Improving Septic Tank Performance by Enhancing Anaerobic Digestion

Abstract

Septic tanks have been used for anaerobic treatment of raw sewage for well over one hundred years, and their basic design has not fundamentally changed over that time. On the other hand, there have been tremendous improvements in our understanding of anaerobic microorganisms and development of high-rate anaerobic treatment technologies particularly since the 1970’s. However, this improved technical knowledge has not yet been applied to improving the century-old septic tank. The Waterloo ‘InnerTube™ Anaerobic Digester’ (‘digester’ or ‘InnerTube’) was developed with consideration of modern understanding of anaerobic treatment systems. This new septic tank design directs the raw sewage into an initial smaller-diameter flexible pipe ‘treatment tube’ within any standard box-like tank without the need for dividing the septic tank into multiple compartments. The InnerTube pipe is kept warm in the septic tank water itself. The InnerTube includes design features that improve the treatment performance of septic tanks including: consistent and warmer initial temperature, creating a flow path that minimizes stagnant zones and elongates the flow pathway, directing the sewage through anaerobic microorganisms (‘biomass’) grown and retained in the tank, separating the liquids and solids retention times as is done in activated sludge, and elimination of the air space for better scum treatment. Multi-year, third party testing of this new septic tank design has demonstrated improved sewage solids digestion over conventional septic tanks. The new design produces improved effluent quality especially with respect to increased total suspended solids (TSS) removal and decreased sludge and scum accumulation. Pump-outs are less frequent and the effluent is more amenable to subsequent aerobic treatment.