Cllr Michael Murphy, one of six to cross-examine Energos MD Nick Dawber, also said he was unconvinced that any proper work had been done to find alternative locations.
However, Mr Dawber insisted there were no health concerns and all emissions would fall well inside EU guidelines for dioxins.
He also said the Health and Safety Executive had withdrawn their objections to the scheme.
Their initial concerns led to the committee deferring decision for three months as Energos clarified a series of issues.
Knowsley council has vowed all elements of the application are properly monitored, and all 25 conditions are adhered to. But opponents are likely to appeal the decision.
