design schemâ¬, that is activatâ¬d sludge process wss ... pâ¬n is re - circulatad to â¬ctivatod sludge ba6in and .... uld not bs the reason tot sludge bulking problâ¬m'.
rJ€Pt9(2)r96-loo
( Receivedon August 29, 1998)
Performance Evaluation of SewageTreatmentplantand Sludge Bio - methanation A, Kapur,A. Kans.l. R.K.p;asad.6nd S, cupto TalaEneryy Researchlnstitute. Daftati SethBlock, Habitat place, Lodhi Road,New Dethi - .l1O OO3 Effici€ncy ot 6owsg6 treatmont plants ia seriously .ff6cted und€r conditionF ot over or under pollution loading. This papor discussesth6 problemsassociatedwith a sewpgerr€armontptsnt ( conventionalschome- activatedstudgoprocess when it is und€r loadod due to over ) d€rign. Poasibl. r6m6dialm6osuresto improveplant 6fficisncy.nd thg fearibility to run anaerobicdig6st€r for such pla.|ts i6 presentgd, INTRODUCTION Urbanseruicoutilitiosof thtd world couriries are undera tr6mendousstressdue to exDonsntialincroas6 in population,Sysl6msot w€rcraupply,s6wag6 and solid waste diEposslsr€ badly atf€ctooon account Of lack of corr€spond;ng 9169,th in infraslruCturo facilities.As a r6sult, environm6ntaldegradatlon occur6in form ol contamin6tedwater supply, dischargeof !ntrost€d wast6w6tor and accumuration ef solid wsrt€s. Domcsticsoclor €s ths msjor conlributor,is rosponsibte tor about 60 % in terms ol organicpollulion load to wster bodi6s.Ot the ro. t3l 6sWAgegeneraledtrom urban cantors in the co. r,ntryonly 10 % is subiected lo trealment betore disposal.ln addilion, lho performancoof s€wsge tr€atmentplantr is dismEldu6 to improper d€Bign and poor maintonancE, iogethorwilh a non - technical 6nd un6killedspproach.The sowsg€ troatment plants ( STP) construcledunder various pollu-
tion ab6l€mentsdhemosduring lsl€ 1980s snd early 1990s failed du6 to the ssme r€asons.Th6 ST Ps w€rc sitheroverloaded,experiencingshock loads, or under loadod(TERI,1998). This works inv6sligatgsths problemBassocistedwith a sewaO€lraatmentplant (conventionalschgme- activatodsludg€ proc6ss)when it is undorloadod du6 to ov€t design.The pepsralso discussos the possible romg. dial m€asuresto improvgpl6nt 6fficiency, DESIGNFEATURESOF THE STP A sgwogelrgatmshtplant bas6don a conv€ntional designschem€,that is activat€dsludgeprocesswss sel€ctedfor this atudy. The ptant is dsslgn6dine modul6rformatfor a capacilyof 3.8 MLD and influenlBOD conc€ntrationof 200 mg/1. Thefinal trealedetfloenl is discharg€dinto a surfacewater drain,whtch joins a river downstr€am.Prelr€alm€nt unit6consistof mediomb6r scroensand grit ch.
TabL 1. De6ign fed?urcs of trcatment onlts
Treatmonl unit Screench€mbor Grhchann€l Primaly a161i1i",
No.ot Sixeof individuat unit,m units
Volum6ol Desjgnconsid€rations holdup,rnr
0.05x0,354 1 7 . 9 x 0 . 9 7 , ( 0 . 4+6 0 . 1 9 8 . 6 x 3 . 0 0+ 0 . 3
NA
A€rationtank
2 0 . 0 0 x 1 0 . 0 0 x 2 .+7 50 . 6
600
Secondary clarifi€r Sludgedig6st€r Sludg6dryingbeds
I 1.00x2.00 0.3 ' 1 2 . 5 x 6 . 0 0+0 . 8 + 2 6 . 0 0x 6 . 0 0
200 770 NA
2
20
177
M6diumbat sct€ens Horizontsl volocitysB 0.3 m/s D.T. 2 hr with skimmerand oil andgr6aso romovalmschantsm D . T .- 6 . 6 h r , M L S S : 2 0 0 0 ms/1, F/M - 0.3 D.T.- 26 d8y
*Whi pool lndia Limited, Fa dabad 121 OOI
96
INDIANJ. ENVINONMENTAL PROTECTION, VOL.19. NO,2, FEBRUARY T9S9 @ 1999 - K.lplna Corporqtton
fable 2. Sampllng locdtiohe, natufe of sdmples and prhmeterc analysec)fot petlotmance evaS8mplinolocEtion Typs of sampte
Gritchamber
Pafam€ters analYzed
CompositoBOD,COD,TS,TSS, TKN,total phospho.
pH,temDeraluro Garb Primary6edime, Composile BOD,COD,TS,TSS, ntationtank DO crab PH PST sludge pH,TS,VS,% solids Grab Aer6tion tank Grab DO,TSS,TSS,IKN, total phosphorus S6condarys€di- CompositeBOD.TSS,DO,TKN m.nlation tank SSTsludge Ana6robic dige9tor
Grab Grab Orab
PH
pH, TSS,VS,SVI pH,VA, alkdlinity, TS,VS
amberfollowod by prim8ry ssdimontationtsnk ( p ST ). Th€ €fllu€nt from PST iB troaled in activated sludg€process,which consists of an aerationtank followed by s€condsrysettlinglank. Wasle stud0€ is collecledin socondary sludg€ pit from where a p€n is re - circulatadto €ctivatodsludge ba6inand remsiningsludgo along with primaryclarifier sludOeis 6entto anaerobicdigost€r8fotlowod by sludge drying b€d3. The filtrat6 from the saod drying beds is 16 - circulat€d back inlo PST. The dgsign f6aturesof each unit 6re oiven in tabl6 1. Ptoaent wastowatcr f low fableS.
Pstfonance
Th6 flow was measur€dduring the month ol Novdmber 1997, Th6 total qu€ntity of sewage 6ntoring into the STP wae 1.1 MLD €t th6 rat€of 140 m,/ hr. No flow conditions wers observeddwing 24 i 0 0 - 7 : 0 0 h r s ; 1 0 : 3 0 - I : 3 0 h r s ;1 6 : 0 0 . 1 9 : 0 O h r s ;a n d 2 0 : 0 0 - 2 2 : 0 0 h r s , Plant parformanc€ To evaluat6the STPperlormanc6, s schedu16 of hourly.samplingand snalys;sof composit€wastewaler froin each unit was dfawn uo. Samoteswsfe composit€dIn proportionlo th€ flow over a periodot 8 hr throughoutthe dsy. Addilionally, grab samples wsre also taken from som€ unitstor 6nalvsis. Compositodand grab sampleswere lh€n analyzed parameters.Tho anin labofatorytor th€ necessary alysiswas carri6dout as per the standardprotocols ( APHA, 1989 ). The sampling loc€tions, param€t€r6an€lyz6dand natureot 6ampl6staken lor pefform6nceevaluationsr6 given in lsbl€ 2. The rcsuIts ol lhs anaiysis€re giv6o in lable S. TheSTPh6d beendesignadfor a-capacityof 3.8 fMLD butwas currentlyreceivingonly 1.1 lvlLD.Ou6 lo d€rective d€signof th. distributionch6mbef,thebypassoutlet providedto di6chargethe wasrewat€rdirecrlyto lhe surlacowslsr drain wa6 alwayskepl open. As s r e s u l tt,h e S T Pw a s t r e a t i n go n l y 5 0 % o f 1 . 1 M L D, lhal is 0.55 MLD in an int€rmittentlashion. Prgtt€atm6nt Solidsaccumulatsdover the bar screens wer6 fou. nd to be putrefying.In lhe gfit chamb€ra lot of sludgo hsd bssn depositedov6r the bod 6nd d€plh ot the accumul€tedsludgg layerwas 6round 12 cm in bolh chanbors.In ths grit chamb6r bubbl€s were
panmeteq lrom each trcatnent units, in nglL
Grit chsmb€r
PSI effluent
PSTsludgs
A6ratlonlank
SST6ltluent
SSTsludge
PH TSS
6.9-7.6 1 8 0 - 26 4
6.7-1.1 120-190
6.'t-7 ,O
6 3-7.4 11 0 - 1 6 0
6.2-6.9 20 0 0 - 3 6 0 0
TS % Solid6 BOD
6.9-7.3 220-1150 ( MLSS)
500-660
460-600
60-160 150-280
io-t,o
500-900 o.5-0.8
coD
TKN Phosphorus2-6 DO
vs
svl
140-230
o.0-0.6
oo io-,, n.r-r.u
1.3-3.6 o.2-2.4 '|uoo-uooo 8 0 - 6 5 0 ( MLVSS)
1999 I NDIANJ. ENVIRONMENTA! VOL.19, NO.2, FEBSUAFY PROTECTION, O 1999 K.l9aoa CorDotdloD
o,2-0.3
1.9-3.3 :
o.at.,
' t1 8 0 - 1 4 0 0 150-200
97
f abl6 4, Peiomance paftmetett of anaercbic dige' steL in mglL P6ram€ler Portposition Top
6 . 8- 6 . 9 5-16 Alkaliniry 12-52 120-165 9 4-112 VS pn
Middl€
Bottom
6.8-7.0 8-12 4 3 - 66 132-'176 9 8 - 1J 6
6.8-7.0 34-78 12A-162 102-120
obs€ruedwhen th6 depositsdsludg€was disturbed which not only confitmslhe deposition of organic lractionof susp€ndedsolids but also indicatsslhe ptocoss inilistionof decomposition Primsly tr6itm€nt Duringtho entho monitoting pefiod one PSTlvas osl of serviceand thsroforemonitotingwas carli6d out in lhs olh6f unil. Psrformancscharact€rislics as obs€rved during plant monitofing aregiven in tsbl6 3. Fromlabls 3, tho Iollowing obsorvations ( a ) SusDended solids and BOD fomoval 6ffici6ncv 25 and 1l %, respoctiv€ly. ls aboul of ths unit ( b ) The BOD/CODtatio in the influent is around 0.65 which after PST reducesto 0.58 ( c ) Dissolvedoxygenin lhe supernatanti6 n€gli' gibl6. ( d ) Totatsolidsin PsT sludgeis about 0.6 %. ( 6 ) VolatilosolidBfroctionin th€ sludgo is aboul 4O Yo. Gas bubblosond sludgellocs were ob3e.vodon the sudac€of lh€ tank. S€plicsupernatant( DG : 0 0.6 mq/L ) is du€ lo decomposhionof lhs seltlsd sludge.Thereis s roduclionin the BOD/COD ratio b€causeof presenceol oit and gt€asein the efflu6nl, lmprop€rromovalol oil and greasois due to poshion of hoppof boing w6ll above tha maximum wal€r level. Biological treatmont ,qclivsledsludgeproc6ss:The sctivstedsludgs ptocessis dssigned on a convonlionalscheme.Tho operatlngcharact€rislics of the proceasare summarized in t6bl€ 3. Th6 s8mplesIn ths aerationlank were colloctednoar the su{sca aorators.Following obsgtv!tionsw€r€ mads during lho lield monitoF ing: ( a ) Aeratorswer€ not fully functional.
( b ) Thetlo6tingsludgebiomasswas prsssnl thesurfaceof thesettlinglank. ( c ) Gas bubbl€swete th€rg on ths 6ud€c€of the settlingtank. ( d ) gntile sludge,that is formsd and cotl6ci6d fr' om th6 SST i5 returnedinto the 6erationtank inst6' ad of the anaerobicdigssteI ( e ) Efticioncyof BOD and SS r€moval was obsor_ vod 6s 23 and 18 % r€spectively. ( f ) S l u d g ev o l u m e i n d o x ( S V l ) o f S S T s l u d g e w a s a r o u n d1 7 0 . The prosencaot gas bubbleson th€ sltlaco of SST and carryover oI sludgsllocs in lhe finat €tfluent cleafly indicatesthe ploblemof tising sludge Bising sludgecan be attfibut6dlo high sludge ag6, low sludge loadingrato 6nd high telention time in SST' Tho sludg€ age is mof€ lhan 2O day and th€ sludgo losding rate is sbout O l kg BOD/kg ts/dav Theso conditions promote gtowth oI Nitrosomonas and Nitrcbact,t baclotia which inltiale nitlificalion ptocessin the aslstion tank. Add€dto this' lhe deten' rion time of th6 s€wag6in the ssT is 6boul 16 hr' which ptovides conducive snvironm€nttot d€nitri' ficalionto occur 6nd ths proc€ssto run in 6xtonded a6rationmode,As s iesult excesssludg€lrom SST is thus, highlv stablesnd can bo dir€ctly dtied over studgedrylng beds.Duringthe processof dBnitriliwhich gets entrap' cation,nitrogengas is 16l€ased th€reforo,beco' floca, osd in the sludgofloc The6o mo lighlersnd riseto the surfac€' Th6 observedvolue of sludge volume ind€x ( SVI ) th€ occulrenceol sludgobulking Ths ocinclicates cu ence of sludgobulking is also confirmedby the f6ct that tho coliect€dsludgeha6very l63s concen' trarionof solidsconlenls( about 0.25 % as again' st lhe normsl t % solidsconconltalion) Batio6ol BOD to nilrogenand BOD to phosphorusis about ' 1 2a n d 1 O O : 3 , I e s p € c t i v e lw y hich 316 in 100: co_ d€ficioncy v6ry good rsng6.Ther€fore'nutriont probl€m' uld not bs the reasontot sludge bulking The DO dsficioncvin many pock6tsof tho aelalion tank promot€slhe glowth of tilamentousorganisms as they ptovidogr€alglsulfacearoaand giv€ lhsm an advanlago8s they tske !p ih€ limil€d supply of oxygenover a larg€rar6a. Anaerobic sludge dig6stor: ln tho 6xaslingoper€tlng pr€ctices,only primary settling tank sludgo is pump€dinto th6 2 anagrobicdige6t6r3.Duling the oD€ratiohof the sludg€ pumps, the valvo oponing
1999 VOI".t9, I{O,2. FEBRUASY INDIANJ, ENVIRONMENYAL PROTECITON' @.t9e0 Ealrrtt Gor9orallo.
fabL
5, Aualitativd assessment of eachunL
Unit
Obs€rvedproblems
Cau6es
Remedialmeasur€s
Barscro€ns
Solic,accumulalion
Unusualamountol d6bris
lncresecleaningfrequency
grjt in bar Excessivo scre€nchamb€i Gril chamb6r
Accumulatedgrit in chamber Overflowing grit chaGas bubblesrisingin grii chambef
Primarysedim6nta-Floatingsludg6 tion tank Scum ovsrflow
Aefation tank
Inadequat6 cl€aningf requ6ncy Flow velocilytoo low Removebottom irregutarity, or reslopoth6 botlom. Flushr€gularlywilh Water Subm6rgeddebris Wash ch€mb6rdsily. Remove d€bris Flow v6locitytoo low Correctllow ralo Pumpsurge problam Sludge accumul€lion6t bollom of chambsf Sludg6d€composingin tank Wotn or dsmaggdscum blades lmproporalignmenlol skim-
Adiust pumpscontrols Wash ch€mbsrdBily.Removo decris Hemovgsludge more frequently or at a highorrare Cl6anoa reploc6wipor blade6 Adjust alignment
Height ot collectinghoppor Undesirablylow solids Ov6fwithdr6walof st0dgo conlenlsin sludge Poor suspond€dsolids Ungvenweir setlingg Hydrsulicoverlo6diog Sludgebulking Pr6sgncoof filarhentousmi. croorgani6ms
Colrectth6 gosition Reducetrequencyand duraljon of pumpingcycles Chang6weir setlings Chockllow iat6 Add nutriont6(N, P). Incre6.6 DO concontration,Corecl pA
Ri6ingsludge
Inc!€as6sludge washing rats to shortonMCRTgnd rsise ths F/M to stop nitrific6tion Incr€a!€tho retutnllow rat6
Anaerobicdig€st6r Poor sup6rnstantquality
Aeration6t iow F/tvl
D€t€ntionof sludgein cl6. riti6r too high Excessive mixing Insufticientsettlinglim6 Too low Bupgrnatant withdrawal polnt Insutticiontsludgewhhdfa-
R€ducemixing Allow longortim€ Ior set ing Use high sup€rnat€ntwithdrawal pon Incr€asethe digested studgo withdrawal Foamin s0pernatont Rissin sludgeblaoket Stop supe.natantwithdrawal Hi0h organicoverloading Beduc6foedingrsle low gasprossu16 Gas leakag6 Ch€ck and repsir leaks |rom valves.digostercovgr and gs3lines High supernstantwithdraw6lContfolsupernatanlwithdrawal rate Thin dig6stedsludge Shorlcircuiting Stop mixing severElhou.s b6Exc€ssivg mixing tore sludge withdr6wal and High6ludgepumpingrate wilhdr8w th€ 6ludg6 by short
INDIANJ. ENVIBONMENTAL PROTECTION, VOL.19. NO.2, FESRUARY I999 @ 1999 ' K.loon. Corgoration
s9
ldwardsthe 66rdiirtn tarik is d6n€raily keDtonoh mostof the dme. Therefore.only occasionallyth6 SSTsludgegoesinto the ans€roblc digest€rs. Sup. €rnalantwithdrawal syst6min ana€robicdigost6r, !9hichis n6c6sssry to mainlainmass baranc6. was 6bsent.Gas leakago waa detectod on th6 roof of thg digost€rnearthe mlxor.Safeti d€vic6s,suchas ptossure r€lief valveswore not instslledwith lh6 digestsr. Thorosultsof lhe analysisof sampl€s ta. ken from inslde ths digestorsrs giv€nin table 4. Thede Indicat€ th5t the subgtfdt€quantily in6ide ths dlge.t€r ia vory dilute for anserobicdigestion 6nd thsreforc,needsto b€ f€ - commi6sioned.This otso co oboEtod thc ob6ervationlhat tnere was negligiblegar productionfrom the dig€sters. Feasibillty of ana€roblc dlg.st€r : Activstodslu_ dge ptocosswas ob3gry€dto lun In the exlendod aerationmodg.Tho 6ubrtr6t6for the diggsioris pS T sludg€65 mosi ot th€ SST.ludgs has been alre. adystabilis6d in tho 6orationtsnk. In future. to run the plantwith sn optimumsfficiency,the qus. ntityof totallolidefrompSTsludgewould be aro. und 160 kg/d6y.tf the percentag. of votaritesotids iBaasumed as 60 % thg qusntityof the gasexp6ctsd to be produc€df.om the pSTehrdgois around 45 me/day,Considsringth6t lhe methan€contenr In the gasas 60 % th6 highgfade coal equival€nt ot thisgas will b€ about 37 kg ( considering the c8loriflcvsluoof highgradeco6lss 21,300 Btu/lb 8ndlh€ utilizationofticiencyofmethan6andcoal aB90 €nd 66 %, relpectively. Conlid6ring rne ma. rketratsof high . gradeco€l €a Fs 4.OO/kg, cssh equivalent of the biogasis aboutRs tSO/osy, To run the anaerobicdigostor,l5 Hp mixorhas b€€nprovid€dwhich is rcquirsdto b6 run for arlo. €sl l8 hr a day.Considering th6t only on€ digeat€r will be put In usotor biogasgonsration, tot€l ol€ctricityconsumption in th€ anaerobic dig€stlonfacilhy would be about 2OO Kwh/dsy. Evenconsidering tho domeEticrat. ot th6 €loctricityaaRs 2.41K Wh total oxpandlture towards running tho digestor wouldb€ aroundRs4gO/dsy.Ther€fore, th6 oltompt for genefslinglho blogssin the existing flow co. ndltionwouldcsuses n9t lossot Ra33o/d€y.This is apartfromthg coatlowsrdomanpower€no sn6lysl8for operation andcontrot oflho digeslorand thg capital and oper€tingco6tof a cohp.ossorto supplyths ga6 from tha plsnt to a noarbycanle€n. Oporation 6nd mointen6nce Operotingstatf at tho STp dld not conform to sr6n.
100
dardsoideline! fdi 6b6riring ancimainieiairi6 io andM ). Sludg6 wilhdrawal frompSTsndSSTwas
1
€rratic.Sludgerecirbulstion to asf€tiontankw6s not bssedon MLSSconcontration. EntiroSST5lud_ ge waarecirculsled to 6€ration tsnk snd pSTslud. go waspompedto th6 digest€rs.R€gulsr clsaning or scr€ons €ndgrit chamber was absent.Laboratory faciliti€s for routing monitoringsnd anstysi6 w6re absenl Ba6€don theserosuhssnd ti6ld oOsOrv6fl. on5,a quantitativeass€ssmont of tho problomsand romgdialmeasureslo improve tho pfocessof 6ach unil ar6givenin table6. An ssrossment of thiski. nd will hslp the plantoperalorsro deal with the - d€y problems€nsuring plant olflcincy day is nor a_-.lo €cteddue to undarlosdinO.
ul p et di
coNcLustoN Th6 SIP hos been do6ignedfor a design copacity of 3.0 MLD but the current flow to the STp is appro_ ximatsly 1.1 MLD. Actual water treat€dby the sTp was 60 %, sincorest 60 % waa be_ -approximatoly Ing drscharg6d into drain from the di6lributionchamD€rto €void ovsflow in the distribution charnbgr tnd prlmafy sedimentation tonk, Thls hag resuttsd in a direct impact on the eflig;gnsy 66p6qit, ag 16a unrl oporalions, The mo6t 6ov6rely6tfecleo procosg is lho 6na€robic dlge6tion. Ther6 was n€gligible bi. ogas production. The setobic ptoceEs wa6 runntng In 6xt€ndsd Eoration mod€ and the exc€ss waated sluoge i6 stabilised to an oxl6nt, srrch lhst d ia un. fit for snaerobic digostjon any furlhor. Scientific
no
ri )9
r€
tio
d i
qlg mainrenance practiceswer€aDront :!:rl!9" 3nd unquElifi6d
{
oparators mannedthe plant.
l
rfi
REFEBENCE APHA.1989. Standafd mgthods tor tho oxaminati. on of watorandwastowaler. tr!l_tl9u. 1998. Lookins backrothink ('eriEtNIndia 2047. Tdts EnorgyReresrchshssd Institu.
at' itl
AU'HOB l'.-sriAmlt Kumar,Research Aasociato,fata Ener. gy-H€se6rch. tnstit!te, Darb6ri Seth Block, Habitst rrac€,LodhiRoad,New D€lhiI I o oo3
3n
iH:.'r.'ir[:rf ffiT'"Tii,ii'iHfi :[:t""qt; pr€ssd., Sri,l€l.f"umar qopuryManaser
( Envho. :. xro,,r r, wnrnpoot ot India Lld., Fsrid6bsd- 121
t a tch
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INDIANI EX]'.NON{SCN'A!PFOIECIION. VO[. 19, NO. 2, FEBiUAEYI9S9 61913 - KdOror corOonttoo
l9S
