Caracterización y aprovechamiento de lodos residuales de una industria láctea ubicada en Cañar para la producción de un biofertilizante mediante un biorreactor piloto

Abstract

This research evaluated the valorization of dairy industry wastewater sludge from the Cañar province as a raw material for producing a solid organic amendment through aerobic composting in a pilot-scale bioreactor. The initial characterization of the sludge revealed an acidic pH of 5.45, a moisture content of 88.61% w/w, and an organic matter content of 91.10% w/w (dry basis). To optimize the composting bioprocess, the substrate was conditioned with wood sawdust, effective microorganisms, molasses, and lime, reaching an initial neutral pH of 6.84. Monitoring was conducted over eight weeks under a semi-batch regime with weekly turnings. The system operated strictly within a mesophilic range, recording temperatures between 16 °C and 20 °C; this behavior is attributed to the high water saturation and the restricted dimensions of the bioreactor. By the end of the process, successful stabilization was achieved, resulting in a pH of 7.98, an electrical conductivity of 431 μS/cm, and an organic matter content of 91.66% w/w (dry basis). An increase due to bioconcentration was observed for available phosphorus (749.53 mg/kg) and exchangeable potassium (1574.41 mg/kg), whereas total nitrogen fell below the limit of detection due to microbial immobilization and volatilization processes. Furthermore, heavy metal concentrations were drastically reduced to 1.32 mg/kg for lead, 0.03 mg/kg for cadmium, and 257.67 mg/kg for aluminum via dilution, chelation, and alkaline precipitation. The obtained product complies with the safety limits established by Agrocalidad (Resolution 218) and Regulation (EU) 2019/1009, with the exception of the final moisture content (75.33% w/w). It is concluded that the product is a technically viable and ecologically safe organic amendment, although it requires a complementary passive drying phase prior to its commercial agricultural application.