Anaerobic Digestion Technology: An Update

A special issue of Bioengineering (ISSN 2306-5354). This special issue belongs to the section "Biochemical Engineering".

Deadline for manuscript submissions: closed (17 February 2023) | Viewed by 14170

Special Issue Editors


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Guest Editor
Biochemical Conversion Department, DBFZ Deutsches Biomasseforschungszentrum, Leipzig, Germany
Interests: anaerobic digestion; biogas; process optimization; feedstock utilization; Techno-economic evaluation; agriculture economics

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Guest Editor
Biochemical Conversion Department, DBFZ Deutsches Biomasseforschungszentrum, Leipzig, Germany
Interests: (bio)electrochemistry; environmental biotechnology; anaerobic digestion; biogas; biofuels; process monitoring; simulation
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Guest Editor
Department of Environmental Microbiology, Helmholtz Zentrum für Umweltforschung, Leipzig, Germany
Interests: anaerobic digestion; biogas; methanogenesis; mixed cultures; enrichment cultures; environmental biotechnology; waste biorefinery; biomimicry; gut microbiology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Biomass degradation under anoxic conditions includes a variety of natural microbial processes, which have a long tradition of biotechnological utilization. Anaerobic digestion (AD), for instance, has been used for decades to treat various waste streams and to produce methane-rich biogas as an important energy carrier from various wastes and crops. AD is a popular, mature technology, and our knowledge about the influencing process parameters as well as about the diverse microbial communities involved in the process has increased dramatically over the last few decades.

However, the AD sector also faces current challenges, such as feedstock availability and price increases, competitiveness of the products, as well as a lack of process monitoring and automation technologies. Germany is one of the European leaders in biogas technology, regarding the number of agricultural plants and their installed capacity. The produced biogas is mainly used for electricity and heat production. Although more than 9.000 German biogas plants still enjoy the generous national subsidy system, this support will be phased out soon, and they have to cope with increasing substrate prices, competition with other renewables, and the requirements of the energy market (e.g., demand oriented power production).

On the other hand, AD offers so much more than biogas alone, and the metabolic flexibility of AD can be the answer to the current challenges. A great variety of substrates can be utilized for AD, including gaseous ones, such as syngas, for example from biomass gasification or hydrogen obtained by the electrolysis of water using electricity from other renewables. AD can be combined with new (bio)technologies, such as (bio)electrochemical technologies, to enhance the efficiency of the process. The product spectrum can also be diversified by shifting AD to anaerobic fermentation, which will lead to the production of carboxylates with a higher economic value. Chemical building blocks can also be obtained by converting methane to methanol, or higher value single-cell proteins can be produced by methanotrophic bacteria. Academic knowledge about the microbiome, the engine driving the AD process, has been accumulating, but the use of this knowledge for the innovation of AD technologies is scarce.

This Special Issue of Bioengineering will publish research articles and review papers dealing with the current advances in the fascinating process of anaerobic digestion and its related processes.

Dr. Peter Kornatz
Dr. Jörg Kretzschmar
Dr. Marcell Nikolausz
Guest Editors

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Published Papers (7 papers)

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Research

15 pages, 1830 KiB  
Article
Anaerobic Digestion of Solid Agricultural Biomass in Leach-Bed Reactors
by Ville Pyykkönen, Erika Winquist, Ari-Matti Seppänen, Markku Vainio, Elina Virkkunen, Kari Koppelmäki and Saija Rasi
Bioengineering 2023, 10(4), 433; https://doi.org/10.3390/bioengineering10040433 - 29 Mar 2023
Cited by 1 | Viewed by 2113
Abstract
This study focuses on the feasibility of the dry anaerobic digestion of solid agricultural biomass for efficient renewable-energy production and nutrient recycling. Methane production and the amount of nitrogen in the digestates were measured in pilot- and farm-scale leach-bed reactors. In the pilot [...] Read more.
This study focuses on the feasibility of the dry anaerobic digestion of solid agricultural biomass for efficient renewable-energy production and nutrient recycling. Methane production and the amount of nitrogen in the digestates were measured in pilot- and farm-scale leach-bed reactors. In the pilot scale, with a digestion time of 133 days, the methane production of a mixture of whole crop fava bean and horse manure corresponded to 94% and 116%, respectively, of the methane potentials of the solid substrates. The mono-digestion of fava beans resulted in relatively low methane production (production/potential ratios of 59% and 57%). In two full-scale experiments, the methane production of mixtures of clover-grass silage, chicken manure, and horse manure corresponded to 108% and 100% of their respective methane potentials with digestion times of 117 and 185 days. In co-digestion, the production/potential ratios were similar in the pilot and farm experiments. High nitrogen loss was observed in the farm scale when the digestate was stored in a stack covered with a tarpaulin during summertime. Thus, although the technology seems promising, attention needs to be paid to management practices to minimise nitrogen losses and greenhouse gas emissions. Full article
(This article belongs to the Special Issue Anaerobic Digestion Technology: An Update)
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13 pages, 2707 KiB  
Article
Influence of Dairy Manure as Inoculum Source on Anaerobic Digestion of Swine Manure
by Jisoo Wi, Seunghun Lee and Heekwon Ahn
Bioengineering 2023, 10(4), 432; https://doi.org/10.3390/bioengineering10040432 - 29 Mar 2023
Cited by 4 | Viewed by 1933
Abstract
Inoculation is a widely used method to improve the efficiency of anaerobic digestion (AD) with a high organic load. This study was conducted to prove the potential of dairy manure as an inoculum source for AD of swine manure. Furthermore, an appropriate inoculum-to-substrate [...] Read more.
Inoculation is a widely used method to improve the efficiency of anaerobic digestion (AD) with a high organic load. This study was conducted to prove the potential of dairy manure as an inoculum source for AD of swine manure. Furthermore, an appropriate inoculum-to-substrate (I/S) ratio was determined to improve methane yield and reduce the required time of AD. We carried out 176 days of anaerobic digestion for five different I/S ratios (3, 1, and 0.3 on a volatile solid basis, dairy manure alone, and swine manure alone) of manure, using solid container submerged lab-scale reactors in mesophilic conditions. As a result, solid-state swine manure inoculated with dairy manure could be digested without inhibition caused by ammonia and volatile fatty acid accumulation. The highest methane yield potential was observed in I/S ratios 1 and 0.3, as 133 and 145 mL CH4·g−1-VS, respectively. The lag phase of swine manure alone was more extended, 41 to 47 days, than other treatments containing dairy manure, directly related to tardy startup. These results revealed that dairy manure can be used as an inoculum source for AD of swine manure. The proper I/S ratios leading to successful AD of swine manure were 1 and 0.3. Full article
(This article belongs to the Special Issue Anaerobic Digestion Technology: An Update)
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19 pages, 2578 KiB  
Article
Implementation of a Pilot-Scale Biotrickling Filtration Process for Biogas Desulfurization under Anoxic Conditions Using Agricultural Digestate as Trickling Liquid
by Alejandra Lenis, Martín Ramírez, José Joaquín González-Cortés, Kristoffer Ooms and Johannes Pinnekamp
Bioengineering 2023, 10(2), 160; https://doi.org/10.3390/bioengineering10020160 - 25 Jan 2023
Viewed by 1619
Abstract
A pilot-scale biotrickling filter (BTF) was operated in counter-current flow mode under anoxic conditions, using diluted agricultural digestate as inoculum and as the recirculation medium for the nutrient source. The process was tested on-site at an agricultural fermentation plant, where real biogas was [...] Read more.
A pilot-scale biotrickling filter (BTF) was operated in counter-current flow mode under anoxic conditions, using diluted agricultural digestate as inoculum and as the recirculation medium for the nutrient source. The process was tested on-site at an agricultural fermentation plant, where real biogas was used. The pilot plant was therefore exposed to real process-related fluctuations. The purpose of this research was to attest the validity of the filtration process for use at an industrial-scale by operating the pilot plant under realistic conditions. Neither the use of agricultural digestate as trickling liquid and nor a BTF of this scale have previously been reported in the literature. The pilot plant was operated for 149 days. The highest inlet load was 8.5 gS-H2Sm−3h−1 with a corresponding removal efficiency of 99.2%. The pH remained between 7.5 and 4.6 without any regulation throughout the complete experimental phase. The analysis of the microbial community showed that both anaerobic and anoxic bacteria can adapt to the fluctuating operating conditions and coexist simultaneously, thus contributing to the robustness of the process. The operation of an anoxic BTF with agricultural digestate as the trickling liquid proved to be viable for industrial-scale use. Full article
(This article belongs to the Special Issue Anaerobic Digestion Technology: An Update)
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19 pages, 3475 KiB  
Article
Effect of Inoculum Microbial Diversity in Ex Situ Biomethanation of Hydrogen
by Washington Logroño, Paul Kluge, Sabine Kleinsteuber, Hauke Harms and Marcell Nikolausz
Bioengineering 2022, 9(11), 678; https://doi.org/10.3390/bioengineering9110678 - 10 Nov 2022
Cited by 5 | Viewed by 1558
Abstract
The effects of the inoculum origin, temperature or operational changes on ex situ biomethanation by complex microbial communities have been investigated; however, it remains unclear how the diversity of the inoculum influences the process and its stability. We explored the effect of microbial [...] Read more.
The effects of the inoculum origin, temperature or operational changes on ex situ biomethanation by complex microbial communities have been investigated; however, it remains unclear how the diversity of the inoculum influences the process and its stability. We explored the effect of microbial diversity of four inocula (coded as PF, WW, S37 and Nrich) on methane production, process stability and the formation of volatile fatty acids as by-products. The highest methane amounts produced were 3.38 ± 0.37 mmol, 3.20 ± 0.07 mmol, 3.07 ± 0.27 mmol and 3.14 ± 0.06 mmol for PF, WW, S37 and Nrich, respectively. The highest acetate concentration was found in less diverse cultures (1679 mg L−1 and 1397 mg L−1 for S37 and Nrich, respectively), whereas the acetate concentrations remained below 30 mg L−1 in the more diverse cultures. The maximum concentration of propionate was observed in less diverse cultures (240 mg L−1 and 37 mg L−1 for S37 and Nrich cultures, respectively). The highly diverse cultures outperformed the medium and low diversity cultures in the long-term operation. Methanogenic communities were mainly composed of hydrogenotrophic methanogens in all cultures. Aceticlastic methanogenesis was only active in the highly diverse sludge community throughout the experiment. The more diverse the inocula, the more methane was produced and the less volatile fatty acids accumulated, which could be attributed to the high number of microbial functions working together to keep a stable and balanced process. It is concluded that the inoculum origin and its diversity are very important factors to consider when the biomethanation process is performed with complex microbial communities. Full article
(This article belongs to the Special Issue Anaerobic Digestion Technology: An Update)
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14 pages, 1470 KiB  
Article
Anaerobic Digestion of Pig-Manure Solids at Low Temperatures: Start-Up Strategies and Effects of Mode of Operation, Adapted Inoculum, and Bedding Material
by Rajinikanth Rajagopal, Vaibhavi Bele, Noori M. Cata Saady, Felipe M. W. Hickmann and Bernard Goyette
Bioengineering 2022, 9(9), 435; https://doi.org/10.3390/bioengineering9090435 - 03 Sep 2022
Cited by 1 | Viewed by 2544
Abstract
The objective of this study was to obtain start-up strategies for the operation of a dry anaerobic digestion (DAD) system treating pig-manure (PM) solids at low-temperatures, and evaluate the effects of operation mode, adapted inoculum, and bedding material on the performance. A DAD [...] Read more.
The objective of this study was to obtain start-up strategies for the operation of a dry anaerobic digestion (DAD) system treating pig-manure (PM) solids at low-temperatures, and evaluate the effects of operation mode, adapted inoculum, and bedding material on the performance. A DAD system coupled with an inoculum system (two-stage DAD) was operated at 20 ± 1 °C to digest PM solids (Total Solids, TS: 27%) with wheat straw or woodchips as bedding materials (TS substrate-mixture: 45%) using a liquid inoculum. Static DAD was also operated in parallel for comparison purposes. Overall, the percolation–recirculation mode of operation was superior to the static mode; the former had more than a 3-fold increase in specific methane yield in cycle 3. Using the adapted inoculum in cycle-2 improved methane yield by 7% and 26% for cycles 1 and 3, respectively, under the percolation–recirculation mode of operation. In addition, the digestate resulting from the digestion of woodchips + PM solids had better physical characteristics than wheat straw + PM solids. Thus, anaerobic digestion of pig-manure solids at low-temperatures with appropriate start-up strategies, inoculum, and bedding material is a promising technology for transforming PM solids into biogas and using its digestate as biofertilizer. Full article
(This article belongs to the Special Issue Anaerobic Digestion Technology: An Update)
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16 pages, 3519 KiB  
Article
Exploring the Epiphytic Microbial Community Structure of Forage Crops: Their Adaptation and Contribution to the Fermentation Quality of Forage Sorghum during Ensiling
by Mudasir Nazar, Muhammad Wajid Ullah, Siran Wang, Jie Zhao, Zhihao Dong, Junfeng Li, Niaz Ali Kaka and Tao Shao
Bioengineering 2022, 9(9), 428; https://doi.org/10.3390/bioengineering9090428 - 30 Aug 2022
Cited by 4 | Viewed by 1385
Abstract
In this study, the effects of epiphytic microbiota from different forages on the fermentation characteristics and microbial community structure of forage sorghum silage were investigated. The gamma irradiated sterilized forage sorghum was treated through sterile water, epiphytic microbiota of forage sorghum (FSm), Sudan [...] Read more.
In this study, the effects of epiphytic microbiota from different forages on the fermentation characteristics and microbial community structure of forage sorghum silage were investigated. The gamma irradiated sterilized forage sorghum was treated through sterile water, epiphytic microbiota of forage sorghum (FSm), Sudan grass (SDm), Napier grass (NPm), and maize (MZm). NPm and SDm inoculated silages showed similar pH value and lactic acid (LA) and acetic acid (AA) contents at day 3 and 60 of ensiling. The final silage of FSm and MZm showed lower (p < 0.05) pH and AA content and a higher LA content compared to the NPm and SDm silages. Bacterial species from the Weisella genus were predominantly present in FSm, NPm, and SDm, while Lactococcus dominated the MZm silage during early ensiling. Lactobacillus was predominant in all inoculated terminal silages. Overall, the four inoculated microbiota decreased the pH value of silage and were dominated by lactic acid bacteria (LAB); however, the NPm and SDm treatments resulted in comparatively higher AA contents which could have an inhibitory effect on the secondary fermentation developed by the yeast and enhanced the aerobic stability of forage sorghum silage. Full article
(This article belongs to the Special Issue Anaerobic Digestion Technology: An Update)
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15 pages, 858 KiB  
Article
Impact of a Pretreatment Step on the Acidogenic Fermentation of Spent Coffee Grounds
by Joana Pereira, Marcelo M. R. de Melo, Carlos M. Silva, Paulo C. Lemos and Luísa S. Serafim
Bioengineering 2022, 9(8), 362; https://doi.org/10.3390/bioengineering9080362 - 03 Aug 2022
Cited by 3 | Viewed by 1897
Abstract
Acidogenic fermentation (AF) is often applied to wastes to produce short-chain organic acids (SCOAs)—molecules with applications in many industries. Spent coffee grounds (SCGs) are a residue from the coffee industry that is rich in carbohydrates, having the potential to be valorized by this [...] Read more.
Acidogenic fermentation (AF) is often applied to wastes to produce short-chain organic acids (SCOAs)—molecules with applications in many industries. Spent coffee grounds (SCGs) are a residue from the coffee industry that is rich in carbohydrates, having the potential to be valorized by this process. However, given the recalcitrant nature of this waste, the addition of a pretreatment step can significantly improve AF. In this work, several pretreatment strategies were applied to SCGs (acidic hydrolysis, basic hydrolysis, hydrothermal, microwave, ultrasounds, and supercritical CO2 extraction), evaluated in terms of sugar and inhibitors release, and used in AF. Despite the low yields of sugar extracted, almost all pretreatments increased SCOAs production. Milder extraction conditions also resulted in lower concentrations of inhibitory compounds and, consequently, in a higher concentration of SCOAs. The best results were obtained with acidic hydrolysis of 5%, leading to a production of 1.33 gSCOAs/L, an increase of 185% compared with untreated SCGs. Full article
(This article belongs to the Special Issue Anaerobic Digestion Technology: An Update)
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