Research Article: A comprehensive analysis of biosorption of metal ions by macroalgae using ICP-OES, SEM-EDX and FTIR techniques

Date Published: October 15, 2018

Publisher: Public Library of Science

Author(s): Izabela Michalak, Małgorzata Mironiuk, Krzysztof Marycz, Amit Bhatnagar.

http://doi.org/10.1371/journal.pone.0205590

Abstract

In the present study, a comprehensive approach to the biosorption process was proposed. Biosorption of Cr(III), Mn(II) and Mg(II) ions by a freshwater macroalga Cladophora glomerata was examined using several advanced techniques including FTIR (Fourier Transform Infrared Spectroscopy), ICP-OES (Inductively Coupled Plasma–Optical Emission Spectrometry) and SEM-EDX (Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy). The enriched biomass can become a valuable, bioactive feed additive for different breeds of animals. Additionally, the collected algal biomass was soaked in water in order to reduce the content of carbohydrate, what is especially important for animals with metabolic disorders. The content of starch was reduced by 22% but additionally some elements–mainly Si, K and P were removed from the biomass. It was shown that the natural macroalga had better biosorption properties than soaked. Cr(III) ions were sorbed by the biomass in the highest extent, then Mn(II) and finally Mg(II) ions. The content of chromium in the enriched algal biomass increased almost ~200 000 times, manganese ~75 times and magnesium ~4.5 times (both for Mg(II) ions used from magnesium sulphate, as well as from magnesium chloride) when compared to the natural Cladophora glomerata. In the case of the soaked biomass the increase of the content of elements in the enriched biomass was as follows ~17 165 times for Cr, ~25 times for Mn and for Mg ~3.5 times for chloride and 3.8 times for sulphate. The type of magnesium salt (chloride or sulphate) had no significant effect on the algal sorption capacity. The proposed mechanism of the biosorption is ion exchange in which mainly potassium participated. The applied FTIR analysis enabled the identification of the functional groups that participated in the biosorption process–mainly carboxyl and hydroxyl. The main changes in the appearance of the spectra were observed for the following wavenumbers– 3300–3400; 2900; 1700; 1400–1500 and 1200–1300 cm-1. The application of SEM-EDX proved that the metal ions were sorbed on the surface of both tested algae.

Partial Text

Nowadays, the novel feeding strategies that will improve animals production, as well as their health are developed and implemented. A series of promising innovations and practices in feed production and feeding includes a balanced and phased feeding, the increase of the quality and level of use of forages in diets, reduction of grains use, a targeted mineral feeding etc. [1, 2]. These proposals are especially important in terms of horse feeding, where a creation of a well-balanced diet is of particular importance. A forage diet, low in non-structural carbohydrates, with a proper content of minerals and vitamins is highly recommended [3]. The second issue is to search for alternative/additional feed ingredients, mainly due to the global demand for grains and the competition between man and the livestock industry with the existing food and feeds [2]. There are several promising new feed resources, rich in biologically active compounds, that can be used as feed additives for animals. One of them is the biomass of algae, both micro- and macroalgae (also called seaweeds). In the literature, most of the attention is paid to marine macroalgae, however freshwater algae, being the result of eutrophication of water reservoirs, are also a rich source of biologically active compounds, such as unsaturated and saturated fatty acids, carbohydrates, amino acids and proteins, phenolic compounds, minerals, carotenoids, vitamins etc., and can constitute a very useful raw material for nutritional applications [3, 4]. The proposed approach is consistent with the concept of the Food and Agriculture Organization of the United Nations (FAO) of the sustainable animal diet, “which integrates the importance of efficient use of natural resources, protection of the environment, socio-cultural benefits and ethical integrity” [2].

This manuscript provides a comprehensive insight into biosorption properties of a freshwater macroalga–Cladophora glomerata, natural and additionally soaked in tap water before this process. The biomass was enriched separately with Cr(III), Mn(II) and Mg(II) ions in a batch system. The initial concentration of metal ions in the aqueous solution (C0) was 200 mg/L, pH 5, the biomass content (CS) was 2 g/L and contact time 3h. The experimental conditions were established in our previous study [12]. After biosorption, the enriched biomass was examined using several techniques such as ICP-OES, FTIR and SEM-EDX. As a control group, the natural and soaked biomass was used. A nutritional value of the natural and soaked Cladophora glomerata was also determined.

Summarizing, in the present research, we investigated biosorption properties of Cladophora glomerata in a native, as well as in a soaked form and then enriched with Cr(III), Mn(II) and Mg(II) ions. We chose these ions, because they are recognized as insulin sensitizers, which in turn in the form of the enriched biomass can serve as a potential clinical feed additive for horses that suffer from EMS. Cladophora glomerata showed the best biosorption properties towards Cr(III) ions, then Mn(II) and finally Mg(II) ions. In both macroalgae–natural and soaked, potassium was the main light metal ion that participated in the ion exchange in biosorption process. FTIR analysis showed that carboxyl and hydroxyl groups were effective for capturing Cr(III), Mg(II) and Mn(II) ions. SEM-EDX technique confirmed binding of metal ions on the surface of algal biomass. Our research clearly showed, that soaked Cladophora glomerata was characterized by the lower ability to bind Cr(III), Mn(II) and Mg(II) ions. Additionally it was found that soaking of algae in water decreased the content of mainly K, P, Mg, Mn in the biomass. Although, biosorption properties of a soaked Cladophora glomerata are reduced, when compared to the native form, it can serve as a low glycaemic component for the production of advanced feed supplements for horses (soaking of algae resulted in the reduction of starch by 22% when compared with natural macroalga). Moreover, the additional advantage of low glycaemic index components in particular produced from Cladophora glomerata might be the possibility to increase its quantity in a daily ration, which in turn will serve the higher amounts of bioactive factors. To summarize, it might be highlighted, that soaking of Cladophora glomerata negatively affected its biosorption properties, but reduced the glycemic index, which is crucial in the feeding of insulin resistance animals.

 

Source:

http://doi.org/10.1371/journal.pone.0205590

 

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