<p>This study investigates the impact of phosphorus-solubilizing fungi (PSF) biofertilizers on soil characteristics in arid Tunisian soils irrigated with treated wastewater. The study aims to evaluate the effectiveness of PSF biofertilizers in enhancing soil properties. In this work, we isolated a fungal strain, identified as Aspergillus flavus OQ269829, from a municipal compost. This strain can dissolve and converting polyphosphates into assimilable phosphorus. The experiment was conducted in hermetic flasks. Over a 30-day incubation period under controlled laboratory conditions, various analyses were performed, including fungal enumeration, respirometric measurement of C-CO₂, bacterial biomass (C and N determination), phosphorus analysis, and dehydrogenase activity. Major results revealed a net phosphorus transformation of 51.61 mg/L in sterile arid soil supplemented with treated wastewater and <i>Aspergillus flavus</i> after 30 days of incubation. Cumulative C-CO₂ measurements showed a significant increase in all soil samples, reaching 18,000 mg C-CO₂/100g soil. This doubled in soil supplemented with fungi, reaching 44,000 mg C-CO2/100g soil. The numeration of fungi in soil appeared higher in soil SWW + P + F with a number 296 10² UFC/g dry soil. Dehydrogenase activity exhibited a higher value of 10.95 µg TPF g-1h-1. Notably, both nitrogen and carbon biomass were highest in the SSWW + F + P treatment, reaching 415.3 mg/Kg and 37.3 mg/Kg of soil, respectively. Fungi can effectively break down complex phosphorus compounds found in wastewater, releasing usable phosphorus for plants and beneficial soil microorganisms. This demonstrates the potential of using fungal bio-inoculants to biofertilize soil and effectively utilize phosphorus-rich wastewater in sustainable agriculture.</p> Graphical Abstract <p></p>