The funds received from the collection of the service charges or rental authorized by this chapter shall be deposited daily with the Director of Finance and shall be accounted for and be known as the Sewer Fund and when appropriated by the City Commission, shall be available for the payment of the costs and expenses of the management, maintenance and repair of the City sewage system and the sewage treatment and disposal works and storm sewers, and any surplus in such Fund shall be used for the payment of the interest on bonds issued and outstanding or which may be issued to provide funds with which to pay the City's portion of the costs of constructing such sewage system or part thereof and such sewage treatment and disposal works, and to retire such bonds when they mature, and for the enlargement or replacement of the sewage system, treatment and disposal works and storm sewers.