The city collector shall report to the board of aldermen, at the regular meetings in each month, all taxes collected on the real and personal delinquent lists; and he shall pay the same into the city treasury, and shall receive credit therefor. He shall turn over to his successor in office all uncollected delinquent lists, receiving credit therefor, and his successor shall be charged therewith; provided, that the board of aldermen may declare worthless any and all personal delinquent taxes which they may deem uncollectible.