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Fiber-based materials have emerged as a promising option to increase the efficiency of water treatment plants while reducing their environmental impacts, notably by reducing the use of unsustainable chemicals and the size of the settling tank. Cellulose fiber-based super-bridging agents are sustainable, reusable, and versatile materials that considerably improve floc separation in conventional settling tanks or via alternative screening separation methods. In this study, the effectiveness of fiber-based materials for wastewater treatment was evaluated at lab-scale (0.25 L) and at pilot-scale (20 L) for two separation methods, namely settling and screening. For the fiber-based method, the performance of floc separation during settling was slightly affected by an 80x upscaling factor. A small decrease in turbidity removal from 93 and 86 % was observed for the jar and pilot tests, respectively. By contrast, the turbidity removal of the conventional treatment, i.e., no fibers with a settling separation, was largely affected by the upscaling with turbidity removals of 84 and 49 % for jar and pilot tests, respectively. Therefore, results are suggesting that fiber-based super-bridging agents could be implemented in full-scale water treatment plants. Moreover, the tested fibers increase the robustness of treatment by providing better floc removal than conventional treatment under several challenging conditions such as low settling time and screening with coarse screen mesh size. Furthermore, at both lab-scale and pilot-scale, the use of fiber-based materials reduced the demand for coagulant and flocculant, potentially lowering the operational costs of water treatment plants and reducing the accumulation of metal-based coagulants and synthetic polymers in sludge. Acute toxicity tests using the model organism Daphnia magna show that the cellulose fibers introduce insignificant toxicity at the optimized fiber concentration. Although dedicated mechanistic studies are required at various scales to understand in detail the influence of fibers on water treatment (coagulation/flocculation time, floc formation, floc size distribution velocity gradient, etc.), the efficacy and scalability of the fiber-based approach, along with its minimal environmental impact, position it as a viable and sustainable option for existing and future wastewater treatment plants., Competing Interests: Declaration of competing interest M. Lapointe and N. Tufenkji have applied for a patent on the use of fiber-based materials for water treatment., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Bacteria are mechanically resistant biological structures that can sustain physical stress. Experimental data, however, have shown that high-aspect-ratio nanopillars deform bacterial cells upon contact. If the deformation is sufficiently large, it lyses the bacterial cell wall, ultimately leading to cell death. This has prompted a novel strategy, known as mechano-bactericide technology, to fabricate antibacterial surfaces. Although adhesion forces were originally proposed as the driving force for mechano-bactericidal action, it has been recently shown that external forces, such as capillary forces arising from an air-water interface at bacterial surfaces, produce sufficient loads to rapidly kill bacteria on nanopillars. This discovery highlights the need to theoretically examine how bacteria respond to external loads and to ascertain the key factors. In this study, we developed a finite element model approximating bacteria as elastic shells filled with cytoplasmic fluid brought into contact with an individual nanopillar or nanopillar array. This model elucidates that bacterial killing caused by external forces on nanopillars is influenced by surface topography and cell biomechanical variables, including the density and arrangement of nanopillars, in addition to the cell wall thickness and elastic modulus. Considering that surface topography is an important design parameter, we performed experiments using nanopillar arrays with precisely controlled nanopillar diameters and spacing. Consistent with model predictions, these demonstrate that nanopillars with a larger spacing increase bacterial susceptibility to mechanical puncture. The results provide salient insights into mechano-bactericidal activity and identify key design parameters for implementing this technology.