Decrease in zinc adsorption onto soil in the presence of EPS-rich and EPS-poor Pseudomonas aureofaciens

Area of Science:

• Environmental Science
• Soil Science
• Microbiology

Background:

• Soil horizons (humic and illuvial) and soil bacteria influence heavy metal adsorption.
• Pseudomonas aureofaciens, an exopolysaccharides-producing bacterium, was investigated for its role in zinc adsorption.

Purpose of the Study:

• To investigate the adsorption of zinc (Zn) onto podzol soil horizons in the presence of soil bacteria.
• To determine the effect of pH and Zn concentration on Zn adsorption.
• To evaluate the role of bacterial exopolysaccharides (EPS) in modulating Zn adsorption.

Main Methods:

• Batch-reactor technique was employed to study Zn adsorption.
• Experiments were conducted as a function of pH (2-9) and Zn concentration (0.076mM-0.760mM).
• Pseudomonas aureofaciens (EPS-rich and EPS-poor strains) were added to soil samples.
• Linear-programming modeling of surface equilibria was used for rationalization.

Main Results:

• The humic horizon showed more efficient Zn adsorption than the mineral horizon.
• Zn adsorption was lower in the presence of bacteria, with EPS-rich bacteria causing a greater decrease.
• Increasing bacterial concentration (0.1 to 1.0 g wet/L) further reduced Zn adsorption yield.
• Modeling revealed differences in binding sites and adsorption constants between soil horizons with and without bacteria.

Conclusions:

• Adsorption of Zn onto humic soil-bacteria systems is significantly lower than in bacteria-free systems.
• EPS-rich bacteria effectively shield soil particles, reducing heavy metal adsorption.
• Abiotic organic-rich soil systems exhibit higher heavy metal removal efficiency compared to systems with bacteria.