AHP-Based Decision for the Selection of a Draw Solution for Anaerobic Osmotic Membrane Bioreactors

The selection of a suitable draw solution (DS) is critically important for the forward osmosis (FO)-based processes since membrane fouling and inhibition caused by DS are the key problems in anaerobic osmotic membrane bioreactor (AnOMBR) systems. This study aims to select a suitable DS for the AnOMBR system treating slaughterhouse wastewater, considering the results of FO performance and the biochemical methane potential (BMP) test. In the first step of the study, the DSs obtained from the literature review were subjected to prescreening, and 18 DSs were evaluated. Eight out of 18 DSs (4 organics and 4 inorganics) were selected using the first analytical hierarchical process (AHP). In the second stage, reverse salt flux selectivity (RSFS), water flux (J w), and reverse salt flux (J s) values were determined to evaluate the FO performance of the 8 selected DSs by batch FO experiments. A BMP test was performed to investigate the inhibition effect of each DS on the anaerobic performance. The experimental results of batch FO and BMP studies were subjected to a second AHP analysis. The second AHP analysis showed that MgCl2 was the most suitable DS. The autopsy analysis demonstrated that the primary source of fouling on the FO membrane was the accumulation of MgCl2 on the membrane’s surface. Although the fouling on the FO membrane did not seriously damage the membrane structure, it caused the membrane surface to become rougher and more hydrophobic.