Biodigester: Biogas and bio fertilisers generation

Solution type: Biogas and bio fertiliser generation

• Objectives:Use of animal, agricultural or industrial process organic matter waste for the production of biogas and bio fertilisers.

• Description: This system allows the anaerobic decomposition of organic matter by means of microorganisms, in the absence of oxygen, for the production of biogas to be applied to electric energy production processes, productive activities, industrial processes, as well as to satisfy household demand. It also allows the production of organic fertilisers and bio-fertilisers that can be used in food production.

There are various types of biodigesters which differ in their operating ranges, process control, waste dilution and retention time of matter and waste:

• Covered lagoon or canvas (tubular types),
• Upflow biodigesters (UASB type)
• Complete mixing reactors (CSTR type

Components

1. Loading: The organic waste is loaded by means of an upstream or loading tank, depending on the type of biomass.
2. Digester: The digester is fed with the organic material, where the mixing of the biomass takes place.
3. Gasometer: The tank with gasometer ensures the storage of the produced biogas.
4. Discharge: The digestate output is accumulated by means of a back or discharge tank for bio-fertilisers.

Biodigester products

• Energy: Biogas can be used to produce electricity and/or can be used for productive activities and household.
• Fertiliser: It can be spread in productive areas, as fertiliser, or be separated into solid and liquid fractions – it can also be enriched as an organo-mineral compound.

Location and selection of soil

The biodigester should be close to the household, in an area without shade and surrounding trees. It should be located at a distance between 12 and 20 metres away from the household, taking care of the wind circulation, to avoid the odour generated by the fermentation. As well as, the smaller distance for greater efficiency of biogas distribution.

Construction

The size and type of biodigester will depend on the amount of organic matter available and the intended use (domestic, agricultural or industrial). Some small-scale biodigesters in Brazil are built in circumference with a diameter of 3 m. and, at a depth of 2 m., are connected with two 16 cm ditches. Connected with two 16 cm wide trenches on opposite sides of the digester walls to the feedstock loading system and the manure and biofertiliser discharge box.

Cost and resources

• • • USD 900

Advantages

• • • Use of renewable energy sources for the production of heat, electricity or as fuel for agricultural machinery. From the management of organic waste and residues, smallholders reduce greenhouse gas emissions and avoid environmental pollution of water and soil that could result from their improper disposal.
    • The efficient use of a biodigester allows smallholders to generate additional income, derived from the reduction of expenses related to energy consumption in production, decreasing dependence on fuel. Barichello et al. (2015) show that small properties can achieve energy savings of 1700 kWh to 5000 kWh per month.
    • Biofertiliser used in the production of fruit, vegetables and forage plants has been shown to increase crop yields, contributing to the substitution of chemical fertilisers and/or organic compounds obtained outside production.
    • Biogas used for domestic purposes such as cooking, lighting and heating has the potential to increase the economic power of small producers and improve basic sanitary conditions in rural areas.

Complexity

The complexity of a biodigester can vary according to the needs and resources available. Small biodigesters, designed for domestic use or small-scale production, tend to be simpler in construction. The complexity increases when incorporating control systems, organic matter feeding and maintenance of the biodigester.

Sources:

• GOMES DE MENEZES et al. O Papel dos Biodigestores na Agropecuária para Mitigação das Mudanças Climáticas: Uma Análise dos Benefícios Ambientais. EMBRAPA, 2023.
• PROJETO PRÓ-SEMIÁRIDO. Construção e Manutenção de Biodigestor. Bahía, Brasil; 2023