Pollution Control at Mill Stage. Lecture 3

Transcription

1 Pollution Control at Mill Stage Lecture 3

2 Waste Sources Cotton: In each of the unit operations or processes performed during bleaching, dyeing and finishing the liquid waste that is generated has a peculiar characteristics. The processes are mainly performed in different ways: (i) Batch wise or (ii) Continuous using different machines Kiers, Jigs The average values of ph range and BOD, total solids(in ppm range) on analysis of waste from various Textile Mill show fairly high values of these parameters indicating high waste discharge.

3 Vat Pollution effect of cotton processing waste Process ph BOD (ppm) Gal waste/ goods Slashing, sizing yarn Desizing Kiering Scouring Bleaching range Mercerizing Aniline black Basic Developed color Dyeing Direct Indigo Nephthol Sulphur

4 Analysis of waste from synthetic fibre finishing mill: ph Range Total solids range (ppm) BOD Avg. (ppm) BOD % OWF avg. Scour and dyeing Rayon processing Salt take off Water proofing Scour and dyeing Acetate processing Scour and bleaching First rinsing Second rinsing Estimated Peroxide Contained Peroxide Estimated 0.0 Scouring first rinse Nylon processing Second rinsing Dyeing Last rinsing Water proofing

5 Analysis of pollution potential of various textile mill solutions Rinse following mercerizing Experimental desize solutions, first rinse following detentiontime for enzyme action Total solids BOD ph Range range range (ppm) (ppm) Caustic kier First boil Second boil Dripping from J box Continuous scour Bleaching First rinse following caustic Second rinse following caustic First rinse following hypochlorite First rinse following peroxide

6 Waste Sources in Wool Wool needs grease scouring to remove all natural and acquired impurities from wool fiber. Pollution potential of various individual wool processes compares well with that of the combinations of various processes. Grease scouring and wash after fulling are the two main sources of pollution Thus it can be generalized that the wool waste water discharges would generate more than 50 % from scouring and the rest from other chemical processes.

7 Waste and Chemical Recovery and Reuse Biologically or chemically treated water may be suitable for reuse in processing or as cooling tower make up. Reuse would result in reduced water consumption and waste water volume. In cotton processing about 15 % of process water can be reused. Recovery of glucose as desizing waste could be effected by evaporation. The recovery of chemicals such as caustic soda from mercerization is by heating the caustic wash liquor. The concentrate when evaporated 90% of the caustic soda can be recovered. In wool use of continuous countercurrent processing can significantly reduce water consumption. Lanolin may be recovered via solvent extraction.

8 Recycling textile waste Recycling and reuse of textile wastes has assumed importance in the recent past in our country. With the rise in the living standards, the demand for textiles and clothing is expected to grow. Like any other industry this industry also generates all categories of industrial wastes namely liquids, solids and gases. Various useful materials can be recovered from these wastes by utilization of new processes. The wastage of raw materials can be reduced by improving manufacturing process at each stage, thereby savings in the major inputs. During the process certain kind of wastes such as solid wastes can be recovered by adopting new technologies, whereby these wastes can be converted into useful materials for other applications.

9 Waste Utilizations Textile industry is one of the largest industries, which consumes energy in the form of heat. New technologies are required to recover some percentage of loss of energy. Wastes utilization in the textile industry is gaining vital importance in the Indian textile industry as international legislations are also to come into force in our country. The country is looking for export market, and hence, certain standards laid down by the European countries have to be adopted.

10 Basically there are two categories of solid wastes: Solid wastes a) Manufacturing waste, which is the waste from the various manufacturing processes. b) Recovered and reclaimed wastes, which is waste collected after use and then reprocessed. The fabric waste from carding, combing, drawing and spinning are called soft waste. Wastes produced after spinning and twisting and in the process for weaving and knitting is called hard waste. Finishing waste are also called locks, which are from the finishing process of the fabric. Reclaimed wastes are mostly in the form of rags and old discarded clothing. There are wool wastes and non wool wastes.

11 Cotton textile mill waste from different processes An integrated cotton textile mill produces its own yarn from the raw cotton. Production of yarn from raw cotton includes steps like opening and cleaning, picking, carding, drawing, spinning, winding and warping. All these sequences are dry operations and as such do not contribute to the liquid waste of the mill. Carding :It is a process in the manufacture of spun yarns whereby the staple is opened, cleaned, aligned and formed into a continuous untwisted strand called sliver. Drawing :It is the process of increasing the length per unit weight of sliver. Combing :A method to remove short fibers, foreign matter from cotton stock by pressing it through a series of needles or combs. Spinning :It is a process by which a long strand of fibres is drawn out to a short strand and converted into a yarn. After drawing out, it is subjected to twisting and the resulting yarn is wound into a bobbin. Winding :It is the process of transfer of a yarn or thread from one type of package to another.

12 Weaving :It is the process of interlocking two yarns of similar materials so that they cross each other at right angles to produce a woven fabric. The entire liquid waste from the textile mills comes from the following operation of slashing (or sizing), scouring and desizing, bleaching, mercerizing, dyeing and finishing. In slashing,(to give it the tensile strength and smoothness necessary fot subsequent weaving) the yarn is strengthened by loading it with starch or other sizing substances. waste originates from this section due to spills,and the floor washings at the weak end. After slashing the yarn goes for weaving.the prepared cloth now requires scouring and desizing to remove natural impurities and the slashing compounds.

13 Wastewater Treatment Treatment with Activated Carbon: use of activatedcarbon for the treatment of textile finishing or dye house effluent is possible where one or more of thefollowing conditions exist: raw water and or effluent treatment costs are very high and or makeup watertreatments are overloaded. An ideal example is carpet mills where use of activated carbon adsorption to treat and then recycle 80 % of wastewater is possible. As no biologicalsludge is formed, solid waste disposal is minimized.

14 Waste from Synthetic fabric processing It has been estimated that the synthetic textile finishing industry can reuse about 10 % of its waste water through recovery. Recovery of Zinc from Viscose rayon processing by ion exchange, precipitation and floatation methods is practiced at many places. Wastes from the manufacture of the synthetic fibre resembles chemical manufacturing wastes, and depends entirely on the raw materials used and the process adopted.

15 The most prominent man made synthetic fibers are Rayon, nylon and polyster. These fabrics require no processing for the removal of natural impurities as they are man made. Manufacture of synthetic fabrics involve two steps: (i) manufacture of the synthetic fibre and (ii) preparation of the cloth. These two steps may be carried out either in one integrated plant, or may be separated in two different plants. A typical synthetic fibre Nylon 6 is obtained through polymerization of caprolactum and subsequent pelletization, drying, remelting in extruders, spinning and twisting.

16 Synthetic textile processing The wastes from this manufacture are usually characterized by a colloidal type turbidity, a typical colour, a low alkalinity (ph around 7.5), high amount of total solids in the order of 2500 mg/l and comparatively small amount of suspended solids. The waste usually contains a large amount of nitrogen, entirely of organic origin. The waste is also characterized by a high COD value (in the order of 500 mg/l) though the BOD is found to be very low (around 50 mg/l)