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The Web of Science (WoS) international multidisciplinary bibliographical database used to identify the contributions published worldwide in the field of various technological domains suggested the contribution of various fields of science, as shown in Figure 1.1.

As is evident from Figure 1.1, the research is dominated by the Environmental Sciences, Metrology and Atmospheric Sciences, and the Water Resources domain collectively, which makes up 20% of the total research. This one fifth share of the contribution is followed by Chemistry/Multidisciplinary with 10%, Biotechnology and Applied Microbiology with 10%, and Soil Science with another share of 10% contribution. Adding on these three chunks of domains forms 50% of the total contribution, which is further strengthened by research from: Medicine/Immunology/Pathology; Biochemistry and Molecular Biology/Plant Sciences; Nanoscience and Nanotechnology/Material Science; Ecology/Marine and Fresh Water Biology; Geochemistry and Geophysics; and Agronomy and Plant Sciences.

Figure 1.1 Emerging research field for selenium removal technologies published worldwide.

Figure 1.2 Selenium research publication trends.

The most influential research that spans over the domains is from Chemistry, Multidisciplinary Sciences, Nanoscience and Nanotechnology, and Material Science. Salt et al. (1995), Matoba et al. (2002), Grätzel (2009), and Elmolla and Chaudhuri (2010) have made significant contributions with the following components:

 judiciously eradicating problematic contaminants from water discharge

 investigating tarn size restrictions

 sewage flow management

 complying with nitrate, sulfate, chloride discharge constraints

 recuperating heavy metal content

 freshwater scarcity/confines

 groundwater treatment technologies

 mine dewatering

 acid mine waste water.

Quantitative assessment of the research has been presented in these publications considering year‐wise research outcome, geographical distribution, and type of collaboration, characteristics of highly productive institutions and the method of communication used by the scientists. In a similar manner, the authors explored the second category of domain shown in Figure 1.1 denoted by Biochemistry & Molecular Biology and Plant Sciences (Mandal et al. 2001; Zhu et al. 2009). The representative research outcomes highlight issues related to polluted soils and waters with key environmental and human‐related health issues, which may be moderately resolved by the emergent phytoremediation expertise. In situ phyto‐extraction and phyto‐stabilization have proved to be significantly effective in the removal of toxic metals from the soil (Khan et al. 2020a). This lucrative plant‐based tactic for remediation benefits from the amazing capability of plants to essence rudiments and mixtures from the atmosphere and to metabolize various molecules in their materials. Toxic heavy metals and organic contaminants are the chief goals for phytoremediation. Lately, facts of the biological and molecular apparatuses of phytoremediation commenced to arise collectively with organic and technological approaches intended to heighten and expand phytoremediation. Organic amendments and hydrologic regimes have also been found to be effective for Se removal by using constructed wetlands microcosms (Zhao et al. 2020) Furthermore, numerous arena prosecutions confirm the possibility of ecological cleaning by means of plants. This survey quintessence on the utmost established subsections of phytoremediation expertise and on the biotic apparatuses that brands phytoremediation exertion. Although plants alone show the ability to remove the toxic agricultural pollutants using different strategies, integrated approaches such as microbes and plant associations (rhizoremediation) are also proving to be effective options for metal removal (Khan et al. 2020b).

Figure 1.3 Artificial Intelligence, Machine Learning, and Deep Learning mechanisms in modeling and prediction of water treatment parameters.

The authors' attention was captured by eminent research in the field of Biotechnology and Applied Microbiology (Reeves 1997; Salt et al. 1998; Vara and de Oliveira Freitas 2003; Eapen and D'Souza 2005; Tang et al. 2015). Significantly, active selenium occurs in oxic and anoxic environments, and this presence plays an important role in carbon and nitrogen mineralization by bacteriological anaerobic breathing. Selenium‐breathing bacteria (SeRB) come from a geologically isolated, primeval or filthy world and play a significant role in the selenium process. The chalcogen selenium and its microbial cycle have aroused few concerns, with comparable operational similarity to oxygen and sulfur. Extracellular polymeric substances (EPS), a high‐molecular‐weight biopolymer originated from microbial metabolism, have been found to reduce selenite into non‐soluble and low‐toxicity elemental selenium, which would prevent the sequence of environmental degradation (Zhang et al. 2020). This collection of publications appears to inspire prospective work on microbes that use selenate and selenite as terminal electron receptors, analogous to well‐researched sulfate‐reducing bacteria. Summaries have been completed lately on the noteworthy developments in the role of SeRB in the biotic selenium cycle and their environmental role, phylogenetic classification, and metabolism, in addition to selenium biomineralization tools and eco‐friendly biotechnological claims.

While the presence of selenium and its role in the domains discussed above is important, there is a remarkable experimental research area in Medicine, Cardiac and Cardiovascular Systems, Immunology and Pathology that shows the significance of selenium in cardiovascular health (Weschenfelder et al. 2020). This group of researchers made a praiseworthy linkage of selenium metabolism and its role in cardiac pathology. It is remarkable to note that the consumption of selenium in the prevention and treatment of cardiovascular ailments remains an indefinable area. From an alternative perspective, the chief purpose of selenium here is antioxidant defense through its amalgamation as selenocysteine into enzyme groups, for example glutathione peroxidases and thioredoxinreductases. Moreover, selenium compounds are various and have multifaceted metabolic effects, and thus there is partial dependence on selenoprotein expression. However, apart from the valuable properties of selenium, proved in clinical observations, selenium certainly may be destructive. It is thought‐provoking that the biological activities of selenium concurrently have consequences that may influence gene expression, the causing negative sequelae typically seen. Selenium nanoparticles (SeNPs) could substantially reduce hyperlipidemia and vascular damage in mice, most likely by controlling the metabolism of cholesterol and reducing oxidative stress by antioxidant selenoenzymes/selenoproteins (Guo et al. 2020). Removal of unsafe inorganic species of selenium, including selenite and selanate, has recently been tested by drinking water researchers for efficacy (Meher et al. 2020).

This review now comes to the most impacted domain: Environmental Sciences, Metrology, Atmospheric Sciences, and Water Resources (Zayed et al. 1998a, 1998b; Amthor 2001; Jiang et al. 2013). Selenium (Se) is one of the vital essentials in food harvests as an outcome of rigorous plant production in several nations. Next, Se has emerged as the focus of research into various parts of the biosphere. This domain presents the contemporary understanding of Se in the agroecosystem. The existence of selenium in the atmosphere from soil to food systems is considered. The most hopeful and pressing potential nanotechnology developments (Yang et al. 2005; Liu et al. 2015) are in agriculture; and the manufacture nano‐selenium elements, and agronomic nanotechnology and its practice and justifiable expansion are also emphasized.

In other research (Smedley et al. 2002), the bioconcentration factor for plants, which plays a significant role in geochemical prospecting and animal nutrition, is studied for a detailed plant/soil system. This paper reveals in‐depth geochemical annotations for an improved understanding of the ecological qualities of Se, such as its resemblance to sulfur and tellurium.

Approximately 20% of the most influential research under discussion comes under the domain of Chemistry, Medicine Science, Multidisciplinary Sciences and Toxicology (Brown et al. 1999; Elmolla and Chaudhuri 2010). The extracts of this research domain consider the average selenium absorptions in forms of water from approximately 0.4 to 16 μg/l. In marine creatures there is a robust association between the Se deposits in the water and those in the body tissues. Many creatures bioaccumulate Se by factors as high as 1000 to 4000, making selenium poisonous to humans and other creatures. Yang et al. (2005) and Lenz and Lens (2009) claim existence of micronutrient for several creatures in trivial quantities; and they claim further that occupational selenium exterminating is frequently unintentional and occasional.

During the publication analysis, Artificial Intelligence (AI), Machine Learning (ML), and Deep Learning (DL) have emerged as a powerful tool to actuate water treatment processes. The most important role of AI, ML, and DL is that it enables efficient prediction and modeling in the conventional water treatment, distribution, and selenium removal processes.

AI methods, comprising Artificial Neural Network (ANN), Genetic Algorithm (GA), and Particle Swarm Optimization (PSO), are deployed (Gupta and Gupta 1998) for the assessment of Se (IV) deletion from aqueous solutions.

Combination of GA and PSO optimizes the specifications of ANN. The authors claimed to reduce the error to less than 3% with this arrangement of AI tools. It is found that ANN‐PSO and ANN‐GA models have proven to be a perfect choice for demonstrating and enhancing Se (IV) removal by the adsorption and reduction apparatuses.

The authors also studied the Publication Agencies mapping for all the most influential research papers discussed here. Figure 1.4 shows Representative Highest Influential Publications for selenium removal technological published worldwide. It can be clearly seen that the highest number of highly cited research is published by Springer, making up 25% of all publications. The next 20% of contributions comes from Elsevier Science BV in Amsterdam. The other well‐regarded publications range from 1 to 10% of total contributions.

The major objective of this section is to present a modality that helps researchers to visualize “outlines” in the said research field to “perceive effects” that may then be unexplored, by recognizing “gaps” in the research field and “limitations” to issues under examination. The authors emphasize that the fundamental outcome of this study is identifying probable innovative areas of study and the constraints.

To add to the discussion discussed so far, some technologies indicating comprehensive treatments, such as desalination and brine management solutions, are observed. A robust ultra‐high recovery reverse osmosis system has been proposed by several researchers for distant commercial set‐ups enabling reverse osmosis to confiscate scaling ions and thereby causing maximum recovery and smooth operations. There are suggestions that low‐slung temperature evaporator‐crystallizers be used. Analysis results indicate that countries are using different treatment technologies, including reduction techniques, phytoremediation, bioremediation, coagulation‐flocculation, electro‐coagulation (EC), electrochemical methods, adsorption, co‐precipitation, electro kinetics, membrane technology, and chemical precipitation. However, the order of use of particular methods varies from country to country.

Figure 1.4 Representative most influential publications for selenium removal technology published worldwide.

Word dynamics analysis was carried out by key words, title, and abstract on the papers published by Asian countries. India and China emerged as the top five Asian countries. The pattern of word dynamics indicated that Se removal using phytoremediation is emerging as main technology, followed by bioremediation and UASB reactor. Adsorption, reduction, and sorption emerge as the dominant methods for Se removal technology in China.