Yorkshire Water has revealed its £78 million overhaul of the Blackburn Meadows treatment works will be completed by next year.
Specialist contractors Earth Tech Morrison have been carrying out improvements to the site since March 2012.
Now Yorkshire Water says all of the work will be completed by Autumn 2014.
The result will be improvements to the quality of the water discharged into the River Don, to help fish and wildlife populations.
Other major aspects of the project include creating the country’s largest storm overflow channel reduce the risk of flooding and pollution incidents during heavy rainfall.
Yorkshire Water is also using sludge treated on site to produce renewable energy to power the works.
A Yorkshire Water spokesman said: “The project will help to fulfil Yorkshire Water’s aspiration to generate 50 per cent of its energy needs from renewable energy by 2020.”
The work at Blackburn Meadows is the company’s biggest project this year.