Environmental Functions and Performance

DSD's key responsibility is to provide and operate the drainage, sewerage and sewage treatment infrastructure in Hong Kong. In 2003, DSD collected and treated 943 million cubic metres of sewage to achieve a high level of sanitation control in Hong Kong. In delivering the service, we operated 65 sewage treatment works, 157 sewage pumping stations and low flow interceptors, 43 submarine outfalls, 2 effluent disposal tunnels and maintained 1514 km of sewers. In flood defence, we maintained 2507 km of drainage channels and drains and 23 flood pumping schemes. In continuously improving the drainage and sewage treatment infrastructure, we are running 69 contracts where construction of new works and upgrading works, as well as major maintenance works, are in progress.

Ever higher public health standard and environmental effectiveness of sewage treatment are put in place. Towards improving Victoria Harbour, the treatment of sewage from some 3 million people equivalent was upgraded from screening to CEPT since 2001 under the HATS (Harbour Area Treatment Scheme) Stage I Scheme.

Table 1.1 Sewage treatment in Hong Kong
Treatment level provided
2001
2002
2003
(Million m3)
(Million m3)
(Million m3)
Percentage
Screening and degritting
571
274
275
29.2%
Primary treatment
4
4
4
0.4%
Chemically Enhanced Primary Treatment
152
485
508
53.9%
Secondary biological treatment
158
148
156
16.5%
Total
885
911
943
100.0%

Performance Measures
We constantly introduce sound management practices and best available technology to make our operations more energy efficient, more ecologically sustainable and more effective in pollution reduction. Considerable achievements were made in 2003. The removal of pollutants, resource consumption and environmental emissions are quantified in Table 1.2.
 

   
Figure 1.1 Sewage treatment facilities in Hong Kong
Table 1.2
Achievements, Resource consumption and Environmental Emissions in 2003

Sewage treatment
2002
2003
Quantity
Total Flow
(Million m3)
911
943
BOD (tonnes)
In
126460
124157
 
Removed
97972
93654
 
Out
28488
30503
SS (tonnes)
In
149620
155693
 
Removed
125049
129563
 
Out
24571
26130
Total N (tonnes)
In
6674
5906
 
Removed
4531
3770
 
Out
2143
2136
Waste
Screenings
m3
19582
20705
Grit
m3
7879
7078
Dewatered sludge
tonnes
300017
305660
Gas emission
Greenhouse gas recovered & flared
million m3
7.8
9.3
Resource Consumption
Power
KWh
229646835
231002217
Chemicals
a. sewage treatment
  ferric chloride
tonnes
13265
13235
  alum
tonnes
4
86
  polymer
tonnes
51
72
b. sludge dewatering
  ferric chloride
tonnes
2959
2912
  polymer
tonnes
650
682
  Calcium nitrate
tonnes
0
0
Effectiveness
BOD removed
77.5%
75.4%
SS removed
83.6%
83.2%
Total N removed
Power consumed (KWh per m3 sewage treated)
0.252
0.245
Power consumed (KWh per tonne BOD removed)
2344
2466


 
2002
2003
Office
Paper consumed
Reams
18380
17300
Envelopes consumed number
133741
148089
Waste paper recycled kg
13068
13108
Power KWh
152 554
159 505
Unit rates  
Paper consumed (ream per staff)  
9.1
8.9


Sewer and Drainage Maintenance
 
Quantity
Drains, channels and water courses cleansed km
1825
513
Silt removed m3
71302
59946
Sewers cleansed km
729
614
Silt removed m3
7343
6351


Abbreviations  
BOD Biological Oxygen Demand
SS Suspended Solids
Total N Total Nitrogen
KWh Kilowatt hour


Through treating municipal sewage, we removed 93654 tonnes of BOD, 129563 tonnes of Suspended Solids and 3770 tonnes of Nitrogen from entering water courses and the sea.

Methane is a strong greenhouse agent which is 21 times more powerful in trapping heat in the atmosphere than Carbon Dioxide is. Last year, 9.3 million m3 of methane generated from anaerobic digestion of sewage sludge in our works was collected and flared, hence reducing its impact on global warming. On-site gas boiler such as the unit at Tai Po Sewage Treatment Works was powered by methane to generate heat for plant use and help reduce demand on electricity or fossil fuel.