Yupadee Chaisuksant

pp. 727 - 740

Abstract

Biosorption of heavy metal ions by algae is a potential technology for treating wastewater contaminated with heavy metals. Adsorption of lead (II) and copper (II) in aqueous solutions by some marine algae
available in large quantities in Pattani Bay including Gracilaria fisheri, Ulva reticulata and Chaetomorpha sp.
were investigated. The effect of pH on metal sorption of the algal biomass and the metal uptake capacity of
the algal biomass comparing to that of synthetic adsorbents including activated carbon and siliga gel were
studied by using batch equilibrium experiments. Each dried adsorbent was stirred in metal ions solutions
with different pH or different concentration at room temperature for 24 hours and the residual metal ions
were analysed using atomic absorption spectrophotometer. The initial concentrations of lead and copper ions
were 70 µg/l and 20 mg/l, respectively. It was found that the effect of pH on metal sorption was similar in
each algal biomass. The metal uptake capacity increased as pH of the solution increased from 2.0 to 4.0 and
reached a plateau at pH 5.0-7.0. The metal uptake capacities of each algal biomass were similar. At low concentrations of metal ions, the metal adsorption occurred rapidly while at higher metal concentration less
metal adsorption by each algal biomass was observed. The metal adsorption of activated carbon and silica
gel occurred gradually and was less than those of algal biomass. The equilibrium data of copper and lead
ions fitted well to the Langmuir and Freundlich isotherm models. The maximum sorption capacity (Q_m) values (mean±SD) of Chaetomorpha sp., U. reticulata, G. fisheri, activated carbon and silica gel for lead ions
were 1.26±0.14, 1.19±0.14, 1.18±0.15, 1.14±0.11 and 1.15±0.12 mg/g, respectively. For copper adsorption, the
Q_m values for G. fisheri, U. reticulata and Chaetomorpha biomass were 15.87±1.03, 14.71±1.02 and 12.35±
1.03 mg/g, respectively. While those of activated carbon and silica gel were not different (Q_m = 8.64±0.95 and
8.16±0.97 mg/g, respectively).
The removal of metals (lead and copper) by each algal biosorbents and activated carbon were also
studied using a continuous flow system. The concentration of each metal was 20 mg/l. It was found that the
column packed with Chaetomorpha biomass had lead removal capacity (1.90 mg/g) higher than those for
U. reticulata and G. fisheri (1.20 and 1.04 mg/g, respectively). For copper, the three algal adsorbents exhibited
similar removal capacities within a range of 7.00-9.60 mg/g, whereas activated carbon column had least
sorption capacity for lead and copper