Nanofabrication of a Biofilm via Spray Coating for Heavy Metal Removal from Wastewater

Abstract

The presence of heavy metal ions like lead (Pb2+), cadmium (Cd2+), zinc (Zn2+), copper (Cu2+), nickel (Ni2+), chromium (Cr3+), and iron (Fe3+) in wastewater can be detected in traces, however, excessive exposure could still result in critical health issues for living organisms and the environment. Hence, the need for the removal of these toxic and non-biodegradable heavy metals is necessary. Membrane technology is one of the promising processes to address this problem, however, the synthetic polymers used nowadays are putting immense pressure on fossil resources and land pollution. Thus, developing a fully biobased membrane can be a remedy to the issue of plastic waste. In this work, a focus is put on the fabrication of such membranes. Two fabrication techniques (vacuum-filtration and spray-coating) were compared and in terms of time of fabrication, limitations, and removal, spray-coating was found to be more practical. The biofilms were fabricated by depositing alginate and cellulose nanocrystals (CNCs) onto pristine mixed cellulose esters (MCE) membrane. The incorporation of CNCs and cross-linking with CaCl2 improved water permeability and mechanical properties of the biofilm. Characterizations were facilitated using SEM-EDS, XPS, contact angle, tensile strength, and zeta potential. The performance of the biofilm was investigated in terms of removal efficiency, water flux, porosity, and pore size. Different parameters were investigated and the optimum CaCl2 concentration, deposition distance, and alginate polymer concentration were found to be 4%, 10 cm, and 3%, respectively. The highest removal obtained for single heavy metal ions (Pb2+) was 96.62%. The adsorption isotherm for the optimized biofilm could be fitted by Langmuir model, yielding a maximum adsorption capacity of 384.615 mg/g. Cleaning the used biofilm with HCl and regenerating it with CaCl2 worked up to three cycles, indicating that the optimized biofilm is effective and potentially sustainable. For the mixed heavy metal ions, the removal sequence was observed to be Cd2+ <Pb2+ <Zn2+ <Cu2+ <Fe3+ <Cr2+ <Ni2+ where Ni2+ was the highest (96.68%) and Cd2+ was the lowest (56.57%). Overall, this work showed that the adsorptive biofilm fabricated via spray-coating could produce a good quality permeate and has great potential for heavy metals removal.

Date of Award	Aug 2023
Original language	American English
Supervisor	Faisal Al Marzooqi (Supervisor)