Since the beginning of this month, these authorities have been joined by Ceredigion, Neath Port Talbot, Newport, Wrexham, Conwy and Torfaen.
Ers dechrau'r mis hwn, mae Ceredigion, Castell-nedd Port Talbot, Casnewydd, Wrecsam, Conwy a Thorfaen wedi ymuno â'r awdurdodau cyntaf.