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