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A Heavy Metal Biotrap for Wastewater Remediation Using Poly‐γ‐Glutamic Acid
Author(s) -
Mark Sonny S.,
Crusberg Theodore C.,
DaCunha Christopher M.,
Iorio Alexander A. Di
Publication year - 2006
Publication title -
biotechnology progress
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.572
H-Index - 129
eISSN - 1520-6033
pISSN - 8756-7938
DOI - 10.1021/bp060040s
Subject(s) - biopolymer , adsorption , chemistry , metal ions in aqueous solution , copper , ionic strength , langmuir adsorption model , metal , bacillus licheniformis , aqueous solution , nuclear chemistry , cadmium , inorganic chemistry , polymer , organic chemistry , biology , bacillus subtilis , bacteria , genetics
Poly‐γ‐glutamic acid (γ‐PGA) obtained from Bacillus licheniformis ATCC 9945 was evaluated as a potential biosorbent material for use in the removal of heavy metals from aqueous solution. Copper (Cu 2+ ) was chosen as the model heavy metal used in these studies since it is extensively used by electroplating and other industries, has been the model for many other similar studies, and can be easily assayed through a number of convenient methods. Cu 2+ ‐γ‐PGA binding parameters under varying conditions of pH, temperature, ionic strength, and in the presence of other heavy metal ions were determined for the purified biopolymer using a specially designed dialysis apparatus. Applying the Langmuir adsorption isotherm model showed that γ‐PGA had a copper capacity approaching 77.9 mg/g and a binding constant of 32 mg/L (0.5 mM) at pH 4.0 and 25 °C. Cu 2+ ‐γ‐PGA adsorption was relatively temperature independent between 7 and 40 °C, while an increase in ionic strength led to a decrease in metal ion binding. Cd 2+ and Zn 2+ ions compete with Cu 2+ for binding sites on the γ‐PGA biopolymer. Metal uptake by γ‐PGA was further tested using a tangential flow filtration apparatus in a diafiltration mode in which metal was continually processed through a dilute solution of γ‐PGA without allowing for equilibrium to be established. The circulating polymer solution was able to complex metal as well as successfully prevent passage of unbound copper ions present in solution through the membrane. Using 500 mL of a 0.2% γ‐PGA solution, up to 97% of a 50 mg/L copper sulfate solution processed at a flow rate of 115 mL/min was retained by the polymer. For a 10 mg/L solution of Cu 2+ as copper sulfate, filtrate concentrations of Cu 2+ never rose above 0.6 mg/L while processing 2.5 L of dilute copper sulfate.