Abstract
Naturally occurring substances or polymeric biomolecules synthesized by living organisms during their entire life cycle are commonly defined as biopolymers. Different classifications of biopolymers have been proposed, focusing on their monomeric units, thus allowing them to be distinguished into three different classes with a huge diversity of secondary structures. Due to their ability to be easily manipulated and modified, their versatility, and their sustainability, biopolymers have been proposed in different fields of interest, starting from food, pharmaceutical, and biomedical industries, (i.e., as excipients, gelling agents, stabilizers, or thickeners). Furthermore, due to their sustainable and renewable features, their biodegradability, and their non-toxicity, biopolymers have also been proposed in wastewater treatment, in combination with different reinforcing materials (natural fibers, inorganic micro- or nano-sized fillers, antioxidants, and pigments) toward the development of novel composites with improved properties. On the other hand, the improper or illegal emission of untreated industrial, agricultural, and household wastewater containing a variety of organic and inorganic pollutants represents a great risk to aquatic systems, with a negative impact due to their high toxicity. Among the remediation techniques, adsorption is widely used and documented for its efficiency, intrinsic simplicity, and low cost. Biopolymers represent promising and challenging adsorbents for aquatic environments’ decontamination from organic and inorganic pollutants, allowing for protection of the environment and living organisms. This review summarizes the results obtained in recent years from the sustainable removal of contaminants by biopolymers, trying to identify open questions and future perspectives to overcome the present gaps and limitations.
Highlights
Introduction iationsWastewater treatments include different methods and techniques with the purpose of restoring, to a desirable quality, water used and/or contaminated by humans or nature.Chemical, biological, or physical processes, or a combination thereof, have been proposed and adopted, but the debate concerning the level of desired quality/purity of water vs costs incurred to achieve that purity is still open.Water must be brought back to a minimized level of deleterious or dangerous effects for both the environment and the user, defining quality requirements and, the best technique to use
Kappa-carrageenan/poly(glycidyl methacrylate) (CG/PG) hydrogel containing numerous functional groups used as an environmental-friendly adsorbent for adsorptive removal of cationic Methylene Blue (MB) has been studied and characterized, showing that some parameters should affect the adsorption of MB (i.e., CG/PG ratios, initial dye concentration, solution pH, time, adsorbent dosage, and solution temperature)
Ag NPs have been fabricated by Ai et al (2012) through a specific ecofriendly light-driven technique for in situ growth on a magnetic alginate/magnetite hybrid (Ag@AMH) biohydrogel, characterized by uniformly dispersed Ag+ ions, causing a catalytic reduction of 4-NP in aqueous solutions [32]
Summary
UV photolysis and photocatalysis, adsorption through activated carbon or perovskite, and ozonation are some of the proposed and widely analyzed wastewater treatments for pharmaceutically active compound degradation, as well as for metal ions and toxic dye removal [28,29,30]. Low-cost “greener”, “eco-friendly”, and renewable alternative biosorbents, based on natural polymers and able to overcome the limitations of actual goldstandard wastewater treatments, have been proposed and analyzed [30,31]. Tunable, and sustainable alternatives, such as natural biopolymer-derived materials from renewable resources, have attracted recent interest due to the decrease in availability of synthetic polymers derived from gas, petroleum, and non-renewable carbon sources [30]. To this aim, a brief and synthetic description of the principal biopolymers and technologies adopted in wastewater treatment has been reported in the following paragraphs
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