Waste-Water Reuse by Improved Application of Existing Techno

8/3/2019 Waste-Water Reuse by Improved Application of Existing Techno

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ed application of the existing technology:with and without chemical pre-

n above site

ABSTRACT

With an ever-growing world-wide demand

for water and decreasing availability,emerging technologies such as ultra-filtration (UF) hold the key to future watertreatment and reuse. The reuse of effluentof wastewater treatment plants (WWTP) forhigh-quality water production will certainlybe an interesting application of UF in theyears to come.

In the present work, we have studiedcrossflow membrane ultra-filtration withperiodic reversal flow considering thepossibility of worst quality feed to the

membrane with and without chemical pre-treatment. The particulate matter remainingafter the biological system is also seenremoved by the pressure driven membranefiltration which appears to be cost savingoption compare to negative pressure suctiontechnology. Pilot tests are carried out over arange of flux and down time operation forvaried quality of feed at two plant site. Theplant was operated continuously at theoptimum flux for the period of two months ateach location. The results obtained usingabove study provides important insights

regarding the coupled membrane filtrationand biological systems. The presentedresults will provide a useful basis for furtherwork in developing better understanding ofprocess optimization.

Keywords: Biological treatment; Ultra-filtration; Membrane Filtration; Waste waterreuse; WWTP effluent, MBR.

INTRODUCTION

Increasingly stringent standards for

wastewater disposal and reuse, makes torethink on the membrane technologies.Although secondary and tertiary treatmentwastewater can be discharged intowaterways it cannot be used for otherprocess utilities directly. The membraneseparation processes are now beingsuccessfully used to obtain water ofrecyclable quality.

However there are limitations associatedwith the membrane technologies and manyresearchers are striving to overcome these

limitations. Pretreatment can be the optionto reduce the fouling of membrane andincrease production capacity. Pretreatmentalso reduces the need for frequency ofchemical cleaning, which is a major factorimpacting membrane life. From theseperspectives, pretreatment offers the greatpotential for improving the efficiency ofmembrane processes.

Studies were performed on the reuse ofWWTP effluent in order to establish thefeasibility of UF technology for domestic

wastewater. A pilot plant of two differentcapacities was designed with the biologicalsystem followed by UF. In the present paperthe ability of biological systems coupled withthe potential performance of a membranefiltration system is shown by its technicalfeasibility reports. Operational costs havebeen estimated on the basis of two pilotplant trails. In the next section we presentthe limitations of membrane technology.This is followed by the experimental detailsand finally we discuss sample of results withour conclusion.

LIMITATIONS OF MEMBRANE

1


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TECHNOLOGY:

Ultrafiltration in water treatment applicationshas proven to be a reliable technology. UFmembranes are capable of removingsuspended solids and colloidal, viruses,

bacteria, and high-molecular suspendedorganic material from the water. Thesecharacteristics of UF instigate us to takepilot trials of UF on wastewater with theinnovative approach of flow reversal.

To alleviate the deleterious effect ofconcentration polarization and membranefouling we tried the concept of periodic flowreversal to enhance membrane flux.

The major drawbacks of the membranefiltration system are as follows:

1. In membrane separation processeswhen dealing with multicomponentfeed streams, no matter how goodis the membrane properties andsystem design, flux decline due tofouling and concentrationpolarization is inevitable.

2. Flux decline problem is a two stepprocess: far field effects(hydrodynamic interactions) andnear field effects (surface forces,

chemical and electro kineticinteractions).

We consider an innovative technique ofreversal flow to manipulate the far fieldhydrodynamics in such a way that soluteconvection-diffusion transport and particlemigration to the membrane surface cannever form a stable layer. If this can beachieved, a substantial increase intransmembrane flux would be possible. Theflow reversal has a great potential incombating flux reducing effects due to

concentration polarization and fouling.Periodic reversal of the flow of the feedstream at the membrane surface results inprevention and mitigation of membranefouling. Consequently, these advantagesare expected to enhance membrane fluxsignificantly.

EXPERIMENTS DETAILS

Materials and Methods:

The biological system followed ultrafiltrationmembrane was installed for domesticwastewater treatment having the production

capacity of 56 cum/day and 102 cum/dayrespectively. The influent feed quality to theultrafiltration at both the pilot trials is asmentioned below in Table No. 1 and TableNo.2.

Table No. 1: Characteristics ofBiologically Treated Sewage Effluent:

Pilot-1 ITCCOD (ppm) 27-170BOD3 (ppm) 3.5-22TSS (ppm) 8-110Turbidity (NTU) 0.5-3.7NO3-N (ppm) 11-28NH3-N (ppm) 20-54

Table No. 2: Characteristics ofBiologically Treated Sewage Effluent:

Pilot-2 SatyamCOD (ppm) 96-76BOD3 (ppm) 40-85pH 7.1-7.7TSS (ppm) 74-148Turbidity (NTU) 0.9-1.3NO3-N (ppm) 25-33NH3-N (ppm) NDLPO4-P (ppm) 1.5-15.4

The system designed consists of the NoritX-flow AquaflexTM 8X60 crossflow UFmembrane element. The membranes aretypically 0.8 or 1.5 mm in diameter,polysulphone material, providing amembrane area of 22 or 35 m2 in oneelement. The PLC automated systeminclude crossflow hollow fiber membranemodule integrated with pneumatically-operated valves so to provide in variousways the filtration, backwashing and crossflushing operations.

Reversal flow membrane filtration:

The forward and reverse membranefiltration system is as shown in the below figno.1.

Fig No. 1: Forward and Reverse FiltrationThe periodic flow reversal phenomenon is

employed in the present pilot trials. The


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Treated effluentMembrane

Module

Bio-Fluidised reactorPre-treatement

membrane filtration system operation is twostep cyclic processes in which step one isforward filtration of duration say, t

fthen

follows a period of backflushing or reversefiltration of duration say, t

b. The periodic

backflushing and reversal flow through themembrane helps to achieve the reversalfouling phenomenon by avoidingconcentration polarization and cake or gellayers formation onto the membranesurface. In fig no. 2 the effect of flowreversal on the membrane filtration systemis shown for the consecutive six cycles of1500s each. As known the flux decline isseen in each cycle and the moment systemreach the steady state flux, the flow reversaland backflush is applied to regain theoriginal flux. The peak of each cycle in figno. 2 is the original flux regain at the start ofthe forward filtration. The membrane thuscan be protected from the external fouling.The only concern is that the time and filtrateused for backflush and cleaning cycleswhich lower the operational savingcontributing to more membrane costcompare to the conventional treatment. Onthe other hand advantages are membranefiltration gives the high and consistenteffluent quality which can be used for theprocess utilities making to rethink on thewater scarcity and reuse.0100090000032a0200000200a20100000000a201000026060f003a03574d4643010000000000010008490000000001000000180300000000000018030000010000006c000000000000000000000011000000230000000000000000000000981b00007326000020454d46000001001803000012000000020000000000000000000000000000004006000048080000cb0000000d010000000000000000000000000000c0190300b81b0400160000000c000000180000000a00000010000000000000000000000009000000100000002c020000

07030000250000000c0000000e000080250000000c0000000e000080120000000c00000001000000520000007001000001000000e1ffffff000000000000000000000000900100000000000004400022430061006c006900620072006900000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001500a41c15001000000008201500881d15001b51896108201500001d150010000000701e1500ec1f15006c50896108201500001d1500200000009f71646d001d15000820150020000000ffffffff6c1b22021a72646

dffffffffffff0180ffff01803fff0180ffffffff000000000000000000000000e0f7f2050100000000000000c800000025000000372e9001000002

0f0502020204030204ff0200e1ffac004009000000000000009f01000000000000430061006c006900620072000000000060db210089a08961694b004b4c1b220294477900341d15009c2d5d6d2000000001000000701d1500701d1500087a5b6d20000000981d15006c1

b22026476000800000000250000000c00000001000000250000000c00000001000000250000000c00000001000000180000000c000000000000025400000054000000000000000000000011000000230000000100000000004b41d5044b41000000001c000000010000004c0000000400000000000000000000002c0200000703000050000000200011001200000046000000280000001c0000004744494302000000fffffffffeffffff2d02000007030000000000004600000014000000080000004744494303000000250000000c0000000e000080250000000c0000000e0000800e0000001

40000000000000010000000140000000400000003010800050000000b0200000000050000000c021701c800040000002e0118001c000000fb020600030000000000bc02000000000102022253797374656d003f3f3f3f0000003f3f3f3f083f3f3f000000003f3f3f3f3f00040000002d010000040000002d01000004000000020101001c000000fb02f5ff0000000000009001000000000440002243616c6962726900000000000000000000000000000000000000000000000000040000002d010100040000002d010100040000002d010100050000000902000000020d000000320a0a000000010

0040000000000c800170120000600040000002d010000040000002d010000030000000000

Fig No. 2: Effect of Reversal flowmembrane filtrationOperation Philosophy:

The membrane is fed by means of twopumps which operate alternatively. Onepump provides feed to the membranes inforward filtration and the second pump is

used for backwashing and chemicallyenhanced backwashing (CEB) atcomparatively high velocity of >960 m/s. UFfiltrate is used in both backwashing andcleaning cycles. The reject and backwashwater is recycled in the system taking itback into the equalization tank thusmaintaining a low food/microorganism ratio(F/M) and/or to reduce the aeration tankvolume. With a lower F/M ratio, thebiodegradation efficiency is better and thesludge production is smaller.

The schematic diagram of the cross-flowultrafiltration system is shown in the fig no.

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3. During forward filtration valves V1, V2and V3 are open, while valves V5 and V6are closed. Valve V4 is Non-return valve(NRV). Feed pump P1 provides the drivingforce for the process. The transmembranepressure (TMP) is measured by means of

two pressure transmitters (PT). At a presetinterval, the filtration stops and valves V1,V2 and V3 close while valves V5 and V6open. Backwash pump P2 then starts andperforms a backwash operation at highvelocity. The backwash cycle helps toremove the suspended solids layer that hasbuilt-up on the feed side of the UFmembrane and is disposed of through valveV6. CEB is performed by dosing chemicalsduring backwashing, followed by soakingthe unit for a preset time and rinsing the unitby performing another backwash.

Fig No. 3: Block diagram of the plantscheme.

RESULTS AND DISCUSSIONS

The plant was operated at both the locationsover the range of the flux and varied feedquality as shown in Table No. 3 and TableNo 4. Effluent of domestic wastewater withand without pretreatment was pumped intothe hollow fiber membrane module. Theoperating pressure and the cross-flowvelocity were controlled at 350 kpa and0.08m/hr by means of the by-pass andpneumatic control valves. The energyconsumption for the pilot-1 and pilot-2 is0.25kwh/m3 and 0.16kwh/m3 for thepermeate production of 56cum/day and 102cum/day respectively.

Table No. 3:The average feed and filtratequality of Pilot-1.

Parameter BOD

(ppm)COD(ppm)

TSS(ppm)

Turbidity

NTU

influent3.5-10 27-170 8-110

0.5-37

Filtrate< 03 < 22 NDL

< 0.2

Parameter NH4-N NO3-N

PO4-P

influent

20-54 11-28

Not

Tested

Filtrate


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loss in pilot-1 i.e. 1500s cycle withproduction loss 23% and operational loss of10% against the production loss of 32% andoperational loss of 20% in case of pilot-2 forthe operation cycle time 600s as shown inTable No. 5. The reason behind choosing

the cycle of 1500s over 600s is the feedquality at pilot-1 was much better than thepilot-2 as shown in fig no. 3 and fig no. 4.The chemical pretreatment was adopted atpilot-.1 Pilot-2 was tested with and withoutpretreatment for observation purpose. Sowe can see that pretreatment helps themembrane technology in increasingproduction capacity thus saving theoperational cost. This shows that feedquality adversely affects the plantproduction. Pretreatment plays the essentialrole to sustain the membrane technology. In

the entire system operation the onlychemical used for the membrane cleaning isthe Hypo-chlorite solution of concentrationranges from 500ppm to 1000ppm once in 3hrs operation cycle.

Flux model:

The net permeate flux over the entire cycleperiod is defined by,

Where Jf

and Jb

are the magnitudes of the

forward and reverse fluxes, respectively.When t

f< t critical, no cake or gel layer is

allowed to form. When t > tf, a cake or gel

layer of rejected material forms on themembrane surface [13].

In the present case studies critical time offorward filtration i.e. t

f, chosen for the pilot-1

and pilot-2 were 1500s and 600srespectively based on the feed quality andminimum production loss in the system. Thepermeate flux behavior of various forwardfiltration time cycles is shown in figure no.4to fig no.7. Figure 4 shows the sixconsecutive cycles permeate flowperformance of the 1500s forward filtration.As shown in fig no. 4 there is completeregain of original flux by the backflushing

and reversal flow technique. The Chemicalenhanced backwash is thus needs toperform every 2.30hrs to 3.00hrs durationand accordingly the cost of filtrateproduction is calculated.

The organic removal with the membranefiltration is an efficient technology as seenfrom the fig no. 8 to fig no. 12. The filtrateBOD and COD values are


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y = - 0 . 0 0 0 4 x3 + 0 . 0 4 5 1 x2 - 1 .1 6 6 8 x +

01

2345678

9

1 0

2 0 1 5 0 3 0 0 6 5 0 1 0 0 01 3 0 01 6 0 0

T im e (

PermeateFlow

(cum/hr)

Fig No. 5: Permeate flow Vs Time for1800s.

y = - 0 .0 0 0 3 x3

+ 0 . 0 5 9 1 x2

- 1 . 4 0 6 6 x +

0

1

2

3

4

5

6

7

8

91 0

2 0 1 0 0 2 0 0 4 0 0 6 0 0 8 0 01 0 0 01 1 5 0

T im e (

Permeateflow

(cum/hr)

Fig No. 6: Permeate flow Vs Time for1200s.

c o m b i n e c o m p a r is

0

1

2

3

4

5

6

7

8

9

1 0

2 0 1 00 2 00 3 00 5 00 7 00 1 00 01 20 01 40 01 60 01 75 0

T i m e

ermeate

low

(cum/hr

R u n - 1 9 0

R u n - 2 1 2

R u n - 3 1 8R u n - 4 1 5

Fig No. 7: Comparative study of flux for900s; 1200s; 1500s; and 1800s systems.

0

5

10

15

20

25

0 1 2 3 4 5

Filtrate BOD, pp

InfluentBOD,ppm

Fig No. 8: Influent BOD Vs Filtrate BODat pilot-1

0100090000032a0200000200a20100000


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Fig No. 9: Influent BOD Vs Filtrate BODat pilot-2

0100090000032a0200000200a20100000000a201000026060f003a03574d4643010000000000010008490000000001000000180300000000000018030000010000006c0000000000000000000000110000002300000000

00000000000000981b00007326000020454d46000001001803000012000000020000000000000000000000000000004006000048080000cb0000000d010000000000000000000000000000c0190300b81b0400160000000c000000180000000a00000010000000000000000000000009000000100000002c02000007030000250000000c0000000e000080250000000c0000000e000080120000000c0000000

1000000520000007001000001000000e1ffffff000000000000000000000000900100000000000004400022430061006c006900620072006900000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001500a41c15001000000008201500881d15001b51896108201500001d150010000000701e1500ec1f15006c50896108201500001d1500200000009f71646d001d15000820150020000000ffffffff6c1b220

7


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Fig No. 10: Influent COD Vs Filtrate COD.

0100090000032a0200000200a20100000000a201000026060f003a03574d4643010000000000010008490000000001000000180300000000000018030000010000006c00000000000

0000000000011000000230000000000000000000000981b00007326000020454d46000001001803000012000000020000000000000000000000000000004006000048080000cb0000000d010000000000000000000000000000c0190300b81b0400160000000c000000180000000a00000010000000000000000000000009000000100000002c02000007030000250000000c0000000e000080250000000c00

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

0000000060db210089a08961694b004b4c1b220294477900341d15009c2d5d6d2000000001000000701d1500701d1500087a5b6d20000000981d15006c1b22026476000800000000250000000c00000001000000250000000c00000001000000250000000c00000001000000180000000c000000000000025400000054000000000000000000000011000000230000000100000000004b41d5044b410000000

01c000000010000004c0000000400000000000000000000002c0200000


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Fig No. 11: Influent TSS Vs Filtrate TSS.

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

00e1ffffff00000000000000000000000090010000000000000440002243

9


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Fig No. 12: Influent Turbidity Vs FiltrateTurbidity.

CONCLUSIONS

Cross-flow membrane filtration pilot trialswere performed at two locations ondomestic wastewater plants with the flowreversal technique. Reversal flow helps toprevent external fouling of membrane. From

the data reported above it is seen thatultrafiltration membrane technology isfeasible to use in domestic wastewater toobtain the recyclable quality water for theprocess utilities. The biological systemcoupled membrane technology is also seento treat the best and worst quality influentwastewater with no change in filtrate quality.The chemical pretreatment reduces the loadon membrane increasing productivity of theplant. The filtrate water being used for theperiodic cleaning of membrane contributesto the net production loss which is among

the major drawback either in the negativepressure suction technology or anymembrane technology for not being costcompetitive. Futuristic work in this line couldbe helpful to make membrane technologymore productive and cost effective.

REFERENCES

[1]Sanjeev Redkar, Vinod Kuberkar,Robert H. Davis, Modeling ofconcentration polarization anddepolarization with high-frequencybackpulsing, Journal of MembraneScience, 121 (1996) 229-242

[2] H.K. Shon, S. Vigneswaran, In S.Kim, J. Cho, H.H. Ngo, Effect ofpretreatment on the fouling ofmembranes: application inbiologically treated sewage effluent,Journal of Membrane Science, 234

(2004) 111120

[3] D. Abdessemed, G.Nezzal, R.Ben Aim, Coagulation-adsorption-ultrafiltration for wastewater

treatment and reuse, Desalination131 (2000) 307-314

[4] H.K. Shon, S. Vigneswaran, R.Ben Aim, H.H. Ngo, In S. Kim, and J.Cho, Influence of Flocculation andAdsorption as Pretreatment on theFouling of Ultrafiltration andNanofiltration Membranes:Application with Biologically TreatedSewage Effluent, Environmental Sci.

Tech. 39(2005) 3864-3871

[5] Hyeok Choi, Kai Zhang,Dionysios D. Dionysiou, Daniel B.Oerther, George A. Sorial, Influenceof cross-flow velocity on membraneperformance during filtration ofbiological suspension, Journal ofMembrane Science, 248 (2005)189199

[6] H. Muhammad, A1-Malack, G.K.Anderson, Coagulation-crossflowmicrofiltration of domesticwastewater, Journal of MembraneScience, 121 (1996) 59-70

[7] Aisyah E. Palupi, Ali Altway andArief Widjaja, The application ofmembrane Bio-Reactor for EastJava Domestic waste watertreatment, Songklanakarin J. Sci.Tech.30 (2008), 131-134

[8] Shamsuddin Ilias, FluxEnhancement in CrossflowMembrane Filtration: Fouling and ItsMinimization by Flow Reversal,Report, North Carolina A&T StateUniversity Department of ChemicalEngineering Greensboro, NC 27411

[9] Sukhtej Singh Dhingra, MixedGas Transport Study through


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Polymeric Membranes: A NovelTechnique, PhD Thesis, Faculty ofthe Virginia Polytechnic Institute andState University, 1997

[10] P.J. Smith, H.K. Shon, SVigneswaran, H. H. Ngo, H. Nguyen,Productivity enhancement in a cross-flow ultrafiltration membrane systemthrough automated de-cloggingoperations, Journal of MembraneScience, 280 (2006) 8288

[11] S.C.J.M. van Hoof, A. Hashim,A.J. Kordes, The effect of ultrafiltration as pretreatment to

reverse osmosis in wastewaterreuse and seawater desalinationapplications, Desalination 124(1999) 231-242

[12] R. Rosberg, Ultrafiltration (newtechnology), a viable cost-savingpretreatment for reverse osmosisand nanofiltration - A new approachto reduce costs, Desalination 110(1997) 107-114

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Waste-Water Reuse by Improved Application of Existing Techno