Phase Separation in Anaerobic Digestion: A Potential for Easier Process Combination?

Abstract

The flexibilization of bioenergy production has the potential to counteract partly other fluctuating renewable energy sources (such as wind and solar power). As a weather-independent energy source, anaerobic digestion (AD) can offer on-demand energy supply through biogas production. Separation of the stages in anaerobic digestion represents a promising strategy for the flexibilization of the fermentative part of biogas production. Segregation in two reactor systems facilitates monitoring and control of the provision of educts to the second methanogenic stage, thus controlling biogas production. Two-stage operation has proven to reach similar or even higher methane yields and biogas purities than single-stage operation in many different fields of application. It furthermore allows methanation of green hydrogen and an easier combination of material and energy use of many biogenic raw and residual biomass sources. A lot of research has been conducted in recent years regarding the process phase separation in multi-stage AD operation, which includes more than two stages. Reliable monitoring tools, coupled with effluent recirculation, bioaugmentation and simulation have the potential to overcome the current drawbacks of a sophisticated and unstable operation. This review aims to summarize recent developments, new perspectives for coupling processes for energy and material use and a system integration of AD for power-to-gas applications. Thereby, cell physiological and engineering aspects as well as the basic economic feasibility are discussed. As conclusion, monitoring and control concepts as well as suitable separation technologies and finally the data basis for techno-economic and ecologic assessments have to be improved.

Methane Production from Confectionery Wastewater Treated in the Anaerobic Labyrinth-Flow Bioreactor

“…In the study, biogas production was high regardless of OLRs, even though the COD removal was lower than noted by other researchers using single-stage tank anaerobic reactors. According to the literature, the separation of metabolic pathways of the digestion enhanced to produce biogas, because the products of the hydrolysis could be added dynamically to the methanogenic stage [1,64,65]. The results of this work could be taken for optimizing the operational conditions of the full-scale plant and also as a starting basis for scaling up the process to the industrial scale.…”

Anaerobic Digestion of Pig-Manure Solids at Low Temperatures: Start-Up Strategies and Effects of Mode of Operation, Adapted Inoculum, and Bedding Material

“…The two-stage system mentioned here denotes a two-tank system interconnected with P-R wherein the methanogenesis occurs in both digesters. This is not to be confused with a two-phase system (phase separation), wherein hydrolysis and acidogenesis occur in one tank and methanogenesis occurs in the subsequent tank [ 29 ]; even though some studies use the ‘two-stage’ lexicon to indicate two phases [ 30 , 31 ].…”

Spatial monitoring of hydrolysis in a plug-flow bioreactor: a support for flexible operation?

“…The two-stage setup holds various advantages depending on the feedstock: (i) a fast acidification of the methanogenesis is prevented in case of a sudden increase of easily degradable matter (e.g., food waste), (ii) the detoxification of inhibiting biomass such as citrus waste (Lukitawesa et al 2018 ) or inhibitors from thermal pretreatment (Li et al 2017 ); (iii) increased hydrolysis of recalcitrant biomass in the first stage under certain process conditions (e.g., acidic or alkaline pH-value) other than optimal for full digestion (Voelklein et al 2016 ; Cheah et al 2019 ), (iv) thermophilic pre-digestion (Garcia-Aguirre et al 2017 ; Qin et al 2017 ), respectively. Two-stage digestion thereby leads to higher yields, improved stability, and the possibility to generate multiple products like short-chain carboxylic acids (SCCAs) and hydrogen beside biogas, as summarized by Janesch et al ( 2021 ). Since the hydrolytic and acidogenic microbial community is more robust towards changes in the environmental conditions, introducing a hydrolysis stage also offers a higher flexibility of the AD system, especially for the on-demand production of methane (Hahn et al 2014 ; Linke et al 2015 ).…”