Grantee Research Project Results
The Osmotic Membrane Bioreactor for the Protection of Human Health and the Environment
EPA Grant Number: FP917304Title: The Osmotic Membrane Bioreactor for the Protection of Human Health and the Environment
Investigators: Bowden, Katie S
Institution: University of Southern California
EPA Project Officer: Packard, Benjamin H
Project Period: August 1, 2011 through July 31, 2013
Project Amount: $84,000
RFA: STAR Graduate Fellowships (2011) RFA Text | Recipients Lists
Research Category: Fellowship - Drinking Water , Academic Fellowships
Objective:
The OMBR system represents a unique and innovative combination of forward osmosis (FO) and MBR technologies to enhance the quality of wastewater effluent for potable reuse applications and for discharge to the natural environment. This system utilizes a submerged FO membrane in a bioreactor. Through osmosis, water diffuses from the bioreactor, across a semipermeable membrane and into the draw solution, a high concentration solution with high osmotic pressure. The FO membrane acts as a barrier to solute transport and provides high rejection of the contaminants in the wastewater stream. The diluted draw solution is sent to a reconcentration process (e.g., reverse osmosis or membrane distillation), which reconcentrates the draw solution and generates a high-quality product water. The main objective of the proposed research is to quantify the technical and economic feasibility of the osmotic membrane bioreactor (OMBR) system to produce high quality product water suitable for potable reuse.
Approach:
The first step is to perform a bench-scale study to evaluate the efficacy of the draw solution in withdrawing water from the bioreactor and not adversely affecting biological treatment. Different inorganic and organic draw solutions will be tested using an FO setup to determine which solutions will be ideal for the OMBR system. Then, design and construction of a long-term laboratory-scale OMBR system and its subsystems will be completed. All systems will be operated in alternating aerobic and anoxic modes in a single reactor. Existing reverse osmosis and membrane distillation subsystems will be modified to be used in conjunction with the FO and bioreactor subsystem as a final treatment step to reconcentrate the draw solution and achieve potable drinking water. The biomass will be collected from a conventional wastewater treatment facility to obtain biomass already acclimated to municipal wastewater. The final product water will be analyzed for the traditional organics, solids and nutrients, as well as for emerging trace organic compounds.
Expected Results:
A laboratory-scale OMBR system (OMBR followed by RO) designed in the PI’s laboratory has undergone preliminary investigation. It was found that the dual osmotic barrier system demonstrated high sustainable flux and removed 99 percent of organic carbon and 98 percent of ammonianitrogen from domestic wastewater influent, respectively. The semi-permeable FO membrane has been shown to reject 98 percent of DOC due to its non-porous composition, enhancing removal efficiencies that can be achieved by microporous membranes used in MBRs. These results indicate the potential for high-performing OMBR systems, especially with optimization measures that will be taken in this study with regards to draw solution and FO membrane selection. In the OMBR system, the lack of hydraulic pressure across the membrane reduces compression of the chemical or particulate foulant layer on the membrane surface, reducing fouling on the membrane and enhancing water flux. Because the flux of the OMBR system can likely be maintained by optimizing hydrodynamic operating conditions or using osmotic backwashing only, it is expected that the FO process will require no chemicals for backwashing, making the process more environmentally friendly. Optimal use of draw solutions also will enhance FO performance, maximizing water flux while minimizing reverse salt transport into the bioreactor.
Potential to Further Environmental / Human Health Protection
More stringent regulations and the potential to produce high-quality effluent make OMBRs an attractive process for domestic wastewater treatment. Substantially reduced costs associated with membrane fouling, membrane backwashing and cleaning, membrane replacement, and chemical consumption and disposal are expected. Consideration of these reduced costs along with the substantially improved removal of both traditional and emerging pollutants give the novel OMBR system great potential for human health and environmental protection.