HOTBIN investigates an interesting composting method

We had an interesting question come in last week!
Was Black Soldier Fly (BSF) composting the most efficient composting system ever?

After many years in composting, we had not come across BSF before, intrigue and a hint of competiveness that any system might be better than the HOTBIN, we did a bit of googling. You learn something new every day!

  • BSF (Hermetia_illucens) is a species of fly with native to America (with a cousin down in Australia). There will be a UK entomologist who will no doubt identify a cousin in UK, but so far not aware – and hence possible reason we have not come across them in UK)
  • It has a niche habitat – rotting food/manure. The fly lays eggs in compost and the larvae (some would say maggots) eat the food waste – and they appear pretty good at it. (This is no different to house flies and or vinegar/fruit flies – BSL are much bigger and eat more!)
  • The larvae are not meant to be allowed to hatch into flies (ie pupate), they are collected and used as chicken feed and/or fishing bait
  • There are a number of specialist bins designed to house, retain and harvest the larvae. As a food waste disposal system, it more closely resembles worm composting.

What about claims to be the “most efficient”? We are always suspicious of ‘fastest and best’ and try and uncover the scientific facts. There was no reference to a specific quote and we did not see the claim on sites listed below. It looks like there is enthusiasm for BSF, as highly efficient and this enthusiasm comes from the visible disappearance of food waste as BSF larvae eat food within 2-4 days. If you compare 4 days to “composting” even hot composting at 30 days – you might think it’s more efficient. But decomposition (eating waste food) is just a set of biochemical reactions involving enzymes – the rules are fixed: the rate at which reactions take place is governed by the Arrenhenius equation – which basically boils down to temperature. BSF Larvae die at 40C, thermophilic bacteria operate at 60C and in many cases 70C.

In simple terms, larvae at 40C work at the same speed as bacteria at 40. If we say composting at 10C is rate X1, then larvae and bacteria at 40C are X8 times faster, but bacteria at 60C are 32 times faster – speed wise, we think no contest!

But is speed what we need to focus on? What are we trying to accomplish? Are we seeking to dispose of food waste fast, make fish bait or make great humus with high nutrient and water holding capacity that dramatically improves soil fertility? (With the added plus of diverting food from landfill).

Nature eventually recycles all plant and animal matter back to carbon dioxide and water. Does it matter if the larvae eat food, then the chickens eat the larvae and then the bacteria eat the chicken poo? Or that the bacteria eat the food (and release carbon dioxide), but leave some residual waste (compost) that gets eaten much later and then finally becomes carbon dioxide. Both routes are carbon neutral and better that sending it to landfill where it will decompose anerobically releasing methane.  BSFL larvae eat the food and produce a small amount of residual compost like material. Composting and hot composting produces a lot of compost for the garden. Compost is beneficial to the soil before it is finally returned to carbon dioxide.

We should perhaps note that for many humans, the reaction (rightly or wrongly) to flies, larvae & maggots are negative. Even though BSF appear as good guy (does not bite, sting or carry diseases problematic to humans), we know from experience (backed up by surveys), that one of the biggest reasons people stop composting is flies and maggots. The prospect of actively promoting lots of maggots in waste food seems at best destined as a specialist area.

http://en.wikipedia.org/wiki/Hermetia_illucens

http://www.thebiopod.com/

http://blacksoldierflyblog.com/about/

http://blacksoldierflyblog.com/bsf-bucket-composter-version-2-1/

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3 Comments

Filed under Compost

3 responses to “HOTBIN investigates an interesting composting method

  1. great article. thanks for the review on black soldier fly composting. if you can handle larvae in your bins and would like to know more visit our website.

  2. Hmm, im a little confused…

    This article says:
    “is speed what we need to focus on? What are we trying to accomplish? Are we seeking to dispose of food waste fast, make fish bait or make great humus with high nutrient and water holding capacity that dramatically improves soil fertility? (With the added plus of diverting food from landfill).”

    But your Facebook page says:
    “About
    The HOTBIN is no ordinary composting bin. It HOT composts all year round to recycle more food and garden WASTE faster. http://www.hotbincomposting.com
    Description
    The HOTBIN was created after challenging science and technology to develop a solution to composting household food waste more efficiently.

    Gardeners will love the speed and rich compost it producers and keen recyclers will be impressed by its environmental benefits. In essence it recycles more types of household food waste, generates rich compost more quickly and delivers efficient hot aerobic composting.

    Now even more food and garden waste can be recycled in your own backyard into great compost. The HOTBIN composts all food waste including meat and fish, not just fruit and vegetable peelings and the clever design ensures there are no odours, flies or rats to worry about.

    We believe the HOTBIN can help you reverse overnight how much waste your household sends to landfill, making it easier to do your bit at home.

    It’s quite simple you can put more IN your HOTBIN.”

    I compost to eliminate as much greenhouse gases from the environment as possible, so speed is a high priority. A bonus is that I’m left with something I can add to my soil. I’d like to see the reports used to source your information:
    “In simple terms, larvae at 40C work at the same speed as bacteria at 40. If we say composting at 10C is rate X1, then larvae and bacteria at 40C are X8 times faster, but bacteria at 60C are 32 times faster – speed wise, we think no contest!”
    – do you mean that at the bins most efficient temp (60C) it works faster than the flies will at their most efficient (40C)?

    • It appears that the HOTBIN can reach hotter temperatures at 60C which we believe means it can work faster.
      Sorry if we confused you, of course the HOTBIN has been designed to compost both food & garden waste in your own back yard, this includes ALL food waste. We know the HOTBIN recycles food waste effectively and it looks like from our desk research that The Black Fly Soldier does an extremely effective job too. I think it really boils down to personal preference and what waste you have to recycle.

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