Dyeing effluent is one of the largest contributors to textile effluent and such colored wastewater has a seriously destructive impact on the environment. Adsorption can be a very effective treatment for decolorization of textile dyeing effluent, but current techniques employ adsorption chemistry that is not particularly environmentally friendly, such as the use of alum. In this study, natural polysaccharides were used as adsorbents for removal of dye molecules from effluent. The results showed that naturally cationic polysaccharides such as chitin and chitosan gave excellent levels of color removal, and this was attributed to a combination of electrostatic attraction, van der Waals forces, and hydrogen bonding. Nonionic galactomannans (locust bean gum, guar gum, cassia gum) were also highly effective in removing dye from effluent, whereas other nonionic polysaccharides, such as starch, were not effective. This was attributed to the structure of the polysaccharides and the relative degree of inter- and intramolecular interactions between separate polymer chains. The pendant galactose residues of galactomannans prevented strong interaction, allowing greater hydrogen bonding with dye; comparatively, starch has extensive chain interactions, and as such had limited potential for hydrogen bonding with the dye molecules at the temperature of application. In addition, hydrophobic interactions between the hydrophobic parts of the dye and the alpha-face of the pendant galactose residues may have contributed to the superior performance. Repulsion between anionic polysaccharides and the dye anions prevented any hydrogen bonding and as such pectin, carrageenans, and alginic acid were not effective in dye removal from effluent. The use of galactomannans derived from plants in this system presents a sustainable method of effluent treatment. The raw materials are derived from renewable plant sources and are available in tonnage quantities, the adsorption system itself is highly effective and does not involve any additional chemical input or treatment other than the use of the adsorbent, and the adsorption agents themselves are nontoxic and biodegradable.

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BackgroundMost cases of human African trypanosomiasis (HAT) start with a bite from one of the subspecies of Glossina fuscipes. Tsetse use a range of olfactory and visual stimuli to locate their hosts and this response can be exploited to lure tsetse to insecticide-treated targets thereby reducing transmission. To provide a rational basis for cost-effective designs of target, we undertook studies to identify the optimal target colour.Methodology/Principal FindingsOn the Chamaunga islands of Lake Victoria , Kenya, studies were made of the numbers of G. fuscipes fuscipes attracted to targets consisting of a panel (25 cm square) of various coloured fabrics flanked by a panel (also 25 cm square) of fine black netting. Both panels were covered with an electrocuting grid to catch tsetse as they contacted the target. The reflectances of the 37 different-coloured cloth panels utilised in the study were measured spectrophotometrically. Catch was positively correlated with percentage reflectance at the blue (460 nm) wavelength and negatively correlated with reflectance at UV (360 nm) and green (520 nm) wavelengths. The best target was subjectively blue, with percentage reflectances of 3%, 29%, and 20% at 360 nm, 460 nm and 520 nm respectively. The worst target was also, subjectively, blue, but with high reflectances at UV (35% reflectance at 360 nm) wavelengths as well as blue (36% reflectance at 460 nm); the best low UV-reflecting blue caught 3× more tsetse than the high UV-reflecting blue.Conclusions/SignificanceInsecticide-treated targets to control G. f. fuscipes should be blue with low reflectance in both the UV and green bands of the spectrum. Targets that are subjectively blue will perform poorly if they also reflect UV strongly. The selection of fabrics for targets should be guided by spectral analysis of the cloth across both the spectrum visible to humans and the UV region.