Sustainable treatment of palm oil mill effluent and repurposing of sludge as a micronutrient resource

Although palm oil mill effluent (POME) is an environmental concern, it is a micronutrient-rich resource that requires valorization. This study investigated the sustainable treatment of POME using Neem ( Azadirachta indica ) leaf extract as a biocoagulant, then conducted the beneficial reuse of the generated sludge as a biofertilizer to realize the waste-to-resource concept, thus closing the loop between sludge waste generation and environmental sustainability criteria. At a dose of 60 mg/L, the Neem coagulant considerably reduced turbidity (92.01%), total suspended solids (TSS) (95.89%), and color (79.73%) at pH 4-5 and exhibited the highest chemical oxygen demand (COD) removal rate of 87.84% ± 1.38% at pH 9. Characterization revealed that the recovered sludge was rich in various valuable micronutrients, including calcium, iron, magnesium, aluminum, silicon, sulfur, and chlorine. The germination index (GI) of okra ( Abelmoschus esculentus ) seedlings grown on the recovered POME sludge mixed with poor sandy soil in a ratio of 2:8 increased to 115% compared with that (80%) of okra seedlings cultivated on sandy soil.