Remediation of Staphylococcus aureus in Contaminated Wastewater using Biochar Supported Nanoscale Zero-valent Iron

Manchanayake MAGK¹, Wewalwela JJ²*, Alahakoon AAYA³ and Gunatilake SR^4
1College of Chemical Sciences, Institute of Chemistry Ceylon, Rajagiriya, CO, 10107, Sri Lanka
²Department of Agricultural Technology, University of Colombo, Pitipana, CO, 10206, Sri Lanka
*Corresponding Author: JJ Wewalwela, Department of Agricultural Technology, University of Colombo, Pitipana, CO, 10206, Sri Lanka.

Published: July 23, 2024

View Pdf

Abstract  

Over the last decade, green synthesis methods for biochar-supported metallic nanoparticles have gained popularity due to their versatile applications in technology. Addressing concerns about microorganism contamination in wastewater, nano zero-valent iron (nZVI) within biochar (BC) inhibits bacteria through reactive oxygen species and interacting with bacterial membranes. This study examines two distinct materials: rice husk (RH) and lignin (Lig), for the synthesis of nZVI. RH was explored via two routes: (1) Synchronous route where iron salt was loaded into raw RH feedstock, followed by pyrolysis at 300 °C and subsequent carbothermal reduction (CR) of iron at 900 °C (BM-nZVI), and (2) Asynchronous, involving iron salt loading onto pre-pyrolyzed RH-BC with subsequent CR (BC-nZVI). For Lig, the study examined: (1) Synchronous route with nZVI deposition on pre-pyrolyzed (1000 °C) Lig-BC, creating surface-deposited nZVI (Lig-s-nZVI), and (2) Asynchronous route by mixing iron salt with dissolved feedstock to embedded nZVI in a carbonaceous carrier, resulting in engraved nZVI (Lig-eG-nZVI). The characterization of synthesized nZVI particles was obtained by SEM analysis. This study shows to comparatively evaluate the biological responses of Staphylococcus aureus (S. aureus) to four variations of BC-supported nZVI materials including the pristine BC of each material serving as the control. Initially, pure bacterial cultures were employed to measure inhibition zones using the well diffusion method, revealing prominent inhibition zones for RH-nZVI, while no significant inhibition was observed for Lig-nZVI and pristine BC. The minimum inhibitory concentration of RH-nZVI against S. aureus was determined to be 0.02 g mL^-1, and optical density at 600 nm (OD₆₀₀) was assessed. By contrast, BC-nZVI reached higher levels of microbe inactivation than BM-nZVI due to the FeC4 layers surrounding nZVI particles, potentially hindering BM-nZVI's reactivity. Testing was conducted on hospital and farm wastewater. Gel electrophoresis, Gram's staining, and catalase test were used to identify microbes in wastewater.

Keywords: Antimicrobial activity; wastewater; lignin biochar supported nZVI; rice husk biochar supported nZVI; Staphylococcus aureus

.