Abstract
The pre-incubation of digestate and recycling of microbes inside a continuously stirred tank reactor (CSTR) are effective ways to optimize the anaerobic digestion process and improve the performance of biogas and methane production, also in existing biogas plants. In this study, a digestate incubation system using a nutrient mix to boost the activity of microbes was coupled to a CSTR to boost biogas and methane production. This system has been tested both on a lab scale and on an industrial scale. On a pilot scale, the system achieved an increase of +16.47 v% in biogas production with respect to the conventional anaerobic digestion process, and an increase of +2 v% in methane content (from 65.94 v% to 67.84 v%). On an industrial scale, the use of this incubation reactor with a capacity of 1 m3 has led to an increase in methane yield of 12 v%. This system allows to maintain the syntrophic relationship between acid-producing bacteria and methanogens and contemporary push the development of methanogens. Moreover, it is an economic system to be integrated into an existing biogas plant given the small volume and the simplicity of the incubation reactor.
Highlights
Anaerobic digestion (AD) is a biochemical process that consists of the degradation of organic matter by bacteria in the absence of oxygen
During hydrolysis complex organic substances are decomposed by bacteria into soluble monomers, which during acidogenesis are converted into volatile fatty acids (VFA)
Olive pomace, and pig slurry were collected at an anaerobic digestion plant in Central Italy, operating under mesophilic conditions, in which they are daily used for feeding the digester
Summary
Anaerobic digestion (AD) is a biochemical process that consists of the degradation of organic matter by bacteria in the absence of oxygen. Biogas is the final product of the anaerobic digestion, which consists of methane, carbon dioxide, and traces of other compounds, such as NH3 , siloxanes, H2 , N2 , and O2 [1]. Anaerobic digestion converts organic matter into biogas via four defined stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. During hydrolysis complex organic substances (carbohydrates, proteins, and lipids) are decomposed by bacteria into soluble monomers, which during acidogenesis are converted into volatile fatty acids (VFA). The third step is acetogenesis, in which the VFA are mainly transformed in acetic acid by hydrogen-producing acetogens bacteria. Methanogenesis, the acetogenesis products are turned into methane by the synergistic action of various mesophilic bacteria [3].
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