15 Dicembre 2015 Istituto Conciario G.Galilei Arzignano
Tweetchat #greenleather2016
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RESEARCH GUIDELINE
OXIDATIVE RECOVERY/TREATMENTHAIR REMOVAL EXHAUSTED LIMING BATH
Why choosing the oxidative process
• Improving the environmental impact outside of the tannery• Improving the healthiness of workplaces within the department lime /
tanning• Production of by-products not contaminated by sulfide (fleshing, sludge) • Elimination of sulfides / sulfates in wastewater destined for treatment• Elimination of treatment systems for the removal of hydrogen sulfide• Applicability in industrial scale as it has a similar configuration to the
present one• Process times comparable with those of the traditional one• Production of finished leather which present less smell
Initial plants limitations
The initial limit was not to be able to use in wooden drum for solutions with high oxidizing power; also being an exothermic reactions it can cause a rise in temperature inside the drum which must necessarily be cooled down.
From this demand arises the need to use a polymeric material endowed with great chemical resistance against :
• Strong Acid solutions• Strong Basis solutions• Hydrogen Peroxide (H2O2)
PPE Drum (semi-industrial scale)
Issues addressed during the trial• The hair that is removed during the depilation process remaining inside
the drum represents a potentially oxidizable material to the oxidizing mixture ; the extraction of the hair out of the drum makes it possible to achieve improvements such as:• Least amount of chemicals used in the process• Improved quality of the discharged water
During the 1ST hour During the 2ND hour
Issues addressed during the trial•The internal drum cooling system does not allow to obtain the desired low temperatures therefore an external heat exchanger is needed to cool the bath more quickly and efficiently to succeed in piloting the temperature inside the drum in the requested range
Plant configuration with heat exchanger
DRUM
SCREWSCREEN
HAIR RECOVERY
HEAT EXCHANGER
Variables investigated during the trial:
• Time of liming stage• Temperature of the liming bath• Addittion of enzymes in the soaking stage• % di NaOH and H2O2 in the hair removal mixture• Fleshing of the hide with the hair still on
Tests summary table (Cow Hide)
# Trial Parameters/ investigated Hair on fleshing
Skin cleaning (Depilation efficency)
Depilation speed
Relaxation of the wrinkles Swelling Evaluation
tanned skin
Evaluation finished leather
1 Alkaline Soaking T=22°C24 Hours no 7 6 Hours 7 7 6 7
2 Alkaline Soaking T=22°C12 hours 6 6 Hours 5 6 5 6
3 Impregnation Liming no X X X X X X
4 Neutral pH Soaking T=24°C24 Hours no 8 5 Hours 7 8 8 8
5Soaking with enzymes
Soaking T=28°C
Depilating Mixture 75%
no 5 9 Hours 6 5 6 6
6Soaking with enzymes
Soaking T=24°C
Depilating Mixture 85%
7 4 Hours 6 6 5 5
7 Immunisation 60 minutes 5 10 Hours 6 5 5 5
Oxidative Liming Environmental Benefits
1. Enhancement of the by products coming from the liming waste water treatment
2. Decrease of chemical products and H2O compared to the traditional liming
3. Recovery of the purified exhausted liming bath
1. Enhancing of the by-products
CLARIFIER
1. Enhancing of the by-products
1° SLUDGE
1° CLARIFIED
1. Enhancing of the by-products
Acidification to pH = 4 with phosphoric acid
2° SLUDGE
2° CLARIFIED1° CLARIFIED
Sludge Analysis
N C SO3
(%) (%) (%)
1st TRIAL 1st SLUDGE 2,9 27,7 1,3
2nd SLUDGE 9,4 37,0 2,7
2nd TRIAL1st SLUDGE 2,2 23,9 0,7
2nd SLUDGE 8,3 38,9 2,0
3rd TRIAL1st SLUDGE 1,9 24,1 1,0
2nd SLUDGE 9,1 38,3 2,4
Mass balance of sludges
Extrated material weight
dry residue at 105 ° C
Extrated material dry weight
% Sludge Compared to the raw material
loaded
Raw Material Weight 1700 [Kg] [Kg] [%] [Kg] [%]
1st TRIALSludge 1st clarification 56 25 14 0,82
Sludge 2nd clarification 130 20 26 1,53
2nd TRIALSludge 1st clarification 58 20 11,6 0,68
Sludge 2nd clarification 95 22 20,9 1,23
Mass balance of sludge
Hides put in to work by Dani in 2014 36824 [Ton] Dry material compared to the
raw material put in to workDry material not sent to the
effluent plant
[%] [Ton]
Hair filtrated during the liming 0,4 147
1st sludge extraction 0,75 276
2nd sludge extraction 1,38 508
TOTAL 932 Ton
2. Reduction of chemical products and H2O
Traditional Liming Oxydative Liming
H2O 460 % H2O 400 %
CHEMICALS 18 % CHEMICALS 18 %
3. Recovery of exhausted liming bath
1st CLARIFIED
Acidification pH=4with Phosphoric acid
2nd CLARIFIED1st CLARIFIED
3. Recovery of exhausted liming bath
End of Liming
After 1st
clarificationAfter 2nd
clarificationNeutralisation 2nd
clarification
Chlorides mg/L 7180 6445 6270 6820
Sulphates mg/L 670 620 700 735
Total Nitrogen (TKN)on filtrated mg/L N 5542 5252 3206 3207
Total Phosphorus on filtrated mg/L P 600 295 12080 10910
COD on filtrated mg/L O2 58160 58455 28400 27415
Acidified bath pH=4with H3PO4
Neutralised bath pH=7withNaOH
End of the following soaking bath (50%)
Sulphates mg/L 530 515 435
Total Nitrogen (TKN)
on filtratedmg/L N 2023 2072 1181
Total Phosphorus on filtrated mg/L P 9200 8243 2375
COD on filtrated mg/L O2 18320 21795 14395
Reuse of bath from 2nd clarification
Re-using the clarified bath in the soaking of the next liming there would be a saving of H2O between 10 % and 12% depending on the recipe and the type of raw material
10% - 12% < consumption H2O
In the following processing
Riduzione consumo H2O
Traditional Liming Oxydative LimingOxydative Liming
With bath reusage
H2O 460 % H2O 400 % H2O 340 %
Oxidative liming Traditional liming
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