'Sequential Coagulation Studies for Primary Treatment of Textile Process Effluent Instead of Acid Neutralization'
By: B.V. Kulkarni, Dr. S. V. Ranade and Dr. A. I. Wasif
Sequential coagulation studies were carried out for primary treatment of textile effluent from different processing units at Ichalkaranji by using jar test apparatus. Various combinations of Alum, Ferric chloride and Lime, were used for the studies. It has been observed that at all the pH values, maximum (65-90%) reduction in COD, (80 to 85%) in colour and TDS removal upto (30-40%) of the actual process effluent is possible to achieve. As far as heavy metal(s) removal is concerned at the said pH, it can be seen that the maximum removal of Ni and Pb upto approx. 99% was observed. Findings of other heavy metals removal, i.e. Cd (96%), Cr (total) (80-90%), Cu (90%), Zn (80 to 90%) and Fe (80%) was observed in various combinations of Alum, Ferric chlorine and Lime, for primary treatment. Such primarily treated textile effluent can be easily treated by biological means.
Key Words - textile effluent, sequential coagulation.
With the ecology being the password of the world today, the country has to focus on environment friendly products and production processes. The textile industry is one of the oldest and second largest industry next to agriculture providing bread & butter to over 20 million people. About 700 textile mills are located mainly at Ahmedabad, Mumbai, Coimbatore, Delhi, Kanpur, Ludhiana and Ichalkaranji. It is one of the leading foreign exchange earners through export of textiles. Therefore, it has to focus its attention on production of environmental friendly textiles and effluent treatment.
Textile industry can be broadly classified in to spinning, weaving, processing and garmenting. The spinning, weaving and garmenting are the dry processes and do not contribute to water pollution. However, it is the wet processing which contributes significantly to water pollution. The pollutants generated mainly from processing of cloth, which consists of desizing, scouring, bleaching, mercerising, dyeing, printing and finishing operations.
The wool processing consists of scouring, stock-dying, carding, fulling, washing, carbonising, dyeing, bleaching, and brightening. Such processing operation involves the use of more than 8000 chemicals e.g. acid, alkali, oil, detergents,dyes,S02, H202 etc. and they generate pollutants which ultimately meet the receiving water bodies reflecting in terms of pH, colour, dissolved solids, suspended solids, acidity or alkalinity, BOD, COD, phenolics, chlorides, oil and grease, sulphate and sodium etc.
Some chemicals such as dyes, detergents, etc. need extra care for proper treatment and disposal of the textile process effluent. Recent research and surveys indicate large quantity of water for specific processes. About 230 Iitres of water are required for processing 1 Kg. of fabric. While similar other investigations indicate that the unit consumes 360 Itr. of water/kg of cloth.
With the advancement of ecofriendly processing the water requirement has been brought down to about 150 It/kg for 100% cotton fabrics and about 90 It. for 100 % polyester fabrics. Summarily, it can be seen that there is no definite figure for water consumption in the textile mills and it varies from mill to mill and one process to other.