A simultaneous treatment of lignocellulosic biomass (LCB) and low density oxodegradable polyethylene (LDPEoxo) was carried-out using Pleurotus ostreatus at microcosm scale to obtain biotransformed plastic and oxidized lignocellulosic biomass. This product was used as raw matter (RM) to produce biochar enriched with phosphate solubilizing bacteria (PSB). Biochar potential as biofertilizer was evaluated in Allium cepa culture at greenhouse scale. Experiments including lignocellulosic mix and LDPEoxo were performed for 75 days in microcosm. Biotransformation progress was performed by monitoring total organic carbon (TOC), CO2 production, laccase (Lac), manganese peroxidase (MnP), and lignin peroxidase (LiP) enzymatic activities. Physical LDPEoxo changes were assessed by atomic force microscopy (AFM), scanning electron microscopy (SEM) and static contact angle (SCA) and chemical changes by Fourier transform infrared spectroscopy (FTIR). Results revealed P. ostreatus was capable of LCB and LDPEoxo biotransformation, obtaining 41% total organic carbon (TOC) removal with CO2 production of 2,323 mg Kg-1 and enzyme activities of 169,438 UKg-1, 5,535 UKg-1 and 5,267 UKg-1 for LiP, MnP and Lac, respectively. Regarding LDPEoxo, SCA was decreased by 84%, with an increase in signals at 1,076 cm-1 and 3,271 cm-1, corresponding to C-O and CO-H bonds. A decrease in signals was observed related to material degradation at 2,928 cm-1, 2,848 cm-1, agreeing with CH2 asymmetrical and symmetrical stretching, respectively. PSB enriched biochar favored A. cepa plant growth during the five-week evaluation period. To the best of our knowledge, this is the first report of an in vitro circular production model, where P. ostreatus was employed at a microcosmos level to bioconvert LCB and LDPEoxo residues from the agroindustrial sector, followed by thermoconversion to produce an enriched biochar with PSB to be used as a biofertilizer to grow A. cepa at greenhouse scale.