BACKGROUND Waste printed circuit boards (WPCBs) are a resource containing a wide array of metals and are of great importance because their metal concentration is much greater than that in the ores. Previous studies have been devoted mostly to copper (Cu) bioleaching from WPCBs because it has the highest proportion ( similar to 10-30%) of all their component metallic elements. The present study focused on an intensified mixed meso-acidophilic bacterial leaching of multi-metals from WPCBs of spent mobile phones, with the system operating under high oxido-reductive potentials (HORPs). Inductively coupled plasma-optical emission spectrometry (ICP-OES), X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray (SEM-EDX) characterization indicated the WCPB sample had recoverable contents of Cu, aluminium (Al), nickel (Ni) and zinc (Zn) which were targeted for bioleaching. RESULTS Shake flask optimization studies, under HORP >750 mV indicated dissolutions of 98.1% Cu, 55.9% Al, 79.5% Ni and 66.9% Zn under optimized conditions of 9 g L-1 iron [Fe (II)], 10% pulp density, initial pH 1.8 and 10% (v/v) as initial inoculum. Under these conditions, at ORP >650 mV, 97.3% Cu, 55.8% Al, 79.3% Ni and 66.8% Zn were achieved in bench-scale (1 L) bioreactor systems without any significant reduction in efficiency (compared to shake flasks) after 8 days of operation. CONCLUSION Variations in co-relatable parameters, such as pH, ORP and Fe (II) concentrations, indicated that these parameters significantly contributed to metal leaching. Operating the system under high and controlled ORPs is a faster and more efficient way to leach multi-metals from WPCBs. (c) 2020 Society of Chemical Industry