Agenda - 10-08-1991 - Laserfiche WebLink

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11. Sewer Collection systems and Networks Sewer collection systems are a very important part of the overall sewer treatment process. In some types of networks, a portion of the treatment takes place within that network. Individual or single - family waste treatment systems do not have a sewer collection network. The waste generally flows directly from a building into the treatment unit. When multiple housing units or buildings are connected to a central waste treatment or disposal system, two basic types of collection network may be used.- 1) The traditional sewer collection system is the gravity i collection network. The gravity sewer collection system s composed of a piping network that is generally very similar to the collection network associated with a municipal sewer system. That is, each individual user's waste water flows.by gravity from a building through a small diameter (411) service line to a larger (8" or greater) central gravity sewer main or system of mains. The central gravity sewer main system eventually discharges into a single main which, in turn, discharges at the low point in the system where the waste treatment and disposal process occurs. The central treatment system must be located at the lowest point in the collection system or a lift pump station much be used to convey the waste from the low point to the treatment system. 2) The pressure collection system, which is also called a STEP system, is configured with a Septic Tank and an Effluent Pump tank for each user. Waste flows by gravity from a building into a septic tank. Effluent from the septic tank flows by gravity into another tank which contains a pump. The waste from each individual pump tank is then pumped into a central pressurized main which conveys the waste to the central treatment system. The central treatment system can be sited independent of topographical considerations. There are advantages and disadvantages to both gravity and pressurized sewer collection systems. Advantages to gravity systems are-1 -6* maintenance requirements, reliability and ease of incorporation into an extended municipal sewer system. Disadvantages to gravity systems are high installation /construction costs and difficulty in mating the system to existing opoggrapphy. Advantages to a pressure sewer systems are the relatively low construction cost and freedom from topography constraints. Disadvantages to pressure collection systems are high maintenance requirements for the mechanically coommpplex pumping and valve components and difficulty in connecting pressure systems to municipal gravity systems. Many municipal sewer providers are reluctant to absorb a non - standard pressure system into their operation. Municipal systems might even require that the pressure system be converted to a standard gravity system. 3