TABLE 4.5 Value of BSFL Converting Fecal Sludge into Different End Products in Three African Cities End product
Dakar, Senegal
Accra, Ghana
Kampala, Uganda
Dry fecal sludge legally discharged per day (tons, thousands)
6
26
16
Value of BSFL converting this sludge to protein for animal feed (US$, thousands)
40,000
235,000–255,000
129,000
Value of BSFL converting sludge to fuel-biogas and selling the remaining residue as biofertilizer (US$, thousands)
—
248,000–258,000
159,000
Value of BSFL converting sludge to biofertilizer (US$, thousands)
12,000
54,000–134,000
81,000
Source: Diener et al. 2014. Note: BSFL = black soldier fly larvae; — = not available.
(temperature and humidity) in which it is grown. BSFL are high in protein and chitin. The fat and protein contents of harvested BSFL also depend on the substrate and, possibly, the time of harvest and different genetic traits (Wang and Shelomi 2017), but this has not been standardized across BSLF feeding studies. Wang and Shelomi (2017) found that BSFL, on average, produced 37 to 45 percent (40.8 ± 3.8 percent) protein (dry weight) and 20 to 36 percent (28.6 ± 8.6 percent) fat (dry weight) across 22 studies. This relatively high fat content is a general biological characteristic of insect larvae. The protein content is on par with other animal feeds like fishmeal (Shumo et al. 2019). BSFL, like all insects, also contain chitin, which originates from the insect’s exoskeleton. Chitin is functionally regarded as a dietary fiber, although studies suggest that it may also have probiotic properties benefiting animals’ gut health (Selenius et al. 2018). BSFL production can be carried out in fully or semi-managed systems. In general, BSFL production includes three phases: (1) egg production, (2) egg hatching and larva growth, and (3) harvesting. BSF breeding and egg laying— called oviposition—require a netted cage in which the adult flies swarm and mate. After mating, the eggs are mixed with an organic substrate and hatch after four days. Next, the larvae grow for about 12 to 14 days. Typically, this process takes place in a stacked crate system (see photo 4.3 for examples of BSF production systems). Last, the BSFL farmers harvest the larvae by removing them from the unconsumed substrate. Alternatively, BSFL can be reared in simpler, semi-managed systems with open containers of organic substrate that attract wild BSF (Nyakeri et al. 2016). However, in unmanaged systems, the BSFL will “self-harvest,” or naturally separate from the substrate at the prepupal stage. This characteristic skips the step of separating the larvae from the substrate; Mainstreaming Insect Farming
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