1. 15 Dicembre 2015
Istituto Conciario G.Galilei Arzignano
Tweetchat #greenleather2016
Guido Zilli, Dani: Da greenLIFE a #greenleather2016
Mariano Mecenero, Dani: We bring on industrial scale a new technique of oxidative liming
Giorgio Pozza, Gruppo Mastrotto: Tanning by-products with high added value to be used in
biocompatible and biosustainable technologies
Marco Colombina, Ikem: New organinc tanning material from renewable source
Franco Cavazza, Ilsa: Recovery processes for the production of fertilizers based on hydrolysed proteins
derived from by-products of the phases of liming and tanning chromium- free
Daniele Refosco, Acque del Chiampo: Full cycle tanneries : the LCA between now and the future

2. RESEARCH GUIDELINE
OXIDATIVE RECOVERY/TREATMENT
HAIR REMOVAL EXHAUSTED LIMING BATH

3. 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

4. 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)

5. PPE Drum (semi-industrial scale)

6. 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

7. 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

8. Plant configuration with heat exchanger
DRUM
SCREWSCREEN
HAIR
RECOVERY
HEAT
EXCHANGER

9. 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

10. 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°C
24 Hours
no 7 6 Hours 7 7 6 7
2
Alkaline Soaking T=22°C
12 hours
 6 6 Hours 5 6 5 6
3 Impregnation Liming no X X X X X X
4
Neutral pH Soaking T=24°C
24 Hours
no 8 5 Hours 7 8 8 8
5
Soaking with enzymes
Soaking T=28°C
Depilating Mixture 75%
no 5 9 Hours 6 5 6 6
6
Soaking 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

11. 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

12. 1. Enhancing of the by-products
CLARIFIER

13. 1. Enhancing of the by-products
1° SLUDGE
1° CLARIFIED

14. 1. Enhancing of the by-products
Acidification to pH = 4
with phosphoric acid
2° SLUDGE
2° CLARIFIED1° CLARIFIED

15. Sludge Analysis
N C SO3
(%) (%) (%)
1st
TRIAL
1st
SLUDGE 2,9 27,7 1,3
2nd
SLUDGE 9,4 37,0 2,7
2nd
TRIAL
1st
SLUDGE 2,2 23,9 0,7
2nd
SLUDGE 8,3 38,9 2,0
3rd
TRIAL
1st
SLUDGE 1,9 24,1 1,0
2nd
SLUDGE 9,1 38,3 2,4

16. 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
TRIAL
Sludge 1st
clarification 56 25 14 0,82
Sludge 2nd
clarification 130 20 26 1,53
2nd
TRIAL
Sludge 1st
clarification 58 20 11,6 0,68
Sludge 2nd
clarification 95 22 20,9 1,23

17. 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 work
Dry 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

18. 2. Reduction of chemical products and H2O
Traditional Liming Oxydative Liming
H2O 460 % H2O 400 %
CHEMICALS 18 % CHEMICALS 18 %

19. 3. Recovery of exhausted liming bath
1st
CLARIFIED
Acidification pH=4
with Phosphoric acid
2nd
CLARIFIED1st
CLARIFIED

20. 3. Recovery of exhausted liming bath
End of
Liming
After 1st
clarification
After 2nd
clarification
Neutralisation 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

21. Acidified bath pH=4
with H3PO4
Neutralised bath pH=7
withNaOH
End of the following
soaking bath (50%)
Sulphates mg/L 530 515 435
Total Nitrogen
(TKN)
on filtrated
mg/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

22. 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

23. Riduzione consumo H2O
Traditional Liming Oxydative Liming
Oxydative Liming
With bath
reusage
H2O 460 % H2O 400 % H2O 340 %

24. Oxidative liming Traditional liming