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 also may 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. Biological treatment is used worldwide because it’s effective and more economical than many mechanical or chemical processes.
Biological treatment usually is divided into aerobic and anaerobic processes. “Aerobic” refers to a process in which oxygen is present, while “anaerobic” describes a biological process in which oxygen is absent. Scientists have been able to control and refine both aerobic and anaerobic biological processes to achieve the optimal removal of organic substances from wastewater.
Biological wastewater treatment often is used as a secondary treatment process to remove material remaining after primary treatment with processes including dissolved air flotation (DAF). In the primary water treatment process, sediments and substances such as oil are removed from the wastewater.
Aerobic wastewater treatment processes include simple septic or aerobic tanks, and oxidation ditches; surface and spray aeration; activated sludge; oxidation ditches, trickling filters; pond and lagoon-based treatments; and aerobic digestion. Constructed wetlands and various types of filtration are also considered biological treatment processes. 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 biological treatment method is the activated sludge process, which is 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.