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Drainage Services Department *~W-I btM!; ~~/J'~5571< JEJI~~ Small Sewage Treatment Facilities on Lantau Island and Outlyi ng Isla nds - 22'lo' + ~ ll O; '.I7 ~ l< o; m~~ •• ~M.~~~*.~.~.~m~llimlli~*.o~~*.~& •• ,~m.~&~ 11=12r8~/J\~)'5*.I!~ , ~*~~3i~m~m1;!:!;)'5*.I!~IR~ a ~73§:@)'5*4~~&.I!~~~ , mllitl~~.m&~~~.~*.~.~~~o 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. ~1r~B'9m~ Our Vision mt±!;titW- #&~ )'J*fDm*~I1IHJFJJ~~~m . tA{JEji~7£~ r:iJ t~ #I~}* a To provide world-class wastewater and stormwater drainage services enabling the sustainable development of Hong Kong . 1±~*~l1Jt:HilB~~±mh:&~~ ~ /J\~ 5'5*~I!~ , ~~B!ffl1-:.z T'~ 5'5*~I!l~Jj;: 3§I~it11:;~ ~!fj})fUi )lijtJj; 5i ttl; it,& ~ ~ iU The sewage treatment processes commonly adopted in small sewage treatment pl ants in remote are as of South Lantau Island and other Outlying Islands are listed below: Oxidation Ditch Rotating Biological Contactor Sequencing Batch Reactor Oxidation Ditch (00) ~~*~.~Jj;~~B!m~ •• :& ••~~ This sewage treatment process is used in Mui Wo and Hei Ling Chau *~I!~ 0 3§I~it1UI~)!t1 5'55~5t~ STW. The OD is a modified form of the activated sludge system. It is an .,~~-.m~m.~3§I~m •••~, elongated closed loop resembling a racetrack equipped with aeration 5'5* )jjEA5M~$1~~U5¥11:; 0 ilID~it1UI~9:j[ equipment called a rotor. Sewage is treated in the loop. The rotating .~~ ••• j[mm•• :&*.*mM.' of the rotor entrains oxygen for the growth of micro-organisms and ~.~.1±~*$~~.~AA.·ilID~m. maintains the flow velocity. This fosters the mixing process and keeps :&1C5i5EB-g , 73'M*$ 55~. 0 the micro-organisms in suspension for assimilating the pollutants. #!l!¥*J.lf; lllUi".l )~ * Screened Sewage liiIJ ~BiiL ilU[ Brush Type Mechanical Aerator ~J1XlIli'911fm* Treated Eftl uent ~h1f iL{ tm :Qi f~);;:j.!\2 jll Oxidation Ditch Final Sedimentation Tanks Jlt )'5*~llf¥Jj;.:E~Hlfflf*JJiim!+ ' 15~EH~mmi )'5*~II~ 0 ~l~~~JilM=#&(~lm~llmJj; 0 ~~§:j:!- #g~ %.~~-@~~~~~*~%*. o .~~~ffl ••U •• ~ , ~*~.g~.~~o~.~~.~~~*.~~ .,a~.g~~M~*~,~.~~*~~~.~~.mffSM , ~a~.g • • ~~.~ , ~.g~.~~.~ DNIf~~. ' !-A1~1l'&~l~~~ 0 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. MJiliJ1f1:!t 4PJllfliN Overview of the Ma Po Ping RBe ~m&5Ji:~)t!l Primary 1:1w'-!~ Sedimentation Tank Rotating Biological Contact ors t~¥*lilitIfjj',J)iJ* _ Screened Sewage lijj~5Ji:i!'&)t!l Final Sedimentation Tanks . _.J ~~**~B~~~.ffl~~ •• ·~~·.~W·~~· •• ~&W~~**~.o~*,~~~W~W~.~~ *~.~~~~~=W~**~.~~.~ffln~~m~&.Hno n~~m~&.Hn*-@M~ftA~~~B~~~tt~~*~~.,a.~m~~~~./~~·m.&.* =@~mo~~.~~-@m*nm.~~~~mftA~*o=~ ••A~./~~~m~,n~ ••fi~~~~ .,~~~*~~~ ••*~,~.~.~~~~&oU~,~*&.~~~.~m.~m.m.~~~~o*~~ ~m~*.~.&.Hno~~~& ••~~~~n~~m~&.Hn'~~~.*~~A~~*~~~m~*o 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. (1) 1Ii*t1 jiB -&;- Aeration I Mixing (2) jJ1i,!\2 Settling - '1_ ~K i . I •••R~ ma* I f (3) lllu]< Decanting ~ Treated Effluent j 555,1b Sludge 1.i' _____• __ • e-.-. _ . _ _ 1_.- ~ . _ _ .~~ • ~ • • JllIfiil Environmental Protection ~**~~.W*.A.M.~fi~~~.~~o~B=W~**~~,m~* ••• **~.,~~~.~ ~m#~jj~ 0 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 5.,:Il;~IID~)}J<i! 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! Sil ver Mine Bay Beach LAMMA ISLAND ~)~)}J<i! Pui 0 Bay Beach T' ~)Y)}J<i! Lower Cheung Sha Beach I~)Y)}J<i! Upper Cheung Sha Beach ±mmi)}J<i! Tong Fuk Beach ~~.~lli~~~~~.~&m~~.H~~5'~*.~.8~~ 7-~~m~~~'~~8.~~.~~~~~o 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 ~~jj£*~$ Discharge Standards 5'5*JE.I!~ JEI!f¥f¥ ... ..... ............................... ........... ............ E3 TSS (2) BOD(3) Sewage Treatment Plants Treatment ~o~fl-~ii ))IL~' t;; C'---jL JJ*f'=/" ~ S) ~ Process (1) Design Flow (m 3/day) ~ (mg/L) (mg/L) 1;:!jjf,jji ~ ~~~PJT SBR 350 ~30 ~20 Chi Ma Wan CI 1;:!*Jd~~pJT SBR 210 ~30 ~20 Chi Sun CI jjf,jji±ffi±lJI~r~ RBC / SBR 600 ~30 ~20 Ma Po Ping Prison :fijt~ 00 1,190 ~30 ~20 MuiWo 5YDft SBR 183 ~30 ~20 Sha Tsui ;q~~r~ RBC 790 ~30 ~20 Shek Pik Prison § ii)ffi JtJt~ pJT SBR 100 ~30 ~20 Hei Ling Chau Annex § ii5 ffi JiUJd~ ~pJT SBR 761 ~30 ~20 Hei Ling Chau LSCI § ii)ffi it1 tAl ~ 00 900 ~30 ~20 Hei Ling Chau 00 §ii)ffi~tm~~~ RBC 177 ~30 ~20 Hei Ling Chau RBC 5~~m ~ ;q5Jt5m TF 170 ~30 ~20 Hung Shing Ye Beach ±1JI)ffi SBR 1,580 ~30 ~20 Peng Chau *~AAf.\,'R Drainage Hotline: 2300 1110 -FJ9:*~ilJ General Enquiries: 2877 0660 .=.*~JL~".Fl£fJ~ Printed in June 2009 E-mai l: enquiry@dsd .gov.hk Drainage Services Department ~ T !W*f:i *~w M1'lJ[ DSD's Website: www.dsd.gov.hk .