Fate of heavy metals in activated sludge: Sorption of heavy metal ions by Nocardia amarae

The overall goal of this dissertation was to investigate the factors that influence the heavy metal accumulation by bacteria to elucidate the role of bacteria in protecting environmental quality from the toxic effects of heavy metals. Nocardia amarae was selected for this research because it is one of the most common filamentous organism found in activated sludge plants.; Batch sorption studies were conducted to determine the ability of N. amarae cells to sorb heavy metal ions from solution. Heavy metals studied in this research were cadmium, copper, and nickel. The sorption isotherms showed that the cells harvested from the stationary and endogenous growth phase exhibited significantly higher metal sorption capacity than the cells from the exponential phase.; The Langmuir isotherm model fitted to the metal sorption data obtained from various mixtures of Nocardia and activated sludge revealed that the mixture containing higher Nocardia levels had higher metal adsorption capacity than the mixture containing lower Nocardia levels. At Nocardia levels above {dollar}6times10sp6{dollar} intersection/g VSS, the metal biosorption capacity of activate sludge increased proportionally with the amount of Nocardia cells present in the mixed liquor, indicating that the presence of Nocardia may increase the biosorption capacity of activated sludge.; The specific surface area of Nocardia cells was determined by a dye adsorption method. N. amarae cells growing at exponential phase have significantly less specific surface area than those growing at stationary phase, indicating that the lower metal sorption capacity of Nocardia cells growing at exponential phase may be due to the lower specific surface area.; The comparison of dye sorption isotherms for Nocardia cells grown in continuous culture revealed that the cell specific surface area increased with decreasing dilution rate, indicating that the cell specific surface area is highly dependent on the steady-state cell culture age. The metal sorption capacity of Nocardia biomass harvested from 3-day HRT chemostat was significantly higher than that of cells harvested from 1- and 2-day HRT operation, indicating that N. amarae cells with a lower growth rate have higher sorption capacity due to higher specific surface area.; The kinetic behavior of metal sorption to N. amarae cells was investigated using a completely mixed continuous flow reactor. The kinetic results closely fitted a second-order reaction, suggesting that a metal ion occupies two sorption sites. Cadmium has the highest predicted sorption density (65 mg/g) while nickel has the lowest (25 mg/g). The desorption data showed the reversible nature of metal biosorption.