what are effluent sewers?

Effluent sewers collect wastewater from homes and transport it to a decentralised treatment facility, allowing the waste to be treated at a suitable single location rather than at each home.

The collection sewers are low-pressure, shallow and small diameter, meaning they do not need deep trenches for installation like conventional gravity systems, which results in a lower cost of construction, reduced project duration, and low disruption to communities.

Ashtecs has partnered with the US company Orenco for design and engineering support. Orenco pioneered the use of effluent sewers in the 1980’s and have supplied this technology for decades across the globe.

Schematic of effluent sewer collection system

Schematic of effluent sewer collection system

key benefits

  • Solution for un-sewered communites with issues such as difficult soil conditions, sensitive water courses nearby, or installing gravity sewer lines is cost-prohibitive

  • Significant construction savings compared to conventional gravity sewer systems

  • Wastewater can be treated at a suitable centralised location

  • Easily transports waste away from sensitive receptors like lakes, streams, or bays

  • Water tight systems meaning no overflows contaminating surrounding areas

  • Low-impact: minimal or no road closures for pipe crossings, no deep trenches, reduced project durations

  • Proven technology in USA since 1980’s and other countries such as Australia, New Zealand and Canada



Orenco system schematic.png
  1. Underground tanks provide primary treatment, so only liquids are conveyed to the treatment plant - tanks typically require pumping out once every 10-12 years.

  2. Pump filters remove solids and lightweight, non-corroding pumps last more than 25 years.

  3. One-inch (25-mm) diameter service lines can be easily installed with a trencher.

  4. Small-diameter main lines follow the contour of the ground, saving on excavation costs. No expensive manholes or lift stations are required.

  5. Filtered effluent is conveyed by gravity from homes at higher elevations, so no pump is typically required.

case studies


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