The CSTR is the most commonly used reactor and CSTRs have been effectively used to treat various types of agricultural residues, domestic and municipal wastewater, fruit and vegetable waste, grass, forest residues, live-stock manure, and many other by-products of various agricultural processes. This system not only gives a better biogas and methane production but also the production and collection of H 2 in the first stage can improve the efficiency of the digestion process.Īnaerobic digestion systems have a variety of configurations, including conventional anaerobic reactors as continuously stirred tank reactors (CSTRs), anaerobic plug flow reactors (APFRs), anaerobic sequencing batch reactors (ASBRs), sludge retention reactors as up-flow anaerobic sludge bed reactors (UASBs), up-flow anaerobic solid-state reactors (UASSs), anaerobic baffled reactors (ABRs), internal circulation reactors (ICs), anaerobic contact reactors (ACRs), anaerobic membrane reactors as anaerobic filter reactors (AFs), anaerobic fluidized bed reactors (AFBRs), and expanded granular sludge blanket reactors (EGSBs). Two stage anaerobic digestion can increase anaerobic digestion process stability, because inhibitory metabolites (VFAs) produced in the first reactor are supplied to methanogens bacteria to improve methane production in the second one. ![]() ![]() In this plant configuration, the first three steps (hydrolysis, acidogenesis, and acetogenesis) are carried out in one bioreactor and the last step (methanogenesis) is carried out in a separate reactor. Two-stage AD systems can increase (improve) the anaerobic digestion process stability, due to the separation of the four phases. In one-stage AD systems, all the four steps of the process (hydrolysis, acidogenesis, acetogenesis, and methanogenesis) are performed in a single reactor and this plant configuration is often associated with the acidification of the reactor, due to the formation of volatile fatty acids (VFAs) as inhibitory metabolites during acidogenesis and acetogenesis. Anaerobic digestion systems are substantially divided into two types: one-stage AD systems and two-stage AD systems. The configurations of the anaerobic digestion reactors and the biomass pretreatment methods are also factors affecting (effecting) digestion efficiency. The carbohydrate and protein content can greatly influence methane production substrates with a high fat content would have a higher potential for the methanogenesis than substrates with the same quantity of carbohydrates. It is of great importance to be aware of various substrate characteristics and their degradation mechanisms during the AD process. The energy yield changes by changing the substrate (i.e., sludge, agricultural waste, food waste, and wastewaters). The AD process performance and both: biogas production rate and composition are strongly correlated with the source of the organic substrate, with the process and operational conditions and with the type of technology used. Various factors influence methane production. In the fourth step, methanogenesis, the acetogenesis products are turned into methane by the synergistic action of various mesophilic bacteria. The third step is acetogenesis, in which the VFA are mainly transformed in acetic acid by hydrogen-producing acetogens bacteria. 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). 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.Īnaerobic digestion converts organic matter into biogas via four defined stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. This system allows to maintain the syntrophic relationship between acid-producing bacteria and methanogens and contemporary push the development of methanogens. On an industrial scale, the use of this incubation reactor with a capacity of 1 m 3 has led to an increase in methane yield of 12 v%. 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%). This system has been tested both on a lab scale and on an industrial scale. 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. 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.
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