Any surplus funds remaining in the hands of the city treasurer of a city of the first class, to the credit of such various funds, may be invested by the board of public works, with the approval of the mayor and city council, in accordance with the provisions of sections 16-712, 16-713, and 16-715, in interest-bearing securities of the State of Nebraska or any political subdivision thereof, in certificates of deposit of banks which are members of the Federal Deposit Insurance Corporation, or in interest-bearing securities of the United States upon an order for that purpose drawn by the board of public works upon the city treasurer. Such securities may be purchased, sold, or hypothecated by the board of public works with the approval of the mayor and city council, at their fair market value, and the interest earned by such securities shall be credited to the account of the utility from which the funds paid for the securities were originally drawn. In cities which have not conferred upon any board of public works the active direction and supervision of the city’s system of waterworks, power plant, sewerage, and heating or lighting plant, the powers and duties conferred upon the board of public works as to the purchase, sale, and hypothecation of such securities shall be exercised by the city treasurer. Securities so purchased shall be held by the city treasurer who shall provide adequate bond for their safekeeping. When sold, the treasurer shall deliver such securities to the purchaser and collect the sale price.