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SUSTAINABLE ENERGY

The biogas plant is the core of the future circular economy. Streams of surplus materials – previously considered as waste from agricultural and industrial processes or other human activities – can be used through biogas digesters and converted into useful energy: fertilizers rich in organic nutrients and new materials.

Given the world population growth and the expansion of new developed and industrial areas, both in absolute and relative terms, we will experience a limitation in the supply of goods – including food – from the linear economy (Sariatli, 2017). A circular economy – thanks to its features – is restorative and regenerative and aims to make the most out of products, compounds and goods values and utility, in every moment (Ellen McArthur Foundation, 2015).

The biogas plant

The anaerobic digestion process is a fermentation process that occurs in a hermetically sealed digester, where organic raw materials, such as manure, food waste, sewage sludge and industrial organic waste are converted into final products like biogas and digestate. The biogas produced is a mixture composed of 50-70% of methane and 30-50% of carbon dioxide and small amount of water vapor, hydrogen sulfide and other minor components and trace elements. The digestate represents the biomass after the anaerobic digestion, and it is pumped out of the digester tank after the biogas extraction.

The digestate is composed of slowly degrading stable organic compounds, such as lignin, nitrogen and phosphorous in various forms and inorganic salts containing phosphorous, ammonium, potassium and other minerals.

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Figure 2. Representation of a classic type of digestor mainly used for the manure treatment (McCabe et al., 2018; modified from Bond and Templeton, 2011).

The Akron S.r.l. R&D Team has developed a product based on a bacterial and fungal enzymes pool that accelerates the decomposition of organic material and makes it possible to exploit it more intensively. The enzymes produced by the pool of microorganisms within the Methazym product speed up the degradation reactions. In particular, fungi as Aspergillus oryzae are deployed and lead to a hydrolytic process expediting. For example, Aspergillus niger produces numerous enzymes such as the cellulase, protease, lipase, xylanase, mannanase, alpha-amylase, glucoamylase, pectinase and tannase, important for the degradations of tannins. In addition, among the Trichoderma viridae enzymes there are the endoglucanase, the cellobiohydrolases and the beta-glucosidase, that work in synergistically important way for the degradation of polysaccharides and lead to a three-fold increase in methane and laboratory gases scale production. Even bacteria, such as Bacillaceae (B. subtilis and B. licheniformis), are important for the conversion of organic material into suspension, proteins, carbohydrates and lipids, as well as amino acids, sugars and fatty acids. Thanks to the production of glutamate dehydrogenase, glutamine and glutamate synthase enzymes, the bacterium assimilates the ammoniacal nitrogen, thus reducing the ammonia formation.

Monitoring environmental factors is crucial for ensuring the microorganisms wellbeing and the biogas production (for instance, the formation of acids and methane should be kept in balance).

Thanks to the presence of metabolites, Methazym makes it possible to reduce the formation of toxic ammonia, thus promoting the methanogens’ growth, increasing the process oof conversion of the biomass into methane. It helps speed up the decomposition of the propionic acid and provides a lot of energy to bacteria. Furthermore, the bacteria present in the digestor can immediately take full advantage of the cell wall, which is generally less accessible because of the fiber cells’ lignification.

Therefore, the Methazym main effect consists in reducing the digestor content viscosity. The substrate can thus be managed more easily thanks to its higher fluidity. Moreover, the production residue characteristics will be: a highly biodegradable organic substance and a high concentration of nitrogen and suspended solids.

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Bibliography

  • A. Sridevi et al., 2015, Saccharification of pretreated sawdust by Aspergillus niger cellulase.
  • E. Group, 2017. Bacillus subtilis: A Healthy Probiotic Strain.
  • Kalia et al., 1994. Fermentation of biowaste to H2 by Bacillus licheniformis.

  • Merlin Christy et al., 2014. A review on anaerobic decomposition and enhancement of biogas production through enzymes and microorganisms.

 

  • L’informatore agrario, 2015 n 14 p 61. I microelementi sono vitali per la digestione anaerobica
  • Parawira, 2011. Enzyme research and applications in biotechnological intensification of biogas production
  • Seale et al., 2011. Process for producing silage for biogas production. Patent application pubblication.

 

  • Kadam PC, Boone DR. Influence of pH on ammonia accumulation and toxicity in halophilic, methylotrophic methanogens. Appl Environ Microbiol 1996;62 (12):4486–92.
  • Krakat et al., 2017. Methods of ammonia removal in anaerobic digestion: a review.

  • Zhong et al.Biotechnology for Biofuels (2016) ”Fungal fermentation on anaerobic digestate for lipid-based biofuel production”
    https://www.sciencedirect.com/science/article/pii/S2215017X17301959

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