A Heavy Metal Biotrap for Wastewater Remediation Using Poly-γ-Glutamic Acid

Abstract

Poly-gamma-glutamic acid (gamma-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+)-gamma-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 gamma-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 degrees C. Cu(2+)-gamma-PGA adsorption was relatively temperature independent between 7 and 40 degrees 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 gamma-PGA biopolymer. Metal uptake by gamma-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 gamma-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% gamma-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.

Investigation of a CuII–Poly(γ‐Glutamic Acid) Complex in Aqueous Solution and its Insulin‐Mimetic Activity

“…In order to determine the coordination sphere of the Cu II ion in Cu II -g-PGA, the complex was prepared in aqueous solution at various pH (3)(4)(5)(6)(7)(8)(9)(10)(11), where the final concentration of CuSO 4 was 10 Â 10 À3 M and that of g-PGA was 1% (w/v). Visible absorption spectra of the Cu II -g-PGA complex in aqueous solution at various pH are shown in Figure 4.…”

“…To ascertain the species present in the coordination sphere of the Cu II ion in the Cu II -g-PGA complex, the complex was prepared at a ratio of 1:0.8 of CuSO 4 and g-PGA (final concentration of CuSO 4 : 1 Â 10 À3 M and g-PGA: 40% w/v) in aqueous solution at various pH (3)(4)(5)(6)(7)(8)(9)(10)(11). The ESR spectra were recorded both at room temperature and liquid Investigation of a Cu II -Poly(g-Glutamic Acid) Complex in Aqueous Solution .…”

“…Poly(glutamic acid) is a poly(amino acid) and it belongs to a class of biodegradable polymers, which is currently being investigated and applied to a wide variety of fields. [1][2][3][4][5][6][7][8] The most interesting potential applications of this biopolymer are in food, cosmetics, medicine, and water treatment because of its water solubility and non-toxicity towards humans and the environment.…”

Removal of Chromium by Biosorption Method (Chitosan)

“…This method was obtained from the work of Mark [17]. Chitosan was used as the biosorbent, the preparation of which is given below.…”

Expression of thepgsBEncoding the Poly-gamma-DL-glutamate Synthetase ofBacillus subtilis (natto)

“…Moreover, it is used as a thickener and a humectant. [9][10][11][12][13] Recent studies have proposed medical applications for PGA. [14][15][16][17][18][19] The pgsBCAywtC operon of B. subtilis (natto) directs PGA synthesis, 1,20,21) and the gene products PgsB, C, A, and YwtC are thought to form a PGA synthetase complex in the cytoplasmic membrane.…”