Organic Transport and Fouling in the Reclamation of Industrial Wastewater with a Hybrid Forward Osmosis - Reverse Osmosis System

Fully reclaiming industrial wastewater instead of sequestering or degrading its components could broadly enhance sustainability across society. Wastewaters that contain high concentrations of hydrocarbons can be particularly challenging to separate due to their tendency to foul membranes. The selectivity of forward osmosis (FO) and reverse osmosis (RO) membranes against small molecules makes them potentially useful in separating this type of complex wastewater. We present a preliminary assessment of a hybrid FO-RO system to reclaim water, hydrocarbons, and inorganics from the wastewater of a fast pyrolysis biomass-to-fuel production facility. The wastewater is concentrated with fouling-resistant FO while RO regenerates the sodium chloride draw solution. To understand the challenges and opportunities of separating this wastewater, performance was investigated as a function of draw solution concentration. When wastewater with 36 g L^-1 total organic carbon (TOC) was concentrated by a 1 M NaCl draw solution, water fluxes across commercial and hand-cast FO membranes stabilized at 1 to 3 L m^-2 h^-1. Similar water fluxes were achieved with 2 M NaCl draw solution, which suggests that fouling might be self-limiting at this water flux. TOC was rejected by the FO membrane at up to 90%. Water flux and TOC rejection in the RO draw solution regeneration stage were also investigated, along with a method for estimating the osmotic pressures of complex composition solutions. Our preliminary results indicate that the FO-RO system may have potential to reclaim complex, foulant-laden wastewaters at modest but stable water fluxes.