Urban composting: MD²

Sustainable model of organic waste management

UNDP in Moldova
Nov 28, 2020 · 6 min read
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When you want to be responsible for your impact on the environment, you wonder what to do with the organic waste from public catering companies in the municipality, which in proportion of 70% are composed of water, which once landfilled, turns into leachate.

Stela Babii and the VerdeGo team looked for solutions for a year and tried several models to follow for organic waste management:

  • Separate collection process and logistics of household waste transportation
  • Anaerobic fermentation technology with Bokashi bran
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Organic waste from public catering establishments is usually considered as rubbish, which is to be quickly removed from production halls and disposed of.

However, today the tariffs applied by sanitation companies are low, not accounting for the real environmental impact of leachate — the foul-smelling and highly toxic liquid, which occurs after the decomposition of organic matter together with plastic packaging and other waste.

Namely, sorting of waste at the source of production is the first and most important stage for the reintroduction into the economic circuit and the transformation of waste into resources.

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A. The separate collection process and the logistics of transporting household waste

Five partner companies were involved. The collection process and transportation logistics were remodeled according to a sustainable model. The challenge was to organize the separate collection process, in order to be convenient for the operators, so that these actions would be naturally integrated in the kitchen processes, and for the workers to be clearly described the steps to follow. An operational manual and job descriptions were developed for each worker and a process map was established for each work point. All these documents set a SUSTAINABLE WASTE MANAGEMENT MODEL for companies to be implemented.

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The next step is to transmit the collected organic matter to a logistics manager, who can be a transporter or a farmer — producer and beneficiary of compost.

It is very important to understand that leftovers are part of the kitchen production process, with all the related expenses, and the capitalization, the transformation from waste into resource is a separate process, which can be handled by a specialized operator, for a specific fee or it can be organized even within catering companies.

In agriculture and horticulture, huge amounts of organic material are produced that are not consumed and can be considered waste. Traditionally, these materials have been composted and the compost has been used as fertilizer on the land. During this traditional composting process, much of the organic material is lost in the form of heat and CO2.Consequently, the carbon/nitrogen (C/N) ratio is very low compared to the original material. The C/N ratio of compost is too low for optimal plant growth. The energy level of the compost does not optimally support plant growth, and N-containing compounds will be used as an energy source for soil life, leading to a relative lack of nitrogen. In addition, huge CO2 emissions are a major burden on the environment.

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With the world’s rapidly growing population, we need all the organic matter to grow food and feed, and we need to take care of the environment.

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To replace traditional composting, we bring another method for treating this waste: Bokashi, which is the Japanese word for “well-fermented organic matter”. Organic materials are stored tightly. During this process, chemical compounds are broken down by microorganisms, the organic material is not completely decomposed into CO2, water and heat.

Compared to traditional composting, when fermented by the Bokashi method, it is possible to significantly reduce energy losses and CO2 emissions.

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From the experiments of the VerdeGo team with organic matter from public catering companies, pre-composed with bokashi, several conclusions were reached:

  1. Bokashi treatment of the material allows it to be stored for 5–10 days, provided that a cardboard substrate is used to absorb excess liquid or to arrange its evacuation from the buckets.
  2. The final anaerobic composting at the specialized station built by the VerdeGo team, which uses worm-composting elements, fully integrates the organic matter produced by the 5 co-river enterprises.
  3. Anaerobic organic matter decomposes without the production of CO2 and heat loss.
  4. Organic material, with or without Bokashi treatment in summer, can be heated to temperatures above ambient temperature (39° C). However, in Bokashi buckets the temperature drops rapidly to values ​​close to ambient temperature. There is no significant heat loss, which indicates that the material is not completely fermented to CO2, H2O and heat.
  5. The total amount of material decreases slightly, when using the Bokashi method, by removing water. In the traditional composting process, odors are eliminated, which are unacceptable in urban conditions.
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Bokashi production compared to traditional composting method:

  • less nutrient loss;
  • considerable reduction in CO2, CH4, NO2 emissions per unit of finished product, a carbon footprint 27 times smaller;
  • less work is needed because it does not need to be ventilated regularly.

If we look now from the point of view of Horeca operators, the advantage of using Bokashi bran is obvious:

  • cleaner production areas, odor exclusion and the production of pathogens;
  • more economically advantageous waste management, not being pressured by the need for rapid disposal of organic matter;
  • in case of organizing a closed circuit, you can grow your own green plants in the kitchen or arrange with living plants the space dedicated to customers.
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For faster results and out of research interest, we also applied worm composting elements, for this purpose being purchased 3 families of earthworms.

MD² — The sustainable model of organic waste management is implemented within the project “Sustainable Green Cities for Moldova” funded by the Global Environment Facility and implemented by the United Nations Development Programme.

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