Is Biofuel from Black Soldier Fly Larvae (BSFL) Hype? | You Decide!by Terry Green on 10/17/14
The natural arc in the evaluation of a new technology progresses in fits and starts beginning not surprisingly with hype and excitement, moving on to disillusionment, and ultimately adoption or rejection of the technology as a business venture based upon its practicality and viability under real world operating conditions. For a technology to succeed it must have demonstrable value. It must pay its way in the business world. This blog discusses proposed farming of Black Soldier fly larvae (BSFL) for biofuel production in the context of its practicality as a business venture.
Several BSF entrepreneurs have proposed in grant applications, and in pitches to investors, and continue to claim in spite of a dearth of evidence in support of their claims, that BSF farming of larvae for biofuel is feasible as a business venture (see, for example,Fly Larvae to Biofuel, Double the biodiesel yield: Rearing black soldier fly larvae, Hermetia illucens, on solid residual fraction of restaurant waste after grease extraction for biodiesel production, Black Soldier Fly Digesters – Converting food wastes into feed, fuel and fertilizer, Prota Culture produces biodiesel and animal feed from organic waste, and Insect Fat, a Promising Resource for Biodiesel ). Consider however what is involved in raising BSF on waste, the effort and cost involved in the recovery of fats from larvae harvested from the waste, and the Feed Conversion Ratio (FCR), all relative to the prospects of succeeding at business through the sale of fats extracted from the larvae for the purpose of refining it into biofuel.
Depending upon the nutritional quality of the waste BSF are grown on, there is evidence that they accumulate as much as 35% of their dry weight as fat by the time they reach the prepupae stage in their life cycle (see Black Soldier Fly larvae breakdown - Biomass; Amino Acids; Mineral Content; Fatty Acids; Anti- Microbial Properties; Soil Amendment, and Insect Fat, a Promising Resource for Biodiesel ). The water content of freshly harvested prepupae is however about 55% of their body weight (see Commercial Production of Black Soldier Flies |Preserving Harvested Larvae ). One metric ton of harvested larvae therefore in dry weight units is only 450 Kg. Since under the best circumstances no more than 35% of the dry weight of the harvested larvae exists in the form of fats, at the very most for every metric ton of larvae harvested one cannot hope to recover more than ~158 Kg of fat (calculated by multiplying 450 Kg x 0.35).
The theoretical limit of recoverable fats extracted from harvested larvae expressed in volume units can be calculated by dividing 158 Kg of fat by the average density of the fats (0.9 Kg per L, see Densities of Vegetable Oils and Fatty Acids) which reveals that the recovery expressed in volume units would at best be ~ 175 L (~46 gallons) per ton of harvested prepupae. The actual recovery in practice would be less than this theoretical maximum. Not all of the fat is easily recovered in the process of crushing, grinding, and organically extracting fats from the tissues in which it was stored.
For the purposes of this analysis, ignore losses. Even assuming maximum recovery under the most ideal conditions, since the wholesale price of biofuel sold through the commodity markets is in the range of $2 to $3 per gallon (see Biodiesel Performance, Costs, and Use, Biodiesel Supply, Demand, and RINs Pricing), gross sales in round numbers, calculated by multiplying 46 gallons x $3 per gallon, would therefore not exceed roughly $150 per metric ton of prepupae harvested. This is not impressive from a business perspective by any stretch of imagination.
But wait. It gets worse! We have ignored labor and energy costs incurred in drying the harvested larvae. We have not factored in costs incurred in capital outlay in building the BSF processing site, the cost of equipment needed for its operation, the cost of labor incurred in hauling, grinding and loading waste needed for growing BSF up to the prepupae stage, labor incurred in propagating, feeding and growing larvae into prepupae ready for harvest, maintenance costs in keeping the site operational, etc.
Additionally, factor in the FCR in growing larvae from waste, ~ 4 in terms of dry weight of food scrap waste needed in growing larvae into prepupae relative to the dry weight of harvested larvae (see BSF Metrics & Yields| Scale Up Production of Black Soldier Flies ). Food scrap, itself, has a water content in the range of 70 to 90% (see Profiles in Garbage: Food Waste, Profiles in Garbage: Food Waste - Part 2, and Water in food). On a wet weight basis, the FCR (assuming an average water content of 80% for food scrap and based on a water content of larvae harvested of 55% ) is therefore ~10. This means it takes ~10 tons of wet food scrap waste to produce one ton of prepupae. So from our calculations on gross sales, namely ~$150 per ton of prepupae harvested, taking into account the FCR, to earn the paltry sum of $150 per ton of prepupae harvested you would have to handle and process 10 tons of food scrap waste as feedstock in growing the larvae to the stage where they were ready for harvesting!
There are alternate waste streams including varying sources of animal manure on which larvae will also grow. But these latter wastes have higher FCR’s then food scrap because of their poorer nutritional content meaning that it would take even more of the latter feedstocks than food scrap to achieve the same yield of prepupae. By now you get the picture. It isn’t pretty!
While it is exciting to think of producing biofuel as a byproduct of BSF farming, the simple truth is that proposals outlining schemes for generating sales through production of biofuel by extracting lipids produced by BSF grown off of waste simply don’t jive with the real world science and business associated with BSF farming.
You may in your own analysis have a different set of numbers to work with, so I leave it to you to decide for yourself what is hype and what works. The important job to get done in this field is to move the arc forward and let the chips fall where they may. The comments offered up in this blog are written in the spirit of critically analyzing what works and what doesn’t based upon our experience in working with BSF at DipTerra LLC with the best data available at this time concerning farming of BSF.
Check back for more to follow on management and strategy issues in scaling up BSF production.
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