All revenues derived from the operation of the sewerage system shall be set aside as collected and deposited in a special fund, separate and apart from all other funds of the city. Such revenues shall be used only for the purpose of paying the cost of operating, maintaining, extending and improving the sewerage system, providing an adequate depreciation fund and paying the principal of and interest on any sewerage revenue bonds which may be issued by the city under the provisions of Article 60 of the Revised Cities and Villages Act. When such revenue bonds shall be issued, then the disposition of the revenue of the sewerage system shall be further governed by the terms of the ordinance which shall authorize such bonds. (Prior code § 38-4-8)