The effect of silica and maghemite nanoparticles on remediation of Cu(II)-, Mn(II)- and U(VI)-contaminated water by Acutodesmus sp.

Abstract

The effect of silica and maghemite nanoparticles (NPs) on the sequestration of Cu, Mn and U by Acutodesmus sp. was investigated with the aim of quantifying the influence of NPs on the remediation efficiency of the alga. Metal removal was thus quantified in NP-only, algae-only and NP-algae batch treatments. Results showed that adsorption in NP-only systems was rapid, attaining equilibrium within 5 min. Removal of Cu was higher with maghemite NPs, while more Mn and U were removed with silica NPs. Reaction kinetics were better described by the pseudo-second-order rate model, and isotherm data were fitted by the Freundlich model. Metal removal in NP-algae systems was ∼12–27 % higher than in algae-only or NP-only systems due to the greater number of sorption sites in NP-algae treatments. NPs also modified algae-metal partitioning: extracellular concentrations were higher and intracellular fractions lower in the presence of NPs relative to controls (without NPs). NP agglomeration in metal solutions was quantified in order to determine the potential for NP absorption by algal cells. Results showed that NPs coalesced to form agglomerates 300 (±100) nm in diameter, which were unlikely to be absorbed through algal cell walls. As some studies have shown metal toxicity to be related to intracellular metal fractions in algae, a combination of NPs and algae for phycoremediation can therefore improve the efficiency of operations both by increasing removed metal fractions and by protecting algal cells from metal toxicity.