All money received from the sale of any bonds issued under this act shall, after the payment of any appropriation made under section 6, be used solely for the purchase, acquisition, construction, improvement, installation, extension, enlargement, adjustment, or repair of the garbage disposal improvement for which the bonds were issued, including any engineering, legal, and other expenses incident to the garbage disposal improvement, and, if determined in the authorizing ordinance, the payment of the interest on the bonds during a period not to exceed the first 3 years following the date of the bonds and the amount required for operation and maintenance prior to the receipt of the first revenues.