Ottawa residents who use compostable plastic liners in their green bins could actually be adding to a massive bill for Ottawa taxpayers.

Although Ottawa's green bin program is growing in popularity, there remains confusion over the type of bags that can be used as liners.

Compostable plastic bags are not accepted in the green bin. That's because if too much plastic gets collected, the final compost product will be less valuable. The city will also be charged millions of dollars in penalties.

"If you use plastic, our contract with Orgaworld, our processor, requires us to pay more money if there's a significant amount of plastic in the material. So for residents of Ottawa – no plastic whatsoever," said Coun. Peter Hume, who spearheaded the program.

The City of Ottawa's website lists the types of liners recommended, such as paper liners, like the bags used for yard waste.

Starting this week, the city is moving to weekly pickup. Hume says tens of thousands of residents are already wheeling their green bins to the curb, with some neighbourhoods at 100 per cent participation.

He predicts the city is on track to compost 50,000 tonnes of organic waste by the end of the year.

With a report from CTV Ottawa's Kate Eggins