Membrane distillation (MD) integrated with crystallization (MDC) for shale gas produced water (SGPW) treatment

Membrane distillation (MD), often integrated with crystallization (MDC), is an attractive treatment option for shale gas produced water (SGPW) because of its ability to handle high salinity as well as the inherent geothermal heat available to this process. To evaluate the feasibility of applying MD process for SGPW treatment, membrane fouling and wetting, which are barrier to its practical application, were systematically examined by varying organic and inorganic constituents, simulating the SGPW from Marcellus shale (USA). The liquid entry pressure (LEP) was first measured to predict the possibility of wetting by the chemical constituents of SGPW, and then a series of lab-scale MD and MDC experiments were performed to elucidate membrane wetting mechanisms. The results revealed that membrane wetting became more pronounced in the presence of oil and grease. The inorganic scaling induced by multivalent ions, such as barium and calcium in SGPW, also enhanced membrane wettability and led to poor permeate water quality. By integrating with crystallization, scalant loading was reduced properly and thus membrane wetting was mitigated effectively. As a result, adopting this MDC process increased total recovery up to 62.5%. Our experimental observations demonstrated that MD could be sustainably operated for SGPW treatment through optimized crystallization for scaling removal as well as effective pre-treatment for organic removal.