Feasibility study into onsite solids separation

Who this is for

What's being delivered

Visit City of Onkaparinga's continuous improvement page to stay up-to-date on the work they've done and the next steps.

About the project

The City of Onkaparinga Council’s community wastewater management systems (CWMS) include septic tanks servicing individual households and businesses. Managing the resulting septage and sludge is a significant operational task, particularly because pump outs are expensive when disposal sites are located far from the collection point.

A large proportion of this material is liquid rather than settled sludge, making transport less cost effective even though much of the liquid could be treated separately. Council currently manages around 200 m³ of septic waste each month and also operates community sewage treatment plants at Sellicks Beach and Willunga, both of which generate additional sludge.

This project explored whether solid and liquid waste could be separated during septic tank pump outs so that thicker solids could be transported for disposal or further treatment, while liquids could be redirected to sewer or septic management systems. The assessment considered available dewatering technologies and key issues such as liquid underflow disposal, unit sizing, operability, moisture content and transport efficiency.

Outcomes

GHD’s review found a strong cost advantage in moving away from the current tankering of raw septage and sludge. While disposal of dewatered material still requires consideration, the report concluded that centralised mechanical dewatering offers a practical way to reduce costs and improve operational efficiency.

Under current conditions, the preferred option is a centralised press, which provides the best balance of cost effectiveness, ease of integration, environmental performance and operational simplicity for Council’s CWMS operations.

Final project report

View the On-site Solids Liquid Separation Final Project Report (PDF 11.0 MB).

Project funding

This project was funded through the Community Wastewater Innovation Fund.

This scheme allocates funding to projects to support innovation within the CWMS sector. Successful applicants are decided through an annual grant round.