Dewatering methanotrophic enrichments intended for single cell protein production using biomimetic aquaporin forward osmosis membranes

Microbial biomass is becoming an alternative source of protein, especially for application in animal feeds formulations. While much progress has been made in biomass cultivation, harvesting after cultivation remains a very costly part of the overall process. This study investigated low-cost forward osmosis for dewatering methanotrophic cultures using biomimetic aquaporin membranes.

Brine and glycerol were used as draw solutions as they are available as inexpensive industrial byproducts. NaCl and MgCl2 were also used to better understand the behavior of brine. With NaCl and brine the highest water fluxes were obtained, but ammonium retention was low and high reverse salt fluxes were measured.

With MgCl2, the highest specific water flux (Jw/Js = 7.5 ± 1.7 L g−1) and a good ammonium retention (~85%) was obtained. Thus, only brines with high content on MgCl2 should be considered for FO applications. With glycerol as draw solution, the solute back flux was the highest without affecting microbial growth or methane yields.

Hence it shows potential as good draw solution, if available as residual stream. Surprisingly there was no significant difference in water fluxes at the different osmotic pressures (30 and 60 atm). Noteworthy biofouling did not affect the water fluxes, except the case when NaCl at 60 atm was used as draw solution.

Overall, this study demonstrates that forward osmosis is a feasible technology for harvesting methanotrophic biomass.