(b) In Suffolk county and Saratoga county, the county sewer agency having the prior consent of the local governing body and the county legislature or a county district shall have an option to purchase the sewer system from the corporation by paying the cost thereof and for all additions and improvements as certified by the engineer as of the date of completion thereof pursuant to section one hundred eighteen, less depreciation on a schedule initially agreed upon but not to exceed thirty years, together with the cost of the land and other costs thereof as of the date of completion. The said county agency or county district may exercise its option by serving written notice on the corporation not less than ninety nor more than one hundred eighty days before the date of taking. The county agency or county district may, instead of making any cash payment agreed or required to be made to the corporation as compensation for such sewer system and land, elect to agree to pay the principal of and interest on outstanding bonds and mortgages issued by or on behalf of such corporation, having a principal amount not exceeding the amount of such cash payment, as such principal and interest shall become due and payable. In the event the county agency does undertake to purchase, maintain and operate such sewer system, it shall do so at the rates established from time to time and agreed to between the county agency and the local governing body, with the costs, including delinquent accounts, assessed against the users until such time as the sewer system is included in a sewer district which shall maintain and operate the sewer system. Notwithstanding the foregoing provisions, in Suffolk county and Saratoga county a county district may elect to acquire the sewer system, including any and all plant sites and other real property pursuant to the provisions of the eminent domain procedure law and in such event the provisions of such law shall apply.