Whenever the cost and expense of any improvement shall be payable by the mode of “payment by bonds,” the whole or any portion of any assessment levied on account of such improvement may be paid without penalty or interest within the first thirty days following the date of the first publication of the notice by the city treasurer that such assessment and assessment roll is in his hands for collection, and the unpaid balance, if any, may be paid in equal annual installments, the number of which installments shall be less by two than the number of years which the bonds issued to pay for the improvement may run, or the lien of any such assessment may be discharged at any time after the said thirty days by paying the entire unpaid portion thereof, with all penalties and costs attaching, together with all interest thereon to date of delinquency of the installment thereof next falling due. The first installment shall become due and payable during the thirty day period succeeding a date one year after the date of the first publication of said notice, and annually thereafter each succeeding installment shall become due and payable in like manner. If the whole or any portion of any assessment remains unpaid after the first thirty day period herein provided for, interest upon the whole unpaid sum shall be charged at the rate fixed in the ordinance providing for such improvement, and each year thereafter one installment, together with interest due upon the whole of the unpaid balance, shall be collected. Any installment not paid prior to the expiration of the thirty day period during which said installment is due and payable, shall thereupon become delinquent. All delinquent installments shall be subject to a charge for interest at the bond rate as herein specified, from the date of delinquency until the date of delinquency of the installment next falling due after the payment of such installment, and to an additional charge of five percent penalty levied upon both principal and interest due on such installment or installments. (Prior code § 13.48.050.)