Adsorption of inorganic mercury from aqueous solutions onto dry biomass of Chlorella vulgaris: kinetic and isotherm study

Abstract

This study focused on kinetics and equilibrium isotherms of mercury biosorption from water using dry biomass of Chlorella vulgaris as biosorbent at pH 5.0. Biosorption tests were performed at 2.0 g/L biomass dosage varying initial Hg concentration from 11.0 to 90.6 mg/L. The Lagergren equation was found to best describe the process, with R of 0.984 and specific rate constant of 0.029 ± 0.004 min. Although equilibrium data were well fitted by the Dubinin and Radushkevich isotherm (R = 0.870; q = 16.6 mg/g), important insights on phenomenological events occurring at equilibrium were concurrently provided by the Lamgmuir one (R = 0.826; q = 32.6 mg/g; K = 0.059 L/mg). FT-IR analysis confirmed that Hg biosorption took place via physisorption. Since C. vulgaris is a fresh-water microalga that can be easily cultivated anywhere, these promising results suggest its possible use as an effective, low-cost biosorbent to treat industrial effluents contaminated by this metal.

Kinetics and Isotherms of Mercury Biosorption by Dry Biomass of Arthrospira (Spirulina) platensis

“…The corresponding q increase from 3.85 to 20.5 g kg B −1 points out conditions of biomass in excess with respect to sorbate, which suggests that biosorption was likely to depend on the specific physicochemical characteristics of sorbent. However, Y at equilibrium sharply fell for C 0 > 48.0 g m −3 reaching only 50.9 % at C 0 = 90.6 g m −3 , thereby confirming the poor Hg adsorption performance already observed at excess Hg levels using Chlorella vulgaris biomass under comparable conditions . Nonetheless, these conditions ensured the highest biosorption capacity at equilibrium (23.1 g kg B −1 ).…”

“…Comparing our system with other cyanobacterial biosorbents, the above q max value was 15 % lower and 21 % higher than those reported for Hg biosorption by Tolypothrix tenuis TISRT 8063 and Calothrix parietina TISRT 8093 . Extending the comparison to microalgal biomass, it was 28–44 % and 15.2 % higher than those of different strains of C. vulgaris , and of Scenedesmus acutus IFRPD 1020 , but 35 % and 68 % lower than those of Spirogyra hyalina and Chlamydomonas reinhardtii , respectively.…”

“…Biosorption tests were performed in triplicate at room temperature (20 ± 0.5 °C) in 100‐mL Erlenmeyer flasks shaken at 150 rpm (Innova 2100, New Brunswick Scientific, Edison, NJ, USA) for enough time to reach equilibrium (120 min). A 2.0‐kg B m ‐3 biosorbent concentration was used to make comparison with previous studies on different metals including Hg . A 1000 g m −3 mercuric nitrate solution in 12 vol % nitric acid was diluted with distilled water up to starting Hg concentrations in the range 11.1–90.6 g m −3 .…”

“…Fitting of isotherm models was checked applying them in their linearized forms (Tab. ) by estimating, in addition to R 2 , the root mean square error (RMSE) and the chi‐square, as previously described .…”

“…Due to their ubiquity , and ability to remove heavy metals such as copper , , chromium , and cadmium , the cyanobacterium Arthrospira (Spirulina) platensis and the chlorophyta Chlorella vulgaris stand out. Recently, the latter proved to be effective in the removal of metallic mercury in concentrations up to about 100 g m −3 , allowing for a maximum adsorption capacity higher than 16 g kg B −1 .…”