Granular organic fertilizers from livestock waste via integrated UF-RO and granulation with soil performance evaluation

The production of granular organic fertilizers from dairy farming waste (cattle manure and dairy cattle wastewater) was evaluated. The wastewater was pretreated using ultrafiltration (UF) integrated to reverse osmosis (RO) to concentrate nutrients (nitrogen, phosphorus, and potassium) and to recover water, improving the sustainability of the process. The concentrated streams were incorporated into solid residues during the granulation process to produce granular fertilizers. The organic fertilizers were evaluated according to their nutrient release potential via soil column leaching tests, soil fertilization potential, as well as environmental (avoidance tests and greenhouse gas emission) and economic perspectives related to their uses. The increase in nutrient content in fertilizers enhances the feasibility of using these materials, as it decreases the required quantity for application and transport. The use of fertilizers formulated from UF concentrate contributes to a greater increase in organic matter in the soil, making them particularly suitable as soil conditioners. On the other hand, fertilizers produced from RO concentrate act primarily as nutrient sources, meeting the immediate needs of plants. Column leaching tests indicated that granular organic fertilizers enhanced nutrient retention in the upper soil layer (0–10 cm), limiting nutrient losses to deeper layers. Compared with incineration, soil application resulted in 32-fold lower GHG emissions (CO₂ and N₂O), corresponding to an approximate 97% reduction. Granular fertilizers also exhibited lower fertilization costs (US$0.26–0.45/ha), with ROc-based formulations being the most economical. Overall, the results demonstrate the technical, environmental, and economic feasibility of producing granular fertilizers from dairy cattle residues, supporting circular economy principles. • RO concentrates nutrients (N, K ); UF reduces Na + and enriches organic matter overall. • Granular fertilizers cut leaching and lower CO₂/N₂O versus liquid or raw wastes used. • RO-granules need smaller doses, lowering transport/application costs per hectare net. • Economic radius rises with RO-granules; competitiveness holds until ~130 km away. • RO permeate enables water reuse in-process, reducing freshwater demand by ~20%.