Human activities create wastewater that can be catastrophic to the environment and also cause water loss (in the form of wastewater, which is 99% water by weight) in places where water is scarce.
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When wastewater contaminates rivers and groundwater tables, the water resource is unusable. Therefore, it is imperative that wastewater is treated before it is released into the environment and, if possible, treated to make it potable.
Wastewater Treatment: An Overview
The objective of wastewater treatment is to reduce pollutants to less than the maximum permissible limits to prevent harm to the environment and human health. To achieve this, wastewater is collected and treated in large plants before being released into the environment. Domestic dwellings, commercial businesses, and heavy industry produce wastewater.
Wastewater follows a determined treatment path to achieve water quality standards, regardless of whether conventional or advanced treatment systems are used. As it passes through the wastewater treatment facility, wastewater is commonly called influent.
The degree and type of wastewater decide the nature of treatment and the engineering scale of the plant. Most wastewater treatment plants consist of primary and secondary treatment.
Stages of Wastewater Treatment
Primary treatment
Primary treatment involves separating and removing solid matter and homogenizing the remaining liquid waste. Due to gravity, this solid matter will either float or readily settle out. Physical processes such as screening and grit removal may be used during primary treatment.
Large objects that could block tank inlets or plug lines are removed during the screening process. Grit chambers slow down the wastewater flow and allow grit to fall out. Solids that can settle in a sedimentation tank are pumped away.
Secondary treatment
The secondary treatment involves a biological process. Wastewater is exposed to aerobic bacteria, where the biological oxygen demand (BOD) is reduced. Aerobic bacteria break down pathogens, other contaminants, and suspended organic matter into carbon dioxide, water, and biosolids. Aerobic bacteria are naturally supplied in wetland habitats. Sewage treatment plants often use baffles with a special coating of aerobic bacteria.
Municipal wastewater is normally disinfected with chlorine or other disinfecting compounds. Occasionally, ultraviolet light or ozone is used.
Tertiary treatment
Tertiary treatment improves the ‘final look’ of water, making it indistinguishable from any freshwater source. It deodorizes, decolorizes, and further oxidizes if necessary. Tertiary treatment is becoming increasingly common in modern wastewater treatment plants.
Tertiary treatment involves removing nutrients such as phosphorus and nitrogen from wastewater. Removing nutrients is an important step in restricting downstream effects such as algal blooms and eutrophication, which destroy ecosystems and habitats.
Based on the influent, wastewater treatment plants may be sewage treatment, municipal wastewater treatment, industrial wastewater effluent treatment, or agricultural wastewater plants.
A Brief History of Wastewater Treatment
As long as urbanization has existed, human waste must be removed to avoid water source contamination and potential disease. In ancient times, many cities had drainage systems, mostly used to remove rainwater. Rome’s Cloaca Maxima (“Great Sewer”) was one example of early sewage management, transporting wastewater and human waste via conduits into the River Tiber.
Wastewater and sewage removal remained largely unchanged and relatively primitive until the 19th Century. Gong farmers, for instance, would remove human waste, which would be used for agricultural fertilizer. Waste dumped into rivers and water sources around urban areas contaminated them. Several outbreaks of disease, such as Cholera, meant that proper solutions were needed.
Local conditions in densely populated areas after the Industrial Revolution often became intolerable, and the aforementioned disease outbreaks and impacts on human health led to the development of sewers which could adequately remove human waste, although this was still deposited into nearby bodies of water, meaning that surface water pollution became a critical problem.
The advent of centralized sewage treatment plants in the late 19th and early 20th centuries in countries such as the UK and the USA markedly improved the health of urban populations and the environment. Wastewater and solid effluent could now be treated by a combination of physical, biological, and chemical processes. Arguably, the development of these technologies has hugely improved global health.
By the mid-20th century, concerns began to be raised with the environmental impact of human activity and waste in particular, leading to more stringent regulations pertaining to the treatment and release of wastewater and effluent into the environment. For example, there was an increase in the pre-treatment of industrial wastewater to prevent toxic chemicals entering the environment.
Today, wastewater treatment plants are large, complex facilities that employ a raft of physical, biological, and chemical processes that can eliminate nearly all contaminants before releasing water back into the environment, providing potable water for the growing world population free of potentially dangerous pollutants and toxic chemicals.1
How Chicago Cleans 1.4 Billion Gallons Of Wastewater Every Day | Deep Cleaned | Insider
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Emerging Technologies
Increasingly strict water standards mean that older wastewater treatment plants require frequent upgrading. However, this is challenging due to limited expansion space. Improved treatment methods largely eliminate this challenge. Some emerging methods include the integrated fixed-film activated sludge (IFAS) and membrane bioreactor processes.
Wastewater treatment plants are becoming increasingly automated to ensure stable operations. Sophisticated technologies such as online analytical instruments (supervisory control and data acquisition) (SCADA), human-machine interfaces (HMIs), and advanced process control software are now commonplace technologies in wastewater treatment plants worldwide.
Advanced technologies reduce the need for supervision, streamline processes, and can help predict and avoid any potential problems which may arise during wastewater treatment.1
Environmental Considerations
Sustainability is fast becoming a key element of wastewater management and treatment. Green technologies such as solar and wind power, economical and ecologically friendly disposal systems, constructed wetlands, and groundwater recharge systems are increasingly used in the wastewater treatment industry.
Moreover, there is a growing recognition that modern wastewater treatment facilities can act as resource recovery facilities. Emerging processes and technologies allow nutrients and industrially important chemicals are not only removed from effluent, preventing their release into the environment, but can be recovered and reused in line with a circular economy model.1,2
Key Companies
The top wastewater treatment and management companies worldwide include Veolia Environment, Xylem, Aquatech International, DuPont, Calgon Carbon, Toshiba Water Solutions, and Ecolab. These companies serve domestic customers and industries like oil and gas, textiles, and food and beverage manufacturers.3
In Conclusion
Wastewater and sewage management and treatment have a long history stretching back into antiquity. While for the bulk of human history, this has been a largely primitive affair, technological progress since the late 19th century has meant that human populations are healthier today thanks to the effective removal of disease and pollution from drinking water and the environment.
Emerging technologies and the growing need for environmental remediation and sustainability (as well as emerging circular approaches to waste management) are driving the industry forward into the 21st century. While significant economic and technological challenges persist, wastewater treatment today is far more efficient than in even the past few decades.
References and Further Reading
- Ambulkar, A et al. (2024) Wastewater Treatment [online] Britannica.com. Available at: https://www.britannica.com/technology/wastewater-treatment (Accessed on 02 November 2024)
- Kesari, K.K et al. (2021) Wastewater Treatment and Reuse: a Review of its Applications and Health Implications Water, Air & Soil Pollution 232, article no. 208. [online] Available at: https://link.springer.com/article/10.1007/s11270-021-05154-8 (Accessed on 02 November 2024)
- James, N (2024) Fluid Frontiers: Top 10 Companies in Water and Wastewater Treatment [online] Verified Market Reports. Available at: https://www.verifiedmarketreports.com/blog/top-10-companies-in-water-and-wastewater-treatment/ (Accessed on 02 November 2024)
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