treatment of tannery wastewater . susan
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Presented bySUSAN ANN JAYAN
II M.SC. , B io technologySchool o f Biotechnology & Genet ic Engineer ing
Bharath iar Univers i ty
TREATMENT OF TANNERY WASTEWATER
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An aerial view.. medium-sized tannery wastewater treatment plant
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Tanning industry
What is tanning?Tanning is the process that converts a part of a
once living animal (i.e., hides and skins) into a non-rotting, soft and durable textile called leather Two types of tanning, broadly :
Vegetable tanning Chrome tanning
Procedures involved..After removal of hairs and flesh, the involved
processes are curing, receiving and storing, soaking, unhairing, bating, pickling, tanning, wringing, sorting, splitting and shaving.
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Chemicals used in a tannery
LEATHER PROCESS CHEMICALS USED
Curing & Preservation Sodium chloride, pentachlorophenol
Soaking, Liming & Unhairing Sodium sulphide, caustic soda, surfactants, milk of lime
Deliming Ammonium chloride, ammonium sulphate
Degreasing Alkyl phenyl ethoxylate
Pre-tanning Basic chrome sulphate
Tanning/retanning Mineral tannages/retannages
Fat liquoring Synthetic at liquors, surfactants from petrochemicals
Finishing Cadmium and lead chrome pigment, nitrocellulose and liquor emulsion water-proofing agent
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Tannery wastewater is characterized by..
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Fate of 1000 kg of wet-salted hides..
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TREATMENT REGIME
Combination of physical, chemical and biological systems
1. Separation of effluents within the tannery Wastewater collection within departments to maintain
separate beamhouse effluents By means of gutters and sluice gates
2. Hair recovery from liming baths To reduce pollution load considerably Special passages of very fine screens Recycling outside the drum
Mechanical separation effectively reduces concentration of suspended solids 30-40% & COD 20-30%
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Rotating drums - for separation of hair
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3. Chrome recovery from Tanning baths Drastic reduction of heavy metal load
Sludge containing high amounts of chromium is usually disposed off in landfills
Re-use of expensive chromium – Add alkaline lime to acidic tanning bath and adjust pH to
slightly above neutrality – bivalent chromium will completely settle
4. Screening operations Fundamental Coarse grid bars
Filtering at 10mm Prevents clogging by coarse pieces of leather, wood, etc.
Rotating brush Filtering at 2-3mm diameter
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Chrome recovery plant, with a filter press
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Rotating brush screening
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5. Equalization & Sulfide oxidation Necessary due to unequal discharge of effluents Sulfide oxidation carried out and the contents are kept
mixed Manganese sulfate may be added to speed up, acting
as catalyst
13Equalization & Sulfide oxidation tank
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6. Flocculation Chemical flocculation for suspended solids &
unyielding colloidal organic matter Flocculants –
metal salts - ammonium sulfate, most effective organic coagulants (polyelectrolytes) – increase size of
sludge flakes
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Flocculation in tanks fitted with agitators
167. Sedimentation Gravitational settling of suspended solids, then disposal of
clarified supernatant into sewers Sedimented sludge is collected by pumps for dehydration
8. Sludge treatment Natural drying beds
Sludge is distributed in layers a few cm high and loses water by filtration on a bed of sand and gravel and natural evaporation
Frequently used in geographical zones with dry hot climate Mechanized systems, e.g., filter presses, continuous belt
presses, centrifugal decanters Used when the quantity of sludge produced each day is high,
because the area needed would be excessive
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9. Biological treatments To reduce the soluble and suspended or colloidal
organic matter in effluents into carbon dioxide and minerals
Bubble aeration systems Lagoon systems Sequencing batch biofilm reactor (SBBR)
Combined with chemical oxidation by ozone. The treatment was carried out at laboratory scale on a real primary effluent coming from a centralized plant treating the wastewater of a large tannery district in Northern Italy [2]
Microbial consortia Fungal and bacterial biosorptive degradation
Bacillus, Rhizopus, Aspergillus, Streptovertcillum, Saccharomyces
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10. Other innovative methods
Use of activated clays in the removal of dyes and surfactants[3] The capacity of sepiolite and acid-activated bentonite to
adsorb anionic dyes normally used in the tannery was compared with conventional adsorbents
Natural bentonite activated with 0.5 M H2SO4 was the most effective adsorbent for ethoxylated nonylphenol.
Use of electrochemical processes as alternative to biological nitrification/denitrification processes, for removal of a variety of pollutants[4] And their combinations are still being studied Quicker and reduction in global plant volume (considering
both biological and electrochemical sections) and sludge generated for disposal
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References
1. http://www.fgmengineering.it >wastewater treatment>tannery
2. Thakur S. T., Environmental Biotechnology – Basic Concepts and Applications. I.K. International Pvt. Ltd; 398-408
3. C. Di Iaconi , A. Lopez , R. Ramadori , and R. Passino. Tannery Wastewater Treatment by Sequencing Batch Biofilm Reactor. Environ. Sci. Technol., 2003, 37 (14), pp 3199–3205
4. A.G Espantaleón et al.,(2003). Use of activated clays in the removal of dyes and surfactants from tannery waste waters. Applied Clay Science, 2003,24 (1-2), pp 105-110
5. Lidia Szpyrkowicz, Santosh N. Kaul, Rao N. Neti. Tannery wastewater treatment by electro-oxidation coupled with a biological process. Journal of Applied Electrochemistry (2005) 35: 381-390
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Luxury with Responsibility..
Thank You…
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