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11 pages, 2219 KiB

Open AccessArticle

Experimental and Mathematical Investigation of Anaerobic Granulate Density via Settling Velocity

by Aljaž Klasinc, Gregor Drago Zupančič, Matjaž Hriberšek, Aleš Hribernik, Aleksandra Lobnik and Matej Zadravec

Processes 2022, 10(9), 1833; https://doi.org/10.3390/pr10091833 - 12 Sep 2022

Viewed by 1176

Abstract

The objective of this study was to determine the density of anaerobic granules on different heights of a full-scale Upflow Anaerobic Sludge Bed reactor. The density was defined through the settling velocities of anaerobic granules, measured in a full-scale Upflow Anaerobic Sludge Bed [...] Read more.

The objective of this study was to determine the density of anaerobic granules on different heights of a full-scale Upflow Anaerobic Sludge Bed reactor. The density was defined through the settling velocities of anaerobic granules, measured in a full-scale Upflow Anaerobic Sludge Bed reactor. In this study, granular density was calculated with the measured settling velocities and developed mathematical model. The developed mathematical model is based on the Stokes model. In the experiment, granules were taken from different heights of an Upflow Anaerobic Sludge Bed reactor, from 0.6 to 7.6 m. The granules’ diameters varied between 1 and 5 mm. The granules were taken from six different heights through the reactor. The settling velocity of the active granules (with gas in the granule pore and on the surface of the granule) was measured first. After the active granules’ settling velocity measurement, the granules were placed in a vortex to obtain degassed granules (granules without any gas in the pores or on the surface), for which the settling velocities were also measured later. It is shown that granules’ densities at different heights are independent of the reactor height. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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28 pages, 5616 KiB

Open AccessFeature PaperArticle

CFD Modelling of the Fuel Reactor of a Chemical Loping Combustion Plant to Be Used with Biomethane

by Pietro Bartocci, Alberto Abad, Arturo Cabello, Margarita de las Obras Loscertales, Wang Lu, Haiping Yang and Francesco Fantozzi

Processes 2022, 10(3), 588; https://doi.org/10.3390/pr10030588 - 17 Mar 2022

Cited by 4 | Viewed by 2121

Abstract

To realize a carbon negative power production technology, it is interesting the option of coupling a Chemical Loping Combustor to a gas turbine. The development of this technology foreseen in the project GTCLC-NEG has some technical barriers, the most important of which is [...] Read more.

To realize a carbon negative power production technology, it is interesting the option of coupling a Chemical Loping Combustor to a gas turbine. The development of this technology foreseen in the project GTCLC-NEG has some technical barriers, the most important of which is the operation of the chemical looping combustor at high temperature and high pressure conditions. To overcome these limits CFD modeling can be performed to optimize the behavior of the combustor and its design process. This work models the FUEL reactor of a chemical looping combustion plant working in batch mode and based on the reactor available at the Instituto de Carboquimica in Zaragoza, Spain. It is used an oxygen carrier mainly based on 60% mass Fe₂O₃ and 40% mass Al₂O₃. Biomethane is fed to the bottom of the fluidized bed with different velocities and mass flows and the composition of the gases at the outlet of the fuel reactor is measured. The results show that it is possible to model a 2 min duration reduction cycle by running the model for a time comprised between a minimum of 4 h and a maximum of 2 days of simulation. Another important result is the modeling of the chemical reactions happening in the reactor. Kinetics is modelled based on Activation energy (66 kJ/mol) and Pre-exponential factor (4.34 × 10¹ m³ⁿ mol⁻ⁿ s⁻¹). The simple kinetic scheme gives reasonable first approximations and can be used to determine the duration of the reaction, the composition of the exhaust gases and the biofuel conversion. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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16 pages, 4039 KiB

Open AccessArticle

Evaluation of the Removal of Organic Matter and Nutrients in the Co-Treatment of Fruit and Vegetable Waste Using a Bioreactor-Constructed Wetlands System

by Francisco Orduña-Gaytán, Norma A. Vallejo-Cantú, Andrea Alvarado-Vallejo, Erik Samuel Rosas-Mendoza, Luis Carlos Sandoval-Herazo and Alejandro Alvarado-Lassman

Processes 2022, 10(2), 278; https://doi.org/10.3390/pr10020278 - 30 Jan 2022

Cited by 4 | Viewed by 2819

Abstract

This article presents the application of a novel system for the treatment of fruit and vegetable waste (FVW) using the combination of treatment by the application of the liquid fraction to an anaerobic hydrolytic bioreactor and a constructed wetland. The batch-fed anaerobic bioreactor [...] Read more.

This article presents the application of a novel system for the treatment of fruit and vegetable waste (FVW) using the combination of treatment by the application of the liquid fraction to an anaerobic hydrolytic bioreactor and a constructed wetland. The batch-fed anaerobic bioreactor (AB) had an average organic loading rate of 44 g COD/L-d and a hydraulic residence time (HRT) of 24 h for the degradation of the liquid fraction of the FVW with an average COD removal of 55%. Subsequently, the constructed wetlands (CWs) were fed a subsurface vertical flow of the effluent from the AB by stepwise concentration increments from 1 to 12 g COD/L and a HRT = 72 h until the limit conditions of the operation were identified. For the tropical ornamental species of the CWs in red volcanic gravel (RVG) and RVG + polyethylene (PE) supports, the monoculture of Hippeastrum rutilum and Spathiphyllum wallisii presented removals of COD, Tot-P, and TKN of 90%, 80%, and 85%, respectively. The polycultures with both species exceeded 90% effectiveness. At the end of both processes, a concentration of ~0.5 g COD/L was achieved, confirming that the use of these technologies together constitutes an efficient system for the treatment of the liquid fraction of FVW. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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14 pages, 1648 KiB

Open AccessArticle

Dry Mesophilic Anaerobic Digestion of Separately Collected Organic Fraction of Municipal Solid Waste: Two-Year Experience in an Industrial-Scale Plant

by Adolfo Le Pera, Miriam Sellaro, Massimo Migliori, Micaela Bianco and Giuseppe Zanardi

Processes 2021, 9(2), 213; https://doi.org/10.3390/pr9020213 - 24 Jan 2021

Cited by 10 | Viewed by 2414

Abstract

In this paper, performance analysis over two years’ operation of an industrial anaerobic digestion (AD) plant of a separately collected organic fraction of municipal solid waste is presented. The continuous plug-flow AD plant is still regularly operating and it has been fully operational [...] Read more.

In this paper, performance analysis over two years’ operation of an industrial anaerobic digestion (AD) plant of a separately collected organic fraction of municipal solid waste is presented. The continuous plug-flow AD plant is still regularly operating and it has been fully operational since September 2018. Since then, it has been supplied with 40,000 t/y of pretreated separately collected organic fraction of municipal solid waste from municipalities of the Calabria region in Southern Italy. The AD process is carried out in a mesophilic regime at 40 ± 0.5 °C, using a constant hydraulic retention time (HRT) of 22 days and a substrate with average total solids and average total volatile solids of 30.0% and 22.2%, respectively. In the last two years, the plant produced an average of 191 m³ and 860 m³ of biogas per tonne (t) of organic input material and of total volatile solids, respectively, with an average methane specific production of 508 m³/t (total volatile solids). The average CH₄ percentage in the biogas was of 59.09%. The obtained results came out from the combination of high organic content of separately collected organic fraction of municipal solid waste, optimized pretreatment system and operating conditions adopted. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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11 pages, 3143 KiB

Open AccessFeature PaperArticle

Stabilization of Anaerobic Co-Digestion Process via Constant the Digestate Solids Content

by Risu Na, Keisuke Uchitani, Kazuto Yoshida and Naoto Shimizu

Processes 2021, 9(2), 197; https://doi.org/10.3390/pr9020197 - 21 Jan 2021

Cited by 2 | Viewed by 2829

Abstract

The process instability of anaerobic digestion (AD) is a common issue and may result in underperformance or short-term process failure. Extensive research has shown that total solids (TS) content in AD has a significant impact on system stability and performance. However, no study [...] Read more.

The process instability of anaerobic digestion (AD) is a common issue and may result in underperformance or short-term process failure. Extensive research has shown that total solids (TS) content in AD has a significant impact on system stability and performance. However, no study has examined the feasibility of stabilizing the AD process by maintaining constant TS content in the digestate. In this study, an innovative control approach based on constant TS content in the digestate during AD was developed using a mass balance equation. Two levels of TS content (desired values of 4% wet basis (w.b.) and 6% w.b.) were compared with conventional control. The process stability was examined by monitoring digestate components and pH. Substrate-specific methane yield (m³ CH₄/kg VS) was used to assess the effectiveness of the controlled conditions. The results showed that the digestate TS content during AD can be controlled and that the digestion process can be stabilized by controlled conditions. In addition, constant TS in the digestate (within 1% w.b. of the desired level) gave increased levels of biogas production (10.2%), methane (13.5%), and substrate-specific methane yield (43.3%) at 4% TS, and respective increases of 16.6%, 21.2%, and 20.8% at 6% TS when compared with standard operation. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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16 pages, 1852 KiB

Open AccessFeature PaperArticle

Biomethanation Potential (BMP) Study of Mesophilic Anaerobic Co-Digestion of Abundant Bio-Wastes in Southern Regions of Tunisia

by Mawaheb Mouftahi, Nawel Tlili, Nejib Hidouri, Pietro Bartocci, Khalideh Al bkoor Alrawashdeh, Eid Gul, Federica Liberti and Francesco Fantozzi

Processes 2021, 9(1), 48; https://doi.org/10.3390/pr9010048 - 29 Dec 2020

Cited by 15 | Viewed by 3374

Abstract

Tunisia is a country that suffers from energy demand problems and environmental matters. Thus, Tunisian authorities desire to encourage the development of renewable energy sources, especially from biological processes, like anaerobic digestion. Therefore, this study is focused on the evaluation of biogas and [...] Read more.

Tunisia is a country that suffers from energy demand problems and environmental matters. Thus, Tunisian authorities desire to encourage the development of renewable energy sources, especially from biological processes, like anaerobic digestion. Therefore, this study is focused on the evaluation of biogas and bio-methane yield from the co-digestion of three available and abundant bio-wastes in the southern regions of Tunisia. The three different raw materials are an organic fraction of municipal solid waste, chicken manure, and olive mill wastewater. In this context, experimental work to evaluate the potential of biogas and bio-methane production was carried out at mesophilic temperature 35 °C and batch mode. The present work highlights the possibility of generating biogas from these organic wastes and reducing the amounts of the wastes to dispose of in landfills. The experimental study of the co-digestion process under specific conditions of carbon to nitrogen ratio (C/N), T, pH, and inoculums to substrate ratio ISR provided a high yield of net methane and net biogas, in comparison with other research works. Results showed a higher specific net methane production per kg of volatile solids, which is equal to 0.338 Nm³ methane/kg VS and 0.430 Nm³ methane/kg VS for two studied cases. The obtained volatile solids reduction was found to be 91% of the initial content, for a hydraulic retention time (HRT) of 40 days. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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14 pages, 2323 KiB

Open AccessArticle

Effect of Heavy Metals in the Performance of Anaerobic Digestion of Olive Mill Waste

by Khalideh Al bkoor Alrawashdeh, Eid Gul, Qing Yang, Haiping Yang, Pietro Bartocci and Francesco Fantozzi

Processes 2020, 8(9), 1146; https://doi.org/10.3390/pr8091146 - 14 Sep 2020

Cited by 27 | Viewed by 4210

Abstract

This study presents an investigation on the effect of heavy metals on the production of biogas during the process of anaerobic digestion (AD) of olive mill waste (OMW). The poisonous effect and the inhibitory influence of Fe, Ni, Pb, Zn, Cu, and Cr [...] Read more.

This study presents an investigation on the effect of heavy metals on the production of biogas during the process of anaerobic digestion (AD) of olive mill waste (OMW). The poisonous effect and the inhibitory influence of Fe, Ni, Pb, Zn, Cu, and Cr on the digestion process are investigated and determined. Biomethanation potential tests are performed for this sake. Adding some of the heavy metals to the AD decreases the efficiency of biogas production and methane concentration and decreases the reduction in the VS, the TCOD, the SCOD, and the organic acid load. A critical increase in the total organic acid and inhibition of methanogenic bacteria was observed due to its toxicity. The toxicity of the heavy metals can be arranged according to increasing order: Cu > Ni > Pb > Cr > Zn > Fe, which leads to rapid poisoning of the active microorganisms. Iron may also exhibit stimulatory effects, but with a low rate and at a certain level. The conclusions of this work are important for the industry and help to understand how to carefully manage the presence of heavy metals in the digestate. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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23 pages, 1953 KiB

Open AccessArticle

New Insights on the Estimation of the Anaerobic Biodegradability of Plant Material: Identifying Valuable Plants for Sustainable Energy Production

by Claudia P. Pabón-Pereira, H. V. M. Hamelers, Irene Matilla and Jules B. van Lier

Processes 2020, 8(7), 806; https://doi.org/10.3390/pr8070806 - 09 Jul 2020

Cited by 8 | Viewed by 2380

Abstract

Based on fifteen European plant species, a statistical model for the estimation of the anaerobic biodegradability of plant material was developed. We show that this new approach represents an accurate and cost-effective method to identify valuable energy plants for sustainable energy production. In [...] Read more.

Based on fifteen European plant species, a statistical model for the estimation of the anaerobic biodegradability of plant material was developed. We show that this new approach represents an accurate and cost-effective method to identify valuable energy plants for sustainable energy production. In particular, anaerobic biodegradability (B_o) of lignocellulosic material was empirically found to be related to the amount of cellulose plus lignin, as analytically assessed by the van Soest method, i.e., the acid detergent fiber (ADF) value. Apart from being theoretically meaningful, the ADF-based empirical model requires the least effort compared to the other four proposed conceptual models proposed, as individual fractions of cellulose, hemicellulose, and lignin do not need to be assessed, which also enhances the predictive accuracy of the model’s estimation. The model’s results showed great predictability power, allowing us to identify interesting crops for sustainable crop rotations. Finally, the model was used to predict B_o of 114 European plant samples that had been previously characterized by means of the van Soest method. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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11 pages, 2105 KiB

Open AccessFeature PaperArticle

Greening the Gas Grid—Evaluation of the Biomethane Injection Potential from Agricultural Residues in Austria

by Bernhard Stürmer

Processes 2020, 8(5), 630; https://doi.org/10.3390/pr8050630 - 24 May 2020

Cited by 7 | Viewed by 4348

Abstract

In order to implement the Paris Climate Agreement, the current Austrian coalition government has included trend-setting targets in its policy statement. “Green gas” plays a key role in this context, as the natural gas grid shall also gradually become renewable. This article analyses [...] Read more.

In order to implement the Paris Climate Agreement, the current Austrian coalition government has included trend-setting targets in its policy statement. “Green gas” plays a key role in this context, as the natural gas grid shall also gradually become renewable. This article analyses the technical biomethane injection potential for agricultural residues based on Integrated Administration and Control System (IACS) data on a municipal level. While a technical biogas potential of 16.2 TWh_CH4 from catch crops, farm manure, straw and beet leaves is available, only about half of it can be fed into the gas grid because of technical and economic reasons. Austria’s biomethane injection potential of 7.4 TWh_CH4 is mainly produced in arable farming regions. In order to further increase this potential, the investment costs of biogas upgrading plants must be reduced, the use of biogenic waste and energy crops must be further promoted and an investor-friendly legal framework must be created. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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27 pages, 4925 KiB

Open AccessArticle

Optimisation and Modelling of Anaerobic Digestion of Whiskey Distillery/Brewery Wastes after Combined Chemical and Mechanical Pre-Treatment

by Burcu Gunes, Maxime Carrié, Khaled Benyounis, Joseph Stokes, Paul Davis, Cathal Connolly and Jenny Lawler

Processes 2020, 8(4), 492; https://doi.org/10.3390/pr8040492 - 23 Apr 2020

Cited by 18 | Viewed by 4850

Abstract

Whiskey distillery waste streams consisting of pot ale (liquid residue) and spent grain (solid residue) are high strength organic wastes and suitable feedstock for anaerobic digestion (AD) from both economic and environmental stand points. Anaerobic digestion of pot ale and pot ale/spent grain [...] Read more.

Whiskey distillery waste streams consisting of pot ale (liquid residue) and spent grain (solid residue) are high strength organic wastes and suitable feedstock for anaerobic digestion (AD) from both economic and environmental stand points. Anaerobic digestion of pot ale and pot ale/spent grain mixtures (with mixing ratios of 1:1, 1:3, and 1:5 by wet weight) was performed after implementation of a novel hybrid pre-treatment (combined chemical and mechanical) in order to modify lignocellulosic structure and ultimately enhance digestion yield. Lignin, hemicellulose, and cellulose fractions were determined before and after chemical pre-treatment. Effects of different inoculum rates (10–30–50% on wet basis) and beating times (0–7.5–15 min) on anaerobic digestion of pot ale alone and of pot ale/spent grain mixtures were investigated in lab scale batch mode with a major focus of optimising biogas yield by using response surface methodology (RSM) in Design Expert Software. The highest biogas yields of 629 ± 8.5 mL/g vs. (51.3% CH₄) and 360 ± 10 mL/g vs. (55.0 ± 0.4) with anaerobic digestion of pot ale alone and spent grain mix after 1M NaOH and 7.5 min beating pre-treatments with 50% inoculum ratio respectively. The optimum digestion conditions to maximise the biogas quality and quantity were predicted as 10 and 13 min beating times and 32 and 38 °C digestion temperatures for anaerobic digestion of pot ale alone and spent grain mix respectively. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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13 pages, 1375 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Biodrying of the Light Fraction from Anaerobic Digestion Pretreatment in Order to Increase the Total Recovery Rate

by Isabella Pecorini, Donata Bacchi and Renato Iannelli

Processes 2020, 8(3), 276; https://doi.org/10.3390/pr8030276 - 28 Feb 2020

Cited by 3 | Viewed by 3650

Abstract

Two pilot-scale tests were carried out to assess if biodrying could be an effective process for the treatment of light fraction produced by an hydromechanical pre-treatment in an anaerobic digestion plant. The trials were performed using two pilot-scale stainless steel cylindrical reactors of [...] Read more.

Two pilot-scale tests were carried out to assess if biodrying could be an effective process for the treatment of light fraction produced by an hydromechanical pre-treatment in an anaerobic digestion plant. The trials were performed using two pilot-scale stainless steel cylindrical reactors of 750 L capacity. Two tests were performed: in Test 1, only the light fraction was used; in Test 2, the light fraction was mixed with a bulking agent composed of garden and pruning waste. In Test 2, the highest temperature (71 °C) in a short time (8 days) was reached. An average water content reduction of 78% in Test 1 and 61% in Test 2 was measured, leading to similar reductions of weight (47–48%) and volume (27–29%). A high biological stability was measured on the final light fraction samples collected from both the tests. Furthermore, the lower heating value obtained after the biodrying treatment complies with the quality specification of the European standard on refuse-derived fuels. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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15 pages, 2092 KiB

Open AccessArticle

Feasibility Assessment of Two Biogas-Linked Rural Campus Systems: A Techno-Economic Case Study

by Liqin Zhu and Congguang Zhang

Processes 2020, 8(2), 180; https://doi.org/10.3390/pr8020180 - 05 Feb 2020

Cited by 1 | Viewed by 2649

Abstract

The principle of sustainable development is becoming more and more prominent in various schools, and the eco-campus in rural areas often has more room for display. The identification and assessment of cost-effective biomass resources appropriate for recycling represent an opportunity that may significantly [...] Read more.

The principle of sustainable development is becoming more and more prominent in various schools, and the eco-campus in rural areas often has more room for display. The identification and assessment of cost-effective biomass resources appropriate for recycling represent an opportunity that may significantly improve the comprehensive efficiency of an eco-campus system, resulting in remarkable investment savings, pollution reduction, as well as reducing energy consumption and resources waste. The economic feasibility of two biogas-linked rural campus systems (Fanjiazhai Middle School, FJZ and Xidazhai Middle School, XDZ, Yangling, China), as well as their key technologies, is investigated, the two systems respectively represent two biobased agricultural production modes. It is found that the initial investment, operating investment, and total revenue of FJZ system is 1.37 times, 2.39 times, and 1.71 times of XDZ system respectively, thus indicating that FJZ campus is proved to be a “larger” system compared to the other one. The operating costs show that reasonable control of labor and transportation costs should be carried out to optimize the economic feasibility of the system. After considering the system’s economic credits obtained from using biogas slurry flushing system and avoiding waste management, the net present value of XDZ system had increased to its 1.5 times, while the FJZ system had increased to its 135%. From the perspective of revenue to investment ratio, XDZ system has a better profit earning efficiency compared to FJZ system. The sensitivity analysis indicates that biogas price, fruit yield, labor use are main factors that have the greatest impacts on the economic performance of these eco-campuses. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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15 pages, 2810 KiB

Open AccessFeature PaperArticle

Anaerobic Digestate Treatment Selection Model for Biogas Plant Costs and Emissions Reduction

by Dinko Đurđević and Ivona Hulenić

Processes 2020, 8(2), 142; https://doi.org/10.3390/pr8020142 - 22 Jan 2020

Cited by 16 | Viewed by 6343

Abstract

Agriculture is one of the leading sectors on the global level contributing to greenhouse gas (GHG) emissions increase. With the utilization of biogas production technology within the agriculture sector, ecological benefits could be achieved, with immediate economic profit. Therefore, to retain economic profit [...] Read more.

Agriculture is one of the leading sectors on the global level contributing to greenhouse gas (GHG) emissions increase. With the utilization of biogas production technology within the agriculture sector, ecological benefits could be achieved, with immediate economic profit. Therefore, to retain economic profit and environmental sustainability, implementation of bioeconomy principles is of key importance. This paper examines four options of digestate treatment, which is identified as one of the highest operational cost for the biogas plant. A simple and robust model in Excel Solver was developed to determine the best solution for minimising GHG emissions and maximise profit for the biogas plant operator, through an upgrade of the plant with digestate treatment technologies. The model was implemented on a case of a Croatian biogas plant and the best solution in terms of GHG reduction and profit increase proved to be fertilizer production (Option 1), through a crystallization process of struvite within the digestate. This option obtains a significant reduction in GHG emissions compared to standard biogas production without additional upgrades (Option 4), by over 90%, and increase of profit for the biogas plant operator, which diversifies the income source and creates multiple positive impacts on the environment. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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12 pages, 2206 KiB

Open AccessArticle

Electrical Conductivity for Monitoring the Expansion of the Support Material in an Anaerobic Biofilm Reactor

by Oscar Marín-Peña, Alejandro Alvarado-Lassman, Norma A. Vallejo-Cantú, Isaías Juárez-Barojas, José Pastor Rodríguez-Jarquín and Albino Martínez-Sibaja

Processes 2020, 8(1), 77; https://doi.org/10.3390/pr8010077 - 07 Jan 2020

Cited by 11 | Viewed by 3476

Abstract

This article describes the use of the electrical conductivity for measuring bed expansion in a continuous anaerobic biofilm reactor in order to prevent the exit of support material from the reactor with the consequent loss of biomass. The substrate used for the tests [...] Read more.

This article describes the use of the electrical conductivity for measuring bed expansion in a continuous anaerobic biofilm reactor in order to prevent the exit of support material from the reactor with the consequent loss of biomass. The substrate used for the tests is obtained from a two-stage anaerobic digestion (AD) process at the pilot scale that treats the liquid fraction of fruit and vegetable waste (FVW). Tests were performed with the raw substrate before anaerobic treatment (S1), the effluent from the hydrolysis reactor (S2), and the effluent from the methanogenic reactor (S3) to evaluate its effect on the electrical conductivity values and its interaction with colonized support material. The tests were carried out in a 32 L anaerobic inverse fluidized bed reactor (IFBR), which was inoculated with colonized support material and using two industrial electrodes at different column positions. The results with the previously digested samples (S2 and S3) were satisfactory to detect the presence of support material at the points where the electrodes were placed since the electrical conductivity values showed significant changes of up to 0.5 V, while with substrate S1 no significant voltage differences were appreciated. These results demonstrate that electrical conductivity can be used as an economic and simple mean for monitoring the support material expansion in order to avoid over expansion in the IFBR. It was also demonstrated that the conditions of the substrate in the methanogenic stage (pH and presence of volatile fatty acids) do not affect the operation of the electrical conductivity detection system. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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13 pages, 1451 KiB

Open AccessFeature PaperArticle

Numerical Comparison of a Combined Hydrothermal Carbonization and Anaerobic Digestion System with Direct Combustion of Biomass for Power Production

by Mohammad Heidari, Shakirudeen Salaudeen, Omid Norouzi, Bishnu Acharya and Animesh Dutta

Processes 2020, 8(1), 43; https://doi.org/10.3390/pr8010043 - 01 Jan 2020

Cited by 28 | Viewed by 3757

Abstract

Two of the methods for converting biomass to fuel are hydrothermal carbonization (HTC) and anaerobic digestion (AD). This study is aimed at designing and analyzing two scenarios for bioenergy production from undervalued biomass (sawdust). In one of the scenarios (direct combustion or DC), [...] Read more.

Two of the methods for converting biomass to fuel are hydrothermal carbonization (HTC) and anaerobic digestion (AD). This study is aimed at designing and analyzing two scenarios for bioenergy production from undervalued biomass (sawdust). In one of the scenarios (direct combustion or DC), raw biomass is burned in a combustor to provide the heat that is required by the Rankine cycle to generate electricity. In the other scenario (HTC-AD), the raw biomass first undergoes HTC treatment. While the solid product (hydrochar) is used to produce power by a Rankine cycle, the liquid by-product undergoes an AD process. This results in fuel gas production and it can be used in a Brayton cycle to generate more power. Energy and mass balance analysis of both scenarios were developed for each unit process by using Engineering Equation Solver (EES). The required data were obtained experimentally or from the literature. The performances of the proposed systems were evaluated, and a sensitivity analysis was presented to help in finding the best operational conditions. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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14 pages, 4677 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

An Incubation System to Enhance Biogas and Methane Production: A Case Study of an Existing Biogas Plant in Umbria, Italy

by Federica Liberti, Valentina Pistolesi, Mawaheb Mouftahi, Nejib Hidouri, Pietro Bartocci, Sara Massoli, Mauro Zampilli and Francesco Fantozzi

Processes 2019, 7(12), 925; https://doi.org/10.3390/pr7120925 - 04 Dec 2019

Cited by 14 | Viewed by 4767

Abstract

The pre-incubation of digestate and recycling of microbes inside a continuously stirred tank reactor (CSTR) are effective ways to optimize the anaerobic digestion process and improve the performance of biogas and methane production, also in existing biogas plants. In this study, a digestate [...] Read more.

The pre-incubation of digestate and recycling of microbes inside a continuously stirred tank reactor (CSTR) are effective ways to optimize the anaerobic digestion process and improve the performance of biogas and methane production, also in existing biogas plants. In this study, a digestate incubation system using a nutrient mix to boost the activity of microbes was coupled to a CSTR to boost biogas and methane production. This system has been tested both on a lab scale and on an industrial scale. On a pilot scale, the system achieved an increase of +16.47 v% in biogas production with respect to the conventional anaerobic digestion process, and an increase of +2 v% in methane content (from 65.94 v% to 67.84 v%). On an industrial scale, the use of this incubation reactor with a capacity of 1 m³ has led to an increase in methane yield of 12 v%. This system allows to maintain the syntrophic relationship between acid-producing bacteria and methanogens and contemporary push the development of methanogens. Moreover, it is an economic system to be integrated into an existing biogas plant given the small volume and the simplicity of the incubation reactor. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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14 pages, 1900 KiB

Open AccessFeature PaperArticle

A Comparative Study of Biogas Reactor Fluid Rheology—Implications for Mixing Profile and Power Demand

by Luka Šafarič, Sepehr Shakeri Yekta, Jörgen Ejlertsson, Mohammad Safari, Hossein Nadali Najafabadi, Anna Karlsson, Francesco Ometto, Bo H. Svensson and Annika Björn

Processes 2019, 7(10), 700; https://doi.org/10.3390/pr7100700 - 03 Oct 2019

Cited by 8 | Viewed by 2877

Abstract

Anaerobic digestion (AD) is an established process for integrating waste management with renewable energy and nutrient recovery. Much of the research in this field focuses on the utilisation of new substrates, yet their effects on operational aspects such as fluid behaviour and power [...] Read more.

Anaerobic digestion (AD) is an established process for integrating waste management with renewable energy and nutrient recovery. Much of the research in this field focuses on the utilisation of new substrates, yet their effects on operational aspects such as fluid behaviour and power requirement for mixing are commonly overlooked, despite their importance for process optimisation. This study analysed rheological characteristics of samples from 21 laboratory-scale continuous stirred-tank biogas reactors (CSTBRs) digesting a range of substrates, in order to evaluate substrate effect on mixing efficiency and power demand through computational fluid dynamics (CFD). The results show that substrate and process parameters, such as solids content and organic loading, all have a significant effect on CSTBR fluid rheology. The correlation levels between rheological and process parameters were different across substrates, while no specific fluid behaviour patterns could be associated with substrate choice. Substrate should thus be considered an equally important rheology effector as process parameters. Additional substrate-related parameters should be identified to explain the differences in correlations between rheological and process parameters across substrate groups. The CFD modelling revealed that the rheology differences among the AD processes have significant implications for mixing efficiency and power demand of the CSTBRs, highlighting the importance of considering the substrate-induced effects on CSTBR rheology before including a new substrate. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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18 pages, 2557 KiB

Open AccessFeature PaperArticle

Biogas Generation through Anaerobic Digestion of Compost Leachate in Semi-Continuous Completely Stirred Tank Reactors

by Alessio Siciliano, Carlo Limonti, Giulia Maria Curcio and Vincenza Calabrò

Processes 2019, 7(9), 635; https://doi.org/10.3390/pr7090635 - 18 Sep 2019

Cited by 24 | Viewed by 5315

Abstract

The composting process of organic fraction of municipal solid waste, besides to the residual compost, generates a wastewater that is characterized by a high organic load. The application of anaerobic processes represents an advantageous solution for the treatment and valorization of this type [...] Read more.

The composting process of organic fraction of municipal solid waste, besides to the residual compost, generates a wastewater that is characterized by a high organic load. The application of anaerobic processes represents an advantageous solution for the treatment and valorization of this type of wastewater. Nevertheless, few works have been focused on the anaerobic digestion of compost leachate. To overcome this dearth, in the present paper an extensive experimental investigation was carried out to develop and analyse the anaerobic treatment of young leachate in completely stirred tank reactors (CSTR). Initially, it was defined a suitable leachate pretreatment to correct its acidic characteristics that is potentially able to inhibit methanogenic biomass activity. The pretreated leachate was fed to the digester over the start-up phase that was completed in about 40 days. During the operational period, the organic load rate (OLR) changed between 4.25 kg_COD/m³d and 38.5 kg_COD/m³d. The chemical oxygen demand (COD) abatement was higher than 90% for OLR values up to 14.5 kg_COD/m³d and around to 80% for applied loads equal to 24.5 kg_COD/m³d. At this OLR, it was reached the maximum daily biogas production of about 9.3 L_biogas/(L_reactord). The CH₄ fraction was between 70%–78% and the methane production yield in the range 0.34–0.38 L_CH₄/g_CODremoved. The deterioration of biogas production started for OLR values that were over the threshold of 24.5 kg_COD/m³d when a volatile fatty acids (VFA) accumulation occurred and the pH dropped below 6.5. The maximum ratio between VFA and alkalinity (ALK) tolerable in the CSTR was identified to be 0.5 g_CH₃COOH/g_CaCO₃. Through an economic analysis, it was proven that the digestion of compost leachate could ensure significant economic profits. Furthermore, the produced digestate had characteristics that were compatible for agricultural applications. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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Review

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22 pages, 2281 KiB

Open AccessReview

Markers for the Comparison of the Performances of Anoxic Biotrickling Filters in Biogas Desulphurisation: A Critical Review

by Emky Valdebenito-Rolack, Rosario Díaz, Felipe Marín, Daniel Gómez and Felipe Hansen

Processes 2021, 9(3), 567; https://doi.org/10.3390/pr9030567 - 23 Mar 2021

Cited by 6 | Viewed by 2787

Abstract

The agriculture and livestock industry generate waste used in anaerobic digestion to produce biogas containing methane (CH₄), useful in the generation of electricity and heat. However, although biogas is mainly composed of CH₄ (~65%) and CO₂ (~34%), among the [...] Read more.

The agriculture and livestock industry generate waste used in anaerobic digestion to produce biogas containing methane (CH₄), useful in the generation of electricity and heat. However, although biogas is mainly composed of CH₄ (~65%) and CO₂ (~34%), among the 1% of other compounds present is hydrogen sulphide (H₂S) which deteriorates engines and power generation fuel cells that use biogas, generating a foul smell and contaminating the environment. As a solution to this, anoxic biofiltration, specifically with biotrickling filters (BTFs), stands out in terms of the elimination of H₂S as it is cost-effective, efficient, and more environmentally friendly than chemical solutions. Research on the topic is uneven in terms of presenting performance markers, underestimating many microbiological indicators. Research from the last decade was analyzed (2010–2020), demonstrating that only 56% of the reviewed publications did not report microbiological analysis related to sulphur oxidising bacteria (SOB), the most important microbial group in desulphurisation BTFs. This exposes fundamental deficiencies within this type of research and difficulties in comparing performance between research works. In this review, traditional and microbiological performance markers of anoxic biofiltration to remove H₂S are described. Additionally, an analysis to assess the efficiency of anoxic BTFs for biogas desulphurisation is proposed in order to have a complete and uniform assessment for research in this field. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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13 pages, 228 KiB

Open AccessReview

Life Cycle Assessment and Economic Analysis of Biomass Energy Technology in China: A Brief Review

by Shuangyin Chen, He Feng, Jun Zheng, Jianguo Ye, Yi Song, Haiping Yang and Ming Zhou

Processes 2020, 8(9), 1112; https://doi.org/10.3390/pr8091112 - 07 Sep 2020

Cited by 34 | Viewed by 5677

Abstract

This study describes the technological processes and characteristics of biomass direct combustion power generation, biomass gasification power generation, biomass mixed combustion power generation, and biomass biogas power generation in terms of their importance and application in China. Under the perspective of environmental and [...] Read more.

This study describes the technological processes and characteristics of biomass direct combustion power generation, biomass gasification power generation, biomass mixed combustion power generation, and biomass biogas power generation in terms of their importance and application in China. Under the perspective of environmental and economic sustainability, the life cycle assessment (LCA) method and dynamic analysis method based on time value are used to simulate and evaluate the environmental loads and economic benefits of different power generation processes. By comparing with coal-fired power generation systems, the environmental and economic benefits of different biomass power generation technologies are illustrated. The results shows that biomass gasification power generation has the best environmental benefits, with a total load of 1.05 × 10⁻⁵, followed by biomass biogas power generation (9.21 × 10⁻⁵), biomass direct combustion power generation (1.23 × 10⁻⁴), and biomass mixed combustion power generation (3.88 × 10⁻⁴). Compared with the environmental load of coal-fired power generation, the reduction rate was 97.69%, 79.69%, 72.87%, and 14.56% respectively. According to the analysis of the technical economy evaluation results, when the dynamic pay-back period and IRR (internal rate of return) were used as evaluation indicators, the biomass direct combustion power generation has the best pay-back period (7.71 years) and IRR (19.16%), followed by the biogas power generation, with higher dynamic payback period (12.03 years), and lower IRR (13.49%). For gasification power generation and mixed-combustion power generation, their dynamic payback period is long, and the IRR is low. If net present value (NPV) is selected as the evaluation index, the biogas power generation appears to be the best because its net present value per megawatt is 11.94 million yuan, followed by direct combustion power generation (6.09 million yuan), and the net present value of mixed-combustion power generation and gasification power generation is relatively low. Compared with coal-fired power generation, direct combustion power generation and biogas power generation present significant economic benefits. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

26 pages, 2262 KiB

Open AccessReview

Approaches in Design of Laboratory-Scale UASB Reactors

by Yehor Pererva, Charles D. Miller and Ronald C. Sims

Processes 2020, 8(6), 734; https://doi.org/10.3390/pr8060734 - 24 Jun 2020

Cited by 11 | Viewed by 9948

Abstract

Up-flow Anaerobic Sludge Blanket (UASB) reactors are popular tools in wastewater treatment systems due to the ability to work with high feed rates and wastes with high concentration of organic contaminants. While full-scale industrial applications of UASB reactors are developed and described in [...] Read more.

Up-flow Anaerobic Sludge Blanket (UASB) reactors are popular tools in wastewater treatment systems due to the ability to work with high feed rates and wastes with high concentration of organic contaminants. While full-scale industrial applications of UASB reactors are developed and described in the available literature, laboratory-scale designs utilized for treatability testing are not well described. The majority of published studies do not describe the laboratory UASB construction details or do use reactors that already had developed a trophic network in microbial consortia under laboratory environment and therefore are more stable. The absence of defined guidelines for geometry design, selection of materials, construction, operation rules, and, especially, the start-up conditions, significantly hamper researchers who desire to conduct treatability testing using UASB reactors in laboratory scale. In this article, we compiled and analyzed the information available in the refereed literature concerning UASB reactors used in laboratory environment, where information on geometry and/or operational conditions were provided in detail. We utilized the information available in the literature and the experience gained in our laboratory (Sustainable Waste to Bioproducts Engineering Center) to suggest a unified operation flowchart and for design, construction, operation, and monitoring for a laboratory-scale UASB reactors. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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12 pages, 501 KiB

Open AccessFeature PaperReview

Review of Anaerobic Digestion Modeling and Optimization Using Nature-Inspired Techniques

by Anjali Ramachandran, Rabee Rustum and Adebayo J. Adeloye

Processes 2019, 7(12), 953; https://doi.org/10.3390/pr7120953 - 13 Dec 2019

Cited by 44 | Viewed by 6320

Abstract

Although it is a well-researched topic, the complexity, time for process stabilization, and economic factors related to anaerobic digestion call for simulation of the process offline with the help of computer models. Nature-inspired techniques are a recently developed branch of artificial intelligence wherein [...] Read more.

Although it is a well-researched topic, the complexity, time for process stabilization, and economic factors related to anaerobic digestion call for simulation of the process offline with the help of computer models. Nature-inspired techniques are a recently developed branch of artificial intelligence wherein knowledge is transferred from natural systems to engineered systems. For soft computing applications, nature-inspired techniques have several advantages, including scope for parallel computing, dynamic behavior, and self-organization. This paper presents a comprehensive review of such techniques and their application in anaerobic digestion modeling. We compiled and synthetized the literature on the applications of nature-inspired techniques applied to anaerobic digestion. These techniques provide a balance between diversity and speed of arrival at the optimal solution, which has stimulated their use in anaerobic digestion modeling. Full article

(This article belongs to the Special Issue Current Trends in Anaerobic Digestion Processes)

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