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3 pages, 174 KiB

Open AccessEditorial

Editorial: Special Issue “From Waste to Energy: Anaerobic Digestion Technologies”

by Christian Aragón-Briceño, Panagiotis Boutikos and Musa Manga

Energies 2024, 17(21), 5420; https://doi.org/10.3390/en17215420 - 30 Oct 2024

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Abstract

Anaerobic digestion (AD) has become a cornerstone in the global pursuit of sustainable energy solutions and effective waste management [...] Full article

(This article belongs to the Special Issue From Waste to Energy: Anaerobic Digestion Technologies)

Research

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16 pages, 4660 KiB

Open AccessArticle

Stimulation of Batch Mesophilic Anaerobic Digestion by Cellulose- and Polysaccharide-Derived Polymers in Landfill Leachates

by Olga Muter, Dita Gudrā, Laura Žorža, Tūrs Selga, Ance Roga, Edmunds Skinderskis, Uģis Eismonts, Kārlis Vonda, Ineta Kalniņa, Dāvids Fridmanis and Andrejs Grīnbergs

Energies 2024, 17(21), 5384; https://doi.org/10.3390/en17215384 - 29 Oct 2024

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Abstract

The fate of biobased and biodegradable cellulose-derived plastics in landfills represents an important topic from economic and environmental points of view. Anaerobic digestion is a cost-effective waste-to-energy technology. The behaviour of six polymer types—that is, cellulose (C), cellulose acetate (CA), viscose (V), nanocellulose [...] Read more.

The fate of biobased and biodegradable cellulose-derived plastics in landfills represents an important topic from economic and environmental points of view. Anaerobic digestion is a cost-effective waste-to-energy technology. The behaviour of six polymer types—that is, cellulose (C), cellulose acetate (CA), viscose (V), nanocellulose (NC), acetate textile (AT), and heteropolysaccharide pectin (P)—was studied under anaerobic batch mesophilic conditions in a landfill leachate for 147 days. The cumulative biogas production was as follows: C>V=CA>>AT>>NC=P. Metagenomic analysis revealed notable variations in the proportion of bacterial and archaeal domains with the highest archaeal abundance in the presence of CA (80.2%) and C (78.5%). At the end of digestion, cellulolytic, hydrolytic, and dehydrogenase activities were measured in the intact samples, as well as the liquid and solid fractions, under aerobic and anaerobic conditions. Cellulolytic activity in P was detected only in the pellet, while in NC, activity was mostly in the supernatant under both aerobic and anaerobic conditions. Scanning electron microscopy and confocal scanning laser microscopy showed a defragmentation and degradation of polymeric substrates as well as microbial colonisation. Based on the results, landfill leachate is appropriate for the anaerobic biodegradation of cellulose-derived polymers; however, the process is polymer specific. Full article

(This article belongs to the Special Issue From Waste to Energy: Anaerobic Digestion Technologies)

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16 pages, 1309 KiB

Open AccessFeature PaperArticle

Optimisation of Biogas Production in the Co-Digestion of Pre-Hydrodynamically Cavitated Aerobic Granular Sludge with Waste Fats

by Marcin Dębowski, Marcin Zieliński, Joanna Kazimierowicz, Anna Nowicka and Magda Dudek

Energies 2024, 17(4), 922; https://doi.org/10.3390/en17040922 - 16 Feb 2024

Cited by 1 | Viewed by 894

Abstract

The characteristics of excess aerobic granular sludge, related to its structure and chemical composition, limit the efficiency of anaerobic digestion. For this reason, pre-treatment methods and compositions with other organic substrates are used. In earlier work, no attempt was made to intensify the [...] Read more.

The characteristics of excess aerobic granular sludge, related to its structure and chemical composition, limit the efficiency of anaerobic digestion. For this reason, pre-treatment methods and compositions with other organic substrates are used. In earlier work, no attempt was made to intensify the methane fermentation of the excess aerobic granular sludge by adding fatty waste materials. The aim of the research was to determine the effects of co-digestion of pre-hydrodynamically cavitated aerobic granular sludge with waste fats on the efficiency of methane fermentation under mesophilic and thermophilic conditions. The addition of waste fats improved the C/N ratio and increased its value to 19. Under mesophilic conditions, the highest effects were observed when the proportion of volatile solids from waste fats was 25%. The amount of biogas produced increased by 17.85% and CH₄ by 19.85% compared to the control. The greatest effects were observed in thermophilic anaerobic digestion at 55 °C, where a 15% waste fat content in volatile solids was ensured. This resulted in the production of 1278.2 ± 40.2 mL/gVS biogas and 889.4 ± 29.7 mL/gVS CH₄. The CH₄ content of the biogas was 69.6 ± 1.3%. The increase in biogas and CH₄ yield compared to pure aerobic granular sludge anaerobic digestion was 34.4% and 40.1%, respectively. An increase in the proportion of waste fats in the substrate had no significant effect on the efficiency of methane fermentation. Strong positive correlations (R² > 0.9) were observed between biogas and CH₄ production and the C/N ratio and VS concentration. Full article

(This article belongs to the Special Issue From Waste to Energy: Anaerobic Digestion Technologies)

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17 pages, 5216 KiB

Open AccessEditor’s ChoiceArticle

Application of Hydrodynamic Cavitation in the Disintegration of Aerobic Granular Sludge—Evaluation of Pretreatment Time on Biomass Properties, Anaerobic Digestion Efficiency and Energy Balance

by Marcin Zieliński, Marcin Dębowski, Joanna Kazimierowicz, Anna Nowicka and Magda Dudek

Energies 2024, 17(2), 335; https://doi.org/10.3390/en17020335 - 9 Jan 2024

Cited by 6 | Viewed by 1745

Abstract

The use of aerobic granular sludge is a promising and future-proof solution for wastewater treatment. The implementation of this technology requires the development of efficient and cost-effective methods for the management of excess sludge. The aim of the research was to evaluate the [...] Read more.

The use of aerobic granular sludge is a promising and future-proof solution for wastewater treatment. The implementation of this technology requires the development of efficient and cost-effective methods for the management of excess sludge. The aim of the research was to evaluate the effects of hydrodynamic cavitation on the efficiency of aerobic granular sludge digestion. Respirometric measurements were performed at a temperature of 38 °C and an initial organic load of 5.0 gVS/L. The changes in the properties of the pretreated biomass, the kinetics of methane fermentation, the amount and composition of the biogas produced, and an energetic evaluation of the process were carried out. A significant influence of hydrodynamic cavitation on the transfer of organic compounds into the dissolved phase was demonstrated. The degree of solubilisation was 37% for COD and 42% and for TOC. The efficiency of CH₄ production from the pretreated sludge reached a value of 496 ± 12 mL/gVS, which corresponds to an increase of 19.6% compared to the raw biomass. The influence of cavitation on the CH₄ content of the biogas was not observed. Strong correlations were found between the efficiency of anaerobic digestion and the concentration of dissolved organic compounds and the hydrodynamic cavitation time used. The gross energy yield was closely correlated with the amount of CH₄. The highest comparable values of 3.12 Wh/gTS to 3.18 Wh/gTS were found in the variants in which the hydrodynamic cavitation (HC) time was between 15 min and 50 min. The highest net energy production of 2890 kWh/MgTS was achieved after 15 min of pretreatment. Full article

(This article belongs to the Special Issue From Waste to Energy: Anaerobic Digestion Technologies)

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17 pages, 1196 KiB

Open AccessArticle

Sweet Sorghum as a Potential Fallow Crop in Sugarcane Farming for Biomethane Production in Queensland, Australia

by Divya Joslin Mathias, Thiago Edwiges, Napong Ketsub, Rajinder Singh and Prasad Kaparaju

Energies 2023, 16(18), 6497; https://doi.org/10.3390/en16186497 - 8 Sep 2023

Cited by 4 | Viewed by 1992

Abstract

Biogas from lignocellulosic feedstock is a promising energy source for decentralized renewable electricity, heat, and/or vehicle fuel generation. However, the selection of a suitable energy crop should be based on several factors such as biomass yields and characteristics or biogas yields and economic [...] Read more.

Biogas from lignocellulosic feedstock is a promising energy source for decentralized renewable electricity, heat, and/or vehicle fuel generation. However, the selection of a suitable energy crop should be based on several factors such as biomass yields and characteristics or biogas yields and economic returns if used in biorefineries. Furthermore, the food-to-fuel conflict for the use of a specific energy crop must be mitigated through smart cropping techniques. In this study, the potential use of sweet sorghum as an energy crop grown during the fallow periods of sugarcane cultivation was evaluated. Nine sweet sorghum cultivars were grown on sandy loam soil during September 2020 in North Queensland, Australia. The overall results showed that the crop maturity had a profound influence on chemical composition and biomass yields. Further, the total insoluble and soluble sugar yields varied among the tested cultivars and were dependent on plant height and chemical composition. The biomass yields ranged from 46.9 to 82.3 tonnes/hectare (t/ha) in terms of the wet weight (w/w) of the tested cultivars, with the SE-81 cultivar registering the highest biomass yield per hectare. The gross energy production was determined based on the chemical composition and methane yields. Biochemical methane potential (BMP) studies in batch experiments at 37 °C showed that methane yields of 175 to 227.91 NmL CH₄/gVS_added were obtained from the tested cultivars. The maximum methane yield of 227.91 NmL CH₄/gVS_added was obtained for cultivar SE-35. However, SE-81 produced the highest methane yields on a per hectare basis (3059.18 Nm³ CH₄/ha). This is equivalent to a gross energy value of 761.74 MWh/year or compressed biomethane (BioCNG) as a vehicle fuel sufficient for 95 passenger cars travelling at 10,000 km per annum. Overall, this study demonstrated that sweet sorghum is a potential energy crop for biogas production that could be cultivated during the fallow period of sugarcane cultivation in Queensland. Full article

(This article belongs to the Special Issue From Waste to Energy: Anaerobic Digestion Technologies)

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18 pages, 2134 KiB

Open AccessArticle

Understanding the Influence of Biochar Augmentation in Anaerobic Digestion by Principal Component Analysis

by Jessica Quintana-Najera, A. John Blacker, Louise A. Fletcher and Andrew B. Ross

Energies 2023, 16(6), 2523; https://doi.org/10.3390/en16062523 - 7 Mar 2023

Cited by 2 | Viewed by 1871

Abstract

Biochar addition in anaerobic digestion has been repeatedly reported to improve methane production, however, this ability is not well understood. This work aims to understand and correlate the most important factors influencing anaerobic digestion performance using principal component analysis along with quantitative and [...] Read more.

Biochar addition in anaerobic digestion has been repeatedly reported to improve methane production, however, this ability is not well understood. This work aims to understand and correlate the most important factors influencing anaerobic digestion performance using principal component analysis along with quantitative and qualitative descriptive analysis to evaluate the variations of methane production with the addition of biochar. Reports from the literature using biochar produced from several feedstocks under variable pyrolysis conditions and therefore different compositions were carefully gathered and compared with their own non-biochar controls. Woody-derived biochars, produced at 450–550 °C, containing an ash content of 3.1–6.3%, and an O:C ratio of 0.20, were responsible for having the greatest positive effect. The amount of biochar added to the digesters also influences anaerobic digestion performance. Increasing biochar loads favours the production rate, although this can be detrimental to methane yields, thereby, biochar loads of approximately 0.4–0.6% (w/v) appear to be optimal. This work provides a guide for those interested in biochar augmentation in anaerobic digestion and identifies the main interactions between the variables involved. Full article

(This article belongs to the Special Issue From Waste to Energy: Anaerobic Digestion Technologies)

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15 pages, 1833 KiB

Open AccessArticle

Ammonia Recovery from Livestock Manure Digestate through an Air-Bubble Stripping Reactor: Evaluation of Performance and Energy Balance

by Alessandro Abbà, Marta Domini, Marco Baldi, Roberta Pedrazzani and Giorgio Bertanza

Energies 2023, 16(4), 1643; https://doi.org/10.3390/en16041643 - 7 Feb 2023

Cited by 7 | Viewed by 2284

Abstract

The recovery of livestock manure, rich in nutrients, as fertilizer in agriculture, could pose the risk of an excessive load of nitrogen on the soil. Ammonia stripping is one of the available technologies for reducing the amount of nitrogen in the digestate obtained [...] Read more.

The recovery of livestock manure, rich in nutrients, as fertilizer in agriculture, could pose the risk of an excessive load of nitrogen on the soil. Ammonia stripping is one of the available technologies for reducing the amount of nitrogen in the digestate obtained by the anaerobic digestion of manure. The study investigated the performance and energy consumption of a full-scale ammonia-stripping plant, equipped with a bubble reactor and working without the use of any alkaline reagent under semi-batch conditions. Stripping tests were conducted on the liquid fraction of the digestate, studying the current and optimized operative conditions of the plant. The main variables influencing the process were pH, temperature, airflow, and feed characteristics. In the experimental tests, the pH spontaneously increased to 10, without dosing basifying agents. Higher temperatures favoured the stripping process, the higher tested value being 68 °C. The airflow was kept equal to 15 Nm³ h⁻¹ m⁻³_digestate in the pre-stripping and to 60 Nm³ h⁻¹ m⁻³_digestate in the stripping reactors, during all tests. The energy requirement was completely satisfied by the CHP (combined heat and power) unit fed with the biogas produced by manure digestion. Results showed anaerobic digestion coupled with stripping to be a suitable solution for removing up to 81% of the ammonium with neither external energy input nor reagent dosage. Full article

(This article belongs to the Special Issue From Waste to Energy: Anaerobic Digestion Technologies)

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Review

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23 pages, 1876 KiB

Open AccessFeature PaperReview

Biochar and Its Potential Application for the Improvement of the Anaerobic Digestion Process: A Critical Review

by Musa Manga, Christian Aragón-Briceño, Panagiotis Boutikos, Swaib Semiyaga, Omotunde Olabinjo and Chimdi C. Muoghalu

Energies 2023, 16(10), 4051; https://doi.org/10.3390/en16104051 - 12 May 2023

Cited by 14 | Viewed by 3580

Abstract

Poor management of organic waste is a key environmental and public health issue as it contributes to environmental contamination and the spread of diseases. Anaerobic digestion (AD) presents an efficient method for organic waste management while generating energy and nutrient-rich digestate. However, the [...] Read more.

Poor management of organic waste is a key environmental and public health issue as it contributes to environmental contamination and the spread of diseases. Anaerobic digestion (AD) presents an efficient method for organic waste management while generating energy and nutrient-rich digestate. However, the AD process is limited by key factors, which include process inefficiencies from substrate-induced instability, poor quality digestate, and poor management of effluent and emissions. Lately, there has been more interest in the use of biochar for improving anaerobic digestion. Biochar can improve methane production by speeding up the methanogenesis stage, protecting microorganisms from toxic shocks, and reducing inhibition from ammonia and volatile fatty acids. It can be applied for in situ cleanup of biogas to remove carbon dioxide. Applying biochar in AD is undergoing intensive research and development; however, there are still unresolved factors and challenges, such as the influence of feedstock source and pyrolysis on the performance of biochar when it is added to the AD process. In light of these considerations, this review sheds more light on various potential uses of biochar to complement or improve the AD process. This review also considers the mechanisms through which biochar enhances methane production rate, biochar’s influence on the resulting digestate, and areas for future research. Full article

(This article belongs to the Special Issue From Waste to Energy: Anaerobic Digestion Technologies)

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