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MITEI EAB 2016
Energy-Efficient Textile Dyeing Effluent Recycling
JaichanderSwaminathan
Prof.JohnH.LienhardV
Dept.ofMechanicalEngineering
Efficient Effluent Recycling Jai Swaminathan 1
MITEI EAB 2016
Problem: Cheap Zero Discharge
• Textile:14%ofIndia’sindustrialoutput– 2000+dyeingunits
• Waterintensive:200L/kg-fabric.Effluentcausespollution:– Heavymetals,organics,salts
• Zero-Liquid-DischargemandatedbycourtsinTamilNadu– Manyindustriesforcedtoshutdown– LargerunitsandexportersachievingZLDwithreducedplantutilization
Challenges• Costofdesalinationplantoperation~ halfoftotaloperatingcosts• ReverseOsmosis(RO)followedbyinefficientthermal
concentrator
Efficient Effluent Recycling Jai Swaminathan 2
MITEI EAB 2016
Conventional Treatment Process
Efficient Effluent Recycling Jai Swaminathan 3
s ≈ 7 g/kg
s ≈ 7 g/kg
s = 70-110 g/kg
COD,BODremoval
COD ≈ 800 mg/kgBOD ≈ 500 mg/kg
s ≈ 40 g/kgTS ≈ 500 g/kg
MITEI EAB 2016
Design Effluent Chemistry for Cheaper Treatment
Efficient Effluent Recycling Jai Swaminathan 4
Treatment
DesalinationMake-upwater
Chemical,biologicaltreatmentsteps
Saltywater(dissolvedimpurities)
Brine
Onlysolidwastes
Crystallizer/solarevaporator
RawEffluent
Nodisposal intoenvironment
Choosethechemicalsaddedintheprocessingsteps
Toreducetheenergyconsumptionforwaterrecyclingandoverallcost
MITEI EAB 2016
Textile Dyeing Process
Efficient Effluent Recycling Jai Swaminathan 5
Process:Multiplebaths– waterandchemicals
ChemicalsWater ~ 6× fabric weight
Heat to control T
Fabric
Bath Effluent
wetting,lubricatingagents,.. fixingagents,detergents..
Preparation Dyebath Post-dyebath
Salts,dyechemicals
𝑠 = 30 − 110g/kg 𝑠~0g/kg
1,2,3,… D D+1,D+2,…N
𝑠~0g/kg
Time/BathNo.
Overalleffluent:𝑠~7g/kg
MITEI EAB 2016
DyebathSalt:NaCl vs.Na2SO4
SodiumChloride• Cheaperperkg
• WithZLDrequirement,polishedbrineofNaCl solutionusingNanofiltration
• 𝑠*+, > 70g/kg
SodiumSulfate• Moreexpensive
• 𝑠*+, <110g/kg
• >90%oftheTDScontributionfromdye-bathsaltused• BothNaCl andNa2SO4 usedsuccessfully inindustry
• Purposeistoenabledye-clothinteraction• Deepershaderequireshigherconcentration• 𝑠*+, correspondstothesalinityrequirementforthedarkest
shade
Jai Swaminathan 6Efficient Effluent Recycling
MITEI EAB 2016
Thermodynamic Advantage
• LowerthermodynamicleastworkforseparationofNa2SO4solutioncomparedtoNaCl solution
High Salinity Desalination Energy Efficiency Committee Meeting 1 7
0
0.1
0.2
0.3
0.4
0.5
5.5 6.5 7.5 8.5
Leas
t Wor
k [k
Wh/
m3 ]
Feed Salinity s [g/kg]
NaClNa2SO4
𝑠𝑐𝑜𝑛𝑐 = 70g/kg 𝑠𝑐𝑜𝑛𝑐 = 110g/kg
Swaminathanetal.,(2016,August).Nanofiltration forhighpermeabilitytextileeffluentdesalination presentedat WaterReuseandRecyclingConference,Nice,France.InternationalDesalinationAssociation
MITEI EAB 2016
Practical: Higher Permeability Membranes
• Bydesigning theeffluentchemistrywithsulfatesasthesmallestanions– possibletoreplaceROwithhigherpermeabilityNF– Rejection>96%
Efficient Effluent Recycling Jai Swaminathan 8
0.9
0.92
0.94
0.96
0.98
1
0 30 60 90 120
Aver
age
Salt
Rej
ectio
n [-]
Feed Salinity [g/kg]
NF270NF90SW30HR
0
20
40
60
80
100
0 30 60 90 120
Pres
sure
[bar
]
Feed Salinity [g/kg]
Osmotic PressureNF270NF90SW30HR
MITEI EAB 2016
Conclusions• Textiledyeingeffluentzerodischarge– coststoohighforprofitable
operation• Choosingsuitablechemicalsintheprocessingstepsreducescostof
desalinationandtherebyoverallsystemcosts
Sodiumsulfateinsteadofsodiumchlorideenables:• 40%lowerthermodynamic leastworkofseparationduetolower
osmoticpressure• Enablesuseofmorepermeablemembranewhilestillachieving>95%
saltrejection– Additional 30%lowerenergyconsumption• Overall:Eliminationofenergyintensivethermaldesalinationsteps.
Membranebasedconcentrationat<70barpressure
• Nextstep:Pilottestingwitheffluentwater
High Salinity Desalination Energy Efficiency Committee Meeting 1 9
MITEI EAB 2016
Pilot Testing
• Partner:SPTextileProcessors,Erode• Pilotplant:onemembraneelement,3m3/day
– 1%totalplantsize– Testpermeatewaterforrecycling
• Goal:measurepressureandsaltrejectionatvarioussalinitylevels– characterize fullscalesystemperformance.
• ReusabilitytestofNFpermeateforvariousstepsinthedyeingprocess
High Salinity Desalination Energy Efficiency Committee Meeting 1 10
