Surfactant-enhanced dead-end ultrafiltration for tertiary treatment of produced water

Abstract

With growing energy demands and more stringent oily wastewater discharge regulations, produced water (PW) is one of the most complex waste streams that must be effectively treated before disposal to the environment or reuse as process water. This study investigated the applicability of surfactant-enhanced multiple-cycle dead-end ultrafiltration operation for the polishing (tertiary) treatment of PW. Sub-micron sized emulsified oils were prepared to mimic PW characteristics in the polishing step. Performance experiments were conducted using lab-scale modules fabricated with commercial ready-to-use hollow fiber membranes and mini-plant testing unit at operating conditions analogous to full-scale application. The influences of dosing anionic surfactant (sodium dodecyl sulfate, SDS) below critical micelle concentration on emulsified oils characteristics, as well as membranes fouling propensity and hydraulic backwashing efficiency were studied. For the first time, a consistent dead-end ultrafiltration performance treating emulsified oils with oil contents up to 50 mg/L was achieved due to a substantially enhanced hydraulic backwashing efficiency (overall permeability recovery range of 72 % - 90 % for different emulsified oils concentrations and SDS concentration of 0.48 g/L). The promoted hydraulic reversible fouling by surfactant-enhanced ultrafiltration was attributed to the minimized hydrophobic-hydrophobic interactions, and the improved access of backwashing water via “facilitated” paths through the formed fouling layer.