Continuous improvement

Overview

Council is working to keep improving its Community Wastewater Management System (CWMS) services.  We want to make sure the service is reliable, efficient and cost effective.   

In 2024 council received funding from the Local Government Association of SA (LGA) through the Community Wastewater Innovation Fund.  This funding supports 2 grant projects that have explored innovative ways to improve the management of CMWS.  

Septic tank desludging project

Usually, septic tanks connected to the CMWS are managed the same as standalone onsite wastewater systems, those that dispose of waste to an underground soakage etc. But, tanks on CWMS discharge to sewer drains (the network) eventually leading to the treatment plant.  Until now, there has been little focus on how best to manage these septic tanks. 

This project looked at how well septic tanks on the CMWS are working in real life, including the quality of wastewater entering the network. 

Current pump out intervals are based on assumptions about sludge build-up, historic flow rates and impacts to onsite systems.  These assumptions don’t match current household sizes or the actual wastewater produced.  

What have we done?

Septic tank testing

To better understand how septic tanks connected to the CWMS are performing, council carried out targeted sampling and analysis.  A total of 78 samples were taken from 26 tanks, testing for:

• Biological Oxygen Demand (BOD)
• Chemical Oxygen Demand (COD)
• Suspended Solids (SS)
• Volatile Total Solids (VTS)
• Total Solids (TS)

BOD and SS were tested at the tank outlet to measure the quality of the effluent entering the network.  VTS and TS were tested to assess how healthy the tanks were. 

The time since the last pump out ranged from four years to more than 10 years. 

Importantly, the testing results showed no major difference in effluent quality between tanks pumped at 4 years and those pumped at 5 years. The project demonstrated that septic tanks were still removing solids effectively even after the current pump out interval.

This suggests there is potential to reduce pump out frequency without impacting the network. 

Network testing

To check whether tank performance matched sewer drain performance, council also took samples within the network.  Samples were taken from pump stations and manholes. A total of 79 samples were tested for:

• Biological Oxygen Demand (BOD)
• Chemical Oxygen Demand (COD)
• Suspended Solids (SS)
• Ammonia (NH₃)

Catchments were compared based on the average time since last pump-out, which ranged from zero to over 10 years. 

Just like the tank testing, there was no drop in effluent quality in catchments where the average pump out interval increased from four to five years.    

Risk-based assessment

Using both sets of test data, council worked with a consultant to develop a risk matrix(PDF, 163KB). This tool helps identify areas of risk based on network features, tank performance, and maintenance history.

This forms the base for moving from a ‘one‑size‑fits‑all’ servicing model to a more targeted, evidence‑based approach.

Next steps

Based on the findings so far, council has increased the planned pump out frequency from four years to five years.

Council will also look for low risk areas where pump out frequency could be extended up to eight years. These areas will be closely monitored to check for any impacts.

If successful, this approach will allow septic tanks to be serviced based on risk. Some tanks, due to network layout or asset age may stay on a five-year cycle, while others may safely move to longer intervals.

This evidence-based model aims to:

• Maintain network performance
• Use maintenance resources more efficiently
• Reduce overall network operating costs
• Provide better value for residents

Desludging process improvements project

Council is looking for ways to make the septic tank pump out across the CWMS more efficient. 

What have we done?

This project looked at whether solid and liquids can be separated during pump outs.  The idea was to send the liquid waste via the network for treatment, while taking solids off site for disposal. 

To support this work, Council partnered with the Centre for Sustainable Infrastructure and Resource Management at University of South Australia.  Honours and Masters students carried out early research to test if this idea could work in practice. 

A specialist consultant then reviewed and built on their findings. 

The study showed this this approach could be possible.  However, issues like odour and noise meant that using mobile equipment is not the best option. 

Next steps

Council is exploring smarter desludging methods to improve efficiency without causing problems within the network. 

While separating solids and liquids during pump outs is not ideal, the project highlighted the benefits of local dewatering equipment. These benefits may include:

• Lower transport and disposal costs
• Reduced fuel use and emissions
• Improved contractor efficiency
• More flexibility in managing the network

Council will continue to investigate options for this type of infrastructure, as well as ways to reuse the end product known as biosolids. 

Most importantly, this work supports council’s move toward a more data-informed, risk-based service. By questioning older practices and testing new ideas, council is building a wastewater service that is more sustainable and cost-effective.

Future focus areas

Council’s review of the CWMS does not end with pump out improvements. Several areas have been identified to explore to support a fair, transparent and sustainable service model.

Wastewater treatment plant optimisation

Council will look for ways to improve how its wastewater treatment plants operate.  This includes reviewing energy use, chemical dosing, process efficiency and asset performance. By improving plant operations and linking them to real flow patterns, council aims to:

• Reduce operating cost
• Extend asset life
• Meet environmental standards
• Deliver ongoing value to the community

Trade waste cost transparency

Another key area is clearly identifying the true cost of collecting and treating trade waste. 

At present, CWMS fees are based on how much wastewater a business is expected to discharge into the network. While volume does affect the system, it is not the only factor.  The strength and quality of the wastewater, such as high organic loads or other contaminants, can impact pumping and treatment needs.

The aim of CWMS charges is to support a user-pays approach, so one type of customer is not covering the cost of another.  However, more local evidence is needed to understand:

• The cost difference between normal domestic wastewater and higher strength trade waste.
• The operational impacts of different discharge qualities.
• The fairest way to allocate these costs.

Future studies will help build a stronger evidence base to support pricing structures that are fair, transparent and matched to real system impacts. 

Our commitment

These projects show Council’s commitment to evidence‑based decision‑making, continuous improvement, and long‑term sustainability of the CWMS. By questioning old assumptions and testing practical new approaches, council is building a smarter, more efficient wastewater service that delivers reliable results and real value for the community.