Low-temperature thermal pre-treated sewage sludge for feeding of black soldier fly (Hermetia illucens) larvae: Protein, lipid and biodiesel profile and characterization

Abstract

Previous work showed that low-temperature thermal pre-treatment of waste activated sludge (WAS) under different temperatures (30, 60, 75, 90 °C) and durations (2, 4, 8, 16 h) prior to black soldier fly larvae (BSFL) rearing could improve the larval growth. In this work, the biochemical profiles of WAS-fed BSFL and the characteristics of biodiesel produced were reported. The BSFL fed with pre-treated WAS had high protein contents (44%–54%) and moderate lipid contents (21%–25%). The WAS pre-treated at 90 °C for 16 h produced BSFL with the highest protein and lipid yields, achieving 69% and 71% of increments, respectively, as compared with the controlled WAS. Subsequently, high conversion of lipid into biodiesel (>90%) could be achieved through the acid-catalyzed transesterification process. The BSFL biodiesel was dominated by saturated fatty acid methyl esters (FAME), with C12:0 being the abundance. This unique FAME profile enabled BSFL biodiesel to have low iodine value, high cetane number and more oxidatively stable as compared with other reported biodiesels like palm oil and rapeseed oil biodiesels. The BSFL biodiesel also satiated the biodiesel standards of EN 14214 and ASTM D6751, except for the flash point, which was still higher and safer than petroleum diesel. In short, the thermal pre-treatment of WAS was effective in promoting BSFL growth and its lipid yield, ultimately leading to higher biodiesel production.