Drinking Water Guidelines Chapter 13 Treatment Processes Coagulation Oct13

8/13/2019 Drinking Water Guidelines Chapter 13 Treatment Processes Coagulation Oct13

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Chapter 13: Treatment

processes, coagulation

Contents

13.1 Introduction.............................................................................................2

13.2 Coagulation process.................................................................................4

13.3 Coagulants and flocculants......................................................................7

13.3.1 Definitions......................................................................................................................... 7

13.3.2 Coagulants........................................................................................................................713.3.3 Flocculants........................................................................................................................7

13.3.4 Health effects....................................................................................................................8

13.4 Coagulation and flocculation...................................................................9

13.4.1 Overview........................................................................................................................... 9

13.4.2 Jar testing......................................................................................................................... 9

13.4.3 erfor!ance an" control.................................................................................................11

13.5 Clarification and sedimentation.............................................................12

13.#.1 Overview..........................................................................................................................12

13.#.2 Clarifier t$%es..................................................................................................................12

13.#.3 O%ti!isation an" %erfor!ance issues............................................................................1#

13. !ime softening and ion e"change............................................................17

13.&.1 'i!e softening................................................................................................................. 17

13.&.2 (on e)change................................................................................................................... 17

13.7 #apid granular media filtration..............................................................19

13.7.1 Overview.......................................................................................................................... 1913.7.2 *ur+i"it$ !onitoring......................................................................................................2,

13.7.3 Filter o%eration............................................................................................................... 21

13.7.4 O%ti!isation of the filtration %rocess.............................................................................21

13.$ %econd stage filtration...........................................................................24

#eferences....................................................................................................25

!ist of figuresFigure 13.1- Conventional coagulation se"i!entation an" filtration....................................#

/ui"elines for Drin0ingwater ualit$ anage!ent for ew 5ealan" 2,13 1Cha%ter 13- *reat!ent rocesses Coagulation 6 e%te!+er 2,13


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Figure 13.2- Direct filtration...................................................................................................#

Figure 13.3- 'a!ella %lates................................................................................................... 13

Figure 13.4- "sor%tion clarifier..........................................................................................13

Figure 13.#- Dissolve" air flotation DF:............................................................................14

Figure 13.&- ctiflo %rocess...................................................................................................1#

Figure 13.7- ;a%i" granular !e"ia filter..............................................................................19

13.1 Introduction*his cha%ter covers the water treat!ent %rocess of che!ical coagulation with or without

se"i!entation. (t also covers the situation where se"i!entation is not followe" +$ ra%i"

granular !e"ia filtration. *he "iscussion on coagulation inclu"es "etails of che!ical coagulants

an" %ol$electrol$tes use" in the %rocess. *he se%arate stages of coagulation- flocculation an"

conventional se"i!entation also calle" clarification: are inclu"e". (n current ter!inolog$

se"i!entation is one of a nu!+er of %rocesses that are grou%e" as clarification. ew highrate

clarification %rocesses la!ella %lates tu+e settlers +uo$ant !e"ia clarifiers "issolve" air

flotation DF: an" ctifloater softening an" other +enefits: +$ using ion e)change is inclu"e" in section 13.& for

co!%leteness although the %rocess "oes not inclu"e coagulation an" "oes not earn log cre"its.

oftening is also "iscusse" +riefl$ in Cha%ter 18- esthetic Consi"erations section 18.3 an" in

Cha%ter 19- !all (n"ivi"ual an" ;oof u%%lies section 19.3.4.

2 /ui"elines for Drin0ingwater ualit$ anage!ent for ew 5ealan" 2,13Cha%ter 13- *reat!ent rocesses Coagulation 6 e%te!+er 2,13


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*he 2,,8 D>5 inclu"e a new section section #.17- lternative %rocesses- treat!ent

co!%liance criteria where+$ water su%%liers !a$ a%%l$ to the inistr$ of Health to have other

treat!ent %rocesses assesse" for a log cre"it rating. *his a%%roach which is e)%laine" !ore

full$ in section 8.4.# of the /ui"elines allows water su%%liers to a%%l$ for a log cre"it rating or

a variation to the %rescri+e" log cre"its: for a treat!ent %lant or %rocess-

a: not covere" in sections #.16#.1& of the D>5

+: that %erfor!s "e!onstra+l$ +etter than its co!%liance criteria

c: that %erfor!s to a lesser +ut relia+le level than s%ecifie" in its co!%liance criteria.

o!e %rocess variation is nor!al an" e)%ecte"B however too !uch varia+ilit$ can result in

treat!ent failures lea"ing to water+orne "isease out+rea0s. n o+ective of the D>5

therefore is to 0ee% %rocess varia+ilit$ within acce%ta+le li!its. n"erstan"ing the causes of

%rocess variations shoul" %revent recurrences. ro+le!s !a$ +e a+le to +e avoi"e" an" the ti!e

s%ent %ro+le! solving can +e re"uce" +$ i!%le!enting an effective ris0 !anage!ent %lan

H;:.

>> 2,,,: %ro"uce" a series of !anuals covering control of coagulation filtration

softening an" the che!icals use" for these see full list of stan"ar"s athtt%-EEwww.awwa.orgEfilesE;esourcesEtan"ar"sEtan"ar"s%rea"sheet.)ls

;is0 !anage!ent issues relate" to the treat!ent %rocesses in this cha%ter are "iscusse" in the-

oH u+lic Health ;is0 anage!ent lan /ui"e H; ;ef. #.1-*reat!ent rocesses 6

CoagulationEFlocculationEe"i!entation.

oH u+lic Health ;is0 anage!ent lan /ui"e H; ;ef. #.2- *reat!ent rocesses 6

Dissolve" ir Flotation.

oH u+lic Health ;is0 anage!ent lan /ui"e H; ;ef. #.3- *reat!ent rocesses 6

Direct Filtration.

oH u+lic Health ;is0 anage!ent lan /ui"e H; ;ef. &.1- *reat!ent rocesses 6

;a%i" an" Filtration.

oH u+lic Health ;is0 anage!ent lan /ui"e H; ;ef. 8.1- *reat!ent rocesses 6

%H "ust!ent.

oH u+lic Health ;is0 anage!ent lan /ui"e H; ;ef. 11- *reat!ent rocesses 6

lant Construction an" O%eration.

;ecor"s shoul" +e 0e%t of all che!icals use" in treat!ent %rocesses. *hese shoul" inclu"e the

su%%lier certification of the s%ecification an" gra"e of the che!ical an" "atasheets routine

!onitoring of the Aualit$ an" stan"ar" of che!icals use" con"itions of its su%%l$ an"

su+seAuent storage. ;ecor"s of actual "osing of the che!ical shoul" show the che!ical na!e

rates an" Auantit$ of the che!ical "ose" the t$%e an" cali+ration of the eAui%!ent use".

!etho" state!ent shoul" give stan"ar" %roce"ures in case of failure or +rea0"own of the

s$ste! with associate" safet$ "ata sheets an" Ha=che! la+elling for all che!icals use".

*he >ater u%%l$ anagers@ Co!!ittee of the ew 5ealan" >ater an" >astes ssociation

5>>: has +een "evelo%ing stan"ar"s for che!icals use" in water treat!ent. *hese cover

alu!iniu! sul%hate h$"rate" li!e fluori"es an" three %ol$electrol$tes.

D>( 2,11: has a list of che!icals that have +een a%%rove" for use in water su%%l$ in the .

http://www.awwa.org/files/Resources/Standards/StandardsSpreadsheet.xlshttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/ConventionalCoag-floc-sediV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/ConventionalCoag-floc-sediV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DissolvedAirFlotationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DissolvedAirFlotationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DirectFiltrationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DirectFiltrationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/RapidSandFiltrationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/RapidSandFiltrationV1.dochttp://www.awwa.org/files/Resources/Standards/StandardsSpreadsheet.xlshttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/ConventionalCoag-floc-sediV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/ConventionalCoag-floc-sediV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DissolvedAirFlotationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DissolvedAirFlotationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DirectFiltrationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DirectFiltrationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/RapidSandFiltrationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/RapidSandFiltrationV1.doc


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Docu!entation of the Aualit$ an" Auantit$ of che!icals use" in the treat!ent %rocess is

i!%ortant for the a%%raisal of the efficienc$ of the %rocesses +eing use" an" !a$ affect which

riorit$ 2 "eter!inan"s are assigne" to a su%%l$ an" the freAuenc$ of sa!%ling reAuire" for

the!.

*he Ha=ar"ous u+stances an" ew Organis!s HO: ct 199& now controls the use of the

following che!icals-

chlorine gas calciu! h$%ochlorite

sul%huric aci"

h$"rochloric aci"

so"iu! h$"ro)i"e

aAua a!!onia

h$"rogen %ero)i"e

%otassiu! %er!anganate.

ince 1 Octo+er 2,,4 users !a$ nee" a 'ocation *est Certificate an"Eor an %%rove" Han"ler*est Certificate. Details are availa+le +$ using the te%+$te% /ui"e to Fin"ing Controls an"

Other seful 'in0s at www.er!an=.govt.n=.

13.2 Coagulation processCoagulation flocculation an" clarification followe" +$ ra%i" granular !e"ia filtration are the

0e$ ste%s in conventional water treat!ent s$ste!s. *his is a well%roven technolog$ for the

significant re!oval of colour an" %articulate !atter inclu"ing %roto=oa eg Cryptosporidiu

ooc$sts an" Giardiac$sts: viruses +acteria an" other !icroorganis!s. (ron !anganese

tastes an" o"ours !a$ also +e re!ove" fro! the water +$ these %rocesses.

(f not re!ove" natural organic !atter can react with chlorine to re"uce "isinfection efficienc$

an" for! chlorinate" organic s%ecies eg "isinfection +$%ro"ucts DGs: so!e of which are

che!ical "eter!inan"s of health significance see Cha%ter 1,- Che!ical Co!%liance an"

Cha%ter 1#- *reat!ent rocesses Disinfection. icroorganis!s re!aining in treate" water

!a$ also %ose ris0s to %u+lic health.

Conventional treat!ent coagulation se"i!entation an" san" filtration: as illustrate" in

Figure 13.1 has several "istinct stages. coagulant is a""e" to neutralise the natural electrical

charges on the colloi"al %articles that %revent the! fro! agglo!erating an" is ra%i"l$ !i)e"

into the water to +e treate". *his %rocess is referre" to as the coagulation stageB it is so!eti!esreferre" to as the colloi" "esta+ilisation %hase. *he %rocess water will then enter a flocculation

cha!+er where further che!icals !a$ +e a""e" "e%en"ing u%on the raw water characteristics

an" the level an" rate of treat!ent to +e achieve". /entle !i)ing "uring this stage allows

%articles to agglo!erate an" for! settlea+le flocs.



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&igure 13.1: Con'entional coagulation, sedimentation and filtration

Clarification usuall$ follows the flocculation %rocess. *$%icall$ in ew 5ealan" this involves

se"i!entation or settling which allows the for!e" flocs to +e se%arate" for su+seAuent re!oval

as slu"ge. Clarification is then followe" +$ filtration which %rovi"es a secon" %olishing ste% for

%articulates that were not re!ove" "uring the clarification ste%. *he D>5 also cover the

situation where ra%i" granular !e"ia filtration "oes not follow the se"i!entation stage.

o!e !e!+rane filtration F: %lants incor%orate a coagulation an" se"i!entation ste%

u%strea! of the F ste%. *he coagulation %rocess !a$ +e continuous or inter!ittent"e%en"ing on the raw water Aualit$.

For raw waters with consistentl$ low colour eg less than 4, *C: an" low tur+i"it$ eg less

than 1, *: "irect filtration can +e a"o%te" as illustrate" in Figure 13.2. *here is no

clarification ste% in this case an" the coagulate" water flows "irectl$ to the filtration %rocess

%rovi"ing the onl$ %articulate re!oval ste%. (f the soli"s loa"ing is too high the filters will

reAuire freAuent washing which !a$ lea" to su%%l$ %ro+le!s.

&igure 13.2: (irect filtration

s new clarification %rocesses are e!erging an" +eco!ing increasingl$ co!!on furthervariances fro! the conventional coagulationEfiltration %rocess !a$ +eco!e !ore co!!on.

'a!ella %lates can +e installe" in %lace of tra"itional se"i!entation tan0s an" tu+e settlers can

+e %lace" in the tan0s. *hese "o not alter the +asic %rinci%les of the %rocess +ut the$ !a$

i!%rove the efficienc$ an" allow higher through%uts for the sa!e foot%rint to +e achieve".



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Dissolve" air flotation DF: can +e installe" in %lace of the conventional se"i!entation tan0

or clarifier: an" this %rocess floats rather than settles the flocs. >i"el$ use" in uro%e an"

now +eco!ing !ore co!!on in orth !erica DF can +e use" for treating !o"erate

tur+i"it$ an" high colour waters. (t is es%eciall$ effective at re!oving algae which can +e

"ifficult to re!ove +$ se"i!entation an" woul" otherwise clog "ownstrea! filters an" for raw

waters that %ro"uce flocs with %oor settling characteristics. *he DF %rocess can +e a goo"

choice for ver$ col" water te!%eratures +ecause it is !ore effective at re!oving the wea0 flocs

that are co!!onl$ %ro"uce" in such waters.

further "evelo%!ent the ctiflo< %rocess is a +allaste" flocculation %rocess which a""s

!icrosan" to the flocculation cha!+er. Coagulation flocculation an" clarification are %rovi"e"

as a single unit.

further variation is the +uo$ant !e"ia clarifier also calle" the a"sor%tion clarifier:. *his

%rocess co!+ines the flocculation an" clarifier into one stage an" effectivel$ acts !ore li0e a

filtration %rocess rather than a settling clarifier. *his %rocess is +est suite" for raw waters of

lower tur+i"it$.

ee >HO 2,,4a: for a "escri%tion of coagulation s$ste!s so!e o%erational as%ects an" a"iscussion on their a+ilit$ to re!ove various organis!s. ;efer also to Cha%ter # of the review

"raft '*2>*; *ool+o) /ui"ance anual 2,,9: which "iscusses issues relate" to

se"i!entation.

*he tal0s of ?enhance" coagulation@ as though this were a new t$%e of water treat!ent

%rocess. 2,,7: states that enhance" coagulation can inclu"e one or !ore of the

following o%erational changes-

increasing the coagulant "ose

changing the coagulant

a"usting the %H eg using aci" to lower the %H to as low as #.#: i!%roving !i)ing con"itions or a%%l$ing a !o"erate "osage of an o)i"ant

a""ing a %ol$!er.

o!e a"vantages of enhance" coagulation are sai" to inclu"e-

i!%roving "isinfection effectiveness

re"ucing DG for!ation

re"ucing +ro!ate for!ation

enhancing arsenic an" ra"ionucli"e re!oval.

Gase" on the a+ove ?enhance" coagulation@ woul" see! to +e little !ore than o%ti!ising the

%rocess.

/ui"elines for Drin0ingwater ualit$ anage!ent for ew 5ealan" 2,13Cha%ter 13- *reat!ent rocesses Coagulation 6 e%te!+er 2,13


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13.3 Coagulants and flocculants

13.3.1 (efinitions

*he a""ition of certain che!icals into the raw water causes %articles to "esta+ilise an" allows

agglo!eration an" floc for!ation to occur. *he general ter!s for che!icals use" for this

%ur%ose are-

coagulants which assist the "esta+ilisation of %articles %articularl$ colloi"al si=es:

flocculants also 0nown as flocculant ai"s or coagulant ai"s: which assist in the oining an"

en!eshing of the %articles together. ost flocculants use" to"a$ are %ol$electrol$tes.

13.3.2 Coagulants

ost ew 5ealan" water treat!ent %lants use alu!iniu!+ase" coagulants eg alu!iniu!

sul%hate alu!: or %ol$alu!iniu! chlori"e Cl 6 Cl is the %referre" acron$! +ecause C

can also !ean %ow"ere" activate" car+on:. lu!iniu! chloroh$"rate CH: has li!ite" usage

!ainl$ in !e!+rane filtration. ver$ s!all nu!+er of %lants use iron+ase" coagulants ferric

chlori"e or ferric sul%hate:. lthough alu! an" Cl are !ost co!!onl$ use" other coagulants!a$ have +enefits in %articular a%%lications such as low tur+i"it$ waters. 5>> 1997

revise" 2,12: %u+lishe" the secon" e"ition of a stan"ar" that covere" alu!iniu!+ase"

coagulants.

Cl an" CH are two of a nu!+er of %reh$"rol$se" !etal salt coagulant solutions that have

+een "evelo%e" in recent $ears. *he 0e$ characteristic of this class of coagulants is that the$

consu!e less al0alinit$ when a""e" to the raw water an" are less affecte" +$ low water

te!%eratures than alu!.

(n a""ition to alu!iniu! an" iron+ase" inorganic: coagulants organic che!icals 0nown as

%ol$electrol$tes !a$ also +e use" as coagulants or flocculant ai"s to assist in %ro"ucing lowtur+i"it$ levels in treate" water. *his is %articularl$ necessar$ for high rate clarification an" high

rate filtration %rocesses.

ol$electrol$te coagulants such as %ol$a!ines %ol$acr$la!i"es an" %ol$DDCs are +eing

use" increasingl$ in ew 5ealan" es%eciall$ on low tur+i"it$ low colour waters where

treat!ent is +$ "irect filtration. *he$ can also +e use" in conunction with inorganic coagulants

in which case the$ are referre" to as a coagulant ai".

13.3.3 &locculants

ol$electrol$tes are now co!!onl$ use" as flocculants in the !aorit$ of water treat!ent %lantsin ew 5ealan". s a flocculant ai" the che!icals are a""e" following coagulant "osing to

increase the si=e strength an" settlea+ilit$ of flocs. ol$acr$la!i"e+ase" %ol$electrol$tes are

the !ost co!!onl$ use" flocculants in ew 5ealan". *hese !a$ +e cationic anionic or non

ionic. *he$ are %ro"uce" with var$ing "egrees of ionicit$ an" in a range of !olecular weights.

*o achieve their full effectiveness %ol$electrol$tes are a""e" after the %ri!ar$ coagulant eg

alu!:. contact ti!e of at least three !inutes is not unco!!on. Contact ti!e in this conte)t is

the ti!e the water ta0es to flow +etween the two "osage %oints.



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13.3.4 )ealth effects

For so!e ti!e concerns have +een raise" in the international technical literature an" +$ interest

grou%s a+out whether there are a"verse health effects on consu!ers fro! resi"uals of che!icals

in "rin0ingwater following treat!ent. s an e)a!%le so!e co!!unities have o%te" not to use

alu!iniu!+ase" coagulants +ecause of unsu+stantiate" re%orts that clai! that the alu!iniu!

in "rin0ingwater %oses a ris0 to %u+lic health "es%ite scientific evi"ence eg rinivasan et al

1999: that a"verse effects have not +een "e!onstrate". Gecause there is no evi"ence of health

ris0 +ase" on >HO 2,,4: the D>5 "o not have a a)i!u! cce%ta+le Ialue I: for

alu!iniu!. >HO 2,12: "oes not change this %oint of view. *hese /ui"elines inclu"e a

"atasheet for alu!iniu!. lternatives to alu!iniu! coagulants e)ist eg iron+ase" coagulants

such as ferric chlori"e +ut there !a$ +e %erfor!ance an" cost %enalties associate" with their

use.

roven concerns "o e)ist for 0i"ne$ "ial$sis %atients if the water that is use" +$ the %atient as

the "ial$sate liAui" contains high concentrations of resi"ual alu!iniu!. sers of "ial$sis

!achines shoul" +e a"vise" to %rovi"e s%ecific %re"ial$sis treat!ent to ensure that resi"ual

concentrations of alu!iniu! an" so!e other conta!inants %otentiall$ intro"uce" +$ treat!ent

che!icals an" "istri+ution !aterials are 0e%t to acce%ta+l$ low levels. *his is a+solutel$ criticalif alu!iniu! is +eing use" in the treat!ent of a su%%l$ for the first ti!e even though D>5

are strictl$ s%ea0ing: onl$ a%%lica+le to water inten"e" for "rin0ing refer section 1.3 of

D>5:.

(f water treat!ent che!icals are use" in such a wa$ that their resi"ual concentration in the

"rin0ingwater "oes not e)cee" the I availa+le research in"icates there will +e no

significant ris0 to health fro! "rin0ing the water for a lifeti!e. However in"ustr$ %ractice is to

o%erate treat!ent %lants significantl$ +elow these levels.

Onl$ flocculants that are s%ecificall$ !anufacture" for %ota+le water use shoul" +e use" in

"rin0ingwater treat!ent. an$ of the !ono!ers use" in the !anufacture of %ol$electrol$tesan" their i!%urities an" resultant "egra"ation %ro"ucts are to)ic an" the !anufacturing

%rocess nee"s to +e controlle" %ro%erl$ to li!it the Auantit$ of unreacte" !ono!er in the

!anufacture" %ol$electrol$te. For e)a!%le acr$la!i"e a !ono!er resi"ual of the !anufacture

of %ol$acr$la!i"es: has %roven to)icit$ an" carcinogenicit$ its I is ,.,,,# !gE':.

%ichloroh$"rin %resent in "i!eth$la!ineEe%ichloroh$"rin cationic %ol$electrol$tes: also has

a I liste" in the D>5 ,.,,,# !gE':. *he 5>> tan"ar"s 1999 +eing revise"

2,12E13: for the su%%l$ of three t$%es of %ol$electrol$tes for use in "rin0ingwater treat!ent

outline !ini!u! reAuire!ents to ensure that high Aualit$ an" low i!%urit$ %ro"ucts are use"

in "rin0ingwater treat!ent a%%lications.

art 3.4 of the in"e) section of the "atasheets lists the che!ical "eter!inan"s with health or%ossi+le health: concerns that can +e foun" in water treate" with coagulants an" flocculants.

*he total "ose of %ol$electrol$tes a%%lie" in the water treat!ent %rocess shoul" +e controlle" to

li!it the resi"uals in the treate" water see Cha%ter 1,- Che!ical Co!%liance. (n %articular the

"oses a%%lie" in slu"ge "ewatering nee" to +e ta0en into account if the su%ernatant water is

rec$cle" into the treat!ent %rocess.

$ /ui"elines for Drin0ingwater ualit$ anage!ent for ew 5ealan" 2,13Cha%ter 13- *reat!ent rocesses Coagulation 6 e%te!+er 2,13


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13.4 Coagulation and flocculation

13.4.1 *'er'ie+

Coagulation an" flocculation %rocesses are inten"e" to for! %articles that are large enough to

+e se%arate" an" re!ove" +$ su+seAuent se"i!entation or alternative clarification %rocesses.

*he coagulation stage occurs when a coagulant such as alu! is a""e" to the water to neutralisethe charges on the colloi"al %articles in the raw water thus +ringing the %articles closer together

to allow a floc to +egin to for!. *he coagulant solution shoul" +e a%%lie" at a concentration of

aroun" ,.# %ercent an" certainl$ less than 1 %ercent >HO 2,,1:. ;a%i" highenerg$ !i)ing

eg !echanical !i)ers inline +len"ers et s%arge !i)ing: is necessar$ to ensure the coagulant

is full$ !i)e" into the %rocess flow to !a)i!ise its effectiveness. *he coagulation %rocess occurs

ver$ Auic0l$ in a !atter of fractions of a secon". oor !i)ing can result in a %oorl$ "evelo%e"

floc.

*he flocculation %rocess which follows coagulation allows s!aller %articles for!e" "uring the

ra%i" coagulation stage to agglo!erate into larger %articles to for! settlea+le an"Eor filtera+le

floc %articles. fter coagulant a""ition the %rocess water is !i)e" slowl$ for a "efine"flocculation %erio" co!!onl$ 1,63, !inutes however the o%ti!u! flocculation ti!e will var$

"e%en"ing on the raw water Aualit$ an" "ownstrea! clarification %rocess. /entle !i)ing "uring

this stage %rovi"es !a)i!u! %article contact for floc for!ation whilst !ini!ising tur+ulence

an" shear which !a$ "a!age the flocs. ffectiveness of flocculation "e%en"s on the "ela$ ti!e

or contact ti!e: an" !i)ing con"itions %rior to an$ flocculants +eing a""e" the rate of

treat!ent water te!%erature an" the !i)ing con"itions within the flocculation cha!+er.

Contact flocculation is a variation fro! conventional flocculation in which the flocculation ta0es

%lace within the clarification %rocess. *he coagulation ste% re!ains the sa!e however the

flocculation cha!+er contains a contact !e"iu!. *his !e"iu! tra%s the flocculating %articles

which will then attach to other %articles there+$ continuall$ increasing the si=e of the flocs untilthe +uil" u% of %articles clogs the !e"ia. Gac0washing is then reAuire" to re!ove the flocculate"

%articles. ;efer to Figure 13.4 u%flow a"sor%tion clarifier:.

13.4.2 ar testing

*he +est a%%roach for "eter!ining the treata+ilit$ of a water source an" "eter!ining the

o%ti!u! %ara!eters !ost effective coagulant reAuire" "ose rates %H flocculation ti!es

!ost effective flocculant ai"s: is +$ use of a ar tester.

s o%ti!u! %H an" coagulant "ose var$ significantl$ with raw water characteristics an initial

thorough investigation into the variations in raw water Aualit$ fro! the source shoul" hel% in

the selection of the a%%ro%riate t$%e of coagulation s$ste! to +e use" an" its "esign. ne)%ecte"

variations in raw water Aualit$ can cause the coagulation %rocess to +e co!%ro!ise" causing

conseAuent %ro+le!s with treate" water Aualit$.

*he nor!al %roce"ure when con"ucting a ar test is initiall$ to fin" the +est %erfor!ing

coagulant an" "ose rate an" then to "eter!ine the o%ti!u! %H for the chosen coagulant an"

"ose rate. erfor!ance is usuall$ u"ge" on tur+i"it$ an" then on colour or I a+sor+ance:

re!oval. Jar tests can also +e use" to co!%are the usefulness of "ifferent flocculant

%ol$electrol$tes +ut not their o%ti!u! "ose ratesB this !ust +e "one on the %lant itself.



10/27

tan"ar" alu!iniu! an" iron salt coagulants are aci"ic an" therefore neutralise the al0alinit$

%resent in the raw water. )cess al0alinit$ after the a""ition of coagulant: is nee"e" to allow

goo" floc for!ation. *he o%ti!u! coagulant "ose a""e" at the wrong %H coul" result in al!ost

no floc for!ation. (n ew 5ealan"@s soft surface waters the o%ti!u! %H for coagulation is often

onl$ achieve" +$ a""ing an al0ali such as so"a ash so"iu! car+onate: or h$"rate" li!e

%erha%s in the range of #62, !gE' see section 13.4.3.

raw water with a high %H an" a low coagulant "e!an" !a$ not reach the o%ti!al %H withouta""ing aci". However unless the aci" reAuire!ent is Auite high the o%ti!u! %H is usuall$

achieve" si!%l$ +$ a""ing e)cess coagulant. *his shoul" not +e "one if it un"ul$ increases the

concentration of alu!iniu! in the finishe" water.

!aller water treat!ent %lants often choose to use Cl to avoi" the nee" to "ose al0ali or aci"

as Cl is !uch less aci"ic than alu! an" is usuall$ effective over a +roa"er range of %H values.

*o assist in !aintaining goo" control of the coagulation %rocess ar tests shoul" +e carrie" out

routinel$ as %art of the %lant %rocess control. *he %roce"ure shoul" +e con"ucte" freAuentl$

whenever changes in the characteristics of the raw water occur eg after rain inta0e changes

etc or when the water treat!ent %lant is %erfor!ing %oorl$.

De%en"ing on the e)%erience of the o%erator an" the e)tent to which the raw water

characteristics have change" since the current "ose rates were chosen the first set of ar tests

usuall$ trials a range of coagulant "oses. )a!ination of the results shoul" in"icate which

coagulant "ose is closer to that reAuire" for re!oval of the colour an" tur+i"it$.

an$ water su%%lies nee" a secon" set of ar tests at "ifferent %H values to give an in"ication of

where the o%ti!u! %H is li0el$ to +e. u+seAuent ar tests fine u% on the "osage selection.

/enerall$ the !ore tur+i"it$ an" colour there is the higher the o%ti!u! coagulant "ose.

)%erience" o%erators will 0now usuall$ fro! the tur+i"it$ how !uch coagulant is nee"e" to

re!ove the soli"s or colour: loa". lu! or iron salts are usuall$ "ose" at a+out 1#6#, !gE'soli" weight eAuivalent:.

*he in"ivi"ual ars are assesse" for a variet$ of factors inclu"ing which "evelo%e" a floc first

which ar@s floc grew the fastest an" +eca!e the largest which settle" fastest an" which gave a

su%ernatant with the lowest colour tur+i"it$ an" coagulant resi"ual. or!all$ the sa!e ar

scores +est on each count. (n so!e "ifficult waters the o%ti!u! "osage con"itions are "ifferent

for colour an" tur+i"it$ re!oval or the o%ti!u! "ose for colour an" tur+i"it$ re!oval results

in e)cessive resi"ual concentrations of coagulant entering the "istri+ution s$ste!. *hese waters

reAuire e)tensive ar testing to "eter!ine the +est co!%ro!ise. *he nu!+er of ar tests nee"e"

to "eter!ine o%ti!u! %ara!eters is learne" fro! e)%erience.

;efer to >> 2,,,: for further infor!ation on the ar testing %roce"ure.

""itional la+orator$ eAui%!ent useful for !anaging coagulation an" su+seAuent treat!ent

inclu"es a +ench tur+i"i!eter colour co!%arator %H !eter al0alinit$ titration eAui%!ent an"

a s%ectro%hoto!eter for !easuring alu!iniu! an" %ossi+l$ iron an" !anganese resi"ual

concentrations following treat!ent. Colour !easure!ent is a fairl$ su+ective test an" rea"ings

!a"e +$ a grou% of %eo%le can have a wi"e s%rea". (f the la+orator$ inten"s to use a

s%ectro%hoto!eter it !a$ +e wise to %urchase a IEvisi+le !o"el +ecause for a %articular

water a correlation can +e esta+lishe" +etween the true colour Ha=en units: an" the I

a+sor+ance !easure" in a 1 c! cell at 2#4 or 27, n! after filtration. I a+sor+ance is a+le to +e

!easure" Auic0l$ an" relia+l$.

1- /ui"elines for Drin0ingwater ualit$ anage!ent for ew 5ealan" 2,13Cha%ter 13- *reat!ent rocesses Coagulation 6 e%te!+er 2,13


11/27

13.4.3 erformance and control

*he %erfor!ance of coagulation an" flocculation is "e%en"ent on a large nu!+er of factors

!an$ of which are interrelate" !a0ing o%ti!isation "ifficult. ource water characteristics

che!ical "ose rates !i)ing con"itions flocculation ti!es the selection of che!icals an" their

or"er of a""ition can all affect %erfor!ance. Control of %H an" al0alinit$ is also essential to

!aintain %erfor!ance.

Clarifier an" filter %erfor!ance will also +e "irectl$ affecte" +$ the overall %erfor!ance of these

stages of the %rocess. (t is therefore critical to !aintain goo" %erfor!ance an" control of

coagulation an" flocculation for overall treat!ent %lant %erfor!ance.

De%en"ing on the %H of the source water %H a"ust!ent %rior to coagulant a""ition !a$ +e

reAuire" to achieve the o%ti!u! %H levels. u+seAuent rea"ust!ent will al!ost certainl$ +e

reAuire" to ensure acce%ta+le %H levels in the "istri+ution s$ste!.

*he o%ti!u! %H for the coagulation %rocess varies with the choice of coagulant. For alu!iniu!

sul%hate it is usuall$ #.# to 7.# for ferric salts it !a$ +e within the range # to 8.#. *he o%ti!u!

%H will var$ with changing raw water characteristics.

an$ surface waters in ew 5ealan" have an al0alinit$ of less than 2, !gE' as CaCO3. 1 !gE'

of alu! !easure" as soli" weight eAuivalent:1will consu!e ,.# !gE' of al0alinit$ as CaCO3:.

(f all the al0alinit$ is neutralise" no !ore floc will for!. Often the alu! "ose that is reAuire" to

coagulate all the tur+i"it$ an" colour %resent reAuires so"a ash caustic so"a or h$"rate" li!e to

+e "ose" to %rovi"e the a""itional al0alinit$ an" !aintain control of the %H. *his co!!onl$

occurs after heav$ rain an" if the al0alinit$ an" %H are not controlle" %rocess failure can result

with tur+i" water an" "issolve" alu!iniu! entering the "istri+ution s$ste!.

Geing a sensitive %h$sicoche!ical %rocess coagulationEflocculation is !ost relia+le when raw

water Aualit$ is consistent when changes occur slowl$ or when a"eAuate auto!ation is use" tores%on" to changes in raw water Aualit$. nfortunatel$ this is not true of !an$ of our strea!s

an" rivers. ee Cha%ter 12- retreat!ent rocesses section 12.3.2 for a "iscussion on the

+enefits of offriver storage.

s raw water con"itions change o%ti!al coagulation "ose rates also change an" careful control

is reAuire" to %revent over"osing an" un"er"osing.

Over"osing can lea" to e)cessive concentrations of coagulant entering the "istri+ution s$ste!

an" waste !one$. *his can occur if the %H an" al0alinit$ are not controlle" at o%ti!u! levels

too. *he gui"eline value for alu!iniu! an aesthetic "eter!inan": is ,.1 !gE' as l which is

a%%ro)i!atel$ eAuivalent to 1.1 !gE' as soli" weight eAuivalent alu!.

n"er"osing can cause %oor re!oval of colour tur+i"it$ an" !icroorganis!s.

Online !onitoring of raw water Aualit$ "eter!inan"s such as %H an" tur+i"it$ will ai"

treat!ent %lant %erfor!ance an" assist in selecting o%ti!u! coagulation "ose rates. (t !a$ +e

hel%ful to !easure I a+sor+ance online if the raw water has high colour.

1 oli" weight eAuivalent alu! refers to l2O4:3.14H2O !olecular weight of #94:. ew 5ealan" liAui" alu! is

"elivere" as 47 wEw eAuivalent to &2 wEv:. o!eti!es alu! "oses are re%orte" as l2O3!olecular weight of

1,2 8.2 wEw of as"elivere" liAui" alu!: or as l !olecular weight of #4 4.3 wEw of as"elivere" liAui"

alu!:.



12/27

Control of the coagulation %rocess can +e auto!ate". *wo control !etho"s use" in ew 5ealan"

for coagulation are the strea!ing current !onitor ver$ co!!on: an" fee" forwar" control less

co!!on:.

trea!ing current !onitors !easure the =eta %otential a !easure of the electrical charge on

the %articles in the water: of the raw water following che!ical a""ition an" this can +e use"

to a"ust the coagulant "ose rate accor"ingl$ as the raw water characteristics var$. *his

%rocess was "escri+e" +$ Ogilvie 1998:.

Fee" forwar" control s$ste!s !onitor natural organic !atter using I light: an" %H in the

raw water %rior to coagulant a""ition an" %re"ict the reAuire" coagulant "ose rates to +e

a%%lie".

13.5 Clarification and sedimentation

13.5.1 *'er'ie+

*he ter! clarification or se"i!entation is nor!all$ use" to "escri+e the settling of the flocs

%ro"uce" +$ the coagulation an" flocculation %rocess. *his is "istinct fro! %resettling of highl$

tur+i" waters in "etention %on"s which is "iscusse" in Cha%ter 12- retreat!ent rocessessection 12.3.3.

Historicall$ clarification involve" the si!%le %rinci%le of %article settling to se%arate the floc

%articles. ew technologies such as "issolve" air flotation DF: an" high rate clarification

%rocesses such as la!ella %lates tu+e settlers ctiflo


13/27

!amella settlers

'a!ella settlers Figure 13.3 !a0e use of incline" %lates or tu+es to increase the effective

surface area for settling an" hence are also 0nown as %late or tu+e settlers: there+$ increasing

the efficienc$ of the clarification %rocess. For a given through%ut the foot%rint of a la!ella

settler will +e consi"era+l$ less than a conventional clarifier. *$%ical surface loa"ing rates are

#61# !Eh. 'a!ella settlers are less vulnera+le to flow fluctuations than conventional clarifiers.

&igure 13.3: !amella plates

0uo/ant media clarifiers

Guo$ant !e"ia clarifiers or a"sor%tion clarifiers Figure 13.4 are a variant on the conventional

clarification stage an" co!+ine flocculation an" clarification into one ste%. *he coagulate" water

%asses through a !e"iu! of +uo$ant a"sor%tion !aterial nor!all$ a %lastic: 0e%t in %lace +$ a

screen. *his allows contact flocculation to ta0e %lace as flocs attach to the !e"ia an" are there+$

re!ove" fro! the water. oli"s will continuall$ +uil" u% until the !e"ia clogs. Gac0washing is

then reAuire" to e)%an" the !e"ia an" re!ove the soli"s.

&igure 13.4: dsorption clarifier

*his %rocess often reAuires a larger %ol$electrol$te "ose an" is +etter suite" to raw water sources

with low tur+i"it$ an" colour. High tur+i"ities will ver$ Auic0l$ clog the !e"ia an" result ine)cessive +ac0washing. *$%ical surface loa"ing rates of 1962# !Eh can +e a%%lie".

(issol'ed air flotation

Dissolve" air flotation DF: as illustrate" in Figure 13.# is a clarification %rocess %articularl$

effective for re!oval of colour an" algae cells that are "ifficult to settle. (t is suite" to !o"erate

levels of tur+i"it$ an" onl$ s!all "oses of %ol$electrol$te are t$%icall$ reAuire". urface loa"ing

rates of 1,612 !Eh are co!!on.



14/27

*he %rocess wor0s +$ inecting ver$ s!all air +u++les near the inlet of the flotation tan0 which

attach to flocs usuall$ alu!iniu! +ase": for!e" in a se%arate flocculation tan0 an" floats

the! to the surface. Flocculation ti!es of 1#62, !inutes are t$%icall$ reAuire". Clarifie" water

is then collecte" fro! near the tan0 +otto!. %ortion of the flow a%%ro)i!atel$ #61, %ercent:

is rec$cle" an" saturate" with air. *he rec$cle" water reenters the flotation tan0 through a

series of no==les causing a %ressure re"uction that releases s!all air +u++les fro! the saturate"

water.

&igure 13.5: (issol'ed air flotation (&

Floate" flocs collect as a slu"ge la$er on the water surface. erio"ic "eslu"ging occurs either +$

h$"raulic floo"ing of the flotation tan0 the slu"ge la$er s%illing over a collection weir or +$

!echanical s0i!!ing which will for! a thic0er slu"ge.

*he infilter DF so!eti!es referre" to as DFF: is a variation of the t$%ical DF %rocess in

which the +ase of the DF tan0 is !a"e into a ra%i" granular !e"ia filter thus incor%orating

clarification an" filtration into one ste%.

ulsed lanet clarifiers

ulse" +lan0et clarifiers use a vacuu! s$ste! to create %ulsations to hol" the slu"ge +lan0et in

sus%ension an" ai" flocculation allowing for higher surface loa"ing rates u% to 3 !Eh:. (n the

u%er%ulsator< s$ste! installe" at the >ai0ato >ater *reat!ent lant: clarification is

enhance" +$ incline" %lates allowing surface loa"ing rates of u% to a+out & !Eh.

ctiflo

*he ctiflo< %rocess is a %ac0age %lant !icrosan" +allaste" clarification %rocess as illustrate"

in Figure 13.&. *he %rocess re"uces flocculation ti!es to a%%ro)i!atel$ #61, !inutes an"

allows ver$ high surface loa"ing rates of 3,64, !Eh u% to 1,, !Eh:. *here are no ctifloater

/ui"elines for hase (I!"#ellen#e in $ater %reatentsets %erfor!ance goals as %art of overall

%lant %erfor!ance to achieve less than ,.1, * filtere" water. *his inclu"es clarifie" water

tur+i"it$-

less than 1., * 9# %ercent of the ti!e when raw water is less than or eAual to 1, *

less than 2., * 9# %ercent of the ti!e when raw water tur+i"it$ is K1, *.



16/27

Des%ite this it has often +een foun" that the se"i!entation %rocess is !ore effective when the

raw water is tur+i"B so!e earlier %lants with low tur+i"it$ raw water too0 a"vantage of this +$

"osing +entonite into the raw water.

0e$ as%ect of consistentl$ achieving L,.1, * filtere" water tur+i"it$ is that changes in raw

water tur+i"it$ shoul" have !ini!al effect on clarifie" water tur+i"it$ an" negligi+le effect on

in"ivi"ual filter tur+i"it$. *his reAuires o%ti!isation of coagulation.

co!!on o%erational %ro+le! in clarifiers of the ho%%er+otto!e" u%flow t$%e in ew

5ealan" is for shortcircuiting currents to occur usuall$ in su!!er an" aroun" the !i""le of

the afternoon. *his can +e attri+ute" to a te!%erature "ifferential +etween the inco!ing water

an" the water in the tan0. *he result is a +illowing of the floc +lan0et an" su+seAuent carr$over

of floc on to the filters. *he sa!e effect can +e cause" +$ algae in the slu"ge +lan0et +eco!ing

+uo$ant "ue to increase" %ro"uction of o)$gen "ue to %hotos$nthesis. High algal %o%ulations

are nee"e" for this effect to +eco!e a nuisance. Clarifiers with goo" inflow !i)ing "o not see!

to e)%erience the sa!e "egree of %ro+le!. *he onl$ satisfactor$ solution to this %ro+le! a%art

fro! fitting tu+e settlers to the tan0: a%%ears to +e to re"uce the flow an" hence the surface

loa"ing rate "uring the %ro+le! %erio".

nother co!!on %ro+le! is e)cessive floc carr$over cause" +$ uneven flows occurring over

the clarifier surface. (ns%ecting an" levelling the outlet weirs to ensure that all receive eAual

flows can correct this. (f the flows are still uneven the inlet flows to each clarifier !ust +e

chec0e" an" a"uste" so that the$ are even. For nonho%%er +otto!e" clarifiers it is also

i!%ortant to ensure that the "istri+ution of the flow within the clarifier is even.

ulti%le tan0s in larger %lants often e)%erience a high freAuenc$ wave in the outlet weirs that

!a$ "isru%t the floc +lan0et. However this generall$ "oes not cause a significant %ro+le!.

For clarifiers using a floc +lan0et goo" control of the +lan0et surface an" regular re!oval of floc

fro! +oth the to% an" +o"$ of the +lan0et an" +ase of the tan0 is i!%ortant. (n conventionalclarifiers the use of slu"ge or gravilectric: cones gives +etter results than the earlier s$ste! of

constructe" corner %oc0ets. Gotto! slu"ge scours shoul" +e o%erate" regularl$ +ase" on

e)%erience: to 0ee% slu"ge fresh an" to %revent e)cessive slu"ge +uil" u%. Gotto! slu"ge has

+een 0nown to go anaero+ic at %lants with a high level of organic !atter or algae in the raw

water.

;egular slu"ge re!oval is i!%ortant for all clarifier t$%es. For DF units "eslu"ging shoul"

also occur regularl$ to %revent slu"ge resettling. *he slu"ge in this %rocess is e)%ose" so it is

i!%ortant that the tan0s are covere" to %revent the rain an" win" affecting %erfor!ance.

Guo$ant !e"ia clarifiers nee" to +e +ac0washe" when the !e"ia +eco!es clogge" again to

%revent e)cessive floc carr$over to the "ownstrea! filtration ste%.

/rowth of algae an" sli!es on the walls of se"i!entation tan0s an" other channels shoul" +e

"iscourage". ;egular cleaning is reco!!en"e" +ecause such !aterial can increase the levels of

"issolve" organic !atter that the %lant !ust conten" with an" can contri+ute to taste an"

o"our %ro+le!s.



17/27

13. !ime softening and ion e"change>ater containing significant concentrations of calciu! an" !agnesiu! is referre" to as har"

water. Har" water can cause scaling of %i%es an" househol" a%%liances an" re"uces the

solu+ilit$ of soa%s an" "etergents in the water.

'i!e softening an" ion e)change %rocesses can +e use" to soften water however +oth are

currentl$ of li!ite" use in ew 5ealan" for "rin0ingwater !ainl$ +ecause on average ew5ealan" waters are softer than those foun" in !an$ other %arts of the worl".

13..1 !ime softening

*he li!e softening %rocess re!oves har"ness +$ che!ical %reci%itation followe" +$

se"i!entation an" filtration therefore showing si!ilarities to the conventional che!ical

clarification %rocess. 'i!e caustic so"a so"iu! h$"ro)i"e: or so"a ash is a""e" to the water

increasing the %H which causes the !etal ions to flocculate an" %reci%itate. *he !etal

%reci%itates are re!ove" "uring the se"i!entation stage %rior to filtration. Other conta!inants

!a$ also co!+ine with the %reci%itates an" +e re!ove" +$ this %rocess.

Calciu! concentrations can +e re"uce" at %H 9.# to 1,.# in li!e softening %rocesses although

!agnesiu! reAuires %H 1,.# to 11.#. everal organis!s are inactivate" at the latter %HB see

>HO 2,,4a: for further infor!ation. *he !icro+ial treat!ent !echanis! of this %rocess is a

co!+ination of inactivation "ue to elevate" %H levels an" re!oval +$ se"i!entation. However

Cryptosporidiuan" Giardiaare not inactivate" +$ high %H levels. ;e!oval of %roto=oa

through this %rocess is solel$ "ue to the se"i!entation an" su+seAuent filtration. ection #.4 of

the D>5 s%ecifies the co!%liance criteria that nee" to +e satisfie" in or"er to Aualif$ for 3 log

cre"its.

single stage li!e softening %lant consists of a %ri!ar$ clarifier an" filtration ste%. n

a""itional clarifier is reAuire" +etween the %ri!ar$ clarifier an" the filtration ste% for twostage

li!e softening. coagulant is a""e" to +oth stages of clarification. *wostage li!e softening can

%rovi"e a""itional Cryptosporidiure!oval "ue to the a""itional se"i!entation stage within

the %rocess. ;efer also to Cha%ter & of the review "raft '*2>*; *ool+o) /ui"ance anual

2,,9: which "iscusses issues relate" to li!e softening.

13..2 Ion e"change

(on e)change is "iscusse" in this section +ecause it is use" freAuentl$ to soften waterB it is not a

coagulation %rocess an" "oes not earn %roto=oal log cre"its. an$ as%ects of ion e)change are

covere" in FE( 442,,4.

(on e)change treat!ent units can +e cationic anionic wea0l$ or strongl$ ionic or !i)e" +e"

"e%en"ing on the reason for its use.

i)e" +e" units are e!%lo$e" for %ro"ucing "eionise" water usuall$ for la+oratories an"

in"ustr$. >HO 2,,#: also "iscusses so!e negative as%ects of "rin0ing "eionise" "istille" or

reverse os!osis water "ue to their tastelessness an" loss of essential !inerals !ainl$ calciu!

an" !agnesiu!. *his is "iscusse" +riefl$ in Cha%ter 1,- Che!ical Co!%liance section 1,.2.2.



18/27


19/27


20/27

*he conce%t of "ual or !ulti!e"ia filters is to inclu"e a relativel$ coarse !e"iu! eg

anthracite: on the to% followe" +$ finer !e"ia +eneath. *his causes "ee%er %enetration of the

%articles +eing re!ove" allowing longer filter runs. o!e !ulti!e"ia filters use a ver$ fine

!e"iu! at the +otto! of the +e" eg garnet:B this allows finer %articles to +e tra%%e" +ut

increases the hea"loss. *he effectiveness of !ulti!e"ia filters "e%en"s on the !e"ia re!aining

se%arate even after !ulti%le +ac0washes. *his is achieve" +$ a +alance +etween the relative

"ensities of each filter !e"iu! an" the +ac0washing con"itions. De%en"ing on the nature of the

%articles +eing re!ove" !ulti!e"ia filters !a$ +e effective without using coagulation.

G$ using a %ol$electrol$te as a coagulant ai" or filter ai" the strength or ?stic0iness@ of the

attach!ent +etween the floc %articles an" the !e"ia grains is increase" allowing higher

filtration rates an" coarser !e"ia gra"ings to +e use" there+$ re"ucing the rate that hea"loss

increases. (t also !eans the filter is less li0el$ to let go of these %articles following flow increases

or surges.

(f too !uch %ol$electrol$te is "ose" the %articles will a"sor+ to san" grains at the to% of the

filter causing the hea"loss to increase too Auic0l$. t a !ore a%%ro%riate %ol$electrol$te "ose

the %articles %enetrate further into the +e" !a0ing !ore use of the full "e%th of the !e"ia an"

allowing !uch longer filter runs. (f the %ol$electrol$te "ose is too low !an$ of the %articles !a$%ass through the +e" if the filter grains are coarse or the filtration rate too high. Ge" %enetration

can +e assesse" +$ !easuring the hea"loss at various "e%ths through the filter.

;a%i" granular filters can +e o%erate" at either a constant rate of flow constant rate filtration:

or at a flow rate that "eclines as hea"loss +uil"s u% "uring a filter run "eclining rate filtration:.

Constant rate filtration is the !ore co!!on !etho" an" is nor!all$ achieve" +$ the control

valve on the filter outlet o%ening %rogressivel$ "uring a filter run to co!%ensate for the +uil" u%

of hea"loss though the +e".

Gac0washing is the ter! use" to "escri+e the cleaning of the filter +$ %assing water often

%rece"e" +$ an"Eor in co!+ination with air: in the reverse flow "irection to when the filter isin nor!al o%eration. i!ilarl$ to the ter! filtration rate the ter! +ac0wash rate in !Eh or

!!Es: is use" to "escri+e the intensit$ of the +ac0wash o%eration. *ra"itionall$ in ew

5ealan" +ac0wash rates were low t$%icall$ 2,62# !Eh: %rece"e" +$ an air scour at a si!ilar

rate. *here are a variet$ of s$ste!s in use inclu"ing air scour followe" +$ water +ac0wash water

onl$ an" co!+ine" airEwater followe" +$ water +ac0wash. o"ern +est %ractice is a co!+ine"

air scourElow rate water +ac0wash the o%ti!al regi!e is 0nown as colla%se %ulsing: followe"

+$ a high rate water +ac0wash as high as ## !Eh:. +e" e)%ansion of 2, %ercent is the

o+ective "uring the highrate +ac0wash to ensure full +e" flui"isation an" a"eAuate cleaning.

ote that to achieve the sa!e "egree of +e" e)%ansion will reAuire higher flow rates in su!!er

co!%are" with winter as war!er water has a lower viscosit$ than col" an" the effects of this

shoul" +e consi"ere" in +ac0wash "esign.

13.7.2 Turidit/ monitoring

*ur+i"it$ !easure!ent is use" to assess the efficienc$ of the filter in achieving %roto=oa

re!oval for co!%liance with D>5. a!%ling !ust +e !a"e on water "irectl$ fro! the

filtration %rocess. *he D>5 reAuire tur+i"it$ !onitoring of each filter unless the %o%ulation

serve" is +elow a threshol" value 6 see *a+le #.3 of D>5:. article counters can also +e use"

to !easure an" o%ti!ise filter %erfor!ance +ut these are not reAuire" for co!%liance %ur%oses.

2- /ui"elines for Drin0ingwater ualit$ anage!ent for ew 5ealan" 2,13Cha%ter 13- *reat!ent rocesses Coagulation 6 e%te!+er 2,13


21/27

lthough tur+i"i!eters are not reAuire" on in"ivi"ual filters at s!aller %lants their use is

strongl$ encourage". *his is +ecause when !easuring a co!+ine" effluent fro! !ulti%le filters

one filter !a$ +e %ro"ucing %oor Aualit$ water that is then "ilute" +$ goo" Aualit$ water fro!

the other filters an" the su+stan"ar" filter@s %erfor!ance woul" not +e notice". Continuousl$

!onitoring each filter will in"icate whether an$ slow start !echanis! filtertowaste the

hea"loss control filter run length filtration rate control an" filter cleaning are o%erating or

selecte" correctl$.

*o earn 3 log cre"its un"er D>5 for %roto=oa re!oval using the coagulation se"i!entation

filtration %rocess or 2.# log cre"its for "irect filtration one of the reAuire!ents is that the

filtrate fro! each filter !ust +e less than ,.3, * for at least 9# %ercent of the ti!e D>5

sections #.4 an" #.#:.

""itional log cre"its are availa+le for enhance" filtration ie in"ivi"ual filter effluent (F:

!onitoring an" co!+ine" filter effluent CF: !onitoring see Cha%ter 8- roto=oa Co!%liance.

*hese will usuall$ +e the stan"ar" ra%i" granular !e"ia filters +ut %ro"ucing a lower tur+i"it$

filtrate. *he stan"ar" tungsten la!% t$%e ne%helo!eter !a$ not +e sensitive enough at such low

*sB a laser tur+i"i!eter !a$ +e reAuire". *ur+i"it$ !easure!ent an" cali+ration is

"iscusse" in Cha%ter 8- roto=oa Co!%liance section 8.#.3.1.

13.7.3 &ilter operation

s soli"s +uil" u% through the +e" hea"loss across the +e" will increase an" at so!e stage

tur+i"it$ will also increase. Gac0washing freAuenc$ can therefore +e triggere" +$ hea"loss

tur+i"it$ or filter run ti!es +ase" on o%erational e)%erience:. *he filter goes through a ri%ening

%erio" when it is +rought +ac0 online "uring which ti!e the filtrate Aualit$ will +e su+

stan"ar". For this reason slowstart "ela$e" starts an" filtertowaste are +eco!ing co!!on

%ractice.

13.7.4 *ptimisation of the filtration process

(ncrease" filtrate tur+i"it$ or resi"ual coagulant eg alu!iniu! or iron: is the %ri!ar$

in"ication of %ro+le!s with a filter however re"uce" run ti!es cause" +$ tur+i"it$ or hea"loss

reaching the set %oint earlier than usual: can also highlight %ro+le!s.

;aw water that has high colour an" low tur+i"it$ an" t$%icall$ with low al0alinit$: can +e ver$

"ifficult to treat %articularl$ when the water is less than sa$ 1,NC. *he floc often onl$ for!s in a

narrow range of alu! "ose an" %H con"itions. (t is usuall$ s!all slow to for! an" light so that

it is ver$ susce%ti+le to shear "ue to flow changes. (t can even +e "ifficult to see. *hese waters

can also result in elevate" alu!iniu! levels in the filtere" water an" hence a""itional attentionshoul" +e %ai" to !onitoring filtere" water alu!iniu!.

(f tur+i"it$ increases are o+serve" across all the filters there is li0el$ to +e a co!!on %ro+le!

u%strea! of the filters. *he following are so!e %ossi+le causes of high tur+i"it$ in the filtere"

water-

nono%ti!al coagulant "osing !a$ cause %oor floc for!ation which can overloa" an"Eor

%ass through the filtersB this can +e cause" +$ selection of an ina%%ro%riate alu! "ose or

coagulation occurring at the wrong %H

o%erational %ro+le!s such as the alu! solution +eing the wrong strength or even run out:

or the auto!atic a"ust!ent to flow rate +eing fault$ or ina"eAuate slu"ge re!oval fro! the

settling tan0s



22/27

"ose %u!%s not %erfor!ing to s%ecificationB a goo" %ractice is to chec0 the %u!% "ischarge

against the "ose setting so!eti!es calle" the stro0e: for e)a!%le +$ using "ose ti!ers or

calculating fro! the weight use" while a !easure" flow has +een treate"

flowrates !a$ have +een increase" too ra%i"l$ causing slu"ge +lan0et insta+ilit$

floc carr$over fro! a %oor clarification %rocess will increase the soli"s loa"ing on to the

filters re"ucing run ti!es an" causing e)cessive +ac0washing

insufficient %ol$electrol$te for the con"itions causing slu"ge +lan0et insta+ilit$ e)cessive %ol$electrol$te "osing which can Auic0l$ +lin" the filter an" re"uce filter runs

there+$ causing the filtere" water tur+i"it$ to increase earlier than e)%ecte"

flow increasing e)cessivel$ through the re!aining filters when one is +eing washe"

"irect filtration +eing a oneste% %rocess is %articularl$ susce%ti+le to su""en changes in raw

water Aualit$ an" flowrate.

(f filtere" water tur+i"it$ is high on a single filter the %ro+le! is li0el$ to resi"e onl$ with that

filter. o!e %ro+le!s their conseAuences an" %otential in"icators are liste" +elow-

+ac0washEair scour flowrates too low resulting in a %artiall$ washe" filter +eing %ut +ac0 into

service

+ac0washEair scour flowrates too high resulting in loss of san" allowing %articles to %ass

through the +e"

insufficient "uration of washing also resulting in a %artiall$ washe" filter +eing %ut +ac0 into

serviceB an elevate" clean +e" hea"loss a+ove nor!al values: on startu% i!!e"iatel$ after a

+ac0wash is a goo" in"ication that insufficient +ac0washing has occurre"

faile" or +loc0e" +ac0wash no==les or un"er"rain s$ste!. *his situation results in e)cessive

filtration rates an" +ac0wash flows through that %art of the filter +e" that is still in o%eration.

O+serving a filter "uring a wash can assist in "etecting in"ivi"ual faile" no==les- the overall

water or air "istri+ution %attern "uring the wash will +e uneven filter flow !eter controller or filtration rate in"icator !a$ +e out of cali+ration

uneven flow s%lit to each filter !a$ cause re"uce" filter run ti!es for so!e filters an"

e)cessive flows to others. (nlet %i%e or channel configurations shoul" +e chec0e".

(f filter runs are longer than e)%ecte" the$ !a$ not +e "ue to i!%rove" Aualit$ of the water

fee"ing the filters. *he$ can result fro!-

+ac0washEair scour flow rates +eing too high or the "uration too long. Overwashing !a$

lea" to !e"ia loss thus re"ucing !e"ia "e%th in the filter: or i!%air!ent of the !e"ia@s

a+ilit$ to a"sor+ %articles. Chec0ing an" recor"ing the !e"ia "e%th at regular intervals can

highlight if !e"ia is +eing lost "ue to over washing %ol$electrol$te "osage is i!%ortant %articularl$ in high rate or coarsegraine" filters. s

!entione" a+ove too !uch %ol$electrol$te can +lin" the filter +ut too little %ol$electrol$te

can result in so!e floc %assing through the +e"

%lants treating raw water with a low tur+i"it$ an" average to high natural organic !atter

usuall$ "irect filtration !a$ %ro"uce filtere" water with a low tur+i"it$ "es%ite ver$ little of

the alu!iniu! +eing re!ove". slower than usual increase in hea"loss in"icates a low

re!oval rate of soli"s. lants treating raw water li0e that shoul" test for alu!iniu! in the

final water to chec0 that the %rocess is o%erating satisfactoril$.



23/27


24/27

(f the filtere" water tur+i"it$ rea"ings ten" to %ro"uce s%i0es chec0 whether-

all filters are res%onsi+le

the filters are returning to service too soon after a wash

the slow start !echanis! is o%erating correctl$

a filter run was e)cessive

the state of the filter +e" an" un"er"rainage s$ste! cause %oor +ac0washing

the hea"loss instru!ents or flow controllers are inaccurate

the treat!ent %lant out%ut increase" too !uch or too ra%i"l$

the flow +alancing s$ste! is o%erating correctl$ eg when a filter is ta0en out of service for

washing:

the filter outlet valve is !o"ulating s!oothl$ enough

!ore %ol$electrol$te is nee"e" to co%e with short %erio"s of high flow

it ha%%ens at the sa!e ti!e as so!ething else eg when %u!% settings or valves are altere"

or when the washwater is returne":.

For further rea"ing tr$ 1999:. ection 4.2 "eals with s$ste! evaluation an" %lant

o%ti!isation section # "eals with in"ivi"ual filter selfassess!ent an" section & with

co!%rehensive %erfor!ance evaluation.

>HO 2,,1: covers a lot of groun" too.

13.$ %econd stage filtrationecon"ar$ filtration is a %rocess where+$ an entirel$ se%arate ra%i" granular filter +o) or vessel

is use" as a secon" filtration stage following a first stage filter ie two se%arate filters use" inseries:.

*o Aualif$ for a""itional log cre"its coagulation !ust have ta0en %lace +efore the first stage

filter which !a$ contain a coarse !e"iu! followe" +$ the secon"ar$ filtration stage that is

t$%icall$ a conventional "ual or !ulti!e"ia filter. ""itional coagulants or !ore co!!onl$:

filter ai"s %ol$electrol$tes: or o)i"ants can +e a""e" +etween the first an" secon" stages.

o!e reasons for using twostage filtration inclu"e-

following "irect filtration if the raw water Aualit$ is varia+le an" the o%tion is chea%er than

+uil"ing se"i!entation tan0s

where the treat!ent %lant occasionall$ e)%eriences %erio"s of stress eg-

when ver$ col" winter water causes alu!iniu! flocs to for! slowl$

or "uring high su!!er flows

to re!ove iron an" !anganese after an o)i"ation stage eg after chlorination

to re!ove grit fro! %oor Aualit$ li!e. t this elevate" %H !ore iron an" !anganese !a$ +e

re!ove" too

to re!ove further organic !atter inclu"ing an$ "isinfection +$%ro"ucts +$ using granular

activate" car+on /C: filters or +iologicall$ activate" car+on GC: filters.



25/27

Co!%l$ing with section #.4- Coagulation se"i!entation an" filtration %rocesses earns 3 log

cre"its. Co!%l$ing with section #.#- Coagulation "irect filtration- treat!ent earns 2.# log

cre"its. econ"ar$ filtration !a$ earn an a""itional ,.# log cre"it for %roto=oal co!%liance

refer D>5 section #.&.

*he secon"ar$ stage filters !ust involve the use of a ra%i" san" "ual !e"ia granular activate"

car+on /C or GC: or other fine grain !e"ia unit %rocess a%%lie" in a se%arate stage

following ra%i" granular or "ual !e"ia filtration. *o Aualif$ a continuous che!ical coagulation%rocess !ust +e in o%eration u%strea! of the first filters. One of the !onitoring reAuire!ents is

that the tur+i"it$ of the water leaving the secon"ar$ filters !ust not e)cee" ,.1# * for !ore

than # %ercent of the ti!e see section #.&.1 of the D>5. ee also 2,,3: an"

Cha%ter 9 of the review "raft '*2>*; *ool+o) /ui"ance anual 2,,9: which

"iscusses issues relate" to secon" stage filtration.

o!eti!es the coagulation %rocess is followe" +$ !e!+rane filtration. (n this situation a

secon" stage filter cannot earn a""itional log cre"its. *he !ain reason is that water that has

%asse" through a ver$ fine filter shoul" not earn an$ !ore log cre"its for %assing through a

!uch coarser filter. co!%liant !e!+rane filter will alrea"$ +e %ro"ucing water with a

tur+i"it$ less than ,.1, * so it is not logical to earn !ore log cre"its for %ro"ucing water thatcoul" have a higher tur+i"it$

#eferences(E>> G1,,,9.&$$& Standard forGranular'ilter(aterial2E&E2,,9:.

>>. 199,. $ater )uality and %reatent4th e"ition:. c/rawHill (nc.

>>. 2,,,. *perational Control of Coagulation and 'iltration +ro#esses. anual 37 2n"

e"ition:. Denver CO- !erican >ater >or0s ssociation.

Dugan Fo) Owens J et al. 2,,1. Controlling Cryptosporidiuooc$sts using conventional

treat!ent. &$$&9312:- &467&.

Drin0ing >ater (ns%ectorate D>(:. 2,11.ist of &pproved +rodu#ts for .se in +u/li# $ater

Supply in te .nited 1ingdo. 'on"on- De%art!ent for nviron!ent Foo" an" ;ural ffairs. ee

www."wi.gov.u0 or htt%-EE"wi."efra.gov.u0E"rin0ingwater%ro"uctsEa%%rove"

%ro"uctsEsoslistcurrent.%"f

Hill * 'ang"on . 1991. orous cera!ic "ual !e"ia filtration. $ater $astes in New Zealand

&&Jul$:- 1962, 22.

awa!ura . 2,,,.3ntegrated Design and *peration of $ater %reatent 'a#ilities2n" e"ition:.

ew Por0- John >ile$ Q ons.

*he ew 5ealan" inistr$ of Health@s /ui"es for "rin0ingwater su%%lies can +e accesse" as >or"

"ocu!ents on the inistr$ of Health we+site- htt%-EEwww.!oh.govt.n=Ewaterthen select

%u+lications an" u+lic Health ;is0 anage!ent lans.

inistr$ of Health.+u/li# 4ealt isk (anageent +lan Guide +4(+ ef6 +5676 %reatent

+ro#esses Coagulation9'lo##ulation9Sedientation. >ellington- inistr$ of Health.


+ro#esses Dissolved &ir 'lotation.>ellington- inistr$ of Health.

inistr$ of Health.+u/li# 4ealt isk (anageent +lan Guide +4(+ ef6 +56:6 %reatent+ro#esses Dire#t 'iltration. >ellington- inistr$ of Health.

http://www.awwa.org/Resources/Content.cfm?ItemNumber=44361http://www.awwa.org/Resources/Content.cfm?ItemNumber=44361http://www.awwa.org/Resources/Content.cfm?ItemNumber=44361http://www.awwa.org/Resources/Content.cfm?ItemNumber=44361http://www.awwa.org/Resources/Content.cfm?ItemNumber=44361http://www.awwa.org/Resources/Content.cfm?ItemNumber=44361http://www.awwa.org/Resources/Content.cfm?ItemNumber=44361http://www.awwa.org/Resources/Content.cfm?ItemNumber=44361http://www.awwa.org/Resources/Content.cfm?ItemNumber=44361http://www.dwi.gov.uk/http://dwi.defra.gov.uk/drinking-water-products/approved-products/soslistcurrent.pdfhttp://dwi.defra.gov.uk/drinking-water-products/approved-products/soslistcurrent.pdfhttp://www.moh.govt.nz/waterhttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/ConventionalCoag-floc-sediV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/ConventionalCoag-floc-sediV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DissolvedAirFlotationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DissolvedAirFlotationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DissolvedAirFlotationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DirectFiltrationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DirectFiltrationV1.dochttp://www.awwa.org/Resources/Content.cfm?ItemNumber=44361http://www.dwi.gov.uk/http://dwi.defra.gov.uk/drinking-water-products/approved-products/soslistcurrent.pdfhttp://dwi.defra.gov.uk/drinking-water-products/approved-products/soslistcurrent.pdfhttp://www.moh.govt.nz/waterhttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/ConventionalCoag-floc-sediV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/ConventionalCoag-floc-sediV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DissolvedAirFlotationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DissolvedAirFlotationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DirectFiltrationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/DirectFiltrationV1.doc


26/27

inistr$ of Health.+u/li# 4ealt isk (anageent +lan Guide +4(+ ef6 +;676 %reatent

+ro#esses apid Sand 'iltration. >ellington- inistr$ of Health.


+ro#esses p4 &dellington- inistr$ of Health.


+ro#esses +lant Constru#tion and *peration. >ellington- inistr$ of Health.

inistr$ of Health. 2,,#.Drinking-water Standards for New Zealand 2005, revised 2008.

>ellington- inistr$ of Health.

FE( 442,,4. %"ate" 2,,7.esidential Cation !"#ange $ater Softeners. nn r+or

ichigan- F (nternational.

5>>. 1997.Standard for te Supply of &luiniu Sulpate for .se in $ater %reatent2n"

e"ition:. ew 5ealan" >ater an" >astes ssociation. ;evise" 2,12.

5>>. 1999.Standard for te Supply of +olya#rylaides for .se in Drinking-water %reatent

(G 1877134244. ew 5ealan" >ater an" >astes ssociation.

5>>. 1999.Standard for te Supply of +olydada# for .se in Drinking-water %reatent(G 18771342#2. ew 5ealan" >ater an" >astes ssociation.

5>>. 1999.Standard for te Supply of !pi-D(& +olyaines for .se in Drinking-water

%reatent (G 18771342&,. ew 5ealan" >ater an" >astes ssociation.

5>>. 2,13.Standard for te Supply of +olyaluiniu Cloride for .se in $ater %reatent

2n" e"ition:. (G 1877134,82. www.watern=.org.n=

Ogilvie D. 1998. trea!ing Current Detection. $ater $astes in NZ1,1 Jul$:- 32 3463#.

rinivasan * Iiraraghavan * u+ra!anian . 1999. lu!iniu! in "rin0ing water- n overview.

$ater S&2#1 Januar$:- 476##.

. 1999. Guidan#e (anual for Coplian#e wit te 3nteri !nan#ed Surfa#e $ater

%reatent ule= %ur/idity provisions. ;e%ort 81#;99,1,.

htt%-EEwater.e%a.govElawsregsErulesregsEs"waE!"+%E!"+%tg.cf!

artnershi% for afe >ater /ui"elines for hase (I.!"#ellen#e in $ater %reatent. ee

infor!ation on this su+ect at-htt%-EEwww."ocstoc.co!E"ocsE1327#,1&3Eartnershi%forafe

>ater!erican>ater>or0sssociation

. 2,,7. iultaneous Coplian#e Guidan#e (anual for te ong %er 2 and Stage 2 D>+

ules. 81#;,7,17. 4&2 %%.

htt%-EEwater.e%a.govElawsregsErulesregsEs"waEstage2Eco!%liance.cf!or

htt%-EEwater.e%a.govElawsregsErulesregsEs"waElcrEu%loa"E2,,7R#R1,R"isinfectionRstage2Rgui"eRst2R%wsRsi!ultaneousco!%liance.%"f

. 2,,9.ong %er 2 !nan#ed Surfa#e $ater %reatent ule, %ool/o" Guidan#e (anual

eview Draft. /o into htt%-EEwww.e%a.govEsafewaterE"isinfectionElt2Ean" then enter- tool+o)

gui"ance !anual review "raft in the ?search@ +o)

>HO. 2,,1. .pgrading $ater %reatent +lants. (G , 419 2&,#, 1. u+lishe" on +ehalf of >HO

+$ %on ress 'on"on. vaila+le on the internet at-

htt%-EEwww.who.intEwaterRsanitationRhealthEh$gieneEo!Etreat%lantsEenEin"e).ht!l

>HO. 2,,4. Guidelines for Drinking-water )uality 200?3r" e"ition:. /eneva- >orl" Health

Organi=ation. vaila+le at-www.who.intEwaterRsanitationRhealthE"wAEg"wA3EenE%rint.ht!lseealso the a""en"a

http://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/RapidSandFiltrationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/RapidSandFiltrationV1.dochttp://water.epa.gov/lawsregs/rulesregs/sdwa/mdbp/mdbptg.cfmhttp://www.docstoc.com/docs/132750163/Partnership-for-Safe-Water-American-Water-Works-Associationhttp://www.docstoc.com/docs/132750163/Partnership-for-Safe-Water-American-Water-Works-Associationhttp://water.epa.gov/lawsregs/rulesregs/sdwa/stage2/compliance.cfmhttp://water.epa.gov/lawsregs/rulesregs/sdwa/lcr/upload/2007_5_10_disinfection_stage2_guide_st2_pws_simultaneous-compliance.pdfhttp://water.epa.gov/lawsregs/rulesregs/sdwa/lcr/upload/2007_5_10_disinfection_stage2_guide_st2_pws_simultaneous-compliance.pdfhttp://www.epa.gov/safewater/disinfection/lt2/http://www.who.int/water_sanitation_health/hygiene/om/treatplants/en/index.htmlhttp://www.who.int/water_sanitation_health/dwq/gdwq3/en/print.htmlhttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/RapidSandFiltrationV1.dochttp://www.moh.govt.nz/moh.nsf/0/5AF58E090CF4098BCC25699600754798/$File/RapidSandFiltrationV1.dochttp://water.epa.gov/lawsregs/rulesregs/sdwa/mdbp/mdbptg.cfmhttp://www.docstoc.com/docs/132750163/Partnership-for-Safe-Water-American-Water-Works-Associationhttp://www.docstoc.com/docs/132750163/Partnership-for-Safe-Water-American-Water-Works-Associationhttp://water.epa.gov/lawsregs/rulesregs/sdwa/stage2/compliance.cfmhttp://water.epa.gov/lawsregs/rulesregs/sdwa/lcr/upload/2007_5_10_disinfection_stage2_guide_st2_pws_simultaneous-compliance.pdfhttp://water.epa.gov/lawsregs/rulesregs/sdwa/lcr/upload/2007_5_10_disinfection_stage2_guide_st2_pws_simultaneous-compliance.pdfhttp://www.epa.gov/safewater/disinfection/lt2/http://www.who.int/water_sanitation_health/hygiene/om/treatplants/en/index.htmlhttp://www.who.int/water_sanitation_health/dwq/gdwq3/en/print.html


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>HO. 2,,4a. $ater %reatent and +atogen Control= +ro#ess effi#ien#y in a#ieving safe

drinking water. > 'eChevallier u. (> u+lishing. 13& %%. vaila+le on the internet at-

www.who.intEwaterRsanitationRhealthE%u+licationsEenEin"e).ht!l

>HO. 2,11. Guidelines for Drinking-water )uality2,11 4th e"ition:. /eneva- >orl" Health

Organi=ation. vaila+le at-

htt%-EEwww.who.intEwaterRsanitationRhealthE%u+licationsE2,11E"wARgui"elinesEenEin"e).ht!l
http://www.who.int/water_sanitation_health/publications/en/index.htmlhttp://www.who.int/water_sanitation_health/publications/2011/dwq_guidelines/en/index.htmlhttp://www.who.int/water_sanitation_health/publications/en/index.htmlhttp://www.who.int/water_sanitation_health/publications/2011/dwq_guidelines/en/index.html

Documents

Drinking Water Guidelines Chapter 13 Treatment Processes Coagulation Oct13