The plot included attacks on US military facilities in an effort to undermine support for Ukraine
It was not immediately clear what had caused the explosion.
Local TV showed footage of thick plumes of black smoke rising from the site.
A group of 250 children visiting a bird park nearby had to be evacuated, the central government's regional office said. All were unharmed.
The plant is operated by privately-owned company Iniciativas Bioenergeticas which produces biodiesel and glycerine there from recycled vegetable oils.
The company did not immediately respond to a request for comment.