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The omnipresence of microplastic pollution in the environment has become a main challenge in recent years. One of the primary concerns is the ecotoxicological impact of microplastics on marine ecosystems, as well as the potential risk to humans related to the accumulation of microplastics in the body. Although it has not yet been scientifically proven, their presence in drinking water is a main concern. Studies have shown various strategies and new material development approaches for effectively removing microplastics. Recently, nanocellulose has emerged as a promising bionanomaterial for wastewater treatment. The purpose of this review is to introduce the potential of nanocellulose for microplastic removal. This study consists of three main points: the synthesis method of nanocellulose, the fundamentals of nanocellulose, and the use of these materials for capturing and removing microplastics. In addition, the potential of nanocellulose for antifouling has also been demonstrated. We also provide information regarding the source, fate, and transportation of microplastics in the environment and how to detect them to obtain a better understanding of how microplastics behave and ultimately end up in drinking water systems. Furthermore, we also discuss major challenges and future perspectives concerning the applications of nanocellulose-based materials in microplastic removal. Overall, nanocellulose is a versatile material and further research should be carried out to explore nanocellulose potential to meet the specific requirements for microplastic removal.

Three phenomena involved in the perikinetic coagulation process were studied with regard to their ability to account for the influence of gravity on the coagulation rate: (1) surface charge effects on the pressure in the gap between two approaching particles, through the streaming potential generated by the squeezing flow; (2) free convection induced by temperature changes in the surroundings; (3) surface roughness and hydration force effects on the interaction force between two particles. In a separate paper flow interactions between two identical spheres are shown to be insufficient to explain the influence of gravity on coagulation rate. Of these phenomena studied, a combination of surface roughness and free convection can explain the influence of gravity on coagulation.

Perikinetic coagulation experiments are reported which were performed under 1gand μgconditions during a flight in a sounding rocket, for dispersions of polystyrene, quartz, and amorphous silica particles. Coagulation rates for dispersions of polystyrene, quartz, and amorphous silica are found to increase significantly under μgconditions compared to 1gconditions. Another set of experiments was performed at 1g,2g,4g,and 7g,with different densities of the continuous phase; also a mixture of two different polystyrene latices was used. The most pronounced effect of gravity on coagulation rate is found for dispersions with a small density difference, on going from 1gto 2g.In this regime a significant decrease in coagulation rates is observed. For the latex mixture at pronounced density differences, gravity-induced coagulation was observed; however, the aggregates formed did not have a lasting contact. The rate constant calculated under μgconditions approaches the theoretical value of von Smoluchowski. By means of a video analysis of the perikinetic coagulation process, the formation of doublets was studied. The “interaction time” for two particles was found to be longer for the density-matched dispersion. Doublets of particles are easily disrupted, and at 1g,free convection currents were observed even at small temperature differences in the system.

Abstract: This paper describes an experimental study on dispersions of monodisperse polystyrene (PS) spheres with a typical radius of 1 μm, dispersed in an electrolyte at high ionic strength, screening the electrostatic repulsion. These suspensions gelate at rest even at low volume fractions of PS particles. The density of the particles is matched with the solvent by using deuterium oxide for volume fractions φ≤0.117. Steady-state flow curves, viscosity as a function of shear rate, are measured and reported for 0.014<φ<0.322. The measured flow curves are analyzed on the basis of two models: 1. In the giant floc model (van Diemen and Stein 1983, 1984; Schreuder et al. 1986, 1987; Laven et al. 1988), at low shear rates, the shear is not distributed homogeneously but is limited to certain shear planes; the energy dissipation during steady flow is due primarily to overcoming the viscous drag on the suspended particles during motion caused by encounters of particles in the shear planes. Though this model was developed for higher solid volume fractions (0.35–0.425), we found that it also describes the rheology of dilute particle gels for 0.15≤φ≤0.3, using the same values for the parameters in the model as in the high solid volume fraction region. For φ<0.15, the model also describes the data if the fraction of distance by which a moving particle entrains its neighbors, is assumed to increase in this φ region. 2. The model of de Rooij (de Rooij et al. 1993, 1994) considers aggregates in shear flow to be monodisperse impermeable spheres with a fractal structure. The permeability is taken into account by considering a hydrodynamic radius smaller than the gyration radius in the Krieger-Dougherty expression for the hydrodynamic contribution to the viscosity. Through the use of a yield criterion the aggregate radius is modeled as a function of shear rate. We found that the model describes our experimental results, with a combination of parameter values used already by de Rooij, but only for φ<0.15.