Waste water treatment process

When you flush the toilet or empty the sink, wastewater goes down the drain and into a network of underground sewer pipes. 

Eventually it ends up at one of the Shoalhaven’s 13 treatment plants The treatment process is broken into 3 stages:

Primary treatment

When it first arrives the wastewater contains not just organic, human waste but a large amount of non-biodegradable waste that needs to be removed before the sewage can be treated. This first stage removes large objects like nappies, cotton buds, face wipes and any other objects that shouldn’t have been flushed down the drain in the first place. It also removes stones, grit and sand.

Secondary treatment

Once all the non-biodegradable waste has been removed the sewage then goes through a secondary treatment, which involves encouraging billions of ‘good’ bacteria to break-down the waste into harmless substances that can be separated out from the water. These substances are called ‘Biosolids’ and can be used as fertiliser for farmland.

The secondary process has three phases:

  • Aeration
  • Settling
  • Decanting
  • Tertiary treatment

The final stage of treatment passes the almost-clean water through some further filters to remove any remaining waste particles. It also disinfects the water using chlorine gas to produce the highest quality recycled water. This water can either be returned safely to our waterways or used to irrigate farms and playing fields in the Shoalhaven.

Tertiary treatment happens in three stages:

  • Filtration
  • Chlorination
  • Bulk Storage