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What is wastewater treatment?

Wastewater treatment consists of a series of physical, chemical and biological processes aimed at eliminating contaminants present in water from domestic, industrial or agricultural use. This process transforms wastewater into an effluent that can be returned to the water cycle with minimal environmental impacts or reused. Contaminants present in wastewater include, but are not limited to, organic matter, nitrogenous compounds, phosphorous, pathogens, heavy metals and emerging micropollutants, whose presence in water bodies can lead to eutrophication, decreased biodiversity, and risks to public health through disease transmission. In addition, the proper removal of these pollutants prevents the degradation of aquatic and terrestrial ecosystems, thus protecting ecosystem services essential for human life and the maintenance of biodiversity. The optimization of wastewater treatment is, therefore, a technical challenge that requires constant updating in line with scientific advances, and regulation in accordance with environmental and public health standards. Currently, there are wastewater treatment systems that operate on the basis of fixed activated sludge treatment, ideal for multi-family dwellings, residential subdivisions, small municipalities or for heavy-duty residential applications. These systems break down organic matter and nutrients in wastewater on-site and with capacities ranging from 10,000 to 160,000 gallons per day (GPD).

Sedimentation

In the first stage, the wastewater enters a sedimentation zone, also known as a clarifier or settling tank. Here, gravity acts as a separation mechanism where suspended solids heavier than water settle to the bottom of the tank, forming primary sludge. This process reduces the load of organic matter and suspended solids entering the next stages of treatment, allowing a more focused treatment of soluble and finely suspended matter. The clarifier is accompanied by filter screens for suspended solids that remain floating in the water. These screens have diagonal openings that retain the solids that have not settled by gravity while the water flow enters through the openings to the next stage of the process. Solids remaining on the surface of the filter screens can be easily removed through an easily accessible plunger mechanism.

Aeration

The water goes to a next step where an air blower installed on the floor introduces oxygen into the treatment tank so that the water arrives with a large amount of air to an air pump. In this pump the air is injected into the bottom of a submerged pipe where the water and air then mix and travel up another pipe to a system that disperses a large amount of wastewater and air into the microbial treatment tank. Aerobic microorganisms require oxygen to metabolize the organic contaminants present in the wastewater. The oxygen supplied during aeration is used in the biochemical processes that convert these substances into carbon dioxide, water and biomass. In addition, the presence of oxygen facilitates the oxidation of organic matter to simpler, more stable forms, which is a key component in the reduction of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) in wastewater.

Fixed media tank treatment

The central component of the treatment system consists of a main tank housing 20 to 200 fixed-film treatment modules or liners, which serve as a habitat for microorganisms. This main tank is equipped with an intensive aeration system. Air is injected into each of these modules to agitate, recirculate and provide oxygen through the fixed media layers. When the robust flow of water and air reaches this point, adsorption of organics, nutrients and pathogenic organisms by the abundant, self-regulating microbes attached to the media takes place. The aerobic microorganisms use the oxygen that reaches the system for oxidation processes of organic matter, decomposing it into carbon dioxide, water and energy, a process known as aerobic respiration. This energy is used by the microbes to grow and reproduce.

Applications of treated wastewater.

In FAST systems for wastewater treatment, after the microorganisms have performed their cleaning function, the water can be used in various applications that do not require potable water, however, the quality of the treated water must be considered to identify its ideal use. Treated water can be used for irrigation of crops, lawns, golf courses and green areas. For this use, it is essential that the water meets quality standards to avoid soil and crop contamination. Wastewater can also be used to recharge subway aquifers through infiltration into the soil, but always taking into account that existing groundwater must not be contaminated.

Benefits of wastewater treatment

  • High efficiency in small spaces: FAST systems are designed to be compact, which is ideal for sites with limited space. They can be smaller than traditional activated sludge systems, making them an effective solution for small communities, residential developments, hospitals, schools, and commercial and industrial facilities.
  • Simplified operation and maintenance: These systems are relatively easy to operate and maintain. With their compact design and robust biological processes, they require less daily attention compared to more conventional treatment systems. Process automation can also reduce the need for constant monitoring.
  • Ideal water for ecosystems: By providing effective treatment, FAST systems ensure that wastewater released into the environment is free of harmful pathogens and contaminants, thus protecting public health and preserving local ecosystems.

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FONATUR: Waste water treatment

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