Abstract
Anaerobic digestion is a biotechnological process, in which microorganisms degrade the complex organic matter to simpler components under anaerobic conditions to produce biogas and fertilizer. This process has many environmental benefits, such as green energy production, organic waste treatment, environmental protection and greenhouse gas emissions reduction. It has long been known that the two main communities of microorganisms (acidogenic and methanogenic) taking part in the anaerobic digestion differ in many aspects e.g. their optimal conditions for cell growth and development. Therefore, the anaerobic digestion in a single bioreactor (BR) (single-phase process) required selected optimal conditions, taking into account the slow-growing methanogens at the expense of fast-growing acidogens, which affects the efficiency of the whole process. This has led in recent years to development of two-stage anaerobic digestion, in which the processes are divided into a cascade of two separate BRs. It is known that this separation of the processes into two consecutive BRs leads to significantly higher energy yields for the two-phase system (H2 + CH4), compared to the traditional single-stage CH4 production process. The present paper aims to review the literature in the field of two-stage anaerobic digestion of organic wastes.
Highlights
Anaerobic digestion (AD) of organic wastes is a very attractive biotechnology during last years mainly in the field of the renewable energy sources and biofuels
The present paper aims to review the literature in the field of two-stage anaerobic digestion of organic wastes
A large quantity of organic waste produced by agriculture, industry and domestic processes are treated by two-stage AD concept (TSAD) processes: 1. Activated sludge (AD and anaerobic co-digestion (AcoD)) [Chow et al, 2020; Zhang et al, 2021; Athanasoulia et al, 2012; Simeonov, 2005; Watts et al, 2006; Zhu and
Summary
Anaerobic digestion (AD) of organic wastes is a very attractive biotechnology during last years mainly in the field of the renewable energy sources and biofuels. In the TSAD system (Fig. 1), relatively fast growing acidogens and H2 producing microorganisms are grown in the first-stage, the hydrogenic bioreactor (BR1 with working volume V1) They are involved in the production of VFAs and H2. From a technical point of view, future research targeting the isolation and immobilization of stable and adapted bacteria to the digestion process, together with studies on the combination of specific biodigesters, pre-treatments, and substrate mixtures, are necessary The development of this sector is fundamental to reach high levels of technological maturity, enabling the scale-up of two-stage digestion, which in most cases occurs only at the bench or pilot scale. It is outlined that by adapting the same anaerobic system for VFAs, biohydrogen and methane individually or simultaneously it could be significantly improved the economic and environmental sustainability The recent survey presents the state of the art (on the base of 163 references, from 2002 to 2022 and our own stidies), including the influence of different parameters, types of bioreactors, microbiology aspects, mathematical modelling and energetical considerations on TSAD processes
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