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Effluent Treatment Process in Garment Manufacturing

Importance, merits, de-merits, techniques, technologies used in Textile Effluent Treatment Plants (ETP)

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The textile industry is one of the leading sectors in the economy as it contributes to total industrial production. The untreated textile wastewater can cause rapid depletion of dissolved oxygen if it is directly discharged into the surface water sources due to its high BOD value. The effluents with high levels of BOD and COD values are highly toxic to biological life.

The high alkalinity and traces of chromium which is employed in dyes adversely affect the aquatic life and also interfere with the biological treatment processes. The quality of such effluent can be analyzed by their physicochemical and biological analysis. Monitoring of the environmental parameters of the effluent would allow having, at any time, a precise idea on performance evaluation of ETP and if necessary, appropriate measures may be undertaken to prevent adverse impact on the environment. The obtained results will be very much useful in the identification and rectification of operational and maintenance problems and they can be also utilized to establish methods for improvement.

What is effluent?

According to the United States, Environmental Protection Agency as wastewater treated or untreated that flows out of a treatment plant, sewer, or industrial outfall. Generally, refers to wastes discharged into surface waters.

According to Oxford English Dictionary, it defines effluent is liquid waste or sewage discharged into a river or the sea.

According to some publications it is defined as liquid waste flowing out of a factory, farm, commercial establishment, or a household into a water body such as a river, lake, or lagoon.

Effluent is liquid discharged from any source. Effluent can originate from municipalities’ industries, farms, ships, parking lots, and campgrounds. There is a connotation that effluent contains contaminants but in the strictest sense, it could be pure water.

The term effluent refers to the left-over dyes and auxiliaries which get washed during the manufacturing processes and create pollution.

Sources and causes of generation of textile effluent

The textile industry involves a wide range of raw materials, machinery, and processes to engineer the required shape and properties of the final product. Waste stream generated in this industry is essentially based on water-based effluent generated in the various activities of wet processing of textiles. The main cause of the generation of this effluent is the use of a huge volume of water either in the actual chemical processing or during re-processing in preparatory, dyeing, printing, and finishing. In fact, in a practical estimate, it has been found that 45% of material in preparatory processing, 33% in dyeing, and 22% are re-processed in finishing [1]. But where is the real problem? The fact is that the effluent generated in different steps is well beyond the standard and thus it is highly polluted and dangerous.

 

What is effluent discharge?

Effluent discharge is liquid waste, other than waste from kitchens or toilets, surface water, or domestic sewage. It is produced and discharged by any industrial or commercial premises, such as a food processing factory or manufacturing business.

Often referred to as ‘trade effluent’ or ‘wastewater’, effluent discharge usually flows from the premises directly into the main sewer network. It cannot enter a river, reservoir, stream or lake unless it is cleaned and treated first. Only surface water can be released into a natural watercourse. If the effluent discharge goes straight into a public foul sewer, it will travel via the sewer network to the nearest wastewater treatment works for handling and processing.

The majority of trade effluent is made up of wastewater, water that has been used in a certain process to create a specific product or facilitate production, including cooling machinery or pipes.

Wastewater composition

As well as the wastewater itself, trade effluent will often contain one or more contaminants including:

  • Fats, oils, and greases (FOGs)
  • Chemicals
  • Detergents
  • Heavy metal rinses
  • Solids
  • Food waste

Larger companies have an on-site Effluent Treatment Plant (ETP). The effluent produced by a process, or processes, is treated before being discharged, if clean enough, into a nearby watercourse.

It’s also worth noting that, sometimes, trade effluent contains so many pollutants that it must be treated even before it is allowed in the sewer. If this is the case, the company in question will have to comply with whatever is required by the corresponding water company. This makes sure the trade effluent is within the consent license limits and safe to enter the sewer.

What is the Effluent Treatment Plant or ETP?

An effluent treatment plant cleans industrial effluents, contaminated water from rivers and lakes, and so on just in order to reuse the water for additional purposes.

Along such lines, water is reutilized and sustained. In fact, such gushing treatment ensures that any contaminant will be expelled from the water making it reusable. It is mostly used in industries such as pharmaceuticals, textiles, tanneries, and chemicals where there is a chance of extreme water contamination. Nevertheless, how this treatment will be applied may vary from industry to industry.

Such treatment plant ensures that the contaminated and polluted water from industries get treated and become reusable before being released back to nature. Without this treatment, it won’t be possible for humans to get clean usable water for household chores.

  • Influent: Untreated industrial wastewater
  • Effluent: Treated industrial wastewater
  • Sludge: Solid part separated from wastewater by ETP

Need for ETP in the textile industry

Clean water is essential for drinking and is needed in millions of other activities like washing, cleaning, construction of a building, manufacturing processes, and other commercial activities. It is a big requirement in industries to clean water which is affected due to their activities. The ETP Plant is designed to solve the wastewater-related issues in Industries.

Textile Industries use a large amount of water from the river in their processes and as a result, produce a large volume of wastewater which is in need of treatment before discharge into the environment. In these industries, different types of chemicals are used in dyeing and other activities. The wastewater generated by them contains harmful substances. It is important for these industries to set up wastewater treatment plants known as ETP Plant for the Textile Industry to decrease the level of polluted wastewater. Wastewater treatment plays a very important role in these industries and it is good for the industries as well. The basic thrust of the technology is to convert the entire quantity of effluent to zero level by separating water and salt using evaporation and separation technology. The concept and the treatment are based on the removal of the entire COD/BOD and the condensate coming out to meet the freshwater quality requirement in the process.

  • To clean industry effluent and recycle it for further
  • To reduce the usage of fresh/potable water in
  • To cut expenditure on water
  • To meet the standards for emission or discharge of environmental pollutants from various Industries set by the Government and avoid heftily
  • To safeguard the environment against pollution and contribute to sustainable development

Design of ETP

The design and size of the ETP depend upon:

  • Quantity and quality of the industries discharge effluent
  • Land availability
  • Monetary considerations for construction, operation & maintenance

Area dimension depends on:

  • Quality of wastewater to be treated,
  • Flow rate
  • Type of biological treatment to be used
  • In case of less available land, CETP (Common Effluent Treatment Plant) is preferred over ETP

Tips for starting ETP

It is important to have a clear understanding of the ETP before choosing to set up one. Thus, this subsection provides with few useful tips before setting up an ETP and the technology to use in the ETPs.

Some of the useful tips are as follows:

  • Selecting the appropriate place- The ETP should not be set up close to the wells or reservoirs of drinking water, wetlands, or water discharge zones
  • A Design Efficient Treatment plant: Choosing a wasted place or idle place would result in saving land. This could be land that is idle and not being used for any industrial process
  • Choosing an appropriate water treatment technology- Studying the effluent type, characteristic and volume can help adopt the ideal technology needed for treatment

Classification of the wastewater treatment process

Treatment Levels & Mechanisms of ETP

  • Treatment levels:
    • Preliminary
    • Primary
    • Secondary
    • Tertiary (or advanced)
  • Treatment mechanisms:
    • Physical
    • Chemical
    • Biological

Preliminary Treatment level

Purpose: Physical separation of big-sized impurities like cloth, plastics, wood logs, paper, etc.

Common physical unit operations at the Preliminary level are:

  • Screening: A screen with openings of uniform size is used to remove large solids such as plastics, cloth, etc. Generally, a maximum of 10 mm is used
  • Sedimentation: Physical water treatment process using gravity to remove suspended solids from water
  • Clarification: Used for separation of solids from fluids

Primary Treatment Level

Purpose: Removal of floating and settleable materials such as suspended solids and organic matter.

  • Methods: Both physical and chemical methods are used in this treatment
  • Chemical unit processes:
    • Chemical unit processes are always used with physical operations and may also be used with biological treatment
    • Chemical processes use the addition of chemicals to the wastewater to bring about changes in its quality.
    • Example: pH control, coagulation, chemical precipitation, and oxidation pH Control:
    • To adjust the pH in the treatment process to make wastewater pH
  • For acidic wastes (low pH): NaOH, Na2CO3, CaCO3or Ca (OH)
  • For alkali wastes (high pH): H2SO4,

Chemical coagulation and Flocculation:

  • Coagulation refers to collecting the minute solid particles dispersed in a liquid into a larger
  • Chemical coagulants like Al2(SO4)3 {also called alum} or Fe2(SO4)3 are added to wastewater to improve the attraction among fine particles so that they come together and form larger particles called
  • A chemical flocculent (usually a polyelectrolyte) enhances the flocculation process by bringing together particles to form larger flocs, which settle out more
  • Flocculation is aided by gentle mixing which causes the particles to collide.

Tertiary / Advanced Treatment

Purpose: Final cleaning process that improves wastewater quality before it is reused, recycled, or discharged to the environment.

Mechanism: Removes remaining inorganic compounds, and substances such as nitrogen and phosphorus. Bacteria, viruses, and parasites, which are harmful to public health, are also removed at this stage.

Methods:

  • Alum: Used to help remove additional phosphorus particles and group the remaining solids together for easy removal in the group
  • Chlorine contact tank disinfects the tertiary treated wastewater by removing microorganisms in treated wastewater including bacteria, viruses, and parasites
  • The remaining chlorine is removed by adding sodium bisulfate just before it’s discharged.
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