet the effluent reuse standards for residual chlorine (over 1 mg/L) and
E. Coli (non-detectable) and yet without exceeding the effluent discharge
standard for residual chlorine, i.e., below 0.2 mg/L (based on EPD’s advice), it
is proposed to use chlorine for disinfection of only a portion of the MBR treated effluent that will be directed to the effluent reuse system, whereas the remaining portion of MBR treated
effluent that is to be discharged will not undergo any chlorine disinfection.
As
illustrated in Figure 6.2, the sewage
treatment plant will mainly consist of an equalization tank, denitrification
tank, membrane bioreactor tanks, effluent storage tanks (with an estimated size
of
The sewage treatment plant will be provided with odour containment and control measures as detailed in Section 3.5.2.2 to minimize the potential odour impact on nearby sensitive receivers.
During
operation of the treatment plant, screenings and dewatered sludge (with a
minimum solid content of 30%) would be generated from the onsite sewage
treatment facility, which will be operated and maintained by Drainage Services
Department. Based on reference to other similar projects, it is anticipated
that a small quantity of these waste, approximately 1.2 m3 per day
would be generated and disposed at the landfill. The dewatered sludge will be
collected by a licensed collector at regular intervals, as determined by the
operation of the BCP. As an alternative
to on-site dewatering of sludge, sludge could be transferred by tankers for
off-site treatment due to its small quantity.
Provided that the handling, storage and disposal of the wastes are
properly managed and accidental release to the surrounding environment does not
occur, adverse environmental impacts are not expected.
6.7 Short Term Measures during Construction Phase
The
sewage generated during the construction stage from the on-site workers or site
offices will be collected in chemical toilets and then disposed off-site periodically
by tankers (see Section 5.5.1). Therefore, no sewerage impacts are expected
from the site during the construction phase.
6.8 Environmental Monitoring and Audit
It
is recommended to conduct regular monitoring of the quality of treated effluent
discharged from the proposed sewage treatment works in order to ensure
compliance with the no net increase in pollutant loading requirement as well as
the relevant licence requirements under the Water Pollution Control Ordinance.
The Project will
generate sewage flow of
Apart from the sewage
to be generated by the proposed BCP and Chuk Yuen Village Resite, a small
amount of sewage (12.56 m3/day) will also be generated by the