Drainage Services Department

*~W-I btM!; ~~/J'~5571< JEJI~~ Small Sewage Treatment Facilities on Lantau Island and Outlyi ng Isla nds

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Sewage produced in communities on Outlying Islands are treated before discharge into nearby

receiving waters. In South Lantau Island and other Outlying Islands, we constructed and operate 12

sma ll sewage treatment plants providing sewage treatment services to a total population of about

50,000. With these sewage collection and treatment facilities we provide a safe environment for the

community and help maintain the quality of the public bathing beaches.

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To provide world-class wastewater and stormwater drainage services enabling the sustainable development of Hong Kong .

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The sewage treatment processes commonly adopted in small sewage treatment plants in remote areas of South Lantau

Island and other Outlying Islands are listed below:

Oxidation Ditch

Rotating Biological Contactor

Sequencing Batch Reactor

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Oxidation Ditch (00)

This sewage treatment process is used in Mui Wo and Hei Ling Chau

STW. The OD is a modified form of the activated sludge system. It is an

elongated closed loop resembling a racetrack equipped with aeration

equipment called a rotor. Sewage is treated in the loop. The rotating

of the rotor entrains oxygen for the growth of micro-organisms and

maintains the flow velocity. This fosters the mixing process and keeps

the micro-organ isms in suspension for assimilating the pollutants.

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Brush Type Mechanical Aerator

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Final Sedimentation Tanks

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Rotating Biological Contactor (RBC)

This sewage treatment process is used in Ma Po Ping, Shek Pik

and Hei Ling Chau STW. A rotating biological contactor is a

type of secondary (biological) treatment process. It consists of

a series of closely spaced plastic discs as media for attached

growth micro-organisms (biofilm). The discs are mounted on a

rotating shaft which is supported just above the corresponding

channel. Micro-organisms grow on the surface of the discs

where biological degradation of the pollutants takes place.

Aeration is provided by the rotating action, which exposes

the biofilm to the air after contacting them with the sewage,

facilitating the degradation of the pollutants.

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MJiliJ1f1:!t 4PJllfliN Overview of the Ma Po Ping RBe

Primary 1:1w'-!~ Sedimentation Tank Rotating Biological Contact ors

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lijj~5Ji:i!'&)t!l Final Sedimentation Tanks

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Sequencing Batch Reactor (SBR)

This sewage treatment process is used in Chi Ma Wan, Chi Sun, Ma Po Ping, Sha Tsui, Hei Ling Chau, and Peng Chau

STP. It is also used in Ngong Ping Sewage Treatment Works, the first tertiary STW with reclaimed water facility.

The SBR is a fill-and-draw activated sludge treatment system . The operation of the SBR, consists of three distinct

periods, AERATION/MIXING, SETTLING and DECANTING . Each tank in the SBR system is filled during a discrete period

of time. During aeration/mixing period, mixing and aeration are carried out in the tank to maintain a certain level of

dissolved oxygen for the growth of micro-organisms. Following the aeration/mixing period, the sewage together with

the micro-organisms are allowed to separate by sedimentation. The treated effluent is subsequently drawn from the

reactor by decanting . For the new SBRs at Sha Tsui and Hei Ling Chau, treatment of influent and discharge of treated

effluent are continuous.

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JllIfiil Environmental Protection

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Sewage contains many types of human enteric organisms associated with various water borne diseases. After secondary

treatment, treated effluent is disinfected by ultraviolet light before discharge via submarine outfalls.

These sewage treatment facilities can improve living environment for the community and help maintain good water

quality in nearby public bathing beaches.

~iilij. Public Bathing Beaches

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Hung Shing Yeh Beach

Jiifi±m)}J<i! Lo So Sh ing Beach

~ mH!~J~)}J<i! Cheung Chau Tung Wan Beach

Ill, .:g-~ )}J<i! Kwun Yam Beach

11fiI~f~ Discovery Bay

llitH'l;~)J1<i! Silver Mine Bay Beach

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Pui 0 Bay Beach

T' ~)Y)}J<i! Lower Cheung Sha Beach

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Upper Cheung Sha Beach

±mmi)}J<i! Tong Fuk Beach

LAMMA ISLAND

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To act proactively in an environmental manner and to provide a

better service to nearby residents, odour management system with

deodourizing facilities have been put into operation in these sewage

treatment works.

.IIiUII¥.J~~1it*.~.. Key Parameters of Treated Effluent

5'5*JE.I!~ Sewage Treatment Plants

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Drainage Services Department

JEI!f¥f¥ ~~jj£*~$ Discharge Standards

... ..... .......... ................ ..... ...... ..... Treatment ~fl-~ 't;; E3 C'--- JJ*f'= S) o~ ii ))IL~ jL /" ~

Process (1) Design Flow (m3/day)

SBR 350

SBR 210

RBC / SBR 600

00 1,190

SBR 183

RBC 790

SBR 100

SBR 761

00 900

RBC 177

TF 170

SBR 1,580

*~AAf.\,'R Drainage Hotline: 2300 1110 -FJ9:*~ilJ General Enquiries: 2877 0660 ~T!W*f:i E-mai l: enquiry@dsd .gov.hk

*~wM1'lJ[ DSD's Website: www.dsd .gov.hk

~ TSS(2)

~ (mg/L)

~30

~30

~30

~30

~30

~30

~30

~30

~30

~30

~30

~30

............ BOD(3) (mg/L)

~20

~20

~20

~20

~20

~20

~20

~20

~20

~20

~20

~20

.=.*~JL~".Fl£fJ~ Printed in June 2009