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WATER AND WASTEWATER MANAGEMENT IN THE TANNING AND LEATHER FINISHING INDUSTRY: NATSURV 10 (2 nd EDITION) Report to the Water Research Commission

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Abstract and Figures

This NATSURV (National Survey) document forms part of a series of such documents reporting on surveys of various industries in South Africa. In many instances, previous surveys were undertaken between 1986 and 2001. The purpose of the new NATSURV documents is to provide more recent and relevant information on water, wastewater, and energy management practices to all stakeholders involved in the chosen industries.
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WATER AND WASTEWATER MANAGEMENT IN THE TANNING
AND LEATHER FINISHING INDUSTRY: NATSURV 10 (2nd EDITION)
Report to the
Water Research Commission
by
CD Swartz1, C Jackson-Moss2, RA Rowswell3, AB Mpofu4, PJ Welz4
1. Chris Swartz Water Utilization Engineers
2. International School of Tanning Technology
3. Tannery Environmental Consulting Services
4. Cape Peninsula University of Technology
WRC Report No. TT 713/17
May 2017
ii
Obtainable from
Water Research Commission
Private Bag X03
Gezina, 0031
orders@wrc.org.za or download from www.wrc.org.za
The publication of this report emanates from a project entitled Water and
wastewatermanagement in the tanning and leather finishing industry: Natsurv 10 (2nd
edition) K5/2490
DISCLAIMER
This report has been reviewed by the Water Research Commission (WRC) and
approved for publication. Approval does not signify that the contents necessarily
reflect the views and policies of the WRC,
nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
ISBN 978-1-4312-0881-4
Printed in the Republic of South Africa
© Water Research Commission
iii
EXECUTIVE SUMMARY
BACKGROUND
In the 1980s, the Water Research Commission (WRC) and the Department of Water Affairs (now the
Department of Water and Sanitation) embarked on a series of national surveys for 16 industries. These
reports were referred to as NATSURV documents, focusing on the water and wastewater management
of these industries. The NATSURV reports of the different industries have been well used by the sector.
However, since the 1980s South Africa and its industrial sectors have either grown or in some cases
shrunk considerably. The landscape has changed, and new technologies and systems have been
adopted by some industries. Thus, some of the information contained in the national surveys can be
considered out of date. Through the UN CEO Water Mandate, water stewardship discussions, water
allocation and equity dialogues, there is also a growing awareness around water use, water security
and waste production. It is therefore considered an opportune time to review the water and wastewater
management practices of the different industrial sectors.
The current project is concerned with the water and wastewater management of the tannery and leather
finishing industry. The first NATSURV document of this industry presented data collected during visits
to 11 of the 20 tanneries in South Africa at the time. The number of tanneries and leather finishing
industries had increased to 35 at the time of this research. Ten tanneries were visited, representing all
the different types, categories and sizes of industry in this sector, namely, bovine, ovine and exotic hides
and skins, wet blue tanning, retanning, full-house tanning and leather finishing.
AIMS
The main aims of the project were to:
x Provide a detailed overview of the tanning and leather finishing industry in South Africa, and its
changes since 1980.
x Determine the water consumption and specific water consumption in the industry.
x Determine wastewater generation and typical pollutant loads.
x Provide recommendations on best practices for the tanning industry.
METHODOLOGY
A thorough search of the internet and available directories were conducted and a database compiled of
tanning and leather finishing industries in South Africa. The tanneries were then contacted via e-mail
and telephone calls. Information was gathered using questionnaires developed for this purpose. Of the
35 tanneries and leather finishers in the country, 10 tanneries were selected to represent different types,
sizes and geographical locations. The selected tanneries were visited for personal interviews and
surveys. During the visits, information and data were gathered on water usage, wastewater generation
and quality, wastewater treatment processes used for treating the wastewater streams, municipal
monitoring data and energy consumption figures.
BEST PRACTICES: WATER USE AND MANAGEMENT
Most tanneries visited for this study use municipal water. However, the cost of water differs from
municipality to municipality. Some tanneries supplement municipal water with borehole water or storm
water during the rainy season. Retanning and leather finishing tanneries consume less water than full-
house tanneries because the downstream processes are less water intensive. This is one of the
advantages of retanning and leather finishing tanneries, as they produce less polluted and smaller
volumes of wastewater than full-house tanneries.
iv
The range of the specific water intake (SWI) for full tanning was found to be 170-550 L/hide, compared
with the 320-744 L/hide reported in the first NATSURV 10 (1989). A target SWI figure is proposed at
50-150 L/hide for wet blue process stages, 100-200 L/hide for dyehouse process stages, and
200-500 L/hide for total tanning and finishing stages.
BEST PRACTICES: WASTEWATER GENERATION AND MANAGEMENT
The effluent from tanneries contains high organic loads as measured by chemical oxygen demand
(COD), and high concentrations of dissolved and suspended solids as measured by total dissolved
solids (TDS) and total suspended solids (TSS). Effluent also contains varying levels of sulphates,
sulphides, chlorides and chromium, which add to the pollutant load on the environment of the
wastewater streams discharged. Municipalities include discharge standards for these pollutants in their
trade effluent by-laws.
Beamhouse processes are the source of all non-limed and limed solid wastes such as fleshings,
trimmings and waste splits. Most of the organic pollution load originates from beam house processes.
Soak water provides most of the wastewater salinity; the remainder comes from acid salts applied to
suppress pelt swelling.
The specific pollutant loads generated by the different types and categories of tanning process vary
considerably for the main pollutants found in the wastewater streams (COD, TDS, TSS, sulphates,
chlorides and chromium). Chapter 6 shows data on the quality of the wastewater (effluent) streams at
the tanneries that were visited, data that was obtained from the tanneries themselves and data from
some of the municipalities to which the tanneries discharge their final effluent. The specific pollutant
loads calculated from this data are also shown, which indicate the considerable variation in ranges.
The integrated wastewater treatment systems in the tanning and leather finishing industry consist of
preliminary treatment (or pretreatment), primary, secondary and tertiary treatment processes. Tanneries
performing wet blue retanning and leather finishing mainly use pretreatment and primary treatment
processes, whereas full-house tanneries use secondary treatment (biological treatment) as well. Some
tanneries in South Africa combine all effluent streams, while others keep effluent streams from the
beamhouse and tanyard separate. The latter is preferable because organic waste is the major
constituent of beamhouse effluent, whereas the tanyard effluent contains high concentrations of
inorganics, which could include chromium.
Cleaner production technologies are continuously being researched, developed and applied to the
tanning industry. A specific focus area is the reduction of salt loadings used in the processes. A number
of recent cleaner production techniques are reported in Chapter 8 of the report.
v
ACKNOWLEDGEMENTS
The project team wishes to thank the following people for their contributions to the project.
Reference Group
Affiliation
Dr Jo Burgess (Research
Manager)
Water Research Commissi
on
Dr Valerie Naidoo
Water Research Commission
Mr P Staples
African Hide Trading
Mr D Boast
African Hide Trading
Mr S Blumberg
Cape Produce Company (Pelts)
Mr F Weideman
Cape Produce Company (Pelts)
Mr D Kruger
Klein Karoo International (KKI)
Mr C du Pisani
South Cape Ostrich Tanning (SCOT)
Mr E van Staden
Wettest Effluent Treatment
Mr S Woods
Woods Tanning
Mr A Woods
Woods Tanning
Mr N Barkhuizen
Rotta Leathers
Mr A Mancotywa
Nelson Mandela Bay Metropolitan Municipality
Mr S Soloman
City of Cape Town
The funding of the project by the Water Research Commission and the contribution of the members of
the Reference Group are acknowledged gratefully.
Project Team:
Mr Chris Swartz, Chris Swartz Water Utilization Engineers (Project Leader)
Dr Clive Jackson-Moss, International School of Tanning Technology
Mr Roger Rowswell, Tannery Environmental Consulting Services
Dr Pamela Welz, Cape Peninsula University of Technology
Dr Seun Oyekola, Cape Peninsula University of Technology
Mr Ashton Mpofu, Cape Peninsula University of Technology
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vii
CONTENTS
EXECUTIVE SUMMARY iii
ACKNOWLEDGEMENTS v
LIST OF FIGURES ix
LIST OF TABLES x
ACRONYMS AND ABBREVIATIONS xi
GLOSSARY OF TERMS xii
INTRODUCTION 1
1.1 Background 1
1.2 Aims, Scope and Limitations 1
OVERVIEW OF THE TANNING AND LEATHER FINISHING INDUSTRY 3
2.1 Overview of the Tanning Process 3
2.1.1 Wet blue or fellmongery processing 3
2.1.2 Dyehouse operations 3
2.1.3 Leather finishing 3
2.2 Changes in the Tanning Industry Since the Previous NATSURV 4
2.3 Size of the Industry 4
2.3.1 Hide and skin production: Global and local trends 4
2.3.2 Leather and footwear production: Global and local trends 5
2.3.3 South African tanneries 6
TANNING AND LEATHER FINISHING PROCESSES 9
3.1 Categorisation of the Tanning Industry in South Africa 9
3.2 Tanning Processes 9
3.2.1 Hide and skin reception and storage 11
3.2.2 Process stages 11
3.2.3 Dyehouse process stages (wet finishing and dry finishing) 13
3.2.4 Beneficial use of tannery by-products 13
3.3 Chemicals and Products Used in Tanning Processes 13
WASTE AND EFFLUENT DISCHARGE REGULATIONS 15
4.1 National Policies 15
4.1.1 Water policy 16
4.1.2 Wastewater policy 16
4.2 By-laws at Local Government Level 17
4.2.1 Industrial effluent tariffs 17
4.3 Summary of Effluent Quality Requirements Relevant to the Tanning Industry 18
WATER USE AND MANAGEMENT 19
5.1 Water Use in the Tannery Industry 19
5.2 Water Source and Consumption 19
5.3 Water Use and Water Management of the Tanneries Visited 19
WASTEWATER GENERATION AND MANAGEMENT 22
6.1 Wastewater Generated in the Tannery Industry 22
6.2 Wastewater Quality at Tanneries and Leather Finishing Industries Visited 23
6.3 Wastewater Treatment 25
6.3.1 Introduction 25
6.3.2 Pretreatment: Screening and preliminary settling 25
6.3.3 Primary treatment 26
6.3.4 Secondary treatment 27
6.3.5 Tertiary treatment 27
viii
6.3.6 Advanced treatment systems 27
6.3.7 Sludge handling 27
6.4 Changes in Tanning Industry Wastewater Treatment and Management Since the 1980s 28
6.5 Summary of Wastewater Treatment Systems Most Widely Used in the Tanning and Leather
Finishing Industry 29
ENERGY USE AND MANAGEMENT 32
BEST PRACTICE FOR WATER USE AND WASTEWATER GENERATION IN
THE TANNERY INDUSTRY 34
8.1 Water Conservation and Demand Management 34
8.1.1 Using low floats and controlled batch washing 34
8.1.2 Recycling wash liquors 35
8.1.3 Processing green hides 35
8.1.4 Green fleshing 35
8.1.5 Integrated process control systems 35
8.2 Cleaner Production Techniques 35
8.2.1 Curing hides and skins 36
8.2.2 Unhairing and liming 37
8.2.3 Deliming and bating 37
8.2.4 Pickling 38
8.2.5 Tanning 38
8.2.6 Wet finishing 40
8.2.7 Finishing 41
LIST OF REFERENCES 43
APPENDIX A: GLOBAL LEATHER INDUSTRY OVERVIEW 45
Major Leather Industry Players: Asia 45
Major Leather Industry Players: North and South America 45
Major Leather Industry Players: Europe 46
Major Leather Industry Players: Africa 46
APPENDIX B: QUESTIONNAIRE 47
ix
LIST OF FIGURES
Figure 2.1: Global production of bovine, ovine and goat hides and skins in 2013 (FAO, 2016) ............. 5
Figure 2.2: Global production of bovine, ovine and goat leather in 2013 (FAO, 2016) ........................... 5
Figure 2.3: Trends in production and trade of leather footwear in South Africa (FAO, 2016) ................. 6
Figure 2.4: Geographical distribution of tanneries in South Africa ........................................................... 8
Figure 3.1: Processes, by-products and waste from wet blue tanning (adapted from European Union,
2013) ......................................................................................................................................................... 10
Figure 3.2: Wet blue (left) and pickled skins (right) ................................................................................. 12
Figure 4.1: National environmental and water policies relevant to the tannery industry ....................... 15
Figure 4.2: Hierarchy of decision-making intended to protect the environment .................................... 16
Figure 6.1: Typical solid and liquid waste generated in tanneries (European Union, 2013) ................. 22
Figure 6.2: Flow diagram of conventional primary, secondary and tertiary treatment processes at a full-
house tannery wastewater treatment plant where effluent streams are separated ............................... 25
Figure 7.1: Typical energy consumption in the tannery industry (%) ..................................................... 33
Figure 8.1: Best practice hierarchy – towards a sustainable future ....................................................... 34
x
LIST OF TABLES
Table 2.1: Size of the tanning and leather finishing industry in South Africa ........................................... 6
Table 3.1: Chemicals used in various processes in the tanning industry .............................................. 14
Table 4.1: Effluent standards of municipalities for water quality parameters regulated for effluents from
tanneries ................................................................................................................................................... 18
Table 5.1: Typical process water consumption (Ramanujam et al., 2010) ............................................ 19
Table 5.2: Water use and management of tanneries visited (Tanneries A1-A5) ................................... 20
Table 5.3: Water use and management of tanneries visited (Tanneries A6-A10) ................................. 20
Table 5.4: Typical water use in tannery production processes .............................................................. 21
Table 5.5: Proposed water use targets ................................................................................................... 21
Table 6.1: Typical effluent constituents from tanning and finishing processes ...................................... 23
Table 6.2: Wastewater quality at tanneries visited in the survey ............................................................ 24
Table 6.3: Solid waste management practices of selected tanneries in South Africa ........................... 27
Table 6.4: Summary of tannery effluent treatment processes ................................................................ 29
Table 6.5: Advantages and disadvantages of wastewater treatment processes used in the tanning
industry ..................................................................................................................................................... 31
Table 7.1: Consumption of thermal and electrical energy (European Union, 2013) .............................. 32
Table 8.1: Major pollutants generated at various stages of leather production ..................................... 35
Table 8.2: Material balance of salt applied in curing one ton of raw hides, with 400 kg salt applied in
curing (40% on weight of raw stock) (Lampard, 2002) ........................................................................... 36
Table 8.3: Summary of selected alternative ‘best available’ technologies and their environmental
benefits (Jackson-Moss, personal communication) ................................................................................ 41
xi
ACRONYMS AND ABBREVIATIONS
WRC
Water Research Commission
NATSURV
National survey
FAO
Food and Agricultural Organization
pH
The measure of acidity or alkalinity of a chemical solution, from 0 to 14
NWA
National Water Act
DWS
Department of Water and Sanitation
WSA
Water Services Act
COD
Chemical oxygen demand
TDS
Total dissolved solids
TSS
Total suspended solids
SWI
Specific water intake
SWU
Specific water use
BOD
Biological oxygen demand
CAS
Conventional activated sludge
TKN
Total Kjeldahl nitrogen
HVLP
High-volume low-pressure
LIRI
Leather Industries Research Institute
xii
GLOSSARY OF TERMS
Basic chromium sulphate – Chromium (III) hydroxide sulphate; Cr(OH)SO4.
Bating – Using enzymes to dissolve and remove some of the interfibrillar proteins of delimed hides and
skins to produce softer leather with a smoother grain surface.
Beamhouse/limeyard – The portion of the tannery where hides are soaked, limed, fleshed and
unhaired when necessary prior to the tanning process.
Bovine – Adjective for animals from the Bovinae sub-family, which includes cattle and buffalo.
Brining – Curing hides by washing and soaking in a concentrated salt solution.
Chrome tanning – Using chromium salts (usually one-third basic chromium sulphate) in the tanning
process.
Collagen – The principal fibrous protein in the corium of a hide of skin.
Conditioning – Softening dried leather by introducing controlled amounts of moisture.
Conventional processing – Tanning processes not modified to reduce environmental impact.
Crust leather – Leather that has simply been dried after tanning, retanning and dyeing, without further
finishing.
Curing – Processes used to prevent bacteria putrefying or rotting hides and skins after they have been
flayed in the slaughterhouse.
Degreasing – Removing, as far as possible, the natural grease in the skin.
Deliming – Removing lime from hides or skins using ammonium salts and/or weak acids.
Drums – Large wooden, stainless steel or polypropylene drums that are rotated at speeds suitable for
a particular tanning process.
Dyeing – Imparting colour on leather by treating it with natural or synthetic dyestuff.
Epidermis – The outer surface layer of the hide or skin that holds the hair roots. It is removed during
the leather-making process.
Fatliquoring – Introducing an emulsion of fats and oils into the wet leather to provide lubrication and
subsequent softness and flexibility.
Fellmongery – Plant in which goatskins or sheepskins are processed to the pickled state.
Filling – Drumming process whereby substances are added to vegetable-tanned leather to create more
compact leather such as vegetable-tanned sole leather.
Finishing – a) Mechanical operations, such as conditioning, staking, buffing, dry milling, polishing and
plating/embossing, that improve the appearance and the feel of leather. b) Applying or fixing a surface
coat to the leather.
xiii
Fleshing – Removing the fleshy, fatty material situated on the insides of hides and skins.
Fleshings – Pieces of subcutaneous tissue, fat and flesh separated from the hide during fleshing.
Float – Volume of water present in the tanning vessel.
Full-house tanning – The total tanning and finishing processes, including beamhouse, tanyard and
dyehouse processes.
Grain – The outermost section of leather that is kept intact in full-grain leathers, but smoothed to some
degree in corrected grain leathers.
Green fleshing – Fleshing performed prior to liming and unhairing.
Hides Skins of larger animals such as cattle.
Horsing – Ageing of hides or skins after tanning or fatliquoring on wooden pallets or a wooden frame.
Leather – A general term for hide or skin that has been treated by tanning or another process to make
it more pliable and to preserve it against decay.
Limed hide or skin – Hide or skin obtained after liming.
Lime fleshing – Fleshing performed after liming and unhairing.
Liming – Soaking in an alkali solution to prepare the skins/hides for tanning and assisting with removal
of hair or wool, epidermis and subcutaneous tissue.
Limeyard Area in the tannery where the hides are soaked and unhaired.
Mineral tanning – The tanning process where mineral salts (usually chromium, but occasionally
aluminium or zirconium) are the tanning agents.
Neutralising Deacidifying chrome-tanned leather.
Ovine – Relating to or resembling sheep.
Paddles – Large wooden vessels fitted with wooden paddles that are rotated to create a stirring action.
Pickled pelt – A skin that has been pickled.
Pickling – The acidification process that follows bating, whereby the skin or hide is immersed in brine
and acid.
Protein – A complex naturally occurring organic material consisting of long interwoven chains of amino
acids.
Raw hide – Untanned hide.
Retanning Applying special products (such as synthetic tannins) to leather to impart specific
properties such as softness, evenness of colour.
xiv
Rinsing/running water washes – Washing accomplished by the continuous inflow and outflow of water
in a treatment apparatus.
Sammying – A mechanical process where excess moisture is squeezed out of the hide material.
Setting – Mechanical operation to remove water and wrinkles, and to flatten the surface of leather.
Settleable solids – The volume of material that settles out of a solution in a defined time period.
Shaving – The process whereby leather is mechanically trimmed to the desired thickness.
Shavings – The fragments obtained from shaving.
Soaking – The first process in the manufacture of leather, which is used to rehydrate and wash the
hides or skins.
Skin – The pelt of a small animal such as a calf, pig or sheep.
Split – The non-grain fraction of a split hide.
Splitting – The horizontal splitting of hides and skins into a grain layer and, if the hide is thick enough,
a flesh layer.
Syntans – Synthetic tanning agents.
Tallow – Non-edible or ‘technical’ fat.
Tanning – The process whereby animal hides and skins are converted to leather.
Tanyard – The part of the tannery where pickling, tanning and basification processes are performed.
Total Kjeldahl nitrogen – The sum of nitrogen present as organic nitrogen, ammonia and ammonium
compounds measured using the Kjeldahl technique.
Trimming – Removing undesirable portions of hides and skins by cutting.
Trimmings – The residues arising from trimming hides and skins.
Upholstery leather – Leather manufactured for covering furniture or for seats of aircraft or vehicles.
Vegetable tanning – Using tannins from plant origin (such as mimosa tree extract) for tanning.
Wetting back – Rehydrating hides or skins.
Wet blue – Chrome-tanned hide that has been sammyed to remove surplus moisture. Further
processing is required to produce leather.
Wet white – A hide or skin that has been limed and tanned with non-chromium agents. It remains off-
white in colour and moist.
1
INTRODUCTION
1.1 Background
In response to several interrelated factors, including higher costs of waste disposal, more stringent
legislative requirements, and increasing environmental awareness, industries are constantly
implementing more sustainable methods to reduce qualitative and quantitative industrial pollutant loads
and to reuse water and waste.
Manufacturing and processing industries consume significant quantities of energy and water, and
generate large volumes of wastewater. This prompted the Water Research Commission (WRC) of
South Africa to commission 16 national surveys (NATSURVs) of various agricultural and non-
agricultural industries (malt brewing, poultry, red meat, edible oil, sorghum malt, beer, dairy, sugar, metal
finishing, soft drink, tanning/leather finishing, laundry, textile, oil and refining, and power generating),
culminating in the publication of 16 separate NATSURV documents between 1986 and 2001. These
documents included information about production processes, water usage, solid waste generation, and
wastewater quality, quantity, and treatment practices. Significant market-related changes have taken
place in many industries over the decades. Much of the information in the original NATSURV series is
outdated; therefore, the WRC commissioned a new series of NATSURV documents. The previous
NATSURV for the tanning and leather finishing industry (WRC TT 44/90, ISBN 0947 447 60 1) was
published in 1989.
1.2 Aims, Scope and Limitations
The environmental issues facing the tannery industry are of particular concern, and wastewater
discharge, air emissions, solid waste disposal, environmental pollution, and employee health and safety
concerns have become increasingly important. Globally, specific discharge standards, and the
occupational safety and health exposure limits are being scrutinised and adjusted. Furthermore, there
is international advocacy to finding alternatives to salt curing and for cleaner production. In general, the
industrialised world has adopted technologically cleaner production methods, whereas the developing
world is mainly promoting waste minimisation while slowly transitioning into cleaner production.
The main objective of this NATSURV document is to stimulate water saving and pollution mitigation by
serving as a comprehensive guide and benchmark tool for a number of stakeholders, including local
governments, industry players, academics, researchers and engineers.
The specific aims of the survey were to:
x Provide a detailed overview of the tanning and leather finishing industry in South Africa, its changes
since 1989 and its projected change(s).
x Critically evaluate and document the ‘generic’ industrial processes of the tanning and leather
finishing industry in terms of current practice, best practice and cleaner production.
x Determine the water consumption and specific water consumption and recommend targets for use,
reuse, recycling and technology adoption.
x Determine wastewater generation, and typical pollutant loads and best practice technology
adoption.
x Determine local electricity, water and effluent by-laws within which these industries function, and
critically evaluate if the trends and indicators are in line with water conservation demand
management and environmental imperatives.
x Critically evaluate the specific industry water (including wastewater) management processes
adopted and provide appropriate recommendations.
2
x Evaluate the industry adoption of the following concepts: cleaner production, water pinch, energy
pinch, life cycle assessments, water footprints, wastewater treatment and reuse, best available
technology and ISO 14 000 to name a few.
x Provide recommendations on the best practice for this industry.
3
OVERVIEW OF THE TANNING AND LEATHER FINISHING INDUSTRY
2.1 Overview of the Tanning Process
The tanning industry processes hides and skins into leather. This is a chemical process that uses large
quantities of water, and hence tanneries produce considerable amounts of both liquid and solid wastes.
Tanneries play an important role in processing a by-product or waste from the meat industry, namely,
the hides and skins. Without the tanning industry, these hides and skins would have to be disposed in
landfill sites or incinerated. Tanneries therefore solve one pollution problem, but create many others
during the processing of hides or skins into leather or partially processed forms of leather. This is true
for most types of leather except for certain exotic skins, where the animals are farmed specifically for
their skins.
‘Hides’ refer to the skin covering from large animals such as cows, oxen, and large game. ‘Skins’ refer
to the skin covering of smaller animals, such as sheep, goats, ostriches, crocodiles and small game.
The tanning process can be divided into three main stages (see Section 2.1.1 to Section 2.1.3), with
each one of these being further sub-divided.
2.1.1 Wet blue or fellmongery processing
Wet blue or fellmongery processing involves the processing of raw hides into a product called ‘wet blue’.
Wet blue is a stable product that cannot rot, and is an internationally traded commodity. The production
of wet blue is the most polluting of all tanning operations. Fellmongery processing refers to the
conversion of raw sheepskins into pickled sheepskins.
2.1.2 Dyehouse operations
Dyehouse operations include splitting and shaving skins or hides to a defined thickness, neutralising,
retanning, dyeing and fatliquoring. After dyeing, the leather is referred to as ‘crust’ leather. The effluent
from the dyehouse pollutes less than the effluent from wet blue processing. Tanneries that carry out the
crusting process usually process the crust leather further into finished leather.
2.1.3 Leather finishing
The finishing of leather involves applying a film to the leather surface to give the leather protection and
durability for its intended purpose. Very little water is used in leather finishing.
It is important to note that not all tanneries carry out all processing stages as discussed in Section 2.1.1
to Section 2.1.3. It has become more common in recent times that certain tanneries will only process
pickled sheepskins or wet blue, and then sell these to other facilities for further processing. This is true
not only globally, but also in South Africa. This change in production has had a major impact on the
effluent and solid waste produced by tanneries, as most pollution is produced when processing hides
or skins up to the pickled or wet blue stage. Many developing countries process pickled skins and wet
blue, and then export this semi-processed material to developed countries that have much stricter
environmental regulations. Some of the newer wet blue plants have been built close to abattoirs or the
source of hides, and are often a way of vertically integrating the value chain for the feedlot businesses.
More information on the tanning processes can be found in Section 3.2.
4
2.2 Changes in the Tanning Industry Since the Previous NATSURV
Since the last NATSURV on the tanning and leather finishing industry was published in 1989, several
changes have taken place. These can be broadly outlined:
x There are fewer tanneries in South Africa.
x Wet blue plants have increased in size.
x Many small tanneries processing hair-on gameskins and taxidermists have been established.
x Many small ostrich tanneries were established, but this number has subsequently decreased.
The implementation of the Motor Industry Development Plan had a significant positive economic effect
on automotive leather production. This resulted in international tanning groups establishing themselves
in South Africa. Currently, there are two tanneries in South Africa that produce large quantities of
automotive leather.
As a result of the deregulation of the ostrich industry, a number of smaller ostrich tanneries were
established to compete with larger ostrich tanneries. Many of these have subsequently closed, or have
been bought by bigger ostrich tanneries. There are three major players left tanning ostrich leather, but
small quantities of ostrich leather are still processed by one or two small tanneries tanning a mixture of
different leathers.
The wet blue plants in South Africa have generally increased in size, but have reduced in number. This
is mainly due to the closure of wet blue plants associated with the automotive industry, and because
South Africa now processes less imported hides for the automotive sector. However, some new wet
blue tanneries have been established. Some feedlot operators have bought into these wet blue plants
in an effort to add value to their product.
Hunting has become big business in South Africa. There are large numbers of gameskins that are
tanned with the hair on or processed by taxidermists. These are too numerous to include in the
NATSURV. Although these taxidermists do use water and hence produce effluent, many of the effluent
streams are reused. Most of their effluent is a soaking effluent. They do not unhair the skins. It is
estimated that in total they consume less water than one large tannery. Many of these small tanneries
are located on farms, use their own sources of water, and discharge into ponds or evaporation dams.
2.3 Size of the Industry
2.3.1 Hide and skin production: Global and local trends
The Food and Agriculture Organization (FAO) of the United Nations regularly publishes the “World
statistical compendium for raw skins and hides, leather and leather footwear”. The latest version of this
document (FAO, 2016) contains data from 1999 to the years 2013 and/or 2014. Unfortunately, only
bovine, ovine and goat hides and skins are included in the document. Pigskins, which are produced in
large numbers in Asia, are excluded, and no comprehensive data is available for ostrich, crocodile and
other ‘exotic’ species that are important from a South African perspective. Tanning and exporting of
these exotic skins and hides is a lucrative industry in South Africa. This sector of the industry has
increased over the years.
As developing countries, Latin America produces 66%, Africa 60% and Asia 96% of bovine hides, sheep
and lambskins, and goat and kidskins for leather (Figure 2.1). Although the developing world produces
more raw hides and skins than the developed world, the developed world is a nett exporter of hides for
leather, while the developing world is a nett importer.
5
Figure 2.1: Global production of bovine, ovine and goat hides and skins in 2013 (FAO, 2016)
In 2013, South Africa accounted for 0.9% (wet salted weight) and 2.7% (dry weight) of world bovine
hides and ovine skins. There has been an upward trend in the production of bovine hides in South Africa
from around 2.4 million pieces in 1999/01 to 3.4 million pieces in 2014. Over the same period, the
production of sheepskins has fluctuated between 8.5 and 9.0 million pieces. Unlike the developing world
as a whole, South Africa is a nett exporter of hides and skins with a gross export value of US$45.5 million
for bovine hides and US$172.3 for ovine skins in 2013 (FAO, 2016).
2.3.2 Leather and footwear production: Global and local trends
Although developing countries produce the largest proportion of bovine (66%) and ovine (60%) hides
and skins, they produce even larger percentages of bovine ‘heavy’ (80%), bovine ‘light’ (67%), and ovine
(83%) leather (Figure 2.2). Because the stringent environmental policies in many developed countries
make the operation of tanneries difficult, they export the hides and skins to be converted to leather in
developing countries. South Africa is anomalous as it falls into the FAO category ‘other developed
countries’ together with Japan and Israel, and is the only African country to do so (FAO, 2016).
Figure 2.2: Global production of bovine, ovine and goat leather in 2013 (FAO, 2016)
In South Africa, the production of heavy leather from bovine animals has increased gradually since
1999, while the production of light leather from bovine animals has shown a slight decrease.
0
50
100
150
200
250
300
350
Bovine
million hides/skins
Sheep & lambskins Goat & kidskins
Latin America
Africa
Asia
North America
Europe
Oceania
Other developed
6
According to FAO data, the production of leather footwear and footwear exports in South Africa has
increased significantly since 2010. Conversely, imports have decreased. The value of exports in 2013
was US$45.6 million. However, these trends are not supported by anecdotal evidence from key players
at tanneries, who stated that the shoe leather industry in South Africa has declined in recent years.
Figure 2.3: Trends in production and trade of leather footwear in South Africa (FAO, 2016)
2.3.3 South African tanneries
Table 2.1 shows the number of hides and/or skins by South African tanneries. The data in Table 2.1 is
categorised according to the types of skin and/or hide and the processing methods used. The tanning
processes are described in Chapter 3.
According to the data collected during the survey and discounting tanneries that process wet blue to
finished leather (finishing tanneries), large- and medium-sized tanneries (≥ 100 hides/day) process
approximately 10 900 to 11 400 wet blue hides, 15 000 to 17 000 pickled and 500 wool-on sheepskins,
and between 1 600 and 2 150 crocodile or ostrich skins per day. Only 200 hides/day are vegetable-
tanned.
Table 2.1: Size of the tanning and leather finishing industry in South Africa
Tannery
Type
Production (typical)
Wet blue and pickled skins
Tannery 1
Wet blue and pickled
sheepskins
3 500-4 000 hides/day from raw to wet blue
4 000-5 000 sheepskins/day from raw to pickled
Tannery 2
Wet blue and pickled
sheeps
kins
2 700 hides/day from raw to wet blue
5 000 sheepskins/day from raw to pickled
Tannery 3
Wet blue and pickled
sheepskins
1 800 hides/day from raw to wet blue
2 000 sheepskins/day from raw to pickled
Wet blue
Tannery 4
Wet blue
1 300 hides/day from raw to wet blue
Tannery 5
Wet blue
1 000 hides/day from raw to wet blue
Tannery 6
Wet blue
600 hides/day from raw to wet blue
Finishing tanneries
Automotive
Tannery 7
Automotive upholstery
4 000 hides/day from wet blue to finished leather
Tannery 8
Automotive upholstery
4 000 hides/day from wet blue to finished leather
Shoe upper
Tannery 9
Shoe upper leather
500 hides/day from wet blue to finished shoe upper
leather
7
Tannery
Type
Production (typical)
Tannery 10
Shoe upper leather
350 hides/day from wet blue to finished shoe upper
leather
Other
Tannery 11
Furniture upholstery
700 hides/day from wet blue to finished leather
Tannery 12
Upholstery
300-400 hides/day from wet blue to finished leather
Tannery 13
Furniture upholstery
< 100 hides/day from wet blue to finished leather
Exotic leather
Tannery 14
Ostrich and crocodile leather
500 ostrich skins/day from raw to finished leather
1
000 crocodile skins or small gameskins/day
from raw to
finished leather (crocodiles) and hair-on (gameskins)
Tannery 15
Ostrich and crocodile leather
250 ostrich skins/day from raw to finished leather
100-150 crocodile skins/day from raw to finished leather
Tannery 16
Ostrich leather
100 skins/day from raw to crust leather
Mixed production
Tannery 17
Mixed production
< 100 hides/day
Tannery 18
Mixed production
< 50 hides/day
Tannery 19
Mixed production
< 100 hides/day
Tannery 20
Mixed production
< 50 hides/day
Tannery 21
Mixed production
< 50 hides/day
Tannery 22
Mixed production
< 50 hides/day
Tannery 23
Mixed production
< 50 hides/day
Tannery 24
Mixed production
< 50 hides/day
Tannery 25
Mixed production
< 50 hides/day
Pickled sheepskins
Tannery 26
Pickled sheepskins
4 000-5 000 sheepskins per day from raw to pickled
sheepskins
Gameskins
Tannery 27
Hair-on gameskins
< 50 hides/day
Tannery 28
Hair-on gameskins
< 50 hides/day
Tannery 29
Hair-on gameskins
< 50 hides/day
Other
Tannery 30
Crocodile leather
650 skins/month from raw to finished leather (< 50/day)
Tannery 31
Wool-on sheepskins
500 sheepskins/day from raw to wool-on sheepskins
Tannery 32
Hair-on hides
< 50 hides/day from raw to hair-on hides
Tannery 33
Vegetable-tanned leather
200 hides/day from raw to vegetable-tanned leather
Tannery 34
Hair-on hides
< 50 hides/day from raw to hair-on hides
Tannery 35
Suede
< 50 hides/day
8
Figure 2.4 shows the geographical distribution of some of the main tanneries in South Africa.
Figure 2.4: Geographical distribution of tanneries in South Africa
9
TANNING AND LEATHER FINISHING PROCESSES
This chapter provides an overview of the major tanning and leather finishing processes applied in South
Africa.
3.1 Categorisation of the Tanning Industry in South Africa
The main categories in the tanning industry are defined as follows:
Hides/skins: Bovine (cattle skins)
Ovine (sheepskins)
Exotic (ostrich, crocodile and game)
Processes: Wet blue (chrome tanning)
Wet white tanning
Vegetable tanning
Leather finishing
Products: Automotive upholstery
Shoe uppers
Furniture upholstery
Hair-on hides
Products from exotic skins
3.2 Tanning Processes
The main purpose of tanning and leather finishing industries is producing durable material for upholstery,
and for making handbags, shoe uppers and other clothing items. Although useful by-products are
generated during tanning, much of the waste is potentially toxic. In keeping with the global ‘Green
Economy’ strategy, there are already cleaner production methods available (refer to Chapter 6 and
Chapter 8). In addition, a great deal of research is being conducted worldwide into the use of ‘wastes’
as resources such as novel feedstocks to produce value-added products. In the future, sustainable
solutions may be found to deal with tannery ‘waste’.
Figure 3.1 shows the hide and skin preparation processes and subsequent tanning processes in a
typical wet blue tannery, together with by-products and wastes. The figure is followed by a summarised
description of each of the processes.
10
Figure 3.1: Processes, by-products and waste from wet blue tanning (adapted from European Union,
2013)
11
3.2.1 Hide and skin reception and storage
The reception stage consists of sorting and trimming: hides and skins are sorted into grades by size
and/or weight and quality, and some of the edges (legs, tails, faces, udders, etc.) of the raw (green,
chilled or chemically cured) and salted (dry salted or wet salted) hides and skins may be removed (green
fleshing). If the hides are not going to be processed immediately, they may be cured (usually by salting)
or chilled.
3.2.2 Process stages
The processing of raw (green, chilled or chemically cured) and salted (dry salted or wet salted) hides
and skins is divided into two sections, namely, the beamhouse section (Section 3.2.2.1), and the tanyard
section (Section 3.2.2.2), with a number of processes taking place in each section.
3.2.2.1 Beamhouse (or limeyard) section
Soaking
Soaking reintroduces water into the hides and skins, washes out any preservatives (usually salt), blood,
manure, urine and dirt, and softens the hides and skins for subsequent processing.
Green fleshing
Fleshing is the mechanical removal of fats and flesh from the inside of hides or skins. Fleshing can be
accomplished before or after liming, and there are advantages and disadvantages to each. From an
environmental perspective, green fleshing is preferable as the tissue is not contaminated with chemicals,
and the amount of chemicals needed for unhairing and liming are reduced. This reduces the amount of
chemicals in the effluent from downstream processes.
Unhairing and liming
The liming and unhairing processes are usually carried out simultaneously. Chemicals (Table 3.1) are
used to:
x Partially hydrolyse polypeptides to relax the structure of the hide or skin.
x Solublise globular proteins.
x Saponify fats.
x Swell hides.
In the case of sheepskins, the wool is recovered as a by-product by a paint unhairing process.
Lime fleshing
Lime fleshing is similar to green fleshing, but it takes place after unhairing and liming. The quality of
hides from lime fleshing is typically superior to those produced using green fleshing. Lime fleshing is the
method of choice in South African tanneries.
Lime splitting and trimming
Splitting is a form of trimming where the hide is mechanically divided into a grain layer and a flesh layer.
This can be accomplished after liming or chromium tanning. Some trimmings may also be processed to
leather (Figure 3.1). Lime splitting reduces the amount of chemicals required in downstream processes.
In South Africa, splitting and shaving are usually performed after tanning.
Deliming and bating
Deliming and bating are processes that use chemicals and enzymes (Table 3.1) to:
12
x Remove residual chemicals and reduce the pH of the hides and skins.
x Soften the hides and skins to assist with chemical penetration in subsequent processing stages.
3.2.2.2 Tanyard section
Degreasing
Excessive amounts of grease in the hide or skin may cause non-uniform penetration of tan or dye. This
causes complications with the finishing processes and creates dark and greasy patches on the finished
leather. Degreasing is particularly important before chrome tanning as chromium salts can react with
the greases and form insoluble chromium soaps, which are very difficult to remove.
Pickling
Pickling is a chemical (Table 3.1) process whereby:
x Acid is added to lower the pH to between 2 and 3 for better penetration of the tanning chemical.
x Salt is added to prevent the hide from swelling under acid conditions.
In the case of pickled sheepskins, the picking process preserves the skin and is the final processing
step.
Tanning
Tanning is accomplished by adding tanning chemicals (Table 3.1) into a drum containing the hides for
an appropriate time period. Most of the ‘leather’ is traded as wet blue. In the case of wet blue, the tanning
agent is trivalent chrome tanning salts. In the case of wet white or metal-free leather, glutaraldehyde is
used as tanning chemical. It needs to be stressed that tanneries only use trivalent chromium, CrIII, Cr3+
or CrIII, which has been found to be non-toxic. Limits for disposal thereof have been relaxed in the
European Union and North America.
Basification is the addition of a mild alkali into the tanning drum to ensure binding of the tanning chemical
to the hide or skin. After tanning, a final wash is carried out to remove any unbound chemicals from the
hide or skin.
Sammying
Sammying is the mechanical removal of water from the wet blue or wet white to a moisture content of
approximately 50%. Drying the hides increases the effectiveness of the downstream splitting and
shaving processes.
Figure 3.2: Wet blue (left) and pickled skins (right)
13
3.2.3 Dyehouse process stages (wet finishing and dry finishing)
Splitting and shaving
Splitting and shaving are mechanical methods used to reduce the thickness of the hide or skin to the
thickness required in the final leather. Splitting after tanning is known as chrome splitting.
Washing
The skins or hides are washed in water to remove residuals from the splitting and shaving operations.
Neutralisation
Neutralisation is the raising of the pH of the wet blue or wet white to allow penetration of chemicals in
subsequent process stages.
Retanning
Retanning is the introduction of different types of chemical into the wet blue or wet white that impart
specific properties (such as flexibility, fullness and texture) on the final leather.
Dyeing
Dyeing is the addition of either powder or liquid dyes to give the leather the desired colour.
Fatliquoring
Fatliquoring is the addition of emulsified oils to make the leather soft and flexible.
Fixation
Fixation is the chemical binding of all the retanning chemicals, dyes and fatliquors to the leather by
lowering the pH in the drum using formic acid.
Final wash
The final wash is carried out to wash out any residual unbound chemicals from the dyehouse processes.
Drying, mechanical finishing and coating
After drying, further finishing of the leather may be performed to achieve the desired product.
3.2.4 Beneficial use of tannery by-products
As shown in Table 3.1, wool and hair may be used to manufacture textiles. Fatty trimmings and fleshings
from the beamhouse are typically rendered at a registered facility to make animal feed. Collagen (for
example for sausage casings) may be manufactured from beamhouse splits and trimmings. In addition,
leatherboard may be manufactured from tanyard splits and trimmings (UNIDO, 1991; Buljan & Král,
2015).
3.3 Chemicals and Products Used in Tanning Processes
Table 3.1 summarises the aims of applying these chemicals in the tanning and leather finishing industry.
14
Table 3.1: Chemicals used in various processes in the tanning industry
Process
Chemicals
Purpose
Wet blue process stages
Soaking
Biocides, surfactants
, degreasers,
enzymes
Reintroduce water and washing of
chemicals and dirt
Liming and
u
nhairing
Lime, sodium sulphide, sodium
hydrosulphide, caustic soda
Chemical
ly remove hair and swell skins
Deliming and
bating
Ammonium sulphate, ammonium chloride,
formic acid, proteolytic enzymes
Remove
lime and calcium
L
ower pH
Soften
hide
Pickling
Salt, sulphuric acid, formic acid, sodium
formate, fungicide
Lower pH of the hide or skin to allow
proper penetration of tanning chem
icals
Tanning
Trivalent chrome tanning salts (wet blue) or
glutaraldehyde (wet white)
Tanning
Basification
Magnesium oxide and sodium bicarbonate
Ensure binding of tanning chemicals to
hide or skin
Dyehouse process stages
Washing
Surfactants
Reintrodu
ce water
S
often and remove shavings, oils or
greases
Neutralisation
Sodium bicarbonate, sodium formate
Increase
pH to allow chemical penetration
Retanning
Syntans, resins, vegetable tannins
Give specific leather
like properties
Dyeing
Dyestuffs
Give the
desired colour
Fatliquoring
Fatliquors (emulsified oils)
Soften
leather and make it flexible
Fixation
Formic acid
Lower
pH to ensure chemical binding of
the chemicals in the previous steps
15
WASTE AND EFFLUENT DISCHARGE REGULATIONS
4.1 National Policies
The Constitution of South Africa stipulates that everyone has the right to an environment not harmful to
their health or well-being. This includes the right to environmental protection for the benefit of present
and future generations through reasonable legislative and other measures to prevent pollution and
ecological degradation, promote conservation, and secure ecologically sustainable development and
use of natural resources. These rights must be balanced with the promotion of justifiable economic and
social development. Regulation that addresses these rights falls under the responsibility of the
Department of Environmental Affairs. The Bill of Rights in the Constitution of the Republic of South Africa
(Act 108 of 1996) enshrines the concept of sustainability. Rights regarding the environment, water,
access to information, and just administrative action are specified in the Act.
These rights and other requirements are further legislated through the National Water Act (NWA), Act
36 of 1998. The NWA provides the legal basis for water management in South Africa by ensuring
ecological integrity, economic growth, and social equity when managing water use. Other policies
relevant to the tannery industry are the National Environmental Management Act, 1998 (Act 107 of
1998), the National Environmental Management: Waste Act, (Act 59 of 2008), and the National
Environmental Management: Air Quality Act (Act 39 of 2004). Broadly speaking, these acts outline the
requirements for storing and handling waste on-site, licensing requirements, establishing waste
management plans, setting limits for air emissions, and setting penalties for offences.
Figure 4.1: National environmental and water policies relevant to the tannery industry
The NWA introduced the concept of Integrated Water Resource Management, which provides for
resource- and source-directed measures to manage the aquatic environment. Resource-directed
measures aim to protect and manage the environment that receives water. Source-directed measures
aim to control the impact on the receiving environment by preventing pollution, reusing water, and
treating wastewater. The integration of resource- and source-directed measures forms the basis of the
hierarchy of decision-making aimed at mitigating the effect of waste generation. This hierarchy is based
on a precautionary approach. The order of priority for water and waste management decisions and/or
actions is shown in Figure 4.2.
South African Constitution
Bill of Rights
(Act No. 108 of 1996)
National Environmental
Management Act
(Act No. 107 of 1998)
National Water Act
(Act No. 36 of 1998)
National Environmental
Management Waste Act
(Act No. 59 of 2008)
National Environmental
Management Air Quality Act
(Act No. 39 of 2004)
16
Figure 4.2: Hierarchy of decision-making intended to protect the environment
4.1.1 Water policy
The recently formed Department of Water and Sanitation (DWS), formerly the Department of Water
Affairs and the Department of Water Affairs and Forestry, is the water and sanitation sector leader in
South Africa. The DWS is the custodian of South Africa’s water resources, and of the NWA and the
Water Services Act (WSA), Act No. 108 of 1997. The DWS is also the national regulator of the water
services sector.
The NWA provides the legal framework for the effective and sustainable management of water
resources within South Africa. The Act aims to protect, use, develop, conserve, manage and control
water resources as a whole, promoting the integrated management of water resources with the
participation of all stakeholders.
The Act stipulates the requirements for, among others:
x Developing a national water strategy and catchment management agencies.
x Protecting water resources through classification.
x Setting reserves (basic human need and ecological).
x Determining resource quality objectives.
x Promoting pollution prevention.
The Act provides for penalties for non-compliance.
The WSA deals mainly with water services or potable (drinkable) water and sanitation services supplied
by municipalities to households and other municipal water users. The Act contains rules about how
municipalities should provide water and sanitation services. Within each municipal area, by-laws are
developed that outline the water supply, as well as effluent discharge regulations and tariffs for that area
(see Section 4.2).
4.1.2 Wastewater policy
Under the NWA, norms and standards for the quality of wastewater or effluent prior to discharge to
sewer have been set. These consist of general and special standards and set limits for aspects such as
pH, temperature, chemical oxygen demand (COD), suspended solids and metals. The test methods to
be performed to determine these levels are also specified. Environmentally sensitive areas where
special more stringent standards apply are listed. Any industries, or municipal or private wastewater
treatment works discharging to rivers or the sea must comply with these limits. In turn, the entity
17
operating a wastewater treatment works must set limits for industries discharging to the works such that
the DWS final discharge limits can be met.
4.2 By-laws at Local Government Level
The handling and management of industrial effluent discharge creates problems for local authorities.
The discharge of large volumes of industrial effluents into municipal sewerage systems, and in
particular the discharge of effluents containing unwanted substances, can have a detrimental effect
on the operation of the biological processes of the sewage treatment works resulting in non-
compliance of the treated effluent with the NWA.
To prevent industries in a particular municipal area from discharging effluent streams that may affect
public streams or the environment negatively, local authorities set requirements with which industries
must comply before they discharge to the municipal sewer. In accordance with these requirements,
industries need to apply for special permits to discharge effluent to the wastewater treatment works.
The by-laws set limits for the quality of the effluent, as well as limits on the discharge of any specific
undesirable substances. In these permits for acceptance of industrial effluent by the municipality, the
maximum volume that can be discharged is indicated, as well as any special measures relating to
the quality of industrial effluent for the specific industry. By virtue of these by-laws and permit
systems, the local municipalities have some control over the types and quantity of industrial effluent
discharged into their sewage treatment works.
The problem with the by-laws for industrial runoff is in their application, and in particular the
calculation of effluent charges for certain industries carrying high loadings and/or undesirable
substances to the sewer discharge. The laws can vary significantly from one municipality to another
to calculate effluent charges, method and frequency of sampling, and limits placed on specific
pollutants that may be discharged. These differences in by-laws and control measures not only lead
to confusion with the regulatory authorities, but also by the industries they serve.
4.2.1 Industrial effluent tariffs
The calculation of industrial effluent tariffs varies significantly from one municipality to the next, depending
on the cost recovery systems of the municipalities, types of industry discharging to the municipal sewer,
and the receiving wastewater treatment works.
4.2.1.1 Principles in respect of industrial effluent charges to recover costs
A rational system should be used to calculate tariffs. The system should ensure that the total annual
cost for the sewerage system and the wastewater treatment plant are recovered. The following are
important principles relating to the preparation of industrial effluent charge calculations:
x The ‘polluter must pay’ principle contained in the NWA should apply. Industries should pay for
their portion of the transportation and treatment costs for effluent disposal or dumping.
x All sewerage rates should be calculated according to the same rationale. Each local municipality
should strive to formulate their tariff structure in such a way that neither a loss nor a profit is
made on the wastewater treatment system.
x As is the case with water and electricity tariffs, the main objectives of sewerage tariffs are firstly
to recover the full costs of providing the service, and secondly to prevent unnecessary waste
and pollution.
18
x The rate charged for an industry must apply to the proportional costs for transport and treatment
of discharge from the relevant industry. These costs include amortisation interest on capital
works.
x The transport costs for the effluent should not be based on geographical location – the same
unit rates for transport should apply to all.
4.3 Summary of Effluent Quality Requirements Relevant to the Tanning Industry
Table 4.1 shows the effluent quality requirements of selected municipalities with tanneries operating
within their area of jurisdiction.
Table 4.1: Effluent standards of municipalities for water quality parameters regulated for effluents from
tanneries
Local authority/
country
pH
COD
(mg/L)
σ-phosphate
(mg/L as P)
TSS
(mg/L)
Electrical
conductivity
(mS/m)
Sulphate
(mg/L as SO4
)
Total
chromium
(mg/L as Cr)
Chloride
(mg/L)
South Africa
City of
Tshwane
6-10
5 000
10 2 000
300 1 800
5 100
City of Cape
Town
5.5
-12
5 000
25 1 000
500 1 500
10 1 500
Nelson
Mandela Bay
Metro
6-12
10 000
- 1 000
500 1 500
20 1 000
Ekurhuleni
6-10
5 000
50 1 000
500 1 800
20 100
Oudtshoorn
6.5
-10
4 000
10 1 000
500 250 5 500
Mossel Bay
6-11
3 000
- 1 000
500 500 10 1 000
Global
France*
6.5
-
8.5
2 000
- 600 - - - -
Italy*
5.5
-
9.5
500 - 200 - 1 000
4.0 1 200
India*
5.5
-
9.0
- - 100 - 1 000
2.0 -
* Buljan and Král, 2011
19
WATER USE AND MANAGEMENT
5.1 Water Use in the Tannery Industry
Selected tanneries representing the different types, sizes and geographic locations in the country were
visited and a survey undertaken of the volumes of water used in the preparation, tanning and finishing
processes. The information was used to calculate the specific water intake (SWI).
5.2 Water Source and Consumption
During leather production, hides and skin undergo a number of successive beamhouse, tanning and
finishing operations. Process water is a vital raw material used in large quantities in almost all
preservation, beamhouse, tanning and finishing processes. Between 25 L and 80 L of process water is
used to process 1 kg of hide (UNIDO, 1991; Covington et al., 2000; Hauber, 2000; Buljan, 2005; Buljan
& Král, 2011, Buljan & Král, 2015).
Table 5.1 shows the typical volume of process water used at each processing stage by the industry at
large (global data).
Table 5.1: Typical process water consumption (Ramanujam et al., 2010)
Type of process
Volume of water used per raw hide weight (L/kg)
Raw to finish
4
0-45
Raw to vegetable
-tanned
25
-30
Vegetable
-tanned to finish
50
-60 (per kilogram of vegetable-tanned leather)
Raw to wet blue
25
-30
Wet blue to finish
20
-25 (per kilogram of wet blue)
Crust to finish
10
-15 (per kilogram of crust weight)
Most tanneries visited for this study use municipal water. However, the cost of water differs from
municipality to municipality. Some tanneries supplement municipal water with borehole water or storm
water during the rainy season. Retanning and leather finishing tanneries consume less water than full-
house tanneries because the downstream processes are less water intensive. This is one of the
advantages of retanning and leather finishing tanneries, as they produce less polluted and smaller
volumes of wastewater than full-house tanneries.
5.3 Water Use and Water Management of the Tanneries Visited
The calculated SWI values of the 10 selected tanneries visited are given in Table 5.2. The use per
process (where this information is available) for different types of tannery are given in Table 5.3.
20
Table 5.2: Water use and management of tanneries visited (Tanneries A1-A5)
Tannery identification
A1 A2 A3 A4
A5
Skins
, hides, raw
material
Exotic
Exotic
Bovine
Mostly
bovine
Mostly bov
ine
Production process
Full
-house tanning
Full
-house tanning
Re
tanning and leather
finishing
Chrome
retanning,
leather finishing
Chrome re
tanning,
leather finishing
Raw water source
Municipal water
Municipal water
Municipal water
Municipal water
Municipa
l water
(boreholes as standby)
Actual daily water
consumption
~
280 L per skin
~
5 000 L per ton
of hides
170
-440 L/hide
Water conservation
measures
Recycling
is currently
being considered
No recycling
is done at
present
The process does not
lend itself
to recycling,
mainly due to the salinity
in the effluent streams
No recycling is done at
present
Rainwater harvesting;
recycling
is
not an option
due to residual colour in
the effluent
Table 5.3: Water use and management of tanneries visited (Tanneries A6-A10)
Tannery identification
A6
A7
A8
A9
A10
Skins
, hides, raw
material
Bovine
Exotic
Bovine; ovine
Bovine; ovine
Bovine; ovine
Production process
From raw to wet blue
Full house
Full house
Chrome re
tanning,
leather finishing
Full house
Raw water source
Municipal water
Own water treatment
plant to treat river water
Municipal water
Municipal water
Municipal water
Actual daily water
consumption
~550
L per hide
~
400 L per hide
Water conservation
measures
The tannery is
considering
rainwater
harvesting
from roofs
Irrigation; recycling for
secondary use
Investigating the
feasibility of recycling
certain effluent streams
No recycling is done at
present
Currently implementing
and further investigating
water sa
vings measures
21
Table 5.4: Typical water use in tannery production processes
Process
SWI
(L/hide)
SWI
(from 2016 survey)
(L/hide)
European
Union, 2013
NATSURV 10,
1989
Hide and skin reception and storage
Curing and storage
Wet blue process: Beamhouse (or limeyard) section
Soaking
55-825 54
Liming and unhairing
41.25-110 34
Deliming and bating
~55 27
Washing (all steps combined)
65
Total
151.25-990
180
270
Wet blue process: Tanyard section
Degreasing
Only sheepskins and pigskins
Pickling and
tanning (chrome) 27.5-82.5 10
Draining, hosing, sammying and setting
Only wastewater
Washing (all steps combined)
- 149
Total
27.5-82.5
159
Dyehouse process (wet finishing and dry finishing)
P
ost-tanning 110-220
Finishing
0-27.5
Total
110-247.5
-
110
Total for all processes
289-1 320
339
170-550
Table 5.5 proposes specific water use (SWU) targets for tanning and leather finishing process based
on available data from the literature and from surveys undertaken in this project.
Table 5.5: Proposed water use targets
Process
SWU
(L/skin)
Wet blue process stages
50
-150
Dyehouse
process stages
100
-200
T
otal tanning and finishing stages
200
-500
22
WASTEWATER GENERATION AND MANAGEMENT
6.1 Wastewater Generated in the Tannery Industry
Figure 6.1 demonstrates that international studies have shown that one ton (1 000 kg) of raw hide yields
approximately 200 kg of leather plus 50 m3 of contaminated liquid effluent, a minimum of 500 kg wet
sludge and 120 kg of solids in sludge (UNIDO, 1991; European Union, 2013).
Figure 6.1: Typical solid and liquid waste generated in tanneries (European Union, 2013)
If all the various waste streams are combined, the effluent contains high concentrations of dissolved
and suspended solids (SS), and organics measured as biochemical oxygen demand (BOD) and/or
COD. The presence of sulphides, chlorides and chromium add to the toxicity of the effluent, and are
included in most discharge standards. An interesting assessment of the toxicity of chromium can be
sourced from the website of the International Union of Leather Technologists & Chemists Societies,
namely, www.iultcs.org (see Appendix B).
Beamhouse processes are the source of all non-limed and limed solid wastes such as fleshings,
trimmings and waste splits (UNIDO, 1991; Frendrup & Buljan, 2000; Buljan, 2012). More than 80% of
the organic pollution load originates from the beamhouse processes, with approximately 70% from
unhairing and liming and 10% from soak liquors (Frendrup & Buljan, 2000; Buljan, 2012). Soak water
provides 60% of wastewater salinity. The remainder comes from acid salts applied to suppress pelt
swelling (UNIDO, 1991; Buljan, 2012). The typical constituents in the effluent are summarised in
Table 6.1. The effluent is challenging to treat, and is discussed further in Section 6.3.
23
Table 6.1: Typical effluent constituents from tanning and finishing processes
Processes
Typical effluent constituents
Tanning processes
Beamhouse (limeyard) section
Soaking
Salt, manure, blood, dirt, globular skin proteins, biocides, surfactants an
d degreasers
.
Liming and
unhairing
Decomposed hair keratin, globular skin proteins, saponified fractions of natural skin
fat, sulphides, lime
and caustic soda.
Fleshing
Hide fats and fleshings in the form of a solid waste
.
Deliming and
bating
Calcium sa
lts, sulphide residues, organic acids, degraded proteins, residual
proteolytic enzymes, ammonium sulphate
and ammonium chloride.
Tanyard section
Pickling
The water used during pickling is not emptied from the drum but is used for the
tanning process.
Ta
nning
The water used during tanning is not emptied from the drum but is used for the
basification process.
Basification
Salt, trivalent chrome (wet blue), glutaraldehyde (wet white), magnesium and sodium
salts, sulphuric acid
and formic acid.
Final wash
Salt, trivalent chrome (wet blue), glutaraldehyde (wet white), magnesium and sodium
salts, sulphuric acid
and formic acid.
Sammying
Salt, trivalent chrome (wet blue), glutaraldehyde (wet white), magnesium and sodium
salts, sulphuric acid
and formic acid.
Dyehouse processes
W
ashing
Surfactants
.
Neutralisation
Sodium salts
.
Retanning
The water used during retanning is not emptied from the drum but is used for the
dyeing and fatliquoring processes.
Dyeing
The water used during dyeing is not emptied from
the drum but is used for the
fatliquoring process.
Fatliquoring
The water used during dyeing is not emptied from the drum but is used for the
fixation
process.
Fixation
Residues of retanning chemicals, dyestuffs and fatliquors
.
6.2 Wastewater Quality at Tanneries and Leather Finishing Industries Visited
Data on the quality of the wastewater (effluent) streams at the tanneries visited was obtained from the
tanneries themselves, from some of the municipalities to which the tanneries discharge their final
effluent, while samples were also taken at six of the tanneries. The data collected as well as the results
of analysis are provided in Table 6.2.
24
Table 6.2: Wastewater quality at tanneries visited in the survey
Tannery identification
A8; A10
A1, A2, A7
A3
A4, A5, A9
Skins/hides, raw material
Bovine; ovine
Exotic Bovine
Bovine
, ovine
Production process
Full house Full-house
tanning
Leather
finishing
Chrome
retanning,
leather
finishing
pH
Effluent quality (mg/L)
Range
6.2-12.7 3.46-9.83
8.0-8.5
Chemical oxygen demand
Effluent quality (mg/L)
Range
880-12 091
412-4 640
Specific pollutant load
(kg/hide)
Range
1 011-1 958
Average
1 320 2 945 3 347-4 978
Total dissolved solids
Effluent quality (mg/L)
Rang
e
7
190-187
470
483-50 115
Average
14
839-22
244
812-7 440 3 367 4 693
Specific pollutant load
(kg/hide)
Average
1.596
Total suspended solids
Effluent quality (mg/L)
Range
78-8 944
Average
839-893 1 268
Specific pollutant load
(kg/hide)
A
verage
0.090
Sulphates
Effluent quality (mg/L)
Range
71-3 707 150-2 700
Average
867 702 2 780
Specific pollutant load
(kg/hide)
Average
0.503
Chlorides
Effluent quality (mg/L)
Range
46-24 902
1 200-6 191
Average
7
467-12 022
2 591 474 2-626
Specific pollutant load
(kg/hide)
Range
Average
0.919 0.241
Total chromium
Effluent quality (mg/L)
Range
0-141.3
Average
1.31-14.0 8.53-46.0
Specific pollutant load
(kg/hide)
Average
0.0006 0.0027
25
6.3 Wastewater Treatment
6.3.1 Introduction
The integrated wastewater treatment systems in the tanning and leather finishing industry comprise
preliminary treatment (or pretreatment), primary, secondary and tertiary treatment processes. However,
every effluent treatment plant is site-specific. Tanneries involved in wet blue retanning and leather
finishing mainly use pretreatment and primary treatment processes, whereas full-house tanneries
additionally use secondary treatment (biological treatment). Some tanneries in South Africa combine all
effluent streams, while others separate effluent streams from the beamhouse and tanyard. It is
preferable to keep streams separate, because organic waste is the major constituent of combined
effluent streams, which contains high concentrations of inorganics, including chromium. Figure 6.2
shows an example of how effluent is kept separated for primary treatment in one South African tannery.
Figure 6.2: Flow diagram of conventional primary, secondary and tertiary treatment processes at a full-
house tannery wastewater treatment plant where effluent streams are separated
6.3.2 Pretreatment: Screening and preliminary settling
Preliminary treatment employs mechanical screens, grit removal apparatus, distribution wells and
equalisation tanks. Self-cleaning screens such as mechanical rotating screens are used to separate
from 30% to 40% of suspended solids from raw waste (UNIDO, 1991). The screens generally have
openings of between 3 mm and 0.5 mm and remove most of the larger solid material, including hair and
other coarse material, sand and/or grit, and grease. Screening also significantly reduces the sulphide
content of the effluent (UNIDO, 1991; Sahasranaman & Emmanuel, 2001; Buljan & Král, 2011).
Preliminary settling of the screened effluent in grit removal chambers can separate out up to 30% COD
in the form of easily settleable organic solids (UNIDO, 1991; Sahasranaman & Emmanuel, 2001).
26
6.3.3 Primary treatment
Primary treatment consists of physicochemical processes whereby (i) fats may be physically separated
and (ii) chemical coagulants and/or flocculants are added to facilitate sedimentation of suspended solids
in primary settling tanks. Coagulation is characterised by an optimum pH, and hence pH correction
chemical/s are added at this stage. Primary treatment should remove the bulk of the main pollutants
from the liquid waste stream/s.
Apart from removing particulate organics, primary treatment precipitates chrome and sulphides from
tanyard chrome floats and beamhouse effluent, respectively (Sahasranaman & Emmanuel, 2001). It is
preferable to precipitate these streams separately because neutralisation of alkaline liquors from the
beamhouse causes the release of gaseous hydrogen sulphide. To prevent malodours emanating from
the liquors, oxidation using a metal catalyst and aeration is often used to cause rapid precipitation of
metal sulphides. However, sulphide regenerates if downstream anaerobic treatment processes are
used. In such cases, direct precipitation using ferrous sulphate and ferric chloride is applied to equalised
effluent, producing a large volume of dark wet sludge.
In South Africa, the chrome streams and the sulphide streams are segregated individually. The lime-
sulphide waste stream undergoes sedimentation (the solids are readily settleable), after which sulphide
oxidation with a catalyst (manganese sulphate) takes place. The stream is then discharged to a
balancing tank. This has several benefits. The chrome liquors are precipitated with magnesium oxide
giving a denser sludge, which can be reacidified with sulphuric acid to CrSO4 for reuse or for drying on
sludge-drying beds. The treatment process includes mixing in a mixing tank, transfer to a settling tank,
drawing off the sludge for reuse or for discharge to sludge-drying beds. The supernatant, relatively
chrome-free, is discharged to the effluent-balancing tank and combined with other liquors.
In all other tannery waste liquors, the streams are discharged to the balancing tank and the mixed liquors
fed to the activated sludge process or aerated prior to chemical precipitation. To limit the possibility of
odour nuisance, tannery waste liquors should not be allowed to become anoxic or anaerobic. The
overflow from the activated sludge system goes to a clarifier where sludge is returned to the activated
sludge system directly. Clarified wastewater is discharged to sewer.
Anaerobic treatment of tannery wastewater containing sulphates gives rise to odour nuisance as a result
of sulphates being reduced to sulphides. Sludges (lime and spent biological sludge), once dewatered,
can be used for composting or soil conditioning.
The advantage of primary settling of lime liquors to remove settleable solids over chemical precipitation
of tannery wastewater is that sufficient alkalinity remains in the effluent during the activated sludge
process to maintain a pH in the alkaline range (above 7.0), and prevents sludge bulking.
Chrome precipitation is achieved by the application of lime to increase the alkalinity of the liquor (to
pH 8) and adding aluminium sulphate (alum) and anionic polyelectrolyte (UNIDO, 1991; Buljan & Král,
2011). Magnesium oxide is more commonly used as it results in a more compact chrome sludge. The
dosage is governed by the character of the effluent and the degree of clarification required (Buljan &
Král, 2011). Following precipitation, the supernatant from the beamhouse and tanyard streams is
equalised in a balancing tank before secondary treatment.
27
6.3.4 Secondary treatment
In full-house tanneries, primary treatment is followed by aerobic or anaerobic biological treatment to
further reduce the BOD. In South Africa, conventional activated sludge (CAS) systems, which are
operated as completely mixed systems with extended aeration, are common. Small tanneries in South
Africa also use ponds.
Anaerobic treatment is potentially an effective process for reducing the volume of sludge at
comparatively lower costs and is widely used in other industries (UNIDO, 1991; Buljan & Král, 2011).
The organic load is digested anaerobically and produces biogas (methane, carbon dioxide and
hydrogen sulphide). However, the tanning industry has not widely adopted anaerobic technologies as
they release hydrogen sulphide, which is toxic and corrosive (Buljan & Král, 2011).
6.3.5 Tertiary treatment
Following primary and/or secondary treatment, clarifiers and sand filter beds are used to separate the
solids from the liquid effluent and dewatering the sludge. The sludge is left for a few days under partial
aerobic conditions allowing further digestion. It is then sun-dried before disposal to landfills. Using drying
beds is a cheap method that requires manual removal of the sludge from the bed when it has dried to
about 30% solids content. Some retanning and leather finishing tanneries use belt filter presses. The
liquid effluent from medium to large tanneries is usually discharged to municipal sewers.
6.3.6 Advanced treatment systems
These are sophisticated treatment methods that can be designed to meet specific effluent quality
targets, but these methods are generally expensive and require expert operation. They include high
efficiency carbon filtration, reverse osmosis, membrane filtration, ion exchange, electrodialysis and high-
rate evaporation.
6.3.7 Sludge handling
In South Africa, solid waste from primary wastewater treatment and dried or filter-pressed sludge from
tertiary treatment (especially from the production of wet blue) is considered to be potentially hazardous
and is disposed to appropriate municipal or private landfill sites (Table 6.3). This can be costly, especially
if the landfill sites are not located in close proximity to the tanneries.
Until recently, chrome sludge had to be disposed of in a toxic landfill site (Class H:h). Recent research
has shown that there is no scientific evidence that Cr in CrIII sludge reverts to CrVI under natural
conditions and it has therefore been deregulated as far as being a potential toxic waste.
Table 6.3: Solid waste management practices of selected tanneries in South Africa
Tannery
Future plans for solid waste management
A1
Installation of an anaerobic digester to reduce sludge volume and generate biogas
.
A2
Biofuel production by waste
to energy companies (previously removed by such companies).
A3
No future plans
.
A4
No future plans
disclosed.
A5
The solids are collected in a skip.
The solids have a moisture content of about 30%. Approximately
two skips are taken away
per month by a waste company.
The tannery is investigating
the possibility of incinerating the wastewater sludge for energy, but is
worried about possible hexavalent chromium formation.
They will therefore eliminate rechroming.
28
Tannery
Future plans for solid waste management
A6
The solid waste is removed by a waste
company. They produce about two skips per month.
A7
No future plans disclosed
.
A8
No future plans disclosed
.
A9
No future plans disclosed
.
A10
No future plans disclosed
.
6.4 Changes in Tanning Industry Wastewater Treatment and Management Since the 1980s
There has been a move away from treating totally mixed effluent, i.e. all wastewaters were discharged
into one drainage system (no segregation) and into one collection tank after screening. The streams
were then treated together either by physico-chemical treatment (sedimentation or air flotation), or
activated sludge, to a system where specific waste streams are segregated from the main stream. This
involved redesigning and reengineering the internal drainage. In addition, two extra collection sumps
had to be constructed – one for each of the specific waste streams (lime liquors and wash, and chrome
tan liquors and wash). By the late 1990s, there was only one tannery using an air flotation system for
treating its effluents.
The old system of combined treatment gave rise to a number of problems, such as odour nuisance as
a result of sulphides (H2S), and almost neutral pH of combined liquor. Other problems included very
high suspended solids from lime liquors having to be kept in suspension and aerated, effluent strength
and pH balancing. Large quantities of sludge were produced with high chromium III content, which
required toxic waste landfill (Class H:h) disposal.
The Leather Industries Research Institute (LIRI) in collaboration with the WRC developed a treatment
system in the 1990s whereby segregation of specific wastewater streams along with their specific
pretreatments addressed most of the abovementioned problems.
Although LIRI did some research in the early 1990s on treating wastewater by biological filtration, it has
not been used by the industry. For biological filtration to be effective, pretreatment (screening) and
primary treatment processes (settling of lime sludge and fat oil and grease removal) need to be very
effective in removing problematic solids and fats that can block up the filter bed. Results from pilot plant
studies indicated that this technology could be used as a secondary treatment process for tannery
effluent.
Similarly, research into using microfiltration was done on tannery effluents to establish the feasibility of
using ultrafiltration and reverse osmosis to remove salts from tannery effluents. It was concluded that
tannery effluent needs a very effective secondary biological treatment or further tertiary treatment to
remove problematic suspended solids, and soluble fats, oils and greases for microfiltration techniques
to be economically viable.
Another advancement made in the 1990s was using bidim or geo-textile in the construction of sludge-
drying beds. The geo-textile was set between the coarse stone underdrainage and the filter sand surface
layer. This prevented the sand from permeating into the stone underdrainage and clogging up the
drainage voids resulting in a longer life span for the drying beds. The drying beds were also more
efficient.
There was a period when several tanneries considered lime/sulphide and chrome recycling; however,
due to the stringent control required during processing and difficulties in maintaining leather standards,
this practice has been discontinued by many. The survey will determine how many tanneries are still
recycling. No tanneries in South Africa are using anaerobic digestion to treat wastewaters or sludge.
29
Regarding wastewater analyses, it is noted in the first edition that two determinants have become more
of an environmental issue recently, namely, salinity or electrical conductivity, and ammonia were not
included in the analyses of the final wastewaters. Both these determinants can have a significant
influence on the water quality discharged by local authorities from a sewage works to a water course.
Ammonia not only comes from the deliming and bating process, but also from the biological breakdown
of the protein (keratin and epidermis) present in most process waste liquors. Electrical conductivity has
become the more acceptable determination measuring dissolved inorganic salts in effluent in the place
of total dissolved inorganic solids.
As a result of salinity in tannery effluents and the consequent water pollution, the biggest advance in
combating water pollution has been moving away from processing salted hides by a number of wet blue
plants. Many of the larger tanneries have resorted to processing green and/or chilled hides.
Furthermore, a number of tanneries processing gameskins have evolved. Here one should differentiate
between those doing hair-on for the tourist trade and those producing leather for other purposes.
The next step is for tanneries to adopt clean technologies where many currently used process chemicals
are substituted by chemicals having less impact on the environment. These include low-sulphide
unhairing, hair-save, ammonia-free deliming, low-salt pickle and high uptake chrome tanning, which are
more environmentally acceptable. Certain dyes and chemicals used in retanning and dyeing, especially
black, had exceptionally high CODs and were replaced by more environmentally acceptable ones.
Although some research was done on treatment of tannery effluents using biological filters with plastic
support media, it was concluded that biofiltration could benefit secondary treated wastewater as a
tertiary treatment to lower COD, nitrogen and suspended solids content. It could also be used as a
secondary treatment where a high standard of pretreatment was implemented to minimise blockages
due to fats and inadequate removal of suspended solids.
Many treatment processes recommended by inexperienced consultants are not appropriate for the
tanning industry as they often require a high level of process control and operator competency to
achieve the desired results.
It was found that a notable improvement in the biodegradation of organics in the aerobic biological
process could be achieved by adding phosphates in the form of a high phosphate content fertilizer. This
also improved sludge digestion and settleability.
6.5 Summary of Wastewater Treatment Systems Most Widely Used in the Tanning and
Leather Finishing Industry
The two most common secondary treatment technologies for tannery wastewater treatment in South
Africa and developing countries are the CAS system with extended aeration and anaerobic ponds.
Sequencing batch reactors and membrane bioreactors have also been introduced in other countries.
Table 6.4 summarises the treatment processes used for treating tannery effluents streams, and
describes the function and benefit of each process.
Table 6.4: Summary of tannery effluent treatment processes
Treatment Stage
Function
Benefits
Primary treatment
Screening
To remove large part
icles of
suspended
solids
Reduces COD and
suspended solids
in
effluent
Fat traps
To reduce fats, oils
Reduces fats
and oils in effluent
30
Treatment Stage
Function
Benefits
Pretreatments
Lime pre
settling
To remove large quantities of
suspended solids
c
onsisting of pulped
hair and
undissolved lime
Improves sulphide oxidation and
lowers
catalyst requirement
Sulphide oxidation
To reduce sulphide content
Minimises odour nuisance and
improves aerobic biological
process
Chrome precipitation
Removes chromium from waste
water
Allows final effluen
t and other
sludges
to meets discharge and
disposal limits
Secondary treatment
Activated
sludge
To break down soluble and suspended
organic matter, NH
3-N and other
constituents
Reduces pollution
and discharge costs
Addition of
phosphates
to
aerobic biol
ogical
process
Improves breakdown of organics
and
process efficiency by ±30%
Reduces pollutants more efficiently
Secondary settling
Removes biomass from effluent
for
sludge return and reinoculation of fresh
effluent with biomass
Allows effluent with min
imal
suspended
solids
and COD/BOD for discharge
Chemical
precipitation
Precipitates suspended solids
Reduces COD/BOD and
suspended
solids
Tertiary treatment
Biofiltration using
plastic media
Reduces further soluble and
suspended solids, fats and COD
Pro
duces a high quality final effluent
with low COD/BOD
Advanced treatment
Ultrafiltration
Removes fine particles of
suspended
solids
and soluble fats
Preparation for
reverse osmosis
reverse osmosis
Removes
total dissolved inorganic
solids
and salts (NaCl)
Preparation for
reverse osmosis
Sludge dewatering
Drying beds
Dewaters sludges by drainage and
evaporation
Reduces potential odour nuisance
and
transport costs to landfill
Centrifuges
Separates water from solids
Reduces potential odour nuisance
and
tr
ansport costs to landfill
Belt presses
Separates water from solids by
pressure between porous cloth
Reduces potential odour nuisance
and
transport costs to landfill
Pressure filter
Separates water from solids by
pressure between plates
Reduces potential
odour nuisance
and
transport costs to landfill
Table 6.5 compares the major advantages and disadvantages of each treatment process. Newer
technologies, including granular activated carbon membrane bioreactors and advanced oxidation
processes may gain traction in the future.
31
Table 6.5: Advantages and disadvantages of wastewater treatment processes used in the tanning industry
Treatment Advantages Disadvantages References
CAS with extended
aeration
x Activated sludge systems are widely used in
South Africa.
x Moderately affordable to install.
x Can achieve high organic removal rates.
x Continuous operation.
x Reliant on good floc formation.
x Occurrence of bulking and foaming due to poor
floc formation and selection of l
ipophilic filaments,
respectively.
x High operational costs for aeration.
x Larger footprint than membrane bioreactor,
sequencing batch reactor and upflow anaerobic
sludge blanket.
x Separate clarifier required for secondary settling.
x Unstable to variable hydraulic and pollutant
loading.
Mandal et al. (2010)
Buljan and Kr
ál (2011)
Membrane
bioreactor
x Products can be recovered.
x Water can be reused.
x No reliance on floc formation.
x Small footprint.
x Adjusts well to variable hydraulic and pollutant
loading.
x No separate clarifier required.
x Highest capital outlay for installation and
operation.
x Membranes prone to fouling, especially for
wastewater with a high fat content.
x Requires skilled operation.
Durai (2011)
Faouziet et al. (2013)
Jaf
arinejad (2016)
Sequencing batch
reactor
x Decreased bulking compared with CAS.
x Small footprint.
x Adjusts well to variable hydraulic and pollutant
loading.
x No separate clarifier required for secondary
settling.
x Treatment cycles can be adjusted to attain
complete nitrogen removal through nitrification-
denitrification.
x Higher construction and operating costs than
CAS.
x Higher energy requirements than CAS.
x Reliant on good floc formation.
x Batch operation.
Singh and Srivastava (2011)
Patil et al. (2013)
Jafa
rinejad (2016)
Anaerobic ponds
x Inexpensive to install and operate.
x Low energy requirements.
x Low sludge production.
x Water cannot be reused.
x Environmental threat due to leakage and
emissions.
x Difficult to desludge.
x Malodorous.
Buljan and Král (2011)
Goswami and Mazumder (2013)
Upflow anaerobic
sludge blanket
x Low sludge production.
x Biogas can be utilised for energy.
x Unstable to variable hydraulic and pollutant
loading.
x Methanogens sensitive to sulphides.
x Long start-up periods required after shutdown.
Rajeswari et al. (2000)
Goswami and Mazumder (2013)
Tamilchelvan and Mohan (2013)
32
ENERGY USE AND MANAGEMENT
Energy consumption in tanneries depends mainly on the following factors (European Union, 2013):
x Production methods.
x Capacity and size of equipment.
x Age and sophistication of motor controls.
x Amount of mechanical handling used to move hides and skins.
x Drying methods used.
x Heat losses from process vessels and from buildings.
x Air exchange rates to meet workplace safety conditions.
x Types of wastewater treatment on-site.
x Types of waste treatment and recovery of energy from waste on-site.
Heat losses may be mitigated by thermal insulation, but may be exacerbated by a low external
temperature. A high moisture content in the air may increase the energy consumed in drying. Energy
use data from one climatic zone may not be an accurate guide to what may be achieved in another.
The age and efficiency of the combustion equipment and boiler plant determine the proportion of the
energy of fuel that is made available as thermal energy in the tannery. A larger central boiler may be
more efficient, but if operations are dispersed on a large site, heat losses from pipework may eliminate
the gains. Table 7.1 and Figure 7.1 show energy consumption by type of energy input.
Table 7.1: Consumption of thermal and electrical energy (European Union, 2013)
Energy input
Energy application
Percentage of overall
consumption
Thermal energy
Drying
32-34
Hot water
32-34
Space heating
17-20
Electric ener
gy
Machinery and process vessels
9-12
Compressed air
1.5-3
Light
1.5-3
33
Figure 7.1: Typical energy consumption in the tannery industry (%)
It is necessary that data be compared for the same stages of the leather-making process. Ideally, energy
use should be monitored and reported separately for each process stage. Most energy-efficient
tanneries do so.
Where more detailed data for energy use is available, it is important that comparisons between tanneries
be made on the same basis. For example, ‘effluent treatment’ may or may not include biological
treatment, which can account for more than 50% of the total energy consumption in the treatment of
tannery effluent.
Energy consumption figures have been obtained for the eight case study tanneries. The mode in which
the figures are captured varies considerably from tannery to tannery (according to the usage per tanning
or dyehouse process, or for the tannery in total). The data has been processed to obtain figures per
hide or skin produced (for the different types of raw material processed).
When relating the energy consumption in the tannery to the actual production output (in terms of usage
per hide or skin processed), the figures vary largely. Values calculated for those tanneries where this
information was supplied ranged from 1.9-4.4 kWh per hide, while the electricity consumption at one of
the exotic leather tanneries was as high as 165 kWh.
Most of the tanneries use coal-fired boilers for heating, and electricity from the local authority for the
machines used in the tanning and leather finishing process. A few of the tanneries have indicated that
they will be investigating the feasibility of using renewable energy in future.
34
BEST PRACTICE FOR WATER USE AND WASTEWATER GENERATION IN THE
TANNERY INDUSTRY
Best practice can be defined as “strategies, activities or approaches that have been shown through
research and evaluation to be effective and/or efficient”. The term is somewhat controversial, because
some people feel that there are always ways to improve, and application of the word ‘best’ suggests
that no further innovation is necessary. The European Union prefers the term “best available
technologies”. Nevertheless, best practice is an accepted term that is widely applied. The catchphrase
“reduce, reuse, recycle” applies to just about all the world’s resources, including water, and forms part
of the best practice hierarchy (Figure 8.1).
Water use, wastewater generation and cleaner production technologies are inextricably linked, and
should be considered holistically by industries seeking to become more sustainable. Reduced water
consumption translates into reduced wastewater generation; reduced chemical usage or less toxic
chemicals improves wastewater quality.
Adherence to best practice technologies can translate into cost savings. However, it is recognised that
in some instances the adoption of best practices may result in inferior products, and a balance needs to
be struck between environmental and economic issues. This is particularly relevant to the wet blue
process in the tanning industry.
Figure 8.1: Best practice hierarchy – towards a sustainable future
8.1 Water Conservation and Demand Management
Reduction in water use can be achieved by decreasing the volume of water used in particular processes
and/or recycling/reusing process water. Specific best available technologies to reduce the water
footprint of the tanning and leather finishing industry are outlined from Section 8.2.1 to Section 8.2.5.
8.1.1 Using low floats and controlled batch washing
Water use and production costs can be reduced considerably by using low-float processing and
controlled batch washing (UNIDO, 1991; Steffen, Robertson and Kirsten Consulting Engineers, 1989;
Sundar et al., 2001; Buljan & Král, 2015). Low-float processing utilises 40% to 80% water on the weight
of material instead of the conventional 100% to 250%, and has been shown to reduce water
consumption by 20-50% (Steffen, Robertson and Kirsten Consulting Engineers, 1989; Sundar et al.,
2001; Buljan & Král, 2015). However, using low floats compromises leather quality (UNIDO, 1991;
Buljan & Král, 2015). Low floats cause the skins/hides, pelts or equipment (vessels) to be susceptible
35
to wear. Dried hides and heavy leather require long floats for proper rehydration and gradual penetration
of the vegetable tannins (UNIDO, 1991; Buljan & Král, 2015). High float levels are preferred by most
tanners as they produce the market-desired leather qualities, particularly the fineness of grain (UNIDO,
1991; Buljan & Král, 2015).
8.1.2 Recycling wash liquors
Wash liquors from bating and neutralisation can be recycled for soaking salted or green hides. The
second lime wash can be used as the basis for new lime or soak liquor. The latter is advantageous
because the alkalinity of the wash liquor accelerates soaking (UNIDO, 1991; Sundar et al., 2001; Buljan
& Král, 2015).
8.1.3 Processing green hides
Processing fresh or chilled skins and hides instead of salted hides theoretically eliminates the need for
process water during soaking and eliminates chlorides in the ensuing effluent, although in practice, a
small amount of salt is generally still added. Processing green hides is particularly applicable for
tanneries that are integrated with, or close to abattoirs (Ludvik, 2000; Buljan & Král, 2015).
8.1.4 Green fleshing
If fleshing is effected before liming instead of after, water consumption and the volume of contaminated
effluent are reduced. In Europe, it is estimated that green fleshing results in 10-20% reduction in process
water demand (Buljan & Král, 2015). However, as with the use of low-float technology, the quality of the
leather may be compromised. Therefore, green fleshing has not been widely adopted in South Africa.
8.1.5 Integrated process control systems
The processors and integrated process control systems in modern tanneries (water meters, automated
valves, etc.) are designed to reduce process water and chemical usage (UNIDO, 1991; Buljan & Král,
2015; Sundar et al., 2001). Manufacturers may offset the capital outlay by expected savings in chemical
and water costs (UNIDO, 1991).
8.2 Cleaner Production Techniques
One of the major environmental benefits to instituting cleaner production technologies is the
improvement in wastewater quality, but water may also be saved. Table 8.1 lists the major pollutants
found in the effluent of typical South African tanneries. Cleaner production technologies seek to
eliminate or reduce the quantity of these chemicals generated by tanneries. A list of these technologies
relevant to particular processes in the tanning industry are provided in Section 8.3.1 to Section 8.3.7,
and summarised in Table 8.2.
Table 8.1: Major pollutants generated at various stages of leather production
Origin
Pollutant
Beamhouse
x
Salt washed out of cured hides and skins.
x
High COD/solids from dissolved hair, skin proteins and process chemicals.
x
Sulphide used to remove the hair from hides and skins.
x
Ammonium ions released from the raw hide or skin and released from the
process chemicals during deliming and bating.
36
Origin
Pollutant
Tanning
x
Salt used in the pickling process.
x
Chrome tanning salts that are were not chemically bound to the leather.
Dyehouse
x
High COD caused by incomplete exhaustion of chemicals.
x
Chromium salts that are extracted from the wet blue during processing.
x
Inorganic salts originating from chemicals and dyes.
x
Dyestuffs not chemically bound to the leather.
Leather finishing
x
Organic solvents released from finishing auxiliaries.
x
Heavy metals from pigments.
8.2.1 Curing hides and skins
Recently there has been a greater international advocacy to find alternatives to salt curing of hides and
skins and replace the salt pickling stage in the tanning process to significantly reduce or remove salt
(NaCl) from tannery effluents. In countries such as Asia, India and Pakistan where desalination by
ultrafiltration and reverse osmosis was implemented under the auspices of UNIDO, this has been a
great failure due to capital cost of equipment, high running costs and the necessary requirements for
brine evaporation and salt landfilling.
Alternative methods to salt curing are green hide processing, chemical curing and chilling. Hides in
countries such as New Zealand, Australia and some European countries are chilled as the favoured
preservation process.
Table 8.2: Material balance of salt applied in curing one ton of raw hides, with 400 kg salt applied in
curing (40% on weight of raw stock) (Lampard, 2002)
Source
Amount
(kg)
Percentage
(%)
Ends up in
Discharge as leachate on account of
dehydration during curing
60 15
Environment
Fallen during handling and transport
40 10
Environment
Fallen during handling, sorting,
trimming in the tannery
15 3.75
Environment
/wastewater
Removed during desalting (*)
50-80 12.5-20
Environment
/wastewater
Washed out in first soaking
120-145 30-36
Wastewater
Washed out in second soaking
45-80 11.25-15
Wastewater
Carried over by hides to further
operations
30-49 7.5-10
Wastewat
er
(*) Not all tanneries practice desalting
Chilling reduces salt by about 60% in effluent, reduces water requirement for processing and hence also
reduces wastewater generated requiring treatment. Lower salinity in effluent improves oxygen uptake
in aerobic processes thereby improving aeration efficiency. Processing time is shortened as only
washing is required. Using a salt-free pickle would have similar advantages.
37
8.2.2 Unhairing and liming
8.2.2.1 Enzyme unhairing
The use of enzymes alone cannot eliminate the ground and fine hair completely and an exclusively
enzyme unhairing process will never be practically possible (Frendrup & Buljan, 2000). Enzymes are
therefore commonly used in combination with other unhairing agents such as alkaline immunisation,
alkaline swelling and sulphide treatment to eliminate ground and fine hair (UNIDO, 1991; Frendrup &
Buljan, 2000; Buljan, 2012). The latest development in this field involves the pressure injection of a
proteolytic enzyme solution on the flesh side of a limed skin or hide (Buljan, 2012). Enzyme unhairing
is especially attractive when good wool or hair quality has high priority (Frendrup & Buljan, 2000; Buljan,
2012). Lime liquors can be recycled and hair retained. The clear advantages of this process are reduced
pollution load and chemical dosages. The organic load emanating from the beamhouse can be reduced
by 60% (Frendrup & Buljan, 2000). The use of enzymes can lead to the production of leather with
cleaner and finer grains and with less grain shrinkage (UNIDO, 1991; Frendrup & Buljan, 2000; Buljan,
2012). Unfortunately, enzyme preparations are rarely used by industry due to the increased cost over
conventional technologies (Frendrup & Buljan, 2000; Buljan, 2012).
8.2.2.2 Use of organic sulphur compounds
There are three types of organic sulphur compound commonly used for unhairing in Europe and Asia,
namely, mercaptoethanol, formamidinesulphinic acid, and a compound based on mercaptoacetic acid
(UNIDO, 1991; Frendrup & Buljan, 2000; Buljan, 2012). These are strong reducing agents that have a
similar mode of action to sulphides, but they are more expensive (Buljan, 2012). Their use considerably
reduces the amount of sulphides in the effluent (Frendrup & Buljan, 2000; Buljan, 2012).
8.2.2.3 Hair saving methods
Sirolime process
The Sirolime process firstly uses hydrosulphide to loosen the hair, then sodium chlorate to oxidise the
sulphide, and finally lime to release the hair into the bath for filtering out (Frendrup & Buljan, 2000;
Buljan, 2012). The unhairing or liming liquors can be recycled and recharged into the process after
filtration (UNIDO, 1991; Frendrup & Buljan, 2000; Buljan, 2012). The resultant pelt is thoroughly washed
and the waste wash liquor may be used for soaking hides (UNIDO, 1991; Buljan, 2012). It has been
shown that effluent sulphide use 80%, lime 93%, and COD 17% less than conventional liming (UNIDO,
1991; Frendrup & Buljan, 2000; Buljan, 2012).
Hair-save reduces COD (±50%); BOD (±50%); fat, oil and grease (±60%); and suspended solids in
effluent streams. It also removes large amounts of settleable solids (hair) upfront, may obviate the need
for presettling when its main function is only to remove undissolved lime. It also reduces the organic
nitrogen and total Kjeldahl nitrogen (TKN) of the effluents, which on breakdown are a considerable
source of ammonia nitrogen (NH3-N) in effluents. This in turn, as the unhairing wastewaters are the
largest contributor to COD, BOD and suspended solids, reduces aeration requirements considerably.
8.2.3 Deliming and bating
Replacing ammonium salts with weak organic acids (such as lactic acid, formic acid and acetic acids,
esters of organic acids, magnesium lactate, and non-swelling aromatic acids) reduces the concentration
of ammonia in the wastewater (UNIDO, 1991; Frendrup, 1999; Ludvik, 2000; Buljan & Král, 2015). It is
also believed that less bating agent is needed for the subsequent bating process if ammonia-free
38
compounds are used (UNIDO, 1991; Buljan & Král, 2015). However, the presence of organic acids
increases the COD in the effluent (Buljan & Král, 2015).
The use of carbon dioxide (CO2) as a deliming agent significantly reduces the concentration of ammonia,
organic nitrogen and BOD in the effluent (Buljan & Král, 2015). There are some drawbacks to using this
technology, including the fact that the effectiveness of deliming of thicker and unsplit hides (more than
1.5 mm) requires enhancement with a small quantity of ammonium sulphate or a salt of a polycarboxylic
acid (Ludvik, 2000; Buljan & Král, 2015). In addition, the process requires precise technical control and
investment in special injection piping.
A non-ammonia alternative to the conventional deliming and bating process will obviate the need for
extended aeration in the aerobic biological process to oxidise NH3-N. By implementing both hair-save
and non-NH3 deliming, significant savings are made regarding oxygen requirements for wastewater
treatment.
8.2.4 Pickling
The main goal should be to avoid or significantly reduce the use of sodium chloride for pickling. There
are various low- to salt-free pickling chemicals available, including non-swelling polymeric and aromatic
sulphonic acids (UNIDO, 1991; Buljan & Král, 2015). However, there is a perception that they have a
negative impact on chrome tanning and leather quality (Buljan & Král, 2015). Therefore, the extensive
adoption of recycling the pickling and tanning floats serves as the current and best practice used by
most tanneries globally (UNIDO, 1991; Buljan & Král, 2015).
8.2.5 Tanning
8.2.5.1 Process optimisation
The optimisation of chrome tanning by manipulating the mechanical action, chrome concentration, pH,
temperature and reaction time improves the chrome uptake and hence reduces the chrome discharge
concentrations (Covington et al., 2000; Ludvik, 2000; Buljan & Král, 2015). It has been shown that as
little as 1.7% Cr2O3 on pelt weight at a pH of 5 can achieve a tanning efficiency of 98% (Covington et al.,
2000; Buljan & Král, 2015).
8.2.5.2 High exhaustion
The high-exhaustion process is achieved by masking the chrome tanning complexes and increasing
collagen reactivity. This improves chrome uptake, thereby reducing the amount of chrome required
(Covington et al., 2000; Buljan & Král, 2015). Common masking ligands include oxalate, acetate,
formate, dicarboxylic acids (short and long chain), polyacrylates (low molecular weight), aliphatic
dicarboxylates, and syntans (UNIDO, 1991; Buljan & Král, 2015). Depending on the thickness of the
pelt, chrome requirements (offer) can be reduced from a standard level of 2.0% to 1.3% (Cr2O3 on pelt
weight), which is a 35% reduction. In addition, chrome use has been shown to increase up to 98%
(conventional 65%) without affecting the quality of the leather (UNIDO, 1991; Covington et al., 2000;
Buljan & Král, 2015). The discharge for high-exhaustion tanning is 4% of the offer, about one-tenth that
of conventional tanning. Coupling high-exhaustion tanning with chrome reuse considerably reduces the
pollution load from the tan yard (UNIDO, 1991).
39
8.2.5.3 Direct recycling of spent floats
Recycling of spent floats is the simplest method for reusing chrome in conventional tanning (Ludvik,
2000; Buljan & Král, 2015). Closed recycling systems reuse only spent tanning floats and sammying
water for tanning in successive cycles, while other recycles are open systems that are characterised by
an increase in the float volume during recycling (Ludvik, 2000; Buljan & Král, 2015). Depending on the
complexity, process control efficiencies from 90-98% can be achieved (Buljan & Král, 2015). An
efficiency of 90% for conventional chrome tanning is easily attainable. This reduces the chrome
discharge from 2-5 kg/t to 0.1-0.25 kg/t raw hide (Ludvik, 2000). A decrease in the effluent sulphate load
from 30-55 kg/t to 10-22 kg/t raw hide is attainable (Ludvik, 2000).
8.2.5.4 Chrome recovery and recycling
Chrome reuse is based on the recovery of chrome by precipitation with alkalis and redissolution with
acid (Covington et al., 2000; Ludvik, 2000; Buljan & Král, 2015). Alkalis such as sodium hydroxide,
sodium carbonate, and calcium hydroxide achieve rapid coagulation rates. Although precipitation with
magnesium oxide is comparatively slow and the chemical is expensive, it produces a dense precipitate
that does not require filtering (UNIDO, 1991; Buljan & Král, 2015). Masked chrome complexes may not
precipitate easily.
Following precipitation, the spent liquor is clarified and filtered and the filter cake is dissolved in sulphuric
acid (Ludvik, 2000). The basicity of the resultant solution is adjusted and the basic chromium sulphate
solution produced is reused for tanning (Ludvik, 2000; Buljan & Král, 2015).
Chrome recovery and recycling can differ according to the choice of precipitating alkali, operating
conditions, clarification methods, and filter cake handling and reuse (Ludvik, 2000). A decrease in
chrome discharge from 2-5 kg/t to 0.1-0.25 kg/t raw hide can be achieved (Ludvik, 2000).
8.2.5.5 The use of alternative tanning agents to chrome
Alternative tanning agents include mineral salts (such as sulphates, chlorides and silicates of titanium,
aluminium, iron and zirconium), vegetable tannins (such as condensable mimosa bark, quebracho
wood, hydrolysable chestnut, Valonea and myrabolans), and organic compounds (such as isocyanates
and aldehydes) (US Environmental Protection Agency, 1976; UNIDO, 1991; Frendrup, 1999; Covington
et al., 2000; Buljan & Král, 2015).
Mineral salts
Basic mineral salts such as aluminium chloride, sodium aluminium silicate and zirconium sulphates are
currently used as retanning salts when certain final characteristics are desired in leather. Ammonium
titanyl sulphate and magnesium-aluminium-titanium complexes have been developed as alternatives to
chromium in the primary tanning process (Frendrup, 1999; Covington et al., 2000; Buljan & Král, 2015).
Zirconium and titanium salts appear to be eco-toxicologically acceptable, but the quality of the leather
falls short of that produced using chrome (Frendrup, 1999; Covington et al., 2000; Buljan & Král, 2015).
Although there is ongoing research to improve the iron tannage process, it currently produces leather
with poor properties.
The use of masked aluminium salt as a pretannage agent produces wet white leather (UNIDO, 1991;
Frendrup, 1999). However, aluminium is considered a toxic metal, and tannage is reversible (UNIDO,
1991). Pretannage with polyphosphate and sulphuric acid, such as using the South African Liritan
40
process, has the advantages of shortened process times, and high chemical uptake that lead to low
effluent pollution load (UNIDO, 1991). However, the process needs careful technical control.
Vegetable tanning
Organic (vegetable) tanning is generally applied to heavy hides to produce sole or industrial leathers
(UNIDO, 1991; Frendrup, 1999; Ludvik, 2000). Developing countries use vegetable tanning on bovine
hides and skins, sheep and goat skins to produce an intermediate, but marketable commodity (UNIDO,
1991). Successive pits with a progressive tannin liquor strengths from weakest to strongest are used for
vegetable tanning (UNIDO, 1991; Frendrup, 1999; Ludvik, 2000; Buljan & Král, 2015). The process
takes up to five weeks, depending on the character of the pelt; it can be sped up by pretanning with
polyphosphate (UNIDO, 1991; Buljan & Král, 2015). In contrast to chrome tanning, vegetable tanning
requires large amounts of tanning agent (typically about 40-50% on pelt weight), with an overall tannin
uptake of about 50-70% of the tanning offer (Frendrup, 1999).
The effluent produced from vegetable tanning is dark and turbid, and contains a higher load of poorly
biodegradable COD than chrome tanning effluent (UNIDO, 1991; Frendrup, 1999; Covington et al.,
2000). In addition, neutral salts derived from extracts and pretreatments are discharged concurrently
(Frendrup, 1999). However, vegetable-tanned leather is easily biodegradable and compostable as
tannins are common in decaying plant materials (Frendrup, 1999).
8.2.5.6 Synthetic organic tannages
Synthetic organic tannages (syntans) are real alternatives that can compete or even outshine chrome
tannage regarding leather properties and/or process technology (Frendrup, 1999; Covington et al.,
2000; Buljan & Král, 2015). Syntans are sulphonated condensation products of hydroxyl-substituted
aromatic compounds (phenol, cresol or naphthalene) with formaldehyde and often with amides (Buljan
& Král, 2015). Although some syntans are easily biodegraded, others are recalcitrant. Those with a
lower potential environmental and human health impact are available commercially, but better
alternatives have yet to be developed (Frendrup, 1999; Buljan & Král, 2015).
8.2.6 Wet finishing
The implementation of advanced post-tanning methods is aimed at reducing the pollution load of
chrome, sulphates, COD, suspended solids and nitrogenous compounds.
8.2.6.1 Neutralisation
The amount of neutralising salts needed should be optimised to minimise the amount that is wasted in
the effluent. Post-neutralisation rinsing water should be reduced as much as possible without
compromising the washing efficiency, and the pH should be properly adjusted to avoid Cr(VI) formation
(Hauber, 2000; Buljan & Král, 2015). Spent floats should be screened to remove chrome-containing
leather fibres (UNIDO, 1991; Buljan & Král, 2015). Commercially available special acrylic polymers with
retanning effects can be used for chrome fixing during the neutralisation stage, reducing the amount of
sodium and sulphate in the effluent (Ludvik, 2000).
8.2.6.2 Retanning, dyeing and fatliquoring
Optimisation of industrial wet finishing systems (retanning, dyeing and fatliquoring) is required to achieve
the lowest possible COD and salt levels in the effluent. Optimised high-exhaustion retanning methods
using appropriate masking agents and amounts (to avoid difficulties with the precipitation) should be
41
implemented (UNIDO, 1991; Ludvik, 2000; Buljan & Král, 2015). The addition of amphoteric polymers
improves the exhaustion of dyes and fatliquoring agents, and has been shown to reduce the COD
discharged from a range of 24-40 kg/t to about 10-2 kg/t raw hide (Ludvik, 2000).
Use of biodegradable retanning agents that produce quality leather with desired properties should be
prioritised as alternatives to chrome (Hauber, 2000). Retanning compounds based on urea-
formaldehyde or melamine-formaldehyde resins, or amino resins should be replaced with non-
nitrogenous compounds such as acrylic polymers. This may reduce the ammonia load from 0.3-0.5 kg/t
to 0.1-0.2 kg/t raw hide (Ludvik, 2000). The introduction of organic chemicals and preparations with
limited biodegradability, high COD values, and dyes containing toxic metals such as lead, cadmium and
Cr(VI) for wet finishing should be avoided (Ludvik, 2000; Buljan & Král, 2015). Fatliquoring agents based
on chlorinated paraffin, benzidine and other azo dyes (which may be reduced to carcinogenic amines)
and those with oxidising properties [cause Cr(VI) formation] should also be avoided (Hauber, 2000).
8.2.7 Finishing
8.2.7.1 Water-based finishing
Water-based systems in conjunction with cross-linking agents are increasingly being favoured because
of environmental concerns about organic solvents (UNIDO, 1991; Buljan & Král, 2015). However, less
toxic and less volatile cross-linking agents should be used, or alternatively, self-cross-linking reactive
polymers containing N-methylolamide groups (Buljan & Král, 2015). However, the drying of water-based
top coats is costly (Buljan & Král, 2015) and thus organic solvents with lower health and environmental
impacts may also be considered.
8.2.7.2 Improved coating techniques
Padding, curtain coating, roller coating, and spraying of leather are substantially different coating
techniques suited to different types of leather article. High-volume low-pressure (HVLP) spray guns
spraying with a large volume of air at low pressure should be used to reduce the loss of coating during
conventional spraying considerably (Buljan & Král, 2015). However, the HVLP technique does not give
completely satisfactory results for some articles, such as upper leather and garment leather (Buljan &
Král, 2015).
Table 8.3: Summary of selected alternative ‘best available’ technologies and their environmental
benefits (Jackson-Moss, personal communication)
Alternative ‘clean’ technologies
Environmental benefit/s
Processing of fresh hides
x Less salt in the final effluent.
x Savings in water consumption.
Recycling of soak floats
x Savings in water consumption.
x Savings in chemical usage.
Use of enzymatic soaking chemicals
x Less use of surfactants.
x Reduced soaking times leading to less energy consumption
.
Use of biodegradable surfactants
x Less chance of surfactants persisting in the environment.
x Reduced impact on aquatic organisms.
Hair
-save unhairing x A 60% reduction in COD of effluent.
x A 50% reduction in sulphide usage.
x A 35% reduction in nitrogen content of effluent.
42
Alternative ‘clean’ technologies
Environmental benefit/s
Low
-sulphide/sulphide-free unhairing
x No sulphides in effluent.
x Reduced odours.
x Reduced COD in effluent.
x Better settling of suspended solids in effluent.
Recycling of liming floats
x Savings in water consumption.
x No sulphides in final effluent.
x Reduced COD in effluent.
Low ammonia deliming
/CO2 deliming
x Reduced ammonium ions in the effluent.
x Less odour.
ThruBlue process
x No salt in effluent.
x No sulphate ions in effluent.
Salt
-free pickling process x No salt in effluent.
Pickle recycling
x Reduced salt in effluent.
x Savings in water consumption.
High
-exhaustion chrome tanning x Reduced chrome in effluent.
Chrome recycling
x Reduced chrome in effluent.
x Savings in water consumption.
Chrome
-free leathers x No chrome in effluent.
High
-
exhaustion retanning chemicals,
dyes and fatliquors
x Less COD in effluent.
x Less dyestuffs in effluent.
Aqueous finishing systems
x Solvent-free air emissions.
43
LIST OF REFERENCES
Bosnic, M, Rajamani, S and Sahasranaman, A (1998) Multiple Stage Evaporation System to Recover
Salt. Vienna.
Buljan, J (2005) Costs of tannery waste treatment. In Leather and Leather Products Industry Panel.
Leon: UNIDO: 1-25.
Buljan, J (2012) Hair-save liming process. In Cleaner Leather Technologies. Shanghai: UNIDO: 1-25.
Buljan, J and Král, I (2011) Introduction to Treatment of Tannery Effluents. Vienna: United Nations.
Buljan, J and Král, I (2012) Benchmarking in the Tanning Industry. Vienna.
Buljan, J and Král, I. (2015) The framework for sustainable leather manufacture. Vienna.
Covington, AD, Ramasami, T, Shi, B, Bailey, DG and Frendrup, W (2000) What is the future of
(Chrome) tanning? Leather manufacture in the new millennium. In J. Buljan, T. Ramasami, B. Shi, W.
Frendrup, and D. Bailey (eds.), Regional programme for pollution control in the tanning industry in
South-East Asia. Casablanca: UNIDO.
Durai, G, Rajasimman, M, Rajamohan, N (2011) Kinetic studies on biodegradation of tannery
wastewater in a sequential batch bioreactor. Journal of Biotech Research, 3: 19-26.
Eenpact (2013) The Leather Industry. Latvia. www.eenpact.eu.
European Union (2013) Best available techniques (BAT) reference document for the tanning of
hides and skins. Industrial Emissions Directive 2010/75/EU (Integrated Pollution Prevention and
Control). Joint Research Centre,͒Institute for Prospective Technological Studies Sustainable
Production and Consumption Unit European IPPC Bureau.
Faouzi, M, Merzouki, M and Benlemlih, M (2013) Contribution to optimize the biological treatment of
synthetic tannery effluent by the sequencing batch reactors. Journal of Material and Environmental
Science 4: 532-541
Food and Agriculture Organization (FAO) of the United Nations (2016) World Statistical Compendium
for Raw Skins and Hides, Leather and Leather Footwear. http://www.fao.org/3/a-i4651e.pdf.
Frendrup, W (1999) Environmental Aspects of the Future of Tanning Methods (Horizon 2050). In 14th
Leather panel meeting. 1-13.
Frendrup, W and Buljan, J (2000) Hair-save unhairing in leather processing. Pollution Control in the
Tanning Industry, (Sept): 1-37.
Goswami, S and Mazumder, D (2013) Treatment of chrome tannery wastewater by biological process:
A mini review. World Academy of Science, Engineering and Technology International Journal of
Environmental, Chemical, Ecological, Geological and Geophysical Engineering, Vol: 7 (11).
Hauber, C (1998) Sources, Detection and Avoidance of Hexavalent Chromium in Leather and Leather
Products. (Aug).
Hauber, C (2000) Formation Prevention and Determination of Cr(VI) in Leather. United Nations
Industrial Development Organization.
Jafarinejad, S (2016) Cost estimation and economical evaluation of three configurations of activated
sludge process for a wastewater treatment plant (WWTP) using simulation. Applied Water Science,
DOI 10.1007/s13201-016-0446-8.
Lampard, G (2002) Salt: Reduce, recycle, reuse or remove? Leather International, Oct 2002.
Ludvik, J (2000) The Scope for Decreasing Pollution Load. Vienna.
Mandal, T, Dasgupta, D, Mandal, S and Datta, S (2010) Treatment of leather industry wastewater by
aerobic biological and Fenton oxidation process. Journal of Hazardous Materials, 180(1-3).
Patil, PG, Kulkarni, GS, Kore, SS and Kore, SV (2013) Aerobic sequencing batch reactor for
wastewater treatment: A review. International Journal of Engineering Research and Technology,
2: 534-550.
44
Patrick, E and Watts, DJ (1992) Waste Reduction Activities and Options for a Manufacturer of
Finished Leather.pdf. Cincinnati.
Rajeshwari, K, Balakrishnan, M, Kansal, A, Lata, K and Kishore, VV (2000) State of the art of
anaerobic digestion technology for industrial wastewater treatment. Renewable and Sustainable
Energy Reviews, 4: 135-156.
Ramanujam, RA, Ganesh, R and Kandasamy, J (2010) Wastewater treatment technology for tanning
industry. Encyclopedia of Life Support Systems (EOLSS): 1-22. http://www.eolss.net/Eolss-
sampleAllChapter.aspx Bibliography.
Republic of South Africa (1996) Constitution of the Republic of South Africa, Act No. 108 of 1996.
Republic of South Africa (1997) Water Services Act, Act No. 108 of 1997.
Republic of South Africa (1998a) National Environmental Management Act, Act No. 107 of 1998.
Republic of South Africa (1998b) National Water Act, Act No. 36 of 1998.
Republic of South Africa (2004a) Air Quality Act, Act No. 39 of 2004.
Republic of South Africa (2004b) National Environmental Management: Air Quality Act, Act No. 39 of
2004.
Republic of South Africa (2008) National Environmental Management: Waste Act, Act No. 59 of 2008.
Sahasranaman, A and Emmanuel, KV (2001) Common Effluent Treatment Plant Kolkata Leather