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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…