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Processes
Special Issues
New Trends and Perspectives on Anaerobic Digestion
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New Trends and Perspectives on Anaerobic Digestion

A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Environmental and Green Processes".

Deadline for manuscript submissions: closed (30 November 2023) | Viewed by 3423

Special Issue Editors

Dr. Pamela J. Welz

E-Mail Website1 Website2
Guest Editor
Applied Microbial and Health Biotechnology Institute, Cape Peninsula University of Technology, Cape Town 7530, South Africa
Interests: anaerobic digestion; waste and wastewater remediation and reuse; microbial ecology
Dr. Oluwaseun O. Oyekola

E-Mail Website
Guest Editor
Department of Chemical Engineering, Faculty of Engineering and the Built Environment, Cape Peninsula University of Technology, Cape Town 7530, South Africa
Interests: anaerobic digestion; waste and wastewater remediation and reuse; biofuels
Special Issues, Collections and Topics in MDPI journals
Dr. Gunnar Sig​ge

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Guest Editor
Department of Food Sciences, Faculty of AgriSciences, Stellenbosch University, Stellenbosch 7600, South Africa
Interests: anaerobic digestion; waste and wastewater treatment; water minimization; irrigation water food safety

Special Issue Information

Dear Colleagues,

Anaerobic digestion is gaining traction as a sustainable source of energy from waste that supports a circular economy. It is imperative that process stability can be achieved at scale with different substrates. Upstream strategies, such as pre-treatment to de-couple hydrolysis and methanogenesis in two-stage reactors, have been widely applied. Co-digestion of different substrates is a simple option to obtain optimal nutrient balances for digestion, but these need to be logically sourced in order to avoid prohibitive transport costs. In most instances, digesters are treated as ‘black boxes’, but knowledge on the microbial community composition and function is significantly linked to process performance.

For this Special Issue, original research on novel pre-treatment methods, new substrates for digestion and/or co-digestion, and downstream applications of biogas and digestates supporting a circular economy, as well as other new techniques and methods, will be considered. Manuscripts detailing links between microbial community composition and abundance, and correlation of these with physicochemical process parameters will be prioritized. Review articles will be considered provided the editors have approved the topic/s up-front.

Dr. Pamela J. Welz
Dr. Oluwaseun O. Oyekola
Dr. Gunnar Sig​ge
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Processes is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • biogas
  • digestates
  • pre-treatment
  • biomethane potential
  • circular economy

Published Papers (2 papers)

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Research

10 pages, 923 KiB  
Article
Effects of Magnetite (Fe3O4) as an Electrical Conductor of Direct Interspecies Electron Transfer on Methane Production from Food Wastewater in a Plug Flow Reactor
by Sang-Yoon Kim, Gui-Seck Bae, Jun-Hyeong Lee, Young-Man Yoon and Chang-Hyun Kim
Processes 2023, 11(10), 3001; https://doi.org/10.3390/pr11103001 - 18 Oct 2023
Cited by 1 | Viewed by 794
Abstract
This study was conducted in order to examine the impact of magnetite (Fe3O4), a conductive material capable of promoting direct interspecies electron transfer (DIET) among microorganisms, on the efficiency of anaerobic digestion in a plug flow reactor (PFR) using [...] Read more.
This study was conducted in order to examine the impact of magnetite (Fe3O4), a conductive material capable of promoting direct interspecies electron transfer (DIET) among microorganisms, on the efficiency of anaerobic digestion in a plug flow reactor (PFR) using food wastewater (FW) as the substrate. The effects of recovering and replenishing magnetite discharged along with the digestate during continuous operation of the PFR were also evaluated. A PFR with a total volume of 17 L was utilized as the reactor for anaerobic digestion. The inoculum was obtained from Icheon Biogas Research Facility, which operated with a mixture of pig slurry and FW in a 7:3 (w/w) ratio. FW was used as the substrate (volatile solids (VS) content of 85,865 mg-VS/L). The PFR was set for operation at 39 °C, and after a stabilization period of approximately 82 days, the hydraulic retention time (HRT) was set at 40 days. The study was conducted in three stages: stage 1 (83~122 days), stage 2 (123~162 days), and stage 3 (163~202 days). For the maintenance of an organic loading rate of 2.12 kg-VS/m3/d, 0.3 L/d of substrate was added every 24 h, and analysis of an equal amount of discharged digestate was performed. The experimental treatments included a control without the addition of magnetite after the stabilization period, treatment (T1) with addition of magnetite (20 mM in digestate) and subsequent recovery and replenishment of magnetite on the discharge of digestate, and treatment (T2) with addition of magnetite (20 mM) without the replenishment of magnetite. Analytical parameters included the characteristics of the discharged digestate (pH, NH4+-N, chemical oxygen demand (CODCr), total volatile fatty acids (TVFAs), and alkalinity), and methane production (Mp). During the period of operation of the PFR after the stabilization period, no significant differences in pH and NH4+-N, based on the recovery and replenishment of magnetite, were observed, and a stably functioning PFR was observed. However, in stage 2, due to the increased degradation of organic matter caused by DIET, the CODCr of T1 and T2 decreased by 9.42% compared with the control. In stage 3, the magnetite content in the reactor in T2 decreased by a maximum of 9.42% compared to T1. In stage 3, the Mp for T2 was similar to that of the control, with a maximum discharge of magnetite of 3.06%, and the Mp decreased by 5.40% compared to T1. Regarding the ratio of methanogens in the community, the results of an analysis of the digestate from stage 3 showed an increase in the community of acetotrophic methanogens, specifically Methanosarcina. The findings of this study confirm that DIET was effectively promoted by maintaining the concentration of 20 mM magnetite in the PFR while using FW as a substrate. Full article
(This article belongs to the Special Issue New Trends and Perspectives on Anaerobic Digestion)
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20 pages, 4383 KiB  
Article
Biological Methanation in an Anaerobic Biofilm Reactor—Trace Element and Mineral Requirements for Stable Operation
by Joseph Tauber, Daniel Möstl, Julia Vierheilig, Ernis Saracevic, Karl Svardal and Jörg Krampe
Processes 2023, 11(4), 1013; https://doi.org/10.3390/pr11041013 - 27 Mar 2023
Cited by 1 | Viewed by 1991
Abstract
Biological methanation of carbon dioxide using hydrogen makes it possible to improve the methane and energy content of biogas produced from sewage sludge and organic residuals and to reach the requirements for injection into the natural gas network. Biofilm reactors, so-called trickling bed [...] Read more.
Biological methanation of carbon dioxide using hydrogen makes it possible to improve the methane and energy content of biogas produced from sewage sludge and organic residuals and to reach the requirements for injection into the natural gas network. Biofilm reactors, so-called trickling bed reactors, offer a relatively simple, energy-efficient, and reliable technique for upgrading biogas via ex-situ methanation. A mesophilic lab-scale biofilm reactor was operated continuously for nine months to upgrade biogas from anaerobic sewage sludge digestion to a methane content >98%. To supply essential trace elements to the biomass, a stock solution was fed to the trickling liquid. Besides standard parameters and gas quality, concentrations of Na, K, Ca, Mg, Ni, and Fe were measured in the liquid and the biofilm using ICP-OES (inductively coupled plasma optical emission spectrometry) to examine the biofilms load-dependent uptake rate and to calculate quantities required for a stable operation. Additionally, microbial community dynamics were monitored by amplicon sequencing (16S rRNA gene). It was found that all investigated (trace) elements are taken up by the biomass. Some are absorbed depending on the load, others independently of it. For example, a biomass-specific uptake of 0.13 mg·g−1·d−1 for Ni and up to 50 mg·g−1·d−1 for Mg were measured. Full article
(This article belongs to the Special Issue New Trends and Perspectives on Anaerobic Digestion)
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