Isolation and characterisation of copper leaching microbes from sanitary landfill for e-waste bioleaching

Abstract

Electronic waste has been the fastest increasing waste generated globally and is predicted to surpass 111 million tons per year by 2050. This trend is concerning, not just due to the growing volume but also due to its high composition of heavy metal elements, leading to potential environmental pollution if not managed properly. However, this issue opens a new prospect in material acquisition through the concept of urban mining via the metal extraction from electronic waste. A conventional method of extraction, i.e., chemical leaching, possesses harmful environmental impact with the production of its residual leachate. Thus, an alternative extraction technique is proposed, known as bioleaching, in which the microbial activity from bacteria mobilized metal into a more soluble form. In this study, bacterial strains were isolated from Malaysia sanitary landfill for bioleaching of copper from waste printed circuit boards (wPCB) with minimal mechanical pre-processing procedure. They were grown in low pH media to utilize their activity for copper bioleaching from the wPCB. Four bacterial strains were successfully isolated. Using 16S rRNA gene sequencing, the isolates were identified as Bacillus sp. strain SE, Bacillus sp. strain SC, Lysinibacillus sp. strain SE2, and Oryzobacter terrae strain S1A. All the isolates showed appropriate bioleaching ability, with strain SC demonstrated the highest copper extraction with up to 23.36 ppm through the two-step bioleaching process. This strain was further evaluated using a copper strip to observe the actual copper extraction and demonstrated a total of 0.80 ±0.02 mg/g copper recovery. These results suggest that copper bioleaching of wPCB is viable as a standalone process.