Extraction and separation of lipids from municipal sewage sludge for biodiesel production: Kinetics and thermodynamics modeling

Safe disposal of municipal sewage sludge is a severe environmental issue in the wastewater treatment plan worldwide due to its enormous volume of generation and containing hazardous substances. The purpose of the present study is to appraise the possibility of utilizing the municipal sewage sludge as a lipids feedstock for biodiesel production. Lipids from the municipal sewage sludge were extracted via the soxhlet extraction method using methanol as a solvent. The soxhlet extraction of lipids was conducted with varying temperature (40–80 °C), treatment time (2–12 h), and sewage sludge to solvent (S/L) rato (1: 05–1:10). The maximum lipids extraction obtained about 27% from municipal sewage sludge using methanol as a solvent at S/L ratio of 1: 10, the temperature of 70 °C, and a treatment time of 8 h. Thermodynamics and kinetics behavior of the soxhlet extraction of lipids were determined using Eyring theory and a second-order rate equation, respectively. Approximately 84% of biodiesel was synthesized from soxhlet extracted lipids using the alkaline transesterification method at a catalyst loading of 5 wt%, temperature of 60 °C, an oil and methanol molar ratio of 1:9, and reaction time of 4 h. The physicochemical characterization of biodiesel showed that the biodiesel properties complied with the American Society for Testing and Materials standards of D6751 (ASTM D6751) and European Nationals standards of 14214 (EN 14214). The finding of the present study showed that the municipal sewage sludge could be consumed as an impending feedstock for biodiesel production.