Wastewater treatment
Wastewater treatment is a process which removes and eliminates
Processes commonly used in wastewater treatment include phase separation (such as sedimentation), biological and chemical processes (such as oxidation) or polishing. The main by-product from wastewater treatment plants is a type of sludge that is usually treated in the same or another wastewater treatment plant.[2]: Ch.14 Biogas can be another by-product if anaerobic treatment processes are used. Treated wastewater can be reused as reclaimed water.[3] The main purpose of wastewater treatment is for the treated wastewater to be able to be disposed or reused safely. However, before it is treated, the options for disposal or reuse must be considered so the correct treatment process is used on the wastewater. Bangladesh has officially inaugurated the largest single sewage treatment plant (STP) in South Asia, located in the Khilgaon area of the city. With a capacity to treat five million sewage per day, the STP marks a significant step towards addressing the country's wastewater management challenges.[4]
The term "wastewater treatment" is often used to mean "sewage treatment".[5]
Types of treatment plants
Wastewater treatment plants may be distinguished by the type of wastewater to be treated. There are numerous processes that can be used to treat wastewater depending on the type and extent of contamination. The treatment steps include physical, chemical and biological treatment processes.[citation needed]
Types of wastewater treatment plants include:
- Sewage treatment plants
- Industrial wastewater treatment plants
- Agricultural wastewater treatment plants
- Leachate treatment plants
Sewage treatment plants
A large number of sewage treatment technologies have been developed, mostly using biological treatment processes. Design engineers and decision makers need to take into account technical and economical criteria of each alternative when choosing a suitable technology.[8]: 215 Often, the main criteria for selection are: desired effluent quality, expected construction and operating costs, availability of land, energy requirements and sustainability aspects. In developing countries and in rural areas with low population densities, sewage is often treated by various on-site sanitation systems and not conveyed in sewers. These systems include septic tanks connected to drain fields, on-site sewage systems (OSS), vermifilter systems and many more. On the other hand, advanced and relatively expensive sewage treatment plants may include tertiary treatment with disinfection and possibly even a fourth treatment stage to remove micropollutants.[7]
At the global level, an estimated 52% of sewage is treated.[9] However, sewage treatment rates are highly unequal for different countries around the world. For example, while high-income countries treat approximately 74% of their sewage, developing countries treat an average of just 4.2%.[9]Industrial wastewater treatment plants
Agricultural wastewater treatment plants
Leachate treatment plants
Unit processes
The unit processes involved in wastewater treatment include physical processes such as settlement or flotation and biological processes such oxidation or anaerobic treatment. Some wastewaters require specialized treatment methods. At the simplest level, treatment of most wastewaters is carried out through separation of solids from liquids, usually by sedimentation. By progressively converting dissolved material into solids, usually a biological floc or biofilm, which is then settled out or separated, an effluent stream of increasing purity is produced.[2][page needed][16]
Phase separation
Phase separation transfers impurities into a
Sedimentation
Biological and chemical processes
Oxidation
Oxidation reduces the biochemical oxygen demand of wastewater, and may reduce the toxicity of some impurities. Secondary treatment converts organic compounds into carbon dioxide, water, and biosolids through oxidation and reduction reactions.[20] Chemical oxidation is widely used for disinfection.[21]
Biochemical oxidation (secondary treatment)
Chemical oxidation
Advanced oxidation processes are used to remove some persistent organic pollutants and concentrations remaining after biochemical oxidation.[19]: 363–408 Disinfection by chemical oxidation kills bacteria and microbial pathogens by adding hydroxyl radicals such as ozone, chlorine or hypochlorite to wastewater.[2]: 1220 These hydroxyl radical then break down complex compounds in the organic pollutants into simple compounds such as water, carbon dioxide, and salts.[23]
Anaerobic treatment
Anaerobic wastewater treatment processes (for example UASB, EGSB) are also widely applied in the treatment of industrial wastewaters and biological sludge.
Polishing
Polishing refers to treatments made in further advanced treatment steps after the above methods (also called "fourth stage" treatment). These treatments may also be used independently for some industrial wastewater.
See also
- List of largest wastewater treatment plants
- List of wastewater treatment technologies
- Water treatment
References
- ^ "wastewater treatment | Process, History, Importance, Systems, & Technologies". Encyclopedia Britannica. October 29, 2020. Retrieved 2020-11-04.
- ^ ISBN 0-07-112250-8.
- S2CID 259296091.
- ^ "PM to open South Asia's largest single STP in Dhaka on Thursday". www.dhakatribune.com. 2023-07-12. Retrieved 2023-07-14.
- ISBN 978-0-07-112250-4.
- ISBN 978-81-224-1507-0.
- ^ S2CID 259296091.
- ISSN 1476-1777. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
- ^ ISSN 1866-3508.
- ISBN 0-07-041878-0.
- OCLC 48053912.
- ISSN 1476-1777. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
- ^ "Pollution Prevention Case Studies". Washington, D.C.: U.S. Environmental Protection Agency (EPA). 2021-08-11.
- OCLC 16087827.
- ^ "Landfills Effluent Guidelines". EPA. 2018-03-16.
- ^ Primer for Municipal Waste water Treatment Systems (Report). Washington, DC: US Environmental Protection Agency (EPA). 2004. EPA 832-R-04-001..
- ISBN 978-0-444-63589-1, retrieved 2020-11-30
- ^ OCLC 389818.
- ^ BERGENDAHL, JOHN. "Applications of Advanced Oxidation for Wastewater Treatment" (PDF). Dept. Of Civil & Environmental Engineering, WPI. Archived (PDF) from the original on 2017-08-29.
- ^ "Water Disinfection - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2023-03-02.
- )
- ISSN 2198-6592.
External links
- Media related to Wastewater treatment at Wikimedia Commons