The Comparison of Fresh and Dry Duckweed to Remove Cr, Cd and Zn From Wastewater

Rahin Islam

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological and Environmental Sciences

Date of Award

Fall 2025

Abstract

The contamination of environments by heavy metals is a significant ecological concern. Duckweed is a promising plant for the remediation of metal-contaminated water, yet a direct comparison of the efficiency between living (fresh) and non-living (dried) biomass in wastewater treatment systems is limited. This study compared the efficacy of fresh and dried Lemna minor in removing hexavalent chromium (Cr⁶⁺), cadmium (Cd²⁺), and zinc (Zn²⁺) from wastewater. Fresh duckweed was cultivated hydroponically to assess active bioaccumulation, while dried biomass was used to evaluate passive biosorption. Experiments were conducted over 168 hours across variable metal concentrations, and the removal behavior was characterized using kinetic and isotherm models. Metal uptake by fresh duckweed followed zero- or first-order kinetics, indicating continuous biological accumulation controlled by transport and metabolic processes. In contrast, dried duckweed reached equilibrium within 4–48 hours, with its adsorption behavior best described by the pseudo-second-order kinetic model and the Langmuir isotherm. Overall, fresh duckweed demonstrated a higher metal removal rate, particularly at low and medium concentrations, whereas dried biomass achieved faster cadmium removal at low concentrations. These findings show that L. minor can provide parallel processes for wastewater treatment: long-term phytoremediation using living biomass and rapid biosorption using dried biomass, offering a cost-effective and environmentally friendly strategy for heavy metal removal.

Advisor

Lin Guo

Subject Categories

Life Sciences

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