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

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

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

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

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

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

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

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

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

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

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

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

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