Tannery process with effluent recycling

Abstract

A recycling process for achieving near-zero emissions of tannery effluent is characterized in that effluent recycling is carried out independently in soaking, liming, re-liming, de-liming bating, pickling chrome tanning, re-tanning, neutralizing, and dyeing procedures. The effluents in the above procedures can be recycled in each step. This process greatly reduces effluent discharge and helps solve the problem of tanning pollution. The process also improves the quality of the finished leather, effectively decreases loose grain rate and increases compactness and fullness of the finished product. The project can reduce chemical material consumption by 15%-55%. For example, the consumption of chromium powder can be reduced up to 65%. Consumption of other chemical materials can be reduced by more than 90%, while certain chemical materials can be essentially completely conserved.

Claims

1. A process for achieving near-zero emissions of tannery effluent, the process comprising the step of recycling an effluent in a soaking procedure, wherein said recycling of said soaking procedure effluent comprises: (a) collecting said soaking procedure effluent from a soaking drum into a collection container; (b) filtering solid wastes out of said soaking procedure effluent; and (c) returning said remaining said soaking procedure effluent, without further chemical treatment to substantially remediate said soaking procedure effluent, to said soaking drum.

2. The process of claim 1, wherein said remaining soaking procedure effluent is uniformly stirred before being returned to said soaking drum.

3. The process of claim 1, wherein said process further comprises (c) detecting a number of microorganisms in said soaking procedure effluent to determine an amount of bactericide to add.

4. The process of claim 1 wherein said soaking procedure effluent comprises: (i) at least one fat decomposition product; and (ii) at least one salt.

5. The process of claim 1 wherein said soaking procedure effluent comprises at least one of NaCl and Na.sub.2CO.sub.3.

6. The process of claim 1 wherein said soaking procedure effluent comprises at least one of hair, keratin, mucoprotein, meat, and blood.

7. The process of claim 1, wherein said remaining said soaking procedure effluent is returned to said soaking drum via an alkali-resistant pump.

8. A process for achieving near-zero emissions of tannery effluent, the process comprising the step of recycling an effluent in a re-liming procedure, wherein said recycling of said re-liming procedure effluent comprises: (a) collecting said re-liming procedure effluent from a re-liming drum into a collection container; (b) filtering solid wastes out of said re-liming procedure effluent; and (c) returning said remaining re-liming procedure effluent, without further chemical treatment to substantially remediate said re-liming procedure effluent, to said re-liming drum.

9. The process of claim 8, wherein said remaining re-liming effluent is uniformly stirred before being returned to said re-liming drum.

10. The process of claim 8, wherein said remaining said re-liming procedure effluent is returned to said re-liming drum via an alkali-resistant pump.

11. The process of claim 8, wherein said re-liming procedure effluent comprises: (i) at least one fat decomposition product; and (ii) at least one salt.

12. The process of claim 8 wherein said re-liming procedure effluent comprises at least one of S.sup.2−, OH.sup.−, Na.sup.+ and Ca.sup.2+.

13. The process of claim 8 wherein said re-liming procedure effluent comprises at least one protein decomposition product.

14. The process of claim 8 wherein said re-liming procedure effluent comprises at least one of enzyme and amine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic flowchart showing a recycling process being used throughout the tanning process.

DETAILED DESCRIPTION OF EMBODIMENT(S)

(2) FIG. 1 illustrates one setup 100 of a near-zero emission tannery.

(3) Soaking procedure 1 using the soaking effluent involves adding (based on the weight of raw hide and skin) 200% soaking effluent, 0.7% soaking agent, 0.3% degreasing agent, 0.5% sodium carbonate and 0.1% sodium sulfide. The mixture then enters a cycle of running for 40 minutes and standing for 40 minutes. The cycle is repeated three times. Then 0.3% bactericide is added. The mixture is then mixed for 20 minutes and then enters a cycle of running for 3 minutes and standing for 57 minutes. This cycle is repeated overnight before running for 40 minutes the next day.

(4) The effluent is then discharged and filtered 31 into a soaking effluent pool where it is stirred uniformly 11. The effluent is pumped out by an alkali-resistant pump, and returned 21 to soaking drum.

(5) Liming procedure 2 using liming effluent involves adding (based on the weight of raw hide and skin) 70% liming effluent, 1.0% limning assistant, and 0.15% sodium hydrosulfide. The mixture is then mixed for 30 minutes. Then 1.2% lime is added and the mixture is mixed for 30 minutes before being left to stand for 30 minutes. Next, 0.5% sodium hydrosulfide is added and the mixture is mixed for 20 minutes and then left to stand for 20 minutes. The hair is then filtered out and 0.5% sodium sulfide, 0.8% lime and 0.1% degreasing agent are added and the mixture enters a cycle of running for 20 minutes and standing for 30 minutes; this cycle is repeated three times. Next, 20% limning effluent, 0.5% sodium sulfide, 0.5% limning assistant, and 1.0% lime is added and the mixture enters a cycle of running for 20 minutes and standing for 20 minutes; this is repeated 2 times. Then the mixture enters a cycle of mixing for 10 minutes and standing for 20 minutes; this cycle is repeated 6 times. Next, 80% limning effluent is added. The mixture then mixes for 10 minutes, before entering a cycle of running for 5 minutes and standing for 55 minutes; this cycle continues over night.

(6) After liming procedure 2 is completed, or in some cases during the procedure, the effluent is discharged and filtered 32 into effluent pool 12. From effluent pool, the liming effluent is pumped out by an alkali-resistant pump 22 and returned to the liming drum.

(7) Re-liming procedure 3 involves adding (based on the weight of raw hide and skin) 100% re-liming effluent, 0.8% lime, 0.2% sodium sulfide, 0.4% liming assistant, and 0.10% sodium hydroxide. The mixture is mixed for 30 minutes and then left to stand for 40 minutes. Then the process enters a cycle of running for 5 minutes and standing for 55 minutes; this cycle is repeated 6 times. The mixture is then left to sit overnight.

(8) After re-liming procedure 3 is completed, or in some cases during the procedure, the effluent is discharged and filtered 33 into effluent pool 13. From effluent pool, the liming effluent is pumped out by an alkali-resistant pump 23 and returned to the re-liming drum.

(9) De-limning bating procedure 4 involves adding (based on the weight of limed pelt) 100% effluent, 0.2% degreasing agent, 0.6% de-limning agent, 1.2% ammonium sulfate, 0.2% hydrochloric acid, and 0.3% acetic acid. The mixture is mixed for 40 minutes and 0.25% bating enzyme is added. Finally the mixture is mixed for an additional 30 minutes.

(10) After de-liming bating procedure 4 is completed, or in some cases during the procedure, the effluent is discharged and filtered 34 into effluent pool 14. From effluent pool, the de-limning bating effluent is pumped out by an alkali-resistant pump 24 and returned to the de-liming bating drum.

(11) Pickling chrome tanning procedure 5 involves adding (based on the weight of limed pelt) 90% pickling chrome tanning effluent, adjusting the effluent to pH 0.7 by adding sulfuric acid and then adding 0.25% mildew preventive. The mixture is then mixed for 10 minutes and then 0.5% formic acid is added. The mixture is then mixed for an additional 20 minutes before adding 0.3% sulfuric acid for 3 times at 10 minute intervals. The mixture is then mixed for 90 minutes before 0.2% fat-liquoring agent is added. The mixture is then mixed for 30 minutes and allowed to sit 90 minutes before 1.8% chromium powder is added. The mixture is then mixed for 30 minutes and an additional 2.2% chromium powder is added. The mixture is then mixed for 60 minutes and then 0.5% sodium formate is added. The mixture is then mixed for 30 minutes before adding 0.25% basifying agent. The mixture is then mixed for 4 hours before finally adding 80% pickling chrome tanning effluent, heating to 35° C. and mixing for an additional 3 hours.

(12) After pickling chrome tanning procedure 5 is completed, or in some cases during the procedure, the effluent is discharged and filtered 35 into effluent pool 15. From effluent pool, the pickling chrome tanning effluent is pumped out by an acid-resistant pump 25 and returned to the pickling chrome tanning drum.

(13) Re-tanning procedure 6 involves adding (based on the weight of shaved leather) 90% re-tanning effluent, adjusting its pH to 2.5 with sulfuric acid, regulating the mixtures temperature to 36° C. and then adding 0.3% formic acid. The mixture is then mixed for 30 minutes and then 1.5% acrylic acid re-tanning agent is added. The mixture is then mixed for another 30 minutes before 1.0% chromium powder and 0.3% fatliquoring agent are added. The mixture is then mixed 60 minutes and 1.0% fat aldehyde is added. The mixture is then mixed for 30 minutes and 0.8% sodium formate and 0.2% sodium bicarbonate are added before the mixture is mixed another 60 minutes. The process then enters of cycle of running for 10 minutes and standing for 50 minutes; this cycle is repeated 5 times.

(14) After re-tanning procedure 6 is completed, or in some cases during the procedure, the effluent is discharged and filtered 36 into effluent pool 16. From effluent pool, the re-tanning effluent is pumped out by an acid-resistant pump 26 and returned to the re-tanning drum.

(15) Neutralizing procedure 7 involves adding (based on the weight of shaved leather) 200% neutralizing effluent, regulating temperature to 35° C., and then adding 2.0% neutralization tannin and 1.5% sodium formate before the mixture is then mixed for 20 minutes. Next 1.2% sodium bicarbonate and 3.0% fatliquoring agent are added before the mixture is mixed for 60 minutes while the pH value is kept between 4.0 and 6.5.

(16) After neutralizing procedure 7 is completed, or in some cases during the procedure, the effluent is discharged and filtered 37 into effluent pool 17. From effluent pool, the neutralizing effluent is pumped out by an acid-resistant pump 27 back into the neutralizing drum.

(17) Dyeing procedure 8 involves adding (based on the weight of shaved leather) 80% dyeing effluent, regulating the temperature to 30° C., and adding 2.5% acrylic acid re-tanning agent before the mixture is mixed for 20 minutes. Next 4.0% dicyandiamide re-tanning agent, 1.5% wattle extract, and 2.0% sulfited vegetable oil are added before the mixture is mixed for 40 minutes. Finally 2.0% dye and 1.5% composite fatliquoring agent are added before the mixture is mixed for 60 minutes.

(18) After dyeing procedure 8 is completed, or in some cases during the procedure, the effluent is discharged and filtered 38 into effluent pool 18. From effluent pool, the dyeing effluent is pumped out by an acid-resistant pump 28 back into the dyeing drum.

(19) While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, that the invention is not limited thereto since modifications can be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.