This work aimed to develop a strategy for fertilizer use optimization and minimized the negative environmental impact by adding value to wastes such as biosolid and paper sludge. Slow-release occluded fertilizers were developed employing biosolids from a wastewater treatment plant (WTP), paper sludge, and clay. Two formulations were prepared to look to control the fertilizer delivery rate, favoring economic and climate impacts. The first one, named FOMI, uses biosolids from a wastewater treatment plant (WTP) and paper sludge in a 3:1 ratio. The second formulation, FOMII, employed WTP biosolids and clay in a 1:1 ratio. The inorganic fertilizers urea (CO(NH2)2), diammonium phosphate DAP ((NH4)2HPO4), and potassium chloride (KCl) were occluded in both formulations in a 50:50 weight-to-weight ratio. The composition of the slow-release fertilizer (SRF) was 10% nitrogen (N), 10% phosphorus (P), and 10% potassium (K). Release kinetics were carried out in water and soil columns to evaluate the rate of nutrient release. The results were compared with mineral fertilizer (F) of equal NPK composition. The results in the water and soil columns showed that the SRF had a minor rate of delivery of nutrients. In the soil columns, FOMI showed better performance with lower percentages of leaching (lower than 15% in 2 days and 75% in 30 days), higher water retention capacity (WRC), and higher cation exchange capacity (CEC). The release in aqueous media was adjusted to the Korsmeyer-Peppas model. The release in the soil columns was adjusted to first-order kinetics. Assays showed significant differences (0.05) between the mineral fertilizer and the slow-release occluded fertilizer developed, and the FOMI met the European Committee for Standardization criteria to be considered SRF. FOMI is a potentially viable formulation for fertilization, being a good alternative to give agronomic value to biosolids and paper sludge by favoring sustainability and the return of organic matter (OM) to soils. Slow release of occluded fertilizers formulated through wastes such as biosolids and paper sludge are a promising alternative for the controlled release of nutrients and other substances (herbicides, pesticides), contributing to the agricultural economy and environment management helping to minimize the excess of fertilizer in the ecosystems.