The certificates of indebtedness or other forms of debt shall bear interest at a rate not to exceed that provided by state law, shall be payable at such times and places as the commission shall recommend and may be secured by a pledge of the whole or any part of the said five percent required to be placed in the renewal and replacement fund. The proceeds of such certificates may be used in retiring certificates of indebtedness previously issued by the mayor and board of aldermen against said five percent or any part thereof, or for the purpose of making major renewals, replacements, extensions and improvements to the said systems, or for the payment of revenue bonds or interest thereon heretofore issued to prevent a default thereof.
La. R.S. § 33:4319