Upgrades to a sewage works in Crawley are nearly complete.
The project at Crawley Sewage Treatment Works, in Radford Road, near Gatwick, will be complete in the next couple of months.
Thames Water started the £28 million upgrade to three sewage works in Crawley, Chertsey and Camberley in February 2010 to protect rivers and wildlife.
The sites had specialist equipment installed to reduce the amount of nitrate left in waste and improve water conditions in rivers for fish and other wildlife.
A Thames Water spokesperson explained: “This is one of the biggest investment programmes we’ve carried out in this five-year period, and it will offer huge benefits to the people living near these sites.
“Not only have we improved the quality of the leftover sewage sludge leaving these treatment works, we have made sure there is less solid waste having to be transported away, which means fewer lorries on the roads.
“All of this work is also good news for the local rivers, as the discharge from the sites is now of an even better standard so we can be sure that we are looking after our local environment too both now and in the future.
“We have also taken steps to reduce potential odour.”
The amount of sewage the site can process has also been increased which will allow it to keep pace with the growing population.
The water treated at the Crawley site runs into The River Mole, which flows north west from Gatwick, through Surrey, to the River Thames.
The spokesperson added: “We also had to do a ‘bird watch’ to check birds weren’t ‘loafing’ around the site as nesting birds can cause problems for Gatwick airport.
“We’ve been monitoring the birds on a weekly basis but there haven’t been any problems. “
“We also installed 150 bat boxes on the site to protect the bats in the area.”