In the event the board shall issue a certificate of public convenience and necessity to the applicant, and approve a loan of a sum, such sum as approved to be loaned, shall be disbursed to the applicant upon the execution of a legally valid and enforceable promissory note, deed of trust, or contract, or any combination thereof, by the new or expanded industry and the applicant, in accordance with the approved plan of repayment. In the event a contract is required by the plan of repayment, the board is authorized to join in the execution thereof. The board is further authorized to require such provisions and covenants in such promissory note, deed of trust, or contract, or any combination thereof, deemed reasonably necessary to carry out the provisions of this chapter and require the repayment of said loans. The board and municipalities are further authorized to institute suit, at law or equity, to cause the repayment of such loans, and to protect the interest of the State of Mississippi, and may employ private counsel to do so.