Anaerobic digestion or biodigestion, is a natural process by which bacteria -under the absense of oxygen- decompose organic waste to produce biogas and a mud with biofertilizer properties called digestate. The biogas generated has a high calorific value and can be used as a source of energy production, while the digestate generated is a sanitized sludge that can be used as a high-quality fertilizer or soil improver.

It is the treatment of biodegradable organic waste (vegetable, lignocellulosic waste, waste of animal origin, among others) in the absence of oxygen.

Product of this process is obtained biogas, which is a gas rich in methane (CH4) in a concentration of 30% to 50% in volume and traces of nitrogen (N2), hydrogen (H2), hydrogen sulfide (H2S), water vapor and ammonia (NH3), and other sulfur compounds may also exist.

The composition of the biogas is highly variable and will depend on multiple factors. Methane is the useful energy component in biogas, having a variable calorific value. In this way, it can be used as a replacement for different energy sources, for example, 1 m3 of biogas can replace approximately 0.58 liters of kerosene, 0.5 to 1.5 kg of firewood, 0.61 liters of gasoline and 0,74 kg of charcoal.

Depending on the climatic conditions, there may be various applications to take advantage of the biogas, such as, for example: cooking of food, lighting, fuel, refrigeration, heating and electricity generation. In comparison with domestic Liquefied Petroleum Gas (LPG), a 10 kg gas cylinder is equivalent to 20 m3 of biogas, due to LPG has a calorific value of 11,739 (kcal / kg), while that of biogas is of 6,000 (kcal / m3).

The biomass generated by the anaerobic process corresponds to digestate, a sludge with biofertilizer properties, which, in certain cases, is cheaper than the biogas obtained in the process, as it does not entail the pollution problems generated by chemical fertilizers.

Since the digestate is already sanitized and stabilized, it can be used as a soil additive or stabilizer in agriculture, soil mixing, as well as in horticulture and landscaping.

With the proper application rate, the nutrients contained in the substrate, such as nitrogen, phosphorus, potassium, sulfur and other micronutrients, will meet the demand for plant growth. In addition, stable, undegraded carbon compounds lead to the formation of the structure in the soil, thus increasing its fertility, functionality, microbial activity, aeration and water storage capacity.

Generally, the process of anaerobic digestion of organic waste occurs inside a reactor or biodigester where the degradation of organic matter and the production of biogas are a function of inputs, temperature, organic loading rate and hydraulic retention time of the organic waste in the digester, among other requirements.

Anaerobic digestion can be applied to the organic fractions of municipal solid waste, silvo-agricultural waste and organic waste from industrial processes, such as waste from the agri-food industry, sludge from sewage treatment plants, among other possible sources of supply. There are different alternatives and configurations to carry out anaerobic digestion and some are mentioned in the following table.

PROJECTS – COMMUNES

Independencia

Benefited entity: Illustrious Municipality of Independencia


Region: Metropolitana


Population:  100.281 inhabitants


Number of homes: 36.666


Area (km2): 7


Tons of RSD generated annually: 46.200


Disposal Site: Loma Los Colorados Landfill


Municipal Environmental Certification: Excellence

Currently, the commune of Independencia disposes of all its municipal waste at the Loma Los Colorados Sanitary Landfill, which is a private final disposal site, located in the commune of Til Til, 62 kilometers away from the center of Independencia.

Reciclo Orgánicos Program is collaborating with technical advice, purchase of containers and the implementation of a pilot project where the Municipality of Independencia will be able to dispose and treat organic waste generated by Enrique Soro and Maruri street markets at the El Mapocho-Trebal Treatment Plant.

This project expects to treat 18 tons of organic waste during 2021, reducing greenhouse gas emissions by 11 (tons CO2-eq).

Molina

Benefited entity: Illustrious Municipality of Molina


Region: Maule


Population: 45.976 inhabitants


Number of homes: 17.338


Area (km2): 1.552


Tons of RSD generated annually: 13.516,3


Disposal Site: El Guanaco Park Sanitary Landfill


Municipal Environmental Certification: Excellence

Currently, the commune of Molina disposes of all its municipal waste in the Parque El Guanaco Sanitary Landfill, a privately owned final disposal site, located in the commune of Teno, 42 kilometers away from the center of the commune.

Reciclo Orgánicos Program is collaborating with the implementation of the Molina Vive Verde Project, which seeks to promote the recycling of organic waste in the commune, in order to reduce the generation of Greenhouse Gases (GHG), through the separation of waste at the source and by its differentiated collection door-to-door at the Villa Altos de San Pedro. This project considers the participation of 306 homes and a Bio-E biodigestion plant for the disposal and treatment of waste.

During the period 2021 – 2040, it is expected the treatment of an average 162 tons per year of organic waste, allowing to reduce greenhouse gas emissions by 1,848 (tons CO2-eq).

Ecoprial

Reciclo Orgánicos Program is collaborating with the implementation of a plant for the reception and processing of organic sludge through a system of anaerobic digesters of continuous flow, to obtain biogas. The biogas will be used as fuel for a generator which injects electricity into the grid in PMGD mode.

During the period 2020-2040, it is expected to treat on average 73,000 tons per year of organic waste, allowing to reduce greenhouse gas emissions for 963,869 (tons CO2-eq).