Metal recovery from printed circuit boards by magnetotactic bacteria

Dumping of used printed circuit boards (PCB's) (diode and resistor) into the environment has been a major threat and its degradation methods are inadequate and time-consuming. Therefore development of novel strategies for the recovery of metals is the need of the hour. The current study was focused on biodegradation of waste printed circuit boards (diode and resistors) with five strains Magnetospirillum sp. RJS2 (KJ570852), Magnetospirillum sp. RJS5 (KM289194), Magnetospirillum sp. RJS6 (KT266803), Magnetospirillum sp. RJS7 (KT693285) and Magnetospirilhun gryphiswaldense (MSR-1). The circuit boards were milled for size reduction and the samples were analysed using particle size analyser and X-ray powder diffraction (XRD). Heavy metals such as cadmium, copper, nickel, lead and zinc were detected in diode from PCB's, whereas arsenic, chromium, copper, lead, silicon, aluminium, silver and zinc were observed in resistors. The samples were treated with the bacterial strains (RJS2, RJS5, RJS6, RJS7 and MSR-1) individually and in consortia for 12 days. Atomic absorption spectroscopy (AAS) analysis revealed the isolate RJS2, MSR-1 and RJS6 showed maximum recovery of cadmium (97%), lead (100%) and nickel (99%) from diode respectively. Similarly from resistor the maximum recovery was observed with RJS2 (copper - 89%) and RJS6 (zinc - 88%). The overall average recovery of cadmium (80%) and lead (66%) was more from treated diode. Similarly, copper (45%) and lead (40%) were recovered from resistors. It was also observed that the isolate RJS2 was effective in metal recovery (52%) from diode and strain RJS6 (66%) for the resistor. Two groups of consortia were developed MAGI (RJS2, RJS5 and MSR-1) and MAG2 (RJS6 and RJS7) based on their growth requirements, where MAGI exhibited better recovery of metals such as nickel (100%), zinc (75%) from diode and cadmium (90%), nickel (22%) and zinc (47%) from resistor as compared to individual strains. MAG2 also exhibited better recovery of lead (57%) from diode and nickel (22%) from resistor. Scanning electron microscope Energy-dispersive X-ray spectroscopy (SEM-EDS) and X-ray fluorescence (XRF) analysis confirmed RJS2 and RJS6 were dominant strains in metal recovery. The study showed the efficacy of Magnetospirillum bacteria in enhanced metal recovery from PCB's, highlighting its possible role in the management of E-waste.