The commissioner shall make a grant to any municipal or regional authority which, prior to July 1, 1969, constructed a volume reduction plant or rebuilt, reconstructed, redesigned or acquired new machinery, equipment or buildings in connection with waste disposal, which grant shall be twenty-five per cent of the principal amount of bond or note obligations of such municipal or regional authority, issued to finance such construction rebuilding, reconstruction, redesign or acquisition and outstanding on said date, exclusive of all interest costs and for which grant application is made on an application prescribed by the commissioner. Such grant shall be paid in equal annual installments at least thirty days prior to the date the municipal or regional authority is obligated to make payment on such bonds or notes, provided any grant under this section shall be reduced by any amount payable to such municipality or region under the provisions of § 22a-218 for the same construction, rebuilding, reconstruction, redesign or acquisition project, such reduction to be prorated over the period remaining for the payment of such bonds or notes.