Increasing environmental awareness coupled with more stringent regulation standards has triggered various industries to challenge themselves in seeking appropriate wastewater treatment technologies. Coagulation−flocculation process is regarded as one of the most important and widely used treatment processes of industrial wastewaters due to its simplicity and effectiveness. This paper provides a critical review on recent studies of coagulation−flocculation treatment processes of various industrial wastewaters. The limitations and challenges for the coagulation−flocculation process such as the toxicity and health hazard posed by inorganic coagulants, production of large amount of toxic sludge, ineffectiveness in removing heavy metals and emerging contaminants, increase in effluent color, inefficient pollutant removal using natural coagulants, and complexity of scaling up procedure are presented. In addition, an overview on the influence of process parameters on treatment efficiency is included in this review. Finally, this review concludes with recommendations for improvements and new directions for this long-established process.

Vermicomposting is a process in which earthworms are used to convert organic materials into humus-like material known as vermicompost. A number of researchers throughout the world have found that the nutrient profile in vermicompost is generally higher than traditional compost. In fact, vermicompost can enhance soil fertility physically, chemically and biologically. Physically, vermicompost-treated soil has better aeration, porosity, bulk density and water retention. Chemical properties such as pH, electrical conductivity and organic matter content are also improved for better crop yield. Nevertheless, enhanced plant growth could not be satisfactorily explained by improvements in the nutrient content of the soil, which means that other plant growth-influencing materials are available in vermicomposts. Although vermicomposts have been shown to improve plant growth significantly, the application of vermicomposts at high concentrations could impede growth due to the high concentrations of soluble salts available in vermicomposts. Therefore, vermicomposts should be applied at moderate concentrations in order to obtain maximum plant yield. This review paper discusses in detail the effects of vermicompost on soil fertility physically, chemically and biologically. Future prospects and economy on the use of organic fertilizers in the agricultural sector are also examined.

Among many other sustainable functional nanomaterials, nanocellulose is drawing increasing interest for use in environmental remediation technologies due to its numerous unique properties and functionalities. Nanocellulose is usually derived from the disintegration of naturally occurring polymers or produced by the action of bacteria. In this review, some invigorating perspectives on the challenges, future direction, and updates on the most relevant uses of nanocellulose in environmental remediation are discussed. The reported applications and properties of nanocellulose as an adsorbent, photocatalyst, flocculant, and membrane are reviewed in particular. However, additional effort will be required to implement and commercialize nanocellulose as a viable nanomaterial for remediation technologies. In this regard, the main challenges and limitations in working with nanocellulose-based materials are identified in an effort to improve the development and efficient use of nanocellulose in environmental remediation.

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2D/2D heterostructures have recently garnered substantial research attention due to their advantageous noble properties such as tunable band structures, high interfacial contact areas, and abundant active sites, which remarkably enhance photocatalytic activity. These intriguing properties render 2D/2D nanostructures highly auspicious in a multitude of photocatalytic energy applications, including water splitting for H2 oxygen (O2) evolution, reduction of CO2, and N2 fixation. As such, this leads to the development of clean energy technology by 2D/2D catalysts and solar energy as the inexhaustible energy resource. Herein, the fundamental principles of 2D/2D hybrid heterostructures and diverse types of interfaces with different material families are systematically discussed. Furthermore, photocatalytic energy applications using 2D/2D heterointerfaces over the recent years are highlighted. Insights into the interplay of 2D/2D heterojunction interfaces and the associated physicochemical properties (e.g., charge carrier dynamics) toward the photocatalytic enhancement are put forward. Last but not least, the challenges and prospects in engineering 2D/2D heterostructure photocatalysts for affordable and clean energy advancements are reviewed, which serve as a guiding star not only in photocatalysis, but also in other applications in the energy realm such as fuel cells, batteries, supercapacitors, and photovoltaics.