WO2019097540A1 - A process leading to zero water discharge in post tanning operations - Google Patents

A process leading to zero water discharge in post tanning operations Download PDF

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Publication number
WO2019097540A1
WO2019097540A1 PCT/IN2018/050738 IN2018050738W WO2019097540A1 WO 2019097540 A1 WO2019097540 A1 WO 2019097540A1 IN 2018050738 W IN2018050738 W IN 2018050738W WO 2019097540 A1 WO2019097540 A1 WO 2019097540A1
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Prior art keywords
streams
oxidation
wastewater
electro
treatment
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PCT/IN2018/050738
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French (fr)
Inventor
Sundarapandiyan Sundaramoorthy
Baddipudi Ramanaiah
Balaraman Madhan
Vimudha MURALIDHARAN
Shakila Shobana THEAGARAJAN
Palanivel SARAVANAN
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Council Of Scientific & Industrial Research
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Priority to CN201880086294.0A priority Critical patent/CN111587227A/en
Publication of WO2019097540A1 publication Critical patent/WO2019097540A1/en
Priority to ZA2020/02769A priority patent/ZA202002769B/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F9/00—Multistage treatment of water, waste water or sewage
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/001—Processes for the treatment of water whereby the filtration technique is of importance
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/30—Treatment of water, waste water, or sewage by irradiation
    • C02F1/32—Treatment of water, waste water, or sewage by irradiation with ultraviolet light
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
    • C02F1/467—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction
    • C02F1/4672—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction by electrooxydation
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/72—Treatment of water, waste water, or sewage by oxidation
    • C02F1/722—Oxidation by peroxides
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/72—Treatment of water, waste water, or sewage by oxidation
    • C02F1/78—Treatment of water, waste water, or sewage by oxidation with ozone
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/22—Nature of the water, waste water, sewage or sludge to be treated from the processing of animals, e.g. poultry, fish, or parts thereof
    • C02F2103/24—Nature of the water, waste water, sewage or sludge to be treated from the processing of animals, e.g. poultry, fish, or parts thereof from tanneries
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2301/00—General aspects of water treatment
    • C02F2301/02—Fluid flow conditions
    • C02F2301/024—Turbulent
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2303/00—Specific treatment goals
    • C02F2303/24—Separation of coarse particles, e.g. by using sieves or screens
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2305/00—Use of specific compounds during water treatment
    • C02F2305/02—Specific form of oxidant
    • C02F2305/026—Fenton's reagent

Definitions

  • the present invention relates to a process leading to zero water discharge in post tanning operations in leather manufacture.
  • the present invention relates to the leather process segment of post tanning wherein no discharge of any kind of wastewater is there.
  • the present invention relates to a process whereby the waste streams generated from the unit process of post tanning are subjected to electro-oxidation that results in treated waste streams amenable for reuse so as to eventually achieve no discharge of wastewater.
  • the process is very much benevolent for the leather industry to attain sustainability.
  • the process is also applicable and suitable for the treatment of wastewater from other manufacturing industries and process industries such as slaughter houses, textile industry, sugar industry, paper industry, oil industry, food industry and hotels.
  • Leather manufacturing processes are associated with many significant environmental impacts. Leather manufacturing processes generate huge amount of wastewater, solid waste and gaseous emissions due to usage of wide range of chemical and chemical products. About 30-35 m 3 of water and 700 kg of chemicals are used for converting 1 ton of hide/ skin into leather. Some of the pollutants emanating from tanneries are highly refractory and toxic in nature. The pollutants generated during pre-tanning are predominantly organic in nature and easily treatable. Conversely, the complex chemicals such as synthetic tanning agents, fatliquors, dyes and phenol-formaldehyde condensates used in post-tanning process render the wastewater not easily treatable.
  • the resultant wastewater contains the residual chemicals viz. syntans, fatliquors and dyes apart from the emissions such as chromium, protein and fat in lower quantities from the leather.
  • the possible inter reaction, the path way and the resultant production of secondary pollutants are dependent on many factors such as chemical nature of the auxiliaries used, their uptake, pH etc. Therefore, the nature and quantity of secondary pollutants generated vary from case to case.
  • End-of-pipe treatment aims primarily at treatment of wastewater to the extent that the wastewater is amenable for discharge.
  • RO is an important membrane process in which wastewater is passed through a semi-permeable membrane at a pressure greater than the osmotic pressure caused by dissolved salts in the wastewater, thereby filtering out the dissolved solids.
  • Major limitation of RO is its higher cost. More than the higher capital cost, it is very important to note that the operating cost is substantial due to higher energy requirement and the exorbitant cost of maintenance of membrane, as reported by Kuppusamy Ranganathan and Sreedevi D. Kabadgi. Journal of Environmental Protection. 2:37-46, 2003.
  • the reject that contains huge amount of dissolved solids needs to be evaporated which is energy intensive and economically unviable.
  • a process of zero wastewater discharge process for pre-tanning operations has been recited earlier in our co-pending patent application no. 2698/DEL/2010, according to which the waste streams from different pretanning unit processes have been segregated, treated and reused appropriately.
  • This zero wastewater discharge process unlike the classical treatment does not lead to the generation of sludge and harmful gaseous emissions.
  • the treatment and reuse of wet-finishing waste stream generated during the post tanning operations is challenging. Wide range of chemicals and chemical products are used in wet finishing which are not used in pretanning operations.
  • the chemical nature of the auxiliaries is modified due to the interaction between the auxiliaries and their interaction with the leathers. Therefore, they are not present in the form or nature that is suitable for reuse.
  • the better strategy for attaining zero wastewater discharge for wet-finishing waste stream shall be to oxidize the residual auxiliaries to the maximum possible extent so as to render the treated wastewater reusable.
  • the earlier patent application addresses the waste streams from pretanning processes, the present invention is connected to the waste streams of post tanning unit processes.
  • the post tanning waste streams especially the wet-finishing wastewater contains mixture of wide range of chemicals and chemical products. And therefore, it is not easily degradable.
  • the present invention is devised to treat the post tanning waste streams and accordingly the process parameters including the choice of simultaneous treatment methods have been designed.
  • the present patent application is different from the copending application in the following aspects:
  • the concept of achieving zero discharge in the earlier patent is based on degradation of the organic pollutants and reutilizing the inorganic pollutants present in the wastewater while reusing
  • the concept of zero wastewater discharge for the post tanning is based on degrading the pollutants present in the wastewater to the extent that it shall not interfere in the process and quality aspects.
  • reuse of the components of the wastewater is not the basis.
  • Electro-oxidation method has been successfully applied for the treatment of wastewater from textile industry, as reported by Mohan et al (Chemical Engineering Technology, 24(7), 749-753, 2001 ); Bhaskar Raju et al (Chemical Engineering Journal, 144, 51 -58, 2008); Bahadir K. Korbahti and Abdurrahman Tanyolag (Journal of Hazardous Materials, 170, 771 -778, 2009).
  • the optimal current density for effective ammonia removal using Ti/Pt electrode was found to be 2 A/cm 2 .
  • Rao et al (Journal of Chemical Technology and Biotechnology, 76, 1 124-1 131 , 2001 ) reported that tannery wastewater was treated by electro-oxidation technique using Ti/Pt, Ti/Mn0 2 anodes and Ti cathode. Tannery wastewater after secondary clarification was treated electrochemically. The efficacy of electrochemical treatment of tannery wastewater using the above said three anodes was evaluated. It was found that Ti/Pt electrode brought about higher COD reduction.
  • the inventors of the present invention realized that there exists a dire need to provide a process for treating the waste streams of post tanning operations which lead to zero water discharge and wherein the process is devoid of sludge and reject from wastewater treatment and reuse.
  • the main objective of the present invention is therefore to provide a process leading to zero water discharge in post tanning operations, that obviates the limitations of the hitherto reported prior art.
  • Another object of the present invention is to segregate the waste streams instead of combining with other streams as practiced in the case of classical end-of-pipe treatment.
  • Still another object of the present invention is to ensure maximum degradation of the residual auxiliaries to the extent that the treated wastewater can be reused.
  • Yet another object of the present invention is to oxidize the residual auxiliaries to the maximum possible extent so as to render the treated wastewater reusable.
  • Still another object of the present invention is to provide sustainable solution to the problem of wastewater emanating from the wet-finishing operations of leather manufacturing that shall obviate the problems of generation of solid wastes from the treatment systems.
  • Yet another object of the present invention is to internalize the hydrological cycle in post tanning segment of leather manufacturing.
  • the present invention relates to a process for the treatment of waste streams of post tanning unit processes.
  • the post tanning waste streams especially the wet-finishing wastewater contains mixture of wide range of chemicals and chemical products and therefore, it is not easily degradable.
  • the present invention is devised to treat the post tanning waste streams and accordingly the process parameters including the choice of simultaneous treatment methods have been planned.
  • the synergistic effect of different treatment systems along with electro-oxidation have been exploited to treat the not-easily-treatable post tanning waste streams.
  • Different recycling scheme has been devised to suit the post tanning unit processes.
  • the present invention does not only involve treatment of wastewater but also the reuse of treated waste streams.
  • the present invention provides a process leading to zero water discharge in post tanning operations wherein the process comprises the following steps: a) segregating the waste exit streams generated in post tanning unit operations to obtain segregated streams, b) subjecting the segregated streams as obtained in step (a) to separation for removal of gross solids having particle size not less than 1.2 mm, to obtain sectional streams, c) subjecting the sectional streams as obtained in step (b) to oxidation under turbulent condition for a period in the range of 15-360 minutes, optionally in the presence of UV radiation, to obtain treated sectional streams, d) reusing the treated sectional streams as obtained in step (c) in further unit operations to achieve zero water discharge.
  • the unit operation used may be such as rechroming, basification, washing, neutralization, retanning, dyeing, fatliquoring and fixation.
  • the separation process may be selected from screen sieving, filtration.
  • the process for oxidation may be selected from electro-oxidation, photo-oxidation, electro-oxidation mediated by hydrogen peroxide in the range of 200 mg/L to 5000 mg/L, ozonation, Fenton reagent treatment, either individually or in any succession.
  • the electrode used in electro oxidation may be selected from Ti/Pt, SS 316 L electrode, carbon electrode, triple oxide coated Titanium electrode.
  • the current density used for electro-oxidation may be in the range of 0.006 A/cm 2 to 0.5 A/cm 2 .
  • the wave length for UV treatment may be in the range of 140 to 300 nm.
  • the means for inducing turbulence may be such as mechanical stirring, bubbling, sonication with power ultrasound in the range of 10 W to 100 W.
  • the flow of ozone in ozonation may be in the range of 1 to 6 g/L.
  • the basic strategy of the present system is that the waste streams are segregated and not combined.
  • the waste streams are passed through screens of size not more than 1.2 mm to remove the gross solids.
  • the waste streams are then treated electro-chemically to remove the organic matter.
  • the electro-chemical treatment opted here is electro-oxidation where electrodes such as graphite, Ti/Pt, triple oxide coated Ti, SS and SS 316 L could be used.
  • the current density varies from 0.006 A/cm 2 to 0.5 A/cm 2 .
  • the treatment time varies from 15 minutes to 360 minutes.
  • Treatment may be carried out under dynamic condition through recirculation of the wastewater at a flow rate varying from 1 L to 400 L per hour. Electro-oxidation may also be coupled with UV treatment of wavelength ranging from 140 to 300 nm . Ozonation may also be done simultaneously with the flow ranging from 1 to 6 g/L.
  • the pH of the wastewater may be kept as such or adjusted to neutral or alkaline condition. The treated waste streams are reused appropriately.
  • ⁇ Rechroming wastewater may be sent to chrome recovery plant
  • Waste stream of washing before neutralization may be reused for rechroming
  • Waste stream of neutralization may be reused for washing before neutralization
  • Waste stream of washing after neutralization may be used for neutralization
  • Waste stream of wet-finishing may be reused for wet-finishing.
  • the oxidation treatment renders the waste streams suitable for reuse every time ensuring the continuous reuse of the treated waste streams such that the wastewater is not discharged at all.
  • the present invention relates to the leather process segment of post tanning wherein no discharge of any kind of wastewater is there. More particularly, the present invention relates to a process whereby the waste streams generated from the unit process of post tanning are subjected to electro-oxidation that results in treated waste streams amenable for reuse so as to eventually achieve no discharge of wastewater.
  • the process is very much benevolent for the leather industry to attain sustainability. Further, the process is also applicable and suitable for the treatment of wastewater from other manufacturing industries and process industries such as slaughter houses, textile industry, sugar industry, paper industry, oil industry, food industry and hotels.
  • the invention encompasses two components namely a. preparation and treatment of sectional streams and b. reuse of the treated sectional waste streams. (a) Preparation and Treatment of Waste Streams
  • the waste streams from each unit process of post tanning such as washing before neutralization, neutralization, washing after neutralization and wet-finishing are segregated.
  • the segregated waste streams are screened to remove the gross solids and treated following electro-oxidation.
  • the electrodes such as graphite, titanium or stainless steel are used.
  • the electrodes may be solid cylinders or shallow cylinders made of sheet of mesh of electrode material (Ti Mesh or SS mesh).
  • the distance between adjacent anode and cathode varies from 0.4 cm to 1.6 cm.
  • the current density varies from 0.006 to 0.5 A/cm 2 .
  • the pH of the waste streams is not altered prior to electro-oxidation.
  • the period of treatment varies depending upon the organic load of the waste streams.
  • the period of treatment varies from 15 minutes to 360 minutes. Electro-oxidation may also be combined with photo-oxidation where UV light of intensity from 140 nm to 300 nm is used. The UV treatment may be intermittent to electro-oxidation. Ozonation is another option prior to electro-oxidation of the waste streams.
  • the ozone dosage may be in the range of 1 to 6 g/L.
  • the treated waste streams are then reused for appropriate unit process.
  • the reuse option is based on the hydrological load and the characteristics of the treated waste stream.
  • BOD not more than 100 ppm
  • TDS not more than 3000 ppm.
  • the present invention provides a process for zero water discharge in post tanning operations, which comprises: a. segregating the exit streams generated in post tanning unit operations to obtain segregated streams, b. subjecting the segregated streams, as obtained in step (a) to separation for removal of solids having particle size not less than 1.2 mm to obtain sectional streams, c. subjecting the sectional streams, as obtained in step (b) to oxidation under turbulent condition for a period in the range of 15-360 minutes, optionally in the presence of UV radiation to obtain treated sectional streams, d. reusing the treated sectional streams, as obtained in step (c) in a unit operation to achieve no water discharge.
  • the unit operation used may be such as rechroming, basification, washing, neutralization, retanning, dyeing, fatliquoring and fixation.
  • the separation process may be selected from screen sieving, filtration.
  • the process for oxidation may be selected from electro-oxidation, photo-oxidation, electro-oxidation mediated by hydrogen peroxide in the range of 200 mg/L to 5000 mg/L, ozonation, Fenton reagent treatment, either individually or in any succession.
  • the electrode used in electro oxidation may be selected from Ti/Pt, SS 316 L electrode, carbon electrode, triple oxide coated Titanium electrode.
  • the current density used for electro-oxidation may be in the range of 0.006 A/cm 2 to 0.5 A/cm 2 .
  • the wave length for UV treatment may be in the range of 140 to 300 nm.
  • the means for inducing turbulence may be such as mechanical stirring, bubbling, sonication with power ultrasound in the range of 10 W to 100 W.
  • the flow of ozone in ozonation may be in the range of 1 to 6 g/L.
  • Example 1 is given by way of illustration only and therefore should not be construed to limit the scope of the present invention in any manner.
  • the present invention is directed to utilize the waste water streams emanating from this post tanning process so as to provide a post tanning process with zero waste water discharge.
  • the claimed invention does not involve any post tanning procedures and thus does not involve any skin/ hides. Rather the present invention is directed to a physico-chemical process for treating the waste water generated in post tanning operations.
  • the sectional streams were screened using .4 mm screens and treated as detailed below.
  • the present invention is directed to utilize the waste water streams emanating from this post tanning process so as to provide a post tanning process with zero waste water discharge.
  • the claimed invention does not involve any post tanning procedures and thus does not involve any skin/ hides. Rather the present invention is directed to a physico-chemical process for treating the waste water generated in post tanning operations.
  • the sectional streams were screened using 0.4 mm screens and treated the as detailed below.
  • the present invention is directed to utilize the waste water streams emanating from this post tanning process so as to provide a post tanning process with zero waste water discharge.
  • the claimed invention does not involve any post tanning procedures and thus does not involve any skin/ hides. Rather the present invention is directed to a physico-chemical process for treating the waste water generated in post tanning operations.
  • the sectional streams were screened using 0.4 mm screens and treated the as detailed below.

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  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Water Supply & Treatment (AREA)
  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Water Treatment By Electricity Or Magnetism (AREA)
  • Treatment Of Water By Oxidation Or Reduction (AREA)

Abstract

In the present invention, the waste streams from the unit processes of post tanning operations are segregated and screened for removing gross solids. They are then treated by electro-oxidation with or without UV treatment. The treated sectional streams are reused for appropriate unit process. The reuse can be carried out continuously to attain zero wastewater discharge in post tanning operations.

Description

A PROCESS LEADING TO ZERO WATER DISCHARGE IN POST TANNING
OPERATIONS
FIELD OF INVENTION
The present invention relates to a process leading to zero water discharge in post tanning operations in leather manufacture. In particular, the present invention relates to the leather process segment of post tanning wherein no discharge of any kind of wastewater is there. More particularly, the present invention relates to a process whereby the waste streams generated from the unit process of post tanning are subjected to electro-oxidation that results in treated waste streams amenable for reuse so as to eventually achieve no discharge of wastewater. The process is very much benevolent for the leather industry to attain sustainability. Further, the process is also applicable and suitable for the treatment of wastewater from other manufacturing industries and process industries such as slaughter houses, textile industry, sugar industry, paper industry, oil industry, food industry and hotels.
BACKGROUND OF THE INVENTION AND DESCRIPTION OF PRIOR ART
Leather manufacturing processes are associated with many significant environmental impacts. Leather manufacturing processes generate huge amount of wastewater, solid waste and gaseous emissions due to usage of wide range of chemical and chemical products. About 30-35 m3 of water and 700 kg of chemicals are used for converting 1 ton of hide/ skin into leather. Some of the pollutants emanating from tanneries are highly refractory and toxic in nature. The pollutants generated during pre-tanning are predominantly organic in nature and easily treatable. Conversely, the complex chemicals such as synthetic tanning agents, fatliquors, dyes and phenol-formaldehyde condensates used in post-tanning process render the wastewater not easily treatable.
Processes viz., retanning, dyeing and fatliquoring are carried out simultaneously. The resultant wastewater contains the residual chemicals viz. syntans, fatliquors and dyes apart from the emissions such as chromium, protein and fat in lower quantities from the leather. There exists ample possibility of inter-reaction of these auxiliaries that would lead to the generation of secondary pollutants. The possible inter reaction, the path way and the resultant production of secondary pollutants are dependent on many factors such as chemical nature of the auxiliaries used, their uptake, pH etc. Therefore, the nature and quantity of secondary pollutants generated vary from case to case. End-of-pipe treatment aims primarily at treatment of wastewater to the extent that the wastewater is amenable for discharge. Reduction of the pollution parameters such as BOD, COD, TS, TSS, TDS to the discharge norms is the requirement of end-of- pipe treatment. The discharge standards are arrived on the basis of the carrying capacity of the earth and atmosphere. Whereas end-of-pipe treatment facilitates reduction of environmental impact, inadequate attention has been paid for the secured disposal of solid wastes that are generated from the wastewater treatment system. In a way the pollutants are trans-located but not truly eliminated.
The biodegradation of wet-finishing wastewater is difficult because phenolic syntan and certain fatliquors are toxic to common microorganism. Though the advanced oxidation techniques such as photochemical degradation, ozonation and sonication are effective, the operating costs are high.
Zero wastewater discharge could be an option for achieving sustainability. Membrane processes have been opted for achieving zero wastewater discharge in Tamil Nadu. Membrane process is efficient in separation of dissolved solids particularly the inorganic solids from the wastewater. RO is an important membrane process in which wastewater is passed through a semi-permeable membrane at a pressure greater than the osmotic pressure caused by dissolved salts in the wastewater, thereby filtering out the dissolved solids. Major limitation of RO is its higher cost. More than the higher capital cost, it is very important to note that the operating cost is substantial due to higher energy requirement and the exorbitant cost of maintenance of membrane, as reported by Kuppusamy Ranganathan and Sreedevi D. Kabadgi. Journal of Environmental Protection. 2:37-46, 2003. Moreover, the reject that contains huge amount of dissolved solids needs to be evaporated which is energy intensive and economically unviable.
A process of zero wastewater discharge process for pre-tanning operations has been recited earlier in our co-pending patent application no. 2698/DEL/2010, according to which the waste streams from different pretanning unit processes have been segregated, treated and reused appropriately. This zero wastewater discharge process unlike the classical treatment does not lead to the generation of sludge and harmful gaseous emissions. However, the treatment and reuse of wet-finishing waste stream generated during the post tanning operations is challenging. Wide range of chemicals and chemical products are used in wet finishing which are not used in pretanning operations. The chemical nature of the auxiliaries is modified due to the interaction between the auxiliaries and their interaction with the leathers. Therefore, they are not present in the form or nature that is suitable for reuse. Hence, the better strategy for attaining zero wastewater discharge for wet-finishing waste stream shall be to oxidize the residual auxiliaries to the maximum possible extent so as to render the treated wastewater reusable. Whereas, the earlier patent application addresses the waste streams from pretanning processes, the present invention is connected to the waste streams of post tanning unit processes. The post tanning waste streams especially the wet-finishing wastewater contains mixture of wide range of chemicals and chemical products. And therefore, it is not easily degradable. The present invention is devised to treat the post tanning waste streams and accordingly the process parameters including the choice of simultaneous treatment methods have been designed. The present patent application is different from the copending application in the following aspects:
■ Whereas the earlier application aims at attaining zero wastewater discharge in the pre-tanning process segment, the present application is connected to the attainment of zero wastewater discharge in the post-tanning process segment. (N.B: The manufacturing of leather can be segregated into four process segments namely pre-tanning, tanning, post-tanning and finishing)
■ Whereas the concept of achieving zero discharge in the earlier patent is based on degradation of the organic pollutants and reutilizing the inorganic pollutants present in the wastewater while reusing, the concept of zero wastewater discharge for the post tanning is based on degrading the pollutants present in the wastewater to the extent that it shall not interfere in the process and quality aspects. I n the present patent, reuse of the components of the wastewater is not the basis.
Over the past 10 years, the electrochemical oxidation has been largely developed for its alternative use for remediation. It currently offers promising approaches for the prevention of pollution problems from industrial effluents. Many studies have been carried out on electro-oxidation of organic compounds and several anode materials have been tested. Electro-oxidation method has been successfully applied for the treatment of wastewater from textile industry, as reported by Mohan et al (Chemical Engineering Technology, 24(7), 749-753, 2001 ); Bhaskar Raju et al (Chemical Engineering Journal, 144, 51 -58, 2008); Bahadir K. Korbahti and Abdurrahman Tanyolag (Journal of Hazardous Materials, 170, 771 -778, 2009). It has been applied in tannery, as reported by Costa et al (Journal of Hazardous Materials, 153, 616-627, 2008), Szpyrkowicz et al (Water Research, 29(2), 517-524,1995) Rao et al (Journal of Chemical Technology and Biotechnology, 76, 1 124-1131 , 2001 ). It has also been applied in distillery, as reported by Manisankar et al (Green Chemistry, 5, 270-274, 2003). Further, the application has been reported for the treatment of domestic sewage, as reported by Vlyssides et al (Journal of Hazardous Materials, 95, 215- 226, 2002). Chiang et al (Water Research, 29(2), 671 -678,1995) reported the application of electro-oxidation method for the treatment of landfill leachate.
As reported by Sheng et al (Water Research, 32(4), 1059-1066, 1998), phenol containing saline wastewater has been treated by electrochemical method, wherein the salinity facilitated the reduction of COD and addition of small amount of H202 also favored the reduction. Tannery wastewater was treated using Ti/Pt and Ti/Pt/lr electrodes for the removal of ammonium salts. In this work, tannery wastewater was mixed with domestic sewage of 10% of the total flow. Electrochemical treatment was carried out at a current density ranging from 1 to 6 A/cm2. It was concluded that Ti/Pt electrode was better for the treatment of tannery wastewater. The optimal current density for effective ammonia removal using Ti/Pt electrode was found to be 2 A/cm2. Rao et al (Journal of Chemical Technology and Biotechnology, 76, 1 124-1 131 , 2001 ) reported that tannery wastewater was treated by electro-oxidation technique using Ti/Pt, Ti/Mn02 anodes and Ti cathode. Tannery wastewater after secondary clarification was treated electrochemically. The efficacy of electrochemical treatment of tannery wastewater using the above said three anodes was evaluated. It was found that Ti/Pt electrode brought about higher COD reduction. COD reduction of 0.0802 kg h 1A 1m 2 and ammonia reduction of 0.27 kg h 1A-1 m 2 were attained with the energy of 5.77 kWh kg 1 of COD and 16.63 kWh kg 1 of NH4+. Detoxification of tannery wastewater had been studied using a system of electrolysis in which Ti/Pt anode and SS 304 cathode were used. Composite tannery wastewater was used in this work. It was concluded that the electrolytic oxidation brought about reduction of phenolic compounds by 95%, reduction of ammonium nitrogen by 64.5%, oxidation of sulphides by 100%, sedimentation of chromium by 100% and reduction in COD by 52%. However, it was also concluded that electrolytic oxidation was not a feasible option for the treatment of composite wastewater from tannery due to the demand of high energy. Vlyssides and Israilides (Environmental Pollution, 97(2), 147-152, 1997) reported that the energy requirement in the electro-oxidation was as high as 200 kWh per kg COD reduction.
The limitations of the prior art may be summarized as follows:
No foolproof process for achieving zero wastewater discharge through recycling and reuse of individual streams generated during post tanning operations has been reported. Reports on treatment and reuse of only few select streams have been reported. However, these do not provide scope or opportunity to achieve comprehensive zero wastewater discharge. The zero liquid discharge, which is in vogue in Tamil Nadu, India, is based on Reverse Osmosis (RO). According to this system, the combined wastewater is subjected to classical primary treatment followed by secondary biological treatment and then reverse osmosis. Whereas the permeate can be reused, the reject is subjected to evaporation and the dry solid mass is collected and stored. Thus, keeping in view the drawbacks of the hitherto reported prior art, the inventors of the present invention realized that there exists a dire need to provide a process for treating the waste streams of post tanning operations which lead to zero water discharge and wherein the process is devoid of sludge and reject from wastewater treatment and reuse.
OBJECTIVES OF THE INVENTION
The main objective of the present invention is therefore to provide a process leading to zero water discharge in post tanning operations, that obviates the limitations of the hitherto reported prior art.
Another object of the present invention is to segregate the waste streams instead of combining with other streams as practiced in the case of classical end-of-pipe treatment.
Still another object of the present invention is to ensure maximum degradation of the residual auxiliaries to the extent that the treated wastewater can be reused.
Yet another object of the present invention is to oxidize the residual auxiliaries to the maximum possible extent so as to render the treated wastewater reusable.
Still another object of the present invention is to provide sustainable solution to the problem of wastewater emanating from the wet-finishing operations of leather manufacturing that shall obviate the problems of generation of solid wastes from the treatment systems.
Yet another object of the present invention is to internalize the hydrological cycle in post tanning segment of leather manufacturing. SUMMARY OF THE INVENTION
The present invention relates to a process for the treatment of waste streams of post tanning unit processes. The post tanning waste streams especially the wet-finishing wastewater contains mixture of wide range of chemicals and chemical products and therefore, it is not easily degradable. The present invention is devised to treat the post tanning waste streams and accordingly the process parameters including the choice of simultaneous treatment methods have been planned. The synergistic effect of different treatment systems along with electro-oxidation have been exploited to treat the not-easily-treatable post tanning waste streams. Different recycling scheme has been devised to suit the post tanning unit processes. The present invention does not only involve treatment of wastewater but also the reuse of treated waste streams.
In an embodiment, the present invention provides a process leading to zero water discharge in post tanning operations wherein the process comprises the following steps: a) segregating the waste exit streams generated in post tanning unit operations to obtain segregated streams, b) subjecting the segregated streams as obtained in step (a) to separation for removal of gross solids having particle size not less than 1.2 mm, to obtain sectional streams, c) subjecting the sectional streams as obtained in step (b) to oxidation under turbulent condition for a period in the range of 15-360 minutes, optionally in the presence of UV radiation, to obtain treated sectional streams, d) reusing the treated sectional streams as obtained in step (c) in further unit operations to achieve zero water discharge.
In another embodiment of the present invention, the unit operation used may be such as rechroming, basification, washing, neutralization, retanning, dyeing, fatliquoring and fixation.
In yet another embodiment of the present invention, the separation process may be selected from screen sieving, filtration. In still another embodiment of the present invention, the process for oxidation may be selected from electro-oxidation, photo-oxidation, electro-oxidation mediated by hydrogen peroxide in the range of 200 mg/L to 5000 mg/L, ozonation, Fenton reagent treatment, either individually or in any succession.
In yet another embodiment of the present invention, the electrode used in electro oxidation may be selected from Ti/Pt, SS 316 L electrode, carbon electrode, triple oxide coated Titanium electrode. In still another embodiment of the present invention, the current density used for electro-oxidation may be in the range of 0.006 A/cm2 to 0.5 A/cm2.
In yet another embodiment of the present invention, the wave length for UV treatment may be in the range of 140 to 300 nm.
In still another embodiment of the present invention, the means for inducing turbulence may be such as mechanical stirring, bubbling, sonication with power ultrasound in the range of 10 W to 100 W. In yet another embodiment of the present invention, the flow of ozone in ozonation may be in the range of 1 to 6 g/L.
DETAILED DESCRIPTION OF THE INVENTION
Leather manufacturing units are in imminent demand of technologies to address the issue of wastewater management in a sustainable manner. The basic strategy of the present system is that the waste streams are segregated and not combined. The waste streams are passed through screens of size not more than 1.2 mm to remove the gross solids. The waste streams are then treated electro-chemically to remove the organic matter. The electro-chemical treatment opted here is electro-oxidation where electrodes such as graphite, Ti/Pt, triple oxide coated Ti, SS and SS 316 L could be used. The current density varies from 0.006 A/cm2 to 0.5 A/cm2. The treatment time varies from 15 minutes to 360 minutes. Treatment may be carried out under dynamic condition through recirculation of the wastewater at a flow rate varying from 1 L to 400 L per hour. Electro-oxidation may also be coupled with UV treatment of wavelength ranging from 140 to 300 nm . Ozonation may also be done simultaneously with the flow ranging from 1 to 6 g/L. The pH of the wastewater may be kept as such or adjusted to neutral or alkaline condition. The treated waste streams are reused appropriately.
The options of reuse of each waste stream are presented hereunder:
■ Rechroming wastewater may be sent to chrome recovery plant;
■ Waste stream of washing before neutralization may be reused for rechroming;
■ Waste stream of neutralization may be reused for washing before neutralization;
■ Waste stream of washing after neutralization may be used for neutralization;
■ Waste stream of wet-finishing may be reused for wet-finishing.
The oxidation treatment renders the waste streams suitable for reuse every time ensuring the continuous reuse of the treated waste streams such that the wastewater is not discharged at all.
In particular, the present invention relates to the leather process segment of post tanning wherein no discharge of any kind of wastewater is there. More particularly, the present invention relates to a process whereby the waste streams generated from the unit process of post tanning are subjected to electro-oxidation that results in treated waste streams amenable for reuse so as to eventually achieve no discharge of wastewater. The process is very much benevolent for the leather industry to attain sustainability. Further, the process is also applicable and suitable for the treatment of wastewater from other manufacturing industries and process industries such as slaughter houses, textile industry, sugar industry, paper industry, oil industry, food industry and hotels.
The invention encompasses two components namely a. preparation and treatment of sectional streams and b. reuse of the treated sectional waste streams. (a) Preparation and Treatment of Waste Streams
The waste streams from each unit process of post tanning such as washing before neutralization, neutralization, washing after neutralization and wet-finishing are segregated. The segregated waste streams are screened to remove the gross solids and treated following electro-oxidation. For the treatment i.e oxidation, the electrodes such as graphite, titanium or stainless steel are used. The electrodes may be solid cylinders or shallow cylinders made of sheet of mesh of electrode material (Ti Mesh or SS mesh). The distance between adjacent anode and cathode varies from 0.4 cm to 1.6 cm. The current density varies from 0.006 to 0.5 A/cm2. The pH of the waste streams is not altered prior to electro-oxidation. The period of treatment varies depending upon the organic load of the waste streams. The period of treatment varies from 15 minutes to 360 minutes. Electro-oxidation may also be combined with photo-oxidation where UV light of intensity from 140 nm to 300 nm is used. The UV treatment may be intermittent to electro-oxidation. Ozonation is another option prior to electro-oxidation of the waste streams. The ozone dosage may be in the range of 1 to 6 g/L.
(b) Reuse of the treated sectional waste streams
The treated waste streams are then reused for appropriate unit process. The reuse option is based on the hydrological load and the characteristics of the treated waste stream.
Following are the requirements of the treated waste streams to be suitable for reuse.
BOD: not more than 100 ppm;
COD: not more than 350 ppm;
TDS: not more than 3000 ppm. An important aspect of the present invention is that endless reuse is possible because of the intermittent treatment.
In an embodiment, the present invention provides a process for zero water discharge in post tanning operations, which comprises: a. segregating the exit streams generated in post tanning unit operations to obtain segregated streams, b. subjecting the segregated streams, as obtained in step (a) to separation for removal of solids having particle size not less than 1.2 mm to obtain sectional streams, c. subjecting the sectional streams, as obtained in step (b) to oxidation under turbulent condition for a period in the range of 15-360 minutes, optionally in the presence of UV radiation to obtain treated sectional streams, d. reusing the treated sectional streams, as obtained in step (c) in a unit operation to achieve no water discharge.
In another embodiment of the present invention, the unit operation used may be such as rechroming, basification, washing, neutralization, retanning, dyeing, fatliquoring and fixation. In yet another embodiment of the present invention, the separation process may be selected from screen sieving, filtration.
In still another embodiment of the present invention, the process for oxidation may be selected from electro-oxidation, photo-oxidation, electro-oxidation mediated by hydrogen peroxide in the range of 200 mg/L to 5000 mg/L, ozonation, Fenton reagent treatment, either individually or in any succession.
In yet another embodiment of the present invention, the electrode used in electro oxidation may be selected from Ti/Pt, SS 316 L electrode, carbon electrode, triple oxide coated Titanium electrode.
In still another embodiment of the present invention, the current density used for electro-oxidation may be in the range of 0.006 A/cm2 to 0.5 A/cm2. In yet another embodiment of the present invention, the wave length for UV treatment may be in the range of 140 to 300 nm.
In still another embodiment of the present invention, the means for inducing turbulence may be such as mechanical stirring, bubbling, sonication with power ultrasound in the range of 10 W to 100 W.
In yet another embodiment of the present invention, the flow of ozone in ozonation may be in the range of 1 to 6 g/L.
EXAMPLES
The following examples are given by way of illustration only and therefore should not be construed to limit the scope of the present invention in any manner. Example 1
Following represents the process of post tanning of wet-blue goat skin. Zero wastewater discharge process is carried out for this manufacturing process. It may be noted that the present invention is directed to utilize the waste water streams emanating from this post tanning process so as to provide a post tanning process with zero waste water discharge. The claimed invention does not involve any post tanning procedures and thus does not involve any skin/ hides. Rather the present invention is directed to a physico-chemical process for treating the waste water generated in post tanning operations.
Figure imgf000013_0001
Figure imgf000014_0001
Figure imgf000015_0002
The sectional streams were screened using .4 mm screens and treated as detailed below.
Figure imgf000015_0001
Following is the reuse scheme of the above process.
Figure imgf000016_0001
Example 2
Following is the process of post tanning of wet-blue cow leather. Zero wastewater discharge process is carried out for this manufacturing process. It may be noted that the present invention is directed to utilize the waste water streams emanating from this post tanning process so as to provide a post tanning process with zero waste water discharge. The claimed invention does not involve any post tanning procedures and thus does not involve any skin/ hides. Rather the present invention is directed to a physico-chemical process for treating the waste water generated in post tanning operations.
Figure imgf000016_0002
Figure imgf000017_0001
Figure imgf000018_0002
The sectional streams were screened using 0.4 mm screens and treated the as detailed below.
Figure imgf000018_0001
Figure imgf000019_0001
Following is the reuse scheme of the above process.
Figure imgf000019_0002
Example 3
Following is the process of post tanning of wet-blue buffalo leathers. Zero wastewater discharge process is carried out for this manufacturing process. It may be noted that the present invention is directed to utilize the waste water streams emanating from this post tanning process so as to provide a post tanning process with zero waste water discharge. The claimed invention does not involve any post tanning procedures and thus does not involve any skin/ hides. Rather the present invention is directed to a physico-chemical process for treating the waste water generated in post tanning operations.
Figure imgf000020_0001
Figure imgf000021_0002
The sectional streams were screened using 0.4 mm screens and treated the as detailed below.
Figure imgf000021_0001
Figure imgf000022_0002
Following is the reuse scheme of the above process.
Figure imgf000022_0001
ADVANTAGES OF THE INVENTION
■ No wastewater is discharged in the post tanning operations.
■ No sludge is generated during wastewater treatment.
■ No harmful gaseous emission from the wastewater treatment.
■ Reduction in chemical input.
■ Major Reduction in water usage. ■ Reduction in space required for wastewater treatment.
■ Water used in post tanning process is recycled back and used in other round of post tanning operations.

Claims

CLAIMS:
1. A process leading to zero water discharge in post tanning operations wherein the process comprises the following steps : a) segregating the waste exit streams generated in post tanning unit operations to obtain segregated streams, b) subjecting the segregated streams as obtained in step (a) to separation for removal of gross solids having particle size not less than 1.2 mm, to obtain sectional streams, c) subjecting the sectional streams as obtained in step (b) to oxidation under turbulent condition for a period in the range of 15-360 minutes, optionally in the presence of UV radiation, to obtain treated sectional streams, d) reusing the treated sectional streams as obtained in step (c) in further unit operations to achieve zero water discharge.
2. The process as claimed in claim 1 , wherein the waste streams generated in post tanning unit operations are selected from rechroming, basification, washing, neutralization, retanning, dyeing, fatliquoring and fixation.
3. The process as claimed in claim 1 , wherein the separation process used is either screen sieving or filtration.
4. The process as claimed in claim 1 , wherein oxidation is done using electro oxidation, photo-oxidation, electro-oxidation mediated by hydrogen peroxide in the range of 200 mg/L to 5000 mg/L, ozonation, Fenton reagent treatment, either individually or in any succession.
5. The process as claimed in claim 4, wherein the electrode used in electro- oxidation is selected from Ti/Pt, SS 316 L steel electrode, carbon electrode, triple oxide coated Titanium electrode.
6. The process as claimed in claim 4, wherein the current density used for electro oxidation is in the range of 0.006 A/cm2 to 0.5 A/cm2.
7. The process as claimed in claim 1 , wherein the wave length for UV treatment is in the range of 140 to 300 nm.
8. The process as claimed in claim 1 , wherein the means for inducing turbulent condition are selected from mechanical stirring, bubbling, sonication with power ultrasound in the range of 10 W to 100 W.
9. The process as claimed in claim 4, wherein the flow of ozone in the ozonation process is in the range of 1 to 6 g/L.
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