In case the Requester who does not receive a decision within the time specified in sub-section (1) or clause (a) of sub-section (3) of section 7, or is aggrieved by a decision of the PIO, as the case may be, may within thirty days from the expiry of such period from the receipt of such a decision, prefer an appeal to the Departmental Appellate Authority for redressal of the grievance .