The 3-A method is a combination of aerobic and anaerobic processes. The main process is the dry methane fermentation. This method allows to stabilize:
- municipal biodegradable waste
- sub-screening of mixed municipal waste
- waste from restaurants, cafeterias, agri-food processing plants and marketplaces
- sewage sludge
- green waste
This process is carried out in a gas-tight fermentation chamber that periodically fills with materials at various stability levels. This variation is achieved through the combination of materials that are partly stabilised with those materials that are freshly harvested. Throughout the process of fermentation bio-gas is created and then directed to the co-generation system, where it is applied to combined electricity and heat production. The solid material remaining from the process is directed to aerobic stabilisation and compost production.
Essential elements of the installation using the 3-A method
- Site for packaging process substrates (waste & sludge)
- Preparation of fermentation charger (new substrates & partly stabilized)
- Biomethane storage
- Co-generation system with heat recovery module
- Heat recovery module
- Energy connection
- Heat connection
Based on the specificity and large diversity of the substrate process, different energy effects of the process are achieved. Cautious estimates allow for the conclusion that from 1 Mg of waste can be used to obtain approx. 170 kWh of electricity and approx. 210 kWh of thermal energy.
The implement of this method to existing waste treatment installations can improve their performance and efficiency. The 3-A method can be used in combination with many different stabilization and composite technologies. The inclusion of this technology may contribute to an increase in capacity or the decrease in odor.
Description of 3-A technology
Harvested biodegradable waste (substrate process) are place in the fermentation chamber with the help of wheel loaders. The modular design of the connection chambers and installations enables us to customize the process to periodic chances in quantity of material as well as it is easy to expand.
Inoculation with bacteria of subsequent portions of material intended for fermentation is carried out by mixing it with partially fermented material.
The use of a set of chambers allows for continuity of the process. One cycle lasts from 21 to 28 days depending on the type and the properties of the batch.
The right humidity of fermented material is achieved through the use of percolate fluid that was formed during the fermentation process. It flows from individual chambers during the process and is sprayed to increase fermentation humidity in waste chambers. The management of percolate takes place in a closed cycle.
In order to maintain optimal processing, the proper temperature must be maintained inside the chamber. This is achieved through heating installation that is located in the walls and floor of the fermentation chamber.
Bio-gas that is created during the fermentation process is carried out to the co-generation system where it is used in the production of heat and electricity. A small portion of recovered energy is designated for the needs of technological processes, the remaining is used for the needs of the user of the 3-A installation.
An example of a practical application of the presented technology is in composting with the biomethane installation in Moosdorf na Bawarii.
This installation annually processes 17 000Mg of biodegradable waste that comes from the Cham district. This waste that is collected separately and also material delivered by citizens from maintenance of green spaces. After the stabilization 3-A method around 15 000 Mg of digested material is carried to areas of the plant where compost is created. The process of fermentation is carried out in seven reinforced concrete fermentation chambers that are 4,0 x 7,0 x 30,0 m in size. The bio-gas obtained in the process supplies a set of co-generation systems with a total electrical power of 840 kW. The heat generated in co-generation is used by local residents for living needs. It is worth emphasizing the very low odor emission both in the composting plant itself and in its immediate vicinity.
The recycling of waste using the 3-A method can be applied to new and existing installations. Modernisation of existing mechanical-biological waste treatment nodes by adding a methane fermentation segment can contribute to the increase in capacity of the entire plant (shortening the oxygen phase). A reduction of the odour nuisance of existing installations is also guaranteed.