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New Frontiers in Anaerobic Digestion (AD) Processes
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New Frontiers in Anaerobic Digestion (AD) Processes

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

Deadline for manuscript submissions: closed (18 December 2022) | Viewed by 59275

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Prof. Dr. Sonia Heaven

E-Mail Website
Guest Editor
Faculty of Engineering and Physical Sciences, University of Southampton, Southampton Boldrewood Innovation Campus, Southampton SO16 7QF, UK
Interests: optimised process configurations and operating regimes for renewable energy production through anaerobic digestion; biomass production for biorefineries; valorisation of food waste; algal biomass systems; membrane bioreactors; bioprocessing of biodegradable municipal waste; industrial wastewaters
Dr. Sigrid Kusch-Brandt

E-Mail Website
Guest Editor
Department of Civil, Environmental and Architectural Engineering ICEA, University of Padova, 35122 Padova, Italy
Interests: biological process engineering; anaerobic digestion (biogas); organic resources; food waste; circular economy; solid waste management; environmental engineering; environmental sustainability
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Charles Banks

E-Mail Website
Guest Editor
Faculty of Engineering and Physical Sciences, University of Southampton, Southampton Boldrewood Innovation Campus, Southampton SO16 7QF, UK
Interests: innovative technology for environmental protection; controlled anaerobic and aerobic biodegradation of municipal and industrial solid wastes; treatment of liquid industrial effluents by biological systems; energy production from digestion of crops and agricultural wastes; development of operating protocols for anaerobic digestion to maximise rates of substrate conversion and biogas yield

Special Issue Information

Dear Colleagues,

Anaerobic digestion (AD) is widely used to process a variety of organic materials, but a major share of its full potential currently remains unlocked.

This Special Issue on “New Frontiers in Anaerobic Digestion (AD) Processes” seeks original contributions that focus on recent developments and advanced concepts related to the valorisation of biomass under application of anaerobic digestion. Topics of interest include, but are not limited to:

  • optimised operating regimes for AD processes;
  • novel or significantly improved reactor configurations;
  • progress in overcoming process inhibitions and ensuring process stability;
  • modelling and control strategies;
  • valorisation of biogas components in high-value applications;
  • integrating AD into biorefinery concepts;
  • integrating AD and renewables in power-to-gas applications;
  • synergistic integration of AD into chemical and biochemical processes;
  • AD process integration at the industrial scale; and
  • sustainable concepts for decentralised, small-scale AD processes.

Prof. Dr. Sonia Heaven
Dr. Sigrid Kusch-Brandt
Prof. Dr. Charles Banks
Guest Editors

Manuscript Submission Information

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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

  • operating regimes and reactor configuration for anaerobic digestion processes
  • modelling and control
  • process inhibition and stability
  • biorefinery concepts
  • integration with other processes and renewables
  • large and small-scale applications
  • biogas production

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Published Papers (15 papers)

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Editorial

Jump to: Research, Review

5 pages, 205 KiB  
Editorial
Unlocking the Full Potential: New Frontiers in Anaerobic Digestion (AD) Processes
by Sigrid Kusch-Brandt, Sonia Heaven and Charles J. Banks
Processes 2023, 11(6), 1669; https://doi.org/10.3390/pr11061669 - 31 May 2023
Cited by 1 | Viewed by 2433
Abstract
Anaerobic digestion (AD) is a bio-based solution designed to convert organic materials into renewable energy and other products, such as soil improver and organic fertiliser [...] Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)

Research

Jump to: Editorial, Review

30 pages, 6012 KiB  
Article
Experimental Evaluation of Continuous In-Situ Biomethanation of CO2 in Anaerobic Digesters Fed on Sewage Sludge and Food Waste and the Influence of Hydrogen Gas–Liquid Mass Transfer
by Davide Poggio, Arman Sastraatmaja, Mark Walker, Stavros Michailos, William Nimmo and Mohamed Pourkashanian
Processes 2023, 11(2), 604; https://doi.org/10.3390/pr11020604 - 16 Feb 2023
Cited by 5 | Viewed by 3752
Abstract
In-situ biomethanation combines conventional biogas production from the anaerobic digestion (AD) of organic matter with the addition of hydrogen to produce a higher quality biomethane gas. However, challenges surrounding its performance and control could hinder its uptake. To investigate this, an automated rig [...] Read more.
In-situ biomethanation combines conventional biogas production from the anaerobic digestion (AD) of organic matter with the addition of hydrogen to produce a higher quality biomethane gas. However, challenges surrounding its performance and control could hinder its uptake. To investigate this, an automated rig was designed and operated to study in-situ biomethanation with sewage sludge (SS) and food waste (FW) feedstocks. The effects that were experimentally investigated included the biogas recirculation rate, stirring intensity, and organic loading rate (OLR). All the results highlighted the rate-limiting effect of H2 gas–liquid mass transfer (measured kLa in the range of 43–82 day−1), which was implied by a lack of evidence of hydrogen-induced biological inhibition and a high average equilibrium hydrogen content in the biogas (a volume of 7–37%). At an OLR of 2 g VS L−1day−1, increasing biogas recirculation and mechanical stirring rates improved the methane evolution rate up to 0.17 and 0.23 L L−1day−1 and the H2 conversion up to 80 and 66% for sewage sludge and food waste, respectively. A lower OLR of 1 g VS L−1day−1 allowed for increased hydrogen conversion but at a lower level of methane productivity. A process model, validated on experimental data, predicted that improving the kLa to at least 240 day−1 would be required for in-situ biomethanation at OLRs common in AD systems in order to achieve a drop-in quality in terms of the biogas, with further downstream treatment required for certain applications. Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)
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23 pages, 2323 KiB  
Article
Anaerobic Co-Digestion of Sewage Sludge and Trade Wastes: Beneficial and Inhibitory Effects of Individual Constituents
by Olivia Berzal de Frutos, Martin Götze, Marc Pidou and Yadira Bajón Fernández
Processes 2023, 11(2), 519; https://doi.org/10.3390/pr11020519 - 8 Feb 2023
Cited by 6 | Viewed by 2391
Abstract
Anaerobic digestion (AD) of sewage sludge can be optimised by adding trade wastes (TWs) because of their nutrient content and boost in biogas formation if non-inhibitory. However, some components in TWs might have an inhibitory impact, such as nitrogen compounds, sulphate, heavy metals, [...] Read more.
Anaerobic digestion (AD) of sewage sludge can be optimised by adding trade wastes (TWs) because of their nutrient content and boost in biogas formation if non-inhibitory. However, some components in TWs might have an inhibitory impact, such as nitrogen compounds, sulphate, heavy metals, metalloids, halogens and organic pollutants (e.g., phenol). This study aimed to understand the impact of TWs on the co-digestion with sewage sludge to identify appropriate TW loads for sustainable AD operation. The composition of 160 TWs was evaluated and the constituents with potential to cause inhibition or toxicity were tested in bio-methane potential (BMP) tests. The compounds studied in BMP tests included ammonia, zinc, copper, aluminium, mercury, arsenic, chloride, sulphate and nitrate. An improvement was observed at concentrations 2–746 mg Zn/L, 1066–2821 mg Cl/L as zinc sulphate and sodium chloride in biogas production, and 2–746 mg Zn/L, 162 mg SO4/L, 25 mg Hg/L as zinc sulphate, sodium chloride and mercury sulphate in methane production, respectively. Considering the TWs characterised and the results of the BMP tests, a volumetric ratio of 10/90 of TWs and sewage sludge is proposed as a suitable feedstock for co-digestion. Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)
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12 pages, 1411 KiB  
Article
Shortening the Standard Testing Time for Residual Biogas Potential (RBP) Tests Using Biogas Yield Models and Substrate Physicochemical Characteristics
by Yanxin Liu, Weisi Guo, Philip Longhurst and Ying Jiang
Processes 2023, 11(2), 441; https://doi.org/10.3390/pr11020441 - 1 Feb 2023
Cited by 3 | Viewed by 1961
Abstract
The residual biogas potential (RBP) test is a procedure to ensure the anaerobic digestion process performance and digestate stability. Standard protocols for RBP require a significant time for sample preparation, characterisation and testing of the rig setup followed by batch experiments of a [...] Read more.
The residual biogas potential (RBP) test is a procedure to ensure the anaerobic digestion process performance and digestate stability. Standard protocols for RBP require a significant time for sample preparation, characterisation and testing of the rig setup followed by batch experiments of a minimum of 28 days. To reduce the experimental time to obtain the RBP result, four biogas kinetic models were evaluated for their strength of fit for biogas production data from RBP tests. It was found that the pseudo-parallel first-order model and the first-order autoregressive (AR (1)) model provide a high strength of fit and can predict the RBP result with good accuracy (absolute percentage errors < 10%) using experimental biogas production data of 15 days. Multivariate regression with decision trees (DTs) was adopted in this study to predict model parameters for the AR (1) model from substrate physicochemical parameters. The mean absolute percentage error (MAPE) of the predicted AR (1) model coefficients, the constants and the RBP test results at day 28 across DTs with 20 training set samples are 4.76%, 72.04% and 52.13%, respectively. Using five additional data points to perform the leave-one-out cross-validation method, the MAPEs decreased to 4.31%, 59.29% and 45.62%. This indicates that the prediction accuracy of DTs can be further improved with a larger training dataset. A Gaussian Process Regressor was guided by the DT-predicted AR (1) model to provide probability distribution information for the biogas yield prediction. Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)
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12 pages, 1180 KiB  
Communication
Toward the Transition of Agricultural Anaerobic Digesters into Multiproduct Biorefineries
by David Bolzonella, Davide Bertasini, Riccardo Lo Coco, Miriam Menini, Fabio Rizzioli, Anna Zuliani, Federico Battista, Nicola Frison, Aleksandra Jelic and Giovanna Pesante
Processes 2023, 11(2), 415; https://doi.org/10.3390/pr11020415 - 30 Jan 2023
Cited by 10 | Viewed by 2916
Abstract
Anaerobic digestion allows for the proper management of agro-waste, including manure. Currently, more than 18,000 anaerobic digestion plants are under operation in EU, 80% of which are employed in the rural context. Tariff schemes for power generation from biogas produced during anaerobic digestion [...] Read more.
Anaerobic digestion allows for the proper management of agro-waste, including manure. Currently, more than 18,000 anaerobic digestion plants are under operation in EU, 80% of which are employed in the rural context. Tariff schemes for power generation from biogas produced during anaerobic digestion of agricultural feedstocks in Germany, Italy and Austria are coming to an end and new approaches are needed to exploit the existing infrastructures. Digesters in the rural context can be implemented and modified to be transformed into sustainable multi-feedstock and multi-purpose biorefineries for the production of energy, nutrients, proteins, bio-chemicals such as carboxylic acids, polyesters and proteins. This paper describes how the transition of agricultural anaerobic digesters into multi-products biorefineries can be achieved and what are the potential benefits originating from the application of a pilot scale platform able to treat cow manure and other crop residues while producing volatile fatty acids, polyhydroxyalkanoates, microbial protein material, hydrogen, methane and a concentrated liquid stream rich in nitrogen, potassium and phosphorus. Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)
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13 pages, 784 KiB  
Article
Biogas Production from Residues of Industrial Insect Protein Production from Black Soldier Fly Larvae Hermetia illucens (L.): An Evaluation of Different Insect Frass Samples
by Harald Wedwitschka, Daniela Gallegos Ibanez and Damián Reyes Jáquez
Processes 2023, 11(2), 362; https://doi.org/10.3390/pr11020362 - 23 Jan 2023
Cited by 15 | Viewed by 4203
Abstract
Insect biomass shows promise as an alternative animal feedstuff with a low climate effect. Industrial insect rearing generates residual materials, such as feed remains and insect excrements, so-called insect frass, which exhibits a high organic content. Commonly, these residues are utilized as soil [...] Read more.
Insect biomass shows promise as an alternative animal feedstuff with a low climate effect. Industrial insect rearing generates residual materials, such as feed remains and insect excrements, so-called insect frass, which exhibits a high organic content. Commonly, these residues are utilized as soil amendment. Information on the suitability of these residues for biogas production is rather scarce. The energetic utilization of insect frass as feedstock for anaerobic digestion (AD) would allow for the simultaneous residue material reduction and bioenergy production. Additionally, synergies in heat management could arise using the exhaust heat of the biogas plant in the insect farming process. In laboratory-scale anaerobic digestion trials, the specific methane yield (SMY) of six different insect frass samples from black soldier fly (Hermetia) rearing were tested in batch biochemical methane potential (BMP) tests. Further, semi continuous anaerobic digestion trials on a lab scale using continuously stirred tank reactors (CSTRs) were carried out with Hermetia insect frass from a pilot plant operation in order to determine the digestibility and process stability of the AD process. The BMP results showed SMY values of the different insect frass samples ranging from 201 ± 9 to 287 ± 37 mL/gVS that are similar to those of other animal excrements, such as cow or pig manure already been used as feedstock in agricultural biogas plants. Results of the semi-continuous digestion of insect frass from the pilot plant operation showed a SMY value of 167 ± 15 mL/gVS, suggesting no process-inhibiting effect caused by the feed material. Although, the high nitrogen content must be taken into account for stable AD performance. Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)
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Graphical abstract

29 pages, 21276 KiB  
Article
Validation of Two Theoretically Derived Equations for Predicting pH in CO2 Biomethanisation
by Yue Zhang, Sonia Heaven and Charles J. Banks
Processes 2023, 11(1), 113; https://doi.org/10.3390/pr11010113 - 31 Dec 2022
Cited by 2 | Viewed by 1784
Abstract
CO2 biomethanisation is a rapidly emerging technology which can contribute to reducing greenhouse gas emissions through the more sustainable use of organic feedstocks. The major technical limitation for in situ systems is that the reaction causes CO2 depletion which drives up [...] Read more.
CO2 biomethanisation is a rapidly emerging technology which can contribute to reducing greenhouse gas emissions through the more sustainable use of organic feedstocks. The major technical limitation for in situ systems is that the reaction causes CO2 depletion which drives up pH, potentially leading to instability and even digestion failure. The study aimed to test fundamentally derived predictive equations as tools to manage H2 addition to anaerobic digesters. The methodology used data from the literature and from experimental digesters operated with excess H2 to a point of failure and subsequent recovery. Two equations were tested: the first relating pH to CO2 partial pressure (pCO2), and the second extending this to include the influence of volatile fatty acids and ammonia. The first equation gave good agreement for data from studies covering a wide range of operating conditions and digester types. Where agreement was not good, this could usually be explained, and in some cases improved, using the second equation, which also showed excellent predictive performance in the experimental study. The results validated the derived equations and identified typical coefficient values for some organic feedstocks. Both equations could provide a basis for process control of CO2 biomethanisation using routine monitoring of pH or pCO2 with additional analysis for volatile fatty acids and total ammonia nitrogen when required. Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)
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Graphical abstract

25 pages, 394 KiB  
Article
Potential for Biomethanisation of CO2 from Anaerobic Digestion of Organic Wastes in the United Kingdom
by Angela Bywater, Sonia Heaven, Yue Zhang and Charles J. Banks
Processes 2022, 10(6), 1202; https://doi.org/10.3390/pr10061202 - 16 Jun 2022
Cited by 7 | Viewed by 3962
Abstract
The United Kingdom (UK) has a decarbonisation strategy that includes energy from both hydrogen and biomethane. The latter comes from the growing anaerobic digestion (AD) market, which in 2020 produced 23.3 TWh of energy in the form of biogas. According to the strategy, [...] Read more.
The United Kingdom (UK) has a decarbonisation strategy that includes energy from both hydrogen and biomethane. The latter comes from the growing anaerobic digestion (AD) market, which in 2020 produced 23.3 TWh of energy in the form of biogas. According to the strategy, this must be upgraded to biomethane by removal of carbon dioxide (CO2): a goal that could also be fulfilled through CO2 biomethanisation, alleviating the need for carbon capture and storage. Results are presented from a survey of publicly available datasets coupled with modelling to identify potential scale and knowledge gaps. Literature data were used to estimate maximum biomethane concentrations by feedstock type: these ranged from 79% for food wastes to 93% for livestock manures. Data from various government sources were used to estimate the overall potential for CO2 biomethanisation with current AD infrastructure. Values for the uplift in biomethane production ranged from 57% to 61%, but the need for more consistent data collection methodologies was highlighted. On average, however, if CO2 biomethanisation was applied in all currently operating UK AD plants an energy production uplift of 12,954 GWh could be achieved based on 2020 figures. This is sufficient to justify the inclusion of CO2 biomethanisation in decarbonisation strategies, in the UK and worldwide. Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)
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16 pages, 11855 KiB  
Article
Hydrothermal Pretreatment of Wheat Straw—Evaluating the Effect of Substrate Disintegration on the Digestibility in Anaerobic Digestion
by Timo Zerback, Britt Schumacher, Sören Weinrich, Benedikt Hülsemann and Michael Nelles
Processes 2022, 10(6), 1048; https://doi.org/10.3390/pr10061048 - 24 May 2022
Cited by 14 | Viewed by 2709
Abstract
The increasing demand for renewable energy sources and demand-oriented electricity provision makes anaerobic digestion (AD) one of the most promising technologies. In addition to energy crops, the use of lignocellulosic residual and waste materials from agriculture is becoming increasingly important. However, AD of [...] Read more.
The increasing demand for renewable energy sources and demand-oriented electricity provision makes anaerobic digestion (AD) one of the most promising technologies. In addition to energy crops, the use of lignocellulosic residual and waste materials from agriculture is becoming increasingly important. However, AD of such feedstocks is often associated with difficulties due to the high content of lignocellulose and its microbial persistence. In the present work, the effect of hydrothermal pretreatment (HTP) on the digestibility of wheat straw is investigated and evaluated. Under different HTP temperatures (160–180 °C) and retention times (15–45 min), a significant increase in biomethane potential (BMP) can be observed in all cases. The highest BMP (309.64 mL CH4 g−1 volatile solid (VS) is achieved after pretreatment at 160 °C for 45 min, which corresponds to an increase of 19% of untreated wheat straw. The results of a multiple linear regression model show that the solubilization of organic materials is influenced by temperature and time. Furthermore, using two different first-order kinetic models, an enhancement of AD rate during hydrolysis due to pretreatment is observed. However, the increasing intensity of pretreatment conditions is accompanied by a decreasing trend in the conversion of intermediates to methane. Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)
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19 pages, 318 KiB  
Article
Exploring Farm Anaerobic Digester Economic Viability in a Time of Policy Change in the UK
by Angela Bywater and Sigrid Kusch-Brandt
Processes 2022, 10(2), 212; https://doi.org/10.3390/pr10020212 - 24 Jan 2022
Cited by 9 | Viewed by 5815
Abstract
The combination of a post-Brexit agricultural policy, the Global Methane Pledge announced during the last United Nations Climate Change Conference in Glasgow (COP26), and urgency of meeting climate goals means the UK has a unique opportunity to create an exemplar through recognition of [...] Read more.
The combination of a post-Brexit agricultural policy, the Global Methane Pledge announced during the last United Nations Climate Change Conference in Glasgow (COP26), and urgency of meeting climate goals means the UK has a unique opportunity to create an exemplar through recognition of the benefits of small-scale farm anaerobic digesters that valorise on-site wastes for renewable electricity and heat, cushioning agri-businesses against energy perturbations. To explore economic viability of farm-based biogas production, combinations of support levels, energy prices, capital cost, internal rate of return (IRR), and digestate value were analysed, employing a 550-cow dairy farm with access to other agricultural wastes. A 145 kWe system utilising 100% of CHP electricity (grid value: £0.1361 per kWh) and 70% of the heat (heating oil value: £0.055 per kWh) could achieve an IRR above 15.5% with a median electricity tariff of £0.1104 per kWh at a heat tariff from £0.0309 to £0.0873 per kWh thermal. Under a subsidy-free regime, the same system could achieve a 10% IRR with electricity prices in the range £0.149 to £0.261 per kWh. High fertiliser prices could increase digestate value, further improving viability. With late-2021 high energy prices, the technology approaches subsidy-free viability, but uptake is unlikely unless wider environmental and societal benefits of on-farm systems can be explicitly valued. Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)
31 pages, 4843 KiB  
Article
Estimating the Methane Potential of Energy Crops: An Overview on Types of Data Sources and Their Limitations
by Yue Zhang, Sigrid Kusch-Brandt, Andrew M. Salter and Sonia Heaven
Processes 2021, 9(9), 1565; https://doi.org/10.3390/pr9091565 - 1 Sep 2021
Cited by 12 | Viewed by 6367
Abstract
As the anaerobic digestion of energy crops and crop residues becomes more widely applied for bioenergy production, planners and operators of biogas plants, and farmers who consider growing such crops, have a need for information on potential biogas and methane yields. A rich [...] Read more.
As the anaerobic digestion of energy crops and crop residues becomes more widely applied for bioenergy production, planners and operators of biogas plants, and farmers who consider growing such crops, have a need for information on potential biogas and methane yields. A rich body of literature reports methane yields for a variety of such materials. These data have been obtained with different testing methods. This work elaborates an overview on the types of data source available and the methods that are commonly applied to determine the methane yield of an agricultural biomass, with a focus on European crops. Limitations regarding the transferability and generalisation of data are explored, and crop methane values presented across the literature are compared. Large variations were found for reported values, which can only partially be explained by the methods applied. Most notably, the intra-crop variation of methane yield (reported values for a single crop type) was higher than the inter-crop variation (variation between different crops). The pronounced differences in reported methane yields indicate that relying on results from individual assays of candidate materials is a high-risk approach for planning biogas operations, and the ranges of values such as those presented here are essential to provide a robust basis for estimation. Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)
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25 pages, 5526 KiB  
Article
Operation of Submerged Anaerobic Membrane Bioreactors at 20 °C: Effect of Solids Retention Time on Flux, Mixed Liquor Characteristics and Performance
by Santiago Pacheco-Ruiz, Sonia Heaven and Charles J. Banks
Processes 2021, 9(9), 1525; https://doi.org/10.3390/pr9091525 - 29 Aug 2021
Cited by 2 | Viewed by 3222
Abstract
Four flat-sheet submerged anaerobic membrane bioreactors ran for 242 days on a simulated domestic wastewater with low Chemical Oxygen Demand (COD) and high suspended solids. Organic loading was maintained around 1.0 g COD L−1 day−1, while solids retention time (SRT) [...] Read more.
Four flat-sheet submerged anaerobic membrane bioreactors ran for 242 days on a simulated domestic wastewater with low Chemical Oxygen Demand (COD) and high suspended solids. Organic loading was maintained around 1.0 g COD L−1 day−1, while solids retention time (SRT) was varied from 20–90 days. This was achieved at a constant membrane flux, maintained by adjusting transmembrane pressure (TMP) in the range 1.8–9.8 kPa. Membrane fouling was assessed based on the required TMP, with mixed liquors characterised using capillary suction time, frozen image centrifugation and quantification of extracellular polymeric substances (EPS). SRT had a significant effect on these parameters: fouling was least at an SRT of 30 days and highest at 60 days, with some reduction as this extended to 90 days. Operation at SRT < 30 days showed no further benefits. Although operation at a short SRT was optimal for membrane performance it led to lower specific methane productivity, higher biomass yields and higher effluent COD. Short SRT may also have accelerated the loss of essential trace elements, leading to reduced performance under these conditions. A COD-based mass balance was conducted, including both biomass and methane dissolved in the effluent. Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)
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16 pages, 1948 KiB  
Article
Batch and Semi-Continuous Anaerobic Digestion of Industrial Solid Citrus Waste for the Production of Bioenergy
by Erik Samuel Rosas-Mendoza, Andrea Alvarado-Vallejo, Norma Alejandra Vallejo-Cantú, Raúl Snell-Castro, Sergio Martínez-Hernández and Alejandro Alvarado-Lassman
Processes 2021, 9(4), 648; https://doi.org/10.3390/pr9040648 - 8 Apr 2021
Cited by 11 | Viewed by 6136
Abstract
The aim of this paper is to describe a study of the anaerobic digestion of industrial citrus solid waste (ISCW) in both batch and semi-continuous modes for the production of bioenergy without the elimination of D-limonene. The study was conducted at the pilot [...] Read more.
The aim of this paper is to describe a study of the anaerobic digestion of industrial citrus solid waste (ISCW) in both batch and semi-continuous modes for the production of bioenergy without the elimination of D-limonene. The study was conducted at the pilot plant level in an anaerobic reactor with a working volume of 220 L under mesophilic conditions of 35 ± 2 °C. Cattle manure (CM) was used as the inoculum. Three batches were studied. The first batch had a CM/ISCW ratio of 90/10, and Batches 2 and 3 had CM/ISCW ratios of 80/20 and 70/30, respectively. In the semi-continuous mode an OLR of approximately 8 g total chemical oxygen demand (COD)/Ld (4.43 gVS/Ld) was used. The results showed that 49%, 44%, and 60% of volatile solids were removed in the batch mode, and 35% was removed in the semi-continuous mode. In the batch mode, 0.322, 0.382, and 0.316 LCH4 were obtained at STP/gVSremoved. A total of 24.4 L/d (34% methane) was measured in the semi-continuous mode. Bioenergy potentials of 3.97, 5.66, and 8.79 kWh were obtained for the respective batches, and 0.09 kWh was calculated in the semi-continuous mode. The citrus industry could produce 37 GWh per season. A ton of processed oranges has a bioenergy potential of 162 kWh, which is equivalent to 49 kWh of available electricity ($3.90). Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)
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Review

Jump to: Editorial, Research

40 pages, 4501 KiB  
Review
Recent Advances in Membrane-Based Biogas and Biohydrogen Upgrading
by Cenit Soto, Laura Palacio, Raúl Muñoz, Pedro Prádanos and Antonio Hernandez
Processes 2022, 10(10), 1918; https://doi.org/10.3390/pr10101918 - 22 Sep 2022
Cited by 13 | Viewed by 5532
Abstract
Biogas and biohydrogen, due to their renewable nature and zero carbon footprint, are considered two of the gaseous biofuels that will replace conventional fossil fuels. Biogas from anaerobic digestion must be purified and converted into high-quality biomethane prior to use as a vehicle [...] Read more.
Biogas and biohydrogen, due to their renewable nature and zero carbon footprint, are considered two of the gaseous biofuels that will replace conventional fossil fuels. Biogas from anaerobic digestion must be purified and converted into high-quality biomethane prior to use as a vehicle fuel or injection into natural gas networks. Likewise, the enrichment of biohydrogen from dark fermentation requires the removal of CO2, which is the main pollutant of this new gaseous biofuel. Currently, the removal of CO2 from both biogas and biohydrogen is carried out by means of physical/chemical technologies, which exhibit high operating costs and corrosion problems. Biological technologies for CO2 removal from biogas, such as photosynthetic enrichment and hydrogenotrophic enrichment, are still in an experimental development phase. In this context, membrane separation has emerged as the only physical/chemical technology with the potential to improve the performance of CO2 separation from both biogas and biohydrogen, and to reduce investment and operating costs, as a result of the recent advances in the field of nanotechnology and materials science. This review will focus on the fundamentals, potential and limitations of CO2 and H2 membrane separation technologies. The latest advances on membrane materials for biogas and biohydrogen purification will be systematically reviewed. Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)
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21 pages, 3641 KiB  
Review
Review of Soft Sensors in Anaerobic Digestion Process
by Pengfei Yan, Minghui Gai, Yuhong Wang and Xiaoyong Gao
Processes 2021, 9(8), 1434; https://doi.org/10.3390/pr9081434 - 19 Aug 2021
Cited by 17 | Viewed by 3358
Abstract
Anaerobic digestion is associated with various crucial variables, such as biogas yield, chemical oxygen demand, and volatile fatty acid concentration. Real-time monitoring of these variables can not only reflect the process of anaerobic digestion directly but also accelerate the efficiency of resource conversion [...] Read more.
Anaerobic digestion is associated with various crucial variables, such as biogas yield, chemical oxygen demand, and volatile fatty acid concentration. Real-time monitoring of these variables can not only reflect the process of anaerobic digestion directly but also accelerate the efficiency of resource conversion and improve the stability of the reaction process. However, the current real-time monitoring equipment on the market cannot be widely used in the industrial production process due to its defects such as expensive equipment, low accuracy, and lagging analysis. Therefore, it is essential to conduct soft sensor modeling for unmeasurable variables and use auxiliary variables to realize real-time monitoring, optimization, and control of the an-aerobic digestion process. In this paper, the basic principle and process flow of anaerobic digestion are first briefly introduced. Subsequently, the development history of the traditional soft sensor is systematically reviewed, the latest development of soft sensors was detailed, and the obstacles of the soft sensor in the industrial production process are discussed. Finally, the future development trend of deep learning in soft sensors is deeply discussed, and future research directions are provided. Full article
(This article belongs to the Special Issue New Frontiers in Anaerobic Digestion (AD) Processes)
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