At La Evidencia, we have imagined to build our Terra Preta in 4 steps thanks to a succession of natural processes in the scope of keeping as much as possible nutrients in the nutrient cycle converting “wastes” into resources. (i) We will mix humanure (i.e: human faeces issue fromdry toilet) with food residues from the cooking, that will be the so-called “Primary Mix”. (ii) We will place the Primary Mix in conditions that triggers its fermentation first, and secondly, its composting. (iii) The fermented and composted Primary Mix will be digested by larva of Black Soldier Fly. (iv) We will separate in three the product of BSF digestion so as to distribute the resulting material to the stage of La Evidencia that will benefit the most of it: BSF pupa; Compost pile; “Compost juice”. Respectively, BSF pupa will be fed to fishes, pile of organic matter will be mixed with biochar in order to create Terra Preta and spread on the floor of the food forest, “compost leachate” will be added to biochar and spread on the floor of the vegetable garden.
(i) The food we eat is full of nutrients but those are not immediately available for intake in our bodies because of the size of aliments and the complexity of molecules that compose nutrients. All food we ingest goes through mastication first, that shred aliments, then dissolution by the acidity of the stomach, before being breaked down by the enzymes secreted by cells of the mouth, intestines and bacteria inhabiting the intestines.
Despite that all the food has undertaken this digestion pathway that renders it as available nutrients for single cells to intake, only a percentage of those nutrients are taken in by our body, the rest is defecated. Using a dry toilet allow us to collect and use this material full in biologically available nutrients (= humanure). At La Evidencia, we will design our life spaces in order to collect this very precious resources and mix it with non-digested food residues, producing the Primary Mix.
(ii) The Primary Mix will be placed in specific conditions in order to be hygienitize (depathogenized) by two processes held by bacteria:
1. Fermentation. Fermenting this organic matter in anaerobic (without oxygen) will enable to kill every potential pathogenic strains. The lack of oxygen hampers pathogenic strains that need oxygen to survive. Over more, bacteria (i.e.: Lactobacillus sp.) striving in anaerobic conditions metabolize sugars and lactates converting them in pyruvate. Pyruvate is, then further transformed mainly to lactic acid and few other metabolic by-products depending on the type of Lactic Acid Bacteria (LAB). Lactic acid renders the medium too acidic to enable other bacteria strains to survive. On top, LAB produce antibiotics, bacteriocins, diacetyl and hydrogen peroxide adding to the hygenienisation effect by killing most of the bacteria in the medium fermented. Scientific studies have shown that Gram-positive bacteria (such as Listeria monocytogenes, Clostridium botulinum and S. aureus), Gram-negative bacteria (such as Salmonella spp. Escherichia coli, coliforms and enterococci) are killed during process of fermentation.
Over more fermentation process add new nutrients to the cycle: Many by-products of bacteria making the fermentation are vitamins (ex: vitamin A, B and C, thiamine, nicotinic acid and biotin), antioxidants or organoleptic substances. Let think of the added value of fermentation on the milk, cabbage, wheat that give out yoghurt, cheese, sauerkraut and bread.
The lactic acid bacteria that we need for this process are only the homofermentative bacteria (bacteria converting sugars to acid lactic such as Lactobacillus plantarum, Lactobacillus casei and Pediococcus acidilactici that we can easily obtain using the juice of sauerkraut.
2. Composting. In a thermophile compost there is 3 phases: initiation phase, thermophilic phase and maturation phase.
Initially there is a rapid growth of mesophilic (medium-heat loving) microorganisms and some thermophilic (high-heat loving) fungi. During this stage there is rapid consumption of available amino acids and a huge growth in microorganism populations, which increase the heat to the point of their own destruction. Next, there is a dominance of thermophilic microorganisms from all three groups (bacteria, fungi, actinomycetes), though some mesophilic organisms may survive through this phase. The majority of composting occurs during this phase, where plant wall materials such as cellulose and hemicellulose are broken down. Once the temperature approaches 70 ºC (158 ºF) the compost is sanitized because the pathogens (that affect both plants and humans) are killed. Finally, as the resources are depleted and converted by these microorganisms, the process begins to slow and the temperature drops. At this point mesophilic organisms once again thrive, pushing out the majority of thermophiles.
During composting, the thermophilic phase (temperature reach up to 80°C) will ensure that every single pathogen (if any survived to the acids, antibiotics and other antimicrobial substances during the fermentation) will be killed off by the heat.
(iii) The Black Soldier Fly (BSF), Hermetia illucens, is of the dipteran family Stratiomyidae. It can be encountered in nature worldwide in the tropical and sub-tropical areas.
At La Evidencia, we will give prepupae of BSF to feed to the carnivorous fishes, the advantages of BSF prepupae are:
1. Feed on every source organic matter not alive: At La Evidencia, we will feed them with the excrements gathered in the shed of the animals (Chiken, ducks, horses, pig and goat) and the Primary Mix.
2. Reproducing and growing very fast: Females fly lays a package of 400 to 800 eggs close to decomposing organic matter. Under optimal conditions, what is in shaded place between 24 and 30°C, with ideal food quality and quantity, the growth of the larvae will require a period of 14-16 days going through five larval stages, the larvae reach the final larval stage: the prepupa. Black soldier fly larvae grow so fast because they are able to eat over twice their own body weight every day.
3. Very rich in nutrients: After emerging from the pupae, the fly lives for about one week. During this short life, it will search for a partner, copulate and (for the female) lay eggs. As a fly, BSF do not feed. Thus BSF pupae fatten up before metamorphising into flies. They build up huge amounts of fat (energy) to burn off as fuel when they're adults.
4. Self-harvesting: Prepupae move out and away from the food source towards a nearby dry, humus-like, shaded and protected environment, it is where the imago emerges from the pupa and fly off. In their quest for a suitable place for metamorphose, prepupae have no difficulty crawling up vertical walls several feet unaided, and they can travel horizontally long distances. It means that if you put a little ramp in their feeding bin with a bucket at the end, they’ll crawl up it and jump right the bin, ready to be harvested.
5. Clean: Their digestive systems naturally destroy harmful bacteria that might be present in their food. They break apart and consume waste so quickly and efficiently that no odor is produced. And because they eat so much and they don't like sharing, they have evolved to somehow emit substances that repel dirty pests like houseflies. Due to their very rapid life cycle, they aren’t host of pathogens.
6. Rich fertilizer: Compost pile after BSF action is very fertile since nutrients are directly available to soil micro-organisms.
(iv) The fourth step is the recycling step; we will recycle every material issued from BSF larva’s feeding and incorporate it in the stage of the agroecosystem where we think that it would be the most beneficial for productivity of the agroecosystem.
1. Self-harvested prepupa will be fed to fishes of a water basin. In that way almost all nutrients that larvaes have intaken and stored in their body in preparation of the costly metamorphose to adult feedless stage will be ingested by carnivorous fishes (such as trout, Salmo spp.). Here, we open the cycle to new forms of live in order to increase the diversity of species, resources, potentiality resulting to an (hypothesized) increase of productivity of La Evidencia. Here, after Air, Earth, and Fire, the fourth classical element of life, Water is added to the agroeosystem.
2. As every animal BSF ingest organic matter, digest the entirety with acids and enzymes in order to make it biologically available, intake only the amount they need or the amount intestinal cells are able to absorb and evacuate the rest. Therefore all organic matter issued from BSF larva meal are nutrients readily biologically available, so, that subtract is very fertile. At La Evidencia, we see this fertile organic matter as the perfect material to mix with biochar (produced in another stade with bamboo; In order to have more information about Biochar, you should read the post here) in the scope of producing Terra Preta. In this ways, porosity of biochar will help to keep all nutrients in the agroecosystem.
3. On another hand while organic matter is piled up in the BSF feeding bin, composting process will occur. During this composting process, beneficial aerobic bacteria will proliferate and consume organic matter together with biologically available nutrients. Water is released during the composting process. When there is excess water it will drain down towards the ground, as it does, it dissolves humic compounds from the compost to form a dark brown liquid. This liquid is commonly called leachate. The brown odourless liquid will be mainly fulvic acid and humic acid, both key humic substances and good for the soil as they hold nutrients and release them. Together with the humic substances, bacteria are also drained off the organic matter and end up in the leachate. If the compost is well aerated during whole composting process, only “good” aerobic bacteria thrive. The compost leachate will be spread on the vegetable garden in order to bring nutrients and beneficial bacteria to the soil. Since mulching the vegetable garden with residues from the pruning of the food forest ensure the presence of fungi also in the soil, the ratio bacteria::fungi will be kept in right balance in the vegetable garden of La Evidencia [In order to understand more about the importance of a good ratio bacteria::fungi in the vegetable garden, you will have to read the next article here].
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