Water Management in Textile Industry – An Overview
Department of Textile Engineering
BGMEA University of Fashion and Technology (BUFT)
Water management is the control and movement of water resources to minimize damage to life and property and to maximize efficient beneficial use. Water management in textile industry is the activity of planning, developing, distributing and managing the optimum use of water resources. It is a sub-set of water cycle management. Water, once an abundant natural resource, is becoming a more valuable commodity due to droughts and overuse. One of the biggest concerns for our water-based resources in the future is the sustainability of the current and future water resource allocation. As water becomes scarcer, the importance of how it is managed grows vastly. Today, most countries are placing unprecedented pressure on water resources. The global population is growing fast, and estimates show that with current practices, the world will face a 40% shortfall between forecast demand and available supply of water by 2030. Finding a balance between what is needed by humans and what is needed in the environment is an important step in the sustainability of water resources. In this paper I will discuss different aspects of water management in textile industry.
Objectives of This Article:
- The activity of planning, developing, distributing and managing the optimum use of water resources, ultimately water management in textile industry.
- Competing demands for water.
- To allocate water on an equitable basis to satisfy all uses and demands.
- Ensuring fresh water supply.
- Water budgeting and analysis of surface and sub-surface drainage systems.
- Changing practices, such as groundwater withdrawal rates.
- Helps to determine future Irrigation expectations. Sustainability of water resources.
Water in Textile Industry:
Water is a very common element in our life. It uses that for our daily activities and we use it for industrial activities. It used in Food factory, Textile industry, ice factory etc. Water cannot use directly. Because many chemicals, hard particles and many impurities present in the water. Such as- Chloride, Sulphate, Carbonate, Bicarbonate of Sodium, Potassium, Calcium and Iron. In impurities salt, microorganism mixed in the water.
Sources of Water:
1. Rain water: Rain water is come from direct cloud. It is the purest of all-natural waters. Many impurities dissolved in the water. Such as Sulphur dioxide, CO2, NH3, and others by product. It is suitable for boiling, washing and dyeing process.
2. Surface water: Surface Waters come from Rain. But the water which has collected from streams, rivers or lakes. The water contains Chloride, Sulphate, Carbonate, Bicarbonate of Sodium, Potassium, Calcium and Iron. This water is not suitable for dyeing and finishing process.
3. Sub-soil water: Sub soil water is less deep water. This water is collected from shallow springs and wells which are about 50 ft. This water usually free from suspended impurities because it has been filtered by its passage through the soil. The water is not suitable for dyeing and finishing process.
4. Deep well water: This water is underground water. The water is obtained 500m below the surface. Organic compound, ammonium salts are present with the water. The presence of salts of calcium or magnesium in solution can be most undesirable in many finishing process.
Impurities of Water:
- Acidity (pH)
- Gases (CO2, O2, NH3)
- Dissolved solids
- Industrial wastes
Water hardness means the amount of dissolved calcium and magnesium in the water. A lot of materials are dissolves in the water. If hardness is found in the water than the water must be go through the softening process before using in the textile.
Types of water hardness:
There are two types of water hardness:
- Temporary hardness: When calcium and magnesium salt are present in the water, it’s known as temporary water hardness. These salts are disappears in boiling process because of that its called temporary hardness.
- Permanent hardness: When the sulphate and nitrate salts of calcium and magnesium are present in the water, it’s called permanent hardness. By boiling these salts cannot disappear.
Water softening is a technique that serves the removal of the ions that cause the water to be hard, in most cases calcium and magnesium ions. Iron ions may also be removed during softening.
Most conventional water-softening devices depend on a process known as ion-exchange in which “hardness” ions trade places with sodium and chloride ions that are loosely bound to an ion-exchange resin or a zeolite (many zeolite minerals occur in nature, but specialized ones are often made artificially.)
1. Non-ionic softeners:
These are generally ethers and polyglycol esters, ethoxylated products, paraffins and fats. These softening agents are generally less efficient than anionic and cationic ones but they withstand the effects of hard waters, acid or basic environment and also stable in presence of cations and anions. As they do not bear any charge, they are mainly applied by forced application like padding methods.
2. Anionic softeners:
Anionic softeners are produced by the condensation of fatty acids. They have good characteristics as lubricating softening agents and give the fabric a full hand. They are unstable in hard water and acid environment.
3. Cationic softeners:
They are usually quaternary ammonium salts, amino-esters and amino-amides. They are recommended for all types of fiber, and can be also applied with exhaustion process in acid environment (pH 4-5). These are also called molecular finishing agents because they form bonds with the cationic group on the surface of the fiber generally with negative electric potential.
Waste Water Management in Textile Industry:
The textile wastewater discharged from printing and dyeing processes is characterized by high chemical oxygen demand (COD), low biochemical oxygen demand (BOD), and heavy color. It is one of the major sources of pollutants in the textile industry. In particular, the COD and color of the wastewater are resistant to conventional wastewater treatment.
Wet air oxidation (WAO) has been shown to be a feasible method to convert the organic pollutants into water and carbon dioxide at elevated temperatures and pressures. Since it can achieve very high conversion rates, the wet air oxidation process typically requires much less space. Furthermore, no additional sludge or concentrated waste is produced as in the case of biological processes. WAO has been demonstrated to be a viable process for the treatment of desizing, scouring, dyeing and printing wastewater from the textile industry. WAO requires high temperatures (about 300oC) and high pressures (over 10MPa), to achieve a high COD removal within a reasonable time scale.
Textile Waste Water Units:
In textile waste water comes from different units of dyeing. A huge amount of waste water takes place for dyeing section in textile.
Textile wet processing plants of Bangladesh may be classed as:
- Knit dyeing units,
- Woven dyeing units,
- Denim plants,
- Printing units, and
- Garments washing units.
Knit Dyeing Unit:
Knit dyeing industries are one of the most highly environment polluting textile industries in Bangladesh. These are mainly engaged in processing export oriented knit fabrics. The treatment procedure and machines of woven fabric dyeing and knit fabric dyeing are quite different. This is because knit fabrics are soft and require gentle handling while woven fabrics are relatively stiffer and may be subjected to tougher treatment options’ For this reason knit fabrics are dyed in winch types of dyeing machine where treatment carried out in a very high M:L ratio like 1:150-200. It was found in various studies that nearly 150 to 200 liters of water is required to dye one kg of knitted goods. Considering all the factors it was found that a knitting factory of 10 ton production capacity generates nearly 100 to I 50 M of waters per hour. However, all the water mentioned above is not equally harmful. Some are very severely polluted while some are mildly polluted. On average, it was found that 50% of waters are polluted and needs to be treated and the rest of the water can discharged directly or subjected to very mild treatment.
Woven Dyeing Unit:
Woven dyed fabric is dyed in a different way than knitted fabrics. The volume of waste water generated from a woven dyeing factory is very low in comparison to knit dyeing process. Apart from this the characteristics of woven dyeing plants are different from those of knit dyeing plants. Before weaving, sizing is carried out to increase the strength of warp yarns. The main component of sizing is Starch. Wet process starts with desizing to remove the starch and other sizing agents from the fabric otherwise subsequent process and dyeing will not be perfect. The discharge from a desizing unit is highly polluted. Generally woven dyeing is carried out at a very low M:L ratio which could be as low as 1:5 (for continuous dyeing) hence the quantity of waste water is very low but the level of toxicity of the effluent is very high.
Denim Dyeing Unit:
Denim plants are particularly weaving plants and produce denim fabrics. In denim plant dyeing and sizing is carried out on the warp yams and after weaving various types of finishing operations are carried out. The effluent discharged from sizing and dyeing units are highly polluted as compared to that of all other wet processing plants and cause substantial impact on the environment. Off course the volume of effluent is relatively lower than that of knit dyeing.
Pollutants associated with printing include suspended solids, solvents, foam, color and metals, and in general, large volumes of water are consumed during the washing-off stages. The main areas of environmental pollution of textile printing includes dyes containing metals, objectionable surfactants, air emissions, water from washing the print blanket, leftover print paste, excess paste from drums, screens and pipes, use of urea as this increases the nitrogen in the effluent. Like denim the quantity of effluent of textile printing industry is very low but highly polluted.
At present there are a lot of garment washing plants which are operating in Bangladesh. There are basically two types washing e.g.
- Normal washing and
- Denim washing.
The denim washing involves a lot of operations like desizing, enzyme washing, finishing etc. These can be achieved by chemical or mechanical methods. Process involves use of volatile chemical. The pollution loads from garments washing plants are not much but quantity is large and requires some sort treatment.
Types of Pollutants in Water:
Preliminary or Pretreatment
Removal of large solids such as rags sticks, grit and grease that may damage equipment or result in operational problems. Preliminary treatment consists of mainly (i) Screening which is adopted in a effluent treatment plant to remove relatively large solid wastes and (ii) Equalization and Skimming – remove grease and oil and homogenize and to remove some BOD and COD. Primary Treatment Primary treatment is intended for removal of floating and settleable materials i.e. suspended solids and chemical organic matter.
Primary treatment consists of the following treatments;
- Coagulation – to coagulate the suspended solid to coagulate.
- Flocculation – to flocculate by coagulants.
- Neutralization – to adjust the pH between 6.5 to 8.5.
- Sedimentation to precipitate small suspended solids.
Secondary treatment is carried out to removal biodegradable organic matters which include removal of BOD and COD and decomposition of organic matter. Biological treatment can be aerobic and anaerobic.
Since the effluent from the textile industry is complex and variable, it is unlikely that a single Treatment technology will be suitable for total effluent treatment. Tertiary treatment includes removal of residual suspended solids/ dissolved solids. Most of the effluent treatment plants use the Adsorbents (granular activated carbon, silica, clays, fly ash, synthetic ion exchange media, natural bio adsorbents, synthetic bio adsorbents).
Without water our textile industry is motionless. So we need a lot of water for our textile industry. We have thought about our water resource and how can we use it more properly and efficiently in future. Besides we have to think about pollution of water. Before discharging the waste water in the canal or pond we have to remove the dangerous chemical from the water. Our country already facing a lot of problems for the waste water of textile. So there is no alternative without waste water management in textile industry. Government should lead all the industries in a proper way so that water resources can be secured.
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.