A municipality or other entity operating a sewage system may retain the amounts of the revenues derived from the payment of costs by industrial users of its treatment works services and expend such revenues, together with interest thereon, for:
(1) repayment to applicable agencies of government of any grants or loans made to the municipality or other entity operating a sewage system for construction of the treatment works;
(2) future expansion and reconstruction of the treatment works; and
(3) other municipal purposes.