The treatment of oily wastewater poses a significant environmental challenge, creating a demand for advanced separation technologies. Membrane technologies, especially ultrafiltration (UF), offer a promising solution. A novel composite polyvinylidene fluoride (PVDF) and polypyrrole (PPy) membrane was created via an in situ polymerization method, which enhances the membrane’s functionality by combining the chemical stability of PVDF with the outstanding properties of PPy, through a simple two-step process that decreases manufacturing costs. The PPy content in the PVDF matrix varies from 0 to 1.5 wt%. The membranes were analyzed for their structure, morphology, hydrophilicity, porosity, mechanical strength, flux, oil rejection, and antifouling performance. Fourier-transform infrared spectroscopy (FTIR) confirmed the successful integration of PPy, which increased hydrophilicity; the contact angle dropped from 68° for pure PVDF to 55.6° at a 1.5% PPy concentration. Scanning electron microscopy (SEM) images showed an evident increase in surface porosity and macrovoid formation; calculated porosity increased from 59.5% to 79.9%, and the hydraulic pore size increased from 2.8 nm to 28.5 nm with 1.5% PPy. Although porosity improved, mechanical strength decreased due to the formation of voids. The enhancement in hydrophilicity and porosity resulted in improved flux recovery (FR), with the PP-1 membrane achieving 93% FR and 93% fouling resistance (Rt), indicating an optimal balance for practical use. These modified membranes successfully reduce fouling, making them easier to clean in oil–water separation applications. PP-1 showed only a reduction in flux but maintained an oil rejection rate over 99%, demonstrating high stability. This combination of PVDF’s durability and PPy’s functionality makes a cost-effective, high-performance membrane that transforms oil/water separation processes for sustainable water security.

Atomic force microscopy was utilized to estimate the adhesion strengths to silicon nitride as well as the cellular elasticities of pathogenic Listeria monocytogenes EGDe cells cultured in media adjusted to five different pH conditions of growth (5, 6, 7, 8, and 9) under water with 0.0027 fixed ionic strength. Particularly, the role of adhesion on the bacterial elastic properties was investigated. The nonadhesive Hertz model of contact mechanics was used to extract Young's moduli of elasticity of bacterial cells from the approach force-indentation data. Additionally, the adhesive models of contact mechanics: Johnson–Kendall–Roberts (JKR) and Derjaguin–Muller–Toporov (DMT) were used to estimate Young's moduli of elasticity of bacterial cells from the retraction force-indentation data. Our results indicated that adhesion to silicon nitride was the highest for cells cultured at a pH of 7. Similarly, bacterial cells cultured at pH 7 were characterized by the highest Young's moduli of elasticities compared to the lower or higher pH conditions of growth. Young's moduli of elasticities estimated from the Hertz model were stiffer than those estimated using JKR or DMT models. As the adhesion between bacterial cells and indenters increased, the difference between the Hertz model and JKR or DMT models estimates of Young's moduli of elasticity increased as well. Contradicting the current norm of using the Hertz model to quantify bacterial elasticity in the literature, our results highlight the extreme importance of utilizing contact mechanics models with adhesion components in them such as the JKR and DMT models to estimate bacterial elasticity.

Forces acting between an atomic force microscopy silicon nitride cantilever and the bacterial surface biopolymers of Escherichia coli or Pseudomonas putida were spatially probed in water. The interactions were fitted to a model of steric repulsion to estimate the bacterial surface biopolymer brush length and grafting density. The forces were further fitted to a Hertz model of contact mechanics modified by Sneddon et al. to quantify Young’s modulus of elasticity for the cells. Contour plots of the quantified properties described above (i.e., the bacterial surface biopolymer brush length and grafting density, and Young’s modulus of elasticity for the cells) based on the location coordinates on the bacterial surfaces were generated. Our contour plots indicated the bacterial cells organize their biopolymers uniquely to help them survive in the environment. Specifically, our results showed that the perimeter of a bacterial cell is characterized by a more flexible as well as longer biopolymer brush compared to those estimated at the center top of the cell. These results suggest that bacteria are likely to use their longer brushes on the edges to facilitate their adhesion by bridging surfaces. Also, they maintain their structural reinforcement by developing higher densities of grafted biopolymers and hence higher elasticities at their centers. Moreover, a stronger linear relationship was observed between the brush thicknesses and the grafting densities for the collapsed brush at the center of the cells when compared to the perimeter of the cells.