Pre-treatment optimization to reduce membrane fouling during produced water treatment with an integrated FO-MD system

During oil exploration, fresh water that is injected into underground reservoirs returns to the surface loaded with hydrocarbons, salts, and other contaminants. This complex solution is typically known as produced water (PW). Generally, different PW streams are generated at a given site, which, after suitable treatment, are sent for re-injection for enhanced oil recovery or to disposal wells. However, there is a potential for water recovery from this hypersaline contaminated stream. Forward osmosis (FO) and membrane distillation (MD) are two low-pressure membrane treatment technologies successfully used in a single hybrid system for PW treatment. During operation, the key foulants on the FO membrane were CaSiO 3 , CaSO 4 , and NaCl, while for MD, they were SiO 2 and CaSO 4 plus emulsified oil, causing pore clogging. Some foulants were tightly bound and not removed by osmotic backwashing or hydraulic flushing, thus requiring pre-treatment. Different pre-treatment techniques, like ion exchange resins and polymeric and ceramic membrane-based ultrafiltration (UF), were assessed in this study. The resins were able to remove bivalent metallic ions successfully from lower concentration streams only and thus caused an increase in FO flux and a reduction in MD flux by disturbing the FO-MD system equilibrium. The higher concentrations of resins and chemicals required for their regeneration make them unsuitable for such applications. On the contrary, PW pre-treated with polymeric and ceramic UF membranes led to increased FO and MD fluxes without any chemical requirement and proved suitable for pre-treatment.