What is biological wastewater treatment?

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Courtesy of Fluence Corporation

Biological wastewater treatment harnesses the action of bacteria and other microorganisms to clean water

Biological wastewater treatment is a process that seems simple on the surface since it uses natural processes to help with the decomposition of organic substances, but in fact, it’s a complex, not completely understood process at the intersection of biology and biochemistry.

Biological treatments rely on bacteria, nematodes, or other small organisms to break down organic wastes using normal cellular processes. Wastewater typically contains a buffet of organic matter, such as garbage, wastes, and partially digested foods. It may also contain pathogenic organisms, heavy metals, and toxins.

The goal of biological wastewater treatment is to create a system in which the results of decomposition are easily collected for proper disposal. Scientists have been able to control and refine both aerobic and anaerobic biological processes to achieve the optimal removal of organic substances from wastewater.

Effective, Economical Treatment

Biological treatment is used worldwide because it’s effective and more economical than many mechanical or chemical processes.

Biological wastewater treatment is often a secondary treatment process, used to remove any material remaining after primary treatment. In the primary water treatment process, sediments or substances such as oil are removed from the wastewater.

The biological processes used to treat wastewater include subsurface applications, such as septic or aerobic tank disposal systems; many types of aeration, including surface and spray aeration; activated sludge processes; ponds and lagoons; trickling filters; and anaerobic digestion. Constructed wetlands and various types of filtration are also considered biological treatment processes.

These processes are usually divided into anaerobic and aerobic processes. “Aerobic” refers to a process in which oxygen is present, while “anaerobic” describes a biological process in which oxygen is absent.

Aerobic Wastewater Treatment

Aerobic wastewater treatment processes include treatments such as activated sludge process, oxidation ditches, trickling filters, lagoon-based treatments, and aerobic digestion. Diffused aeration systems may be used to maximize oxygen transfer and minimize odors as the wastewater is treated. Aeration provides oxygen to the helpful bacteria and other organisms as they decompose organic substances in the wastewater.

A time-honored example of an aerobic treatment method is the activated sludge process. This is a proven biological wastewater treatment widely used for the secondary treatment of both domestic and industrial wastewater. It is well suited for treating waste streams high in organic or biodegradable content and is often used to treat municipal sewage, wastewater generated by pulp and paper mills or food-related industries such as meat processing, and industrial waste streams containing carbon molecules.

An exciting new technology, the membrane aerated biofilm reactor (MABR), refines this process to use 90% less energy for aeration. Air is gently blown into a spirally wound membrane in a tank, with air on one side of the membrane and mixed liquor on the other. Nitrification-denitrification is achieved by a biofilm that forms on the membrane. The result is an effluent suitable for irrigation or release into the environment.

Anaerobic Treatment

By contrast, anaerobic treatment uses bacteria to help organic material deteriorate in an oxygen-free environment. Lagoons and septic tanks may use anaerobic processes. The best-known anaerobic treatment is anaerobic digestion, which is used for treating food and beverage manufacturing effluents, as well as municipal wastewater, chemical effluent, and agricultural waste.

Anaerobic digestion produces biogas, which lets users create a source of income from waste.

Further Treatment

The type of biological treatment selected for wastewater treatment, whether aerobic or anaerobic, depends on a wide range of factors, including compliance with environmental regulations on discharge quality.

Biological treatments are often supplemented with treatments including chlorination and carbon filtration, as well as technologies like reverse osmosis and ultrafiltration.

Researchers continue to look for ways to optimize conventional biological wastewater treatment. In one example, Finnish researchers added iron sulfate to wastewater before biological treatment to reduce phosphorous in tough-to-treat pulp mill wastewater. Other researchers have used ultraviolet light to remove challenging substances such as chemical residues and pharmaceutical compounds. And, MABR’s groundbreaking aeration model saves so much energy that it makes treatment possible in remote areas.

So, while biological treatment has a long history, it’s continuing to evolve in ways that make it more effective, efficient, and available.

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