Transforming environmental liabilities into resources: the potential of organo-mineral fertilizers from petroleum waste and sewage sludge

Urban residue can be reused as inputs for forest production systems. This study evaluated the potential of organo-mineral fertilizers (OMFs) formulated from oil drilling cuttings from pre- and post-salt layers combined with sewage sludge for the early growth of Eucalyptus urograndis . However, field evidence on their use as fertilizers in forest systems remains scarce. Therefore, the raw residues and OMFs were chemically characterized prior to field application. The field experiment included an unfertilized control, mineral fertilization, and OMFs based on pre- and post-salt cuttings applied at 50%, 100%, and 200% of the recommended application rate. The drilling cuttings showed an alkaline pH and high macronutrient content; however, high levels of extractable sodium (Na) required prior washing. The sewage sludge presented high organic matter and macronutrient content. In the soil, OMFs increased exchangeable calcium (Ca), Na, and available phosphorus (P). The 200% pre-salt treatment showed the highest Ca and Na levels compared with the control and mineral fertilization. For P, OMFs generally increased soil P relative to the control, with the 200% post-salt treatment standing out. No differences were observed in soil iron (Fe), barium (Ba), and aluminum (Al) concentrations among treatments. Under field conditions, early eucalyptus growth was generally similar among treatments, with occasional advantages of mineral fertilization over the higher pre-salt rates. Overall, OMFs are promising, but long-term assessments are needed to confirm fertility gains and ensure environmental safety through periodic monitoring of potentially toxic elements.