39 Recycle and reuse of textile waste water

R. Sukanya Devi

epgp books

 

 

 

 

Introduction

 

Water is a scarce natural resource and it is very essential for all living beings. Recycling and reuse of water is an effective method to utilize water. The textile industry consumes large quantities of water and produces large volumes of waste water from different processes. In this session we are going to have a look at the recycling and reuse of treated waste water from the textile wet processing industry

 

Wastewater as a resource

 

Dilution of Domestic and industrial waste water is not a viable solution both practical and economic aspects. Since,there is no dilution available in the receiving water bodies, it is important that no wastewater is discharged into them even after treatment. The efforts should be to use entire wastewater after proper treatment for industrial use again or for inferior usage. Many companies are coming in this business. Focus should be to promote such business. This will benefit the water quality in many ways:

  1. reduce pollution
  2. save water
  3. save nutrients
  4. reduce over-exploitation of water resources

Recycled water

  • Reclaimed or recycled water (also called wastewater reuse or water reclamation) is the process of converting waste water into water that can be reused for other purposes.
  • Reuse of water can be classified as
  • Direct potable reuse water
  • Indirect potable reuse water

Need for recycled water

 

Industrial and population growth. A growing population increased the need for power generation, for example, which placed greater demands on water use.

 

Fresh water costs. The cost of clean, fresh water is continually increasing, and is impacting all regions.

 

Regulatory requirements. Many industrial sites have wastewater discharge permits that include flow and quality restrictions. Moreover, EPA Industrial Effluent Guidelines are often revised.

 

Social responsibility. Protecting the world’s resources is a global concern: the general public is paying attention. Negative publicity around a company’s water use can have an impact on a company’s sales/growth.

 

Discharge costs. Sewer and wastewater costs have increased at a higher rate than fresh water costs.

 

Water scarcity. Many regions in North America are susceptible to drought. Additionally, some industrial plants have limited access to clean/fresh water.

 

Wastewater processing limitations. In many industries, plant wastewater treatment capacities have not increased proportionally with plant production. Plants are challenged to meet higher flows and have limited operational resources.

 

Sustainability efforts. Many companies strive towards sustainability by utilizing economically sound programs that help minimize a plant’s negative environmental impact while conserving energy and natural resources.

 

Applications of recycled water

 

Reuse may include

  • Irrigation of gardens and agricultural fields
  • Replenishing surface water and ground water(i.e., ground water recharge).
  • Water also be directed toward fulfilling certain needs in residences (e.g. toilet flushing), businesses, and industry,
  • Even be treated to reach drinking water standards.
  • Reuse of treated water by the same industry
  • For construction activities ( concrete mixing)
  • Artificial lakes

Factors influencing recycling and reuse of water

  • Limited primary fresh water sources
  • Awareness on environmental pollution
  • To reduce and eliminate discharges of wastewater into receiving environment.
  • Scope to overcome political, community and institutional constraints
  • Minimization of infrastructure costs ( total treatment and discharge costs) Environmental benefits of water recycling

Reuse of water provides benefits to environment such as

  • Provides additional source of water
  • Recycling helps to find ways to decrease the diversion of water from sensitive eco systems
  • Decrease / reduce wastewater discharge
  • Reduction and prevention of pollution
  • Tailoring water quality to a specific water use reduces the energy needed to treat water.
  • The reuse and recycling of wastes for agricultural purpose would not only help to reduce the pollution and requirement of fresh water for such use but also would supplement the much needed nutrients and organic manure to the plants.
  • The segregation of waste water streams may help in reducing waste water volume and waste strength and may help recycling and reuse of majority of waste streams.

Classification of surface water in India

 

In India, the Central Pollution Control Board (CPCB), an appex body in the field of water quality management, has developed a concept of “designated best use”. According to which, out of several uses a particular water body is put to, the use which demands highest quality of water is called its “designated best use” , and accordingly the water body is designated. The CPCB has identified 5 such “designated best uses” as tabulated below

Textile wet processing

 

Textile wet processing uses huge quantities of water for finishing of the textile materials. For treating one kilogram of the textile fabric approximately 110 litres of water is used. The processed waste water is termed as effluent and the waste water after processing is treated in many ways in order to convert the waste water into reusable water.

 

Input/ output analysis of textile wet processing industry

Characteristics of textile waste water

 

The amount of water consumed by various types of fabrics varies from industry to industry depending on the dyeing process and the type of fabrics produced. In fact, it has been found that 38 % of water is used during process of bleaching, 16 % in dyeing, 8% in printing, 14 % in boiler and 24 % for other uses. As a result of various processes, considerable amounts of polluted water are released. The fact is that the water let out after the production of textiles is well beyond the standard and contains a large amount of dyes and other chemicals which are harmful to the environment.

 

Treatment of textile waste water

 

The two major problems with textile wet processing industries include (i) enormous consumption of water and (ii) discharge of dyes and allied organic chemicals. The environmental law for the dyeing effluent in India is very stringent and this necessitates the need for efficient treatment methods that must follow Zero Liquid Discharge (ZLD). Zero-liquid discharge (ZLD) is a water treatment process in which all wastewater is purified and recycled; therefore, leaving zero discharge at the end of the treatment cycle. These secondary pollutants and their disposal is a serious problem, thus there is need to shift from ZLD towards Zero Waste Plants. This can be attained by focusing on complete removal of dyes, and other organics from the effluents before their discharge on to the soil and water bodies, in addition to water recovery.

 

Flow diagram of zero liquid discharge

 

The treatment of waste water from the textile chemical processing units, generally undergo the following treatments.

 

Primary and Secondary treatment

 

The conventional treatment systems like Physico-chemical treatment followed by biological treatment system are installed in majority of textile industries. The first step in the wastewater treatment is to mix and equalize the waste water streams that are discharged at different time, and different intervals from different stages in the processes. Some industries also prefer screening, oil trap prior to equalization for removal of solids and oil and grease. Equalization ensures that the effluent have uniform characteristics in terms of pollution load, pH and temperature. The effluent is then subject to flash mixing for the addition of coagulants such as lime, alum, ferrous sulphate, ferric chloride, poly-electrolyte and processed through clari-flocculator or flocculator and settling tank. Selection of appropriate coagulants and doses of chemicals is determined on the basis of treatability study of effluent samples. The chemical treatment helps in reduction of color and suspended solids. A significant reduction in BOD and COD values is also observed. This Physico-chemical treatment is followed by biological treatment process which further reduces BOD and COD values. The textile process houses which undertake chemical processing do not have much organic load in their effluents. In such cases, the recent trend is to set up an activated adsorption system or an Ozonation unit instead of biological treatment.

 

Tertiary treatment

 

Textile effluents may require tertiary or advance treatment methods to remove particular contaminants, dissolved salts or to prepare the treated effluent for reuse. Some common tertiary operations are removal of residual organic color compounds by adsorption and removal of dissolved solids by membrane filtration. Sometimes the wastewater is also treated with ozone or other oxidizing agent to destroy many contaminants. Evaporation and crystallization are other methods to minimize effluent disposal problems.

 

Advance methods for tertiary treatment

 

Adsorption

 

The adsorption process is used to remove color and other soluble organic pollutants from effluent. The process also removes toxic chemicals such as pesticides, phenols, cyanides and organic dyes that cannot be treated by conventional treatment methods. Dissolved organics are adsorbed on surface as waste water containing these is made to pass through adsorbent. Most commonly used adsorbent for treatment is activated carbon. The activated carbon once it is saturated needs replacement or regeneration. The chemical regeneration can be done within the column either with acid or other oxidizing chemicals.

 

Ion Exchange

 

Ion exchange process is normally used for the removal of inorganic salts and some specific organic anionic components such as phenol. In the ion exchange process the impurities from the effluent streams is transformed into another one of relatively more concentrated with increased quantity of impurities because of the addition of regeneration chemicals.

 

Reverse Osmosis

 

After primary, secondary and/or tertiary treatment, further purification by removal of organics and dissolved salts is possible by use of reverse osmosis. The process of reverse osmosis is based on the ability of certain specific polymeric membranes, usually cellulose acetate or nylon to pass pure water at fairly high rates and to reject salts. To achieve this, Water or waste water stream is passed at high pressures through the membrane. The applied pressure has to be high enough to overcome the osmotic pressure of the stream, and to provide a pressure driving force for water to flow from the reject compartment through the membrane into the clear water compartment. RO membranes are susceptible to fouling due to organics, colloids and microorganism. In a typical reverse osmosis system, the feed water is pumped through a pre-treatment section which removes suspended solids and if necessary, ions such as iron and magnesium which may foul the system. The feed water is then passed through the reverse osmosis modules at high pressure.

 

Flow chart of textile waste water treatment plant

Use of recycled water

  • Secondary treatment : Biological oxidation and disinfection
  • Surface irrigation of orchards and vine yards
  • Non-food crop irrigation
  • Restricted landscape impoundments
  • Ground water recharge of non-potable aquifer
  • Wetlands, wildlife habitat, stream augumentation
  • Industrial cooling process

Tertiary and advance treatment

  • Textile processing industry utilizes the total amount of water after tertiary treatment for its own process. Apart from this it can be used for
  • Landscape and golf course irrigation
  • Toilet flushing
  • Vehical washing
  • Food crop irrigation
  • Unrestricted recreational impoundment
  • Indirect potable reuse – ground water recharge for potable aquifer and surface reservoir augmentation

Reuse norms for various applications

Quality issues of waste water reuse

  • There is no evidence of increased enteric diseases in housing areas irrigated with treated reclaimed wastewater
  • No evidence of significant risk of viral or microbial diseases due to effluent aerosols from spray irrigation with reclaimed water

Future of water recycling

  • Water recycling has proven to be effective and successful in creating a new and reliable water supply without compromising public health
  • Textile industry at the maximum utilizes the water for its own process due to zero liquid discharge treatment process. Solution for effective discharge of sludge is required
  • Textile industry requires cost effective advanced treatment methods
  • Non potable reuse is an accepted method and will continue to grow

 

Conclusion

 

So far we have discussed about the recycling methods and the reuse of the waste water from textile industry and it is very essential to preserve , effectively utilize and reuse water for sustainable growth of our country.

 

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REFERENCES and URLs

  1. Mani, P, Madhusudanan, M (2014), Zero Liquid Discharge scheme in a Common Effluent Treatment Plant for textile industries in Tamilnadu, India, Nature Environment and Pollution Technology, 13(4), 769-774.
  2. Chavan R.B (2001), Indian textile industry – environmental issues, Indian Journal of Fibre and Textile Research, 26, 11-21.
  3. http://www.gcpcenvis.nic.in/Manuals_Guidelines/textile_guidelines_final.pdf