Academic journal article Journal of Sustainable Development

Efficiency of Cu(II) Removal from Aqueous Media as a Function of Algal Extract Polysaccharide Content

Academic journal article Journal of Sustainable Development

Efficiency of Cu(II) Removal from Aqueous Media as a Function of Algal Extract Polysaccharide Content

Article excerpt

Abstract

Proper stewardship of our environment necessitates biodiversity preservation and the wise use of resources. Species that may be pests, such as some algae, may also be used innovatively to mitigate their ecological impact. In this study, we extracted polysaccharide mixtures from three algae-Undaria, Laminaria, and Ulva-under three sets of conditions. The nine extracts contained different polysaccharide compositions and varying carboxylic acid contents. The extracts were converted into their respective algal gels by polyion complex formation with chitosan. The gels were examined for their ability to remove Cu(II) ions from aqueous solutions by ion exchange. The removal efficiency was dependent on the algae extraction conditions, which affected the polysaccharide content of the extracts. Among the gels, those derived from the alkaline extractions of Undaria and Laminaria exhibited higher Cu(II) removal efficiencies than from the other extracts. Gels prepared from extracts with higher uronic acid contents exhibited better removal Cu(II) efficiencies. We expected that an extract's carboxylic acid content would be proportional to its removal efficiency, because the acidic groups in the polysaccharide bind to the divalent heavy metal ions. However, this proportionality was not observed: extracts that included sulfated polysaccharides were less efficient at ion removal, despite their carboxylic acid content. This can be explained by the structural differences in the adsorption sites between alginate and those of the sulfated polysaccharide. Thus, an environmental deficit was converted into a potential economic benefit in the removal of heavy metals from water.

Keywords: algae, polysaccharide, extraction conditions, removal efficiency, bivalent copper, biodiversity

1. Introduction

1.1 Aichi Biodiversity Targets

The importance of ecosystems and biodiversity is being increasingly appreciated in terms of their economic benefits (Bishop et al., 2010). Intelligent use of biodiverse resources is important for sustainable development because ecosystem services (such as provisioning, regulating, supporting, and cultural) are supported by biodiversity. Scientific approaches to sustainable development have been reported in various fields such as nature conservation (Alvarez & Larkin, 2010), plastics recycling (Chen et al., 2006), research (Wu et al., 2009), and education on the sustainable use of bioresources (Kanno et al., 2011). At the 10th Conference of the Parties of the Convention on Biological Diversity (CBD-COP10) held in Nagoya, Japan, delegates from more than 100 countries agreed on a new strategic plan, known as the "Aichi Biodiversity Targets" (Secretary of the Convention on Biological Diversity, 2010). This plan comprises a shared vision, a mission, strategic goals, and 20 ambitious yet achievable goals. A study on the utilization of species that are both problematic and potential resources is one possible way to achieve strategic goal B of the Aichi Targets, the reduction of direct pressures on biodiversity and promotion of sustainable use.

1.2 Utilization of Algae

One use for algae, the biosorption of heavy metal ions by both dead and alive Ulva, has been reported by many researchers (Areco et al., 2012; Karthikeyan et al., 2007; Kumar et al., 2006; Kumar et al., 2007; Sari & Tuzen, 2008; Turner et al., 2007). Materials that react with heavy metal ions have the potential not only to be developed into water treatment agents, but also be used in the biomaterials area. For example, Shi et al. reported interesting properties for a low molecular weight polysaccharide extracted from Ulva (Shi et al., 2013). They synthesized an iron(III) complex of the extracted polysaccharide and found that it effectively protected mice from radiation-induced damage in bone marrow cells and the immune system. Moreover, they revealed the anti-radiation and anti-oxidative activities of the complex. …

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