New Trends in Emerging Environmental Contaminants

Clean water and unpolluted air and soil are very critical for sustaining human life and the ecosystem. The importance of these resources has long been recognized. Nevertheless, a significant portion of these essential resources is contaminated, affecting millions of human lives and the productivity of the ecosystems globally. Among the various contaminants detected in the environment, new and emerging pollutants pose a great challenge due to their increasing presence and unknown toxicity. This book is a compendium of chapters by different authors, reviewing various aspects of emerging contaminants in different environmental compartments. The current understanding of fate, transport, and degradation of emerging pollutants in different environmental sectors is discussed. The method of detection and the challenges associated with the degradation of these contaminants are also discussed. The book also reviews both conventional and advanced treatment technologies, including adsorption, electrooxidation, membrane filtration, advanced oxidation process, and application of nanomaterials in removing these pollutants from the environment. The authors believe that the book will be of great use to the professionals and students involved in environmental science and engineering research.

Currently, severe contamination of water bodies has led to the scarcity of usable water for drinking and other purposes. The heavy emergence of pollutants in the aquatic environment ranging from ng/l to mg/L is just a consequence of drastic and speedy anthropogenic activities. As compared to developed countries, developing countries, in general, face a more serious impact of alleviating contaminants in water bodies owing to the lack of adequate studies on the current status of water contamination as well as the fate and impact of ECs in wastewater and surface water. Further, the occurrence of pollutants (generally, organics) in wastewater is increasing non-regulated manner above the safe limits. These are not only harmful to aquatic flora and fauna but also for terrestrial lives and recently have been observed by advanced analytical detectors. These trace compounds are termed emerging contaminants (ECs) derived from pharmaceuticals (PhACs), personal care products (PCPs), endocrine disrupting compounds (EDCs). In this book chapter, we would thoroughly discuss the above-mentioned individual types of emerging contaminants in detail and also present the survey on their local distribution aqueous matrix in India. Finally, we would elaborate on the possible solution to tackle this problematic situation of ECs dumping into wastewater and surface water.

An emerging class of pervasive pollutants, microplastics are being increasingly detected in almost all the environmental matrices. Microplastics are plastic particles having a size of less than 5 mm, either formed from the disintegration of large plastics in the environment due to natural and anthropogenic factors, named as secondary microplastics, or manufactured that way for industrial and commercial uses, namely primary microplastics. They occur in a variety of shapes such as beads, fibres, fragments, foams, etc. in nature. As an emerging pollutant, they are gaining popularity among researchers due to massive abundance and yet to be identified potential impacts on different tiers of the ecosystem. This chapter reviews the occurrence and abundance of microplastics in all the environmental compartments, various detection methods, different sources of generation, and their fate and transport in air, water, and soil. A discussion on current trends of their exposure levels on biota and ecotoxicological effects is also included. Further, the potential of microplastics as the carriers of other organic pollutants and leaching out of toxic chemicals from microplastics are also reviewed.

The production of synthetic polymers has increased in manifolds since the advancement of petroleum engineering. These cosmopolitan artificial materials are now persistent in almost every ecosystem on planet earth. This could be attributed to the higher tendency of polymer disintegration and lower polymer degradation in the ambient environments. The processes of polymer disintegration lead to the formation of microscopic plastic particles, referred to as ‘microplastics’. Significant research in emerging environmental contaminants focuses on microplastics, their occurrence in terrestrial and aquatic ecosystems, and adverse effects on biota, humans and other environmental compartments. Therefore, taking account of the background, this chapter summarizes the different strategies for the chemical extraction of microplastics from soil samples and further qualitative and quantitative analysis via distinct spectrophotometric techniques. All over the world, rivers, lakes, and associated floodplains are some of the most polluted ecosystems. The Indian rivers, including Meghna, Brahmaputra and Ganges are polluted with 72,845 tonnes of plastic loads per annum which eventually is transported into the oceans. The existing literature also presents a picture that microplastic pollution studies are usually focused on aquatic ecosystems such as oceans, lakes and rivers. However, microplastic pollution in floodplain soils is a major neglected research question. Therefore, this chapter aims to focus on the occurrence of microplastics in terrestrial soils such as floodplains, their origin and sources, and how to extract and quantify microplastic presence in the geological samples. Furthermore, microplastics are non-uniform in terms of their physicochemical characteristics and degradation. Numerous forms of microplastics pollute aquatic and terrestrial ecosystems. Therefore, an emphasis is also laid down on the microplastic control and remediation techniques in these natural ecosystems for scientific inquiry.

Environmental contamination caused by microplastics (MPs) is an issue of grave concern which is pervasive in global water, air, and soil. Wastewater treatment plants (WWTPs) are recognized as the vital source of MPs into the environment. Hence understanding the fate and behavior of MPs in WWTPs is of utmost importance. Studies have also reported the presence of MPs in the treated effluent. Challenges in MPs removal in different treatment units need to be identified, and advancements of existing treatment technologies are to be explored for enhancing the removal of MPs in WWTPs. This chapter presents the occurrence and fate of MPs in different treatment processes such as biodegradation, adsorption, membrane processes, filtration, electrocoagulation, and advanced oxidation processes. The removal efficiency of MPs in different treatment units, the mechanism of removal, and the challenges involved in removing MPs in each treatment unit are discussed in detail. The efficiency of the existing treatment technologies in WWTPs are compared, and the modifications suggested by recent studies to improve the removal of MPs are presented in this chapter.

Around the world, about seven million people die each year from air pollution. World Health Organization (WHO) has reported that 9 out of 10 people breathe air that exceeds the WHO guideline values for the concentration of pollutants. The highest exposure is observed in low and middle-income countries. Urbanization and industrialization have led to the formation of many new chemical pollutants. The list of such emerging pollutants (EP) in the atmosphere is ever increasing. The sources and health impacts caused by EPs are still not well understood due to various reasons such as the paucity of monitoring data and lack of efficient detection methodology. Consequently, regulatory standards are missing for many of the EPs. The detection of such pollutants is difficult due to their complex behavior and sources in the atmosphere. Chloroform (CHCl₃) is one such EP in air, which is categorized as 2B carcinogen (probable human carcinogen) by the United States Environmental Protection Agency (US-EPA). CHCl₃ gets readily absorbed in the human body, where 60–80% of the inhaled quantity is absorbed and gets distributed throughout the body. The concentration of CHCl₃ found in indoor air is 10 folds higher than the outdoor air. Despite serious health effects caused by CHCl₃, it is not frequently monitored and included in National Ambient Air Quality Standards (NAAQs) of different countries. To address the knowledge gap, an in-depth analysis of literature was conducted. The toxicity profile of the compound, its spatial and temporal distribution, fate in the atmosphere, monitoring methods and health effects caused by it are discussed. The information presented will help policymakers to add/modify the regulatory standards on Chloroform in future amendments.

Phthalate esters (PAEs) are industrial chemicals widely used in large quantities as additives, mainly in the plastic industry. They are colorless sticky liquids that are highly toxic and one of the most frequently detected persistent organic pollutants in the environment. They can leach out from plastic materials and cause severe health issues in living organisms. Their high occurrence in different environmental matrices results in widespread human exposure causing notorious endocrine-disrupting effects, subsequently producing adverse effects on reproduction, growth, and development in human beings as well as the marine ecosystem. Therefore, a better understanding of their occurrence and measurement is required for developing suitable treatment technologies. Recent research studies suggest that advanced treatment methods are sustainable approaches for removing these persistent compounds from the environmental system. This chapter provides an overview of the properties and different types of PAEs, their toxicity, exposure, detection, and measurement techniques in various environmental matrices. Further, the chapter also reviews the various treatment technologies for the removal of PAEs from the environment.

As human lifestyle is improved over the years due to technological, medical and many more developments but in the same time, it has also increased new environment and health challenges. The Emerging contaminants (ECs) are uncontrolled disposal of pollutants, they include group of synthetic chemicals in worldwide use such as water disinfection by-products, pharmaceuticals, chemical fertilizers, pesticides, gasoline additives, and man-made nanomaterials, etc. Pharmaceutical compounds (PCs) are the emerging pollutants, which need to be regulated. They have large potential of causing environment damage, ecosystems as well as human and animal health. Due to huge consumption of pharmaceuticals, effluents contains anti-diabetics, stimulant drugs, and antimicrobials compounds and many more. The decomposition of ECs is dependent on the chemical and biological persistence of ECs, their physicochemical characteristics, the technique applied, etc. The methods to trace and degrade/remove the PCs are very critical to address the issue. Several techniques have been adopted to minimize their hazards like adsorption, coagulation, constructed wetland, advanced oxidation process, membrane reactors (reverse osmosis, nanofiltration, microfiltration, etc.) and photocatalysis, etc. In this chapter, the different types of PCs and their affects will be summarized. The techniques involved to remove/degrade the compounds will also be discussed.

In recent years, pharmaceuticals have surfaced as a novel class of pollutants due to their incomplete degradation in sewage treatment plants and their characteristic ability to promote physiological predicaments in humans even at low doses. Of the several physical, chemical and biological techniques studied for the degradation of drugs, microbial degradation is regarded preferential due to its energy intensive nature, lower ecological footprint as well as considerably lower production of toxic by-products. This chapter reviews the information on the microbial degradation of various classes of drugs including antibiotics, non-steroidal anti-inflammatory drugs, antihypertensives, antidepressants and anticancer drugs. Numerous bacterial, fungal and algal strains have shown substantial efficiency in degradation of various pharmaceuticals, mostly through co-metabolism using the drug as the secondary carbon source. A wide array of enzymes like dehydrogenase, hydrolase, oxidoreductase, oxidase, dioxygenase, monooxygenase, decarboxylase and many more are typically involved in the microbial degradation of pharmaceuticals. The ability of microbes to degrade pharmaceuticals is commonly attributed to their possession of functions analogous to mammalian CYP2C9 and CYP3A4. These isoforms of cytochrome P450 are majorly responsible for metabolism of drugs in humans. Hydroxylation by CYP450 is the most commonly reported initial step in the microbial degradation of drugs, and processes like decarboxylation, dehydrogenation, dechlorination, subsequent oxidation, demethylation, hydroxylation, cleavage of the ester group often constitute the degradation pathways. Although the efficiency and kinetics of degradation are known for most of the microbial strain, the degradation pathway is explained for very few because of the technical difficulties arising during the elucidation process. Though microbial degradation of pharmaceuticals is proving an attractive alternative in lab studies due to irrefutable advantages, the scaling up process is tedious and challenging due to several limitations with respect to microbial growth conditions and subsequent handling of microbial contamination.

Biochar is a carbon-rich product obtained under reducing thermal conditions by the decomposition of biomass. The feedstock characteristics and production methods are the key factors in biochar production. In addition, the modification by different methods improved the morphological and physicochemical properties of biochar and offered diversified use in wastewater treatment. Biochar is extensively used in the removal of emerging contaminants (ECs) like personal care products (PCPs) and pharmaceutically active compounds (PhACs), which are not removed well during conventional wastewater treatment. The status quo of functionalization and characterization of the biochar and recent advancements in the use of as-derived or modified biochar in ECs removal from wastewater will be discussed in this chapter.

The topic of emerging contaminants has gathered attention all over the world. Emerging contaminants (EC) are anthropogenic compounds detected in the environmental matrices in minimal concentrations. The major classification of emerging contaminants are pharmaceuticals, endocrine disruptors, personal care products, per and polyfluoroalkyl substances, pesticides, nanomaterials and microplastics which are associated with diverse range of commercial and personal care products and throughout their life cycle are released into different environmental zones such as air, water, soil, biota and reach different receptors. The knowledge on remediation of these emerging contaminants from different environmental media is limited and still evolving. Among all the available treatment technologies, adsorption shows promising results for remediation due to low cost, ease of operation, and higher efficiencies. Moreover, adsorption is suited for trace contaminants as adsorbents can be functionalized with specific functional groups that show high affinity for the target contaminants. The choice of natural materials further enhances the sustainable aspect of the treatment process, as it would recycle and reuse them in the form of adsorbents. The natural material reviewed in the chapter includes, fruit waste, agricultural waste, Moringa oleifera, chitosan and rice husk for their potential for adsorption applications. The current review overviews adsorption of emerging contaminants, emphasizing its mechanisms and the factors affecting adsorption. The predominant adsorption mechanisms of emerging contaminants are diffusion, electrostatic interaction, hydrophobic interaction, ion exchange, hydrogen bonding and π-π bonding. It mainly describes remediation of significant classes of emerging contaminants through various natural adsorbents like activated carbon, biochar, food, and other agricultural waste.

The incidence of emerging contaminants in receiving water bodies is a threat to ecology and human health. Anthropogenic activities through industrialization and modernization contribute to the release of toxic pollutants such as pesticides, disinfectants, pharmaceuticals, personal care products, detergents, surfactants, wood preservatives, flame retardants, persistent organic pollutants, and their degradation products. These emerging contaminants do not have a defined set of regulations and are hazardous even if present in trace concentrations. Existing conventional physicochemical and biological wastewater treatment methods are not intended to remove emerging contaminants, owing to their trace occurrence (ng/L to µg/L), extremely recalcitrant nature, and associated bioaccumulation. Recently, nanotechnology has evolved as a fundamental significance to provide alternative and efficient wastewater treatment options. This chapter highlights the latest advances in Nanotechnological methods available to remove emerging contaminants from wastewaters. The potential use of nanoscale materials such as nanosorbents, nanofilters, and nanocatalysts in the degradation of emerging contaminants is discussed. In addition, the possible hazards related to the use of engineered nanomaterials, potential obstacles in the application, and the future perspectives are discussed.

Critical shortage of potable water is a grand challenge of current time due to our deliberate exploitation of one of our precious and limited resources. Water safety is threatened by a diverse range of pollutants including potentially toxic inorganic and organic substances, microalgae, bacteria and radioactive wastes because of the acute toxicities, mutagenic and carcinogenic nature of the pollutants. Moreover, pharmaceuticals and personal care products, antibiotics, microplastics and engineered nanomaterials are contaminants of emerging concern due to their endocrine disrupting nature and other acute effects. Magnetic nanoparticles (MNPs) are promising for wastewater treatment by virtue of their excellent catalytic and adsorption performance and ability to fast and facile separation by the application of external magnetic fields. Iron oxide NPs such as magnetite (Fe₃O₄), ʋ-Fe₂O₃, α-Fe₂O₃, and goethite (α-FeOOH) are the most commonly available MNPs till date. Application of MNPs and their hybrid composite offer unprecedented opportunities to improve water remediation technologies for the removal of multiple pollutants from traditional to emerging contaminants. In this chapter, recent progress in the development of MNPs and their hybrid materials-based techniques for the removal of emerging pollutants from wastewater have been surveyed. The potential development and execution barriers regarding both technical challenges and engineering concerns are surveyed along with future directions to overcome them and improve water security.

The increasing occurrence of contaminants such as pharmaceutically active compounds, endocrine-disrupting compounds, nanomaterials, surfactants, personal care products is an emerging concern in the water sector. Some of these emerging contaminants are toxic to all life forms, are bio-resistant, and can sustain after primary and secondary wastewater treatment. Conventional water treatment processes are also ineffective in removing these compounds. Advanced oxidation is a potential technique and can degrade and mineralize complex organic molecules. Advanced oxidation processes (AOPs) rely on the in-situ generation of reactive chemical species (RCS) such as hydroxyl radicals for degradation. Most of the RCS with higher oxidizing potential is short-lived, and hence the effective production of these compounds is crucial for this technology’s success. The plasma-mediated AOP is an emerging technology superior to other conventional AOPs due to its ability to generate RCS at a controlled rate without using chemical agents. Moreover, the nonthermal plasma can also produce the RCS at controlled temperature and ambient pressure and, therefore, very suitable for commercial-scale processing. The plasma produces a cocktail of reactive species whose collective effect enhances the efficacy of the process. However, before translating this technology to the commercial scale, it is essential to make it affordable and energy-efficient. In this regard, significant studies are being carried focusing on reactor design and its optimization. The chapter reviews the recent developments in plasma-based reactors and their application in the degradation of emerging contaminants. The chapter also highlights the current challenges and prospects of plasma-based technology in treating emerging contaminants and various operating parameters influencing the process.

The increasing occurrence of emerging contaminants in the water bodies is a significant concern worldwide due to their potential health effects and recalcitrant nature. The conventional treatment methods are not efficient in removing these complex organic molecules to a safe level. In this context, access to state-of-the-art techniques holds the key to removing these contaminants and protect public health and other forms of life. The advanced oxidation processes, which rely on highly reactive chemical species, are suitable for treating these pollutants. The semiconductor-based photocatalytic process is economical, relatively greener, and well documented among the advanced oxidation processes reported. The materials, including titanium dioxide, zinc oxide, cadmium sulfide, molybdenum oxide, and other oxide forms of transition metals, and their derivatives are investigated as photocatalysts. However, the technology’s success depends mainly on the sunlight utilization capability of the photocatalyst, low recombination rate, and photocatalyst stability. These limitations can be overcome by doping/co-doping/supporting these catalysts with carbon and its allotropes, metal and metal oxide, non-metal, or rare-earth metals. However, doping with graphene is gaining interest due to its excellent surface-to-volume ratio, charge carrier capability, thermal and mechanical stability, electron conductive and storage properties, and can form visible light-activated semiconductor nanocomposite. This chapter reviews the recent development of graphene-modified semiconductor photocatalyst employed for the photocatalytic degradation of emerging contaminants. The synthesis protocol, mechanism of degradation, and factors influencing the efficiency of the degradation are discussed.

In recent years, the effect of emerging contaminants (ECs) has been a threat to humans and wildlife. The advancement in water and wastewater treatment technologies is not very efficient enough for the removal of ECs. ECs have very high toxic levels, and even their traces can cause a dangerous effect on the ecological system and are rarely traceable in wastewater effluent. Due to difficulties in conventional processes for removing ECs, new methods like membrane technologies are being used. Therefore, membrane processes like Reverse Osmosis (RO) and Nanofiltration (NF) have broad applicability. Even though these treatment processes are energy-intensive, these technology’s removal efficiencies are better than conventional methods. This chapter consists of recent studies on the removal of ECs using reverse osmosis and nanofiltration. Different pharmaceuticals, antibiotics, Endocrine Disruptor (EDCs), and pesticides are mentioned, and their removal efficiencies by RO and NF methods are reviewed from recent works of literature. The chapter also highlights the characteristics and effects of emerging pollutants on water bodies. The newer technologies like Membrane Bio-reactor (MBR) are also reviewed along with various technologies like Advanced Oxidation Processes (AOPs) combined with RO/NF process for ECs removal. Finally, an outline of current knowledge gaps and future research scope related to the application of RO and NF for wastewater treatment is recommended.

Emerging contaminants (ECs) have huge impacts on all living beings, and conventional treatment processes like coagulation, precipitation, and chlorination have limited capability for removal. So, a tertiary and combined treatment process is required. Alternative treatment technologies include adsorption, chemical treatment, and membrane filtration. However, the associated operating cost, ECs rejection, fouling propensity, and by-product formation are some of the drawbacks. Membrane distillation (MD) is one of the promising membrane technologies for emerging contaminants removal. In MD, The vapor pressure difference between the hot feed and cold permeate is a driving force. MD technology has some added advantages like low-pressure requirements, less fouling susceptibility, low-temperature requirements, and only vapor mass transfer, i.e., 100% non-volatile compounds retention. MD employs a low temperature and pressure so fouling is less compact and is easily cleanable. MD technology has been studied for desalination, hypersaline brine treatment, chemical separation and can potentially remove emerging contaminants. The MD technology does not require very high-quality heat; solar heat, waste heat, or cogeneration-based heat utilization is possible. This way, MD can be operated on renewable energy and becomes sustainable and carbon neutral. MD technology has also been integrated with other efficient treatment technologies like Forward Osmosis (FO), Reverse osmosis (RO), and Nanofiltration (NF), providing a leading edge compared to other treatment methods. This chapter elaborates on various available MD technologies, possible materials, configurations, operating parameters, and energy requirements. We have also highlighted future research trends and challenges for MD treatment technology’s sustainable and commercial application.

In many of the developing countries, people do not have assess to clean water and clean sanitation, and consumption of contaminated water results in the spread of waterborne diseases. Unfortunately, many parts of developing countries do not have centralized water treatment facilities. Therefore, people are practicing some traditional water treatment methods in households. Point-of-use (POU) water treatment systems are one such method of household water treatment systems and are playing an important role in reaching one of the sustainable development goals that are clean water and sanitation. There are various methods available for POU water treatment, mainly the physical removal methods (Biosand filtration, membrane filtration), chemical treatment methods (chlorine disinfection, coagulation/ flocculation disinfection), and light and heat-based methods (boiling, solar disinfection, UV disinfection). All these methods have their own advantages with limitations. However, membrane-based POU water treatment has registered significant importance compared to other methods. Even in developed countries, people are using POU water treatment systems under various circumstances. In addition, in many countries, there is a growing concern about emerging contaminants in drinking water and is important to study POU water filters for the removal of emerging contaminants. Therefore, in this chapter, various types of technologies available for POU water treatment, membrane-based POU water filters, and the performance of household POU water filters in removing emerging contaminants have been discussed.

The advancement in technology may have created an easy lifestyle, but it has also generated many pollutants that are toxic and cause severe issues for human health called emerging pollutants (EPs). These EPs result from excessive use of chemicals to enhance our daily lives and provide for people’s basic needs. Although we may have found several ways to detect some of these EPs by continuous development in technology, the issues of complete removal of them still persist. The chapter seeks electrocoagulation as one of the effective methods to remove the EPs as it is easy to operate technology and requires low cost and maintenance. This method utilizes the combination of electricity and sacrificial metal electrodes to remove pollutants in the form of flocs which either settles in the bottom or float on the reactor’s top surface. This chapter further highlights the occurrence, issue, and fate of the EPs. It also describes the electrocoagulation treatment method, its mechanism, and parameters that affect the system operation, along with the applicability of emerging pollutants removal. It is suggested to create and manage a database of EPs that shall help in tracking different classes of EPs in the environment. The results observed from exhaustive literature studies are positive and encouraging for the development of this technique to remove EPs from wastewater efficiently.

With the growing energy crisis, industrialization, rapid urbanization, and increased population, it is necessary to sort out environmental pollution and energy crisis issues. The detection of newly identified or emerging contaminants (ECs) into our aquatic environment is of serious concern for the health and safety of the whole ecosystem, and the existing conventional wastewater (WW) treatment processes are not designed to treat these unidentified contaminants. In this context, Bio-electrochemical systems such as microbial fuel cells (MFCs) are considered a prospective technology in removing these ECs and electricity generation from WW through microbial metabolisms. The MFC unit includes an anode, cathode, cation-sensitive membrane, and an external wire. MFCs have shown significant advantages, including converting substrate into energy, operating at wide ranges of temperature and pH with diverse biomass, generating a meager amount of activated sludge from WW, and zero energy requirement for aeration. Additionally, MFCs have been seen as a resolution for water and energy issues due to their capability to treat WW and electricity generation. However, MFCs have numerous challenges in-field applications, such as turbulence in each compartment, membrane resistance in the proton transportation process, etc. This chapter focuses on the application of MFCs towards the removal of various ECs from the aqueous environment. Applications of MFC technology can also be worked in its power generation ability and sustainable energy generation. Although the current applications of MFC technology are still at the laboratory level, it has a great potential for commercial applications in the near future.

The limited availability of fossil fuel sources coupled with the health and environmental risks associated with their use lead to the increased focus on renewable energy resources such as solar photovoltaics (PV) as a potential energy source for the future. Currently, significant research is focused on improving the efficiency (i.e., reducing the cost per watt power) and long-term reliability of solar cells to make PV cells competent with fossil fuels. On the other hand, little attention is given to understanding and assessing long-term environmental impacts associated with the contaminants produced during the manufacturing and application of solar cells. Hence, it is imperative to review and evaluate the critical environmental issues relevant to solar PV, especially in emerging PV technologies. This chapter will introduce different PV technologies, including silicon PV, thin-film PV, and perovskite solar cells, and outline the materials and the processes used in PV technologies. A review of the health and environmental impact of Sn- and Pb- based PV technologies and the need for alternative technologies such as Sn- and Pb-free perovskite PV will be presented. The potential environmental, energy, and health impacts and a review of possible mitigation strategies related to perovskite solar cells-induced hazards are also presented.

Colloidal contaminants such as pathogenic microorganisms and engineered nanoparticles enter subsurface from various sources such as land application of wastewater, reuse of untreated sewage for irrigation and sanitary landfills. Understanding colloid transport in the subsurface is essential for assessing the safe distance of drinking water wells from the source of contamination, bioremediation of contaminated sites, and degree of treatment required for land application of wastewater. There is a large disparity in the length scales associated with colloid transport in soil. This includes micrometre, centimetre, tens of centimetres, metre and kilometre scales which are representative of a single soil capillary, representative elementary volume scale, 1D lab scale, 3D lab scale, and the field scale, respectively. Colloid deposition mechanisms are scale dependent and are governed by the heterogeneity at that scale. Hence, the observed transport processes and the estimated parameters at a smaller scale may not simulate the observations at a larger scale. It is imperative to link the processes and the associated parameters across scales to better predict transport behavior at larger scales. This chapter discusses the mechanisms of colloid retention in porous media at various scales, the effect of heterogeneity on colloid transport at each scale, and upscaling of transport processes.