3.10 Vermicomposting of Biowaste

Hi and welcome back. After looking at composting and
anaerobic digestion, the most common approaches
for organic waste treatment, in this module,
I’ll try to give you a brief overview on vermicompostingor worm composting. This is one other
biowaste treatment approach. Vermicomposting is using worms
and microorganisms to process biowaste
in a controlled manner, and to produce valuable soil amendment
called vermicompost or worm compost. Actually, if the main focus
is to grow and market worms, then we call the process vermiculture
rather than vermicomposting. But really, it’s the same principle. The process of using worms
is quite straightforward: we feed biowaste to earthworms. Some earthworms
are more suitable than others and we will look at that in just a minute. The worms eat the biowaste,
they grow and they reproduce. We shall look at what they eat
and what not. As the biowaste passes through
the gut of the worms it becomes vermicompost. So vermicompost is really only a fancy way
to say worm poop. During the process of vermicomposting, we as waste managers need to ensure
that the worms are happy. They need to have a favorable environment so that they can feed and reproduce and we shall look at those parameters. Then we will look at suitable technologies
with some examples. Finally, we will conclude
with looking at the products of this waste treatment process,
the vermicompost and the worms. First, let us start off
with the suitable worms. First of all, it’s important to remember
that the common earthworm is actually not the ideal worm
for vermicomposting. Why not? Well, this is the type of worm
that digs deep burrows into the soil and does not feed as quickly
and has a very low reproductive rate. The ones that we are looking for
are the surface dwellers. We call these the epigeicgroup. These are worms which live within
the organic material on the surface and you’ll find them in compost heap
or in your manure pile. Eisenia Foetida and Lumbricus rubellus,
the first two on the list here, are the most popular
used in vermicomposting. They have a high reproduction rate and they’re very flexible
regarding environmental conditions, so actually, quite ideal. Here’s a picture of Eisenia Foetida. It is one of these surface dwellers. It can process large amounts
of organic matter up to its body weight each day. It has a high reproduction rate. Populations can be expected to double
every one to three months. First let’s look at the adult worm. It can be recognized by the presence
of bulge on its front end. Eisenia Foetida is a hermaphrodite which means that
it is both female and male. However, two individual worms
are still needed for reproduction. When they mate, they lay side-by-side
and exchange sperm. Then the worms deposit cocoons. These are roundish
and a few millimeters in diameter. An average of three worms develop
in each cocoon and these hatch after about three weeks. The baby worms then feed and grow
into mature worms over a period of eight to ten weeks. So what wastes can we feed to the worms? Suitable waste are fruit
and vegetable waste, plant waste, even bread, rice and various staple foods. What does not work so well
is meat or fish waste, fats, grease, oil, butter, dairy products or salty or vinegary waste. Now, let us look at the ideal
environmental conditions for the worms to work as waste managers. Temperature is ideal in the 20’s. Below 15 will slow down their activity. Above 32, the worms will want to leave and at 35 degrees Celsius,
they start to die. For hot climate, this means
keeping them shaded and moist. Moisture is important. It should always be between
70 and 85 or slightly higher. pHshould be neutral
or slightly above neutral. pH below 7, so acidic,
is harmful to the worms and will also increase the risk
of red mites which are predators of the worms. Worms need air to breathe,
so the system should be aerated. Worms do not like light,
so we should keep them shaded and we can actually use the light if we want to move them away
from somewhere, for instance, to harvest the vermicompost. Let’s look at some other
operating conditions. We should provide the worms
with bulky carbon-rich bedding. Typically this is shredded paper
or cardboard. Stocking densities are recommended
between 2.5 and 10kg per square meter. Below 2.5, the worms will not
reproduce as fast because they don’t find each other. And above five to ten,
there will be competition for food, so they’ll be stressed out by that. It is nice to feed a particular size
of smaller than five centimeters because they can process it easier. And often the waste
is even semi-composted, slightly degraded, so it can be fed
easier to the worms. Feeding rates, we can estimate about 50%
of the worm mass per day as feeding material. So 50% of the body mass of a worm can actually be processed
by the worm per day. However, we should not feed this in layers
of more than 10 centimeters thickness. Over 10 centimeters,
the waste tends to heat up through the microbiological process, and therefore is not very suitable
for the worms. Now let’s look at different technologies. We’ll look at worm bins and beds. This can be operated at household level, medium-scale neighborhood level,
or even large scale facilities. Sometimes, but not so often,
we also see worm windrows. Here are some examples
of household scale worm bins. Different trays where you can
feed the worms with your food scraps. Although such bins
are commercially available, you can also make them yourself
with normal plastic bins as are shown in these pictures. Here is an example from Indonesia. It’s an example of vermiculture
in these plastic bins. Weekly, about 10%, so a corner of each bin is harvested and the worms are removed. These worms are then sold as shrimp feed or processed to medicinal capsules
for human consumption. This is also in Indonesia and you see it’s quite easy
to just use one corner in the neighborhood and to stack this with different boxes
where vermicomposting is done. Here an example from rural India where the vermi bins are made
with cement rings. And here, an example from the Philippines. Here you see how the bins are covered
with these bamboo mats to keep them shaded and protected. This is another example
from the southern India, nearby Chennai. You see this hut with a thatched roof. Inside are these cement bins
with vermicompost. What you can also see is this grid,
this mesh that covers the worm bins to keep predators out. Finally, also a larger example from the US
with these automized vermi bins. This has an automatic feeding and it also has an automatic
harvesting system on the bottom through a breaker. Now let’s look at the products
for vermicomposting. As the feed passes through
the earthworm gut, the material is mineralized,
and plant nutrients are made available. The grinding effect of the gut
leads to the formation of small granules. That is quite typical when you take
vermicompost into your hands, you see those granules. Nitrogen content of vermicompost
is typically higher than compost. It’s around one to two percent and the nutrients
are easily available to plants. Furthermore, the enzymes
and microorganisms from the gut are also very beneficial for soil
and plants, even suppressing diseases. Leachate from the worm bins
can also be used as a liquid fertilizer. This is typically used
in small scale systems and they call this Worm Tea. Earthworms are rich in protein
up to 65%, with all essential amino acids. They are considered a good probiotic feed
for fish or for poultry. In the last 10 years,
earthworms have also been studied with regard to their medicinal properties. What researchers agree on
is their anti-blood clotting effect. So they were found to be effective
in treating thrombotic diseases. Worms are also finding new uses
as a source of collagen for pharmaceutical industries. Now you got excited about vermicomposting
and this module is just about over. Here are some references
if you want to read more and have more details
about vermicomposting. Let’s summarize what we’ve talked about. We’ve talked about the worms, the ones that are suitable
and not suitable, their life cycle. We’ve talked about
environmental conditions which are suitable for vermicomposting
that need to be aerated, it needs to be moist,
it needs to be shaded. We looked at daily feed which could be
up to 50% of worm weight per day. We also looked at examples
of small and large scale facilities in different parts of the world, and we looked at the properties
of the products, the nutritive value
of vermicompost in agriculture, and the worms as animal feed. Thank you very much for listening.

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