Analysis of extracellular polymeric substances and membrane fouling of a MB-MBR treating shipboard slops

This work concerns the simultaneous effects of salinity and hydrocarbons on the biological activity and membrane fouling of a moving bed-membrane bioreactor (MB-MBR) fed with real high-salinity oily wastewater generated from the washing of oil tankers (slops). A biological treatment was possible with a proper biomass adaptation by means of a stepwise increase of slop concentration in six operational phases. The mechanism of microorganisms’ adaptation to salinity and total petroleum hydrocarbons (TPH) started in Phase IV, where the feeding was characterized by 7.4  gCl−⋅L−1 and 9  mgTPH⋅L−1, in which the removal efficiencies of chemical oxygen demand (COD) and total organic carbon (TOC) initially collapsed to 15 and 30%, respectively, and subsequently rose to 85 and 90%. Moreover, the TPH removal efficiency rose from 8 to 35% and then reached 70% at the end of the study. During Phase IV, the suspended biomass produced a great amount of extracellular polymeric substances (EPS) in bound polysaccharides form (EPSbound,C) as storage of carbon to face the stressful conditions generated by salinity and hydrocarbons. However, a strong inhibitory effect of the pollutants toward the suspended biomass implied a collapse of EPSbound,C in the last phase, during which the system was fed only with slop. Simultaneously observed was an increase in protein fraction of soluble microbial products (SMPP), which was mainly because of the cell lysis of microorganisms. Therefore, the high biological removal efficiencies achieved in the last phase were mainly due to the biofilm growth on mobile carriers. Correlations between the irreversible cake resistance (RC,irr) and EPSbound,C, and between pore blocking resistance (RPB) and SMPP, highlighted that the hydrophilic EPSbound,C favored the irreversible cake deposition on the membrane surface, whereas SMPP mainly contributed to an increase in pore blocking.