|Manual, Alternative Wastewater Collection Systems (218 pp, 17.4 MB) (EPA/625/1-91/024) October 1991
This manual represents a comprehensive treatment of alternative collection systems (ACS) for small-community wastewaters. It provides the history, applicability, design, construction, operation, maintenance, and costs of all three major categories of alternative collection: pressure sewers, small-diameter gravity sewers (SDGS), and vacuum sewers.
The current surge of ACS application began around 1970, when the costs of conventional sewerage were found to be prohibitive in rural areas owing to their depth of burial and other construction demands. All of the alternative sewers use light-weight plastic pipe with shallow burial. This method saves as much as 80 percent of the cost of conventional gravity sewers, but the savings are partially offset because of the need for additional components (not required for gravity sewers) at each service connection.
Two major types of pressure systems are described in detail: the grinder pump and the septic tank effluent pump. The former grinds household wastewater and pumps it into the main, while the latter uses a septic tank prior to pumping. Both have been used widely and successfully.
At one time, there were two distinct design approaches to SDGS. One used conventional gravity sewer methods of constant grade between control points. The other followed the natural ground slope and emphasized very small pipe size. Currently, SDGS is designed in a manner that follows the ground surface but eliminates the troublesome tankage and undue size restrictions of the latter approach. Detailed design versus performance and cost information is provided.
Vacuum sewers use a different approach from pressure sewers. Pressure sewers have a central vacuum station imposing the necessary forces on the small-diameter pipeline. Although there are fewer U.S. installations of vacuum sewers than SDGS or pressure sewers, their use is on the upswing. The history of these systems in the U.S. and their cost and operation requirements are covered in detail in the manual.
This publication represents more than two decades of experience with these systems. Small rural systems have been identified as a priority environmental problem in many nations, and alternative collection systems represent a major solution to one of the most expensive aspects of this problem.
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