Optimization of osmotic backwashing cleaning protocol for produced water fouled forward osmosis membranes

Abstract

Produced water (PW) is a contaminated effluent from oil and gas operations that can be treated using forward osmosis (FO) before discharge. However, the FO membrane suffers fouling issues during PW treatment, which can be addressed using the osmotic backwashing (OB) technique. In this study, desalter effluent (DE) was used as feed solution (FS) and water-oil separator outlet (WO) as a draw solution (DS). Long-term experiments of 5 cycles of 20 h each were performed with OB executed between the cycles. With 60 min OB, the active layer facing feed solution configuration outperformed the active layer facing draw solution configuration with a stable 35% higher flux and lesser specific reverse solute flux (SRSF). Further optimization was done between 60, 30, and 2 × 30 min OB protocols. Effective flux recovery (water recovered minus water used for OB) and system availability (total time minus OB time) measured the system efficiency. The 30 min OB exhibited the highest system efficiency, with 3% higher flux recovery and 52% lesser SRSF achieved with real streams. The major foulants on the active layer were CaSiO3 and NaCl, while CaSiO3, CaSO4, and NaCl were identified on the support layer. Membrane characteristics remained the same after OB; hence, 30 min OB is feasible for cleaning the PW fouled FO membranes.