New approach for processing eco friendly garment leather

Environmental safety is a major concern and with increasing demand from the western world for eco-friendly leather products, there are also much stronger norms/legislation for reducing the limits on harmful effluents coming from the leather industry. The concentration of chromium, sulfide and formaldehyde and the content of total solids, total dissolved solids, total suspended solids, BOD and COD in the effluent, should be as prescribed. Hence, new technologies have to be adopted to reduce the pollution and to make leather environment-friendly. There are various technologies available: one of which is applied in this project for the manufacture of eco-friendly garment leather. The analysis of the physio-chemical characteristics of the effluent is also carried out. This new technology is then compared with the conventional process to differentiate the magnitude of the parameters related to environmental concern. Introduction Untreated liquid effluent from the leather industry, adversely affects the streams, land and sewers where it is discharged. Apart from hair and suspended solids, the chemicals used (basic chromium salts, surfactants, ammonium salts, sodium sulfide, dyes, oils etc) also appear in the effluents. Animal proteins and fats exert a substantial amount of BOD value in the tannery effluent. Cr(VI) and arsenic compounds are toxic and other chemicals adversely affect water quality. Suspended solids such as hair, flesh and lime increase the turbidity of the land water, thereby reducing photosynthesising capabilities by the suspended microbial flora present in ground water. Ground water quality may be seriously affected if large quantities of dissolved solids such Cr, arsenic and chloride appear on land from liquid waste discharges. Fertility of the land is also adversely affected by wastewater from the tanning industry. If wastewater is discharged into municipal sewers, there is a possibility of blockages in the pipelines due to the formation of calcium carbonate from lime and the presence of hydrogen sulfide further accentuates the problem of wastewater handling.¹ Toxic effect of chrome on health Although the opinions regarding toxicity of Cr(III) and Cr(VI) vary, one thing is common. The accumulated concentration of Cr(VI) in the human body which crosses the limit, gives rise to the possibility of so many physiological disorders that chrome in general tends to be blamed and termed as toxic to human physiology. The toxicity of chrome falls into three types: 1) Direct contamination of Cr(VI) with the skin or the soft portion of human glands (which may have transparent blood capillaries) may be absorbed directly. The continuous storage of Cr(VI) may cross the concentration level above which Cr(VI) is toxic to the human body. 2) The inhalation of chrome in dust form may lead to an increase in the concentration of chrome in the lung or blood capillaries surrounding the pulmonary tubes and a toxic effect may be experienced. 3) A chrome absorbed as Cr(III) if remaining in the digestive canals or stomach of humans may be oxidised by the pancreas. This could have a carcinogenic effect. In general the Cr(VI) compounds are corrosive under certain circumstances to the tissues of the human body. The chromic acid (H2CrO4) is particularly corrosive because of its strong oxidising capacity. Skin reactions are of two types: 1) Cr Ulcers 2) Cr Dermatitis 3) On the Nasal Septum: The inhalation of chromic acid fumes or chromate dust lead to ulceration and perforation of the nasal septum apart from possibility of increasing concentration of Cr(VI) in the blood vessels and surrounding the pulmonary tubes. 4) On respiratory tracts: as mentioned above the prolonged inhalation of chrome dust may result in a) congestion of the respiratory tract; b) congestion of larynx; c) chromic inflammation of lungs; d) chromic bronchitis and bronchopneumonia; e) asthma. Chrome may also act as a mutagen by directly changing the DNA bases. However, although the experiments with animals have shown the mutagenic capacity, there is no basis for its carcinogenic effect especially with respect to man. But since precaution is the best method of prevention, the presence of Cr(VI) is unacceptable in leather. But Cr(VI) is very mobile owing to its capacity to diffuse through biological membrane. Once it diffuses in tissue, it may be reduced to Cr(III) and thus participate in the specific bond formation as done by Cr(III). It is necessary to consider the total chrome combination of Cr(III) and Cr(VI) since the appearance of Cr(III) and Cr(VI) is governed by the degree of oxidation. Cr(III) is physiologically unstable and tends to form insoluble hydroxide in alkaline pH which accumulates in the spleen, liver and in bone marrow. However, at very low concentrations it is an essential component of many living organisms. Toxic effects of sulfide The toxicity threshold for fish daphnia and activated sludge with respect to S-2 are relatively low. The reduction properties of soluble sulfides exist even in the soil condition. When present on land, irrespective of oxygen rich or oxygen deprived environments, it affects the fertility of land (by reducing the oxygen holding capacity of land). If tannery waste is discharged onto a particular piece of land for one or two consecutive years it could cause the soil to become barren. The slightly acidic pH of land which is generally less than 7 (pK1 of H2S is 7.0) can form the toxic HS- (sulfurated hydrogen gas). The same is highly lethal at a concentration of 700 ppm giving an acute toxic effect at 100 ppm. The sulfide may cause serious corrosion since it is oxidised biologically to H2SO4 on the pipe walls. Toxic effects of dissolved salts The inhibition of enzymatic activity is visible in a range of 50 -100g/l of NaCl, as the usual concentration of the NaCl in tannery effluent is 5-10g/l. The problem due to dissolved salt is solvable but the storage of the effluent salts may cross that 50-100g/l limit and reduce the fertility of soil. Eco-Toxicity of nitrogenous compounds 1) Organic nitrogen (ammoniacal nitrogen-reduced form) One gram of organic carbon requires approximately 2.6gm of oxygen for total oxidation whereas one gm of reduced nitrogen requires 4.1gm of oxygen; because of the higher oxygen demand, the reduced nitrogen or ammoniacal nitrogen has higher toxic effects. Ammonia is hydrolysable and can readily penetrate the tissues making it dangerous. 2) Reduced nitrite-nitrates Action or receiving water along with significant phosphorous input, the presence of nitrite or nitrates varies the growth of algae. The growth of algae leads to a high rate of reduction in dissolved oxygen impregnated water because of the high rate of reduction of dissolved oxygen. The anaerobic condition prevails in the lower water layers such as phana (plant which can grow even at a very low concentration of dissolved oxygen). These conditions where all phana will quickly die are termed as 'eutrophication'. These lead to virtual death of any stagnant lake or water ponds. Although this process is reversible it takes a long time to revert to the initial stage or to get back to the equilibrium. Health hazards The conversion of NO3 to NO2 by bacteria whereby the NO2 may lead to other problems with drinking water Methanoglobinemia, ie cyanosis of well water as it increases the concentration of ethane in the anaerobic condition in well water. Formation of nitrosoamine which is very carcinogenic for humans. Methanoglobinemia is the oxidised form of haemoglobins in blood; it may be produced due to the action of nitrites. NO2 Fe2+ ©Fe3+ haemoglobin methano-globinemia It takes away from haemoglobin therefore reducing haemoglobin's ability to carry oxygen. This reaction easily takes place in infants since the pH is less acidic in the stomach of infants compared with adults. But if the reaction is in the first stage then the infant can be cured since the reaction is reversible. In order to reduce the ecological impact of leather production, new technologies were studied and applied, mainly in industrialised countries. These clean technologies can be applied at various stages of leather manufacture. Regarding chemicals used for effluent treatment, a more efficient use of existing chemicals and some new specialities which are biodegradable can be found in tanning operations. Eco-friendly technologies mainly include: harmless chemicals with better use, a decrease or prevention of waste materials, processes which reduce volume or waste product toxicity. However, leather production will always yield proteins in solution that should be eliminated through the most adapted resources. At the same time, the necessary production of important qualities of solid waste should be orientated towards easily upgradable refuse categories, ie non-chemically stabilised. In order to eliminate them as soon as possible in the fabric cycle, acceptable economic resources have to be found for their improvement. Finally, a search for new, less toxic products which can be used 100% has to be carried out. However, it must be pointed out that although they permit good or high reduction of the load in the effluent, some eco-friendly technologies aimed at reducing the liquid discharge cannot be used in the process line because they do not produce finished leather of the same characteristics as leather from a conventional process. Other technologies exist but they are still experimental and are reserved to specific use of the leather or are still difficult to operate. They need to be confirmed before application in leather manufacture. Raw material preservation The way to preserve raw hides and skins is of a great importance to obtain good quality leather at the final stage but it is also significant regarding salt and organic pollution generated during the soaking stage when hides and skins are washed. Several possibilities are available to partially or totally eliminate the salinity and collect organic pollution at an early stage. It is difficult to remove the salinity of the effluents as the technologies applied use costly equipment. In several countries, salt pollution is strongly restricted in order to protect the drinking water. The eco-friendly technologies available for raw material preservation are: * Treatment of fresh or chilled hides and skins * Partial salt elimination * Preservation with biocides Soaking Nowadays, the first phase of the tanning process is frequently speeded up by using enzymatic products that can be considered less toxic than sulfide. In other respects, the use of less harmful antiseptics will reduce the overall toxicity of the waste while preventing excessively rapid bacterial growth. Most of these products are more expensive than PCP (up to five times more) and may not have the same long-lasting effect. The new technologies are clearly less toxic than some products currently used such as phenyl mercury acetate, trichlorophenate, pentachlorophenol. The banning of PCP in leather, shoes and leathergoods imported by Germany has accelerated the withdrawal of these products in Asian and South American countries. Unhairing - liming The unhairing-liming operation is undoubtedly the largest contributor to the net pollution for tanneries. Conventionally, mixing the hides with lime and sodium sulfide leads to residual floats containing 55% of suspended solids, 55% of COD, 70% of BOD5, 40% of nitrogen and 76% of the toxicity of tannery effluent. The eco-friendly technologies available are: * Enzymatic treatment * Hair saving unhairing-liming methods * Direct recycling of liming floats * Splitting limed hides * CO2 deliming * Weak acid deliming Much research has been carried out into enzymatic treatment: dehairing and pilot programmes established with regard to the partial or even total replacement of sodium sulfide in the unhairing liming process. Today, except for small skins that are processed through sweating, the use of enzymatic products is mainly a partial substitution of sodium sulfide. On-site tests have yielded widely varying results that could not justify full-scale industrial use. A keratin-selective enzyme that does not attack collagen has yet to be found; such a process could result in a 30% to 50% reduction in pollution for this phase of tannery process. Hair brings about an important discharge load of COD and nitrogen, and recovery systems enabling eliminating from the treatment float before dissolution have been proposed. Residual hair can be used, however, for fertilization and composting. It is useful to mention the use of weak acid deliming operations (lactic acid, acetic acid etc), but their cost limits their application to specific cases. This cost is 50-100% greater than the conventional scheme, although the application rate is not more than 0.5 to 1% of the pelt weight. With the recycling of pickling floats, for the same reasons that lead to a lowering of the quantity of salts discharged during soaking, the pickling phase is now more strictly controlled. An earlier limitation of the float volume to 50-60%, led to a reduction of the amount of sodium chloride used in this stage of the process. Today, recycling of pickling float is common practice in many tanneries to reduce the salt pollution. After collection, the used float is sieved and its acidity (mainly from formic and sulfuric acids) is controlled in the laboratory. After readjustment to initial pH value, the float is reused for the following cycle. In practice, salt savings are about 80% and reduced acid consumption is estimated at 25%, although more formic acid is saved than sulfuric acid. Tanning operations Chromium tanning salts are used today in 90% of tanning processes. Only the trivalent form is used for tanning operations and this chemical cannot be replaced, except for special purposes, to give the same quality of leather. If its concentration in waste exceeds an acceptable level, it strongly limits any possibility of upgrading, or disposing of the waste at an acceptable cost. Therefore, today, the primary objective is the best possible use of chrome as this substance remains irreplaceable. The operations that precede the actual tanning have an influence on the chrome salt behaviour on the hide, and clean technologies exist for pickling operations. The other technologies available are * Wet-white preparation * Recycling of pickling floats * Direct recycling of chrome tanning floats * Two stage recycling of tanning floats * Recycling after precipitation * Tanning products that improve the exhaustion rate * Other mineral tanning * Improvements in tanning equipment Wet-white production In order to limit the amount of chrome containing wastes obtained after tanning (mainly splits and shavings), these operations need to be carried out earlier in the tanning process. The splitting of limed hides, in spite of its reduced precision, has several advantages. Shaving, which increases skin temperature up to 65-70°C, appears possible only once pretanning has already taken place. The use of aluminium salts as well as glutaraldehyde, zirconium, titanium, magnesium, on their own or combined with dialdehyde-based synthetic tanning agents, makes it possible to split and shave the leather of which tanning and character are perfectly reversible. In spite of the obvious advantages of such technology (good valorisation of pretanned waste, possibility of sorting before tanning, and improvement in surface yield), certain factors limit the diffusion of such a process. Current retanning and dyeing processes have to be somewhat adapted, as they react differently with aluminium pretanned leather. Retanning-dyeing-fatliquoring chemicals: today, Eco-friendly technologies suitable for this production cycle are principally based on the products used; especially dye and pigments. Chromium (VI), lead and cadmium salts can still be found in some types of older dyes and pigments. Some azo-dyes containing carcinogenic amino-compounds such as benzidine, have to be banned from tannery use. For re-tanning based on Cr(III), the same problem encountered with tanning arises. In some cases, the concentration of this element in the discharge is equivalent. Good practices should lead to an elimination of this kind of retan, or a selective recovery circuit, but not a recycling system in the process itself. Fatliquoring oils used in the tannery are often composed with chlorinated alkane sulfonates and fatty acid methyl ester sulfonates that are now questionable because of the organic halogen quantities they can generate. As a result of the regulation on absorbable organic halogens AOX, the chlorinated fatliquoring products will be replaced. Various substitutes are on the market to satisfy new laws in this field. Methodology Raw material used: cow calf skins Number of pieces: 11 Average size: 4 sq ft Acknowledgement Authority of Dr B R Ambedkar National Institute of Technology (Deemed University) Jalandhar for providing all kind of facilities for carrying out this research and correspondence for publication. CLRI, RCED, Jalandhar, for providing all sorts of facilities for carrying out the sample trial and using the testing facilities there. All the distributors of different leather chemicals companies in and around Jalandhar for providing sample chemicals to carry out the trials.