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 III

Compiled by JJ. . BuljanBuljan, I. Kral, I. Kral

3. 3. Sludge dewateringSludge dewatering

• Sludge thickeners• Sludge pumps• Filter press• Centrifuge• Belt filter press• Flow-chart of the physical-chemical

(primary) treatment• Sludge drying beds

Progressing cavity pumpProgressing cavity pumpused for sludge transferused for sludge transfer

Cavity

Stator

RotorHousing

Driving axeINLET

DISCHARGE

Gravity thickenerGravity thickener

Gravity thickenerGravity thickener

Recessed plate filter pressRecessed plate filter press

Slurry tank

Compressor

Air pump

Air injection

Clarified water

Clarified water

Plate

Cloth

Sludge cake layer

Emulsion layer

Continuous counter-currentContinuous counter-currentsolid bowl centrifugesolid bowl centrifuge

Belt filter pressBelt filter press

Belt filter pressBelt filter pressSludge

inlet

Belt/cloth

Drained water Sludgecake

CharacteristicsCharacteristicsof sludge dewatering of sludge dewatering

equipmentequipmentDecanter Belt press Plate filter

press

Way of operation Continuous Continuous Batch

Sludge conditioning required required not required

Washing water not required required not required

Labouronly

supervisiononly

supervisionrequired during cake discharge

Sensitive to sludge variability very sensitive very sensitive less sensitive

Energy required (electricity) high medium low

Maintenance sophisticated medium low

Dry matter content in sludge Dry matter content in sludge depending on process stage depending on process stage and/or type of dewatering and/or type of dewatering

equipmentequipmentTreatment stage, equipment DS content

%Sludge after primary clarifier 3 - 5

Thickened mixed primary and secondary sludge (at specific load of about 60 kg DS/m2.d) 6 - 8

Chamber filter press with chemical conditioning 35 - 45

Belt filter press with use of PE 20 – 25

Centrifuge – decanter 20 - 30

Sludge after stabilization with CaO (mostly after belt filter press or centrifuge) 60 - 90

MIXED EFFLUENT

SERVICE WATER

DrainDrain Drain Drain

CATALYSTMnSO4 ALUM LIME POLYELECTROLYTE

EQUALIZATION TANKWITH PUMPING STATION

(with ejectors for mixing and aeration)

COAGULATIONTANK

FLOCCULATIONTANK

PRIMARY SETTLING TANK

FLOW MEASUREMENTCHANNEL

END FLOW MEASURINGWITH FLOW SUMMARISING

PRIMARY TREATED EFFLUENTTO FURTHER

(biological) TREATMENTe.g. at the municipalWastewater works

CHAMBERFILTER PRESS

GSLUDGE

THICKENER

SLUDGE DRYINGBEDS (optional)

PRIMARY SLUDGEPUMPING STATION

INLET PUMPINGSTATION

FINE SCREEN

AUTOMATICCOARSE SCREEN

Submersible pump

Dosing pump

Motor

Gate valve

Gate valve

Agitator

Simplified flow-chart of thephysical-chemical (primary) treatment

Sludge drying bedSludge drying bedss

Sludge approx. 500mmSand 1-3 mm, approx. 150mmSand 3-6 mm, approx. 150mmBroken stone or gravel 6-15 mm,approx. 100mmBroken stone or gravel 15-50 mm,approx. 100mm

Drainage wateroutlet

Drainage wateroutlet

Sludge inlet

Sludge inlet