Bioaccumulation of Rare Earth Elements from Waste Luminophores in the Red Algae, Galdieria phlegrea

Abstract

The pressure to develop environmentally friendly recycling methods for rare earth elements (REEs) is increasing. The unicellular red alga Galdieria phlegrea was used as an experimental organism to examine the bioaccumulation of REEs from luminophores, the e-waste from lighting technologies. Algal cells were cultured mixotrophically in a liquid medium with the addition of glycerol as a source of carbon. Luminophores from two different sources (energy saving light bulbs—CFL, fluorescence lamps—FL) were added to the medium in the form of a powder. Cell number was monitored to follow the growth of the algal culture, and pigments were extracted and measured spectrophotometrically. The content of individual REEs in the luminophores and the resulting algal biomass were determined using inductively coupled plasma mass spectrometry (ICP-MS). Total REEs were twofold higher in luminophores from CFL than from FL. The most abundant element in both preparations of luminophores was yttrium, representing about 90% w/w. Growth of cultures incubated in the presence of CFL and FL luminophores was enhanced, but more so in the case of FL. The total level of REEs that accumulated in biomass differed with the type and concentration of luminophore used. The most abundant element that accumulated in algal biomass was yttrium, followed by europium and lanthanum. The chlorophyll content of the algae was enhanced markedly by luminophore treatment, but to a greater extent with luminophores from CFL. This study shows that Galdieria phlegrea can grow in the presence of luminophores and can accumulate REEs. The enriched biomass is a promising template for further applications in biotechnology.