The molar ratio of methanol to rubber seed oil (RSO), catalyst loading, and the reaction time of RSO biodiesel production were optimized in this work. The response surface methodology, using the Box–Behnken design, was analyzed to determine the optimum fatty acid methyl ester (FAME) yield. The performance of various nanomagnetic CaO-based catalysts—KF/CaO-Fe3O4, KF/CaO-Fe3O4-Li (Li additives), and KF/CaO-Fe3O4-Al (Al additives)—were compared. Rubber seed biodiesel was produced via the transesterification process under subcritical methanol conditions with nanomagnetic catalysts. The experimental results indicated that the KF/CaO-Fe3O4-Al nanomagnetic catalyst produced the highest FAME yield of 86.79%. The optimum conditions were a 28:1 molar ratio of methanol to RSO, 1.5 wt % catalyst, and 49 min reaction time. Al additives of KF/CaO-Fe3O4 nanomagnetic catalyst enhanced FAME yield without Al up to 18.17% and shortened the reaction time by up to 11 min.

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There are 101 municipal wastewater treatment plants in Thailand supplied with electricity and cannot collect wastewater treatment fees. Alternative sources of energy for municipal wastewater treatment would reduce the electricity costs and future fossil energy uses. The Nonthaburi wastewater treatment plant (WWTP) is located in the Northwest of Bangkok and selected due to its available data. The solar energy source is applied to the Nonthaburi WWTP due to the light intensity and the area to install. By comparing to the wind and the biogas sources, the wind speed and the sludge production are not sufficient, respectively. Besides the estimated installation cost of the solar-cell panels among three companies, the NPV of 25 years and the IRR of three percent rate, the area required for installation is an affecting factor for the plant consideration.