Fly-tipping and a lack of value for money have been raised as issues that could become problems in commingled collection areas which apply Government incentive schemes.
Householders might attempt to reduce rubbish collection charges by placing it in recycling bins, the Campaign for Real Recycling (CRR) said.
The warnings came from quality material group the CRR as the Department for Environment, Food and Rural Affairs (Defra) guidance notes consultation for waste incentive pilot schemes closed.
Berryman Glass recycling manager for south east and East Anglia Brian Head said: Financial incentives to encourage recycling will help increase capture rates, but collection systems where kerbside operatives are unable to operate any form of quality control prior to loading materials onto the vehicle will surely collect more rubbish.
He said his company had to abandon a free commercial glass collection because of this type of contamination.
Combining householder incentives with commingled collections is asking for trouble, doubly so if compaction is involved, Head added.
Cylch chief executive and CRR chairman Mal Williams said that while the Government was concerned about fly-tipping, it was not looking at one of the most likely fly-tipping locations, the commingled wheelie bin.
Novelis recycling national manager Andy Doran said: Householder incentives need to be part of an integrated approach that accounts for both quantity and quality. Applied to commingled collections, it will mean more tonnage into the MRF, so the authority will pay more in gate fees, but without a proportional increase in recycling diversion. With MRF rejection rates already at 9% this is a serious value for money question.