Luiz Henrique Da Silva Correa

Topic

Safer Alternatives to Prevent Biofouling in Reverse Osmosis Polyamide Membrane Systems

Department of Civil Engineering

Date & location

• Thursday, June 27, 2024

• 7:00 A.M.

• Virtual

Reviewers

Supervisory Committee

• Dr. Heather Buckley, Department of Civil Engineering, University of Victoria (Supervisor)

• Dr. Caetano Dorea, Department of Civil Engineering, UVic (Member)

• Dr. Caren Helbing, Department of Biochemistry and Microbiology, UVic (Outside Member) 

External Examiner

• Dr. Oliver Iorhemen, Department of Environmental Engineering, University of Northern British Columbia 

Chair of Oral Examination

• Dr. Bob Chow, Department of Biology, UVic

   

Abstract

Biofouling is the main technical barrier to the widespread application of reverse osmosis (RO) technology in addressing worldwide water scarcity. Biofouling reduces permeate production, escalates energy demands, and exacerbates the environmental impacts associated with RO technology. To overcome these challenges, this PhD project proposed a platform to select and test safe and green anti-biofouling agents to prevent biofouling in drinking water RO system applications. The platform consisted of a screening protocol followed by a validation protocol. The proposed platform was applied to assess the applicability of nine chemicals (MIT: 2-methyl-4-isothiazolin-3 one; DBNPA: 2,2-dibromo-3-nitrilopropionamide; SBS: sodium bisulfite; SB: sodium benzoate, PE: phenoxyethanol; LAE: ethyl lauroyl arginate, PHMGH: Polyhexamethylene guanidine hydrochloride; BDMDAC: Benzyldimethyldodecyl ammonium chloride; SNP: Sodium nitroprusside) for preventing membrane biofouling in RO potable water applications. The screening protocol involved three phases: a comprehensive review, antibiofouling testing, and polyamide membrane compatibility testing. The comprehensive review investigated the applicability of the selected biocides in preventing and controlling biofouling in RO systems. It evaluated their antimicrobial efficiency, hazard levels, membrane compatibility, and suitability for drinking water treatment. Antibiofouling testing involved biofouling experiments on a CDC biofilm reactor with the minimum concentrations determined in microtiter plates. Confocal Scanning Laser Microscopy (CLSM) and Scanning Electron Microscopy (SEM) were used to analyze the biocides' anti-biofilm efficacies under dynamic conditions relative to the minimum biofilm inhibitory and eradication concentrations. Polyamide membrane compatibility testing assessed membrane compatibility via rapid membrane degradation tests. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Atomic Force Microscopy (AFM), and SEM were used to assess the polyamide membrane damage due to exposure to biocides.  

The screening protocol revealed that DBNPA and MIT pose hazards to both human health and the environment, making them unsuitable as a full-scale solution to prevent biofouling in RO potable water applications. SBS was also considered to be unsuitable due to its low antibiofilm efficacy and pH dependency. PE and SB were deemed unsuitable due to their moderate antibiofilm efficacy and incompatibility with polyamide membranes. BDMDAC was considered unsuitable for biofouling control in RO potable water applications due to its inefficacy against biofilms and common biofilm forming microorganisms in RO systems. Further research beyond this PhD is required to assess the suitability of PHMGH and SNP for use in RO potable water applications, given their early stage of development and limited available information in the literature. Among the examined chemicals, LAE was the only biocide to successfully pass all phases of the proposed screening protocol, emerging as a promising safe chemical alternative to prevent biofouling in RO systems. LAE showed the highest efficacy against P. aeruginosa biofilms among the tested biocides, successfully preventing biofilm formation by over 98% and removing existing biofilms by more than 99% from RO membranes. Additionally, rapid membrane degradation tests indicated that LAE did not cause morphological or chemical damage to the membranes. Consequently, LAE was the only biocide recommended to advance to further experiments in a RO benchtop system outlined in the validation protocol. 

Therefore, considering the current need for greener alternatives to prevent biofouling in RO polyamide membrane systems in potable water applications, this PhD project has the potential to contribute to the use of RO technology for the provision of reliable, secure, and safe water supply to municipalities, industries, marginalized groups, remote work sites, and Indigenous communities. This was accomplished by establishing a platform to screen anti-biofouling agents for preventing biofouling in RO drinking water applications, alongside the identification of a promising biocide (LAE) to address membrane biofouling in RO drinking water applications.