Testing successfully demonstrated the operation of an electrochemical flow cell for more than 1000 h to recover 13-14 wt% sodium hydroxide from an alkaline waste solution. The nickel cathode, platinized-titanium anode and cationic membrane exhibited no visible signs of attack upon inspection after testing. The membrane experienced a slow, but steady decline in current efficiency, from a high of greater than 95% down to approximately 90% after 1079 h. We attribute the loss in current efficiency to the accumulation of silicon and aluminium within the membrane structure.