Description of Technology

The RetroFAST® System is installed between the building sewer and the disposal field or soil absorption system (SAS) designed and constructed in accordance with 310 CMR 15.100 – 15.279. The System is designed for use with existing on-site septic systems providing wastewater treatment for rejuvenation of biologically failed SAS’s. The RetroFAST® installation is designed for residential strength wastewater and is available in three size models the 0.15, 0.25, 0.375 with rated capacities of 3, 4 and 5 persons per household.

The RetroFAST® System is inserted through a manhole in the outlet side of a one or two compartment septic tank with the media submerged. The System uses the BioMicrobics FAST aerobic treatment process utilizing submerged media for fixed film bacterial growth. The FAST process is currently MassDEP approved as the RetroFAST® and is certified by NSF under Standard 40 and 245. The System insert consists of a liner containing the submerged media and an airlift draft tube to provide aeration and mixing within the liner or aerobic zone. The media used is PVC or polyethylene cross-flow textile. All of the aerobic treatment and mixing occurs within the aerobic zone, which allows the contents of the septic tank outside of the liner to function as originally intended. Aeration and circulation are provided by a blower that pumps air into an airlift draft tube that extends down the center of the media inducing circulation of wastewater, providing oxygen and waste mixing. The FAST process does not require the continuous addition of bacterial supplements to maintain the bacterial population.

Treated effluent passes out of the RetroFAST® through a pipe connected to the outlet of the septic tank. The continuous circulation of the wastewater establishes velocities in the media that assist in sloughing of excess biomass from the media exposing a new surface on which growth continues. Sloughing biomass passes down through the media and settles to the bottom of the tank below the insert. The accumulated biomass and entrapped organic solids are gradually digested under aerobic conditions. A vent pipe is installed for System venting of vapors created by the process.

The remote-mounted, above-ground blower is the System’s only moving part. A small blower control panel with an alarm designed to activate if the blower fails is typically installed.

This treatment process and clarification is designed to produce a septic tank effluent quality approaching secondary treatment levels, significantly reducing biological oxygen demand (BOD5) and total suspended solids (TSS).

The highly treated septic tank effluent with excess dissolved oxygen is discharged for disposal to the failing SAS to aid in digesting the excessive biomat. With continued operation, the System is designed to diminish the biomat and return the SAS to full function.

Pumping of the System is estimated to be required at three to five year intervals.

Massachusetts Technology Approvals

Approval Type	General	Remedial	Provisional	Pilot
Secondary Treatment
Nitrogen Removal Credit
Phosphorus Removal Credit

Please check the Title 5 Innovative/Alternative Technology Approval Letters webpage at Massachusetts DEP for the most up-to-date information.

Test Center Reports & Data