Electricity generation and wastewater treatment of oil refinery in microbial fuel cells using Pseudomonas putida.

Microbial fuel cells (MFCs) represent a novel platform for treating wastewater and at the same time generating electricity. Using Pseudomonas putida (BCRC 1059), a wild-type bacterium, we demonstrated that the refinery wastewater could be treated and also generate electric current in an air-cathode chamber over four-batch cycles for 63 cumulative days. Our study indicated that the oil refinery wastewater containing 2213 mg/L (ppm) chemical oxygen demand (COD) could be used as a substrate for electricity generation in the reactor of the MFC. A maximum voltage of 355 mV was obtained with the highest power density of 0.005 mW/cm² in the third cycle with a maximum current density of 0.015 mA/cm² in regard to the external resistor of 1000 Ω. A maximum coulombic efficiency of 6 × 10⁻²% was obtained in the fourth cycle. The removal efficiency of the COD reached 30% as a function of time. Electron transfer mechanism was studied using cyclic voltammetry, which indicated the presence of a soluble electron shuttle in the reactor. Our study demonstrated that oil refinery wastewater could be used as a substrate for electricity generation.

Cell age, suspending medium and metal ion influence the susceptibility of Escherichia coli O157:H7 to water-soluble maltose chitosan derivative.

The effects of cell age, suspending medium and metal ions on the susceptibility of Escherichia coli O157:H7 to the water-soluble maltose chitosan derivative were investigated. In addition, the leakage of glucose, protein (absorbance at 280 nm) and lactate dehydrogenase (LDH) induced by maltose chitosan derivative in saline solution and deionized water, was examined. Cells of E. coli O157:H7 in the mid-exponential phase (6 h) were most susceptible to the chitosan derivative followed by cells in the late-exponential phase (12 h) and stationary phase (24 h). In addition, it was found that the susceptibility of the test organism to the maltose chitosan derivative was less in saline solution than in deionized water. The viable population of E. coli O157:H7 in deionized water containing the maltose chitosan derivative (500 ppm), was reduced from ca 7.6 log cfu/ml to a non-detectable level after 10 h of incubation at 37 degrees C compared to a viable population of ca 6.2 log cfu/ml noted in the chitosan derivative-containing-saline solution. After cells of E. coli O157:H7 were exposed to the chitosan derivative in deionized water, a marked increase in the levels of glucose, protein and LDH activity was observed in the supernatant of cell suspension compared to cells of test organism exposed to the saline solution containing chitosan derivative. Metal ions were also found to reduce the antibacterial activity of chitosan derivative. Their effectiveness increased at greater concentrations and varied with the kinds of metal ions with Ba(2+) the most effective and Mg(2+) the least effective.

Antibacterial activity of N-alkylated disaccharide chitosan derivatives.

Antibacterial activity of the water-soluble N-alkylated disaccharide chitosan derivatives against Escherichia coli and Staphylococcus aureus was investigated. It was found that the antibacterial activity of chitosan derivatives was affected by the degree of substitution (DS) with disaccharide and the kind of disaccharide present in the molecule. Regardless the kind of disaccharide linked to the chitosan molecule, a DS of 30-40%, in general, exhibited the most pronounced antibacterial activity against both test organisms. E. coli and S. aureus were most susceptible to cellobiose chitosan derivative DS 30-40% and maltose chitosan derivative DS 30-40%, respectively, among the various chitosan derivatives examined. Although the disaccharide chitosan derivatives showed less antibacterial activity than the native chitosan at pH 6.0, the derivatives exhibited a higher activity than native chitosan at pH 7.0. Antibacterial activity of the chitosan derivatives (DS 30-40%) against E. coli increased as the pH increased from 5.0 and reached a maximum around the pH of 7.0-7.5. The effect of pH on the antibacterial activity of chitosan derivatives against S. aureus was not as pronounced as that observed with E. coli. Population reduction of E. coli or S. aureus in nutrient broth increased markedly upon increasing the concentration of chitosan derivatives from 0 to 500 ppm. No marked increase in population reduction was noted with further increase in the concentration of chitosan derivatives even up to 2000 ppm.