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  • Marcel Hendrickx

The perfect recipe for a good quality compost

When you hear the word “Composting” most people think of a bin at the bottom of the garden, filled with peelings and grass clippings, which somehow convert to rich, nutritious compost some 12 to 18 months later, but obtaining quality compost isn’t easy.

At a larger scale, "surface" composting may take place, this happens when organic waste is incorporated into the soil at a superficial level, but it doesn’t allow the matter to decompose properly. In fact, any biowaste that is piled up in an oxygen-free environment, produces methane.

Methane’s global warming power is 25 times greater than that of CO2 this is something we definitely want to avoid.

For composting to be fulling aligned with ecological benefits, it requires that a specific set of parameters are reached and this is most easily achieved with a mechanical solution.

What is quality compost?

Compost is essentially humus. Thanks to the wonders of nature, in a natural and humid environment, fauna such as insects, worms, bacteria and moulds etc decompose organic matter transforming it into humus. Most of us recognise this humus as a deep rich brown or black product, that crumbles when handled and is easily spread on flower beds and vegetable patches. Creating the compost in a controlled environment ensures it is also free of all pathogens and weeds.

What are the benefits of good compost?

When compost is spread on the ground or on crops, it has two main benefits: fertilization and soil improvement.

Fertilization is the capacity of the compost to provide nutrients such as nitrogen, phosphorous, potassium and magnesium to feed plants directly.

Compost improves soil quality by storing organic matter in the soil, which in the longer term stimulates microbial activity, improves its structure and its ability to retain water. With compost, we first feed the soil to nourish the plant.

One ton of compost provides approximately 300kg of organic matter or 216kg of humus, for an organic matter stability index (ISM) of 72%. It is precisely this indicator that measures the quality of a compost, essentially telling us what percentage of compost will turn into stable organic matter, i.e. humus. The higher this index, the more stable the organic matter and the richer the soil.

A quality compost is therefore one that has a high OMSI index.

Composting is a living process! In order to obtain good compost, we need to create the conditions favourable to microbial life; organic carbon, sufficient aeration and constant humidity.

What does it take to make a good compost?

Carbon-rich waste

The starting material needs to be balanced in nutrients so that the microorganisms can start the fermentation process.

Organic matter is composed mainly of nitrogen and carbon. The higher the carbon / nitrogen ratio, the slower the compost degrades which in turn provides a more stable humus. The ideal ratio is between 25 and 35, this means that the organic matter entering the compost contains 25 to 35 times more carbon than nitrogen.

Carbon-rich bio-waste includes woody material such as branches, wood, cobs, dead leaves, sawdust or cardboard. Soft and wet materials such as fresh grass clippings, sludge, effluent, fruit and vegetable peelings are rich in nitrogen.

Meat and animal protein materials already have the perfect balance of carbon and nitrogen so can be added without worrying about ratios. Kitchen waste, including meat and fish, is also welcome in the compost. Like all organic matter, they will eventually break down.

In non-mechanical composters it is best to avoid meat as it can create bad odours and attract parasites. Electromechanical composters accept all types of food waste as they can reach the temperature parameters required to kill pathogens and be completely hygienic.

Compost needs water

Water is essential for life and for compost! It is the water that allows bacteria, moulds, worms and other insects to live in the compost. Good quality compost is slightly damp. If it is too dry, the mixture will heat up and carbonize the organic material. But, if the mixture is too wet, the fermentation process does not have enough oxygen: it synthesizes methane and leads to rotting. In the end, the compost would be of lower quality.

Ideal humidity levels range between 40 and 70% by mass, depending on the composting phase. This again is the beauty of an electromechanical composter which will take measurements so that operators are reliably informed of humidity levels and can intervene when necessary.

Compost needs air

Like water, air is also essential for bacteria to break down organic matter. This action must take place under aerobic conditions, that is to say in the presence of oxygen. The absence of oxygen creates anaerobic conditions, in this case, the organic matter simply ferments, causes bad odours and emits methane.

A well aerated compost can be achieved in two ways:

The incorporation of green waste that will allow air to pass through, such as straw or chipped wood or, the compost is regularly aerated mechanically by being turned over and mixed, or a combination of both. In a home compost, turning and mixing can be done with a simple fork, more powerful, automated tools are preferred for managing larger quantities.

Compost needs controlled acidity

To create favourable conditions for degradation, a neutral environment is best. pH will vary depending on the type of waste present in the compost and its maturity. If the materials used are very acidic, calcium can be added during the composting process to increase the alkalinity.

To guarantee the quality of the compost that is created at the end of the process it is important to know what is going into it at the beginning.

HORECA Sustainability Solutions supports its customers in finding the best composting recipe based on the type of waste being disposed.

Compost needs controlled temperature

Compost naturally rises in temperature during the first few days. It can reach 60 to 70 °C thanks to the activity of microbial populations which give off heat. Maintaining high temperatures makes it possible to eliminate pathogens, diseases and parasites as well as destroying or inhibiting the germination of weeds.

At temperatures below 45 ° C the survival of most germs is 180 to 240 days. Between 45 and 55 ° C, their survival is only a few days. A temperature of 55 ° C or above for several days reduces the risk to almost zero, this high temperature is easily achieved with Upcycle’s technology.

Even if not required by legislation, it is good practice to ensure that you can provide proof of treatment to those who may be purchasing or using your compost.

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