Design, Construction, and Testing of the Forward Osmosis Secondary Treatment System to Treat Bioreactor Effluent

The Forward Osmosis Secondary Treatment (FOST) system is designed to process effluent from the Membrane Aerated Biological Reactor (MABR) that is currently under development at Johnson Space Center (JSC). The influent to the MABR composed of humidity condensate, urine, laundry, and hygiene wastewater. The FOST system functions as a post treatment step to the MABR by removing ammonia, ions, dissolved solids, and suspended solids. It also provides a physical barrier to microbial and viral contamination. It is assumed that a post treatment thermal catalytic reactor, such as the International Space Space Station (ISS) Volatile Removal Assembly (VRA), will be used to remove trace organics and sterilize the product. The FOST consists of two spiral wound forward osmosis (FO) membrane modules and an Energy Recover Device (ERD) Reverse Osmosis (RO) membrane system. The system is designed to achieve at least 85% water recovery rate and produce product water with dissolved solids less than 2 g/L. This paper outlines the design, the fabrication, and the testing results of the FOST system. Membrane integrity tests indicate that the FO water flux rates are 1.69 ± 0.42 LMH and 2.65 ± 0.35 LMH with an average sodium chloride concentration in the osmotic agent (OA) of 7.8 ± 2.3 g/L and 7.4 ± 2.4 g/L respectively. Using 50 liters of TTU effluent as the feed solution and 10g/L NaCl in the Osmotic Agent tank, the water recovery rate is 86.4% and the average water production rate is 14.3 LPH. The Enhance Ammonia Removal (EAR) downselect indicates that based on a total mass for one hundred 60L of FOST feed solution (using TTU effluent), it cost only 3.4 Kg of acid to lower the pH of the feed tank compared to 16Kg using the University of Puerto Rico (UPR) EAR system, 5400Kg using activated carbon, and 2000Kg using zeolite. As a result, to remove ammonia in the FOST feed streams, pH adjustment is suggested.