The $95 million project came in $13 million under budget and on time.
Ms Davies said the plant would prove an important investment for the south-west metropolitan corridor.
“Up to 20 million litres of wastewater from households and businesses bounded by Naval Base to the north, Singleton to the south and Byford to the east will be treated at the plant each day,” she said.
“By 2070, it is expected the plant will be expanded to treat up to 160 million litres of wastewater a day, which will service about 800,000 people and make it one of the largest wastewater treatment plants in Perth.”
Wastewater is 99.97 per cent water and comes mostly from showers, baths and washing machines.