Treatment and energy utilization of oily water via integrated ultrafiltration-forward osmosis–membrane distillation (UF-FO-MD) system

Oily water of high salinity and temperature causes challenges to eco-environment. Instead of being considered as only pollutants treated by integrated membrane system, oily water was also considered and utilized as driving-energy resource for the system in this work. This paper proposed and studied integrated UF-FO-MD system for not only treatment of oily water but also utilization of its high salinity and temperature (i.e., osmotic and thermal energies). 50kDa ceramic membrane was selected for oily water treatment because of high oil recovery rate, low flux decline rate and great reduction of downstream FO-MD fouling, and corresponding membrane fouling mechanism was proposed. After UF, oily water was simultaneously used as FO draw (sewage as FO feed) and MD feed to utilize its osmotic and thermal energies for FO-MD running. Oil content largely influenced FO-MD fouling, while temperature and salt content had little influence. Three scenarios of dynamic mass-transfer process and temperature-salt content equilibrium curve for FO-MD were proposed, which provide guidance for oily water utilization to control mass-transfer process. UF-FO-MD system efficiently treated both oily water and sewage, and recovered high-quality water by utilization of oily water energies at low-energy cost. Oily water after treatment and utilization met reinjection standard. This work helps for oil-field wastewater treatment and utilization to realize water recovery, energy utilization and pollution reduction.