Doctor of Philosophy
Chemical and Biochemical Engineering
Microplastics generated from the breakdown of larger plastic pieces are the emerging contaminant in aquatic ecosystems at high levels, due to inappropriate disposal or mismanagement. With a particle size within 2-5 μm, it has been reported that microplastics are extensive pollutants in water bodies. However, with a wide variety of scientific articles recording the abundance of plastics in the aquatic environment, there is a lack of studies examining microplastics removal. Although multiple studies have used sedimentation and filtration as separation techniques to remove microplastic particles, no study has been able to remove these pollutants without secondary water pollution.
The focus of this study was to investigate the potential use of foam generated from rhamnolipids biosurfactant to remove polyethylene and car tire residue microplastics. Rhamnolipids are a type of biosurfactant that can mimic its chemical counterparts and display less toxicity, higher biodegradability and higher frothing ability.
The research was divided in four stages. In the first stage, the ability of rhamnolipids for the removal of polyethylene microplastic particles was assessed using a microplastic removal system. Then, a two-level factorial Placket Burman design was used for the identification of key parameters for the PE removal efficiency. The effects of rhamnolipids concentration, PE concentration, time, air flow rate, NaCl concentration and system configuration on PE recovery were investigated. The analysis carried out demonstrated the rhamnolipids’ potential as a foaming agent and its ability to remove 92.42% of PE particles when the system operated for 40 min with a rhamnolipid concentration of 5 g/L, a PE concentration of 0.5 g/L, air flow rate of 2 Lpm and NaCl concentration of 0.5M as the medium. The ANOVA analysis identified the variables rhamnolipid concentration and operating time, as critical parameters that influence the PE removal efficiency.
In the second phase of the study, response surface methodology was used to investigate the effect of the variables rhamnolipid concentration (X1), operating time (X2), PE microplastic size (X3) and PE concentration (X4) and their impact on PE removal. This evaluation found that the variables operating time and its interactions with the rhamnolipid concentration and PE size parameters, can significantly impact the removal of polyethylene powder at the 5% level. A least squares quadratic fit that correlates the predictors and the response variable was created with an R2 of 0.82.
Finally in the third stage of the study, the efficiency of rhamnolipids foam for the removal of car tire residue was assessed. Response surface methodology was used to investigate the effect of the 3 variables rhamnolipid concentration (X1), operating time (X2,), Ctr size (X3) and Ctr concentration (X4) and their impact on Ctr removal (Y). The analysis found that the predictors X1, X2 and X3 have a significant effect on the response variable with pvalues of less than 0.05. The interactions X1X2, X1X3, X2X3, and the squared terms X12, X22 and X32 were also found to be significant. The factor X1, had the strongest effect on Y with an estimated coefficient of 39.811 and a low p-value of 1.5761e-06. A multiple regression that correlates the parameters and the response value was developed with an R2 of 0.89.
Summary for Lay Audience
Microplastic particles are contaminants of emerging concern due to their recalcitrant nature and their abundance in various environments. Although multiple research projects have focused on reporting their occurrence in water bodies, to the best of our knowledge, no study has investigated the potential use of biosurfactants to capture and remove microplastics.
The focus of this study was to investigate the potential use of foam-based rhamnolipids for the removal of polyethylene and car tire waste microplastics. Rhamnolipids are a type of biosurfactant that can mimic their counterparts in terms of biodegradability, low toxicity, and high foaming ability. Moreover, previous research indicated the ability of rhamnolipids to remove several contaminants from water. Since the ability of rhamnolipids to remove heavy compounds was confirmed through several investigations, this study studied the microplastics removal efficiency of rhamnolipids foam. This investigation is divided into six chapters. Chapter 1 presents an introduction to the research and thesis structure; chapter 2 provides a literature review on microplastics in the environment and biosurfactant production. Chapter 3 presents the results on the first phase of experiments regarding the design of the microplastics removal unit and assessment of the system for the removal of PE microplastics particles using rhamnolipids. Chapter 4 provides the results of the investigation of the PE removal efficiency using different PE sizes and concentrations of rhamnolipids. Chapter 5 reports the results of the investigation of the Ctr removal efficiency using rhamnolipids, and chapter 6 summarizes the conclusions of the study and provides some recommendations for future work.
Giron, Ana M., "Investigation of Microplastic Removal Using Foam Produced from Rhamnolipids" (2023). Electronic Thesis and Dissertation Repository. 9380.