Traditional Chinese Simplified Chinese Email this article
LCQ7: Sewage treatment and water quality of rivers and streams in Tuen Mun and Yuen Long

    Following is a question by the Hon Albert Ho and a written reply by the Secretary for the Environment, Mr Edward Yau, in the Legislative Council today (May 7):


    Regarding sewage treatment and water quality of rivers and streams in Tuen Mun District and Yuen Long District, will the Government inform this Council:

(a)  of the current levels and daily handling capacity of the sewage treatment facilities in the above two districts (broken down by district and facility), where the treated sewage is discharged, and whether the facilities concerned can treat all the sewage generated daily in those two districts; if not, of the current daily quantity of sewage in the two districts which is untreated and directly discharged into rivers, streams and Hong Kong waters;

(b)  in the past three years, whether the Government had carried out regular inspections targeted at illegal connection of sewers for discharging sewage in Tuen Mun District and Yuen Long District; if so, of the number of sewers which have been proved to be illegally connected but have not yet been removed so far; among them, the number of those which are illegally connected to the Tuen Mun River, and whether the Government has any plan to remove all such sewers;

(c)  in the past three years, of the overall compliance with the Water Quality Objectives of the rivers and streams in Tuen Mun District and Yuen Long District, as well as the levels of heavy metals and Escherichia coli (E. coli) in such rivers and streams; and

(d)  of the current locations where water samples are taken for monitoring the water quality of the Tuen Mun River; the quality of the water samples taken at these locations in the past three years and, among such water samples, whether any of them were of "Bad" and "Very Bad" quality; if so, whether the Government has studied the reasons for the bad quality of water at those locations; if it has, the outcome of the study?


Madam President,

(a)  The Yuen Long area is divided into two sewage catchments and served by two regional sewage treatment works, namely, the Yuen Long Sewage Treatment Works (YLSTW) and the San Wai Sewage Treatment Works (SWSTW). The treated effluent from these two plants is discharged to Shan Pui River in inner Deep Bay and to Urmston Road, Castle Peak respectively. The capacities of these two plants with planned upgrades as necessary will be sufficient to handle the sewage generated in the catchments within the planning horizon.  Relevant details concerning the two treatment works are as follows:

Sewage    Major areas    Treatment      Design
Treatment  at present      Level          Capacity
Works                                      (m3/d)
_________  ___________    _________      _________

YLSTW    Yuen Long        Secondary*      70,000
SWSTW    Tin Shui Wai &  Preliminary**  164,000
          Yuen Long
          Town Centre

*  We plan to provide further disinfection treatment
    to the effluent of YLSTW.
**  We plan to upgrade the treatment level of SWSTW
    from preliminary to Chemically Enhanced Primary
    Treatment plus disinfection with further
    expansion of capacity to 246,000 m3/d.

    Notwithstanding the above, around 3,600 kg of organic load (in terms of 5-day Biochemical Oxygen Demand (BOD5)) is still discharged to rivers in Yuen Long every day. Currently, we plan to provide by 2014 four regional trunk sewerage networks as well as village sewerage for 44 villages in the Yuen Long area. This will help reduce the polluting load.

    At present sewage from the Tuen Mun catchment is conveyed via the existing public sewerage network to the Pillar Point Sewage Treatment Works (PPSTW) for preliminary treatment. The treated effluent is disposed of to the Northwest Waters through a submarine outfall located to the south of the River Trade Terminal. The design capacity of PPSTW is 235,000 m3/day. The treatment level of the PPSTW will also be upgraded from preliminary treatment to chemically enhanced primary treatment in the near future with a marginal increase in capacity. The planned upgrade will be sufficient to handle the additional sewage flow from the catchment within the planning horizon. The existing untreated pollution load discharged to rivers in the Tuen Mun area is estimated to be about 800 kg of BOD5 per day. We plan to provide sewers to unsewered areas, including villages, in Tuen Mun for the collection of sewage.

(b)  Environmental Protection Department (EPD) has from time to time conducted investigations of buildings and shops in Tuen Mun and Yuen Long to identify expedient connections. Upon confirming the sources of the expedient connections, we would request the owners/occupiers of the concerned premises to rectify the problems as quickly as possible. At the present moment, we are closely monitoring the progress of 40 outstanding cases in Yuen Long.

    At present, investigations have not revealed obvious expedient connections to the Tuen Mun River. However, there are unsewered villages in the upstream area. Sewage produced from these villages is not treated properly and thus indirectly affects the water quality of the river. The Government is planning to provide sewers to these villages in order to improve the water quality of the river in the upstream section.

(c)  The Water Quality Objective compliance rates and levels of heavy metals and E. coli of the rivers in Tuen Mun and Yuen Long Districts from 2005 to 2007 are summarised in Annex 1.

(d)  The locations of the six water quality monitoring stations monitored by EPD along the Tuen Mun River are shown in Annex 2. Two stations (TN1, TN2) are in the upstream section, three (TN3, TN4, TN5) are in the midstream section, and one (TN6) is in the downstream section. The Water Quality Index gradings of the six monitoring stations for 2005, 2006 and 2007 are as follows:

TN1                  Bad (2005, 2006, 2007)
TN2                  Excellent (2005 & 2007);
                    Good (2006)
TN3, TN4, TN5 & TN6  Good (2005, 2006, 2007)

    The "Bad" grading of TN1 in the upstream section was largely due to pollution from unsewered villages. Two dry weather flow interceptors have been installed at locations near Siu Hong Court and Tuen Mun San Hui to curb the impact of village sewage on the Tuen Mun River. This has improved greatly the water quality downstream of TN1.

Ends/Wednesday, May 7, 2008
Issued at HKT 14:51


Print this page