Journal of Scientific & Industrial Research Vol. 60, June 2001, pp 443-450 Water Management in Leather Industry V John Sundar, R Ramesh, PS Rao, P Saravanan, B Sridharnath and C Muralidharan Central Leather Research Institute, Adyar, Chennai 600 020, India Received: 02 June 2000; accepted: 10 November 2000 Leather industry, like paper and textile industries, consumes large quantities of water. Such excessive usage, resulting from adoption of traditional processing methods and equipments, lead to acute water availability and eftluent treatment problems. Presently, about 30 billion litres of water is being used by this industry annually. A systematic study made at CLRI to reduce the excessive usage and further minimise water consumption in leather processing through optimisation and recycle and reuse strategies. The role of newer equipments, such as the hide processor and th e compartmental drum in minimising water usage in leather processing has also been studied extensively. Most of the protocols standardised at CLRI were implemented at select tanneries in Indi a and Sri Lanka, which resulted in better water management in the leather processing industry. The results of such detailed studies have been incorporated in the paper. Introduction vation efforts. The major responsibility, however, falls Water utilisation by mankind may be divided into three on the industry. broad categories, agricultural, domestic and industrial. Apparently, there is no dearth of water as 80 per cent of the earth's surface is covered by water. Even then, the Water Usage in Leather Industry world is heading towards a water crisis because 97.5 per cent of the global water reserve is salt water and only Water is an important medium in leather processing. 2.5 per cent constitutes fresh water reserve. Out of the Almost all the unit operations of leather making use water fresh-water reserve, 68.8 per cent is present as glaciers as a processing medium. Nearly 40-45 L water/kg raw­ and permanent snow cover, 30 per cent as fresh ground hide or skin is used by tanneries for processing finished water, and only 0.3 per cent is present in the form of leathers. With annual raw- hide or skin processing of the lakes and rivers and 0.9 per cent as soil moisture. The order of 690,000 tonnes, total water requirements for world population also doubled between 1940 and 1990 the industry approximate 30 billion litres. Such huge and so did the per capita water consumption from 400 to volume of water, used in leather processing, poses two 3 problems, vi z. , availability of water in required quantity 800m • The World Bank has, recently estimated that the demand for water could be expected to grow by over and the treatment of effluents thus generated, as almost 1 entire quantity of water used in processing is let out as 650 per cent in the next three decades • effluent. Apart from pollution load, the huge quantities In spite of India being one of the wettest countries in of effluent require large in vestments on effluent water­ the world, with average annual rainfall of about 1200 treatment plants. mm, it is ironic that drought conditions and floods are witnessed simultaneously year after year. A major por­ Conventional Leather Processing Technology tion of 400 Mham of rainwater is lost by way of seep­ The leather processing activities can be broadly cat­ age, evaporation and run off to sea and she is able to egorised into Beam house, Tanning and Post-tanning utilise only 38 Mham, nearly one-tenth of the total rain­ operations. fall, with irrigation accounting for 92 per cent of it, leav­ Beam House Operations ing a mere 8 per cent for domestic and industrial use ~ . Thus, the composition between human and industrial Soaking, liming, deliming-cum-bating and pickling are demands comes under sharp focus of the water conser- the unit operations under this category which are briefly discussed below: *Author for correspondance 444 J SC IIND RES VOL 60 JUNE 200 1 Soaking Tanning Salted hides and skin s constitute major raw materi al Tanning basicall y aims at stabi I isati on of hide. which fo r processin g by the industry; the salt content varyin g is obtain ed th rough treatments w ith a variety of agents between 25-35 per cent by weight. The first operati on in li ke vegetable tanning materi als, mineral tanning salts, leather processing is to reverse the changes brought about syntheti c tannins, alde hydes, etc. T he choice of tanni ng in curing and bring hides and skins back to the ori gin a l meth od and the agent depends c hi efly on the properti es condition as they were fl ayed. Generall y, soaking is cl one required in the fini shed leath er, cost of materials and the to remove salt absorbed by hides and skins during cur­ type of raw material. The most common tannin g sys­ in 0'a and ' al so , to rehydrate the skin. Other mate ri als li ke tems used are vegetable, chrome or a combination of dirt , dun b>a blood and some of the inter fibrill ar protein s both. As more th an 80 per cent of fini shed leath er, pro­ are also removed during soaking. In soaking, 6,000-9,000 duced in India, is through chro me tannage, the paper is L water/t hide is used. ori ented towards technologies concerned with process­ Liming ing of such leathers. Liming - is carried out in two stages-in the first Conventi onall y, chro me tannin g invo lves treating stage, hair or wool and fl esh are loosened whi ch fac ili ­ pickled pe lt with basic chromiu m sul phate, using water tate their mechani cal removal; and in th e second stage, as th e medium. After ascerta ining suffic ie nt penetrati on th e hide matri x structure is opened up w hi c h promotes of chromium by examining the cross--sec ti on, the pH of diffusion of chemicals in subsequent operati ons. The first the tanning bath is raised to 3.8-4.0. Water in the range stage is designated as de/wiring operation and the sec­ of I ,500-2,000 Lit pe lt is used in tanning process. ond is termed as reliming. In the cl ehairing operati on, a Post-tannin g Operations paste, containing li me, sodium sulphide and/or an en­ zyme, is used while for re liming, 3-3.5 per cent li me Post-tanning techn ology covers wet processes th at are soluti on is used. Water to the tune of 4,000-6,000 Lit perfo rmed on tanned leathers and consists of rechrome hi de is used in liming . After re liming, the hides are ta nning, ne utra li sati o n , re ta nnin g , dye ing and fles hed and weighed. The weight thus obtain ed is termed fat liquoring. as pe lt-weight and it forms the basis of oth er operati ons Rechrome Tanning up to tanning. T he levell ed chrome tanned hi des are treated w ith Deliming-cum-bating basic chromium sulphate in order to equali se chrom ium Deliming is carried out usin g ammonium chl oride or in tanned leathers, and the process consumes water be­ ammonium sulphate to neutralise and remove the lime tween 2,000-3,000 Lit chrome tan ned leathers processed. from pe lt. The end-point is ascerta ined w ith phenol ­ Neutralisation phthale in , and absence of pink colour in dicates absence T he ac idi ty of leather is neutrali sed and, with th is, of lime. Treatment of de limecl hides with enzymatic the charge characteri sti cs of leath er are a lso a ltered. T he preparati ons (i e, bates), fo r removal of scud, short hair surface charge of chrome-tanned leather, w hi ch is hi gh ly and to improve grain characteri sti cs is called bating. cati oni c, is reduced during neutrali sation to less pos i­ Completion of bating is ascertained by retenti on of thumb ti ve nature so th at the uptake of ani onic retanning agents, impression or squeezin g out the air through the skin. dyestuffs and fat liquors could be regulated . Thus, neu­ Water, at the rate of 4,500 to 5,000 Lit hide, is used in trali sation makes it possible to achi eve a better and uni­ cl eliming and bating. form distribution of processing agents d uring subsequent Pickling processing. Neutralisation is carried out in three stages, viz, washing, neutrali zation, and agai n washin g, requi r­ The process of conditioni ng clelimecl and bated pe lts in g 5,000 to 6,000 L water/t tanned leathe r. for chrome tanning is called pickling. Typically, pe lts are treated with I 0 per cent brine solution initially. Then Retanning sulphuric acid is added in feeds to attain equilibrium By nature, a c hrome-tanned leath er lacks fullness due cross-section pH of 2.8-3.0. In pickling, 800- 1,000 L to lower molecular weight of chro me complexes. Hence, u t MPrft hirJP. is li S~ rl . r hrnmP. t ~ nn ~ rll ~<~ th ~ rs are alwavs subiected to retanning. SUN DAR eta/.: WATER MANAGEME TIN LEATH ER II DUSTRY The type of retannage and amount of retanning materi ­ Better Water Management: Proven Strategies als va ry depending upon th e characteri sti cs desired in CLR l has evo lved a number of water manage men t the final leather.