Small Diameter, Variable Grade, Low Pressure, Sewage Collection System:or STEP system was one of the first constructed in 1976 in southwest Oregon for the communities of Glide and Idlewylde Park. In 1999 a STEP system was installed in the town of Flamborough near Guelph, Ontario and in 2001 a system was completed in Carp, Ontario. A 1994 publication "An Introduction to Communal Sewage Systems" - PIBS 2856E, lists small diameter variable grade sewers as an option for consideration by Ontario municipalities and private developers. Sand Filtration Inc. has STEP/STEG packages from Orenco Systems Inc., and engineering design assistance available for Ontario Engineering Firms. Case Studies are available.
Community Collection Systems - are becoming recognized as the best solution for collecting and transporting wastewater in small to mid-sized communities, new subdivisions, and environmentally sensitive areas. These systems are often one-fourth to one-half the cost of conventional gravity sewers. When properly designed, they are easy to install and maintain, they require less costly treatment systems, and their treated effluent can be re-used for irrigation. Orenco's ProSTEP™ Sewage Collection Systems feature equipment that is superbly engineered, corrosion resistant, durable, lightweight, and fully warrantied. ProSTEP™ Sewage packages include both pump collection systems (often called STEP systems) and gravity collection systems (often called STEG systems). Design assistance for engineers is available through our in-house engineer. Hundreds of communities across North America are successfully collecting and treating their wastewater with Orenco's ProSTEP™ Sewage Collection Systems. For examples, click on "Case Studies."
Septic Tank Effluent Pumping System (STEP)
During the past 20 years, the use of pressure sewers has become a proven technology. Pressure sewers are not required to be on-grade, but rather can follow the topography, over hills and valleys and around rock outcroppings. Therefore, costly manholes are avoided entirely. Septic Tank Effluent Pumping (STEP) systems have been particularly successful. A system at Glide, Oregon, with 400 pumps, has performed satisfactorily since 1977.
The septic tank removes most of the grease and larger suspended solids, making possible the use of smaller, less expensive and more efficient pumps to move the effluent from the homeowner's septic tank into the pressure sewer collection system. Each service has a pump and float switches that pump septic tank effluent into the collection system on an "as-required" basis. STEP services are equipped with an alarm system to signal failure. The septic tank has up to 12 hours of "built-in" storage to allow time to replace the failed pump.
Effluent from the septic tank effluent pumps is discharged into the pressure collection system. A typical pressure collection system consists of relatively small diameter Class 200 PVC pipe buried with enough cover to protect the pipe from surface damage and freezing. For subdivisions up to 100 homes, most of the pipe would be 2 to 4-inches in diameter. Thirty inches of cover over the top of the pipe is generally adequate in cold climates. Because the collection pipe used is PVC pressure pipe, it is inherently watertight, preventing any infiltration of groundwater. The size of the treatment facilities can be reduced when compared with conventional gravity systems that typically experience infiltration and inflow of ground and surface water.
The STEP sewer line will have high points where gases can collect and impede the flow of effluent. To keep the pipe full, air release valves are installed to eliminate gas accumulation and negative pressures. In addition, valves and clean-out assemblies, called Pigging Ports, are placed at pipe connections and in long runs to ensure an easily maintainable system.
The house service lines are installed from the lateral sewer to each buildable lot (or each cluster of lots). The service line is terminated at each lot with a backflow prevention device (check valve) and a PVC ball valve. These valves are enclosed in an accessible valve box for hook-up by the property owner as his lot is developed.
The purchase of the on-site system (septic tank), the interceptor tank, and the pump and control system is deferred until the parcel owner wishes to connect to the system. At the time of construction the on-site package is installed by a Licensed Installer and after other site improvements have been made in order to prevent damage.
Septic Tank Effluent Pressure collection system have been found to cost approximately $6,000 to $9,000 (Can) per home including the treatment plant and final disposal of effluent, depending on the number of homes. They are much easier to construct and do not have major impacts to the neighborhoods due to their construction.
Advantages of The STEP System
Since the individual on site facilities are deferred to the time of home construction, those costs are borne by the homeowner. The major advantage of the STEP system is that it is easily adaptable to existing septic tank systems. Existing septic tanks can be retrofitted with effluent pumps, floats and controls provided they are of a suitable capacity and they pass an onsite test for watertightness. The septic tank can retain approximately 90% of the grease commonly encountered in household waste, therefore eliminating clogging problems with the pumping system and force mains.
A STEP on-site system normally has at least 12-24 hours of storage capacity, which is an important consideration if power blackouts occur. A final advantage of a STEP system is that the septic tank effluent is already anaerobically stabilized, therefore greatly reducing the concern for the shift in energy levels due to gas production. If the effluent is to be treated in a biological treatment process, the on-site anaerobic system becomes an important part of the treatment process.
Amino acids, protein and complex nitrogen compounds are broken down efficiently on site. A wastewater of more uniform quality and quantity is sent to the secondary aerobic plant (recirculating sand filter for example)for treatment, providing more reliability in that treatment process.
Disadvantages of STEP System
The major disadvantage of using a STEP system is that the septage (grease and sludge) must eventually be pumped from each individual septic tank in the system. However, pumping should not be required for at least 6 to 10 years for single family residences. There is a great deal of data available which would indicate that the sludge buildup in a septic tank should average 10 gallons per capita per year. As a result, a program to periodically monitor and dispose of the septage would need to be developed.
Other disadvantages arise from the fact that anaerobic septic tanks generate odors and methane gas. The odors are due to the hydrogen sulfide generated from the anaerobic action of the septic tank. To alleviate odor problems care should be taken to insure the lid to the effluent pump chamber is air-tight to control gases and odors. An adequate venting system must be in place.
INTERESTING WEB SITES
Orenco Systems Inc. supplied the pumps and controls for theHolmes Harbor Sewer and Glide, Oregon STEP System.
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