Before any political subdivision shall receive any loan it shall have executed with the state tax commission a repayment agreement, a copy of which must also be filed with the bureau of pollution control of the department of natural resources, after which the bureau shall enter upon its minutes a certificate certifying that the waste disposal plant has been approved, a copy of which certificate must be delivered to and filed with the Mississippi State Tax Commission. The repayment schedule hereinabove provided for shall not be construed to prohibit any recipient from prepaying any part or all of the funds received.