INTRODUCTION TO THE TREATMENT OF TANNERY EFFLUENTS Introduction to treatment of tannery effluent - Part 1 (of 6) United Nations Industrial Development Organization INTRODUCTION TO THE TREATMENT OF TANNERY EFFLUENTS What every tanner should know about effluent treatment Part I Compiled by J. Buljan, I. Kral United Nations Industrial Development Organization (UNIDO) 1

1. Load, norms, in-house treatment Introduction to treatment of tannery effluent - Part 1 (of 6) 1. Load, norms, in-house treatment Pollution load Discharge norms General overview of treatment of tannery effluents Segregation of streams Treatment of spent liming floats Treatment of chrome-bearing floats Linking of individual tanneries to a CETP or MWWW In view of ever increasing legal and social pressures, no tanner can afford the luxury of not being familiar with main issues and principles of environmental protection pertaining to tannery operations. Pollution prevention, persistent promotion of cleaner leather processing, ultimately leading to lower treatment costs, remains the supreme priority. Yet, despite all preventive measures, there is still a considerable amount of pollution load to be dealt with by the end-of-pipe methods. The purpose of this presentation(s) is to help a tanner or a tannery manager, possibly a well-trained leather technologist, to familiarise with basic principles and methods of treatment of tannery effluents. This knowledge should make him/her better equipped for a dialogue with the factory's own environmental unit, environmental authorities and NGOs. With the view of keeping it short and concise there are many simplifications and omissions of details; thus, for in-depth understanding of the complexities of treatment of effluents and solid wastes (sludge) it is recommended to consult extensive literature on this subject. All data and information here refer to combined chrome tanning because it is still by far the most prevailing leather tanning method. Due to varieties in raw material, process, chemicals, water consumption etc. it is small wonder that figures about pollution load in the literature vary a lot and should be interpreted very cautiously. Charts and tables presented here below may give the general idea, the usual reference being a tonne of wet salted hides. United Nations Industrial Development Organization (UNIDO)

Introduction to treatment of tannery effluent - Part 1 (of 6) LEATHER PROCESSING PRODUCTS Wet-blue Raw hides TANNERY Site Crust TANNERY Plant/Building(s) Chemicals Finished leather Effluent for treatment Water Air pollution Fresh air Here we have a general overview of all material inputs and outputs in leather processing. Solid waste Processing Disposal United Nations Industrial Development Organization (UNIDO)

Introduction to treatment of tannery effluent - Part 1 (of 6) WATER pollutants SOLID pollutants RAW HIDES AIR pollutants Soaking BOD,COD, SS, TDS, organic N Green fleshing Fleshings (fat containing organic matter) BOD,COD, SS, TDS, alkalinity, sulphides, organic N, ammonia N Unhairing Liming Hair, lime, organic matter containing sludge H2S Lime fleshing BOD,COD, SS, TDS, alkalinity, sulphides Lime fleshings (fat containing org. matter) Lime splitting Trimming Lime split and trimmings (limed organic matter) Deliming Bating BOD,COD, TDS, ammonia N NH3 Degreasing (sheep/pigskins) BOD,COD, TDS, ammonia N Pickling Tanning BOD,COD, SS, TDS, acidity, salts, chrome, vegetable tans, syntans At macro (strategic) level, it should be borne in mind that wet blue production is capital and NOT labour intensive and it brings rather low added value. However, possibly even more important is the fact that the major part of pollution load emanates from this stage of process !!! Please note a significant amount of solid and air discharges/pollutants. Sammying BOD,COD, SS, TDS, acidity, salts, chrome, vegetable tans, syntans Chrome splitting Chrome split (chrome containing org. matter) Shaving LEGEND: BOD – Biochemical Oxygen Demand COD – Chemical Oxygen Demand TDS – Total Dissolved Solids SS – Suspended Solids Shavings (chrome containing org. matter) WET-BLUE United Nations Industrial Development Organization (UNIDO)

Introduction to treatment of tannery effluent - Part 1 (of 6) WATER pollutants SOLID pollutants AIR pollutants WET-BLUE Retanning, dyeing Fat liquoring BOD,COD, TDS, chrome tans, dyes, fats Drying Buffing Trimming Chrome trimmings (chrome and prefinishing chemicals containing org. matter) CRUST Finishing Reminder of finishing agents Solvents, CH2O While the pollution load from this stage is comparatively much lower, the COD emanating from certain retanning agents can be of recalcitrant character i.e. very hard to degrade and making the additional, tertiary treatment unavoidable. LEATHER LEGEND: BOD – Biochemical Oxygen Demand COD – Chemical Oxygen Demand TDS – Total Dissolved Solids SS – Suspended Solids United Nations Industrial Development Organization (UNIDO)

Introduction to treatment of tannery effluent - Part 1 (of 6) WATER pollutants RAW HIDES SOLID pollutants AIR pollutants Soaking BOD,COD, SS, TDS, organic N Green fleshing Fleshings (fat containing organic matter) Unhairing Liming BOD,COD, SS, TDS, alkalinity, sulphides, organic N, ammonia N Hair, lime, organic matter containing sludge H2S Lime fleshing BOD,COD, SS, TDS, alkalinity, sulphides Lime fleshings (fat containing org. matter) Lime splitting Trimming Lime split and trimmings (limed organic matter) Deliming Bating BOD,COD, TDS, ammonia N NH3 Degreasing (sheep/pigskins) BOD,COD, TDS, ammonia N Pickling Tanning BOD,COD, SS, TDS, acidity, salts, chrome, vegetable tans, syntans Sammying BOD,COD, SS, TDS, acidity, salts, chrome, vegetable tans, syntans Chrome splitting Chrome split (chrome containing org. matter) Shaving Shavings (chrome containing org. matter) WET-BLUE Too often our attention is focused only on pollutants contained in the floats/effluent; however please note the substantial amount of solid waste – by-products and air emissions. Retanning, dyeing Fat liquoring BOD,COD, TDS, chrome tans, dyes, fats Drying LEGEND: BOD – Biochemical Oxygen Demand COD – Chemical Oxygen Demand TDS – Total Dissolved Solids SS – Suspended Solids Buffing Trimming Chrome trimmings (chrome and prefinishing chemicals containing org. matter) CRUST Finishing Solvents, CH2O Reminder of finishing agents LEATHER United Nations Industrial Development Organization (UNIDO)

EXAMPLE OF MASS BALANCE OF CHEMICALS IN LEATHER PROCESSING Introduction to treatment of tannery effluent - Part 1 (of 6) EXAMPLE OF MASS BALANCE OF CHEMICALS IN LEATHER PROCESSING kg/t of wet salted hide Chemicals Added in process In/on leather & splits Wasted Chrome oxide (Cr2O3) 25 12 13 Organic tannins 20 5 Fatliquors 22 17 Dyestuffs 4 1 Acids, bases, salts 191 - Tensides 3 Enzymes Finishing products 100 88 Total 452 72 380 Even many practical tanners are surprised by the amount/percentage of chemicals not absorbed by leather: typically more than 80 % of the total amount offered. United Nations Industrial Development Organization (UNIDO)

TYPICAL TOTAL POLLUTION LOAD Introduction to treatment of tannery effluent - Part 1 (of 6) TYPICAL TOTAL POLLUTION LOAD Conventional process, expressed as concentration in combined raw effluent Parameter Unit Biochemical oxygen demand (BOD5) mg O2/l Chemical oxygen demand (COD) Suspended solids (SS) mg/l Trivalent chromium (Cr3+) mg Cr/l Sulphides, S2- mg S/l Total Kjeldahl Nitrogen (TKN) mg N/l Chlorides, (Cl-) mg Cl/l Sulphates (SO42-) mg SO4/l Oil and grease Total Dissolved Solids (TDS)* pH Average total pollution load 2000 4000 150 160 5000 1400 130 10000 6 - 9 Typical limits, surface waters 30 - 40 125 - 250 35 - 100 1.5 - 2.0 1.0 - 2.0 100 Locally specific 5.5 - 9.5 It is given here for a conventional process and expressed in terms of concentration in effluent at water consumption level of 45 m3/tonne of w.s. hide. Nowadays, with better water management and lower water consumption the concentration is much higher and, thus the purification task in order to reach the norms shown in the last column is more difficult. *The main constituents of the TDS are chlorides (Cl-) and sulphates (SO42-) listed earlier. United Nations Industrial Development Organization (UNIDO)

TYPICAL TOTAL POLLUTION LOAD Introduction to treatment of tannery effluent - Part 1 (of 6) Conventional process, kg/t of wet salted hide Tannery with 5 t/day wet-salted input Parameter Biochemical oxygen demand (BOD5) Chemical oxygen demand (COD) Suspended solids (SS) Trivalent chromium (Cr3+) Sulphides, S2- Total Kjeldahl Nitrogen (TKN) Chlorides, (Cl-) Sulphates (SO42-) Oil and grease Total Dissolved Solids (TDS)* pH kg/t 90 180 7 7.5 225 63 6 450 6 - 9 kg/day 450 900 35 37.5 1125 315 30 2250 It is given here for a conventional process and expressed in terms of load per tonne of w.s. hide, i.e. regardless of water consumption and that is why parameters expressed in this manner are safer indicators of pollution load. *The main constituents of the TDS are chlorides (Cl-) and sulphates (SO42-) listed earlier. United Nations Industrial Development Organization (UNIDO)

IN-HOUSE SEGREGATION OF STREAMS Linked to a CETP Introduction to treatment of tannery effluent - Part 1 (of 6) IN-HOUSE SEGREGATION OF STREAMS Linked to a CETP Screens To the treat- ment plant Grit floating matter chamber SULPHIDE OXIDATION UNIT Post-tanning effluent Soaking and other effluent Septic tank (optional) Sanitary effluent Tanning liquor Screens Screens Liming effluent TANNERY S h o w e r s, t o i l e t s CR-RECOVERY UNIT Strict segregation of streams, i.e. of soaking, liming, tanning and post-tanning streams is essential for efficient treatment of effluents, possible recycling and staff health and safety. In case of retanning with Cr-containing agents it is desirable to remove the residual Cr from that spent float too. Recovered Cr-liquor United Nations Industrial Development Organization (UNIDO)

EFFLUENT HANDLING WITHIN TANNERIES SOAKING EFFLUENT 20 mm 10 mm SULPHIDE OXIDATION (optional) MnSO4(H2O) dosing 20 mm 10 mm LIMING EFFLUENT TRANSPORT TO SLUDGE LANDFILL Sludge drying beds (optional) CROME RECOVERY PLANT (optional) NaOH dosing Steam 20 mm 10 mm TANNING LIQUOR Recovered Cr-liquor RECYCLED Grit and floating matter (grease and oil) chamber 6 mm Cr-sludge Diatomaceous earth H2SO4 Sulphide oxidation with manganese sulphate as catalyst is a kind of standard. Chrome recycling using NaOH for precipitation and H2SO4 for re-dissolving is most common method but some prefer precipitation with MgO or even “endless” direct recycling of chrome float. Good Cr management, resulting – inter alia – in low Cr content in the common sludge is essential in improving the scope of options for ultimate chrome reutilization and/or safe disposal. Impurities TO TANNERY EFFLUENT COLLECTION AND CONVEYANCE SYSTEM POST-TANNING & OTHER EFFLUENT Septic tank (optional) SANITARY EFFLUENT

TYPICAL EFFLUENT TREATMENT SETUP VARIANT: CETP for a tannery cluster River/channel Reservoir/lake/sea TANNERY SITE CETP Common Effluent Treatment Plant TANNERY PT Pre-treatment In a well organized typical tannery cluster, there is mandatory sulphide oxidation and Cr recovery and simple pre-treatment in each individual tannery followed by full treatment in the common effluent treatment plant (CETP) and final discharge into a water recipient. Other tanneries S S2- oxidation Cr recovery

TYPICAL EFFLUENT TREATMENT SETUP VARIANT: Final treatment together with urban wastewaters at the municipal plant River/channel Reservoir/lake/sea Communal and other effluent MWWW Municipal Wastewater Works TANNERY SITE PhCh Physical- Chemical treatment TANNERY PT Pre-treatment In industrialized countries each tannery has to have full physical-chemical treatment within the tannery compound before discharge into sewage channel for joint treatment at the municipal wastewater works, MWWW. However, nowadays it is often insisted that both primary and secondary (biological) treatment have to be carried out before discharge into municipal sewer. S S2- oxidation Cr recovery