Effect of a side-stream voltage supplied by sludge recirculation to an anaerobic digestion reactor

doi:10.1016/j.biortech.2019.122643

Bioresource Technology

Volume 300, March 2020, 122643

https://doi.org/10.1016/j.biortech.2019.122643 Get rights and content

Highlights

•
Study of effect of side stream voltage supply to an anaerobic digestion reactor.
•
Side stream voltage supply shows similar effects to main stream voltage supply.
•
Side and main stream voltage supply enrich the H₂-producing bacterial communities.
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The side stream process provided practical application direction.

Abstract

This study showed that side stream voltage supplied by sludge recirculation from an auxiliary bio-electrochemical anaerobic digestion (ABEAD) reactor appears to have a similar effect as main stream voltage supply to an anaerobic digestion (AD) reactor. The increased sludge recirculation rate enhanced the operation stability at a high OLR. H₂-producing bacterial community was improved in bio-electrochemical anaerobic digestion (BEAD) and ABEAD reactors and was increased with increase in sludge recirculation rate. Despite the dominance of hydrogenotrophic methanogens in all reactors, high operational performances of BEAD and ABEAD reactors supports the results of H₂-producing bacteria increase in those reactors. The ABEAD reactors having 1/7 of the capacity of the main AD reactor showed possibility of integration of BEAD technology into new and existing facilities economically. The findings of this study would provide useful information for approaching the commercialization of BEAD and suggest direction of further research for practical applications.

Graphical abstract

Introduction

Nowadays, anaerobic digestion (AD) is gaining increasing attention because of the transition from a fossil fuel-based economy to a sustainable bioenergy-based economy (Verstraete et al., 2005). Studies on AD have focused on the enhancement of the process performance, one method of which is the combination of microbial electrolysis cells (MECs) and AD to create a bio-electrochemical anaerobic digestion (BEAD) system (Escapa et al., 2016). BEAD overcomes several bottlenecks of traditional AD by enhancing 1) methane yield, 2) process stability at high organic load rate (OLR), 3) stabilization rate, 4) organic removal efficiency (ORE), and 5) microbial activity (Park et al., 2018a, Park et al., 2019a, Liu et al., 2016a). Various laboratory-scale studies have demonstrated the superiority of BEAD through basic studies on reaction mechanism, changes in microbial communities, configuration, and material suitability of electrodes, and further studies on scale-up and commercialization are underway (Park et al., 2019a, van Eerten-Jansen et al., 2015, Cui et al., 2016). However, despite continuing efforts to commercialize BEAD, engineering problems such as increased electrochemical loss, dead space in the reactor, limited mass transfer, and increased internal resistance remain unsolved (Beegle and Borole, 2018). The practical application potential of BEAD can be improved by enhancing existing AD reactors and developing new systems (De Vrieze et al., 2018). To apply BEAD into existing AD reactors, the following issues with respect to efficiency and economic viability need to be considered: 1) deterioration of operational conditions of existing AD reactors for electrochemical device installation, 2) difficulty in securing durability and maintainability for long-term electrode operation, 3) selection of electrode materials with economic and functional efficiency, and 4) need for a stabilization period for changes in species for enhancement in electro-active microorganisms (Park et al., 2019b). Recently, various studies have described the role of voltage in BEAD. Voltage supply does not improve the amount of methane production from the same amount of substrate; however, it can contribute to the methane production rate and can improve the stabilization rate (Park et al., 2018a, Dou et al., 2018). Moreover, the voltage supplied to the BEAD reactor and the MEC indirectly and intermittently exhibits the same effect as directly supplied voltage, which has important implications in terms of the voltage supply method (Cho et al., 2019, Chen et al., 2017, De Vrieze et al., 2014). An engineering approach considering economic viability is important to determine the feasibility of applying this technology (De Vrieze et al., 2018). Intermittent voltage supply is related to bio-electrochemical reaction time. This could be substituted to space separation by controlling retention time of bio-electrochemical reactor (Cho et al., 2019). Recently, Park et al. (Park et al., 2019b) demonstrated the possibility of recovering AD performance through a side-stream voltage supply via sludge recirculation, emphasizing the need for additional research considering engineering factors for the practical use of BEAD. Their study confirmed that supplying voltage through the auxiliary bio-electrochemical anaerobic digestion (ABEAD) reactor to the anaerobic digestion reactor, where the optimal conditions have been affected during high-load operation, has a significant effect on AD performance recovery and microbial community structure changes. They also reported that supplying a side-stream voltage significantly enhanced AD efficiency (Park et al., 2019b). These results provide new implications for the practical use of BEAD, but the applicability of the technology still remains uncertain because the appropriate circulation flow rate and economic value, considering economic viability and efficiency, have not been analyzed. High applicability of BEAD could be provided by a side-stream auxiliary reactor that can be easily applied into a new or an existing full-scale AD reactor (Park et al., 2019b). Furthermore, an innovative voltage supply method and minimization of the BEAD reactor size may accelerate the practical application of BEAD (De Vrieze et al., 2018, Srikanth et al., 2018). The process feasibility and performance of the side-stream method need to be analyzed to provide directions for commercialization of BEAD.

In this regard, based on the results of the previous studies, this study evaluated the effect of side stream voltage supplied into the main AD reactor by sludge recirculation on methane production rate, electrochemical characteristics, and microbial community structure changes under a high OLR. In addition, by analyzing the economic value of the sludge recirculation for the side stream voltage supply, the potential for practical application of BEAD is proposed.

Section snippets

Reactor setup

In this study, six reactor setups were analyzed. The six setups were configured as follows: anaerobic digestion (AD), anaerobic digestion with electrodes (ADE), BEAD, auxiliary bio-electrochemical anaerobic digestion with 5, 15, and 30 times of working volume per day based sludge-recirculation rate (ABEAD(R_5V), ABEAD(R_15V), and ABEAD(R_30V), respectively). The working volumes of the AD, ADE, BEAD, and ABEAD(R_xV) (main AD reactor 700 mL + auxiliary BEAD reactor 100 mL) reactors were set to

Reactor performances

Changes in pH, alkalinity, effluent TCOD, and VFAs at each experimental stage are shown in Fig. 2, while the daily methane production and methane yield are shown in Fig. 3. Methane production was similar at each experimental case during the S1-S3 stages. A sudden decrease in methane production was observed at the S4 (OLR: 8.0 kg-COD/m³·d) for the AD case with a decrease in pH and alkalinity to 6.0 ± 0.7 and 7017.8 ± 1866.4 mg/L as CaCO₃, respectively, which stopped the biogas production. Thus,

Conclusion

The performance of side-stream voltage supply by ABEAD was similar to that of main stream voltage supply. Differences in performance related to recirculation rate imply that the hydraulic mean residue time of ABEAD reactors should be lower than that of ABEAD(R_30V) reactor. Bio-electrochemical hydrogenotrophic methanogenesis was the main pathway, and high recirculation rate contributed to H₂-producing bacterial enrichment. The energy requirement for sludge recirculation for side-stream voltage

Funding

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2018R1D1A3B07048118) and was supported by the Korea Ministry of Environment as Waste to Energy-Recycling Human Resource Development Project (YL-WE-19-001).

CRediT authorship contribution statement

Jun-Gyu Park: Writing - original draft. Hye-Jeong Kwon: Data curation. Michal Sposob: . Hang-Bae Jun: Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Effect of a side-stream voltage supplied by sludge recirculation to an anaerobic digestion reactor

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Reactor setup

Reactor performances

Conclusion

Funding

CRediT authorship contribution statement

Declaration of Competing Interest

Renew. Sust. Energ. Rev.

Bioresour. Technol.

Int. J. Hydrog. Energy

Water Res.

Water Res.

Sci. Total Environ.

Renew. Sustain. Energy Rev.

Bioresour. Technol.

Bioresour. Technol.

Bioresour. Technol.

Water Res.

Water Res.

Appl. Energy

Anaerobe

Bioresour. Technol.

Water Res.

Renew. Energy

Appl. Energy

Sci. Total Environ.

Chemosphere