Current and Emerging Adsorbent Technologies for Wastewater Treatment: Trends, Limitations, and Environmental Implications

Abstract

Wastewater generation and treatment is an ever-increasing concern in the current century due to increased urbanization and industrialization. To tackle the situation of increasing environmental hazards, numerous wastewater treatment approaches are used—i.e., physical, chemical, and biological (primary to tertiary treatment) methods. Various treatment techniques being used have the risks of producing secondary pollutants. The most promising technique is the use of different materials as adsorbents that have a higher efficacy in treating wastewater, with a minimal production of secondary pollutants. Biosorption is a key process that is highly efficient and cost-effective. This method majorly uses the adsorption process/mechanism for toxicant removal from wastewater. This review elaborates the major agricultural and non-agricultural materials-based sorbents that have been used with their possible mechanisms of pollutant removal. Moreover, this creates a better understanding of how the efficacy of these sorbents can be enhanced by modification or treatments with other substances. This review also explains the re-usability and mechanisms of the used adsorbents and/or their disposal in a safe and environmentally friendly way, along with highlighting the major research gaps and potential future research directions. Additionally, the cost benefit ratio of adsorbents is elucidated.

Efficacy of Indole Acetic Acid and Exopolysaccharides-Producing Bacillus safensis Strain FN13 for Inducing Cd-Stress Tolerance and Plant Growth Promotion in Brassica juncea (L.)

“…The scarcity of irrigation water compels farmers to use untreated wastewater and industrial effluents for crop production particularly in developing countries [7,51]. While it is known that wastewater increases crop production due to dissolved nutrients and beneficial impacts on soil properties, it is also a source of heavy metals in soils and growing crops [9,52]. Heavy metals are potentially toxic for plants, animals, and human beings due to their non-biodegradable nature [53][54][55].…”

Valorization of Agri-Food Wastes as Sustainable Eco-Materials for Wastewater Treatment: Current State and New Perspectives

“…Lignin and cellulose have as primary components –OH and –COOH functional groups that can substitute the H + with As(III), Cd(II), Cr(IV), Hg(II), Pb(II), and Ni(II) as metalloids and metal ions in order to generate complexes, as it was tested for grape and apple wastes, grounds from tea and coffee, nutshells, leaves, algae, rice, and sunflower plants [ 41 ]. In order to enhance the adsorption capacity and reinforce the functional groups potential of these agricultural waste-derived adsorbents, their structure can be modified by different physical and chemical pre-treatments, obtaining carbonaceous materials (biochar), with high surface area and pore volume [ 42 , 43 ].…”

“…According to Younas et al, there is a real challenge regarding the treatment methods of wastewaters in correlation with the pollutant sources [ 41 ]. The authors identified two main sources, natural and derived from anthropogenic activities, emphasizing the generation sources for those pollutants that seriously affect the environment and health.…”

“…Most research was developed in adsorption capacities and mechanisms with low interest for regeneration studies. In the latest years, this aspect was developed in different studies whilst emphasizing the importance of regeneration and final use disposal of spent adsorbents as potentially dangerous wastes [ 41 ]. The regeneration of the adsorbents could be a valuable benefit, their high potential of reusability leading to cost, disposal, and natural resources reductions.…”

“…Regarding the evaluation of the adsorption process as a viable option for water treatment, two basic components have to be evaluated, namely efficiency (adsorption capacity) and adsorbent cost [ 41 ]. If agri-food wastes are used as adsorbents, usually, the efficiency is related to a commercial adsorbent (activated carbon).…”