Septic Tank Effluent Pump (STEP) and Gravity (STEG) Collection Systems: Myth Busting the Value of Using Septic Tanks as Part of a Wastewater Collection System?

In the United States more than one in four households relies on septic tanks as part of their wastewater treatment process. More than 99% of septic tanks are part of an onsite septic treatment and disposal system. Less than 1% of septic tanks are used in Septic Tank Effluent Pump (STEP) Systems and Septic Tank Effluent Gravity (STEG) Systems. Both STEP and STEG Systems utilize the septic tank to provide primary treatment of the wastewater before it enters the wastewater collection, conveyance and treatment system.Septic tanks provide primary treatment of wastewater at a low cost, with minimal energy consumption and with relatively low maintenance requirements. The effluent from a septic tank is consistent in strength and biosolids are reduced in the tank by anaerobic digestion. Despite the positive attributes of the septic tank, most wastewater collection systems are designed to convey all raw wastewater offsite for centralized treatment. The possible value of adding a septic tank before conveying the wastewater offsite is rarely considered. When STEP and STEG systems are considered, the septic tank is often seen as an unnecessary liability.The septic tank can provide direct cost benefits in capital costs and operating costs. Additionally, indirect cost savings can be achieved in the treatment process. Also, logistical benefits associated with emergency wastewater storage, flow monitoring and illegal wastewater discharges can also be realized. The benefits, when fully identified and quantified can more that justify the value of providing a septic tank prior to offsite wastewater collection, conveyance and treatment.