Membrane Bioreactor for treating petroleum refinery effluent: treatment performance, membrane fouling mechanism and fouling control

Abstract

The work developed discusses the potential use of MBR to treat refinery effluent and operational strategies that may mitigate fouling. At first, MBR performance was evaluated in terms of pollutants removal and fouling investigation in conditions of shock load. The results demonstrated that MBR was able to reduce effectively the pollutants, meeting guideline standards of disposal and reuse for non-potable ends. FTIR results showed that organic matter was removed by biological oxidation and/or retained by adsorption in the biological sludge or retention in the UF membrane. Furthermore, SMP was produced during treatment. In terms of membrane permeability, the results showed that the soluble fraction of mixed liquor contributed significantly to membrane fouling due to the presence of SMP fraction. Secondly, the sludge filterability was studied as an important parameter to evaluate sludge properties and the potentiality of membrane fouling in MBR. Three filterability assessment methods described in the literature were compared regarding their capability to sense sludge quality variation and reproducibility treating petroleum refinery effluents. This study showed that, among the methods evaluated, Time To Filter was the most effective to assess the filterability both in terms of its capability to detect sludge quality variation and reproducibility. The results have also shown that filterability is directly related to membrane fouling potential, and can be used as a tool to monitor and control fouling process in MBR. Significant filterability correlations among colloidal TOC, EPS and floc size were found. The third study assessed the long-term use of cationic polyelectrolyte to improve the sludge filterability, as well as membrane fouling control in bioreactor membrane while treating refinery effluents. Corrective and preventive cationic polyelectrolyte dosages have been added to the MBR in order to evaluate the membrane fouling mitigation in both strategies. The results have confirmed that the use of this product increased sludge filterability, and reduced membrane fouling. During monitoring time stress events occurred due to increase in oil and grease and phenol concentrations in the MBR feed. The preventive use of cationic polyelectrolyte allowed a more effective and stable sludge filterability with lower consumption without decreasing MBR pollutant removal overall performance.