SMITH AND LOVELESS SINGLE HOME FAST SYSTEM
Figure 1. Schematic of a FAST unit in relation to other septic system components
The FAST system uses a Fixed Activated Sludge Treatment process to treat and denitrify wastewater. The FAST process is a two zone design which consists of a primary anaerobic settling zone and an aerobic biological treatment zone. Solids are trapped in the primary settling zone. The aerobic biological zone consists of a submerged media bed which is colonized by nitrifying bacteria naturally present in sewage. Wastewater is recirculated between these two zones allowing both nitrification and denitrification to occur. The FAST unit is purchased as a module which is fitted into a 1500-2000 gallon conventional precast or fiberglass septic tank. Figure 1 presents a schematic diagram of the FAST unit. A detail of the unit itself is presented in Figure 2.
The treatment process in the FAST unit is as follows: wastewater flows from the dwelling into the primary settling zone of the septic tank. Solid matter settles out in the solids collection zone at the bottom of the tank. The FAST unit sits in the septic tank liquid with its media bed submerged. An air blower located above ground forces air down a central tube to the bottom of the submerged media. As the air rises up through the media it acts as an airlift and carries wastewater with it. The wastewater is flows up through and is dispersed over the top of the media bed. The media, which has a high surface area-to-volume ratio, serves as a site for the growth of nitrifying bacteria. The air blower on a residential unit operates at about 200 cubic feet of air per minute, so that the wastewater surrounding the submerged media is turbulent and appears to be actively bubbling. The high rate of air exchange maintains the media in an aerobic state, allowing efficient nitrification to occur. When the wastewater reaches the top of the media a portion flows out through a channel back into the primary settling zone of the septic tank. This zone is anaerobic and is the site of denitrification. With each pass through the media a portion of the wastewater passes out through a baffle and flows to the leaching field. The amount which flows out at any time at is dependent on liquid inflow to the tank, as the liquid level in the tank remains constant. Because the air blower runs continuously the wastewater is recirculated many times through the nitrifying media and the denitrifying anaerobic zone before being discharged. Thus, efficient nitrification and denitrification is achieved.
The two-zone design of the FAST unit provides for a stable wastewater treatment process. Because the media bed is submerged and remains wet, it is capable maintaining bacterial growth during periods of low water use and somewhat extended periods of no use. Also, because the area containing the media has a capacity of about 400 gallons, the wastewater treatment process is relatively stable even when a surge load is delivered to the system.
The FAST unit is located below the ground surface except for the air blower portion which is elevated about 2 feet above ground level. However, it is possible to locate the air blower unit remotely, up to 60 feet away, from the FAST unit. For example, the air blower could be located in a nearby garage or shed. In this case, only a vent from the FAST unit will show on the ground surface.
Figure 2. Schematic of a FAST unit.
DEP, in its Provisional Approval for the FAST unit, recognizes that the unit is capable of producing finished effluent with total nitrogen content of 19 mg N/L. The FAST unit is also capable of 90-95% removal of BOD and total suspended solids (TSS). BOD and TSS in finished effluent are both consistently less than 30 mg/L. These effluent concentrations exceed secondary treatment standards for BOD and TSS which require that a minimum of 85% of influent BOD and TSS be removed and that BOD and TSS in finished effluent not exceed 30 mg/L. Limited data suggest that the unit is capable of a 1-log reduction of fecal coliform. A UV disinfection unit is also available for systems where the leach field has inadequate separation to groundwater; the UV disinfection unit is purportedly capable of producing effluent with fecal coliform consistently less than 10 FC/ 100 ml.
Operation and maintenance of the unit appear to be fairly simple. The only moving part of the unit is the air blower. This makes mechanical failure unlikely and simple to remedy should it occur. The air blower is also equipped with an alarm system which is activated if the blower fails. If the submerged media starts to clog and wastewater flow through the media slows, the air pressure in the media rises and this also activates the alarm on the air blower. Smith and Loveless recommend that the solids be pumped from the bottom of the tank once a year. Units equipped with a UV disinfection unit will require more frequent maintenance to ensure that the UV unit is functioning effectively. DEP requires that all FAST systems be under a maintenance agreement and that a Massachusetts Certified Wastewater Operator will be responsible to oversee operation of the system. J and R Engineered Products, Inc., the New England distributors of the FAST system, will provide a contract for operation and maintenance and may be contacted regarding the cost of this contract. DEP also requires that influent and effluent from the system be monitored monthly for the first six months and quarterly thereafter for the following parameters: pH, BOD, TSS, TKN, nitrate and ammonia.
The cost of a residential FAST unit, which can treat up to 900 gallons per day, is approximately $5000.00. The unit must be installed in a 1500 or 2000 gallon septic tank; a precast concrete tank of this size costs $1000-1500. The unit can be retrofitted to an existing 1500-2000 gallon septic tank, provided the tank is watertight and the dimensions of the tank are sufficient to allow 16-18 inches of liquid depth below the FAST unit. In addition, there are labor costs for installation of the unit plus the cost of a conventional Title 5 leach field. The optional UV disinfection unit costs about $1000.00. Several residential FAST systems have been installed in the towns of Cohassett, Hingham, and Hull. These units are becoming increasingly popular in Barnstable County. A large commercial FAST was installed at the Coonamesset Inn in Falmouth, and appears to be achieving very substantial nitrogen removal. In addition, the “99″ Restaurant in Mashpee uses a FAST unit.
The FAST system is manufactured by Smith and Loveless, Inc., 14040 Santa Fe Trail Drive, Lenexa, KS 66215. Sole New England distributors are J and R Engineered Products Inc., 271 Leonard St., Raynham MA 02767 (508) 823-9566.