Biofouling reduction in a MBR by the application of a lytic phage on a modified nanocomposite membrane

Abstract

Biological contamination of membranes is an unavoidable problem in membrane bioreactor (MBR) systems. In addition, biofouling caused by antibiotic resistant bacteria (ARB) has become a critical issue not only for environmental health but also for the operation of membrane processes. This paper highlights the potential applications of lytic phage therapy on a modified nanocomposite membrane (polyvinylidene fluoride (PVDF)–sulfonated graphene oxide (SGO)) to control bacterial fouling on membranes and ARB in MBRs. An antibiotic resistant bacterium (E2) and a respective phage (P2) were isolated from municipal wastewater and used in a MBR system as a membrane foulant and antifoulant, respectively. The isolated bacteria were screened further for antibiotic susceptibility and the minimum inhibitory concentrations (MICs) were determined. E2 was found to be resistant to various concentrations of ampicillin, cefotaxime, vancomycin, tetracycline, and gentamicin. The phage treatment efficiency was examined by membrane flux. In the nanocomposite membrane, the E2 + P2 suspension showed a much higher flux (125 L m⁻² h⁻¹) than the E2 suspension (60 L m⁻² h⁻¹). Up to 57% higher flux was observed in the phage treatment, suggesting that the lytic phage prevented bacterial multiplication and biofilm formation. The multiplicity of infection (MOI) was examined to determine the optimal number of phages required to kill the bacteria. Scanning electron microscopy (SEM) was used to observe the bacterial infection and biofouling reduction due to the phage treatment. The modified nanocomposite membrane was aimed at protein fouling reduction (pore blocking resistance) and lytic phage addition was aimed at bacterial fouling reduction (cake layer resistance). The different types of fouling resistance of the membrane were estimated to distinguish between phage treatment and modified membrane efficiency. Based on the results of fouling resistance and SEM, the phage could reduce the membrane cake layer resistance and the modification of the membrane reduced the pore blocking resistance. The synergistic combination of phage treatment and the modified membrane reduced both types of biofouling. A separate cleaning system was installed and examined to avoid disturbing the normal MBR process (killing of bacteria in the feed solution by the phages).