The effect of HRT and carriers on the sludge specifications in MBR to remove VOCs from petrochemical wastewater

Abstract

This work employs two membrane bioreactors (with and without carrier) to evaluate the influence of carrier and hydraulic retention time (HRT) on the sludge specifications when removing organic volatile compounds (e.g. styrene and ethylbenzene) from petrochemical wastewater. This study is conducted during three various HRTs. The results indicate that the optimum HRT (e.g. 15 h.) was achieved in the reactor with carrier during biological removal and membrane fouling minimization. During the optimum HRT, the biological removal efficiency for styrene, ethylbenzene, and COD is 99.8 ± 0.1%, 99.8 ± 0.1%, and 99 ± 0.8%, respectively, and the concentration of styrene and ethylbenzene in the exit air reached to the minimum concentration (e.g. 0.1 and below 0.1 ppm, respectively). The fluctuation of the transmembrane pressure indicates a slight variation for the reactor with carrier rather than without carrier. Further, the sludge particle distribution in reactors demonstrates that the HRT reduction decreases the sludge particle size. This is also validated by flocculation ability tests. Finally, the alteration of soluble microbial product (SMP) and extracellular polymeric substance (EPS) in two reactors during all the HRTs show that the SMP is the main reason for fouling of the membranes and the EPS is not the main factor for sludge flocculation.

Keywords:

• Membrane bioreactors
• Suspended carrier
• Sludge specifications
• VOC and HRT

Acknowledgment

The authors would like to thank the support from the Iranian Ministry of Petroleum, National petrochemical Company.