One-stage Anaerobic Digestion Research Articles

Benchmarking composting, anaerobic digestion and dark fermentation for apple vinasse management as a strategy for sustainable energy production

Looking for renewable energy sources is one of the main targets in the transition to low-carbon economies. Bioenergy appears as an alternative with great potential, but firstly, it requires addressing all aspects that can limit its environmental viability. Stillage has been identified as an environmental concern of the bioethanol production. Thus, eco-friendly strategies for valorizing this resource should be pursued. In this work, three strategies such as composting (non-energy valorization), one-stage anaerobic digestion (with the aim of biogas production), and dark fermentation followed by anaerobic digestion (scheme under development to produce biohydrogen and biogas) were evaluated under a life-cycle perspective; and through process modeling based on literature data. The aim is to identify the advantages and disadvantages of dark fermentation for the management of apple stillage. To do this, a cradle-to-gate and attributional framework were followed, considering impact and damage perspectives. Results showed a very significant environmental load (around 99%) of composting compared to the selected energy recovery schemes, considering the added value of compost and the associated emissions versus those of biofuels. Otherwise, small differences were found between single-stage anaerobic digestion and dark fermentation (up to 16%), mainly, due to changes in chemical consumption and organic matter degradation efficiency.

Anaerobic co-digestion of agricultural residues produced in Southern Greece during the spring/summer season

Anaerobic digestion (AD) is a well-known environmentally friendly technology, that even though has been investigated extensively, in Greece there is still a lack of experimental knowledge on locally available substrates’ valorisation. This study aimed to assess a continuous one-stage AD system for the valorization of Southern Greece’s spring/summer residual biomass. The most suitable substrate in Southern Greece during the spring/summer season is 10% corn silage, 14% cattle manure, 66% unsuitable for human consumption watermelons, and 10% tomato processing residues, in terms of methane yield maximization during anaerobic co-digestion. Regarding the system operational conditions, the hydraulic retention time (HRT) was set at 20 d, while the initial organic loading rate (OLR) of 2 g COD/(L·d) was applied, which was increased gradually, up to 7 g COD/(L·d). The reactor operated successfully for the applied OLRs 2–5 g COD/(L·d), while a further increase led to inhibition phenomena. Even if propionate accumulated up to 5 g/L, it successfully coped with the correction of alkalinity levels (up to 6.4 g CaCO3/L). The system’s efficient operation paves the way for residual biomass treatment in one-stage systems, without substrate dilution, at high OLRs, that can be applied in countries characterized by a surplus of the aforementioned residues.

THEORETICAL COMPARATIVE STUDIES OF THE BIOGAZ YIELDS FROM ONE-STAGE AND TWO-STAGE ANAEROBIC DIGESTION PROCESSES

This paper deals with the theoretical comparison of biogas and energy yields of one-stage anaerobic digestion processes (OSAD) with biomethane production and two-stage anaerobic digestion processes (TSAD) producing biohydrogen and biomethane. The comparative study of the biogas yield from OSAD and TSAD systems is performed on the base on mathematical models obtained in our previous papers. The possible maximal yields of biohydrogen and biomethane are calculated by the static characteristics and extremum points of both systems. Simulation results suggest that in comparison to OSAD, the increase in biogas (biohydrogen and biomethgane) production of TSAD can reach to 75.18%. The energy produced from two-stage anaerobic digestion processes is 1.32 to 1.486 times greater than those from one-stage anaerobic digestion processes (depending of the inlet organics concentrations), which means TSAD is a better choice considering biogas and energy production.

Two-stage anaerobic digestion of food waste: Enhanced bioenergy production rate by steering lactate-type fermentation during hydrolysis-acidogenesis

This study proposed a lactate-based two-stage anaerobic digestion (AD) process to enhance bioenergy production rate from food waste (FW) and investigated the effect of inoculum addition and culture pH on hydrolysis-acidogenesis and further methanization. A series of batch fermentations were performed with an enriched lactate-producing consortium and without inoculum addition under controlled (5.7) and uncontrolled pH (initial 6.7) conditions. The interplay between the studied factors dictated the fate of lactate, particularly if it is produced and accumulated in the fermentation broth or is consumed by butyrogenic bacteria. Only the self-fermentation of FW with uncontrolled pH resulted in lactate accumulation (0.2 g/g volatile solid (VS) fed) with limited off-gas production (0.32 NL/L) and VS losses (≈16%). Such lactate-rich broth was successfully digested through biochemical methane potential tests, resulting in a maximum bioenergy production rate of 2891 MJ/ton-VS fed per day, which was two-fold higher compared to that achieved by one-stage AD.

Impacts of molybdate and ferric chloride on biohythane production through two-stage anaerobic digestion of sulfate-rich hydrolyzed tofu processing residue

Biohythane production through one-stage anaerobic digestion of sulfate-rich hydrolyzed tofu processing residue has been hampered by high H2S production. Herein, two-stage anaerobic digestion was investigated with the addition of molybdate (MoO42-; 0.24–3.63 g/L) and ferric chloride (FeCl3; 0.025–5.4 g/L) to the dark fermentation stage (DF) to improve biohythane production. DF supplemented with 1.21 g/L MoO42- increased hydrogen yield by 14.6% over the control (68.39 ml/g-VSfed), while FeCl3 had no effect. Furthermore, the maximum methane yields of methanogenic fermentation were 524.8 and 521.6 ml/g-VSfed with 3.63 g/L MoO42- and 0.6 g/L FeCl3 compared to 466.07 ml/g-VSfed of the control. The maximum yields of biohythane and energy were 796.7 ml/g-VSfed and 21.8 MJ/kg-VSfed with 0.6 g/L FeCl3 when the sulfate removal efficiency was 66.7%, and H2S content was limited at 0.08%. Therefore, adding 0.6 g/L FeCl3 is the most beneficial in improving energy recovery and sulfate removal with low H2S content.

Effect of hydrothermal pretreatment on two-stage anaerobic digestion of food waste and Enteromorpha: Digestion performance, bioenergy efficiency, and microbial community dynamics

The effects of hydrothermal pretreatment (HTP) on the performance, bioenergy efficiency, and microbial community dynamics of two-stage anaerobic digestion (AD) of food waste (FW) and Enteromorpha were analyzed. The results showed that hydrogen production and total volatile fatty acids (VFAs) concentration in the dark fermentation (DF) stage and cumulative biomethane yield in the methanogenic stage exhibited an increasing trend in response to increasing HTP temperature. The highest hydrogen and biomethane yields of 62.7 ± 0.3 and 590.6 ± 8.0 mL·gVS−1 were obtained at HTP temperature of 140 °C, which were 242.6% and 11.8% higher than those in two-stage AD with untreated substrates (designated as RTCK), respectively. Simultaneously, bioenergy generation yield (BGY) of 21.18 ± 0.44–24.21 ± 0.32 kJ·gVS−1 in two-stage AD achieved bioenergy conversion efficiency (BCE) of 71.69–80.37% and process energy efficiency (PEE) of 22.31–39.01%, which showed 14.27–16.91% and 24.83–31.15% improvement compared to one-stage AD, respectively. HTP significantly altered the bacterial communities, resulting in the enrichment of butyric- and acetic-type fermentation bacteria and the inhibition of propionate-type fermentation bacteria. This study demonstrated that HTP could improve the performance and achieve a higher BGY in two-stage AD.

Comparison Study of Dynamic Models for One-stage and Two-stage Anaerobic Digestion Processes

Compared to traditional one-stage anaerobic digestion processes (OSAD) with biomethane production, this paper focuses on the study of biogas yield of the two-stage anaerobic digestion processes (TSAD), which are able to produce simultaneously biohydrogen and biomethane from lignocellusic materials. The one-stage and two-stage systems for anaerobic digestion are obtained based on our previous papers. Additionally, the static characteristics and extremum points of both systems are also investigated. The tracking of maximum points is realized by fuzzy-PID controller. Simulation results suggest that in comparison to OSAD, the increase in biogas production of TSAD can reach to 75.18% by control action, which means TSAD is a better choice considering biogas production.

Combination of ultrasonic and acidic pretreatments for enhancing biohythane production from tofu processing residue via one-stage anaerobic digestion

Tofu processing residues (TPR) have received more attention as a source of bioenergy. However, their low solubility has hindered biohythane generation. Consequently, the ultrasonic and H2SO4 pretreatments were combined and compared for the first time to improve the hydrolysis of organic matter and carbohydrate and increase free amino nitrogen generation from TPR. Besides, the impact of pretreatments on biohythane generation was investigated. Under the optimal conditions of 7.54% substrate level, 8% H2SO4 concentration, 80 °C and 50 min, the coincident ultrasonic-H2SO4 pretreatment enriched the contents of soluble chemical oxygen demand, reducing sugar, and free amino nitrogen to 49675 mg/L, 26 g/L, and 1721 mg/L, respectively, greater than individual pretreatments. Also, Biohythane yield increased by 4.24–13.61% over control (389.42 ± 23.7 ml/g-VSfed). Furthermore, hydrogen yield at 42.5 ± 2.08 and 28.1 ± 1.07 ml/g-VSfed and sulfate removal efficiency at 93 and 92% were significantly improved with ultrasonic-H2SO4 and H2SO4 pretreatments, respectively, indicating acidogenic and sulfidogenic activity enhancement.

Metagenomic analysis reveals the fate of antibiotic resistance genes in two-stage and one-stage anaerobic digestion of waste activated sludge

Waste activated sludge (WAS) from wastewater treatment plants is an important reservoir of antibiotic resistance genes (ARGs). The fate of ARGs in this process was not revealed previously. The present study applied metagenomic approach to examine the occurrence and fate of ARGs in thermophilic alkaline fermentation followed by mesophilic anaerobic digestion (TM), by comparison with mesophilic alkaline fermentation followed by mesophilic anaerobic digestion (MM) and one-stage mesophilic anaerobic digestion (M) process. The removal efficiency of two-stage anaerobic digestion (AD) to total ARGs is higher than that of one-stage AD. The hydrogen and methane production stages of two-stage AD processes have dissimilar impact on the fate of ARGs. Macrolide, lincosamide, and streptogramin (MLS) resistance genes were enriched, especially in the hydrogen production reactors of TM and MM processes. Statistical analysis of metagenomic profiles analysis suggested that bacA may be the differential ARG subtype of two-stage AD process. ARG-like sequences encoding antibiotic efflux pump, antibiotic inactivation and antibiotic target alteration mechanisms were identified as the dominant ARGs resistance mechanisms in all samples. Procrustes analysis showed that microbial community composition structured the resistome. Co-occurrence patterns between ARGs and microbial phylogeny revealed that 26 bacterial species might be potential hosts of 94 ARG subtypes.

Two-stage anaerobic digestion of orange peel without pre-treatment: Experimental evaluation and application to São Paulo state

Abstract Orange juice production is an important industry worldwide, specifically in Brazil, which is the leading producer. Nevertheless, approximately 50 % of the feed used for industrial production of orange juice is wasted, primarily as peels, a promising raw material for being used in the different biotechnological processes. This study evaluated the potential of two-stage anaerobic digestion (reactor of 4.3 L total volume) to valorize orange juice residues. The system replaced the use of other pretreatments and increased methane concentration (approximately 60 % compared with about 50 %) and volume (by 13 %) relative to one-stage anaerobic digestion. The accumulated biogas yield was 0.79 L/g SVT and 0.49 L/g SVT for the methanogenic and control reactors, respectively. Also, the anaerobic reactors were able to start-up with high solids feed, which could be applied to the Upflow Anaerobic Sludge Blanket (UASB) reactors currently in operation in the citrus juice industry. The potential electric power generated was estimated as 97.5 × 103 MWh/year, which might be used on-site or sold back to the energy grid where it represents 0.2 % of the total energy used by Sao Paulo State. The potential greenhouse gas mitigation from the substitution of electric energy from the Brazilian energy grid to a more renewable one from biogas burning was estimated to be 9.05 × 103 tCO2eq/year. The results demonstrated that two-stage anaerobic digestion is a promising technology for the disposal of orange peel waste while producing a useful bioenergy product.

Enhancing energy recovery from corn straw via two-stage anaerobic digestion with stepwise microaerobic hydrogen fermentation and methanogenesis

Abstract Anaerobic digestion (AD) technology attracts increasing concerns for organic waste disposal, renewable energy production as well as organic fertilizer preparation. However, the AD of cellulosic substrate is limited by low efficiency. Microaeration has recently been used to improve the AD efficiency. However, the inhibition of methanogenesis by microaeration limited its application. To enhance the energy recovery from AD of corn straw and avoid the inhibition of microaeration on methanogenesis, two-stage AD including microaerobic hydrogen fermentation (stage I) and methanogenesis (stage II) was investigated. Results showed microaeration had beneficial effects on hydrogen fermentation, methane production and energy recovery depending on the oxygen loading level. At the optimized initial pH of 7.5 for hydrogen production, microaerobic hydrogen fermentation achieved the maximum hydrogen yield of 24.3 mL/g VS (volatile solid, 37 °C and normal pressure) with the oxygen loading of 5 mL/g VS, which was 70% higher than that without microaeration. Overall, the two-stage AD performed better in methane yield and energy recovery than one-stage AD. When the oxygen loading during hydrogen fermentation was 10 mL/g VS of corn straw, the maximum total energy recovery of 10.6 kJ/g VS was obtained, which was 18% higher than that of one-stage AD. The two-stage AD consisting of microaerobic hydrogen fermentation (stage I) and methanogenesis (stage II) is a promising way to enhance the energy recovery from AD of cellulosic substrates like corn straw.

Fate of antibiotic resistance genes during anaerobic digestion of sewage sludge: Role of solids retention times in different configurations

In this study, three anaerobic digestion experiments were established to investigate the effects of solids retention times (SRT) on the fate of antibiotic resistance genes (ARGs) including anaerobic digestion of sewage sludge (CK), one-stage anaerobic digestion of microwave pretreatment sludge (MW) and two-stage anaerobic digestion of microwave pretreatment sludge (Acid stage and CH4 stage). The response of ARGs to the SRT varied significantly from ARG types and reactor configurations. Shorter SRT could avail the ARGs reduction for CK and two-stage digestion, while MW need longer SRT for the ARGs reduction. Concerning the variance of microbial community caused by reactor configurations, the role of SRT was limited. The partial redundancy analysis and structural equation models analysis indicated that the role of SRT on the ARGs fate could be attributed the most to the co-selection from heavy metals.

Biohythane production in two-stage anaerobic digestion system

Hydrogen (H2) and methane (CH4) are the potential alternative energy carriers with autonomous extensive and viable importance. These fuels could complement the advantages, and discard the disadvantages of each other, if produced simultaneously. Considering their complementary properties, co-production of a mixture of H2 and CH4 in the form of biohythane in two-stage anaerobic digestion (AD) process is gaining more interest than their individual production. Biohythane is a better transportation fuel than compressed natural gas (CNG) in terms of high range of flammability, reduced ignition temperature as well as time, without nitrous oxide (NOx) emissions, improved engine performance without specific modification, etc. Other than production of biohythane, performing two-stage AD is advantageous over one-stage AD due to short HRT, high energy recovery, high COD removal, higher H2 and CH4 yields, and reduced carbon dioxide (CO2) in biogas. For improved biohythane production, various aspects of two-stage AD need to be emphasized. Keeping the facts in mind, the process of two-stage AD along with microbial diversity in comparison to one-stage AD has been discussed in the previous sections of this review. For large scale commercial production, and utilization of biohythane in automobile sector, its execution needs evaluation of process parameters, and problems associated with two-stage AD. Hence, the later part of this review describes the production process of biohythane, concerned microbial diversity, operational process parameters, major challenges and their solutions, applications, and economic evaluation for enhanced production of biohythane.

Profiles and drivers of antibiotic resistance genes distribution in one-stage and two-stage sludge anaerobic digestion based on microwave-H2O2 pretreatment

Three anaerobic digestion (AD) processes of waste activated sludge (WAS) were established including the control (mono-WAS), one-stage AD and two-stage AD along with microwave-H2O2 pre-treatment (MW-H2O2) to investigate the profiles and drivers of antibiotic resistance genes (ARGs) distribution concerning co-selection from heavy metals, intI1 and microbial community through qPCR and high-throughput sequencing method. Results showed that MW-H2O2 could reduce the absolute gene copies of all ARGs while increased the relative abundance of most ARGs. After subsequent AD, both total ARGs quantities and relative abundance were enriched while two-stage AD showed some advantages over ARGs abundance reduction. Besides, AD was more effective on the potential pathogens reduction than MW-H2O2. AD could reduce the role of intI1 on the spread of ARGs, while mantel test and procrustes analysis indicated that the variation of ARGs abundance was closely associated with the discrepancy of bacterial community.

Hydrogen and methane production from vinasse using two-stage anaerobic digestion

Abstract Vinasse is mainly produced during the brewing or liquor production, which is an potential substrate for biogas production. However, due to the rich content of easily degradation components in vinasse, the fermentation system during the initial AD stage of vinasse is easily acidifying, which leads to the fermentation system unstable, even failed. In this study, mesophilic hydrogen and methane production from vinasse through two-stage anaerobic digestion was investigated. In addition, one-stage anaerobic digestion of vinasse was also conducted to compare with two-stage anaerobic digestion. During two-stage anaerobic digestion, the hydrogen and methane yield were 14.8 and 274 ml/g VSsubstrate, respectively. The methane yield from two-stage anaerobic digestion was 10.8% higher than that of one-stage. During the methane production process, the lag-phase of two-stage anaerobic digestion was 9.1 days less than that of one-stage. In addition, the VS removal efficiency and energy recovery of two-stage anaerobic digestion were 10.4% and 12.9% higher than those of one-stage. Two-stage anaerobic digestion for hydrogen and methane production could efficiently improve the substrate utilization efficiency and energy recovery of vinasse.

Dark fermentation, anaerobic digestion and microbial fuel cells: An integrated system to valorize swine manure and rice bran

This work describes how dark fermentation (DF), anaerobic digestion (AD) and microbial fuel cells (MFC) and solid-liquid separation can be integrated to co-produce valuable biochemicals (hydrogen and methane), bioelectricity and biofertilizers. Two integrated systems (System 1: AD+MFC, and System 2: DF+AD+MFC) are described and compared to a traditional one-stage AD system in converting a mixture (COD=124±8.1gO2kg−1Fresh Matter) of swine manure and rice bran. System 1 gave a biomethane yield of 182 LCH4kg−1COD-added, while System 2 gave L yields of bio-hydrogen and bio-methane of 27.3±7.2LH2kg−1COD-added and 154±14LCH4kg−1COD-added, respectively. A solid-liquid separation (SLS) step was applied to the digested slurry, giving solid and liquid fractions. The liquid fraction was treated via the MFC-steps, showing power densities of 12–13Wm−3 (500Ω) and average bioelectricity yields of 39.8Whkg−1COD to 54.2Whkg−1COD.

Energy conversion of biomass crops and agroindustrial residues by combined biohydrogen/biomethane system and anaerobic digestion

Aim of this study was to evaluate the suitability of ensiled giant reed, ensiled maize, ensiled olive pomace, wheat bran for combined systems (CS: dark fermentation+anaerobic digestion (AD)) producing hydrogen-rich biogas (biohythane), tested in batch under basic operational conditions (mesophilic temperatures, no pH control). Substrates were also analyzed under a single stage AD batch test, in order to investigate the effects of DF on estimated energy recovery (ER) in combined systems. In CS, maize and wheat bran exhibited the highest hydrogen potential (13.8 and 18.9NLkgVS−1) and wheat bran the highest methane potential (243.5NLkgVS−1). In one-stage AD, giant reed, maize and wheat bran showed the highest methane production (239.5, 267.3 and 260.0NLkgVS−1). Butyrate/acetate ratio properly described the dark fermentation, correlating with hydrogen production (r=0.92). Wheat bran proved to be a promising residue for CS in terms of hydrogen/methane potential and ER.

Characterization of Food Waste and Its Digestate as Feedstock for Thermochemical Processing

The products of a commercial one-stage anaerobic digestion and a laboratory-scale pyrolysis of raw food waste (RFW) and digestated food waste (DFW) were characterized to evaluate the treatment effect, product yield, and physicochemical properties. The pyrolysis of the RFW and DFW resulted in generation of 7.4 and 5.3 wt % of gas and 60.3 and 52.2 wt % of bio-oil, while biochar yields decreased with an increase in the pyrolysis temperature. Differential thermogravimetric tests of RFW and DFW show 20% in both solid residues produced at a temperature of 550 °C, indicating a relatively low impact of the digestion process on the RFW. The mineral matter content was found to be lower for RFW compared to DFW. The variation in the content of fixed carbon and volatile matter reflected the effect of anaerobic degradation of the food waste. The bio-oils showed a low concentration of phenols, esters, and derivatives of hydrocarbons for DFW compared to RFW. The specific heat capacities were determined for RFW and DFW, ...

Can two-stage instead of one-stage anaerobic digestion really increase energy recovery from biomass?

The supremacy of two-stage on traditional one-stage anaerobic digestion (AD), in terms of overall energy recovery (ER) from biomass has often been proved. However, the process conditions ensuring this result, as well as the reasons for higher efficiency, have always been unclear. In this work, a new standardized approach is proposed: optimization at lab-scale of both hydrogen and methane generation processes allowed comparing the maximum potential ER of both two-stage (as H2+CH4) and one-stage AD (as CH4). Relatively high bio-hydrogen yields were obtained testing four different organic substrates (ER of 1–1.6MJkg−1VS-added). Biomethane generation resulted in ER in the range of 9–19MJkg−1VS-added., similarly for two-stage and one-stage systems. The overall ER resulted in significantly higher (8%–43%) for the two-stage in the large majority of experimental conditions and never significantly lower. These preliminary results should drive further research to better understand the conditions that can drive the two-stage AD to higher performance.

Reducing the risk of foaming and decreasing viscosity by two-stage anaerobic digestion of sugar beet pressed pulp

Anaerobic digestion (AD) of sugar beet pressed pulp (SBPP) is a promising treatment concept. It produces biogas as a renewable energy source making sugar production more energy efficient and it turns SBPP from a residue into a valuable resource. In this study one- and two-stage mono fermentation at mesophilic conditions in a continuous stirred tank reactor were compared. Also the optimal incubation temperature for the pre-acidification stage was studied. The fastest pre-acidification, with a hydraulic retention time (HRT) of 4days, occurred at a temperature of 55°C. In the methanogenic reactor of the two-stage system stable fermentation at loading rate of 7kgVS/m³d was demonstrated. No artificial pH adjustment was necessary to maintain optimum levels in both the pre-acidification and the methanogenic reactor. The total HRT of the two-stage AD was 36days which is considerably lower compared to the one-stage AD (50days). The frequently observed problem of foaming at high loading rates was less severe in the two-stage reactor. Moreover the viscosity of digestate in the methanogenic stage of the two-stage fermentation was in average tenfold lower than in the one-stage fermentation. This decreases the energy input for the reactor stirring about 80%. The observed advantages make the two-stage process economically attractive, despite higher investments for a two reactor system.