UNIVERSITÀ DI PISA
Facoltà di IngegneriaDepartmento di Ingegneria Civile e Industriale
Corso di Dottorato in Ingegneria Civile e Ambientale
TESI DI DOTTORATO
Evaluation of Sonication Process in
Vegetable Tannery Wastewater Treatment
A Souri,
UNIVERSITÀ DI PISA
Facoltà di IngegneriaDepartmento di Ingegneria Civile e Industriale
Corso di Dottorato in Ingegneria Civile e Ambientale
Ph.D. Dissertation
Evaluation of Sonication Process in
Vegetable Tannery Wastewater Treatment
Alireza Mohammadi Aghdam
July 2017
Tutor: Prof. Renato Iannelli
Coordinatore: Prof. Massimo Rovai
Evaluation of Sonication Process in
Vegetable Tannery Wastewater Treatment:
Pilot Study
© Alireza Mohammadi Aghdam, 2017.
Tutor:
Prof. Renato Iannelli, University of Pisa, Dept. of Energy, Systems,
Territory, and Construction Engineering
DESTEC -‐ Largo Lucio Lazzarino, 1
IT-‐56122 Pisa, Italy
Coordinatore:
Prof. Massimo Rovai, University of Pisa, Dept. of Agriculture, Food
and Environment (DAFE)
DiSAA -‐ Via Del Borghetto, 80
IT-‐56100 Pisa, Italy
References to this publication should be written as:
Aghdam, M., A. (2017).
Evaluation of Sonication Process in Vegetable
Tannery Wastewater Treatment:
Pilot Study. PhD Dissertation, University of
Pisa. ISBN: 978-‐88-‐90228-‐95-‐7.DOI: 10.13131/UNIPI/ETD/07062017-‐165752
Cover:Cuoiodepur wastewater treatment plant (right),
Ultrasonication Sonicator (left)
ISBN: 978-‐88-‐90228-‐95-‐7
Typeset in L
AT
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Abstract
Evaluation of Sonication Process in Vegetable Tannery Wastewater Treatment
The tanning industry in Italy represents a significant contribution to the European economy. At the same time, it is well known that this industry generates significant amounts of contaminated wastewater. Vegetable Tannery wastewater contains high concentrations of organic matter (COD) with a significant percentage of recalcitrant organic compounds. Vegetable tannery wastewater shows several drawbacks due to the complexity of the chemical composition. Contaminants must to removed to avoid significant environmental impacts. In another hand, Activated sludge processes are key technologies in wastewater treatment. These biological processes produce massive amounts of waste activated sludge (WAS) or otherwise bio-solids. Mechanical, thermal, and/or chemical WAS conditioning techniques have been proposed to reduce the sludge charge. Among the WAS treatments; the pre-treatment with Sonication is one of the most innovative processes.
Primary attention is focused on the effect of high-frequency Sonication on reducing organic matter with or without using H2O2 and Aeration. The parameters affecting the
removal of the organic matter (COD) and soluble COD (SCOD) and total nitrogen (TN) and total organic carbon (TOC) were also analyzed and compared. Particular attention is then made on how the presence of H2O2, affects the performance of the process, and how
it affects the combined Sonication and biological processes.
In other words, the study focuses on the effect of Sono lysis on waste activated sludge solubilization and anaerobic biodegradability of vegetable tannery wastewater and primary sludge of a plant treating tannery wastewater, located in Santa Croce (Tuscany, Italy). The results obtained from a pilot scale study developed in the Tannery wastewater treatment plant (Cuoiodepur).
In the test carried out, the combination of a Sonication pre-treatment with using H2O2
showed satisfactory results regarding reduction COD and SCOD on vegetable tannery wastewater and primary sludge for recovery and reuse in the tannery treatment cycle. The Sonication pre-treatment was able to remove approx. 25% of COD, and SCOD in wastewater and more than 40% of reducing COD and 18% increment of SCOD in the primary sludge of vegetable tannery wastewater. Moreover, the effect of sonication with using H2O2 in total suspended solid (TSS) and volatile suspended solid (VSS)
respectively was 35% and 30%. In another hand, the results showed 27% reduction of total organic carbon (TOC) in the primary sludge of vegetable tannery wastewater.
Key Words: Vegetable Tannery wastewater, Sonication, Waste Activated Sludge, Pretreatment, Biodegradability, COD, Soluble COD, Total Organic Carbon
Abstract iv
Introduction xiii
1. Tannery Industrial Sector ... 1
(The Vegetable Tanning Technics in Italian Leather Industry: Generalities and Environmental Issues) 1.1 The Tannery Wastewater Treatment ... 1
1.1.1 The Tanning Industry ... 1
1.1.2 The Tanning Industry In Italy and Worldwide ... 2
1.1.3 Introduction of the Tanning Process ... 3
1.2 The Environmental Impact of the Industrial Sector ... 11
1.2.1 The Waste and Gaseous Effluents of the Tanning ... 14
1.2.2 The Liquid Effluents of The Tanning ... 15
(Chemical and physical characteristics of the waste) 1.3 The State of the Art of Tannery Wastewater Treatment ... 16
(Pre-Treatment and Primary Treatment) 1.4 The Tanning District of Santa Croce... 22
1.4.1 The Consortium Cuoiodepur ... 27
2. Sonication
38
2.1 Introduction ... 38
2.2 Sono Chemical Methods and Application ... 38
2.2.1 Theory of Ultrasonic Cavitation ... 39
2.2.2 Molecular Effects of Ultrasound ... 42
2.3 Deployment and Integration with Conventional System ... 43
2.3.1 Effects of Sonication on Disinfection ... 52
3. Biodegradability ... 65
3.1 Introduction ... 65
3.2 The Fractions of COD ... 65
3.3 Biodegradability Test ... 71
3.4 Fractionation Techniques of COD ... 75
3.5 The Estimate of the Biodegradable COD ... 76
3.6 Respirometry and Titrimetric Applied to the Nitrifying Biomass ... 77
3.7 Effects of Sonication on Sludge and Wastewater Degradability ... 84
3.7.1 Ultrasonic Pretreatment of Sludge ... 87
3.7.1.1 Pre-Treatments on Waste Activated Sludge ... 87
(Solubilization - Thermal and Ozone) 3.7.1.2 Effect of Sonication on Sludge and Wastewater ... 89
(Biodegradability and Flow ability) 3.7.1.3 Treatment of Sonication on Waste Activated Sludge ... 90
(Physical and Chemical Characteristics) 3.7.1.4 Effects of Sonication on Sludge Degradability and Methane ... 92
Production 3.7.2 Sonication in the Presence of Catalysts and Chemical Additives for Making ... 93
Degradability and Treatment of Organic Pollutants in Wastewater 3.7.2.1 Heterogeneous Sono Catalytic Degradation ... 95
3.7.2.2 Combination of Ultrasound and Different Chemical Additives ... 97
4. Advanced Oxygen Process ... 108
4.1 Introduction ... 108
4.2 Design Factors for the Combined System ... 118
4.3 Industrial Wastewater Treatment by AOPs/Bio-Treatment Technology... 121
4.4 Respirometry and Titrimetric Applied to the Nitrifying Biomass ... 124
4.4.1 Multiple Analysis Reprogrammable Titration Analyzer for the Kinetic ... 126
Characterization of Nitrifying and Autotrophic Denitrifuing Biomass 4.5 Advanced Oxidation Processes (AOP) Involving Ultrasound for ... 128 Wastewater Treatment: A Short Review With Emphasis on Cost Estimation
4.6.1 Selection of the best Treatment of Wastewater Treatment ... 135
4.7 AOPs as a Post-Treatment Stage ... 137
4.8 Integrated Advanced Technologies for the Remediation of Industial Wastewater ... 139
5. Advanced Monitoring of Biological Processes in Industrial ... 141
Wastewater Treatment 5.1 Introduction ... 141
5.2 The Fundamentals of Respirometric Techniques and Titration ... 143
5.3 Respirometric Techniques and Titration for the Activated Sludge ... 145
Process 5.3.1 Molecular Techniques for the Monitoring of the Activated Sludge ... 157
Processes 6. Evaluation of Applicability of Sonication within the ... 162
Wastewater Treatment Train of Cuoiodepur Plant 6.1 Aims and Scope of Performed Lab Activity... 162
6.1.1 Sonication in the Presence of Chemical Additives for Treatment of ... 162
Recalcitrant Organic Compounds in Wastewater 6.1.2 Future Direction of Sono chemical Processes ... 163
6.1.3 Aims and General Description of performed Experiments ... 164
6.2 Materials and Methods ... 164
6.3 Results and Discussion ... 167
6.3.1 Total COD Reduction ... 167
6.3.2 Soluble COD Variations ... 177
6.3.3 pH Increasing ... 184
6.3.4 Temperature Increase ... 186
6.4 Comparison with Literature Results ... 188
7. Evaluation of Applicability of Sonication within the ... 191
Sludge Treatment Train of Cuoiodepur Plant 7.1 Aims and Scope of Performed Lab Activity ... 191
7.1.1 Pretreatment Methods to Improve Sludge Anaerobic ... 191
Degradability 7.1.2 Sonication Pretreatment of Sludge ... 193
7.1.3 Treatment of Sonication for Improving Solubilization and ... 193
Anaerobic Biodegradability of Primary Sludge 7.1.4 Summery of Proposal Experiments ... 193
7.2 Materials and Methods ... 194
7.3 Results and Discussion ... 195
7.3.1 Total COD Reduction ... 195
7.3.2 Soluble COD Increment ... 199
7.3.3 Total Suspended Solid (TSS) Reduction ... 202
7.3.4 Volatile Suspended Solid (VSS) Reduction ... 205
7.3.5 pH Reduction ... 208
7.3.6 Temperature Increasing ... 209
7.3.7 Total Nitrogen (TN) ... 210
7.3.8 Total Organic Carbon (TOC) ... 211
7.4 Comparison with Literature Results ... 212
7.5 Conclusion ... 213
8. Conclusions and Future Developments ... 216
8.1 Estimated cost of treatment per M3 of COD removed... 219
Figure 1-1 - Chemical Reactor with Rectangular Gate………...6
Figure 1-2 - Longitudinal Section of a Drum and Handling of Liquids and………6
Skins to its Internal Figure 1-3 - Layout of the CETP, Cuoiodepur Spa………..25
Figure 1-4 - Site Plan of Cuoiodepur Spa…….………..………27
Figure 1-5 - Flow Diagram of the Current Configuration of the System Cuoiodepur..………..33
with Recommended Values of Dry Weather Flow in Output from each Treatment Figure 1-6 - Shemetic Fluxogram of the Effeluent Treatment of Cuoiodepur CETP………36
Figure 2-1 - Diagram of Ultrasound Range………38
Figure 2-2- Molecular Effects of Ultrasound………43
Figure 2-3- Experimental System of U, F, and U+F……….44
Figure 2-4 - Schematic Diagram of the Regions in a Cavitation Liquid where……….54
where Chemical Reactions Take Place Figure 2-5 - Ultrasonic Systems Typically used for Sono Chemical Treatment………55
Figure 3-1 - Diagram of The Estimate of the Biodegradable COD using BOD………..69
Measurements Figure 3-2 - Typical Distribution of Fractions of COD in Swage Wastewater………71
Figure 3-3 - An Injection of Acetate and Biodegradable Substrate Leads to………74
an Increase of the Speed of Consumption of Dissolved Oxygen Figure 3-4 - Diagram of Dissolved Oxygen Performed by Monitoring the……….74
OUR in Endogenous Conditions and Subsequently OUR Relative to the Dosage of Wastewater Figure 3-5 - Injection of Tannery Wastewater after Oxidation of Sulphides………75
Figure 3-6 - Sample Characterization of a Tannery Wastewater………..75
Figure 3-7 - Sample of Specific Uptake Rate………79
Figure 3-8 - Sample of Respirometric Toxicity………80
Figure 3-9 - Evaluation of Biological Activity based on Dosage Titration Solution………83
Figure 4-1 - Suitability of water treatment technologies according to COD Contents………110
Figure 4-2 - Advanced Oxidation Processes (AOPs) and its possible Combination………...118
Figure 4-4 - Strategy for the Selection of the Best Treatment Option for a Specific………137
Toxic and/or Non-Biodegradable Industrial Wastewater Figure 6-1 - Total COD Reduction (%) - Before Sonication and After Aeration (24 hr.)………..168
Figure 6-2 - Total COD Reduction (%) - After Sonication and After/Before Aeration………..169
(3 hr. Sonication - Without H2O2) Figure 6-3 - Total COD Reduction (%) - After Sonication and Before Aeration……….170
Without / With Various H2O2 Figure 6-4 - Total COD Reduction (%) and Total Average COD (mg/l) After ……….171 and Before Aeration, Without / With Various H2O2
Figure 6-5 - Total COD Reduction (%) - After Sonication and Before Aeration………...173 Without H2O2
Figure 6-6 - Total COD Reduction (%) - After Sonication and Before Aeration……….174 With 4mM H2O2
Figure 6-7 - Total COD Reduction (%) - After Sonication and After Aeration………174 With 4mM H2O2
Figure 6-8 - Total COD Reduction (%) - After Sonication and After Aeration………176 Without H2O2
Figure 6-9 - Soluble COD Reduction (%) - Before Sonication and After Aeration………..177 Figure 6-10 - Total Soluble COD Reduction (%) - After Sonication and……….178 After/Before Aeration 3 hr. Sonication (without H2O2)
Figure 6-11 - Total Soluble COD Reduction (%) - After Sonication and……….179 Before Aeration With / Without H2O2
Figure 6-12 - Total Average Soluble COD (mg/l) - After Sonication and………180 Before Aeration Without / With Various H2O2
Figure 6-13 - Total Soluble COD Reduction (%) - After Sonication and……….181 Before Aeration Without H2O2
Figure 6-14 - Total Soluble COD Reduction (%) - After Sonication and……….182 Before Aeration With 4mM H2O2
Figure 6-15 - Total Soluble COD Reduction (%) - After Sonication and……….182 After Aeration With 4mM H2O2
Figure 6-16 - pH Variation - Before Sonication and Before/After Aeration………184 Without H2O2
Figure 6-17 - pH Variation - After Sonication and Before/After Aeration……….…………..185 Without H2O2
Figure 6-18 - pH Variation - Before/After Sonication and Before Aeration………185 With / Without H2O2
Figure 6-19 - Temperature Increase - After Sonication and Before/After………..…186 Aeration Without H2O2
Figure 6-20 - Temperature Increase - Before/After Sonication and Before………..……… 187 Aeration With / Without H2O2
Figure 7-1 - Potential Location for Sludge co Treatments in a Classical wwtp...192 Figure 7-2 - Total COD Reduction (%) – Before/After Sonication……….195 Figure 7-3 - Total COD Reduction (%) – Before/After Sonication...196
With 40 mM H2O2
Figure 7-4 - Total COD Reduction (%) - After Sonication……….197 Without / With H2O2
Figure 7-5 - Soluble COD Increment (%) - Before/After Sonication……….199 Figure 7-6 - Total COD Increment (%) – Before/After Sonication……….200 With 40 mM H2O2
Figure 7-7 - Total COD Increment (%) - After Sonication……….201 Without / With H2O2
Figure 7-8 - Total Suspended Solid (TSS) (%) Reduction………..202 Before/After Sonication
Figure 7-9 - Total Suspended Solid (TSS) Reduction (%)………..203 Before/After Sonication With 40 mM H2O2
Before/After Sonication
Figure 7-12 - Volatile Suspended Solid (VSS) Reduction(%)………. 206
Before/After Sonication With 40 mM H2O2 Figure 7-13 - Total VSS Reduction (%) - After Sonication Without / With H2O2...………207
Figure 7-14 - pH Variation - Before/After Sonication Without H2O2 ……….……….208
Figure 7-15 - pH Variation - Before/After Sonication With 40 mM H2O2...………..208
With 40 mM H2O2 Figure 7-16 - Temperature Increase - Before/After Sonication WithouH2O2...………….209
Figure 7-17 - Temperature Increase - Before/After Sonication With 40 mM H2O2……….209
Figure 7-18 - Total Nitrogen (TN) (%) Variation - Before/After Sonication……… 210
List of Tables
Table 1-1 - Water Consumption for Individual Processes of Tanning………14
Table 1-2 - Breakdown of the Polluting Load of each Processing Stage………..14
Table 1-3 - Distribution of Load Nitrogen of each Processing Stage………..15
Table 1-4 - Chemical and Physical Characteristics of Tannery Wastewater………..16
Table 1-5 - Average Characteristics of the Effluent from the Sedimentation Tank……….28
Table 1-6 - Average concentrations of pollutants in industrial wastewater entering………...29
the plant Cuoiodepur Table 1-7 - Average Characteristics of the Industrial Raw Influent………....29
Table 1-8 - Average Characteristics of the Effluent from the Tertiary Treatment………30
and Final Neutralization Table 2-1 - Advantages and Disadvantages of Ultrasound-Induced Disinfection Systems………….62
Table 6-1 - Average Characteristics of Sonication Test with various Quantities of H2O2.………….171
Table 6-2 - Characteristics of Sonication Operation with various Quantities of H2O2..………..172
Table 6-3 - Average Characteristics of Sonication Test with 4 mM of H2O2 ...175
Table 6-4 - Average Characteristics of Sonication Test with various Quantities of H2O2…………..180
Introduction
Having now completed this doctoral research, I feel it appropriate to give a brief introduction to this thesis, explaining the merit and method of this research before introducing the content itself. Environmental engineering is a topic with characteristics of extreme transversality, so much so that the identity of the topic can even be obscured when overlap with other disciplines becomes excessive. Chemistry and biology, for example, are basic sciences from which the environmental engineer must be able to draw with extreme ease. Translated from a professional point of view, the ability to take advantage of the skills acquired in different disciplines, and the application of these to a project when working with students of that field, is fundamental to maintaining good dialogue. For these reasons, it is my opinion that the role of the environmental researcher is to utilise their versatility to address the issue of interest as seen through different cultural points of view, rather than to develop their own disciplinary language. This determines the particular ability to integrate different scientific skills, and over time, to carve out a role with technical connotations that will be recognisable in civil and environmental fields: this is where the role of sanitary engineer should aim to be. This conviction was the driving force for the research and experimental investigations that I have conducted for my doctoral thesis, and I have tried to propose an approach that is interdisciplinary, rather than multidisciplinary, to address the application of ultrasonic wave irradiation in vegetable tannery wastewater treatment.
The background science and technology, which can be consulted for a search on biodegradability in tannery wastewater treatment, yields a limited number of independent studies. On the other hand, one can draw on a rich literature related to tanning processes, including many recent publications studying the use of sonication in wastewater treatment. In this thesis, the following topics are discussed: advanced oxygen process (AOP), a detailed literature search on the professional monitoring of the biological processes of wastewater treatment, and evaluation of applicability of sonication within wastewater and sludge treatment. The sonication experiment was carried out within a joint laboratory; University - Enterprise CER2CO, located within the company Cuoiodepur Spa, over a period of approximately twelve months beginning in October 2014.
The introductory chapter of my doctoral thesis, while respecting separation between disciplines, also draws on the relationship between the two through the integration of content and language. To begin, it was decided to draw a picture connecting industrial wastewater processing characteristics and the issues concerning treatment. While not wishing to produce a comprehensive report on state-of-the-art technology or the organisation of Italian and international tanning protagonists industry-wide, it was
Introduction
deemed useful to have a reasonable amount of information. Therefore the elements necessary for a correct approach to wastewater processing techniques and, more generally, to improve the environmental sustainability of the productive sector, were researched and are reported. The tanning process is then described in order to highlight the steps that are contributing to the pollution load, allowing identification of processes that pose the problems for, and are most distinguished from, the management of waste, liquid, and effluents. The industrial sector is also described in order to highlight the importance of application of technology in the efficient treatment of effluent. Finally, given the diversity of the quality of treatments in literature, it was considered useful to present the state of the art techniques of tannery wastewater treatment. The case of the Tuscan industrial tanning district was used as a model, as they have undertaken experimental investigations, both as a production model and as a tool for the solution of environmental concerns. In this regard, it is important to emphasise that organisation into districts, typical of the leather industry in Italy, is one of the key elements used to address growing competition.
At a level that is internationally sustainable for the environment, the districts unite to create consortia for the purposes of carrying out activities of mutual interest, such as purification, which is, in the context of production, certainly not negligible in cost. These consortia, with sufficient critical mass to invest in research, are places where the development and application of innovative technologies occurs; the sonication technique for example, can undoubtedly find a place here. This cooperative technological solution has caused a growing interest in research and development, as is evidenced by the evolution of a bibliography of technical and scientific merit. This interest arises for different reasons: for example the potential of sonication as a capable, stable high quality treatment for effluents, or the need to understand the relationship between biological processes and removal of organic pollutants. Some elements, not directly related to the evolution of research on sonication, have however recently increased the scope of the research. Legislative restrictions have been imposed in recent years, and these will presumably tighten in the future. These legislations have broadened the range of attractive technologies from an economic point of view, making sustainable solutions, considered in the past too expensive, now a viable and desired option. In parallel, the costs of sonication, and operating expenses related to the consumption of energy and reagents, have continuously dropped. This is due in part to a number of factors: the realisation of economies of scale, greater competition between production houses, and the improvement of materials and processes.
Despite the efforts made by the scientific community, a full assessment of the effects of the introduction of sonication in biological treatment, is still some way from being complete. This is due in part to the variability in the treatment chain as a whole; selection biomass in an activated sludge plant is in fact dictated mostly by characteristics of the wastewater input, environmental conditions, and the mechanism of separation. The study of biological treatment requires analysis of the deep interrelations between the biological system and the process of separation. The ability to understand the complex mechanisms
that come into play, as well as analysis of the industrial process and technology of treatment, therefore, requires careful choice of the tools available to interpret the observed phenomena. In the study of wastewater treatment, understanding, control, and optimisation of biological processes are central elements. On the other hand a trial treatment of a strongly typed effluent, such as tanning wastewater, assumes a significant role of treated matrix, and provides the opportunity to characterise this matrix through analysis aimed at identifying specific chemical compounds.
For this analysis, it was considered that, so far as a possible, complementary monitoring tools typical of sanitary engineering, microbiology and analytical chemistry should be used. In particular; respirometry, molecular analysis techniques, and liquid chromatography. Given the application of the subject matter and the high correlations between phenomena studied, it is considered important to emphasise a search on biodegradability and advanced oxygen processes in the treatment of industrial wastewater, which are difficult to separate from the design of experimental investigations.
In the last twenty years, suitable models have been developed to explain the phenomenology of activated sludge process, and also methods of investigation that would allow the verification of models and estimated parameters. Reference modelling, affirmed over time and now adopted internationally, is recognised by the IWA (ASM 1, ASM 2, etc.). As an alternative means to estimate the kinetic parameters and stoichiometric models, respirometric and titration techniques are increasingly being applied. The modelling proposed by the IWA is, however, designed and validated for the necessary treatment of municipal wastewater, and can be applied correctly to processes conducted with age sludge. The same can be said of respirometric investigations with procedures standardised for the same conditions. The IWA models are, therefore, a useful reference point for the most common respirometric methods, but they can and should be adapted to the particular context. With regard to the substance of the research, experimental investigations are carried out to investigate the many topics of interest inherent in the sonication treatment of industrial wastewater. Some techniques are considered more innovative from the scientific point of view, some are more useful from a practical point of view, and some are more appropriate to the study of tannery wastewater treatment. The key points can be defined under particular categories as follows:
Assessment of the applicability and efficiency of sonication in tannery wastewater treatment through investigations at a pilot scale.
The observation of differences between traditional technology and sonication in terms of pollutant removal efficiency and the selection of biomass, through monitoring of pilot plant chemical-physical parameters.
Analysis of how mixing effluent of secondary wastewater of tannery with bio-sludge affects processing, investigated in different pilot installations.
Analysis of the composition of the non-biodegradable fraction of treated wastewater, through the integration of analytical respirometric techniques.
Introduction
The experimental investigations which were used to explore theoretical assumptions, the materials, methods, and the results were constituted by a continuous evolution of monitoring techniques, conduction processes, and configuration of the machinery which evolved over a period of almost one year, This type of investigation is aimed at wastewater in particular, namely that of the vegetable tanning process, as the sonication and monitoring techniques used have rarely been applied. The investigation involved a phased approach to the identification of the characteristics of the processes, from simple to complex, with a breakdown of the problems and a gradual adaptation of methods of monitoring and analysis.
Chapter One
1. Tannery Industrial Sector
(The Vegetable Tanning Technics in Italian Leather Industry:
Generalities and Environmental Issues)
1.1 The Tannery Wastewater Treatment
1.1.1 The Tanning Industry
In the study of tannery wastewater treatment, the first difficulty is with the fragmentary discussion that emerges from an analysis of the related bibliography. The element that characterizes the wastewater is the raw material, the skin, the processing of which gives rise to effluent with marked differences depending on the type of industrial process applied. Despite the differences, which are descended from varieties of the upstream process, it is still possible to extrapolate a set of characteristics common to the tannery wastewater and its treatment. Industrial processes give rise to a wide variety of waste, whether in solid, liquid, and gas that must be subjected to individual treatment processes to respect the limitations imposed by the relevant regulations. One of the most advanced industries in Europe is tanning, research in 1998 found that the European tanneries active on the surface were about 3000, and Italy is the country that produces most of the products made with leather. That tanning is considered one of the most polluting industries in absolute as well as one among those at highest water resource needs: to turn a cubic meter of raw material infinite matter ready to sell consume between 25 and 80 m3 of water. The waste produced by these processes contain blood, hair, proteins, animal fats, alkalinity, calcium, sulfides, sulfates, chlorides, and in high concentrations and dependent on the type of tanning, tannins, and trivalent chromium. The latter two substances are of significant importance in the tanning industry because responsible for the attachment of the collagen that allows the material to last in time and to resist to external agents.
The intention of the first part is to make a picture for connecting between the industrial processing, the characteristics of the waste and, the problems inherent in their treatment. In this discussion, which does not pretend to be exhaustive on the subject of tannery wastewater treatment, will be explored in detail regarding the waste of vegetable tanning. The wastewater of vegetable tanning, resulting from the production of leather, although quantitatively less important than that of chrome tanning but it has very pronounced characteristics and can prevail in the treatment of a mixed discharge.
Through the description of the industrial process, we will introduce the effluent of tannery process and its impact on the environment. Characteristics of the wastewater depend on qualitative and quantitative. Then present the state of the art of tannery wastewater treatment and describe the case –Tanning Industries in Tuscany- to give a complete view of tanning technology and organization in the Italian and international stakeholders. In addition, tanning process describes to distinguish, quantity and quality and the phases of originating pollutants, for providing the elements to consider and identify a separate treatment of wastewater among those processes that pose the most significant problems.
1.1.2 The Tanning Industry In Italy and Worldwide
The Italian industry, historically in the leather sector has a major role. Globally, the value of exports leather industry amounts to about 35 billion euros and sees the first places like Italy and China main exporters (18% and 19% respectively of the market share). The industry tanning is historically an important sector in Spain, Germany, South Korea, Brazil, and India is presented as one of the future leader markets. While there was not exported in the international market, reserve market was a very substantial internal production, 0.7 million tons of skin / year (Ram, B. et al., 1999).
The main importers of the finished product are the states with 26% of world share. In Italy, the leather sector is comprised of approximately 2,400 companies and employs approximately 30,000 employees, with annual sales, covering the period 2000-2005 of about € 7 billion, corresponding to approximately 65% of the turnover of the tanning industry in the European (UNIC, 2003). The most global industrial sectors in Italy, as can testify to the data of export of finished products and those relating to imports raw material (raw hides and semi). Exports, reaching 130 countries, in fact, represent about 2/3 of the total turnover, while the supply foreign raw material, which covers 85% of the needs of the industry, originated from 120 different countries.
The sector organized in industrial districts specialized by processing and by the destination of goods. The Arzignano district, Zermeghedo and Montebello Vicenza, in the Veneto region, produces about half of the national turnover and consists of 764 companies working mainly cattle hides and provider to the footwear, furniture, and clothing. In Tuscany, there is the second Italian leather district for sales: consists of about 870 factories, which operates mainly in the processing of cattle hides, mostly aimed at Footwear (Prescimone et al., 2005). Among the districts, Venetian and Tuscan have differences in the process of production: the first establish with the large companies that search the market depend on economies and the second composed of smaller companies that provide final flexibility production and high product variety.
Introduction of the Tanning Process
As it regards the remaining two Italian industrial districts, in the area of Solofra, in Campania, 368 companies are located and, between Turbigo and Castano Primo, in the province of Milan. Finally, there are about 140 companies working sheep and goatskins destined to leather goods and footwear. The industry is mainly composed of small and medium-sized enterprises: the 2,400 companies present in Italy only about 4% have more than 50 employees and only about 400 (16%) over 20 employees. Keep in mind though that the lower end (up to nine employees), they form the majority of companies that process them in others, where production phases are frequently limited to operations mechanical low complexity (UNIC, 2003). Because of this structure, from a quantitative point of view, the strip of companies over 50 employees alone represent more than half of the national production tanning.
1.1.3 Introduction of the Tanning Process
The tanning is a technological process of transformation of animal skin in a material which keeps some characteristics of the raw skin (tensile strength, viscoelasticity, resistance to abrasion), improves other (temperature resistance and vapor permeability). Some rather eliminate the (exposure to microbial attack) (Manzo et al. 1999). The tanning business can be considered a system that allows to retrieve and turn a waste product, rawhide, into a valuable product with high value added. The leather is obtained for the most common from skins of animals for slaughter (Cattle, pigs, sheep, goats, etc.) that represent a valuable by-product the food industry, has a considerable commercial value. Anyone can calculate an average of one kg of raw skin will get about 300-400g - 600-700g of finished product and waste. From a quantitative point of view, the polluting load of the wastewater and effluents tanning process, therefore, derive in large part from abundant wastewater matter first (60-70%). While, that are characterized over that by the characteristics of the skin, in a consistent way by the products used in the process industrially. Understanding the features of the wastewater require the study of the characteristics of the skin and the products and its processing.
The Raw Material
The skins of mammals are primarily the same as regards their histological constitution and in their cross-section; from the outside inwards, is they can distinguish three main layers: epidermis, dermis, and subcutaneous layer. From the chemical composition of a cowhide it is constituted on average by 64% water, 33% protein, 2% fat, 0.5% minerals and 0.5% of other substances.
The epidermis, in cowhide, represents about 1% of its thickness, and is the part outer; during its transformation into leather, except the processing of fur skins, is eliminated by calcination with all its annexes (Hair follicles, sebaceous and sweat glands, etc.). Both epidermis and the hair are mainly composed of keratin, a protein characterized by the presence of residues and then cystine disulfide bonds between adjacent protein chains R-CH2-CH2-SS-R. This particular structure gives the keratin a significant resistance to attack proteolytic and chemical to dilute acids and bases. While making it very easily attacked by substances having a reducing action; This derives from the use of the sulfide sodium, as a reducing agent, in the preliminary stages of the tanning process (Caniglia and Maffè, 2001). The second layer of cowhide, the dermis, represents about 85% of its thickness, it is located below the epidermis and is the skin layer that by the action of the tanning agent is turned into leather. The dermis is composed of connective tissue whose component main are collagen fibers. In addition to the dermis collagen, it is also contained elastin proteins together with other unstructured cementing action, such as albumin and globulins, which are eliminated in the machining of Riviera. In the dermis there are two layers in different structure: or papillary layer or higher, it is located between the epidermis and the base of the hairs. E 'it characterized by a dense network of fibers collagenic fragile oriented perpendicular to the skin surface. The papillary layer is necessary as it is the most precious skin
that is called "bloom." or the reticular layer or lower, is the innermost layer of the dermis and is located in contact with the subcutaneous tissue. These fibers that are woven in different directions are the responsible of the characteristics of physical resistance of leather and go to constitute that takes the name of "crust." The subcutaneous tissue, finally, which represents about 14% of the thickness of the skin, is located under the dermis and has the task of setting the skin to the underlying tissues. It consists mainly of fat and collagen fibers arranged parallel to the surface of the skin.
The subcutaneous tissue is mostly removed during the "skinning" of the animal and, like the epidermis, it is eliminated during the process tannery in the operation of "fleshing." The residue of fleshing takes the name of fleshing whose disposal, or more often reuse, is rather an expensive date the large quantity produced and because of the presence of a high concentration of sulfides that on it is absorbed.
The component of the skin is most interesting the Tanner is collagen, the protein that It reacts directly with the substances used in the tanning process. The fibers of collagen forms, in fact, most of the skin discarnate, shaved and ready for tanning. Collagen is a fibrous protein: each collagen fiber is constituted by a together fibril diameter of about 0.1 uM, and each fibril is formed by filaments tropocollagen diameter of about one hundred times lower.
Introduction of the Tanning Process
Chains polypeptide are macromolecules formed by a sequence of α-amino acids, joined other by peptide bonds, which in solution at neutral pH, are dipolar ions. The state of ionization depends on the pH of the medium, whereby in a very acidic solution, the group carboxylic does not have the ability to dissociate while the amino function is protonated; vice versa in alkaline solution.
The possibility of ionization of the polypeptide chains as a function of the pH of the medium It is of fundamental importance in the tanning process; It is in fact by varying the pH value of the medium which can regulate the penetration of the compounds into the fibers of collagen (Loewe, 1979).
Preservation of Leather
After the slaughter of the animal and an initial cleaning of the skin, the first primary treatment is aimed at its preservation, to avoid the decomposition before it reaches the skin and can be worked in the tannery. The treatment most frequently used to keep the skin in this phase is a salting process. The action of the salt is twofold, that is, acts both implementing a partial dehydration, both carrying a bacteriostatic action against most microbial agents. This action, in general, is enhanced by the addition of CaCO3 (2.5%)
and naphthalene (1 - 2%) (Martignone, 1997). The conservation skin is the origin then a substantial amount of salts in the waste and wastewater produced by subsequent machining processes.
Processes of the Wet Skin
The tanning process can be conducted in various ways depending on the type of raw skin and the type of product want to accomplish. Leatherworking for leather production takes place mainly using wet processes (processes chemical, chemical-physical, enzymatic), and using dry processes (processes mechanical). In the next paragraphs will be described only the processing steps in wet because, as a result of the chemical reactions involved and the active use reagent, give rise to most of the pollution load in tannery wastewater. The wet processing of the skin takes place in suitable reactors, of a different type to according to the degree of mechanical agitation to be impressed to the skin, including the Tini, the Aspi and the kicker (Figure 1-1) and (Figure 1-2).
Figure 1-1 - Chemical Reactor with Rectangular Gate
Figure 1-2 - Longitudinal Section of a Drum and Handling of Liquids and Skins to its Internal
The wet process of leather processing is constituted by a multiplicity of treatments, which can be grouped into the following categories.
Introduction of the Tanning Process
Works of Riviera and pickling: first operations, chemical and mechanical, to which it undergoes the raw skin, and are used to prepare the tanning.
• Tanning: the set of operations that allow obtaining a cross-linking stable collagen fiber of the dermis
• Retanning, dyeing and fattening: chemical treatments to enhance the aesthetic characteristics and product quality of the skin
• Finishing: group of processes carried out on the dry skins with the aim of protect the surface and improve the appearance
Work Riviera and Pickle
The work of the Riviera are the level of manufacture of the skin with the highest environmental impact because it produces about 80% of the polluting load overall source leather tanning, and among them, the phase of hair removal-calcination is, from the point of view quantity, the more pollution. A major part of the polluting load product this phase is essentially due to the use of high amounts of Na2S and residues interfibrillar protein,
keratin, and fragments of hair. The work of the Riviera are made up of the following stages: Greening - The greening restore skin, asportation salt used in the conservation, cleaning it and causing them to absorb the water lost as a result of the preservation treatment. Products are used, together with large volumes of water, they are constituted by surfactants, alkalis (Such as sodium carbonate, sodium hydroxide), bactericides and proteolytic enzymes (Caniglia and Maffè, 2001).
Liming and hair removal, usually these two phases are conducted in the same treatment bath, although the objectives are different. With hair removal, they have removed the hair and skin. From the chemical point of view, depilation consists in the process of hydrolytic degradation of keratins epidermis and hair, through their partial or complete solubilization. The hydrolytic process occurs by the action of reducing agents in the alkaline environment, ranging in break the bonds of disulfide bridges between polypeptide chains parallel. People reductant most important and most widely used is the sodium sulfide. The action reducing ion sulfide (HS) is increased if performed in the alkaline bath; this is the main reason for which is dosed with Ca(OH)2. With the liming,
the dermal tissue, however, is loosened getting relaxation of collagen fibers to increase the reactivity and the absorption capacity tanning products and also a part of the subcutaneous fat layer is eliminated by partial saponification. The lime is the reagent more responsible for this process, although it is traceable a synergistic action of depilatory agents. During the calcination, the lime also shows a strong tendency to hydrolyze the amide groups of the amino acids glutamine and asparagine, with the following release of ammonia nitrogen in the subsequent washing. They are also used:
sodium hydrogen sulfate, proteolytic enzymes, sulfate dimethylamine, auxiliary to surface-active action (that have the effect of favoring the penetration of products of the liming and emulsify fat) (Beef, 1998). The bathroom exhausted from this treatment, at a glance, contains products destruction of the hair, epidermis, and interfibrillar proteins, as well as the same reagents, which are usually assayed in excesses, such as sulfides and alkalis.
Fleshing - Split: The Fleshing is a mechanical operation by which they delete traces of meat and fat in the subcutaneous layer (Called fleshing). The abundant production of fleshing associated with this process, in addition to being the source of a refusal quantitatively important, constitutes one of the primary sources of sulfides which are accompanied with it. The split It allows to align and reduce the thickness of the skin in all its extension. A following the split, you get the flower (top layer of skin) and the crust (Lower layer of the skin).
Liming - Maceration: skins that come out during hair removal have a pH very high, on average around 11.5/12.5, for the presence of lime precipitated between the fibers or in solution in the interstices along with depilatory agents. Since the step of maceration is the use of enzymes, it is necessary that it is preceded by a deliming treatment, so that the pH does not inhibit the activity of enzymes themselves.
Liming - Deliming itself is:
• In the removal of lime deposited or solution between the fibers • Elimination of the agent depilatory alkaline, i.e., the sulfides • In the regression of the swelling of the skin
Commonly, as deliming agents they are used acids (sulfuric, hydrochloric, lactic, formic, glycolic). To avoid a differentiation in the change in pH in the various layers of the skin, which can compromise the strength characteristics of the final of the material, it is important that the deliming takes place slowly. This condition is obtainable using an appropriate balancing of acids and agents buffering agents including ammonium sulfate (NH4)2SO4, and ammonium chloride (NH4)Cl that contributes to the load of the
wastewater.
Maceration - Reached: deliming with a pH = 8-9, it is carried out subsequent treatment of maceration; with the aid of proteolytic enzyme products is operates a further demolition waste keratin of skin and hair, the proteoglycans, and proteins structured interfibrillar still not completely removed.
Introduction of the Tanning Process
further lower the pH of the skin in such a way as to eliminate the residual lime and, above all, in such a way as to avoid that in the subsequent tanning step, if obtained to the example with inorganic salts (such as chrome salts), precipitation occurs tanning agent. Typically, the pickling is conducted by the addition of inorganic acids (especially sulfuric and hydrochloric acid) or organic acids (formic and lactic acid); thereby skin is brought to values of pH equal to 2.5-3. The acid bath so it allows to remove the calcium compound that had not been eliminated in the phase of un-calcination maceration, both inactivates the carboxyl groups of the side chains of protein towards the tanning salts, so as to facilitate the penetration of the agents tanning agents within the fibers.
The Tanning
In the Riviera, the task of removing from the skin layer keratin epidermis and hair, get rid of the subcutaneous layer and purify dermis protein interfibrillar and non-collagenous structures. In the Riviera follows the tanning phase, that goal is to create cross-links irreversible among the smallest structural units of the collagen, which are the chains polypeptide. This operation provides to the skin characteristics typical of the finished product, high shrinkage temperature, resistance to chemical attack and bacterial properties do not become hard to dry state. Tanning agents blocking them and giving the skin characteristics of hydrophobicity that promote the cross-links between polypeptide chains parallel, they differ for the different types of bond that fail to establish; to the example, chromium salts bind to collagen via coordinative bonds, while the vegetable tannins through hydrogen bonds and bipolar type. Because the tanning process leads to the product of high quality, it is necessary to follow two phases:
• The stage of penetration of the tanning agent within the structure of the skin • The step of fixing the tanning agent for the generation of cross-links
In the tanning steps, on the one hand, the stabilization of the skin by reaction of tanning agents with the polypeptide chains. The other is embodiment of large tanning molecules from part of the collagen fibers. The skin thus gains further characteristics that determine the quality of the finished product, such as softness to the touch, flexibility, fullness, firmness and hydration capacity. This is the reason that a good leather is obtained by exceeding, dosing the reactants and the quantity stoichiometry.
It should be distinguished in two main types of tanning: the tannins (or vegetable tanning) and chromium.
The vegetable tannins used in the tanning of the skin are usually grouped into two categories:
1 - Hydrolysable tannins (tannins or pyrogallic, from the core base them features). They are so named for their ability to be readily hydrolyzed by acid, alkali, enzymes and heat. By hydrolysis, the tannins are well separated into acid gallic, ellagic, into other compounds of phenolic nature and monosaccharides (mainly glucose).
2 - Condensed tannins. Unlike the hydrolysable tannins, condensed tannins hardly tend to hydrolyze in the presence of acids, being characterized by very stable nuclei joined by bonds - C - C - C -. Conversely, more easily condensed tannins tend to polymerize (Berto, 1997). The tannins have a broad range of compounds and referre to polyphenols. They are extracted from different types of plants (for example from mimosa bark, the leaves of sumac, from the branches of the chestnut tree, the fruits of myrobalan, from the seeds of the tamarind) by leaching with water in countercurrent material properly shredded
The spread and the reactivity of the tannins are linked, as well as to the size of tannin molecules, to their molecular structure, the acidity of the tanning bath, to some neutral salts present, to temperature, viscosity, the concentration, the handling in the reactor and to the time. Skins vegetable tanned is employed for the production of sole leather.
Chrome Tanning
Chrome tanning is performed through the use of chromium salts such as agents mineral tanning. The high stability of the cross-links generated from chromium salts, it allows producing leathers with high shrinkage temperature and high strength to the hydrolytic attack of acids and bacteria. This is due to the peculiar characteristics chemical ion Cr (III), which make it particularly effective in crosslinking and stabilization of the collagen. The chromium salts are used as tanning agents in complex salts of Cr (III), in which the ion Cr (III) is often tied to 6 molecules of water [Cr (H2O)6]+3. The ability of a chromium
salt to form transverse bridges between chains polypeptide adjacent collagen depend on the trend of salt to generate ions necessary that favor the formation of bridges. Between the metal complexes, for which create aggregated to higher molecular weight and larger, so that succeed better to reach the active sites of the chains of collagen and establish ties. Among the salts of Cr mostly used in the tanning step is the basic sulfate of Cr to 33% - [Cr (H2O)6]2 (SO4)3, which is the most used, the sulfite of Cr, the complex salts of Cr
with organic anions.
Retanning, Dyeing, and Fattening
The processes of retanning, dyeing and fattening serve to differentiate the finished product to depending on the destination. They are used, and accordingly, are found in effluents:
The Environmental Impact of the Industrial Sector
• Dyeing dyes water-soluble or dispersed and fattening oils and animal fats or vegetable oils of marine animals, synthetic oils, and mineral oils
To retanning phase following drying, the staking that causes a softening of the skin to stretch, that has the function of lead a thorough drying of the skin at the same time subjecting them to an action of drawing and stabilization of the dimensions
Finishing
With finishing ennobled the appearance of leather, as well as protect the surface: this operation consists of various mechanical machining and chemical, to improve the appearance of the skin. In general, on the flower are applied, with different types of machines, polymer resins, casein, waxes, pigments, and dyes.
1.2 The Environmental Impact of the Industrial Sector
Issues regarding the environmental impact of the tanning processes are relevant to
Effluents solid, liquid and gaseous fuels and implications depend strictly on the kind of tanning operated, whether to chromium or tannin or if carried on the skin crude or semi. Although this work aimed at technologies liquid effluent treatment, it should be stressed here relations which they exist not only between the types of upstream processing and the process of treatment wastewater downstream but also between the processes of effluent treatment and solid and gaseous that in the liquid phase.
The elements that determine potential impacts on the environment are a result of processing steps described in the previous paragraphs:
• A ratio between raw material and finished product slowly tilted for the advance with the result of a production of waste consisting of:
• A substantial hydro requirement • The quality and quantity of the waste • The development of odorous substances
From a global point of view, the leather does not affect significantly on unbalance of the biogeochemical cycles of the first compounds of environmental interest. As regards the carbon cycle, one can observe how the energy requirements the industry is not high compared to the value of production. The possibility reusing the scraps in agriculture (for fleshing and for sludge of tanning vegetable) and as inert material (sludge of chrome tanning) makes possible a partial carbon fixation in solid form.
As for the nutrients, the phosphorus is not practically used in the processes tannery and is present in minuscule concentrations in the effluent. Nitrogen is both originated from the
solubilization of the compounds in the skin, as reagents are used. However, the waste being relatively balanced, it is possible to operate by biological almost complete de nitrification; the speech may be slightly more complex for that fraction of organic nitrogen, always present in tannery wastewater, which ammonification is not in conditions typical of activated sludge plants. Locally instead tanning processes are the source of severe problems related the environmental impact mainly concerning pollution of the air and the bodies receiving water: This depends on primarily on the organic load, one significant fraction is poorly biodegradable, of the color and salinity of wastewater and the potential emission of hydrogen sulfide. The difficulty in management of gaseous effluents, rich in hydrogen sulfide, often a cause of degradation areas which are affected districts industrial tannery, is associated with the multiplicity sources of pollution that are placed along the entire chain of production and treatment of wastewater and waste.
Hydrogen sulfide (H2S) is a colorless compound, toxic and foul smelling; the smell is
warned separately for concentrations greater than 7μg / m3. It turns out to be harmful to
concentrations above the 10.000μg / m3, while for frequencies of the order of 70,000 g /
m3 can cause serious damage to the eyes. Concentrations above 450.000μg / m3 can be fatal, because the acid sulfide is a powerful chemical and suffocating, by binding to hemoglobin, prevents access of oxygen in cellular metabolism. The guide value against odors nuisance is set by the World Health Organization to 7μg / m3, while the lines are
driving advise not to exceed the threshold of 150 mg / m3 as a daily average. In the tannery wastewater, is significant the presence of reduced compounds (sulfides and sulfites) and oxidized (sulfates) sulfur; the sulfate ion, which can reach 2 g / L in the effluent is a source of high salinity, while the sulfide ion is subject to desorption (as hydrogen sulfide). This poses problems of acute pollution and widespread that depends on not only on the concentrations of sulfide ion at the bottom of the factory but by the reduction of sulfate to sulfide in anaerobic conditions. This aspect, if one part has constituted in the past a deterrent to the adoption of biological treatment processes anaerobic, is influential on treatment technologies even in conditions aerobic and anoxic. The wastewater and gaseous effluents of the leather industry from a quantitative point of view a significant separation of the solids takes place in the stages of preparation of the skin. During which originate waste products quantitatively important mainly consisting of parts of the raw material which are not used, or cornices and hair, and in products resulting from the conservation of the skin and, mainly, of sodium chloride. The separation of solids by liquid effluents during these phases it has a fundamental role to the next wastewater treatment for two reasons:
The compounds of waste, predominantly protein, resulting from these stages can be easily reused for the production of fertilizers, at this stage of the process they, in fact, not be contaminated by the presence of compounds that are used in successive phases. In particular, by chromium, the lack of an efficient separation in this phase constitutes a burden for the treatment in wastewater treatment plant had to the need to treat a more substantial organic load, salt, and mainly sodium chloride. Presents mostly a type of problem similar in that once passed in solution can not be removed if not Speeds prohibitive; in this case, the problem does not arise so much regarding costs for the
The Environmental Impact of the Industrial Sector
treatment, but rather regarding compliance with the rules on the limits drain. Gaseous effluents subject to treatment consisting in drafts containing acid sulfide (H2S) which is
used especially in the phase of hair removal and that desorbs from solutions used in measurement so much more substantial than the lower the pH. The presence of sulfide is one of the elements that characterize the tanning industry and has a series of significant consequences on all stages of processing and treatment of effluents. Emissions of hydrogen sulfide coming from industrial processes they are treated directly in tanneries, usually bringing the ion in solution and sending it to the wastewater treatment industry. A consistent flow of sulfides adsorbed on waste products; it is instead subject to desorption in steps of conditioning of the solid fraction: this generates additional gas streams to be treated and consequently a further share of liquid effluents rich sulfide ions. Liquid effluents of the leather industry, the world production of water from the tanning industry amounts to about 300,000,000 m3/year (Beef, 1998), consumption approximately equivalent to that for use domestic of about 4,000,000 people. The amount is not very high, however, as does counterbalance by an organic load approximately equal to more than 100 million population equivalents. In Italy is working around 12-13% of the leather world, however, the production of wastewater does not reflect this percentage because, as often happens in most technologically advanced countries, the skin is partially machined starting from pickle instead of from crude from the hair. Leather not universally applied in a single process, but some different operations from country to country and from tannery to tannery: from this leads to a difficulty in representing the tannery effluent as a matrix with distinct characteristics.
Most of the tanneries in the world operate a chrome tanning; it is estimated that about 90% of the skin is being treated with this process (Superno et al., 2005). The consumption of the water used during the processes of tanning is not equal for each industry but varies depending on the treatment used, the raw material used and final production: the manufacturing of leather goods finished using products of intermediate processing have a consumption of water less than that tannery that treats skin fresh. Most of the steps of the working of the tanneries occur in any case water and, consequently, the treatments tannery wastewater represents one of the most important problems of this sector. For a plant of the traditional tannery, the average consumption of water is between 15 and 80 m3 per ton of raw material it worked. Both in the case of chrome tanning and in that the tanning tannin to the waste tanneries are characterized by high values regarding organic load, nitrogen and suspended solids as well as by high salinity primarily due to chlorides, sulfides, and sulfates. Those derived from vegetable tanning, also, are distinguished by the presence of vegetable and synthetic tannins used in the production process. The wastewater coming from the different processes of the whole cycle of processing of hides are usually directed to a single collector. However, it is useful to identify processes, which originate the various fractions of the polluting load. And it is possible for a standardized process for tanning cowhide does see the following table for the consumption percentage of water per ton of material raw skin products (Bajza and Vrcek, 2001), (Zengin et al., 2002) and (Cassano et al., 2001). As can be seen in Table 1-1 accessing data reported by authors different range leads to very large on the
attribution of water consumption at each processing phase. This confirms the poor standardization of procedures employed.
Table 1-1 - Water Consumption for Individual Processes of Tanning
Process Screening Liming& Skiving& Calcination Pickle Tannery Retanning,Dye,Finishing Depilation Washing
Water 17-24% 7-31% 12 -22% 6 -9% 2-6% 2-11% 25 -42%
Consumption
Taking into consideration the key stages of the industrial process, it is possible Evaluate the pollutant load of each stage of miling (Table 1 – 2 ):
Breakdown% of the pollution parameters for the different processing phases
Table 1-2 - Breakdown of the Polluting Load of each Processing Stage (Beef, 1998)
Parameter Greening Calcination Deliming Pickling-Tannin Other
BOD5 10 68 5 1.5 14.5 COD 15 55 5 1.5 25 SST 5 55 - - 40 Salinity 65 - 8 20 7
1.2.1 The Waste and Gaseous Effluents of the Tanning
About 75% of the organic load (BOD and COD) is produced in the operations of Riviera, and the primary load comes from the process of hair removal. In this phase, by hydrolysis under basic conditions and reducing agents, which allows you to remove the hair and keratin; the amino acids that make up keratin are therefore a fraction relevant COD and soluble organic nitrogen which constitutes the load of wastewater. A significant portion of the COD (about 45%) and BOD (about 50%) comes by calcination, while the process of removal of hair is one in which it has the increased production of suspended solids (about 60%). The drains of the process of deliming contain sulfides, ammonium salts and calcium (in an amount dependent on the particular treatment) and have a weak alkalinity. After pickling and tanning, however, substances in sewage are consequently the technique of tanning adopted: in the case of chrome tanning these compounds are substantially chromium salts and acids (the pH is about 4); tanning with tannin instead increases the organic load. The nitrogen is presented in the effluent as ammonia nitrogen and organic, both soluble particulates; nitrogen compounds are a distinguishing feature for tannery wastewater because the load is relevant because the conditions of biological processes are not ideal for nitrification and because of a fraction of organic soluble results hardly ammonification. In Table, 1-3, are shown the processes that originating the most of the nitrogen in the wastewaters.
