(740b) Integrated Forward Osmosis-Membrane Distillation Process for Sustainable Treatment of High Tds Produced Waters

Horizontal drilling and hydraulic fracturing make the extraction of tightly bound hydrocarbons from shale formations economically feasible. Brine management has become a key issue for the future of unconventional onshore oil and gas industry. In recent years, forward osmosis (FO) and membrane distillation (MD) have been widely investigated for treating wastewaters containing high levels of total suspended solids (TDS). Here we aim to demonstrate the feasibility of a hybrid FO-MD process for water recovery from high TDS produced waters, obtained from Southwestern Energy operations in the Marcellus shale. In FO-MD hybrid system, the FO process draws water from the feed solution while MD process reconcentrates the diluted draw solution and produces pure water. The integration of FO-MD processes combines the advantages of both processes and can provide high permeate quality and low membrane fouling. Cellulose triacetate (CTA) obtained from HTI (Albany, OR) and ethylene chlorotrifluoroethylene (ECTFE) obtained from 3M (Maplewood, MN) were employed as FO and MD membranes, respectively.

Experiments with raw and pretreated produced water, containing 57,000 mg L^-1 TDS, were carried out in the integrated FO-MD system. Sodium chloride in de-ionized water was used as FO draw solution and was continuously regenerated using the MD system. Although the individual FO process had relatively high rejection to TDS and total organic carbon (TOC), these contaminants could also accumulate in draw solution after a long-term experiment. The MD process provided an effective rejection to contaminants in the draw solution after FO process and the integrated system revealed nearly complete rejection of TDS and TOC. Feed water was concentrated up to 50% in the hybrid system. Next, the concentrated feed was treated using an individual MD and was further concentrated up to 300,000 mg L^-1 TDS under variety of operating conditions. The results of this study highlight the potential for employing FO-MD to treat high salinity wastewaters from unconventional gas extraction.