The city’s sewage treatment plant takes what people send down their drains and toilets and turns it into water clean enough to put in the Neuse River and something euphemistically called biosolids, which is used as fertilizer.

In a few years, the treatment process will also create a third product: compressed natural gas, enough to run up to 50 GoRaleigh buses a day.

City and state officials held a ceremony Wednesday to begin a $148 million upgrade to the Neuse River Resource Recovery Facility, which treats sewage from Raleigh and several other Wake towns served by the city’s utilities department. The part of the plant that treats solids and gets them ready to use as fertilizer is about 25 years old and needs to be replaced.