The refunding bonds shall be special obligations of the municipality and shall be payable from and secured by a lien upon the revenues of the enterprise as shall be more fully described in the resolution of the governing body authorizing the issuance of the refunding bonds, having due regard to the cost of operation and maintenance of the enterprise and the amount or proportion, if any, of the revenues of the enterprise previously pledged. Any municipality may by resolution of its governing body pledge for the security of the refunding bonds a fixed amount without regard to any fixed proportion of the gross revenues of the enterprise.