It is the chairman's responsibility to address unacceptable behaviour by members of the public during public participation. Remind your chair to read the appropriate section of the standing orders. If the chair does not address the matter, you may ask the chair, or if the chair fails to do so, you may propose a motion that the individual be no longer heard, which requires a simple majority of votes.
As an aside, six minutes is more than most councils allow for a member of the public to speak.