TABLE OF CONTENTS
6 Sewerage and sewage treatment implications
6.2 Population and Employment Data
6.3 Methodology of Sewerage Impact Assessment
6.4 Proposed Water Reclamation Plant
6.5 Existing and Planned Sewerage Infrastructure
6.6 Estimation of Sewage Discharge
6.8 Proposed Effluent Polishing Plant
6.9 Proposed Food Waste Pre-treatment Facilities
6.11 Treated Sewage Effluent Reuse
6.12 Proposed Emergency Bypass and Normal Discharge Route
6.14 Potential Impacts by the Proposed Sewerage System
6.15 Recommend Mitigation Measures
List of Tables
Table 6‑1 Population Summary of the Project in Revised RODP
Table 6‑2 Unit Flow Factors for Residential, Commercial and Industrial Population from GESF
Table 6‑3 Peaking Factors for Various Population Ranges
Table 6‑4 Global Unit Load Factors
Table 6‑5 Treatment Standard of STLMC EPP
Table 6‑6 Proposed Water Quality Standards of TSE Reuse
Table 6‑7 Summary of Estimated Sewage Discharge in Residential Site
Table 6‑8 Summary of Estimated Sewage Discharge in Commercial Site
Table 6‑9 Summary of Total Sewage Discharge
Table 6‑10 Projected Pollutant Concentration
Table 6‑11 Global Unit Load Factors
Table 6‑13 Sewage Discharge Build-up
Table 6‑14 Implementation Phasing for Major Sewage related Infrastructure
List of Figures
Figure 6‑1 Location Plan of EPP and Co-located Facilities
Figure 6‑2 Proposed SPSs location
Figure 6‑3 Proposed Emergency Bypass
Sewage Catchments in North-East New Territories
Population and Employment for Estimation of Sewage Flow
Table 6‑1 Population Summary of the Project in Revised RODP
Residential population |
159,000 |
Employment population |
165,000 |
Unit Flow Factors
Table 6‑2 Unit Flow Factors for Residential, Commercial and Industrial Population from GESF
Description |
Type |
Unit |
UFF per Employee (m3/head/d) |
UFF for commercial Activities (m3/head/d) |
Total Unit Flow Factors (UFF) (m3/head/d) |
Residential |
Public Housing (R1) |
Person |
|
|
0.19 |
Residential1 |
Private Housing (R2) |
Person |
|
|
0.27 |
Private Development in Non-residential Land use2 |
Private Housing (R2) |
Person |
|
|
0.27 |
Residential |
Modern Village |
Person |
|
|
0.27 |
Hotel |
Dining (J10) |
Employee |
0.08 |
1.50 |
1.58 |
Advanced
Manufacturing- |
General |
Employee |
0.08 |
0.2 |
0.28 |
Advanced Manufacturing- |
J6 |
Employee |
0.08 |
|
0.08 |
R&D Wet Lab Staff |
J2 |
Employee |
0.08 |
0.25 |
0.33 |
R&D Wet Lab Administration Staff |
J6 |
Employee |
0.08 |
|
0.08 |
R&D Dry Lab Staff |
General |
Employee |
0.08 |
0.2 |
0.28 |
R&D Dry Lab Administration Staff |
J6 |
Employee |
0.08 |
|
0.08 |
Retail |
J4 |
Employee |
0.08 |
0.20 |
0.28 |
Dining |
J10 |
Employee |
0.08 |
1.50 |
1.58 |
Entertainment |
J11 |
Employee |
0.08 |
0.20 |
0.28 |
Data Centre |
J6 |
Employee |
0.08 |
|
0.08 |
Office |
J6 |
Employee |
0.08 |
|
0.08 |
Convention |
J11 |
Employee |
0.08 |
0.20 |
0.28 |
Ancillary commercial |
J3 |
Employee |
0.08 |
0.10 |
0.18 |
Logistic |
J3 |
Employee |
0.08 |
0.10 |
0.18 |
GIC Facilities |
J11 |
Employee |
0.08 |
0.20 |
0.28 |
Residential/ Talent Accommodation |
J11 |
Employee |
0.08 |
0.20 |
0.28 |
1. The residential (private housing) means that the whole land parcel is solely for housing development, with minimal retail GFA to serve the residents.
2. Private development in non-residential land use means that the land parcels includes residential and other land uses
Table 6‑3 Peaking Factors for Various Population Ranges
Population Range |
Peaking Factor (including stormwater allowance) for facility with existing upstream sewage |
Peaking Factor (excluding stormwater allowance) for facility with new upstream sewage |
Sewers |
||
< 1,000 |
8 |
6 |
1,000 – 5,000 |
6 |
5 |
5,000 – 10,000 |
5 |
4 |
10,000 – 50,000 |
4 |
3 |
> 50,000 |
Max (7.3/N0.15,2.4) |
Max (6/N0.175,1.6) |
Sewage Treatment Works, Preliminary Treatment Works and Pumping Station |
||
< 10,000 |
4 |
3 |
10,000 – 25,000 |
3.5 |
2.5 |
25,000 – 50,000 |
3 |
2 |
> 50,000 |
Max (3.9/N0.065,2.4) |
Max (2.6/N0.065,1.6) |
Note
N = Contributing population in thousands
Table 6‑4 Global Unit Load Factors
Trades |
Unit |
Percentage (%) |
SS (kg/d) |
BOD (kg/d) |
COD (kg/d) |
TKN (kg/d) |
NH3N (kg/d) |
E.coli (no./d) |
Domestic (Residential) |
Person |
100 |
0.04 |
0.042 |
0.09 |
8.5x10-3 |
5x10-3 |
4.3x1010 |
Commercial G/IC(1) |
Employee |
100 |
0.059 |
0.087 |
0.173 |
9.2 x10-3 |
4.8 x10-3 |
3.5 x1010 |
Industrial (R&D and Adv. Manu) |
Employee |
10(2) |
0.059 |
0.087 |
0.173 |
9.2 x10-3 |
4.8 x10-3 |
3.5 x1010 |
Flow |
40(3) |
559 (mg/L) |
452 (mg/L) |
1130 (mg/L) |
62 (mg/L) |
29 (mg/L) |
3.5 x1010 |
|
flow |
50(4) |
800 (mg/L) |
800 (mg/L) |
2000 (mg/L) |
100 (mg/L) |
52 (mg/L) |
3.5 x1010 |
|
Schools (5) |
Student |
100 |
0.034 |
0.034 |
0.07 |
6.7 x 10-3 |
3 x10-3 |
3.5 x1010 |
Note: References from Sewage Manual Part 1 Table 4
(1) Unit Load Factors (Commercial, G/IC & Industrial) is the sum of Unit Load Factors for commercial activities and employed population.
(2) It is assumed 10% load from Industrial follow Commercial (Employed Population + Commercial Activities)
(3) It is assumed 40% load with similar characteristics to measured sewage at Tai Po Industrial Estate
(4) It is assumed 50% load could reach upper limits in WPCO TM Table 1
(5) Unit Load Factors of Schools is based on the number of school students
Parameter |
Unit |
Design Standard |
5-day Biochemical Oxygen Demand (BOD5) |
mg/L |
10 (95 percentile) |
Total Suspended Solid (TSS) |
mg/L |
10 (95 percentile) |
Ammonia Nitrogen (NH3-N) |
mg/L |
2 (annual average) |
Total Nitrogen (TN) |
mg/L |
10 (annual average) |
Total Phosphorus (TP) |
mg/L |
1 (annual average) |
Escherichia coli (E. coli) |
cfu/100ml |
1001 (Upper limit) |
Note: Monthly geometric mean is adopted
Table 6‑6 Proposed Water Quality Standards of TSE Reuse
Water Quality Parameter |
Unit |
Water Quality |
E. Coli |
cfu/100mL |
Not detectable |
Total residual chlorine (TRC) |
mg/L |
≥
1 (out of treatment system) |
Dissolved oxygen (DO) |
mg/L |
≥ 2 |
TSS |
mg/L |
≤ 5 |
Colour |
HU |
≤ 20 |
Turbidity |
NTU |
≤ 5 |
pH |
- |
6 - 9 |
Threshold odour number (TON) |
TON |
≤ 100 |
BOD5 |
mg/L |
≤ 10 |
Ammonia nitrogen |
mg/L |
≤ 1 |
Synthetic detergents |
mg/L |
≤ 5 |
Note:
1. Apart from TRC which has been specified, the water quality standards for all parameters shown above shall be applied at the point-of0use of the system. HU = Hazen Unit. NTU = Nephelometric Turbidity Unit,
2. The parameters are referenced to Technical Specifications on Grey Water Reuse and Rainwater Harvesting issued by WSD in May 2015, which is also referred to the target water quality standard adopted in North East New Territories Area project.
· To avoid cross connection and hence contamination, all pipes and fittings used for the TSE water supply and distribution system should be purple in colour for distinguishing them from the pipes and fittings used for the fresh water supply and distribution systems.
· Regular checking/inspections of the TSE supply and distribution systems for possible cross connection to the fresh water supply and distribution system should be carried out. The use of non-toxic dye may be adopted in the checking/inspections
· Warning signs should be permanently displayed where public access to TSE is possible (except for toilets) notifying the employees, visitors and the public at large that treated effluent is being used and is not suitable for drinking.
· Storage of sodium hypochlorite solution will be required and this is not a hazardous material. Thus, the storage is not considered as Potentially Hazardous Installation (PHI)
· Savings in fresh water supply, thus reduces the water to be diverted from the Dongjing River, and helps to relief the fresh water stress in downstream Dongjiang River that is often in needs of fresh water.
· Savings in energy consumption to convey the fresh water from the Dongjiang River, thus reduces the carbon footprint and contributes to the substainabilities of the communities.
· Savings in fresh water supply system expansion requirement
· Reduces the pollution to be discharged to the environment.
Planned Sewerage Infrastructure
Estimated Sewage Discharge from the Development
Table 6‑7 Summary of Estimated Sewage Discharge in Residential Site
Land Use Type |
Population |
Total ADWF (m3/day) |
Village |
70 |
20 |
Public Housing (R1) |
104,000 |
19,719 |
Private Housing (R2) |
24,000 |
6,495 |
Private Development in Non-residential Land use (R2) |
31,000 |
8,497 |
Sub-total |
159,000 |
34,731 |
Note:
1. The Residential accommodation includes OU(I&T)1.1.1, OU(I&T)1.1.2, OU(I&T)1.1.3, OU(MU)2.1.11, OU(MU)1.2.1 and G.5.11
2. Total may not add up due to rounding
Table 6‑8 Summary of Estimated Sewage Discharge in Commercial Site
Land Use Type |
Employment |
Total ADWF (m3/day) |
Hotel (J10) |
1,500 |
2,371 |
Advanced
Manufacturing- |
22,8001
|
6,391
|
Advanced
Manufacturing- |
11,4001 |
913 |
R&D Wet Lab Staff (J2) 3 |
21,5002 |
7,088 |
R&D Wet Lab Administration Staff (J6) 3 |
5,4002 |
430 |
R&D Dry Lab Staff (General) 3 |
43,0002 |
12,028 |
R&D Dry Lab Administration Staff (J6) 3 |
10,7002 |
859 |
Retail (J4) |
9,000 |
2,416 |
Dining (J10) |
2,200 |
3,592 |
Entertainment (J11) |
2,200 |
637 |
Data Centre (J6) |
600 |
47 |
Office (J6) |
7,700 |
618 |
Convention (J11) |
700 |
187 |
Ancillary commercial (J3) |
5,000 |
903 |
Logistic(J3) |
6,200 |
1,107 |
GIC Facilities (J11) |
12,500 |
3,501 |
Residential/ Talent Accommodation (J11) |
1,700 |
479 |
Sub-total |
165,000 |
43,567 |
Note:
1. Advanced Manufacturing is divided into 2 categories, Admin Staff : Manufacturing Staff = 1 :2
2. R&D is divided into 4 categories, Dry Lab : Wet Lab = 2:1; Admin Staff : Lab Staff = 1:4.The Unit Demand of R&D are reference to LMCL
3. The Unit Demand of R&D are reference to LMCL
4. Total may not add up due to rounding
Total Sewage Discharge
Table 6‑9 Summary of Total Sewage Discharge
Category |
ADWF (m3/day) |
Residential Discharge |
34,731 |
Commercial Discharge |
43,567 |
Other Contribution1 |
11,359 |
Sub-total of Proposed
Development |
98,623 |
Flexibility for receiving additional sewage flow from developments, existing villages, reject water from WRP and centrate from FWPF |
26,377 |
Total Sewage Discharge |
125,000 |
Notes:
1. Other contribution includes the discharge from NOL, Sport Centre and Swimming Pool, EPP, Schools, DCS, Private Hospital and Food waste pre-treatment plant.
Table 6‑10 Projected Pollutant Concentration
Trades |
Development Parameter |
SS (kg/d) |
BOD (kg/d) |
COD (kg/d) |
TKN (kg/d) |
NH3N (kg/d) |
E.coli (no./d) |
Domestic (Residential) |
159,977 |
6,340 |
6,720 |
14,400 |
1,360 |
800 |
6.68x1015 |
Commercial G/IC |
45,813 |
2,700 |
3,990 |
7,930 |
420 |
220 |
1.60x1015 |
Industrial (R&D and Adv. Manu) |
107,801 |
16,650 |
14,960 |
45,080 |
2.920 |
732 |
3.77x1015 |
Schools |
12,600 |
428 |
428 |
882 |
84 |
50 |
4.41 x1014 |
Total |
326,191 |
15,891 |
20,512 |
41,855 |
2,857 |
1,588 |
1.27 x1016 |
Table 6‑11 Global Unit Load Factors
Trades |
Unit |
Percentage (%) |
SS (kg/d) |
BOD (kg/d) |
COD (kg/d) |
TKN (kg/d) |
NH3N (kg/d) |
E.coli (no./d) |
Domestic (Residential) |
Person |
100 |
0.04 |
0.042 |
0.09 |
8.5x10-3 |
5x10-3 |
4.3x1010 |
Commercial G/IC(1) |
Employee |
100 |
0.059 |
0.087 |
0.173 |
9.2 x10-3 |
4.8 x10-3 |
3.5 x1010 |
Industrial (R&D and Adv. Manu) |
Employee |
10(2) |
0.059 |
0.087 |
0.173 |
9.2 x10-3 |
4.8 x10-3 |
3.5 x1010 |
Flow |
40(3) |
559 (mg/L) |
452 (mg/L) |
1130 (mg/L) |
62 (mg/L) |
29 (mg/L) |
3.5 x1010 |
|
flow |
50(4) |
800 (mg/L) |
800 (mg/L) |
2000 (mg/L) |
100 (mg/L) |
52 (mg/L) |
3.5 x1010 |
|
Schools (5) |
Student |
100 |
0.034 |
0.034 |
0.07 |
6.7 x 10-3 |
3 x10-3 |
3.5 x1010 |
Note:
References from Sewage Manual Part 1 Table 4
(6) Unit Load Factors (Commercial, G/IC & Industrial) is the sum of Unit Load Factors for commercial activities and employed population.
(7) It is assumed 10% load from Industrial follow Commercial (Employed Population + Commercial Activities)
(8) It is assumed 40% load with similar characteristics to measured sewage at Tai Po Industrial Estate
(9) It is assumed 50% load could reach upper limits in WPCO TM Table 1
(10) Unit Load Factors of Schools is based on the number of school students
Figure 6‑1 Location Plan of EPP and Co-located Facilities
Sewerage/sewage treatment facilities |
Parties responsible for construction |
Parties responsible for maintenance |
Twin rising mains |
Sewerage Project Division of Drainage Services Department |
Mainland North Division of Drainage Services Department |
Sewage pumping stations |
Sewerage Project Division of Drainage Services Department |
Sewage Treatment Division 1 of Drainage Services Department |
Sewage treatment facilities |
Sewerage Project Division of Drainage Services Department |
Sewage Treatment Division 1 of Drainage Services Department |
Figure 6‑2 Proposed SPSs location
Figure 6‑3 Proposed Emergency Bypass
Total Sewage Discharge with 10% allowance (cum/d) |
Total Sewage Discharge without 10% allowance (cum/d) |
|
2031 |
13,856 |
12,596 |
2034 |
65,315 |
59,377 |
Post 2034 |
125,000 |
113,636 |
Year |
EPP |
WRP |
FWPF |
Pumping Station in Site OU(SPS)1.2 |
Pumping Station in Site OU(SPS)3.2 |
Pumping Station in Site OU(SPS)5.7 |
2031 |
~65,000 m3/d |
112,500 m3/d |
100 tpd |
0.67 m3/s |
1.17 m3/s |
2.12 m3/s |
2035 |
125,000 m3/d |
|
|
|
|
|
· Applied peaking factors for all major treatment units and electrical and mechanical equipment to a void equipment failure;
· Standby unit for all major equipment would be provided in case of unexpected breakdown of pumping and treatment facilities such that the standby pumps and treatment facilities could take over and function to replace the broken pumps; and
· Back-up power for dual power supply would be provided in case of power failure to sustain the function of pumping and treatment facilities