Removal of arsenic (V) from aqueous solutions using chitosan-red scoria and chitosan-pumice blends

In different regions across the globe, elevated arsenic contents in the groundwater constitute a major health problem. In this work, a biopolymer chitosan has been blended with volcanic rocks (red scoria and pumice) for arsenic (V) removal. The effect of three blending ratios of chitosan and volcanic rocks (1:2, 1:5 and 1:10) on arsenic removal has been studied. The optimal blending ratio was 1:5 (chitosan:volcanic rocks) with maximum adsorption capacity of 0.72 mg/g and 0.71 mg/g for chitosan:red scoria (Ch-Rs) and chitosan:pumice (Ch-Pu), respectively. The experimental adsorption data fitted well a Langmuir isotherm (R-2 > 0.99) and followed pseudo-second-order kinetics. The high stability of the materials and their high arsenic (V) removal efficiency (similar to 93%) in a wide pH range (4 to 10) are useful for real field applications. Moreover, the blends could be regenerated using 0.05 M NaOH and used for several cycles without losing their original arsenic removal efficiency. The results of the study demonstrate that chitosan-volcanic rock blends should be further explored as a potential sustainable solution for removal of arsenic (V) from water

Increasing uniformity of biosurfactant production in Starmerella bombicola via the expression of chimeric cytochrome P450s

Sophorolipids are one of the best known microbial biosurfactants and are produced by several yeast species. The best studied producer is Starmerella bombicola, a non-pathogenic yeast associated in nature with bumblebees. Sophorolipids are built up of the rare disaccharide sophorose, which is attached to a fatty acid through a glyosidic bound. Sophorolipids produced by S. bombicola mainly contain oleic acid as the incorporated hydrophobic group. Other chain lengths can, to a certain content, be incorporated by feeding the yeast with substrates of alternative chain lengths. However, the efficiency for such substrates is low as compared to the preferred C18 chain length and defined by the substrate specificity of the first enzymatic step in sophorolipid biosynthesis, i.e., the cytochrome P450 enzyme CYP52M1. To increase product uniformity and diversity at the same time, a new strain of S. bombicola was developed that produces sophorolipids with a palmitic acid acyl chain. This was achieved by heterologous expression of the cytochrome P450 cyp1 gene of Ustilago maydis and feeding with palmitic acid. Optimization of the production was done by protein and process engineering

The many faces of chitosan : derivatization to improve antimicrobial and metal removal properties

Global warming, fossil fuel depletion and an increasing world population form the basis of many research topics that prioritize a sustainable future for planet Earth and its inhabitants. The reduction and valorization of waste streams creates challenging opportunities for the adjustment of existing industrial processes together with the development of new technologies and products. In this context, chitosan has been thoroughly studied, since it is sourced from waste streams and applied as a building block for added value materials. Chitosan is a polymer of biological origin and is mainly obtained from chitin, which can be found as a structural component in the exoskeleton of crustaceans or insects, or in the cell wall of yeasts and fungi. The unique chemical and biological properties of chitosan, e.g. antimicrobial activity, sorption capacity, biocompatibility, biodegradability, are valued in many fields. However, chemical modification is often necessary to create or increase the desired properties. In this research project, chitosan was chemically modified to obtain multiple derivatives that were tested for three distinct applications. The antifungal, antifouling and metal adsorbing properties were evaluated. Additionally, a novel depolymerization method was established, which allowed to synthesize chitooligosaccharides. The variety of application fields demonstrate the future potential of this compound

Production of long-chain hydroxy fatty acids by Starmerella bombicola

To decrease our dependency for the diminishing source of fossils resources, bio-based alternatives are being explored for the synthesis of commodity and high-value molecules. One example in this ecological initiative is the microbial production of the biosurfactant sophorolipids by the yeast Starmerella bombicola. Sophorolipids are surface-active molecules mainly used as household and laundry detergents. Because S. bombicola is able to produce high titers of sophorolipids, the yeast is also used to increase the portfolio of lipophilic compounds through strain engineering. Here, the one-step microbial production of hydroxy fatty acids by S. bombicola was accomplished by the selective blockage of three catabolic pathways through metabolic engineering. Successful production of 17.39 g/l (omega-1) linked hydroxy fatty acids was obtained by the successive blockage of the sophorolipid biosynthesis, the beta-oxidation and the omega-oxidation pathways. Minor contamination of dicarboxylic acids and fatty aldehydes were successfully removed using flash chromatography. This way, S. bombicola was further expanded into a flexible production platform of economical relevant compounds in the chemical, food and cosmetic industries

From lab to market : an integrated bioprocess design approach for new-to-nature biosurfactants produced by Starmerella bombicola

Glycolipid microbial biosurfactants, such as sophorolipids (SLs), generate high industrial interest as 100% biobased alternatives for traditional surfactants. A well-known success story is the efficient SL producer Starmerella bombicola, which reaches titers well above 200g/L. Recent engineering attempts have enabled the production of completely new types of molecules by S. bombicola, e.g. the bolaform SLs. Scale-up of bolaform SL production was performed at 150L scale. The purified product was evaluated in detergent applications, as classic SLs are mostly applied in eco-friendly detergents. In this paper, we show that they can be used as green and non-irritant surfactants in for example (automatic) dishwashing applications. However, due to the presence of an ester function in the biosurfactant molecule a limited chemical stability at higher pH values (>6.5) was noticed, (therefore called 'non-symmetrical' (nsBola)) which, is a major drawback that will most likely inhibit market introduction. An integrated bioprocess design (IBPD) strategy was thus applied to resolve this issue. The strategy was to replace the fed fatty acids with fatty alcohols, to generate so-called "symmetrical bolaform (sBola) sophorosides (SSs)," containing two instead of one glycosidic bond. Next to a change in feeding strategy, the blocking of the fatty alcohols from metabolizing/oxidizing through the suggested omega-oxidation pathway was necessary. For the latter, two putative fatty alcohol oxidase genes (fao1 and fao2) were identified in the S. bombicola genome and deleted in the bolaform SL producing strain (Delta at Delta sble). Shake flask experiments for these new strains (Delta at Delta sble Delta fao1 and Delta at Delta sble Delta fao2) were performed to evaluate if the fed fatty alcohols were directly implemented into the SL biosynthesis pathway. Indeed, sBola sophorosides (SSs) production up to 20 g/L was observed for the Delta at Delta sble Delta fao1 strain. Unexpectedly, the Delta at Delta sble Delta fao2 strain only produced minor amounts of sBola sophorosides (SSs), and mainly nsBola SLs (alike the parental Delta at Delta sble strain). The sBola sophorosides (SSs) were purified and their symmetrical structure was confirmed by NMR. They were found to be significantly more stable at higher pH, opening up the application potential of the biosurfactant by enhancing its stability properties

Dialdehyde carboxymethyl cellulose cross-linked chitosan for the recovery of palladium and platinum from aqueous solution

Platinum (Pt) and palladium (Pd) have widespread applications, such as in catalysts, jewelry, fuel cells, and electronics because of their favorable physical and chemical properties. Recovery of Pt and Pd from secondary sources is of great concern due to the increased market demand and limitation of the natural reserves of these precious metals. The aim of this research is to achieve recovery of Pt and Pd ions from dilute aqueous solution using dialdehyde of carboxymethyl cellulose (DCMC) crosslinked chitosan (Ch-DCMC). The DCMC was prepared by periodate oxidation of carboxymethyl cellulose (CMC). Both the DCMC and Ch-DCMC were characterized before and after Pt or Pd adsorption using Fourier-transformed infrared (FTIR) spectroscopy, X-ray powder diffraction (XRPD), and scanning electron microscopy (SEM). The effect of cross-linking ratios of chitosan and DCMC (1:1, 1:0.8, 1:0.5, 1:0.25 and 1:0.1) on the Pt and Pd recovery was studied. The optimal cross-linking ratio was found to be 1:0.25 (chitosan: DCMC) with maximum adsorption capacity of 80.8 mg/g Pt and 89.4 mg/g Pd. High selectivity for Pt and Pd compared to base metals and common anions was achieved

Functionalized chitosan adsorbents allow recovery of palladium and platinum from acidic aqueous solutions

Platinum (Pt) and palladium (Pd) are precious metals considered critical in our society and are needed in a variety of sustainable technologies. Their scarcity urges the increase of recycling from secondary waste streams through new and efficient recovery techniques. Adsorption is an established recovery method for liquid streams, where chitosan shows promising results as a low-cost adsorbent, derived from biomass. This biopolymer is able to capture metals, but suffers from a low stability under acidic conditions and poor adsorbing properties. In this study, three new chitosan derivatives were synthesized and employed for Pd(II) and Pt(IV) recovery from acidic solutions. Specific and simple modifications were selected based on their known affinities for these metal ions and taking into account the principles of green chemistry. The prepared derivatives consist of 1,10-phenanthroline-2,9-dicarbaldehyde cross-linked chitosan (Ch-PDC), [2,2'-bipyridine]-5,5'-dicarbaldehyde cross-linked chitosan (Ch-BPDC) and glutaraldehyde cross-linked chitosan grafted with 8-hydroxyquinoline-2-carbaldehyde (Ch-GA-HQC). For all derivatives, the adsorption occurred fast and equilibrium reached within 30 min. The Langmuir isotherms revealed a maximum adsorption capacity for Pd(II) and Pt(IV) of respectively 262.6 mg g(-1) and 119.5 mg g(-1) for Ch-PDC, 154.7 mg g(-1) and 98.3 mg g(-1) for Ch-BPDC and 340.3 mg g(-1) and 203.9 mg g(-1) for Ch-GA-HQC. Such adsorption capacities are considerably higher compared to the biosorbents reported in the literature. Excellent physical properties in homo-and heterogeneous systems and high regeneration performances demonstrate that chitosan-based adsorbents are very promising for Pd(II) and Pt(IV) recovery from acidic solutions