Flow Regulator-HK STP Guidelines

8/12/2019 Flow Regulator-HK STP Guidelines

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UNIV RSITY OF HONG KONGLIBRARY

Hong Kong Collectiong i f t f r o mH o n g K o n g . Envi ronmenta l Protection Dept.


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GUIDELINES FOR THE DESIGN OFSMALL SEWAGE TREATMENT PLANTS

E n v i r o n m e n t a lProtection DepartmentSolidWaste Control Group25thFloor SouthernCentre130 H e n n e ssyRoadWan ChaiHong Kong

M a r c h 1990


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CONTENTSPage

1. INTRODUCTION 52. GENERAL DESIGN CONSIDERATION 53. DESIGN PARAMETERS 84. PRACTICAL DESIGN AND INSTALLATION 115. OPERATION AND MAINTENANCE 196. ENVIRONMENTAL CONSIDERATIONS 20APPENDIX 1: ABBREVIATIONS AND GLOSSARY OF

TERMS 21APPENDIX 2: SOIL PERCOLATION TEST FOR SOAKAWAYDESIGN 23APPENDIX 3: FLOW AND LOAD FOR DIFFERENT TYPESOF DEVELOPMENT 24

LIST OF FIGURESPage

Figure1 Good Vehicular Access and Proper Entrance to a SewageTreatment Plant 7

Figure2 EffectiveEqualization Volume in an Equalization Tank 9Figure3 Headroomand W a l k w a yRequirements 12Figure4 Typical Details of Flow Regulation Tank 14Figure5 Typical Longitudinal Section of Rectangular SedimentationTank 15Figure6 Typical Section of a Square/Circular U p f l o w Sedimentation

Tank 16Figure7 Typical Arrangement of Chlorination System 18


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GUIDELINES FOR TH E DESIGN OF SMALLS E W A G E T R E A T M E N T PLANTS1. INTRODUCTION

M a n y a r e a s o f H o n g K o n g a r e n o t s e r v e d by public f o u l sewers .P r i v a t e d e v e l o p e r s i n t h e s e a r e a s a r e t h e r e f o r e r e q u i r e d t o p r o v i d e t h e i r o w nsewage tr e a tm e n t facilities t o t r e a t th e s e w a ge to a c c e p ta b l e s ta n d a r d s f o r d ir e c td isc ha r g e in to th e r e c e i v in g w a t e r s . T he se g uid e l in e s h a v e b e e n p r e p a r e d with av i e w t o p r o v i d i n g A u t h o r i z e d P e r s o n s a n d d e s i g n e r s with ge n e r a l a d v i ce o n th edesign o f sm a l l se w a g e tr e a tm e n t p l a n ts (S TP ) fo r p r i v a t e d e v e l o p m e n t up to2 0 0 0 p o p u l a t io n e q u iv a l e n t. In p r e p a r i n g th e guide l ine s , specia l e m pha sis isp l a c e d o n t h e p r o b l e m s th a t a r e u s u a l l yf o u n d w i th sm a l l p l a n ts a n d a p p r o p r i -ate design safety m a r g in s a r e in c o r p o r a te d . Fo r p l a n ts s e r v i n g p o p u l a t i o ne x ce e d in g 2 0 0 0 th e d e sig n e r sh o u l d a p p r o a c h th e E n v ir o n m e n ta l P r o te c t io nD e p a r t m e n t to d isc us s th e p o s sib il ity o f a d o p t in g a m o r e r a t io n a l d e sig napproach.The func t ion o f an STP is fo r t r e a t i n g c o l l e c t i v e l y a n y wastes of thek i n d that a r e o r d i n a r i l y d i s c h a r g e d f r o m toile ts, wa ter c lo sets, ba ths, sho we rs,sinks, basins a n d o t h e r s a n i t a r y a n d kitchenfitm e n ts . The m a in c o n c e r n s of theE n v ir o n m e n ta l P r o te c tio n D e p a r tm e n t o n the se sm a l l se wa ge t r e a tm e n t p l a n tsr e l a t e b o t h to the a d e q u a c y o f the tr e a tm e n t p r o c e sse s p r o p o s e d a n d also to theu n c e r t a in ty in e n s ur in g p r o p e r l o n g te r m o p e r a tio n a n d m a i n te n a n c e a n d he n c eth e possibility o f discharge o f s u b s t a n d a r d effluent . The f o l l o w i n g guide l inest h e r e f o r e h i gh l ig ht th e im p o r t a n c e o f g o o d p l a n t de s ig n , w h ic h a m o n g o th e ro bj ectiv es, s h o u l da i m to m a kefuture o p e r a t i o n e a s y a n d r e l i a b l e ,

I t s h o u l d b e n o t e d h o w e v e r ,that fo r sm a l l d e v e l o p m e n ts with a p o p u -l a t io n o f le s s th a n a b o u t 5 0 , th e u se o f sm a l l se w a g e tr e a t m e n tplants should bea v o ided as fa r as po ssible . The po ssibil ity o f p r im a ry t re a tm en t (e .g. septictank) f o l l o w e d b y s o a k w a y , which essentially results i n n o open discharge o fwastewa te r , should a lways be exa m in ed. Unle ss site pe rco la t io n tes ts hav es ho w n t his to b e im p r a c tic a l a n d a d v e r se c o n d itio n s p r e v e n t, a s e p tic t a n ktogether with its soakaway system will bep r e f e r r e d fo r these situations. Detai lso f so a k a w a y p e r c o l a t io n te s ts a r e g iv e n in A p p e n d ix 2 .The W a t e r P o l l u t i o n C o n t r o l O r d i n a n c e c o n t r o l s th e discharge o fwastewate r , inc luding t rea ted ef f l u ent i n t o w a t e r s w i t h i n a r e a s d e s i g n a t e d a sW a t e r C o n t r o l Z o n e s . The A u t h o r i z e d P e r s o n s m a ycontact th e E n v i r o n m e n t a lP r o te c tio n D e p a r tm e n t fo r in f o r m a t io n r e g a r d in g de ta i ls of the legislativec o n t r o l r e l e v a n t t o d i s c h a r g e s f r o m sm al l STP.A glossa ryo fte r m s isgiv enin A p p e n d ix 1.

2. GENERAL DESIGN C O N S I D E R A T I O N2.1 I n o r d e r to a s c e r ta i n th e ef f l u ent qual i ty re quire m en ts , a designe r isen co ura ged to l ia ise with E PD by subm itting the f o l l o w i n g in f o r m a tio n ,pr io r to the design o f STP:


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b l o c k a n d l o c a t i o n p l a n s o fsite ; m a xim um n um be r o fp e r s o n s (r e s id e n ta n d n o n - r e s id e n t ) to bes e r v e d ; p r e s e n c e o f sh o p s , r e s ta u r a n t so r o t h e r service t r a d e s ; possibilityo f the n e e d fo r future e x t e n s i o n sto the p l a n t; p r o p o se d l o c a tio n o f discharge.Based o n s uc h in fo r m a t io n , E P D will th e n f o r m u l a te th e r e q u i r e de ff l ue n t q u a l i ty s ta n d a r d s .

2.2 All e l e m e n t s of the STP s h o u l d be o p e n to vie w a s f a r a s possible fo re a s yo p e r a tio n a n d m a in te n a n c e .2.3 M e c ha n ic a l e q u ip m e n t which is critical to the f u n c t i o n i n g of the STPs h o u l d be provided with on- l ine s tandby uni ts . Fo r e x a m p l e , a n o n - l i n es ta n d by p um p at the e q u a l i z a t i o n t a n k a n d a n o n - l i n e s t a n d b y c h l o r i n ed o s i n gp um p at the ch l o r i n a tio n ta n k sh o u l dbep r o v i de d .2.4 E n tr a n c e to th e S T P s ho u l d b e b y a p r o p e r d o o r w it ho u t th e u se o f ste p so r l a d d e r s a n d accessible by a vehic le .A se c o n d p e d e s tr ia n e n tr a n c e / e x its h o u l d be p r o v i d e d a s f a r a s possible fo r e m e r ge n c y p u r p o se s at theopposi te e n d o f th e p l a n t ro o m .2 .5 D u e c o n s id e r a tio n s ho u l d b e given to the possible in i t i a l low f low con-dition b e f o r e full p o p u l a t i o n is a c h i e v e d . A m u l tip l e o f sm a l l e r u n its(with g a t e o r o t h e r shut-off a r r a n g e m e n ts ) sh o u l d b e p r o v id e d a s fa r a spossible in lieu o f a sin gle l a rge un i t.2.6 E x ce s siv e q u a n titie s o f gr e a s e a n d o i l m a y c a u se m a l f u n c t io n o f a n STP .In suchcases, a r r a n g e m e n ts s ho u l d b e m a d e w h e r e p r a c tic a b le fo r gr e a sea n d o il to b e re m o v e d a t so u r c e . A p r o p e r l y de sign e d gr e a se trap shouldbe p r o v i d e d w h e r e r e s t a u r a n t s or garages are to be s e r v e dby the STP.I n g e n e r a l , agreasetrapsho uld bedesigne d to p r o v id e a m in i m um w a te rr e t e n t io n tim e o f 20 m in u te s f o r a l l wastewater discharged f r o m res-t a u r a n t k itc h e n s du r in g p e a k f l o w p e r io d s.2 .7 Sw im m in g p o o l filter b a c k wa s h , if any, should bedischarge d to the STPfo r tr e a t m e n t. Design of the STP s h o u l d t a k e i n t o a c c o u n t t h e f l o w a n d

loadings of such wastewate r . Poo l wate r i tse l f should however bed r a i n e d to t he sto r m w a t e r system .2.8 Under specia l circum stan ces, a n a u t o s t a r t s t a n d b y p o w e r g e n e r a t o r m a ybe require d if it iscon sidered thatdischar ge o f u n t r e a t e d w a s t e w a t e r to aspecific water course is unacceptable e v e n f o r a b r i e f p e r i o d d u r i n gp o w e r fa i lur e .2.9 A n S TPdesign subm issio n should include, but is not lim ited to :

k e y p l a n sh o w in g l o c a t io n o f d e v e l o p m e n t a n d e if lue nt dischargelocation; p l a n a n d sect ion showingth e l o c a t i o n of STP within th e d e v e l o p m e n tin r e l a t i o n t o r e s i d e n t i a l u n i t s a n d s u r r o u n d i n g facilities;


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nemornnnranrarr

SEWAGETREATMENTROOM PLANT

tvNDOUBLE WIDTHA C C E S S DOOR

FIG. 1 GOOD VEHICULAR ACC ESS AND PR OPERE N T R A N C E T O A SEWAGE TREATMENT PLANT


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p r o c e s sa n d in s tr u m e n ta t io n dia g r a m s; hydraulicpr o fil e together with suppo r t in g ca lculat io n s; d e ta i l e d p r o c e s s d e s ig n c a l c u l a ti o n ; d e ta i l e d dr a w i n g s w i th p l a n a n d e l e v a tio n s ho w in g p l a n t r o o m l a y o u t,inc ludingp i p e w o r ka n de q uip m e n t; r o u t e o faccessto the p l a n t ro o m a n d acce ss withinth e STP; v e n t i l a t i o na n d lightin g de tai ls; e q u ip m e n t sc he d ul e s h o w in g n u m b e r o f duty a n d standby units ,m a k e , m o d e l n u m b e r , c a p a c ity e tc . The s c h e d ul e s h o u l d be s h o w no nth e d r a w i n g ; e q u ip m e n t c a ta l o g ue s a n d o p e r a t i o n / m a i n t e n a n c e m a n u a l .

3. D E S IG N P A RA M E T E R S3.1 The d e s i g n e r s h o u l d give a r e a so n a b l e e stim a t e o f p o p u l a t i o n a n d ad e ta i le d b r e a k do w n o f th e to ta l f lo w r a te in th e c a l c ul a t io n .3.2 Theb a s ic d e sign p a r a m e t e r s fo r r e s id e n tia l p o p u l a ti o n s s ha l lbe t a k e n a sfo l lo ws:

0.46 m3 /h/d (cu.m . p e r h e a dp e r d a y ) 5 5 g B O D / h / d 5 5 g S S / h / dF o r o t h e r t y p e s o f p o p u l a t i o n , r e f e r e n c e s ho u l d b e m a d e to C iv il E n -g i n e e r i n g M a n u a l V o l . 6 a n d W a t e r S up p lie s D e p a r tm e n t P r o v isio n a lS t a n d i n g O r d e r 1 3 0 9 , r e l e v a n t d a t a o f which ha s b e e n attached a sA p p e n d i x 3. If service t r ades (shops, r estaurants e tc . ) occur in thed e v e l o p m e n t, th e fl o w s a n d l o a d s o f th e t r a d e s sh a l l a l so b e in c lu de d a sp e r A p p e n d i x 3.

3.3 The d e s ig n p e a kflowa r r i v in gat the STP as a p r o p o r tio nof dry w e a t h e rf l o w (DWF)s ha l l b e t a k e n a s : 4 D W F fo r po p u l a tio n o v e r 1000, 6 D W F fo r p o p u la tio n u n d e r 1000.E ith e r th e S TP ca n b e d e sign e d fo r t he a b o v e p e a k fl o w r a t e o r i t c a n b edesigned to cater for a p e a kflow of 3 D WF, excessflow o v e r 3 DWFb e in g e q ua l i ze d i n a n e q u a l i za t io n t a n k . In th e lattercase the fe e d p um p sm u st b e s iz e d a c c u r a t e l y to a v o id e x ce s siv e p e a k fl o w r a t e p r o d u c ti o n .E q u a l i z a t i o n t a n k s s h o u l d b e d e s i g n e d t o h o l d t h e e x c e s s f l o w f o r ap e r i o d o f tw o h o u r s . O n l y th e ta n k v o l u m e a b o v e t he d u ty p u m p c u t-inl e v e l should bec o n s id e r e d a se ffective e q ua l iz a tio n v o l um e .

3 .4 P r im a r y s e d im e n ta t io n t a n k s sh a l l b e d e sign e d f o r : m a x im u m s ur fa c e l o a d in g o f 4 0m3/m2/d a t p e a k fl o w , m in i m um re te n tio n tim eo f 2h o u r s a t p e a kf l o w , m a x im um w e ir l o a d in go f 250m3/m/d a t p e a kf lo w .


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* DIS TA N C E V TOSATISFYTHEREQUIREMENT THAT PUMP S T A R T SNOT TO EXCEED 10 TIMES PER HOUR

HIGH LE V E LA L A R M

PUMP CUTIN L E V E L -

PUMP CU TO FF LEVELAS N E A R T OINVERT ASPOSSIBLE

EFFECTIVEEQUALIZATIONVOL U M E

1:50

FIG.2 EFFECTIVE EQUA LIZATION VOLUME IN ANEQUALIZATION TANK


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3.5 Finals e dim e n ta t io n ta n k s sh a l lbed e sig n e d f o r : m a x i m u m surface l o a d i n g o f 3 5m3/m2/d a t p e a k flow if t he y a r ep r e c e d e dbyR o ta t in g B io l o gic a l C o n ta c t o r (RB C ) o r biologicalfilter s, m a x i m u m surface l o a d i n g o f 2 2m3/m2/d a t p e a k flow if t he y a r ep r e c e d e dby the e x te n d e d a e r a t io n p r o c e s s, m in im um re te n tio n tim eo f 2h o u r s a t p e a kflo w.3.6 The r e d u c t i o n o f to ta l B O D b y diffe r e n t stages of the p r im a r y tr e a tm e n tprocesses should bet a k e n a s f o l l o w : e q u a l iz a tio n t a n k n i l c o a r se sc r e e n n i l fine scr e e n (m a x . o p e n in g2 m m ) 7.5 p r im a r y se d im e n ta tio n 3 0 fine screena n d p r i m a r y se d im e n ta tio n 3 0T he n e t B OD l o a d g o i n g i n t o the s ubse q u e n t bio l o g ic a l p r o c e sse s s ho u l db e c o m p u te d a c c o r d in g ly .

3.7 Bio lo gical pro cesses shouldbedesigne dto thef o l l o w in g o r g a n ic l o a d in g : R B C : 1 0 g total B O D / m2 /d (i.e. p e r s q.m . o f R B Csurface) e n t e r i n g i n t o t h e R B C o r a s r e c o m -m e n d e d bym a n u fa c t ur e r , wh ic he v e rissm a l l e r , E x te n d e d a e r a t io n : 0 .0 7kg to ta l B OD /kg ML SS/d a n dMLSSin ther a n g e b e t w e e n 2 0 00 an d 3 5 0 0m g/L , Pla stic bio lo gical : 0.5 kg t o t a l BOD/m3/d (i.e.per c u.m . of m e d iafilter(Biofilter) v o l u m e ) o r a s r e c o m m e n d e d by m a n u fa c tu r e r ,whichev er issm a l le r . Fo r o the r bio l o g ic a l tr e a t m e n t m e t ho d s , su ch a s s e q ue n tia l ba t chreactor, contact stabilization and other patented processes e tc . , o rganicl o a d i n g s p r o p o s e d in the design should be justified by s u p p o r t i n gd o c u m e n ts su ch a s r e l e v a n t l ite r a t u r e , l o c a l m o n ito r i n g r e s u l ts a n dcata logues .

3 .8 Chlorination tanks should bedesigne d fo rm in im um 3 0m in u te s c o n ta c ttim e at p e a kflow.3 .9 Sludge quan titie s gen er a ted f r o m th e pro cesses sho uld inc lude:

so l ids r e m o v e d fr o m p r im a r y se d im e n ta t io n , w hic h s ho u l d beta k e n a s70 o f th ei n f lu e n t SS. sludgeyield f r o m biological processes, which should be ta k e n as 0.5 kgsolids/kg B O D r e m o v e d w he n p r e c e de d by p r im a r y s e dim e n ta tio n , o r1 kg solids/kg B OD r e m o v e d w he n n o t p r e c e d e d by p r im a r y s e dim e n -tation.In the l a t te r case n o in c lusio n o f pr im a ry s ludge is n ecessary .

3.10 So l id c o n c e n tr a t io n o f s e d im e n ta t io n ta n k sl u dg e sha l l be ta k e n a s : 1 fo r e x te n d e d a e r a t io n sl ud ge , 2 for RBC, biologicalf il te r an d p r i m a r y sl ud ge .

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4. P R A C T I C A L DESIGN AND INSTALLATION4. 1 A p o r t a b l e su bm e r s ib le p u m p s ho u l d b e p r o v id e d in o r d e r to a l l o wflexibilityin o p e r a tio n . T his p u m pc a n b eused to recyclethep la n t effluentto m a i n ta i n the STP in aw o r k in g c o n d itio n w h e n in c o m in gflow isl o w .4.2 A ge n e r a l he a d ro o m o f 3 m s h o u l dbem a in ta in e d fo r e n c lo s e d o r u n d e r -g r o u n d STPwith artificial v e n t i l a t i o n . T h i s m a y be r e d u c e d t o 2 .5 m a tlocalized p o i n t s, e .g. u n d e r b e a m s .4.3 Fo r e n c l o s e dSTP, a m in im uma ir v o l um e of 14m3 sho uld be p r o v i d e d .Artificial v e n t i l a t i o n s h o u l d bep r o v id e d with n o t less t h a n 10 a ir c h a n g e sperhour. Ven ti l a t io n exhaust pipes sho uldbe c a r r i e dup to a height notlessth a n 1 ma b o v ether o o fo f thebuildin ga t whichthe STP islocated.4.4 Access w al kw ays o f m in i m u m 0 . 75 m c le a r w i d th sh o u l d b e m a i n t a in e dwithin the STP for access t o a l l a r e a s r e q u ir in g m a i n te n a n c e a n doper-ation. W a l kw a y s sh o u l d h a v e safety rai ls (preferably stain l ess stee l ) a n dtoe b o a r d s . W a l k w a y s s ho u l d be laid to a 1:25 crossfal l to p r e v e n tp o n d i n g if of so l id co n st ructio n a n d they sho uld n o t b e o bstructed byc r o s sin g p ip e w o r k .4.5 W h e r e l e v e l s v ary, s tai rcases sho uld be p r o v id e d a n d n o t c a t l a d d e r s o rs te p ir o n s .4 .6 A l l t a n k s s ho u l d b e p r o v i de d with s t a i n l e s s s t e e l l a d d e r o r s t e p i r o n s f o raccess. Mild steel should n o t b e used. Step i ro n s sho uld be spaced a t300 m m c /c h o r i zo n ta l l y a n d 2 50 m m c /c v e r tic a l l y.4.7 If a ta n khas to be co v e r e d, o p e n m e s hflooringsho uldbe used.4. 8 P r o v i s i o n o f a n e m e r g e n c y b y-p a s s to the STP is not a l l o w e d u n d e rn o r m a l c ir cu m sta n c e s .4.9 Fresh w a t e r t a p s fo r h o s e s a n d h a n d w a s h i n g sho uld beprovided in theSTP atc o n v e n i e n t lo c a tio n sand sho uldbes h o w non the drawin gs.4.10 E lect r ica l distr ibutio n bo a rds and c o n t r o l p a n e l s s h o u l d be instal led inl o c a t i o n s n o t liable t o f l o o d i n g a n d t h e l o c a t i o n s s h a l l be sho wn in thed r a w i n g s. P a n e l s s h o u l d h a v e a de hum idifyin gheater.4.11 The c o n t r o l p a n e l s h o u l d i n c o r p o r a t e a mimic/schematic diagram anda l l l a b e l s s h o u l d b e i n b o t h E n g l i s h a n d C h i n e s e . A l l v a l v e s , penstocks,p u m p s e t c. sh o u l d be a p p r o p r i a te l y l a b e l le d .4.12 H o u r s r u n m e t e r s s ho u l d b e p r o v id e d fo r a l lm a jo r e q u ip m e n t torecordth e totalh o u r s o f o p e r a t i o n . T h e y s h o u l dbe o f thenon-resettablety p e .4.13 Scree n s sho uld be p r o v id e dto p r e c e de p u m p s .4.14 M e c h a n ic a l s cr e e n s s ho u l dbe the static type or of the t y p e h a v i n g ther a ke s m o v i n g in the bar o p e n i n g sand not on the b a r . E i th e r m a n u a l or

m e c h a n ic a l b y -p a s s sc r e e n s s ho u ld a l w a y sbe p r o v i de d .The duty screen11


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FIG. 3 HEADROOM AND WALKWAY REQUIREMENTS

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c h a n n e l s h o u l d h a v e a high l e v e l o v e r f l o w i nt o th e s t a ndb y s cre e nc ha n n e l so that the flo wdiv e r ts a u to m a tica l l y t hro u g hth es ta n db y scre e nin ca se th e du t y o n e is b l ocke d.4.15 E x ce ss iv e sc re e n ch a n n e l w i dth w h ich r e s ul ts in s h a l l o w d e p t h o f f l o ws h ou l d be a v o i d e d . In case o f s m a l l d e v e l o p m e n ts w he r e the sm a l l e stm e c h a n ic a l sc re e n c o m m e r c ia l l y a v a i la b l e is still to o wide, a m a n u a lscreen may be used.

B a r s o f s cre e n s h ou l d be e x t e n d e d to the i n v e r t of the c h a n n e l . Fo rm a n u a l sc r e e n s , c o n s id e r a t io n sh o u l d begiv en to : accessby o p e r a t o r ; e a s e o f r e m o v a l o f s cre e ni ng s by operator, i ncl u di ng p rovi s i on o fs uita b l e r a ke ; d r a i n i n g o f screenings; b a g g i nga n d s t ora g e o fs cre e n in g s.

4.16 A p e r f o r a te d / m e s h ty p e dr a i n t r a y (o f stainless steel o r p l a s tic m a t e r i a l )s ho u l db e p r o v id e d to a l l o w th e s c r e e n in gs to d r a i n p r i o r to p a c k a g in g .4.17 P u m p s um p s (in c l udin g e q u a l iz a t io n ta n ks) s ho u l d be designed to lim itth e p u m p s ta r t s to n o t m o r e tha n 10t im e s /h o u r .4.18 E l e ctr ica l v o l ta g e fo r l e v e l s e n s o r s in p u m p s u m p s sh o u l d n o t e x ce e d24V to a v o id e l e c tr ica l h a z a rd .4.1 9 H ig h l e v e l a l a rm s s ho u l d b e p ro v ide d in a l l p u m p su m p s . T his s ho u l d b ein th e fo r m o f v is ua l a n d a u d io a l a r m s c o n n e c te d to a s uita b l e c o n s ta n tl ym a n n e d l o c a t i o n .4.20 Pum ps should be careful ly ch os e n t o co r r e s p ond t o t h e de s i g n du t ypoint. F l ow re g u l a t i on t a nks w i t h cont ro l w e i r s h ou l d b e u s e d i f on l yb ig ge r p u m p s a r e a v a i l a b l e .4.21 Comminutors, especia l ly the enclosed type, a re discouraged as theyo f t e n c a u se o p e r a t io n a l p r o b l e m s in th eSTP.4 .2 2 S e dim e n ta t io n ta n ks s ho u l dbe designe d e ither asr e c ta n g ul a r horizontalflowt a n k ,or as s q u a re / c i rcu l a r u p w a rdflow ta n k . For h o r i z o n t a lflowtank, the l ength to width ratio s h ou l d not b e l e s s t h a n 2 . T h e u s e oftan ks with le n gth to width ratiob e tw e e n 1 a n d 2 sh o u l d be a v o id e d .4.23 U p w a r d fl o w s e d im e n ta t io n t a n k s s ho u l d b e p r o v id e d w ith m in im u m60h o p p e r w a l l sl o p e s to f a c il ita t e e a sy sl ud ge c o l l e c tio n a n d r e m o v a l .4.24 H o r i zo n ta l fl o w s e d im e n ta t io n ta n k s s ho u l d b e p r o v id e d w ith a m e c h-anica l scraper system o n a n o m in a l f l o o r slope, discharging to a sludge

h o p p e r . Tw in t a n k s s ho u l d p r e f e r r a b l ybeused. If singletank isused, th es c r a p e r s h o u l d b e o f t h e t y p e t h a t a l l o w s t h e u n d e r w a t e r parts t o b em a i n t a in e d w i th o u t th e n e e d o f s hu ttin g d o w n th e ta n k .13


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RATE OF EQUALIZED FLOWDEPENDS ON RELATIVE HEADOF THE TWO WEIRS

E X C E S S F L O WQ q BACKTOE Q U A L I Z A T I O N TANK

EQUALIZED FLOWq TO D OW NSTREAMUNITS

PUMP WITH FLOWRATE Q > q

FROM EQU ALI ZATI ON TANK

FIG. TYPICAL DETAILS OF FLOW REGULATION TANK DESIGN FL O W R A T E = q )

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SCUM TOSLUDGE STORAGETANK

SLUDGETOSLUDGE STORAGETANK C U T L E T BAFFLE

INLETBAFFLE

INLET OUTLET

FIG. 5 TY PIC AL LONGITUDINAL SECTION OFRECTANGULAR SEDIMENTATION TANK


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SCUMTOSLUDGE HOLDINGT A N K

FLOATINGSURFACESKIMMER\

OUTLET

NOTE : O U T L ET WEIR AND BAFFLETO BE P R OV IDE D A LON GTH E WH OLE PERIPHERY

ADJUSTABLE WEIRPLATES, PREFERABLYV - N O T C H -

SLUDGE TOSLUDGE HOLDINGTANK

SLUDGEHOPPER

60 MINIMUM

EXCEED 5 0 0 n

FIG. 6 T Y P I C A L S E CT IO N OF A SQUARE/CIRCULARUPFLOW SEDIMENTATION TANK

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4.25 Adjusta ble we irs sho uld be used fo r se d im e n ta t io n ta n k s to e n a b l e finel e v e l l i n g . V-notch weirs should be used where wide f low var iat ionoccurs. The side-wal l height should b e n o t less t h a n 1 m in o r d e r toav o i d s l u dg e c a r r y o v e r . T h e l ay o u t sh o u l d b e su c h t h a t t h e i n l e t a r -r a n g e m e n t n e v e r be co m e s subm e r ge d insludge .4.26 A c ha m b e r s ho u l d b e p r o v i d e d a t th e fin a l s e d im e n ta t io n ta n k o u tl e ta f t e r th e weir fo r insta l l a t ion o f r e c ir c ul a t io n p u m p in the e v e n t th a t th eactual in i t ia lflow ism u ch l o w e r t ha n th e designfl o w(see4. 1 a b o v e ) .4 .2 7 S lu dg e in sedim en ta t io n ta n ks sho u l d b e r em o v ed as f r e q u e n t l y a s p o s -sible, at l eas t o n c ep e r d a y b y a suita ble s ludge withdra wa l dev ice such a ssub m er s ib le s lu dg e p u m p s, airlifts o r v a l v e s . A sc um r e m o v a l de v i ceshould also be provided. The sludge and scum r e m o v a l de v ice shouldh a v e i n d e p e n d e n t a d j u s t a b l e c o n t r o l . I n s p e c t i o n t r o u g h s h o u l d b e p r o -v ided a t the discharge e n d fo r inspe ctin g the qual i ty o f s ludge withdra wnso that a d ju stm e n t to thewithdra wa l syste mm a y bem a d e a c c o r d in g l y.4.28 Chlor inat ion facility should inc lude a f l a s h m ix in g d e v i ce fo l l o w e d by ap l u gf lo wc o n ta c t t a n k . Baffles should be p r o v id e d in c h lo r in a t io n ta n k sto p r ev en t sh o r t - c i r c u i t i n g . L at e r a l baffling should be used fo r s h a l l o wtanks a n d u p - a n d - o v e r baffling sho u l d b e u sed f o r dee ptanks.4.2 9 Wh en t e r t ia r y tr e a tm e n t is r e q u ir e d, c h l o r i n a t io n sho u l d b e p l ac ed a f t e rte r t ia r y tr e a tm e n t.4.30 S lu dg e s to r a g e ta n ks sho u l d b e p r o v ided wit h a e r a to r s wh en t he y a r el o c a t ed in e n c lo s e d p l a n t r o o m s to m a i n ta in th e aer o b i c c o n di t i o n of thesludge. However , s ludge sto rage tanks should p r e f e r a b l y b e v e n t i l a t e dsep a r a t e l y to the ex t e r i o r .4 .31 Sludge pum ps should bedesigne d with positiv e suctio n hea d tom in i m izethe po ssibil ity o f c lo ggin g.4.32 The dia m eter of the s ludge d raw -off p i p e w o r k s h o u ld be o f a m in i m u md ia m e t e r o f 80 m m in o r d e r to p r e v e n t p ip e b lo c ka g e s.4.33 A sl udge dewa te r in g m ac h in e sho u l d bep r o v id e d . Fo r s m a l l STPs e r v i n gless than 100 p o p u l a t i o n , it may be acceptable to p r o v i de a sludges t o r a g e t a n k f o r w e tdisp o sa l p r o v idedthat:

a s to r a g e t a n k c a p a b le o f h o l d in g 6 0 d a y s sl ud ge v o l u m e be p r o v id e d , vehicular accessis m ai n t a in ed fo r desludging t an ker s , w r itte n c o n fir m a t io n is p r o v id e d f r o m a desludgingcontractor u n d e r -taking to c a r r y out the w o r k a n d specifying th e ultim a te dispo sal sitefo r t h e w e t sludge.

4.34 An a u to m a t ic f l o w m ea sur in g dev ic e wit h n o n - r e s e t t a b l e type to ta l izersho u l d b e p r o v ided a t su itab l e l o c a t io n fo r m ea sur in g t he fl o w fo r S T Pse r v in g a p o p u l a tio n o f m o r e th a n 5 0 .17


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V

PLAN SECTIONAL ELEVATION

L A T E R A L BAFFLING FO R S H A LL O W T A N K

v >PLAN S E CTI ON A L E L E V A TION

UP AND OVER BAFFLING FO R DEEP TANK

CHLORINATEDEFFLUENT

v i/

HYDRAULIC FALL200mm TYPICAL

POINT OF APPLICATIONOF CHLORINE

SEC O ND ARYEFFLUENTPIPE

-CHLORINEC O NT AC TTANK

FIG. 7 TYP IC AL AR R AN GEM EN T OFCHLORINATION SYSTEM

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4.35 An e a sil y a c ce s sib le s a m p l in g p o i n t s h o u l d be p r o v i d e d fo r t a k i n gs a m p l e s of the tr e a te d effluent.5. OPERATION AND M A I N T E N A N C E5.1 In selecting th e typeo f tr e a tm e n t p r o c e s s, th e designers should take duec o n s i d e r a t i o n of thea v a i l a b i l ityo fc o m p e t e n t o p e r a t o r s.5.2 O n l y c o m p e te n t te c h n ic ia n s s ho u l d b e a s sign e d to o p e r a t e th e STP . T heo p e r a t o r s h o u l d be fully c o n v e r s a n t w i t h th e r e c o m m e n d e d o p e r a t i n gp r o c e d u r e s a sstipula ted in theo p e r a t io n a n d m a in te n a n c e m a n u a l.5.3 If a n ypart of the STP has to bec o v e r e d, o p e n m e s h fl o o r in g sh o u l d beused to a l l o w e a s y v i s u a l i n s p e c t i o n . C o n c r e t e c o v e r s s h o u l d be a v o i d e da s f a r a s p o ss ib l e . I f c o n c r e t e c o v e r s l a b s h a v e t o b e u se d , th e y s h o u l d b el iftable by twom e n , i.e .totalwe ight shouldbele ss than 60 kg.5.4 Screen in gs should be r e m o v e d da il y a n d th e r e fo r e sc re e n l o c a t io n s

should be so designed to e n a b l e e a sy sc r e e n i n gs r e m o v a l . Sc re e n in g ss h o u l d be d r i p p e d d r y a n d p a c k e d in h e a v y d u t y p o l y t h e n e b a g s fo rsubsequent disposa l .5.5 The STP s h o u l d be k e p t in a tidy state by g o o d h o u s e k e e p i n g . Thisin c l u de s r e g u l a r h o s in g d o w n a n d s c r a p i n g th e wa lkways, white washingth e w a l l s, c l e a n in g a n d p a in tin g m e t a l w o r k s , m a i n t a in in g adequatelightinga n d v e n t i l a t i o n e t c .5.6 S p a r e p a r t s sufficient fo r 2 y e a r s o p e r a t i o n a s p e r m a n u fa c tu r e r s'r e c o m m e n d a tio n sh o u ld be p r o v id e d with th e e q u ip m e n t su p p l y.5.7 P o w d e r ty p e fire extinguishers a n d lifebuoy should be p r o v i d e d i n a neasily accessible a r ea in the p lant . A fi rs t-a id box should a lso bep r o v id e d in t he p l a n t.5.8 A n o p e r a t io n a n d m a i n te n a n c e m a n u a l sh o u ld b e sub m itte d fo r a p -p r o v a l . T he c o p y that is to be p la ced in the STP sho uld be in r ing binde rf o r m a t w i th a l l p a p e r s l a m in a t e d o r e n c lo s e d in p l a s tic . It sh o u l d c o n ta i na t least th e f o l l o w i n g in f o r m a t io n , w ith a n e sse n tia l su m m a r y inChinese:

n a m e a n d a d dr e s s o f d e sign e r a n d c o n tr a c to r a n ddate o f in s ta l l a tio n ; p r o c e ss a n d in s tr u m e n ta t io n d ia g r a m ; detai led descr ipt io n o f t r ea tm e n t pro cesses; c o n t ro l m e c ha n ism ; wirin g dia gra m o p e r a t i n g p r o c e d u r e s f o r a l l tr e a tm e n t p r o c e s se s in c l ud in g l ike l yo p e r a t i n g p r o b l e m and tro uble shoo tin g techniques; r o u tin e m a i n te n a n c e s ch e dul e fo r a l l p r o c e sse s a n d e q uip m e n t (daily,weekly,m o n th l y , a n n u a l c h e c kl istsetc.); start up a n d s hu t d o w n p r o c e d ur e s ;

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e q u ip m e n t sc h e d ul ewith n a m ea n d c o n t a c t a d dr e s s o f l o c a l a g e n t s ; list o f s p a r e p a r t s p r o v i d e d o n site a n d r e c o m m e n d e d sto c k le v e l s a tw hich newo r de r s m u stbep l a c e d ; s a m p l i n ga n d testin gfr e q u e n c y a n d p r o c e d u r e sfo r on-site testing; e m e r ge n c y p r o c e d u r e (fire, p o w e rf ai lure , etc.); p l a n t safety p r e c a u t i o n s ; s a m p l elo g sheets.

5.9 A C h in e s e v e r s io n o f th e d a i l y w o r k s ch e d ul e , l a m in a te d o r e n c l o se d inpla stic sho uld be pro v ide d in the STP.6 . E N V I R O N M E N T A L C O N S ID E R A T IO N S6.1 STP sho uld be r e g a r d e d a s p o t e n t i a l s o u r c e o f n u i s a n c e to the r e s i d e n ta n d t h e public, a n d t h e r e f o r e due c o n s i d e r a t i o n s h o u l d be giv en to the

m in i m iz a tio n o fodour,n o is ea n d safety p r o b le m s.6.2 STP should be site d with goo d buffering distance f r o m houses, o re n c l o se d t o m in i m iz e a d v e r s e im p a c t. O p e n S TP s ho u ld be f e n c e d o ff tok e e p a w a y t r e s p a s s e r s .6.3 D u e c o n s id e r a tio n s h o u l d b e giv e n to o d o u r p r o b l e m f r o m STP.V e n t i l a t i o n e x h a u s t p i p e s s h o u l d b e t a k e n t o r o o f l e v e l , o r e l s e o d o u rtr e a tm e n t o r m a skin g facil itie s m a y be re quire d (e .g. act iv ated ca rbo n ,p e a t filters etc.).6.4 T o m in i m ize n o ise p r o b l e m f r o m STP, the design er sho uld co n sider theuse o f s il e n c e r s, s o u n d b a r r i e r s , a n ti- v ib r a t io n m o u n t in g a n d b l o w e r swith m o t o r s o f l o w r .p .m . ( n o t e x c e e d in g 1 0 0 0 r . p . m . ). P r o v is io n o f a na i r b l o w e r i s d is co u r a g e d . A l te r n a t iv e l y , u se o f s ub m e r s ib l e e j e c t o r sshould beconsidered which would resultin quieter operation. The in takea n d e xhaust g r il l s o f the v en til a tio n system sho uld a lso be design edp r o p e r l y to reduce th e whistl ing noise a n d s h o u l d n o t p o i n t t o w a r d sn e a r b y b u i l d i n g s . R e f e r e n c e s h o u l d be m a de to CAPractical Guide fo rth e Re ductio n o fIn dustr ia lNoise published by th is D e p a r tm e n t.6.5 STP sho uld be designed to m in i m iz e v is ua l im p a c t . L a n d sc a p i n g w i thbushes a n d t r e e s ise n c o u r a g e d, but not in p l a c e s w h e r e the l e a v e s m a yfal l into th etanks.

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APPENDIXABBREVIATIONSANDGLOSSARYOFTERMS

1 . Activated sludgeA seco n dary (bio logica l) tre a tm e n t p ro cess in which sewage is ae ra ted witha biologica l ly act ive s ludge causing th e m i c r o o r g a n i s m s to r e m o v ep o l l u t a n t s f r o m th e s e w a g e . A further settlem en t s tage is r e q u i r e d tos e p a r a t e th e sludge.

2. BaffleA dev ice used in a t a n k to p r o m o te am o r e u n ifo r mf lo wth r o u g h th e ta n ka n d to avoid short-circuiting.

3. Biochemical oxygendemand BOD)T he a m o u n t o f d isso l v e d o x y g e n c o n s um e d b y m ic r o b io l o g ic a l a c tio nw h e n a sa m p le is in cubated, usua l lyfo r 5days a t 20C. It is a m e a s ur e o fth e c o n c e n tr a t io n o f b io l o g ic a l l y d e g r a d a b l e p o l l u t a n t s in t he s a m p l e .

4. Biologicalfilter Biofilter)A t y p e o f se c o n d a r y tr e a t m e n t p r o c e s s w h ic h c o n s ists o f a b e d o f in e r tm ate r ia l (m o ulded p las tics, c l in ker , s to n es e tc .) o n to which m icro -o r g a n ism s willg r o w s o a s to p r o m o te a e r o b ic d e g r a d a tio n o f se w a ge .

5. ComminutorAg r in d e ro r s h r e d d e r t h a t c o n v e r t sbulkysolid wastes in to sm a l l p a r tic les .

6. Dry weather flow DWF)The a v e r a g e d a i l y flow to the tr e a tm e n t p l a n t w ith o u t th e influence o fsto r m w a te r in f il tr a tio n d u e to r a i n s to r m s .7. Extendedaeration

The e x t e n d e d a e r a t i o n p r o c e s s is a type o f secondary (biological) treat-m e n t . It is am o d ific a t io no f the c o n v e n t i o n a l a c t i v a t e d s l u d g e p r o c e s s a n do p e r a t e s in the e n d o g e n o u s p h a s e o fg r o w th , in which there i s n o t e n o u g hf o o d r e m a i n i n g in the systemto s u p p o r t a ll of the m ic r o o r g a n ism s p r e s e n t .The m ic r o o r g a n ism s a re a e r a t e d a n d suspended within the sewage, whereae ro bic degra dat io n o f the po l lutan ts take s p lace . Residence tim e is o f theo r d e r o f 2 4 h o u r s c o m p a r e d t o a r o u n d 6 h o u r s in c o n v e n tio n a l a c tiv a te dsludge tanks.8. Mixedliquorsuspendedsolids MLSS)The co n cen tra tio n o f dry so l ids ( in m il l igram s pe r l itre ) o f m ixed l iquor inth e a e r a t io n ta n k o f a ne x te n d e da e r a t io n /a c t iv a t e d sludgeplant.9. PrimarytreatmentThe tr e a tm e n t o f sewage to a stage where th e sett leable po l lutants a r e

r e m o v e d byp hysica lm e a n s ( usu a l l y g r a v itys e d im e n ta t io n ).21


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APPENDIX 1 (Cont d.)0 . Primarysedimentationtank

A primary treatment process. It is a gravity sedimentation tank in whichthe majority of settlable solids are removed f r o m the crude sewage flowingthrough it. It is placed before the secondary (biological) treatmentprocesses.

1 1 . Rotating biological contactor RBC)A typeofsecondary treatment process. It is a unit consisting of a series ofclosely spaced, parallel discs, mounted on a rotating shaft which issupported just above the surface of the waste water to be treated. Micro-organisms grow on the disc surface where aerobic degradation of thepollutants takes place.

12. Secondarysedimentation tankPart of the secondary treatment process (e.g. biological filters or anactivated sludge plant) in which settleable solids or humus resulting f r o mthedegradationofpollutantsare separated f r o m the e f f l u e n t .

1 3. SecondarytreatmentAlso called biological treatment, referring to the treatment of sewage to astage wherethe pollutants (settleable, colloidal and dissolved) are removedbiologically by the action of microorganisms.

14. SeptictankA primitive type of primary treatment process. It takes the form of asettlement tank in which the sludge isretained for sufficient time for theorganic matter to undergo anaerobic decomposition.

15. SewageThewater-borne wastesof a community.

16. SludgeAmixture of solids and water produced during the treatment of sewage.

17. Sludge yieldThe quantity of solids left over at the end of the secondary treatmentprocesses, consisting of dead cells, surplus microorganisms, non-biodegradable matters.

18. Suspended solids SS)Solidsin suspension in sewage liquors as measured by filtration through aglassfibre filter paper followed by washing and drying at 105C. Expressedin milligramsperlitre (mg/L).

19. Tertiary treatmentA further stage of treating sewage f o l l o w i n g secondary (biological)treatment processes, usually by filtering the secondary e f f l u e n t to removesuspended solids. Consequential removalof residual BOD may also occur.

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A P P E N D I X 2SOIL P E R C O L A T I O N TEST FOR SOAKAWAY D E S I G N

PERCOLATION TEST FOR DETERMINING ABSORPTION CAPACITY OF SOILa . E X C AV A TE A H O L E 3 0 0m m S QU A R E T O T HE S A M E D E P T H O F TH E P ITO R T R E N C H .b. FILL T H E H O L E W I T H A P P R O X I M A T E L Y 150mm O F W A T E R A N D A LL O WT O S E E P A W A Y C O M P L E T E L Y .c. REFILL T H E H O L E W I T H W A T E R T O A D E P T H O F 1 5 0 m m A N D O B S E R V ET H E T IM E , I N M I N U T E S , FO R W A T E R T O SE E P C O M P L E T E L Y A W A Y .d . D I V ID E T H E T I M E B Y 6 T O G IV E T IM E T A K E N TO F A L L 2 5m m F OR U S EI N T A B L E B E L O W . LLOW BLE LOADING OF SOAKAWAY SYSTEMS

T I M E I N M I N U T E SFO R W A T E R TO F A L L25 m m IN TEST PI T1 OR LESS

25

1030

A L L O W A BL E L O A D I N G I N L I T R E S P E R m2 P E R D A YD RA I N T RE N CH BO T T O M A R E A

163130

986933

P IT P E R C O L A T IO N A R E A21 6175130

9445

THE A L L O W A B L E LO A D I NG S H O U LD E Q U A TE W I TH THE W A T E R C O N -SUMPTION RATE FOR THE A PPR OPR IA T E C L A S SOF D E V E L O P M E N T .MINIMUM CLEARANCE REQUIREMENTS FOR SOAKAWAY SYSTEMS

DISTANCE FROM SOAKAWA YSYSTEMS m)B U I L D I N G 3W E L L S 30S T R E A M W H E R E THE 15(30)*B E D IS L O W E R T H A NINVERT OF S OA KA WA YSYSTEMPOOL S 7.5(30)*CUTS OR 30E M B A N K M E N T S

*THESE D I S T A N C E S S H O U L D B EI N C R E A S E D TO D IS T A N C E SS H O WN IN B R A C K E T S IF THEW A T E R F R O M T H E S T R E A M O RP O O L I S U S E D O R L I K E L Y T O B EU S E D FOR D R I N K I N G ORD O M E S T I C P U R P O S E S .

PATHSB E A C H E SGROUND W A T E RT A B L E

1.530( F R OM HWM )0.6( B E L O W IN V E R T )

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A P P E N D I X 3FLOW AND L OAD FOR D I F F E R E N T TYPESOF DEVELOPMENT

FLOWType ofdevelopment Recommended design flow rateL/head/day)Res id en t ia l Rl 300Res id en t ia l R2 370Residential R3 460Res id en t ia l R4 460M o d e r n V i l l a g e H o u s i n g 300Traditional Type V i l la ge Ho u s in g 18 5TemporaryHousingA r e a(THA) 18 5Schools( No t i n c l u d in g c a n t e e n ) 2 3 ( st ud e n t s, staff

etc.)Offices ( N o t i n c l u d i n g c a n t e e n ) 55Services (shopsetc.) 70 ( fo r e q u iv a l e n tpopulation)R e s t a u r a n t s / c a n t e e n s 0.5m3/m2 kitchenarea/dayExplanatory noteson types of development

Privatehou singblocksin Rl zones,Private Sector Participation Schem esandHou singAu thori ty Ho meOwnershipSchemesRe s ide nt ia l O n e ( R l ) is the highest d ensi ty r es id ent ia l p l anned use .P o p u l a t i o n d e n s i t i e s m a y b e a r o u n d 1 740 p e r so n s p e r h e c t a r e , with am a x i m u n p l o t r a tio o f 8.0 .G e n e r a l l y , d e n s itie s a n d p l o t r a t io s fo r P r iv a t e S e c to r P a r t ic ip a t io nS c h e m e s a n d H o u sin g A uth o r ity H o m e O w n e r s hip Sc he m e s a r e s im il a rtoth o se f o u n din Rl estates.

Privatehousingblocksin R2zonesR e s id e n t ia l T wo (R 2) is a m e d iu m d e n s ity r e s id e n tia l p l a n n e d u se .P o p u l a t io n de n sitie s m a y b e a r o u n d 1 0 5 0 p e r s o n s p e r h e c ta r e , w ith am a x i m u m p l o t r a t i o o f 5 .0 .

Privatehousing in R3 and R4 zones,villasandbungalowsResid ent ia l Three (R3) is a m e d iu m t o l o w d e n s ity r e s id e n tia l p l a n n e du se . P o p u l a ti o n d e n s itie s m a y b e a r o u n d 47 0 p e r s o n s p e r h e c t a r e , w it ha m a x i m u m p l o t ratio of 3.0. Resid ent ia l Four (R4) is a l ow d ensi tyr e s id e n tia l p l a n n e d u se . B u il d in g h e i g ht is r e s tr ic te d to n o m o r e t ha n2sto re ys witham a x im u m p l o t r a tio o f0.4. Modern VillageHouses

These a r e l im ited to asite a r e a o fa p p r o x im a te l y65sq ua r e m e tr e s a n d toa height of 3 sto re ys, a n d w h ic h a r e in th e N e w Te r r i to r ie s S m a l l H o u seC a t e g o r y .

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LOADType of developmentR e s i d e n t i a l , a l l ty p e sS c h o o l ( n o t i n c l u d i n g c a n t e e n )Office ( n o t i n c l u d i n g c a n t e e n )Factories ( n o t i n c l u d i n g i n d u s t r i a land c a n t e e n w a s t e s )ServicesRestaurants/Canteens

Recommended BOD load( g / h e a d / d a y )55232323

RecommendedSS load(g/head/day)55232323

to bepro-rata to e q u i v a l e n t r e s id e n t ia lpopulation3 0 0 g/m 2 kitchenarea/d 300 g/m2 kitchenarea/d

T h e u s e o f g a r b a g e g r in d e r sm a y i n c r e a s e th e p e r c a p i ta c o n tr i b utio no f B O D b y a b o u t 3 0 a n d o f S S b y 6 0 , a n d such increases should be ta k e ninto acco un t in the design of the STP.

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HKP628 24G94Guidelinesfor the design ofs m sewage treatment plantsHongKong : Solid WasteControlGroup, Environmental

MQQ01

Date D u e


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Flow Regulator-HK STP Guidelines