Doctor of Philosophy
Chemical and Biochemical Engineering
Excessive and cumulative release of toxic metals from industrial effluents due to rapid industrialization has posed hazard to aquatic ecosystem integrity and environmental/ human health. The inadequacy and high cost of traditional metal treatment technologies coupled with the imposition of stricter environmental regulations and guidelines for industrial point source discharges have increased the demand for economically feasible alternative methods.
Application of natural and abundant sorption material known as biosorbents comprising microbial biomass, agriculture waste, and industrial waste biomass, has gained international attention in scientific world as a low-cost and effective method for removal of heavy metals from aqueous solutions. However, this method has not been able to gain the attention of industry for large-scale applications thus far.
This research was aimed to further evaluate the potential of biosorption technique in more realistic conditions appealing to industry by exploiting locally available biosorbents undergoing minimum pretreatment steps, combining living and non-living microbial biosorbents without any heat-inactivation, employing continuous-flow systems, and regenerating the used biomass for recovery of the mixture of heavy metals.
The toxic metals of interest for biosorption in this work were copper, lead, and zinc, and biosorbents selected were cells of Saccharomyces cerevisiae as a microbial biomass and Acer saccharum tree leaves as an agro-waste. Sorption performances of the biosorbents were evaluated through classical adsorption equilibrium isotherms and kinetics in batch systems, and supplemented by dynamic continuous flow studies, which may serve as a basis for equipment sizing and scale up of the biosorption systems.
Batch sorption studies revealed that pseudo-second order and Langmuir isotherm models were suitable to describe the metals sorption kinetics and equilibrium, respectively. Evaluation of biosorption performance and selection of best biosorbent using the Langmuir isotherm constants correctly were thoroughly discussed based on dynamic equilibrium between the metal species and biosorbents active sites.
Design of experiment technique was used to determine model equations describing the removal efficiencies of mixture of the target metals by Saccharomyces cerevisiae with respect to operating conditions such as pH, metal concentration, and biomass dose. The selectivity order of Pb2+> Cu2+> Zn2+ was achieved by yeast cells with Pb2+ ions removal efficiencies reaching up to 98%. Process optimization helped to evaluate the simultaneous effects of pH, initial metal concentration, and biomass dose on competitive biosorption of metals by yeast cells. Characterization of metal-biomass interactions responsible for biosorption was studied employing zeta potential, BET, FT-IR, and SEM-EDX techniques. The results suggested the involvement of electrostatic interactions, ion exchange, interaparticle sequestration, and a weak surface binding in adsorption of the metals by the selected biosorbents.
The use of unmodified yeast cells in a self-contained continuous system was shown to be an effective metal biosorption method by minimizing biomass pretreatment and preparation steps as well as achieving an on-line and concurrent biosorbent production and metal biosorption within the same system.
Biosorptive performance of maple leaves in multiple column sorption-desorption cycles showed no degradation on metal capacity of the biomass (18.3 mg Cu/g) with increasing cycles despite shortening breakthrough times. Biomass regeneration efficiencies up to 98% were achieved using a weak acid as eluent. The presented simplified mass transfer model based on rapid local equilibrium and an apparent dispersion coefficient well simulated the dynamic operation of the packed bed biosorption column.
Research conducted in this thesis can be of value to industries searching for efficient, simple, and green alternative metal treatment methods to meet the regulatory limits for the heavy metals discharges at a lower cost.
Amirnia, Shahram, "Biosorption Processes for Removal of Toxic Metals from Wastewaters" (2015). Electronic Thesis and Dissertation Repository. 2929.