Aerobic Treatment Unit (ATU)

An Aerobic Treatment Unit (ATU) is an advanced onsite wastewater treatment system that introduces oxygen into the treatment process to promote aerobic bacterial activity. Unlike conventional septic systems that rely on anaerobic (oxygen-free) decomposition, ATUs use mechanical aerators or air pumps to inject air into the treatment chamber, dramatically accelerating the breakdown of organic matter. The result is effluent that is significantly cleaner than what a conventional system produces — typically achieving 85-98% reduction in biochemical oxygen demand (BOD) and total suspended solids (TSS). This higher-quality effluent means ATUs can use smaller drain fields, spray distribution systems, or even surface discharge in some jurisdictions. ATUs are commonly required in environmentally sensitive areas near lakes, rivers, coastal zones, or drinking water aquifers, and on lots too small or with soil too poor for conventional drain fields. The trade-off is higher installation cost (roughly 2-3 times a conventional system), ongoing electricity consumption for the aerator, and mandatory maintenance contracts in most states — typically requiring quarterly inspections by a certified technician to verify oxygen levels, check mechanical components, and ensure effluent quality meets permit standards.