More storage and processing infrastructure will be built at the waste water recycling centre in Avonmouth.
Wessex Water is planning to start construction in early 2024 with the project expected to take five years to complete.
The early stages of the scheme will prepare the ground for the infrastructure, such as the treatment tanks and pipework, that will be installed on the expansion site later.
Wessex Water will boost the size of the centre off Kings Weston Lane by installing tanks and biological reactors on land it already owns to break down and handle more incoming sewage, ensuring the quality of treated wastewater continues to be improved before it is released back into the environment via the Severn Estuary.