INTRODUCTION TO T HE T REATMENT OF TANNERY EFFLUENTS
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INTRODUCTIONINTRODUCTION TOTO TTHE THE TREATMENTREATMENTOF TANNERY EFFLUENTSOF TANNERY EFFLUENTS
What every tanner every tanner should know about effluent treatment
United Nations Industrial Development Organization
Part I
Compiled by JJ. . BuljanBuljan, I. Kral, I. Kral
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1. 1. Load, norms,Load, norms,in-house treatmentin-house treatment
• Pollution load• Discharge norms• General overview of treatment of tannery effluents• Segregation of streams• Treatment of spent liming floats• Treatment of chrome-bearing floats• Linking of individual tanneries to a CETP or
MWWW
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TANNERY Site
LEATHER PROCESSINGLEATHER PROCESSING
TANNERY Plant/Building(s)
Finishedleather
Crust
Wet-blue
Fresh air
Water
Chemicals
Raw hides
Solid waste
Air pollution
PRODUCTS
Effluent fortreatment
Processing Disposal
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Green fleshing
H2S
NH3
UnhairingLiming
Lime fleshing
Lime splittingTrimming
DelimingBating
Degreasing(sheep/pigskins)
PicklingTanning
Chrome splitting
Soaking
WATERpollutants
SOLIDpollutants
AIRpollutantsRAW HIDESRAW HIDES
LEGEND:BOD – Biochemical Oxygen DemandCOD – Chemical Oxygen DemandTDS – Total Dissolved SolidsSS – Suspended Solids
Sammying
WET-BLUE
Shaving
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LEATHERLEATHER
Solvents, CH2O
Drying
BuffingTrimming
Retanning, dyeingFat liquoring
Finishing
WATERpollutants
SOLIDpollutants
AIRpollutants
CRUST
LEGEND:BOD – Biochemical Oxygen DemandCOD – Chemical Oxygen DemandTDS – Total Dissolved SolidsSS – Suspended Solids
WET-BLUE
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LEATHER
Green fleshing
H2S
NH3
Solvents, CH2O
UnhairingLiming
Lime fleshing
Lime splittingTrimming
DelimingBating
Degreasing(sheep/pigskins)
PicklingTanning
Chrome splitting
Drying
BuffingTrimming
Retanning, dyeingFat liquoring
Finishing
Soaking
WATERpollutants
SOLIDpollutants
AIRpollutantsRAW HIDES
CRUST
LEGEND:BOD – Biochemical Oxygen DemandCOD – Chemical Oxygen DemandTDS – Total Dissolved SolidsSS – Suspended Solids
Sammying
WET-BLUE
Shaving
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ChemicalsAdded in process
In/on leather &
splitsWasted
EXAMPLE OF MASS BALANCE OF CHEMICALSEXAMPLE OF MASS BALANCE OF CHEMICALSIIN LEATHER PROCESSINGN LEATHER PROCESSING
kg/t of wet salted hide
Chrome oxide (Cr2O3) 25 12 13Organic tannins 25 20 5Fatliquors 22 17 5Dyestuffs 5 4 1Acids, bases, salts 191 - 191Tensides 3 - 3Enzymes 5 - 5Finishing products 100 12 88 Total 452 72 380
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Parameter Unit
Biochemical oxygen demand (BOD5) mg O2/l
Chemical oxygen demand (COD) mg O2/l
Suspended solids (SS) mg/lTrivalent chromium (Cr3+) mg Cr/lSulphides, S2- mg S/lTotal Kjeldahl Nitrogen (TKN) mg N/lChlorides, (Cl-) mg Cl/lSulphates (SO4
2-) mg SO4/l
Oil and grease mg/lTotal Dissolved Solids (TDS)* mg/lpH
TYPICAL TOTAL POLLUTION LOADTYPICAL TOTAL POLLUTION LOADConventional process, expressed as concentration in combined raw effluent
*The main constituents of the TDS are chlorides (Cl-) and sulphates (SO42-) listed earlier.
Average total
pollution load
2000
4000
2000
150
160
160
5000
1400
130
10000
6 - 9
Typical limits, surface waters
30 - 40
125 - 250
35 - 100
1.5 - 2.0
1.0 - 2.0
100
Locally specific
Locally specific
Locally specific
Locally specific
5.5 - 9.5
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TYPICAL TOTAL POLLUTION LOADTYPICAL TOTAL POLLUTION LOADConventional process, kg/t of wet salted hide
Tannery with 5 t/day wet-salted input
*The main constituents of the TDS are chlorides (Cl-) and sulphates (SO42-) listed earlier.
kg/day
45090045035
37.537.5112531530
2250
Parameter
Biochemical oxygen demand (BOD5)
Chemical oxygen demand (COD)
Suspended solids (SS)
Trivalent chromium (Cr3+)
Sulphides, S2-
Total Kjeldahl Nitrogen (TKN)
Chlorides, (Cl-)
Sulphates (SO42-)
Oil and grease
Total Dissolved Solids (TDS)*
pH
kg/t
90180907
7.57.5225636
4506 - 9
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IN-HOUSE SEGREGATION OF STREAMSIN-HOUSE SEGREGATION OF STREAMSLinked to a CETP
Recovered Cr-liquor
ScreensTo the treat-ment plant
Grit floating matter
chamber
Sep
tic
tank
(o
ptio
nal)
San
itar
y ef
flu
ent
TANNERYTANNERY
S h
o w
e r
s,
t o
i l e
t s
Soa
kin
g an
d o
ther
eff
luen
t
Scr
eens
Lim
ing
effl
uen
t
Tan
nin
g li
qu
or
Scr
eens
Pos
t-ta
nn
ing
effl
uen
t
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EFFLUENT HANDLING WITHIN TANNERIESEFFLUENT HANDLING WITHIN TANNERIES
CROME RECOVERY PLANT(optional)
SULPHIDE OXIDATION
(optional)MnSO4(H2O) dosing
Steam
H2SO4
DiatomaceousearthCr-
sludge
Impurities
Recovered Cr-liquor
RECYCLED
20 mm 10 mm
LIMING EFFLUENT
20 mm 10 mmTANNING LIQUOR
POST-TANNING & OTHER EFFLUENT
SOAKING EFFLUENT
20 mm 10 mm
6 mm
TO TANNERY EFFLUENT
COLLECTION AND CONVEYANCE
SYSTEM
Grit and floating matter(grease and oil) chamber
Septic tank(optional)
SANITARY EFFLUENT
Sludge drying beds(optional)
TRANSPORT TO SLUDGE LANDFILL
NaOH dosing
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TANNERY SITE
TYPICAL EFFLUENT TREATMENT SETUPTYPICAL EFFLUENT TREATMENT SETUPVARIANT: CETP for a tannery cluster
TANNERY
Oth
er t
ann
erie
s
CETP
Common Effluent Treatment PlantPT
Pre-treatment
SS2- oxidation
CrCr
recovery
Riv
er/c
han
nel
Riv
er/c
han
nel
Res
ervo
ir/l
ake/
sea
Res
ervo
ir/l
ake/
sea
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TANNERY SITE
TYPICAL TYPICAL EFFLUENTEFFLUENT TREATMENT SETUP TREATMENT SETUP
TANNERY
Communal and other effluent
MWWWMunicipal Wastewater Works
PT
Pre-treatment
PhChPhysical-Chemicaltreatment
SS2- oxidation
CrCr
recovery
Riv
er/c
han
nel
Riv
er/c
han
nel
Res
ervo
ir/l
ake/
sea
Res
ervo
ir/l
ake/
sea
VARIANT: Final treatment together with urban wastewaters at the municipal plant