For discussion PWSC(96-97)61
on 6 November 1996

ITEM FOR PUBLIC WORKS SUBCOMMITTEE
OF FINANCE COMMITTEE

HEAD 704 - DRAINAGE
Evironmental Protection - Sewerage and sewage treatment
278DS - Sewage sludge conditioning facilities

Members are invited to recommend to Finance Committee the upgrading of 278DS retitled "Shatin sewage treatment works sludge conditioning facilities" to Category A at an estimated cost of $102.6 million in money-of-the-day prices.

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PROBLEM
PROPOSAL
PROJECT SCOPE AND NATURE
JUSTIFICATION
FINANCIAL IMPLICATIONS
PUBLIC CONSULTATION
ENVIRONMENTAL IMPLICATIONS
LAND ACQUISITION
BACKGROUND INFORMATION

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PROBLEM

The existing sludge dewatering facilities at Shatin Sewage Treatment Works (STW) cannot dewater sludge to a dry solids content of 30% by weight before we dispose of it at strategic landfills.

PROPOSAL

2. The Director of Drainage Services, with the support of the Secretary for Planning, Environment and Lands, proposes to upgrade 278DS to Category A at an estimated cost of $102.6 million in money-of-the-day (MOD) prices to provide new sludge dewatering facilities in Shatin STW.

PROJECT SCOPE AND NATURE

3. The project comprises -

1. supply and installation of sludge dewatering facilities including -
   1. four centrifuges;
   2. four sludge feeding pumps and associated equipment;
   3. a polyelectrolyte chemical dosing system;
   4. electrical power distribution and automatic control systems;
2. construction of a sludge mixing tank and pipes;
3. modification of some existing structures; and
4. demolition of the existing sludge dewatering facilities.

JUSTIFICATION

4. In November 1993, the London Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matters¹ resolved, among other issues, that marine dumping of industrial waste should cease as from January 1996. Accordingly, we have discontinued marine dumping of the mixed sludge and shifted the disposal to strategic landfills since early 1996.

5. Meanwhile, the Integrated Sludge Disposal Strategy Study initiated by the Director of Environmental Protection concluded that we need to dewater the sludge to a dry solids content of 30% by weight before disposing of it at strategic landfills. This is because a vast increase in wet sludge, if maintained at a high moisture content, will cause operational problems at the landfills as well as environmental problems arising from leachate generation and possible contamination of surface water. The present sludge dewatering facilities at Shatin STW which is responsible for treating all sludge generated from operations at the STW and the Shatin Water Treatment Works are capable of dewatering sludge to a dry solids content of 10% by weight only. As an interim measure, we have contracted out the dewatering service at an annual cost of $26.2 million for 1995-96 and 1996-97. The contractor is able to achieve a 30% dry solids content by weight. We need to provide sludge dewatering facilities which could meet this standard on a permanent basis.

6. In order to upgrade the sludge dewatering facilities at Shatin STW, we need to provide high performance centrifuges to produce a high quality filtrate which can ensure consistent performance in the sewage treatment process. In addition, we need to modify some of the existing structures. These include adding baffle walls, concrete plinths and channels for cable ducting, and making structural improvements to the affected structures so that they can accept higher loading. The affected structures are the marine pumping station, sludge feed pump house, balancing tank and the centrifuge house.

FINANCIAL IMPLICATIONS

7. We estimate the capital cost of the proposed works to be $102.6 million in MOD prices (see paragraph 8 below), made up as follows -

8. Subject to approval, we will phase the expenditure as follows -

9. We have derived the MOD estimate on the basis of the Government's forecasts of trend labour and construction prices for the period 1997 to 2001. We will tender the proposed works under a fixed-price lump-sum contract. We adopt this form of contract as the major part of the works will be the supply and installation of electrical and mechanical equipment for which the scope of works is well defined.

10. We estimate the annually recurrent expenditure to be $20.8 million³ and will charge the entire cost to the Sewage Services Trading Fund. Taking into account the current cost of $26.2 million per annum for contracting out the dewatering service, which is also a charge to the Fund, we expect to achieve a net saving of $5.4 million per annum when the new facilities start operation. Subject to the Legislative Council passing a Resolution on appropriation of assets to the Trading Fund, the works under this project will, upon completion, become assets in the Trading Fund valued at cost.

11. Based on the current level of sewage charges, the proposed project by itself would lead to a decrease in sewage charges by about 0.8%.

PUBLIC CONSULTATION

12. As the project only involves enhancement and replacement works inside STW, we consider public consultation unnecessary.

ENVIRONMENTAL IMPLICATIONS

13. The Director of Environmental Protection completed an Environmental Review of the proposed project in March 1995 and concluded that an Environmental Impact Assessment is not necessary because the proposed new facilities will produce drier sludge and will reduce noise as well as odour levels within Shatin STW. The Director of Drainage Services will provide and maintain odour control equipment to ensure that the odour level within the site boundary of Shatin STW will be minimal. We will transport the dewatered sludge to strategic landfills and make suitable arrangements during transportation to avoid any off-site odour impacts.

14. For short term impact, we will add pollution control clauses in the contract to control dust, odour, noise and site run-off impact during construction.

LAND ACQUISITION

15. This project does not require land acquisition.

BACKGROUND INFORMATION

16. We upgraded 278DS to Category B in January 1996. We have completed the detailed design and drawings for the project using in-house staff. We plan to start the proposed works in January 1997 for completion in October 1998.

1 -- The United Kingdom (UK) and the People's Republic of China are parties to the London Convention. Hong Kong is obliged to observe the decision of the Convention because UK has applied the Convention to Hong Kong since 1975; and the Joint Liaison Group has agreed that the Convention will continue to apply to Hong Kong after 30 June 1997. Since waterworks sludge is clasisified as industrial waste, we need to stop marine dumping of mixed sludge generated from the operation at Shatin STW.
2 -- This cost is for overseas inspection of the high performance centrifuges mentioned in paragraph 6 which are not available in the local market. We will need to attend precision tests at the suppliers factory overseas before their delivery.
3 -- The recurrent expenditure of $20.8m is for operating and maintaining the proposed facilities ($7.52m) and for contracting out the transportation of dewatered sludge to landfills ($13.28m).

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