Microwave- vs Ultrasonic-synthesis of magnetic Moringa oleifera coagulant for the reduction of chemical oxygen demand in palm oil wastewater

High chemical oxygen demand (COD) in palm oil mill effluent (POME) caused destruction of aquatic ecosystem and a proper solution is required. In this study, synthetic magnetic nanoparticles and protein extracted from Moringa oleifera seed were used for the synthesis of magnetic Moringa oleifera (MMO) for the removal of COD in POME. The performance of two different synthesis methods including microwave and ultrasonic irradiation were comparatively monitored by studying various parameters for the fabrication of MMO. High efficiency of COD removal by the microwave-assisted sample, with mass fraction of magnetic nanoparticles (MNPs) of 0.6 wt%, synthesis time of 50 s and power of 200 W was proven in the coagulation test, with 90% COD removal. In comparison, there was 68% removal of COD at the same synthesis time, with mass fraction of MNPs of 0.2 wt% and ultrasonic-intensity of 60%. From the analysis of coagulation performance, both techniques showed the same best dosage (1.0 g/L), initial pH (8.0) and settling time (15 min). However, the COD removals were 85.8% and 77.0% for the microwave and ultrasonic-synthesis, respectively. This study has shown the microwave synthesis of MMO is a feasible and cost efficient process that can be adopted as an alternative technique for the production of an excellent coagulant. (C) 2021 The Authors. Published by Elsevier B.V.