Separation of Inorganic Components from Industrial Wastewater Via a Hybrid Forward Osmosis-Reverse Osmosis System

Separation of Inorganic Components from Industrial Wastewater Via a Hybrid Forward Osmosis-Reverse Osmosis System

Douglas A. Huttes, Xi Zhe Ong, Leif M. Templeton, Haley D. White, Laura H. Arias Chavez

Department of Chemical Engineering, Tennessee Tech University, Cookeville Tennessee 38505 United States

Driven by increasing need for sustainable water and energy, new technologies are being developed to provide these critical resources without waste. Renewable bio-feedstocks can be pyrolyzed to generate energy along with process containing residual hydrocarbons and inorganics, which currently must be treated or disposed of as hazardous waste. Here we assess the potential for a hybrid forward osmosis (FO) - reverse osmosis (RO) system to reclaim all components of this complex wastewater. Fouling-resistant FO performs the first separation while RO regenerates the FO draw solution. This dual membrane configuration provides two selective barriers to protect permeate quality. Solute transport through each of these membranes can also be customized by independently adjusting the pH of the feed (wastewater) solution and the NaCl draw solution. By exploiting the pH-dependency of speciation for different contaminants, wastewater components can be sequestered in different parts of the hybrid system to achieve optimal fractionation. We quantified the transport and recovery of ammonia, cyanide, nickel, and zinc containing species across commercial and hand-cast FO membranes as a function of pH, recovery, and draw solution concentration. Water flux and solute transport through commercial RO membranes at different pH and draw solute concentrations were also investigated. Stable water flux (at approximately 2 L m^-2 h^-1) with raw wastewater can be achieved in the FO stage using a 1 M NaCl draw solution. Transport of inorganic solutes depends on a complex combination of factors, in particular pH and the type of membrane used. Comparing the observed pH dependency of solute transport with that expected for particular compounds (e.g., free cyanide vs. organic cyanides) also provides insight into the specific composition of the wastewater. These preliminary results suggest that the FO-RO hybrid system could be an effective process for reclamation of industrial wastewater and that additional study of this approach is warranted.