Turning food waste into fertiliser and energy
Small-scale biogas plants for the food service sector
Becoming more energy independent. How can food waste from kitchens and dining rooms be used for heat and electricity? How can food service businesses handle resources more sustainably and save money? MEIKO GREEN Waste Solutions is working with Rheintalgas to find out. The result? TBC.
MEIKO GREEN Waste Solution and Rheintalgas e.V. are energy pioneers. They are developing a profitable small-scale biogas plant for food-service businesses. These plants will exclusively process food waste, turning it into clean energy and natural fertiliser. Their aim: to noticeably reduce environmental impact, cut energy costs and save money. So how will these visionaries achieve their goal? By using valuable kitchen waste and leftovers in the following three categories:
- Preparation waste like peel, leaves, etc. – this is generated during food preparation
- Surplus should not be made, as far as can be avoided, but a certain amount always will be
- Leftovers remaining on diners' plates
In future, the kitchen waste and food leftovers in this area will be collected in a tank storage system and transformed into district heating and natural fertiliser inside a small-scale biogas plant. This kind of container biogas plant can process up to 1,000 kg of liquid waste per day. That sounds like a lot. It is. But the first priority it always to avoid waste at the food preparation stage. Plus, let's not forget that this quantity is not coming from just one business, but several.
The key: the small-scale biogas plant will be installed in the centre of the village. That keeps journeys short in both directions: for the food waste coming to the small-scale biogas plant and for the fertiliser leaving it for local farms. That's down to 10–20 km per journey from the previous 50–100 km.
The biogas is burnt inside the container to provide district heating for the local network. The system heats approx. 30 homes in an average year.
Plus, the obvious position will help local residents and businesses to become more aware of the issues around food waste from both kitchens and dining. How do I avoid food waste? How do I best separate and recycle it? I can see the whole process just outside my front door!
‘There is so much potential in biogas plants. And food waste from food service businesses is the ideal feed material, producing bioenergy and high-quality fertiliser.’
Dr. Michael Meirer, Head of Consulting at MEIKO GREEN Waste Solutions
Small-scale biogas plants – how they work
Restaurants, company canteens and hospitals collect the food waste they generate in their kitchens and dining rooms, storing it in a tank system. Each organisation uses an infeed station like the MEIKO GREEN BioMaster to collect and shred their waste, turning it into a liquid with roughly the same consistency as a smoothie and rich in energy. This is then fed through a pipe system to a storage tank, all with no odours.
A lorry will then collect this food waste and carry it approx. 10 km to the biogas plant. Some biogas plants receive their waste in bins but that is far from odourless. The system described here pumps the liquid waste into a tank measuring 30 m³ in a mobile container with no nasty smells. It takes 30 days for the microorganisms to digest the waste in the closed system – i.e. without oxygen – producing biogas and fertiliser.
Around 10–20% of the waste volume is converted into biogas and burnt in a gas burner, generating heat that is transferred to pipes immediately adjacent to the burner. There, it is piped just a few metres into the district heating network. This heat (up to approx. 600 kWh district heating per day) can warm up to approx. 30 homes.
80–90% of the original quantity of organic waste remains as digestate and is pumped into a tank measuring 14 m³. Local farmers collect this high-quality, natural fertiliser 2–3 times a month and spread it on their fields. In seasons when no fertiliser is needed, they still collect it and store it in tanks on the farm.
The plant is monitored digitally and the operator is immediately informed of any malfunction by push notification on their smartphone.
The benefits of a small-scale biogas plant that runs on food waste
- With the principle of staying local, all feedstuffs stay close by and are converted into heat and natural fertiliser without the need to travel. This system can partially replace the need to import fossil fuels and synthetic fertilisers. That helps communities to become more independent.
- This collection and storage process is practically contaminant free and guarantees high-quality food waste from kitchens and plates, as well as optimum conversion into energy.
- Processing using a closed system is odourless and efficient
- A versatile system: all the technical expertise and high concentration of engineering art that you will find in a large biogas plant but in the space of a shipping container. The whole plant can easily be transported by lorry and quickly be ready for action in another location.
Heating that uses biomethane instead of natural gas
To stay within the target 1.5 °C planetary warming, we will need to use all available sources of renewable energy. The German Biogas Association (Fachverband Biogas e.V.) has released a background paper, ‘Sustainable technical volume potential for methane from biogas plants’, making clear that biogas can contribute to our energy transition. If all of the digestible waste in Germany was converted into biogas, it could replace 42% of the natural gas the country imports from Russia. More renewable energy in the energy mix means lower CO2 emissions. In 2020, Germany saved around 20 million tonnes of CO2 by using biogas.