Section 53J. Notwithstanding sections 53 and 53F1/2, in any city, town or district that borrows money to pay for improvements for which betterments or special assessments are assessed, revenues from such betterments and assessments, including interest charged thereon, shall be reserved for appropriation for the payment of debt issued in connection with such improvements. Any such revenues received by the treasurer shall be kept separate from all other monies of such city, town or district. Interest earned on the revenues shall remain with and become part of such revenues available for appropriation. No appropriations from the revenues for payments of principal and interest on such debt issue for any fiscal year shall exceed the same percentage of the principal and interest payment due in such year as the percentage of project costs for which the betterments or special assessments are assessed. Any surplus remaining after such debt is repaid shall belong to any enterprise fund established under section 53F1/2 that the improvement for which the betterments or special assessments are assessed is part of, or, if no such enterprise fund is established, to the general fund of such city, town or district.