Review of Colloid (Nano‐ and Micro‐Particle) Transport and Surface Interaction in Groundwater. William P. Johnson and Eddy F. Pazmino. The Groundwater Project. 111 pp. ISBN: 978‐1‐77470‐070‐9. DOI: https://doi.org/10.21083/978‐1‐77470‐070‐9

Abstract

Colloid (Nano- and Micro-Particle) Transport and Surface Interface in Groundwater by William P. Johnson and Eddy F. Pazmino is a textbook that consists of 111 pages and 11 chapters and serves as an introduction to colloids in groundwater, with a focus on their transport, because the distribution of the colloids in groundwater is mainly governed by their transport. Instead of a comprehensive review of contributions to the literature, this textbook is intended to directly summarize current knowledge of colloid transport in groundwater. This textbook can be helpful for both beginners and researchers to learn the models simulating colloid transport in groundwater and explore the complex mechanisms governing the transport. The book belongs to the Groundwater Project, the works of which are available for free via the website https://gw-project.org/, operated by the Groundwater Project. The Groundwater Project is a nonprofit organization in Canada that is committed to advancing education by creating free high-quality groundwater educational material that is available online for all. Investigation of colloid transport in groundwater is critical to understanding a variety of natural processes and engineered applications such as transport of pathogenic colloids (e.g., viruses, bacteria, and protozoa) and colloid-associated contaminants in the subsurface, and soil and groundwater remediation using nanomaterials (e.g., nanoscale zerovalent iron) and microbes. Deposition is one of the primary factors that govern transport of colloids in groundwater. This textbook presents the state-of-the-art using the Lagrangian method to quantify colloid deposition rates and transport. The Lagrangian approach quantifies colloid trajectories and, accordingly, the deposition and transport based on Newton's second law. The colloid trajectories are controlled by both nanoscale interactions between colloids and surfaces and pore-scale forces such as fluid drag, diffusion, and gravity. This textbook provides basic and advanced information on the aforementioned interactions and forces and how they can be addressed and simulated across the nano, pore, and continuum scales. This textbook has a logical organization of the content by sequentially presenting nanoscale interactions, pore-scale transport processes, and continuum-scale colloid transport (i.e., in an upscaling order). A feature of this textbook is that the authors have incorporated numerical modeling freeware (Parti-Suite) into the text to allow both early-career and advanced researchers to explore presented concepts. The software can clearly visualize trajectory simulations of colloid populations. In addition to the trajectory simulation, the Parti-Suite software provides calculations of colloid–surface interaction energies and forces and collector efficiencies, as well as simulation of the breakthrough curves and retention profiles from column transport experiments at continuum scale. Videos in the Parti-Suite software can be watched by clicking linked figures in the textbook. The Parti-Suite software can be freely downloaded via the link https://wpjohnsongroup.utah.edu/trajectoryCodes.html. Chapter 1 states the scope of this textbook, the book approach, and the goals of the book. Chapter 2 introduces groundwater colloids. In this chapter, the authors present the definition of colloids and the significance of investigating colloid transport in groundwater. They demonstrate that while this text does not directly address colloid aggregation, the mechanisms elucidated in this study facilitate an understanding of the colloid transport behavior in the presence of colloid aggregation. Chapter 3 shows the ranges of size from solutes to the largest colloids and highlights that forces such as gravity and diffusion distinguish the contrasting transport behaviors across the range from solutes to colloids. Because colloid–surface and other interactions are normally cast in either form, this chapter makes a review of distinguishing forces vs. energies by using release of an airborne particle at a given height on a wind-free day as an example. Chapter 4 first briefly introduces solute interaction with colloids. This chapter then introduces DLVO (Derjaguin–Landau–Verwey–Overbeek) theory, DLVO energy maps under favorable and unfavorable conditions (i.e., in the absence and presence of repulsion energy barriers, respectively), and the concept of the “zone of colloid–surface interaction” (over which DLVO interactions act). This chapter has a detailed description of the nanoscale interactions of colloids with surfaces, including van der Waals interaction, electric double layer force, and short-range interactions such as Born repulsion, Lewis acid–base interactions, and hydration repulsion. This chapter also shows how the impact of roughness on colloid–surface interactions is included in the DLVO module of Parti-Suite. Chapter 5 presents pore-scale colloid transport including delivery of colloids to collector surfaces, their subsequent interaction with surfaces, and their potential detachment following attachment. The chapter first reviews experimentally observed effects of favorable vs. unfavorable condition on pore-scale colloid motion in near-surface fluid, colloid attachment, colloid detachment, and the impact of roughness on colloid transport. The chapter then describes the process of simulating pore-scale colloid transport using a mechanistic force and torque balance for representative collectors. The chapter further discusses a number of approximate approaches developed to simulate pore-scale colloid transport, such as correlation equations as a shortcut to collector efficiency, and attachment efficiency as a shortcut to unfavorable collector efficiencies. The chapter finally compares colloid transport with solute transport at the pore scale. Chapter 6 presents experimental observations of colloid transport at the continuum scale and simulated continuum-scale transport. The chapter shows experimentally observed impacts of favorable vs. unfavorable conditions on breakthrough-elution concentration histories and profiles of retained colloid concentrations at the continuum scale, and practical implications of the continuum-scale experimental observations. The simulation of continuum-scale transport includes simulating continuum scale hydrodynamic processes and reactive transport using rate coefficients, and mechanistic linking of rate coefficients to pore- and nano-scale processes. This textbook is also aimed to correct ongoing misperceptions regarding mechanisms governing colloid transport, attachment, and retention. Examples of the misconceptions include: (a) smaller colloids undergo lesser filtration; (b) attaining equilibrium in batch experiments indicates that filtration does not apply (used to argue that nanoparticles partition rather than undergo filtration); (c) correlation equations are colloid filtration theory and correlation equations are empirical; (d) the attachment efficiency under unfavorable conditions reflects only the chemistry, and so is a single value across the physical parameters such as colloid size or fluid velocity; and (e) greater retention near the entrance of a porous medium is the same as nonexponential retention. This textbook increases the knowledge of colloid transport in groundwater through discriminating analysis and insightful organization of the material. I highly recommend this book to students, teachers, and practitioners in fields such as environmental science, hydraulics, hydrology, and hydrogeology. My own students have great experience of using Parti-Suite software for trajectory simulation of colloids in porous media. For example, the Parti-Suite software was used to simulate the trajectories of colloids from bulk solution to the collector surface to account for the impacts of surface roughness and hydrodynamics on colloid deposition by incorporating the impacts into surface torque balance, and the simulation was published in Environment Science and Technology (https://doi.org/10.1021/acs.est.1c07305). Chongyang Shen: Writing – original draft; Writing – review & editing. This review was supported by National Natural Science Foundation of China (41922047). The authors declare no conflict of interest.