Sewage Reticulation – What Option is best for you?

Annual Conference

Recently, Pattle Delamore Partners Ltd (PDP) was engaged by several District Councils to investigate sewage reticulation options for communities of various sizes with different cultural / environmental interests. The different reticulation options considered include conventional gravity reticulation, pressure sewer reticulation (including grinder pump systems and septic tank effluent pressure (STEP) systems) and vacuum sewer reticulation.

This paper discusses a number of projects and the site-specific challenges associated with each project when investigating and developing a reticulation scheme, from conceptual to the detailed design phase. In some cases, a preliminary design of a reticulation scheme had already been completed however various issues and challenges were encountered during further detailed site investigations that made the scheme no longer feasible / practical. In general, some key issues that needed to be addressed included:

  • Cultural issues – E.g. public concerns on the transfer of raw sewage from one catchment to another.
  • Physical constraints – E.g. high groundwater levels which would lead to increased construction costs, as well as increased operating costs associated with ongoing infiltration / inflow for gravity sewerage.
  • Costs and affordability – E.g. comparing capital, operating and life-cycle costs between options on a “like-for-like” basis.

In addition, careful consideration was required as to the effects on the downstream wastewater treatment plant. In some situations, an advantage of a STEP system over a grinder pump system was that onsite pre-treatment could potentially reduce the capital and operating costs associated with providing further treatment at the downstream treatment plant. However, in other situations, a grinder pump system had the benefit of retaining the biologically available carbon in the raw wastewater, potentially avoiding the need for additional chemical dosing at the treatment plant in order to provide supplementary carbon for nitrogen removal.

Each project assessed the options available and resulted in a different reticulation outcome. This paper discusses the site-specific factors that influenced each preferred option. It also presents a multi-criteria decision matrix that was developed to allow for an evaluation of the reticulation options on a holistic basis and to enable the right selection of a reticulation option at an early stage in the project timeline.

Conference Papers

2.00 Sewage Reticulation What Option Is Best For You.pdf

pdf
873 KB
08 Nov 2017

2.00pm D Kim.pdf

pdf
3 MB
08 Nov 2017