The executive director is charged with the duty of making effective the declared public policy of the state and municipalities as hereinabove set forth, and for that purpose is hereby authorized and empowered to determine whether the public convenience and necessity require that any municipality shall have the right to acquire lands, and thereon to erect enterprises, and expansions thereof and thereto, conditioned, however, that the municipality, if so required by him, shall take security upon the existing building or buildings at the time of entering into contract for the expansion of existing buildings and facilities, and to operate them and to dispose of or rent, let or lease such lands and enterprises. Each municipality within this state shall have the right to apply to the executive director for a certificate of public convenience and necessity as to whether the general welfare requires that such municipality enter into a given enterprise. In determining whether such certificate shall be issued, the executive director may hold public hearings or private hearings, make such investigations as he may desire; and he shall have power to summon witnesses, administer oaths, hear testimony and make a record of all things had and done at such hearing or investigation, and may issue such certificates of convenience and necessity as he deems advisable.