Performance evaluation of hybrid OMBR-MD using organic and inorganic draw solutions

The performance of two inorganic divalent salts (CaCl_2, and MgCl₂) and two organic salts (CH₃COONa and Mg(CH₃COO)₂) was compared with commonly used NaCl in an osmotic membrane bioreactor (OMBR) integrated with a membrane distillation (MD) system. The system was investigated in terms of salinity buildup, flux stability, draw solution (DS) recovery and contaminants removal efficiency. Results indicated that organic DSs not only lessen the salt accumulation within the bioreactor but also increase the pollutant removal efficiency by improving biological treatment. Of all the draw solutions, NaCl and CaCl₂ produced rapid declines in water flux because of the high salt accumulation in the bio-tank as compared to other salts. The DCMD system successfully recovered all organic and inorganic draw solute concentrations as per OMBR requirements. Membrane flushing frequency for the MD system followed the order Mg(CH₃COO)₂ > CH₃COONa > CaCl₂ > MgCl₂ > NaCl. More than 90% removal of chemical oxygen demand (COD), NH₄ ⁺-N, and PO₄ ^3--P was achieved in the permeate for each salt because of the dual barriers of high-retention membranes i.e., forward osmosis and MD.