Aerobic treatment units (ATUs) offer a suitable environment for microorganisms to treat wastewater. These pre-engineered advanced wastewater treatment systems are alternatives for small system designs with space restrictions and limited room for conventional treatment or where centralized sewerage is not available. ATUs are applied on sites with poor soils, shallow vertical separation distances to limiting conditions, and horizontal setback restrictions. Some systems can be designed for the treatment of high strength wastewater or where total nitrogen removal is required.
Understanding Aerobic Treatment Units
Mechanically induced aeration is engineered to produce a residual oxygen concentration of at least 2 mg/L or 2 ppm along with mixing within the unit. The oxygen and mixing processes support microorganisms as they break down the organic portion of the waste. In addition, mechanisms are used to keep solids out of the effluent and keep bacteria in the treatment process. The resulting effluent produced from an ATU is higher quality than from a septic tank in terms of total suspended solids (TSS), biological oxygen demand (BOD), and in some instances, ammonia (NH3) and total nitrogen (TN).
Whether in a residential or commercial system, the system choice and design are key to the longevity and sustainability of the ATU. In addition, having a good site plan, installation guidance, a plan for educating the customer, and a strategy for operation and maintenance (O&M) are important.
In most cases, regulations will dictate what treatment levels need to be achieved and for what purpose. For a single-family home, certified systems typically are applied using the appropriate model number of the ATU for the flow and treatment level required, but in larger or commercial systems it is important to choose a proven system for the specific application. Providing the system location as well as influent flow (i.e., volume and schedule) and strength to system manufacturers is necessary for them to provide a proper treatment plan for the application.
The geographical location is important because temperature and altitude can have big effects on the system and must be considered. It also is important to understand what resources are available for operation and maintenance in the area, as this will make a difference in the type of technology chosen and some design elements that may go into the system. Sludge management is critical to proper functioning, so a remote location may require additional sludge holding or treatment to be on the site.