Evaluation of Organic and Inorganic Draw solutions using Submerged Osmotic Membrane Bioreactor (OMBR) for Municipal Wastewater Treatment

Abstract

In this study, chloride and acetate based salts were investigated as draw solutions to evaluate their viability in osmotic membrane bioreactor (OMBR). Two inorganic divalent chloride based (CaCl2, and MgCl2) and two acetate based (NaOAc and MgOAc) organic salts were compared with commonly used NaCl. For the production of clean water and draw solute recovery, direct contact membrane distillation (DCMD) unit was coupled with OMBR setup to develop hybrid OMBR-MD system. Results demonstrate that organic draw solutions (DS) were able to mitigate the issue of salinity buildup in bioreactor as compared to inorganic DS. Prolonged filtration runs were observed with MgCl2 and MgOAc in contrast with other DS at same molar concentration. Rapid decline and high initial water flux was witnessed with NaCl and CaCl2. Significant membrane fouling was observed with NaOAc as compared to other salts. In comparison with inorganic DS, organic salts were found to reveal the improved characteristics of mix liquor in terms of sludge filterability, particle size, and biomass growth. Moreover, the degradation of soluble microbial products (SMP) and less accumulation of carbon content in bioreactor was observed with acetate based salts. More than 98% removal of NH4+-N, COD, and PO43--P was achieved in permeate for each salt because of dual barriers of high retention membranes (FO and MD).