Nonliving biomass of marine macrophytes as arsenic(V) biosorbents

The present study was aimed at assessing the performance of different nonliving macrophytes sampled in the Adriatic coast in arsenic(V) sorption. Full factorial experiments were carried out where the main factors were the macrophyte species (brown algae: Cystoseira, Dictyopteris, and Eisenia; green algae: Caulerpa and Ulva; red algae: Ceramium, Gracilaria, and Porphyra; and seagrass: Zostera), biosorbent washing pre-treatment (deionized water, acid pH 2 and basic pH 10), equilibrium pH (in the range 1 to 8), under relatively high (10 mg L-1) and relatively low (100 mu g L-1) arsenic concentration. All species exhibited significant adsorption. Indeed, they showed a good performance, with the highest observed value of about 1.3 +/- 0.1 mg g(-1) for the red alga Ceramium and the seagrass Zostera, comparable with those of activated carbon and other low-cost adsorbents reported in the literature under similar experimental conditions. Moreover, red algae known in the literature to be bad cationic metal sorbents showed very good arsenic sorption performance. This work shows that the performance of arsenic biosorption depends on many factors: the different composition and structure of outer layer of the macrophytes, arsenic speciation and functional group availability under different pH, and eventual counter-ion interactions with arseniate.