ABSTRACT
The regulations concerning the levels of concentration of metals in drinking water are becoming more and more stringent. As a consequence, the discharge levels for industrial wastewater are strictly controlled. Conventional processes such as precipitation, solvent extraction, membrane processes, and ion-exchange and chelating resins can be inappropriate for technical limitations (difculty to reach discharge levels), environmental reasons (production of toxic sludge), or economic criteria. Biosorption has retained a great attention for the last decades as an alternative to conventional processes. This technique consists in using materials of biological origin for the sorption of metal ions, dyes, etc. The concept is based on the use of functional groups present at the surface of these materials for binding metal ions through adsorption, ion exchange, chelation, reductive precipitation, etc. A wide diversity of materials have been tested including agriculture subproducts, waste materials from food industry, and valorization of wastes from water compartments (e.g., invading algal biomass). Algal and fungal materials represent emblematic examples of biomass that were tested for metal sorption (Gonzalez Bermudez et al. 2012, Guibal et al. 1992, 1995, Kleinuebing et al. 2010, 2011, Svecova et al. 2006, Yipmantin et al. 2011). For example, algae are mainly constituted of cellulosic compounds, alginate, fucoidan biopolymers (Davis et al. 2003), and diatomaceous materials. Fungal material is characterized by the presence of proteins, carbohydrates, and more specically chitin-based materials as main constituents of cell wall. However, the main commercial source of chitin-based products comes from the valorization of crustacean shells. The complexity of the structure of these raw materials, the possible interactions between their different components, and the possible variation in their composition (e.g., depending on the extraction process, on the growing conditions) may explain, in some cases, their limited efciency, the variability in their sorption properties, and also the difculty to elaborate some advanced materials based on these resources. This may also explain that a great attention has been paid to the extraction of their main active components (i.e., alginate for algae and chitin/chitosan for fungi and crustacean shells). Among the great diversity of biopolymers available in nature, the present work focuses on these two emblematic polysaccharides because of their wide availability and because they are complementary in terms of functional groups (i.e., carboxylic acid groups for alginate, basic amine groups for chitosan), stability range (acidic solutions for alginate, neutral/alkaline solutions for chitosan), and application (afnity for different metal ions due to the difference in their functional groups, with regard to hard and soft acid-base theory). Though these biopolymers can be readily modied by chemical grafting of specic reactive groups to improve their reactivity and their selectivity (Guibal et al. 2000b), the present study is limited to the use of raw materials (with the exception of chitosan grafting that is required for using the biopolymer in acidic solutions) (Alves and Mano 2008, Guibal et al. 2000b, 2002, Yang et al. 2011). These materials can be also used for the encapsulation and immobilization of liquid or solid compounds for preparing new sorbents (Guibal et al. 2009, Krys et al. 2013).
