Bioconversion of dairy manure by black soldier fly (Diptera: Stratiomyidae) for biodiesel and sugar production
Introduction
Biofuel has been considered as an alternative option to reduce consumption of petroleum. Bioethanol and biodiesel are two kinds of biofuel. Biomass resources can be converted into biofuel. Biofuel production is still a relatively small scale in comparison to those refining fossil fuels. The difference is primarily caused by high production costs (Seungdo and Bruce, 2005).
Biofuel has been made from feedstock such as starch, vegetable oil, or animal fats (Marina et al., 2009). However, using the feedstock for fuel production instead of human food is unacceptable. The production cost is the major problem of biofuel, therefore it is important to develop cheap feedstock. An alternative way would be developed with cheap waste, such as dairy manure, to produce bioethanol (Liao et al., 2008, Predojević, 2008). Dairy manure was considered as a pollution source rather than a valuable resource which contains undigested organic matter to pollute the environment (Ann et al., 2002).
Currently no studies have been conducted on the hydrolysis of dairy manure after treatment with Hermetia illucens L. (Diptera: Stratiomyidae). H. illucens, which usually known as black soldier fly larvae (BSFL), are voracious consumers of dairy manure (Newton et al., 2005, Westerman and Bicudo, 2005). It can reduce manure dry matter by up to 56% (Sheppard, 1983). The black soldier fly is a non-pest insect distributed throughout the tropics and subtropics and is useful for managing large amount of animal manure and other biosolids. Its life cycle is divided into four stages (egg, larva, pupa and adult). Adults mate and then laid eggs in cracks near larval habitats (Sheppard et al., 1994). The eggs required about 102–105 h to hatch at 24 °C. Under appropriate conditions, the larvae can reach the prepupal stage in 2–3 weeks (Sheppard et al., 2002). BSFL which high in protein, are good feed for fish and chicken in both backyard and commercial purpose (Sheppard et al., 1994, Zuidhof et al., 2003, Erickson et al., 2004).
In this study, BSFL were inoculated into dairy manure for 21 days, the grease was extracted from dried BSFL, and it can be used as the material for biodiesel, and the digested dairy manure was hydrolyzed into sugars which can be further used.
Section snippets
Biomass
H. illucens colony has been maintained for more than 10 generations at Huazhong Agricultural University, Wuhan, China. In this research, fresh dairy manure was obtained from the Dairy Center of Huazhong Agricultural University. About 1200 of 10 days old BSFL were inoculated into 1248.6 g fresh dairy manure (582 g dry wt) by triplicates. The cultivation conditions were temperature (27 °C), humidity (60–75%) in an open barrel with humid cotton gauze. After 21 days, most of the larvae prepupated and
Grease extraction and quality from BSFL
About 1200 BSFL reduced 1248.6 g of fresh manure to 273.4 g dry digested dairy manure within 21 days, and BSFL converted the nutritive material into protein and fat from the fresh dairy manure. About 70.8 g dried BSFL was obtained in the end. The results showed that the extraction rate of immersing method was 22.9%, the Soxhlet extraction method was 21.9%, and the ultrasonic method was 15.7%. Totally, 16.4 g of BSFL grease was gotten from the 70.8 g dry BSFL.
BSFL grease is yellow with a peculiar
Conclusions
This study suggests that H. illucens holds a high promise for converting waste manures into a valuable commodity, which is in accordance with the concept of circular economy. The bioconversion of dairy manure by BSFL to produce biodiesel and sugar was investigated in this study. In short, 15.8 g of biodiesel can be processed from 1248.6 g fresh dairy manure by 1200 BSFL in 21 days, the residual larvae (54.4 g) can be used as animal feedstuff. Furthermore, 96.2 g sugar was obtained from the digested
Acknowledgements
This research was supported by a grant from the International Collaboration Programs (2007CA006).
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