In the context of sustainable and circular agriculture, this study assesses the comparative impact of soil amendment with treated sewage sludge and chemical fertilizers on soil quality and fertility. Three agricultural plots of equal size were monitored: a control plot, a plot amended with sludge from a wastewater treatment plant, and a third plot amended with chemical fertilizers. A physicochemical and bacteriological characterization of the sludge was carried out over six months, followed by a 12-month soil analysis campaign based on ISO standards. The parameters evaluated included organic matter, total nitrogen, phosphorus, potassium, C/N ratio, electrical conductivity, pH, water retention, microbial biomass, and crop yield. The results show that the treated sludge significantly improves organic matter content (+133%), water retention (+20%), and crop yield (+62%) compared to the control plot, while offering performance comparable to or even superior to that of chemical fertilizers. In the long term, sludge improves soil structure and fertility, although electrical conductivity increases slightly. This study demonstrates the potential of treated sludge as a sustainable input for circular agriculture. These findings highlight the potential of biosolids for sustainable agriculture in semi-arid regions.