The next generation of pressure sewer systems

Introducing improvements to the technology

South East Water installed its first pressure sewer system (PSS) in Australia at Tooradin in 2001. In 2003/4 additional PSS systems were installed at Warneet and Cannons Creek that, together with some small infill developments, totals an installed base of 8000 units.

South East Water's experience with PSS has been extremely positive, particularly in a backlog sewerage environment where it results in a significant reduction in disturbance to the local community and environment. Typical benefits include: small diameter pipe-work at shallow depths; trenchless construction; minimal impact; no sewers/easements in backyards; and no inflow/infiltration (potential leakage is minimised by use of welded, joint PE pipes and no need for manholes).

The recently designed Flinders Sewerage Scheme and future backlog projects are in areas that are remote, have a highly seasonal population and a very undulating topography. 'us' - Utility Services, an alliance of South East Water and Thiess Services/Siemens consortium reviewed the available PSS technology and determined that no existing system would satisfy all future requirements. 'us' - Utility Services, in a technical partnership with Mono Pumps (Australia), have developed the next generation in pressure sewer technology - the Mono Eco 1-60 Pressure Sewer Pump Unit.

The key improvements that 'us' - Utility Service and Mono have introduced into pressure sewer technology with the development and utilisation of the Eco 1-60 include:

• True 24 hour emergency storage - 600 L storage above alarm level allows next day attendance to 'call outs' (particularly to remote areas without fear of spills);
• Longer life rotor and stator with sustained pumping up to 60 m head - Greater flexibility to design network in undulating areas where pumps will see high dynamic heads;
• Over pressure protection (OPP) - This protects both the pump and network from pressure spikes whilst also providing a means to integrate the PSS with the transfer system, utilising the dispersed 24 h emergency storage available in each property.

At Flinders, the main transfer pumping station has been designed having no contingency storage and using a small pressure vessel instead of a wet well. Under normal operation the pump station operates at atmospheric pressure with an open air release valve. However, in an emergency event, the pressure vessel can fill, seal and become pressurised, consequently surcharging and pressurising the network. When the pressure sewer pumps see a pressure over 65 m they automatically shut off until the pressure drops below 65 m. This engages the dispersed storage at each property.

• Telemetry linked control system - Alarms direct to operators - not dependent on customer response; operators can obtain pump unit information remotely for fault diagnosis before attending pump 'call outs'; remote 'global shutdown' of nominated pumps within a PSS system during a power failure or other incident to avoid sewer spills to the environment - therefore minimising the complexity and time taken to locate and manually shut isolating valves.
• Dry well pump - Enables safe and clean 'on-site' dry-well maintenance of the pump and the sealed wet well eliminates potential confined space issues.