Vacuum sewage collection systems

In Japan, many regions are expected to experience a gradual decline in population, aging and depopulation of rural areas in the future, making the profitability of sewerage projects a major issue. In many rural municipalities, the low residential density, topographical and geological conditions, and surrounding construction environments are factors that make the cost of pipeline construction using natural flow pipelines relatively high. The vacuum type sewage collection system is a true value as a sewage collection method in such difficult locations.

A vacuum sewage collection system collects and conveys sewage by mixing it with air through the differential pressure between the vacuum generated in the pipelines and the atmosphere, and consists of three elements: a vacuum valve unit, a vacuum pipeline, and a vacuum station. Sewage drained from homes and other buildings flows into the vacuum valve unit through the on-premises drainage system using natural flow pipelines. When a certain amount of sewage flows into it, the vacuum valve automatically activates to suck sewage and air into the vacuum pipeline. As the suctioned air expands in the vacuum pipeline, the sewage becomes a gas-liquid multiphase flow that is collected and conveyed to the vacuum station.

1. Shallow burial depth
   Vacuum conduits are laid in a "saw-tooth" longitudinal profile, allowing for shallow burial depths.
2. Smaller pipe diameter
   The collection and conveyance of sewage is done using air expansion, and the conveyance speed is high, allowing for smaller pipe diameters.
3. Easy to avoid buried objects
   Buried objects can be avoided by passing over or under them as long as the pipe loss is acceptable.

Because a vacuum is maintained inside the piping, even if damage should occur, sewage will not leak outside if the damage is minor. Its high airtightness prevents groundwater and other liquids from infiltrating the pipe. In addition, it does not require cleaning because of the high transport speed of the sewage. This system also sucks in suspended solids when the vacuum valve is activated, thus preventing scumming.

Electricity required for sewage collection and conveyance need only be supplied to the vacuum station, making power outage countermeasures easy. Polyethylene pipes with excellent "earthquake resistance" as well as "strength," "chemical resistance," and "corrosion resistance" can be used as the pipe material for vacuum conduits.