LIQUID AND SOLID WASTE IN THE TANNING PROCESS. TECHNOLOGICAL CHOICES IN RELATION TO THE CONTEXT

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1 LIQUID AND SOLID WASTE IN THE TANNING PROCESS. TECHNOLOGICAL CHOICES IN RELATION TO THE CONTEXT R. Lupo, S. Galluzzi, C. Cellai STUDIO DELTA Srl, Via Puccioni, S. Croce sull Arno (PI) - Italy The transformation of animal skin into leather requires a complex technological cycle in which large quantities of water and chemical products are used, and considerable quantities of liquid and solid waste, of varied composition, are produced. In this study we analyse the solutions adopted for the reduction of the environmental impact of the processing in two very different contexts: a consortium system for purification and recycling for a group if companies located within the same territory, and an internal system of purification and recycling adopted by a single company isolated from other productive activities. The two entities taken into consideration use the same production cycle and have to dispose of liquid and solid waste in proportion to the volume of leather processed. The technological cycle for the production of leather, liquid and solid waste Below is a flow chart of the tanning production cycle in which we have highlighted the quantities and types of products entering and exiting the system. The proposed chart represents a generalisation of a large number of variables which can be applied to the system, depending on the individual processes; it is nevertheless fairly representative of an average situation, useful for the comparison which is the subject of the present study. The chart illustrates solely the chrome tanning of the cattle skins, since this represents a majority share of world production. 1

2 MASS BALANCE CHROME LEATHER PROCESSING 1000Kg leather Fresh salted skin: 350Kg dermal matter, 150Kg salt, 500Kg water Fresh skin: 450Kg dermal matter 550Kg water 24Kg scraps 50Kg hair Kg fleshing waste 30Kg sludge cutting and scraps bath and rinsing fleshing dehairing and liming rinsing lt water +35Kg calcium hydroxide +35Kg sulphur+5-6kg mercaptan ~12000lt water with: Kg dermal matter, dirt, hair+20kg Na 2 S, lime, salt, strong alcalinity, BOD 5 and soluble matter 300lt water deliming, bating rinsing 260kg leather 750kg water 260Kg dermal matter 750Kg water pickel chrome tanning tanning fixing rinsing Chrome tanned: 260Kg dermal matter 500Kg water 17Kg chromium oxide 8Kg salt Pressing Storage Wet Blue 610Kg chrome leather +5000lt water +15Kg ammonium sulphate +10Kg acid +5500lt water +125Kg sodium chloride + +15Kg sulphuric acid Kg chromium oxide +30Kg sodium bicarbonate On reutilisation in tannery: 150lt water, ~6Kg chromium oxide ~1500lt water with: 6,5Kg chromium oxide 5000lt water with: calcium, Na 2 S, calcium and ammonium salt +5kg dermal matter, ph=8 ~4400lt water NaCl, chromium salt, NaSO 4, H 2 SO 4 ~5kg organic matter ~0,5Kg chromium oxide, ph=6 ~150lt water with: NaCl, chromium salt, NaSO 4 +5Kg organic matter, ph=4 44kg scraps from splitting 38kg shaving Splitting, shaving 225Kg dermal matter 300Kg water 8Kg salt Grain side 380Kg Split 153Kg 2

3 cutting dying stuffing rinsing Drying 14500lt water +chrome and vegetable tanning +natural or synthetic oils +emulsifying agents + dye substances +acids ~ 14500lt water with products not exhausted 225Kg dermal matter 60kg water 15Kg chromium oxide Grain leather 210Kg split 75Kg Drawing 2kg fluffing powder Fluffing Finished 24kg of scraps Cutting and selection 205Kg dermal matter 54Kg water 5Kg salt Grain leather 190Kg Split 75Kg Legend: Solid waste Incoming products Composition of skin Liquid waste Process Flow chart 1: mass balance chrome leather processing 3

4 The two entities compared in the present study are: Individual company WYNY DO BRASIL, Ibipora Londrina Parana Brazil Consortium of companies from the leather industrial district of the municipalities of - Castelfranco di Sotto (PI) - Fucecchio (FI) - Montopoli in Valdarno (PI) - Ponte a Egola (PI) - Santa Croce sull Arno (PI) Individual Brazilian tanning company Wyny do Brasil is located in Brazil, in a region in which there are several tanneries located at an average distance of km from one another. For this type of company the problem of the disposal of solid and liquid waste has to be tackled individually, without the possibility of resorting to solutions of a consortium or territorial nature. Wyny do Brasil is a tannery of medium/large dimensions, selected to represent the situation of companies existing in an isolated situation within the territory. It produces chrome leathers (1,500-2,000 wet blue skins per day), sole leathers (1,000-1,500 skins tanned in vats with vegetable tannins per day) and a small percentage of crust processed leather. The average weight of the processed skins is 31 kg per piece, that is on average 93 tons are processed per day for an average daily production of 3,000 skins; annual production 26,000 tons equivalent to approximately 900,000 skins % of these products are destined to exportation, and of these 60% to the European markets and the remaining 40% to the Asiatic markets. The tannery has a staff of employees and reaches an annual turnover of 35/ 45,000,000. Table 1 shows the limits for discharge into the river laid down for the individual company by the competent authorities, depending on the specific characteristics of the river in which the tannery is authorised to discharge. 4

5 Parameter Limit measurement unit COD 350 mg/l Sulphurs <1 mg/l Settleable solids <1 ml/l Ammoniacal nitrogen 5 mg/l Chromium trivalent <2 mg/l Chromium hexavalent <0.5 mg/l Table 1: river discharge limits for the individual company Italian tanning consortium The district consortium of companies under consideration is made up of approximately 450 tanneries and 400 other companies involved in the industry, which taken as a whole account for approximately 10,000 workers. Approximately 400,000 tons of raw skin are processed per year, and 200,000 of crust and Wet Blue for a production subdivided as follows: - 35% of the national leather production destined to : - 70% uppers for footwear; - 20% clothing; - 10% leather accessories; - the industrial area of Ponte a Egola produces 95% of national sole leather. Sales - 40% of the production is exported, 50% to the European market and the remaining 50% to the US and Asian markets. The annual turnover of the entire district is around 2 billion Euro. The discharge limits imposed by national legislation for the river waters are illustrated in table 2: Parameter Limit measurement unit COD 160 mg/l Sulphurs <1 mg/l Settleable solids 80 ml/l + Ammoniacal nitrogen NH 4 15 mg/l Chromium trivalent <2 mg/l Chromium hexavalent 0.2 mg/l Table 2: river discharge limits for the district 5

6 Production, treatment and discharge of liquid and solid waste for the individual Brazilian tanning company Wyny do Brasil The tannery in question possesses: - a plant for the treatment of general liquid waste; - a recovery and recirculation plant for the liming baths; - a recovery and recirculation plant for the chrome tanning baths; - an internal landfill; - a recycling system for the chrome originating from solid waste; - an agreement for the delivery of solid waste devoid of chrome to a composting plant. The tannery s system for the disposal of solid waste is strongly influenced by the territorial features of the tannery. When the meteorological conditions permit the transport of the solid waste to considerable distances, the solid organic waste devoid of harmful pollutants (e.g. chrome) is transported to a composting plant for the reutilisation of protein waste. When this is not possible, this waste is dissolved through the use of acids and the wastewater obtained is treated in the general waste plant. The solids containing chrome are in any case dissolved using acid and the resulting wastewater is screened. The liquid is delivered to the chrome recovery plant along with the wastewater originating from the tanning drums, and then treated for reutilisation in the subsequent phases of tanning; the solids recovered after screening are compacted and delivered to the landfill. In this manner the chrome enters the purification process in extremely modest quantities and may be found in minimal quantities only in the sludge delivered to the landfill. Tables 3, 4 and 5 show the available solutions for the disposal of the process waste and the quantities involved averaged over the annual production of Production (tons) 25,400 Waste delivered to landfill (%) 41.2 Reutilised waste (%) 58.8 Reutilised waste(kg/ton of leather produced) 0.33 Waste generated (ton/ton leather) 0.56 Table 3: production and destination of waste in the year 2003, compared with production 6

7 N Volume Waste/total(%) waste/raw Production Phase of disposal (tons) (Kg/ton) (ton/g) 1 Internal landfill Municipal landfill Treatment and recycling in process Recovery, treatment and delivery to general treatment plant 5 Treatment and composting Marketing Return to supplier Boiler Total 14, Table 4: volumes destined to the various disposal systems Type of waste Phase of treatment Production (tons) waste/processed (Kg/ton) Production (tons/g) General waste: pieces, solid waste from conduit cleaning Waste from the administrative sector similar to urban waste Resold waste: drums, paper etc Packaging returned to suppliers Chrome shaving Pickeled shaving Pieces of chrome-tanned leather Pieces of pickeled leather Resold vegetable leather shaving Primary sludge deriving from the treatment of general wastewater* Fleshing pieces Pieces of vegetable leather Fleshing waste Liming recovery sludge and re-fleshing waste Total 14, * sludge from biological treatment at 7% of dry matter up to June Following the setting in operation of a centrifuge (June 2004) sludge with 25-26% dry matter is obtained. Table 5: disposal of the various liquid and solid waste produced 7

8 Chrome recovery 130m3/day Liming recovery 200 m3/day General wastewater treatment Screening Screening Vegetable tanning 20 m3/day Other water 850m3/day Air Homogenisation Liming storage Screening Screening Sedimentation flotation Sedimentation Biological oxidation 800m3 Homogenisation 700 m3 Air Storage acidification H 2 SO 4 Clarified storage 1 Primary sedimentation To the drum tumblers To the drum tumblers Air Aerobic sector Anoxic sector 1 Composting 1 lagoon 5000 m3 Air II lagoon 5000 m3 1 Landfill Sludge treatment Raising Biological sedimentation 180 m3 Polyelectrolyte Centrifuge Landfill Clarified discharge Legend: Water Sludge In red modifications operational from 2004 Flow chart 2: water treatment and recycling plants 8

9 Production, treatment and discharge of liquid and solid waste for the consortium system The existing Tuscan leather district developed over the years from an innumerable series of tiny, small and medium-size enterprises which emerged in a scattered and spontaneous manner; today this type of structure has become the veritable strong point of the entire system. Because of its origins, effectively, the leather district represents a model which is perfectly idiosyncratic at global level, which could probably not be reproduced in a different context. Over the last fifty years there has been a continual transformation of the tanning activity in terms of co-operation, above all within the sphere of environmental protection. In line with this policy, four centralised purification plants have been set up, each of which is different in terms of characteristics and type of treatment, but all in line with the most advanced technologies for water treatment and effectively representing a platform at international level within which experimentation, research and development have always played a role of primary importance. Like the liquid waste purification plants, the system for the recycling and disposal of solid waste is also differentiated, with the creation of three different plants for the added value recycling of solids. The flow charts below illustrate the situation of the leather district: Annual production of liquid waste: 8,000,000 m3 Aquarno (S. Croce s/a) 25-30,000 m3 Cuoiodepur (Ponte a Egola) 6-8,000 m3/day CCF (Fucecchio) 4-6,000 m3/day CDC (Castelfranco di sotto) 3,500 m3/day Sludge produced through purification of effluents: 200,000 tons/year (35-40% SS) Flow chart 3: situation of the disposal of liquid waste 9

10 Consorzio Aquarno SpA - Non profit-making company for the management and treatment of the tanning waste originating from the industrial area of S. Croce sull Arno; - the capacity of the plant is 25,000 m 3 /day for industrial wastewater (calculated on 5.5 days/week for 48 weeks) and 5,000 m 3 /day of domestic wastewater, for a total of effluents currently treated of 3.95 million m 3 industrial/year and 1.8 million domestic/year; - Aquarno also treats the effluents generated by Ecoespanso, Consorzio Recupero Cromo and others, transported via tank trucks (domestic and industrial); - it employs approximately 50 persons; - the plant was set up in 1974, involving overall investments of approximately 52.7 million Euro; - the management costs are approximately 22.8 million Euro, 11.8 for the treatment of water and 11 for that of the sludge. Consorzio Cuoiodepur SpA - Cuoiodepur has a licence from the S. Miniato town council for the management and treatment of industrial and civic waste; - the capacity of the plant is 7,500 m 3 /day for industrial wastewater (calculated on 5.5 days/week for 48 weeks) and 3,500 m 3 /day for domestic wastewater, for a total of million m 3 industrial/year and 1.5 million domestic/year; - it employs approximately 40 persons and occupies an area of approximately 13 hectares; - the plant was set up in 1980, involving overall investments of approximately 47 million Euro; - the management costs are approximately 12.5 million Euro. Consorzio conciatori di Fucecchio SpA - The capacity of the plant is 4,000 m 3 /day for industrial wastewater (calculated on 5.5 days/week for 48 weeks) and 1,500 m 3 /day for domestic wastewater, for a total of effluents currently treated of million m 3 industrial/year and million domestic/year; - it employs approximately 22 persons; - the plant was set up in

11 Consorzio depuratore Castelfranco di Sotto Srl - The capacity of the plant is 1,800 m 3 /day per industrial wastewater (calculated on 5.5 days/week for 48 weeks) and 1,800 m 3 /day for domestic wastewater, for a total of effluents currently treated of ,000 m 3 industrial/year and ,000 m 3 domestic/year; - it employs 7 persons; - the plant was set up in For the liquid waste containing significant quantities of chrome, there is a special plant for treatment/recovery: the Consorzio Recupero Cromo. Consorzio Recupero Cromo SpA - Non profit-making company for the management and treatment of the waste from tanning or re-tanning (containing chrome) originating from approximately 240 companies; - the capacity of the plant is m 3 /day of wastewater containing concentrations of chrome such as Cr 2 O 3 of 3 4 g/l; - it employs approximately 12 persons; - the plant was set up in 1981, involving overall investments of approximately 6 million Euro; - the tannery pays 0.23 Euro/kg for the regenerated chrome, which has a content of 9-10% in weight as Cr 2 O 3 ; - the quantity of chrome recovered annually is 500 tons of Cr 2 O 3. 11

12 Shaving (Cr) 35-40,000 tons/year Trimming (Cr) 15-20,000 tons/year Fleshings 70-80,000 tons/year Other 40-50,000 tons/year Solid waste from processing: approx. 180,000 tons/year Sludge tons/year SGS (S. Croce sull Arno) Fleshings Flow chart 4: situation of the disposal of solid waste Ecoespanso (S. Croce sull Arno) Sludge Toscana Azoto (S. Croce sull Arno) Organazoto (Ponte a Egola) Shavings and trimmings Consorzio S.G.S. SpA - This is a company for the recovery of the fats and proteins from the fleshings, serving approximately 240 tanning companies ; - the plant treats approximately 80,000 tons/year of fleshings; - it employs approximately 50 persons; - the cost (inclusive of transport) is 65 Euro/ton; - the plant has involved overall investments for approx. 5.3 million Euro. Ecoespanso Srl - Non-profit making company for the treatment of excess sludge originating from 3 purification plants on the right bank of the Arno; - Ecoespanso is entrusted with the management and disposal of the sludge. This service was previously performed by the CIS when the final destination of the sludge was primarily the landfill; - the plant was set up in 2000, and involved overall investments of approximately 23.2 million Euro; - the capacity of the plant is approximately tons/hour of treated sludge; 12

13 - the plant is made up of two units: Plant for the production of sludge for composting: this treats the sludge mechanically to reduce the contents into dry substance as much as possible, assisting the operation with the addition of lime and other additives to increase the fertilising power; Inertion plant: this is a treatment of pyrolysis, sintering and expansion which generates an inert final product that can be utilised in various sectors, especially in the civil construction industry. Organazoto and Toscana Azoto - These treat approximately 180 tons/day of chrome shavings and trimmings for the production of organic nitrogenous fertilisers; - the cost (inclusive of transport) is Euro/ton. Conclusions The following tables show the comparative costs of the purification of the general wastewater: Individual Brazilian tanning company Wyny do Brasil. The annual cost for the purification of the general wastewater is approximately 108,000, divided as follows: Cost entry Energy 33.4 % Products 11.3 % Staff 26.4 % Disposal 16.8 % Sundry 6.4 % Trucks 5.7 % The costs for this treatment are around 4.95 per ton of raw skin processed, which means that on average the impact on the production of the company is as follows: per m 3 of waste produced per raw skin processed. 13

14 Italian tanning consortium The annual cost for the purification of the general wastewater is approximately 30.2 million, divided as follows for the four plants mentioned: Aquarno: 11.8 million CCF: 3.7 million CDC: 2.2 million Cuoiodepur: 12.5 million These costs can be attributed to the various cost entries as follows: Cost entry Staff 9.4 % Chemical products 22.1 % Electricity 7.7 % Sludge 48.2 % Sewers 2.3 % Maintenance 5.4 % Sundry 4.9 % The conditions for the development of a single-sector industrial district reside in its own specific production capacity, which can be achieved and maintained at a high level thanks to a broad and ongoing exchange between the small and medium sized enterprises present within a relatively small geographical area. In this sense, the examples of the relocation of entire industrial zones for tanning to geographical contexts remote from urban and abandoned areas does not always represent the ideal solution to the question of the environmental problems connected with the tanning process: the strength of an industrial district frequently derives from the possibility of accessing a large market of specialised workers, and from the proximity of access to the raw materials and the elements necessary for production (machinery, chemical products etc.) The specific reality of the industrial district described has made it possible to tackle the various environmental problems, succeeding not only in surviving within the context of European regulations, but actually increasing its production (today, in the tannery sector Italy accounts for 14

15 60% of European production). It is effectively the creation of consortium organisations which emerges as the sole possibility for successfully tackling all the problems relating to tanning pollution: control agencies, centres for training and research, and trade associations are the elements that operate within the context of the consortiums for the promotion of research and technological transfer. Only in this manner is it possible to address the complex environmental management which demands that such districts should avoid conflicts, should preserve the water resources and always play a key role in the legislation relating to these spheres. On the other hand, an individual company, in a context such as that of Brazil, with the availability of extensive surface areas which can be utilised for the treatment of water and for the utilisation of the tanning waste at agricultural level, disposes of optimal conditions for reducing the cost of disposal while complying with the legislation in force. At an economic level it is difficult to compare the two realities, since the financial situation is intrinsically connected to the general context within which they are located. The differences which emerge in the profit and loss accounts for the two situations are extremely wide-ranging, and cannot be explained without resorting to a much broader analysis and vision of the two realities within which they exist. 15