A $9.3 million project to expand Orange's sewage treatment facilities has been completed, which Council says will meet the future needs of our growing population.

The upgrade of the Orange Sewage Treatment Plant, located on the north-eastern side of the city, replaces the facility’s ageing inlet works, which are the first stage of the treatment process when wastewater enters the plant.

Orange Mayor Tony Mileto said this project was vital infrastructure for the future growth of our city and would meet the needs of a population of up to 60,000.

"You just have to look at the data and how much we're increasing each year and I can tell you that there's no shortage of people who are enquiring about relocating to Orange," Cr Mileto said.

"It's a very popular city for obvious reasons, so we need to be in a position to manage those expectations of people who want to come here, whether that's through land release, or whatever... There's a lot of enquiry there, a lot of demand, so to meet those expectations we need to have the infrastructure in place to be able to do that."

The new state-of-the-art system increases the plant’s ability to process higher volumes of wastewater to a better standard and will help improve the environmental impact of the plant by reducing downstream nitrogen levels in Blackmans Swamp Creek.

The upgraded equipment includes filtering screens which remove large particles from the sewerage greater than 5mm in size and withstand flows up to 1250 litres per second, which is more than double the previous screens.

A new vortex grit removal system removes sand and grit particles less than 5mm in size and is much more energy efficient than the previous aeration system.

During heavy rain, the new plant is also able to screen greater volumes of stormwater, increasing from 900 litres per second to 2500 litres per second, which improves compliance with NSW Environmental Protection Authority (EPA) regulations.

Infrastructure Policy Committee Chair Cr Jeff Whitton said the upgrade might be out of sight, but was a core component for the future.

“These types of projects are the bread and butter of ensuring we have the critical infrastructure in place,” Cr Whitton said.

The project also included earthworks such as improved access roads and the construction of a 6.5-metre ‘Dincel’ retaining wall.

The upgrade was funded by Orange City Council through sewer charges.