Water Pollution Reduction in the Textile Industry

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Why was the project undertaken? 

During the 1970’s Hammarsdale was being developed as an industrial Hub to provide employment in KwaZulu. The textile industry in particular was being attracted to the area. The Department of Water Affairs and Forestry constructed the Hammarsdale Waste Water Treatment Works (HWWTW) to service the new industrial hub. There was poor environmental planning for the expanding Hammarsdale Hub. Because of this the quality of water in the Sterkpruit River was declining and the organic capacity of the HWWTW was at its limit. The effluent discharged by companies to the HWWTW was in certain circumstances highly corrosive and in one instance led to sewerage pipes being damaged and requiring replacement. Inlet screens designed to remove excessive materials were producing 25 cubic meters of waste per week that had to be disposed of at a low hazard waste disposal site. 

The high strength organic coloured effluents from the textile industries together with that arising from a chicken abattoir overloaded the works thus resulting in the colouration of the Sterkspruit River. This pollution was exacerbated since the treatment works was not designed to remove salts from the textile industries, which passed directly through the works into the River. Unfortunately the salt issue remains a problem but two companies, Gelvenor and Dano Textiles are investigating recycling their effluent and implementing cleaner production technologies to reduce the load. 

In 1982 Umgeni Water took over the HWWTW who assisted the University of Natal to deal with the issue of capacity by involving the Hammarsdale Industrial Conservancy in a campaign to persuade industry to reduce industrial waste loads. These efforts to minimise waste and encourage cleaner production resulted in energy, water and effluent treatment savings, but still there was little improvement in the quality of effluent delivered to HWWTW. At this stage Umgeni Water was applying an effluent tariff at a flat rate, which did not account for effluent strength. As a result there was no legal or financial incentive to reduce effluent loads. 

What Processes were undertaken? 

The incorporation of Hammarsdale and the nearby township of Mpumalanga into eThekwini Municipality and the Water Services Act of 1997 were significant factors leading to the reduction of effluent load. The Water Services Act stipulated that Municipalities were to become Water Services Authorities. Etekwini Municipality chose to own and operate Hammarsdale WWTW and having by-laws to support the collection of sewerage rates and to levy an additional charge for high strength effluent. 

The by-laws required that companies discharging to the Hammarsdale WWTW were permitted. A cooperative agreement between the Norwegian Pollution Control Authority and eThekwini Municipality led to the development of a five year integrated pollution control permit. The permit set targets for effluent colour. The permit also placed stress on waste minimisation / source control techniques which would reduce the salinity and therefore the electrical conductivity (a unit used for the measurement of the salt content of water) of discharged effluent. 

This approach to tariffs and pollution control permits was the innovative spark which led to the accelerated development of waste minimisation / source control techniques which could ensure that the effluent from the textile industry was at an acceptable standard. 

The development of the waste minimisation / source control technology, which was installed at Gelvenor, was funded by the European Union and the Water Research Commission. Gelvenor was identified since it was an ISO 14001 compliant company and, together with the potential trade effluent incentives was the most likely to succeed. This was an important decision, as the area needed a successful example to market the idea of cleaner production and better environmental controls. 

Project Description This project has two main components. The first is the five-year integrated pollution control permit, which sets targets for effluent colour, electrical conductivity and places stress on waste minimisation / source control techniques. 

The second component was the development of the waste minimisation / source control technology, which could benefit companies through reduced tariffs. In Gelvenor’s case this led to a reduction of chemicals, water and electricity in the production processes, and the discolouration of water was addressed through coagulation and settlement of the dyestuff in its effluent. 

What Positives have resulted from this project? 

Positives Hammarsdale Industrial township is now on the road to becoming more economically and environmentally sustainable. This has happened for various reasons. 

Firstly, the cost of utilities has been reduced to companies. Once cleaner production technology has been installed in the textile industry this can lead to reduced water use because consumption can be reduced if the treated effluent is recycled. For example, recycled water can be used in cooling towers and in air conditioning plants and this could lead to a savings of 40% on water. Further uses for the recycled water will be for dying, in toilets and for cooking. 

Because the quality of the effluent has improved, Gelvenor is being charged at a lower tariff, which can lead to a savings of R100, 000 per month. Using the same incentive scheme Rainbow Chickens also reduced its wasted load by 50%. This means that there is 25% less waste to treat at the works and therefore eThekwini, does not have to extend HWWTW with massive savings. The use of the cleaner production technology has released capacity at HWWTW, which can now be used to extend sanitation to approximately 8500 households in nearby Mpumalanga. 

The financial and environmental sustainability of certain companies has improved due to reduced water bills and effluent disposal costs yet improving environmental controls. These savings would more than finance the cleaner production technology at a rate of R4.5 million per annum. Gelvenor’s profit margin would increase after paying off the equipment cost over five years but Rainbow would recoup its costs in less than two. 

Because water effluent is cleaner the ecosystems of the Sterkspruit River and the Shongweni Dam will automatically improve. This will also improve the sustainability of farming in the immediate area and nature reserve surrounding Shongweni Dam will also have cleaner water input. 

Negatives: 

The only negative is that it is difficult to address the salt issue since technology for salt removal from water is extremely expensive. Two companies however are investigating the salt removal and re-use of the water. 

What were the most important lessons learnt in this project? 

Co-operative governance really works. Because of the shortage of skills national and local government teamed up with international experts, local academics and parastatal organizations in order to address a common goal. No action by an individual organization would have succeeded on its own. Stakeholder collaboration need not be on a formal basis provided that the goal is clear, but does require a champion. 

Stakeholder collaboration can extend the use of the technology. 

-The University of KwaZulu-Natal is researching with Water Research Commission funding the re-use of saline effluents from textile mills. 

-Dano Textiles is investigating cutting-edge technology using nitrogen blankets in its dye-baths to reduce the quantity of sodium hydrosulphite and thus the salt content of its effluent. 

-Dye-bath effluent treatment trials have been launched using excess anaerobic sludge digestion capacity at Mpumulanga wastewater works. 

The cost of technology can be prohibitive. De-salination technology, despite major strides still remains a prohibitively expensive means of treating textile mill effluent. Farming still remains a problem because of salinity issues but the aesthetics and the organic contamination from Hammarsdale would improve.

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Warp Knitting, Production of warp knitted fabric

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Knitted fabrics are divided into two general types: (1) those produced by weft knitting, where one continuous yarn forms courses across the fabric; (2) those produced by warp knitting, where a series of yarns forms wale’s in the lengthwise direction of the fabric. 

Warp Knitting 

This form of knitting is very different from standard hand knitting; the earliest warp knitting machine was Crane’s tricot machine (England), built about 1775. In warp knitting, a yarn is fed to each needle from the lengthwise direction. A bar guiding the yarns to the needles can move from side to side, or to the front or back of the needle, so that the loops can be interlocked in a zigzag pattern. Very wide (over 400 cm, nearly 170 in.), flat fabric can be produced by warp knitting, at speeds in the order of 1,000 courses per minute, giving almost 3 m2/min (3.6 sq. yds./min). The two main machine (fabric) types are tricot and raschel. 

Diagram of simple warp knit fabric. 

Tricot warp knitted fabric: Tricot is a machine with one needle bar (spring beard type) and one to three guide bars, +0 3++most are two-bar or three-bar. The spring beard needle, accepting mainly filament yarns, has limited the depth of texture that can be achieved in tricot fabrics; some fine spun tricot, produced on machines with hybrid needles, was introduced many years ago, but does not seem to have taken hold in the market place. Tricot does not ravel, can curl somewhat, and has almost no stretch or “give” lengthwise but a little crosswise. 

Raschel warp knitted fabric: Raschel is the other main warp-knitting machine. Fabric from these machines may be of any weight or thickness from lace to carpet; the one feature they share is a pillar-and-inlay effect; Wales like hand crochet chains forming the “pillar” with other yarns laid in to form patterns or the main body of the fabric, usually making up the right side. Raschel machines have one or two needle bars (usually latch, but may be spring beard), set horizontally on wide or narrow machines with 1 to over 30 guide bars. The multi guide bar types are used mostly for laces; most of our moderate-priced laces are knit on this type of machine. They do not have the depth of texture that the twisted Leavers laces or the embroidered Schiffli laces have. Powernet, knit on the raschel machine, incorporates elastomeric yarn to give one- or two-way power stretch for contour fashion Variations on raschel-type machines include crochet, ketten raschel, and Cidega machines. The latter, similar to raschel, can knit various fabrics side by side, and so is used for many narrow trims called “braids,” such as gimp and ball fringe. 

Minor Warp Knits: Simplex is a machine with two horizontal needle bars and two guide bars, producing a double tricot type of warp knit in a fine gauge, with two threads to each loop. The needles in one bar are directly behind those in the other, in much the same way that needles in the weft knit interlock are aligned; like interlock, simplex looks like plain-stitch jersey on both sides. The fabric is very firm and stable, used for its greater firmness in lounge wear, uniforms, and gloves.

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Weft Knitting, Produce weft knitted fabric

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Weft Knitting 

There are three fundamental stitches in weft knitting: (1) plain knit stitch, (2) purl stitch, (3) rib stitch. Novelty stitches are variations of these three stitches. The hand method of knitting is weft knitting. On a knitting machine, the individual yarn is fed to one or more needles at a time 

1. Plain-knit Stitch: The plain knit is the basic form of knitting. It can be produced in flat-knit or in tubular (or circular) form. The flat knit is also called jersey stitch because the construction is like that of the turtleneck sweaters originally worn by English sailors from the Isle of Jersey; it is sometimes called balbriggan stitch after the hosiery and underwear fabrics made in Balbriggan, Ireland. Plain flat knits may be shaped or full-fashioned. The knitting is done with a row of latch or beard needles arranged in a linear position on a needle plate or in a circular position on a cylinder. All the needles are evenly spaced side by side and are moved by cams, which act on the needle butts. The spacing of the needles is referred to as the gauge, gage, or cut. As applied to many flat knits and some circular ones, gauge refers to the number of needles in 11/2 inches; for example, a 60-gauge machine would have 40 needles per inch. 

2. Purl Stitch: This construction is also referred to as the link-sand links stitch after the German word “links,” or on the left). It is made on flat-bed and circular machines by needles using hooks on both ends to alternately draw loops to the front of the fabric in one course and to the back in the next course. It is a slower and more costly technique. The fabric looks the same on both sides and resembles the back of the plain knit. Like the plain knit, the purl knit will run up and down if a loop is broken. But a purl knit fabric will not curl at the edges. 

3. Rib Stitch: Rib-knit fabrics have alternating lengthwise rows of plain and purl stitches constructed so that the face and back of the fabric appear alike. This may be produced either on a flat rib machine or a circular rib machine. In the flat rib machine, one set of needles is placed opposite the other set of needles is placed opposite the other set of needles in an inverted V position of 45 degrees to the horizontal; in the circular rib machine, one set of needles is placed vertically in a cylinder and the other set of needles is placed horizontally on a dial. In both machines, one set of needles pulls the loops to the front and the other set pulls the loops to the back of the fabric. Each set of needles alternately draws loops in its own direction, depending upon the width of the rib desired. 

For example, rib stitches can be 1 x 1, 2 x 2, 2 x 1, 3 x 1, and so on. A combination of 1 x 1 and 2 x 2 is called an accordion rib. Rib construction is costlier because of the greater amount of yarn needed and the slower rate of production Rib knits are made on a two-bed machine with one set of needles forming the loops for one wale and the other set of needles forming the alternating wale.Rib knits have greater elasticity in the width than in the length. They are stable and do not curl or stretch out of shape as do the jersey knits. For this reason, they are often used to make cuffs and necklines on weft knitted garments. Rib knits are reversible unless the number of stitches in the alternating wales is uneven, as in a 2 X 3 rib.

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Knit Fabric; Different types and classification of knitted fabric

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Single Jersey Knits Fabric  

Knitting Machines with one needle bed and one set of needles are called jersey machines or single-knit machines. With one set of needles used for knitting and one needle bed, all needles face the same direction; all stitches are pulled to the same side of the knitted fabric. As a result, single jersey fabrics have a smooth face with a vertical grain on the right side of the fabric and a width wise grain on the back side. The knittig loops formed by the jersey machine are formed in one direction only, which gives a different appearance to each side of the fabric. The basic knit fabric produced by this knitting machine is known alternately as a plain, single knit, or jersey. The terms are interchangeable.Jersey stretches slightly more in the crosswise than the lengthwise direction. If one stitch breaks, the fabric may ladder, or run. Jersey fabrics tend to curl at the edges and are less stable than are some other types of knits. This is the result of the pressures exerted during knitting. In addition jersey knits may twist or skew after laundering, as the twisting tensions imposed during the knitting process are relaxed. 

Special finishing techniques are used to overcome these tendencies and maintain fabric stability; the principal ones use starches, gum mixtures, polyvinyl acetate emulsions, and resins. 

A great many items of hosiery, sweaters, and other wearing apparel are made from plain jersey knits. Consumer Brief 16.1 highlights one of the common uses of jersey knit fabrics: Tshirts. Plain knit fabrics can also be made into designs of two or more colors by use of a patterning mechanism that controls the selection and feeding of yarns and types of stitches to create jacquard knits. 

Double Jersey Knit Fabrics 

The term double knit is generally applied by consumers to fabrics that are, technically, double jersey fabrics. Double jersey fabrics are also made on two-bed knitting machines, but the arrangement of the needles is different from that for knitting rib fabrics. The layers of loops alternate from one side to the other, locking the two layers together. Double knit fabrics have the same appearance on both sides of the fabric, that is, exhibiting the appearance of the face or outer side of a single knit on both sides. Twice as much yarn is incorporated into double knit fabrics as into comparable single knits 

Interlock Knit fabric

Interlock knits are produced on a special machine that has alternating long and short needles on both beds. Long and short needles are placed opposite each other. Long needles knit the first feeder yarn; short needles knit the second feeder yarn. The fabric created is an interlocking of two 1 X 1 rib structures. The resulting fabric, like double knit fabrics, is thicker than single knit fabric, and more stable in the width wise direction. Interlock fabrics have been traditionally used for underwear. They are produced more slowly than are other rib knits and are generally made in plain colors or simple patterns because the addition of pattern slows down the manufacture even further 

High Pile Fabrics 

High-pile fabrics, such as imitation furs and plushes, are usually knitted by a jersey machine. While the knitting is taking place, a sliver of staple fiber is fed into the machine. These fibers are caught in the tight knit and are held firmly in place. Although any staple fiber can be used for the pile, the greatest quantity of these fabrics are made with acrylic and modacrylic fibers in the pile. By using staple fibers of varying lengths, adding color through fiber dyeing or printing on the surface of the pile, and by shearing or brushing the pile, an enormous variety of effects can be achieved. The use of knitted pile fabric ranges from excellent imitations of furs, such as leopard, tiger, mink, or mouton, to colorful pile outerwear, coat linings, or pile carpet fabrics.

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Gauge and Quality; Knitting machine element to produce knit fabric

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Gauge and Quality 

The size of the needle and the spacing of the needles on knitting machines determine the number and size of the knit stitches and their closeness those are known as knitting element. Each wale is formed on one needle. The number of needles is equal to the number of Wales. The closeness of the stitches determines whether a knit fabric will be lightweight and open or heavier and more dense. The term gauge is used to describe the closeness of knit stitches. Gauge is the number of needles in a measured space on the knitting machine. Higher-gauge fabrics (those with more stitches) are made with finer needles; lower gauge fabrics are made with coarser or larger needles. 

The term cut is also used to designate the number of needles per inch in the needle bed of a circular weft knitting machine. To describe the stitch density of a single or double knit fabric, the fabric may be designated as an 18-, 20-, 22-, or 24cut fabric. The higher the cut, the closer the stitches; the lower the cut, the coarser the fabric. 

Varying types of knitting machines measure gauge over different distances on the machine. For example, circular knit hosiery measures the number of needles in 1.0 inch, fullfashioned knitting in 1.5 inches, and Raschel knits in 2.0 inches. 

Because of these differences, it is best to keep in mind the generalized principle that the higher the gauge, the closer the stitches. 

The quality of needles used in manufacturing knit goods is related directly to the quality of the fabric produced. Needles of uneven size and quality will produce knit fabrics with unevensized stitches and imperfect surface appearance. 

In warp knits, those knits in which the yarns interlace in the long direction, one or more yarns are allotted to each needle on the machine, and those yarns follow the long direction of the fabric. For weft knits, those in which the yarns interlace crosswise or horizontally, one or more yarns are used for each course, and these yarns move across the fabric. In weft knits, one yarn may have from twenty to several hundred needles associated with it. To summarize, weft knits can be made with one yarn, but warp knits must have a whole set of warp yarns, that is, one or more for each needle. 

Once the basic distinction between warp and weft knits has been made, further subdivisions of knit classifications are usually based on the types of machines used in their production. The majority of knit fabrics are named after the machines on which they are constructed. For this reason, the discussion of knitted fabrics that follows is organized around the types of machines used in manufacturing knit fabrics and the types of knit fabrics made on these machines. 

1. Flat or circular jersey, or single knit, machine: one needle bed and one set of needles. 

2. Flat or circular rib machine: two needle beds and two sets of needles. 

3. Flat or circular purl, or links-links, machine: two needle beds and one set of needles.

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Loop Formation in knit fabric structure

Loop Formation 

The spring beard needle is formed from one piece of thin wire. One end of the needle is drawn into thinner dimensions and is curved to form a hook. The flexible outer side of the hook can be pressed against the stem of the needle to close the hook for sliding a formed loop off and beginning a new loop. In 1847 Matthew Townshend invented a different type of hook known as the latch needle, which has come to be the most widely used type of needle. Its operation s similar to that of the spring beard needle, except that instead of having to mechanically press the flexible wire of the needle closed so that the forming yarn loop will not slide off, a latch closes to hold the yarn in place. 

1. The old loop is held on the stem of the needle. The latch is open (a). 

2. The hook grasps the yarn to begin forming a new loop (b). 

3. The needle falls, the old loop rises, closing the latch of the needle (c). 

4. The old loop is cast off (d and e). 

5. The needle tises, and the new loop slides down to the stem of the needle, pushing the latch open again, and the needle is ready to repeat the cycle (f).

Loop formation in knit fabric

Yet a third type of needle, the compound needle, is used almost exclusively for warp knitting. The compound needle has two components, a tongue and a hook Its motion is as follows: 

1. The old loop encircles the hook; the tongue is in such a position as to leave the hook open. 

2. Both tongue and hook rise; a new yarn is fed to the hook. 

3. Both tongue and hook descend, but the tongue descends more slowly, thereby closing the hook. 

4. As the needle descends, the held loop slides off, forming a new loop. 

5. The needle returns to its initial position, the hook ascending more rapidly, thereby opening the hook again. 

For weft knitting with either needle type, a cam system provides the action for lifting the needles as the yarn is fed in. A small projection called a butt is located at the bottom of the needle. The butt is held in a groove formed by a system of cams or shaped pieces. The movement of the butt in the grooves between the cams causes the needle to rise and fall. 

The engaging by the needle of a new piece of yarn is called feeding. Devices called feeders are located to introduce the yarn to the needles. The number of feeders can vary, but obviously the more feeders a machine has, the higher will be the speed of fabric forming on the machine, since each needle produces a loop each time it is activated and if many needles are activated more frequently, many courses can be formed at the same time. 

Another important element of some knitting machines is the sinker. The already formed fabric may need to be controlled as the subsequent knitting action takes place. A thin steel device called the sinker may be used to hold the fabric as the needle rises, support the fabric as the needle descends, and push the fabric away from the needle after the new loop has been formed. Sinkers are generally mounted between the needles. Some machines, however, do not use sinkers but instead use the tensions placed on the completed fabrics for control.