Removal kinetics of organic carbon from palm oil mill effluent by native duckweeds and its potential as a biofertilizer

Abstract

In the present study, the potential of Azolla pinnata as a phytoremediator of organic carbon and nutrients from palm oil mill effluent (POME) was examined. Seventy-two plastic containers each containing 2 L of POME with four Chemical Oxygen Demand (COD) concentrations (35, 70, 110, and 200 mg/L) and 5 g of A. pinnata with four plastic containers as a control contaminant for each COD concentration were examined. The results have shown that A. pinnata could take up and accumulate organic carbon (COD) and the nutrients (phosphate (PO₄3−), nitrate nitrogen (NO3-N), and ammonia nitrogen (NH3-N)) with a high removal efficiency. The kinetic data of COD were found to follow a pseudo-second-order kinetic model, especially at concentrations within 70 to 200 mg/L (R2 > 98.75 %). A pseudo-first-order kinetic model best fits the initial COD concentration of 35 mg/L (R2 = 95.98 %). The Langmuir-type isotherm best described the COD uptake capacity (qe) (12.5, 9.5, 7.3 and 4.6 mg COD/g adsorbent) by plant sorption for initial COD concentrations of 200, 110, 70, and 35 mg/L, respectively. The findings from this study indicated that POME can be utilized by A. pinnata as a cultivation medium leading to the recovery of biomass as a biofertilizer for better sustainability development goals.