Our wastewater treatment process

Our wastewater treatment plant has served Canberra’s needs for decades, but some of our assets are aging and elements of the treatment process are nearing capacity. We have a responsibility to protect our environment and continue providing high-quality wastewater services to our community. To do this we need to upgrade, or replace, elements of our treatment process. 

Our plans include two significant projects for our primary wastewater treatment plant, Lower Molonglo Water Quality Control Centre (LMWQCC). The first project is focused on our bioreactors and the other targets biosolids.


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Bioreactors – secondary treatment process

Our current process

Microorganisms are a critical part of our wastewater treatment process. They convert the nitrogen found within our wastewater into nitrogen gas, minimising the impact on our river ecosystem.

Something so vital to our treatment process, and the environment, needs dedicated infrastructure – which is where our secondary treatment process comes in. These tanks house our microorganisms while they get the job done. 

An opportunity to improve
Our secondary treatment process is approaching capacity. To meet the growing needs of Canberra, we are looking at options to increase this capacity to a level which will service our community for the next 50 years.

Our team is investigating different options for upgrading the secondary treatment process in a staged approach. We have assessed nine options and identified the risks and benefits of each. 

Our options

From the nine options we assessed, we have shortlisted the following: 

  • Option 1: Convert our existing bioreactors into a Membrane Bioreactor (MBR)
    An MBR is a combination of membrane filtration with a biological treatment process. 
  • Option 2: Duplicate the existing process (with updated technology)
    For this option, we would construct additional process trains but integrate newer technology. 
  • Option 3: Aerobic Granular Sludge (Nereda ®)
    This trademarked process treats wastewater in smaller tanks while using less electricity.
  • Option 4: Integrated Fixed Film Activated Sludge (IFAS)
    The IFAS system consists of tanks filled with small pieces of plastic that create a habitat for microorganisms to attach and grow. This increases the number of microorganisms that can fit within each tank, which saves space and electricity. 

Options assessment:
These options will go through a rigorous multi-criteria analysis. Circular economy opportunities, in particular, will be considered.

How long will it take? 
We are hoping to commence construction between 2025-28.

Biosolids treatment 

Our current process

We separate Canberra’s waste into liquid and solids as part of the wastewater treatment process. Any organic solids we separate are known as biosolids. 

Solids are placed within one of two furnaces, where the intense heat destroys pathogens and contaminants. This creates a product we call Agri-Ash, which retains elements of lime and phosphorus. Agri-Ash is a beneficial soil enhancer used on farmland. On average, we collect Agri-Ash three days per week for distribution to local farmers.On average, we collect Agri-Ash three days per week for distribution to local farmers.

The liquids are treated until they are safe to be released back into the environment through the Molonglo River.

An opportunity to improve
Our furnaces are approaching the end of their service life and maintenance is becoming expensive. So, we are considering how to treat biosolids moving forward.

Our goal is to replace the old furnaces with environmentally sustainable, and energy efficient, technology to service our growing community over the next 50 years.

We have consulted with experts, and industry partners, from across the globe to identify a shortlist of viable treatment alternatives. These options provide a reliable service that continues to protect human health and the environment. They also help maximise resource recovery by producing energy or providing us with a product that can be re-used (like Agri-Ash).

Our options:
Of the 17 options we carefully assessed, five have been shortlisted:

  • Option 1: Fluidised Bed Combustion (FBC)
    This option is similar to our existing furnaces (by using intense heat), but is much more efficient and reliable. FBC produces electricity to offset our plant’s onsite use. It also creates an ash like the Agri-Ash we are already producing. 
  • Option 2: Anaerobic Digestion (AD)
    This option processes the solids from wastewater using anaerobic biological processes. The biosolids produced by this process can be used on farmland. The methane produced can either be converted into electricity or used to dry biosolids.
  • Option 3: AD plus external biodegradable waste streams
    This process is like Option 2, but it is amplified by extra waste streams from local industry. This helps others by taking their waste and creates more electricity from methane. 
  • Option 4: AD plus off-site composting
    This process is the same as Option 2, except it includes processing waste off site at a third-party composting facility. This composted product can be used on gardens or farmland. 
  • Option 5: Gasification  
    This option is like Option 1, but combustion occurs in a low oxygen environment. The product from this process is a biochar which is more beneficial to agriculture than Agri-Ash because of its higher organic content. This process produces electricity to offset our plant’s onsite use. 

Options assessment:
These options will go through a rigorous multi-criteria analysis. Circular economy opportunities, in particular, will be considered.

How long will it take?
We are hoping to commence construction between 2025-28.