The removal of pathogenic bacteria and dissolved organic matter from freshwater using microporous membranes: insights into biofilm formation and fouling reversibility

Abstract

Pathogenic bacteria in drinking-water pose a health risk to consumers, as they compromise the quality of portable water. Chemical disinfection of water containing dissolved organic matter (DOM) causes harmful disinfection by-products. In this work, 4-hydroxybenzoic acid (4-HBA) blended polyethersulfone membranes were fabricated and characterised using microscopic and spectroscopic techniques. The membranes were evaluated for the removal of bacteria and DOM from synthetic and environmental water. Permeate flux increased from 287.30 to 374.60 l m⁻² h⁻¹ at 3 bars when 4-HBA increased from 0 to 1.5 wt.%, suggesting that 4-HBA influenced the membrane’s affinity for water. Furthermore, 4-HBA demonstrated antimicrobial properties by inhibiting bacterial growth. The membrane with 1 wt.% 4-HBA recorded 99.4 and 100% bacteria removal in synthetic and environmental water, respectively. Additionally, DOM removal of 55–73% was achieved. A flux recovery ratio (FRR) of 94.6% was obtained when a mixture of bacteria and humic acid was filtered, implying better fouling layer reversibility during cleaning. Furthermore, 100% FRR was achieved when a multimedia granular filtration step was installed prior to membrane filtration. The results illustrated that the membranes had a high permeate flux with low irreversible fouling. This indicated the potential of the membranes in treating complex feed streams using simple cleaning protocols.

Keywords:

• Microporous membrane
• dissolved organic matter
• microfiltration
• pathogenic bacteria

Acknowledgements

The authors would like to acknowledge the Institute for Nanotechnology and Water Sustainability (iNanoWS), the University of South Africa (Florida, Science campus), the Institute for the Development of Energy for African Sustainability and the College of Agriculture and Environmental Science for laboratory facilities and technical assistance in conducting the experimental work.

Author credit statement

Mamba PP conceptualised the study, performed experiments and wrote the first draft; Msagati TAM was responsible for supervision and review of the manuscript; Nkambule TTI was responsible for supervision, resources and review of the manuscript; Mamba BB was responsible for supervision and reviewed the manuscript; and Motsa MM conceptualised the study, reviewed manuscript drafts and was responsible for supervision and data generation.

Disclosure statement

The authors have no conflicting interest to declare.

Additional information

Funding

The Authors are grateful to the National Research Foundation (Ref: MND210521603023) and the Institute for Nanotechnology and Water Sustainability (iNanoWS) for funding this research work.