Msc: Sustainable Engineering : Chemical and Process Engineering
Biogas
Biogas typically consists primarily of methane (CH4 comprising 50–75% by volume) and carbon dioxide (CO2, comprising 25–45% by volume) as its principal constituents. It can be utilized, after the preliminary removal of undesirable compounds such as hydrogen sulphide (H2S) and others, in internal combustion engines for the combined production of heat and electricity (European Biogas Association, 2022).
There is the option to separate CO2 from biogas to achieve a higher purity of methane gas (typically required to be above 96–97% by volume), referred to as biomethane. Lombardi et al,( 2020) state that replacing fossil fuels with biomethane, derived from readily available waste materials, offers a more efficient way to conserve energy compared to just using biogas for energy production. This approach also promotes a greener, low-carbon economy and can significantly reduce carbon emissions in both public and private transportation, helping the EU reach its target of 14% renewable energy use in transport by 2030.
The European Union has seen a rapid increase in interest in upgrading biogas to biomethane, reflected by a significant growth in the number of biomethane plants and production volumes, with Germany leading the way followed by the United Kingdom (Lombardi and Francini, 2020).
Biofertilizer
Chemical-intensive agricultural techniques have significantly reduced soil carbon and nutrient availability. This is due to the plant matter not being recycled into the soil. Recycling biomass matter (fixed carbon, macro- and micro-nutrients) promotes soil and water ecology, leading to healthier food and carbon sequestration. (Subbarao et al, 2023). Improving soil carbon can increase production and sequester carbon, according to scientific communities and international bodies.
Anaerobic digestate improves soil qualities, including water retention, nutrient retention, bulk density, pH neutrality, electrical conductivity, and soil conditioning. Technological interventions in agricultural residue management are vital for increasing productivity, ensuring food security, and lowering greenhouse gas emissions. This is a crucial step towards meeting the SDGs' food security and zero hunger targets. (Babu et al. 2022). Hence, using anaerobic digestate as a biofertilizer is an environmentally friendly practice in sustainable agriculture.
According to Subbarao et al,(2023), anaerobic digestate when applied as a biofertilizer increased by 63% carbon sequestration by soil compared by to 4% when using untreated maize silage. Slepetiene et al. (2022) found that anaerobic digestate also has a good impact on soil organic carbon levels. The study found that frequent addition of anaerobic digestate, which includes stabilized carbon forms, can increase soil organic carbon and humic content (substances and acids) in the near term, eventually conserving soil organic matter.