The city clerk shall by virtue of his office be the collector of accounts due the city for sewage disposal service under the provisions of this chapter and all funds so collected shall be remitted to the city treasurer to be held by the city treasurer in a special fund, designated as the "sewage disposal fund" and such revenues shall be used exclusively for the administration, operation, maintenance, repair, replacement, extension, enlargement, betterments, depreciation and obsolescence of its sewage disposal system and may be used to pay principal of and interest on any bonds issued on account of said sewer system, either general obligation bonds or revenue bonds or both, except bonds issued for any such project the cost of which is payable from special assessments, and said revenues shall be used for no purpose other than those specified herein and shall not be applied to the construction or reconstruction of sewers, the cost of which is provided by law to be paid from special assessments in a benefit district. (Prior code § 9-405)