Sustainable insect-based cattle manure bioconversion for enhanced biodiesel production

Abstract

Insect-mediated manure treatment has emerged as a sustainable and viable option for manure valorization; however, further improvements to enhance treatment efficiency are necessary. To enhance the bioconversion of cattle manure, this study employed a co-feeding strategy for black soldier fly larvae (BSFL). When BSFL were fed with cattle manure, the larval dry weight remained stagnant at 1.1 ± 0.2 mg per larva (n = 20) until day 21 and slightly increased to 6.9 ± 0.9 mg on day 24. To enhance growth, nutrient-rich food waste was strategically mixed with manure at ratios of manure 7 to food waste 3 (M7:F3) and manure 3 to food waste 7 (M3:F7). The larval dry weight for M3:F7 and M7:F3 was 32.0 ± 1.5 and 19.7 ± 1.4 mg on day 24, representing 4.6-fold and 2.9-fold higher than the cattle manure-only condition. The lipid content of BSFL fed the M3:F7 diet (42.6 wt%) was higher than that of M7:F3 (19.7 wt%). In addition, the feed (waste) reduction rates of M7:F3 and M3:F7 by BSFL were 60.5 and 80.5 %, suggesting that the M3:F7 mixing ratio was more effective in enhancing lipid accumulation and waste reduction. After rearing BSFL, lipids were extracted and further converted into biodiesel, achieving waste-to-energy transformation. The biodiesel productivity in the M3:F7 feeding systems was 141.6 ± 23.7 mg g−1 waste, which was 4.8-fold higher than that in the M7:F3 feeding systems. Also, the CO2 emissions per unit of biodiesel produced by BSFL were lower in the M3:F7 (4.1 ± 0.4 g) than in the M7:F3 feeding systems (12.7 ± 1.9 g).