Two-stage Anaerobic Digestion Research Articles

Sequential production of hydrogen and methane using hemicellulose hydrolysate from diluted acid pretreatment of sugarcane straw

Sugarcane straw is not effectively used in the industry currently. However, sugarcane straw hemicellulose hydrolyzate (HH) application as raw material for H2 and CH4 production is a promising alternative. In this work, the two-stage anaerobic digestion (TS-AD) approach led to 37.86 mLH2/L.h and 40.12 mLCH4/L.d, while the single-stage anaerobic digestion (SS-AD) generated 46.11 mLCH4/L.d. Hence, the two-stage process was energetically favorable than the single-stage by approximately 33%. Additionally, the comparison with standard medium (composed of glucose, xylose, and arabinose) applied as raw material indicated that although hydroxymethylfurfural and furfural from HH were not responsible for the decrease in H2 production, they extended the adaptive phase of methanogenic archaea during the methanogenesis. Hemicellulose hydrolysate is an attractive raw material for two-stage anaerobic digestion.

Biohythane: a Potential Biofuel of the Future.

Today, the world is becoming more dependent on fossil fuels. The major drawbacks of these non-renewable energy resources include an extreme environmental pollution and an extinction threat. Several technologies including microalgal biodiesel production, biomass gasification, and bioethanol production have been explored for the generation of renewable energy especially, biofuels. One such promising research has been carried out in the generation of biohythane which has the potential to become an alternative fuel to the existing non-renewable ones. It has been reported that biohydrogen can be produced from organic wastes or agricultural feedstocks with the help of acidogens. Dark fermentation can be carried out by acidogens to produce biohydrogen under anaerobic conditions by utilizing lignocellulosic biomass or sugarcane feedstocks in the absence of light. The spent medium contains volatile short-chain fatty acids like acetate, butyrate, and propionate that can serve as substrates for acetogenesis followed by methane biosynthesis by methanogens. Therefore, the sequential two-stage anaerobic digestion (AD) involves a production of biohydrogen followed by the biosynthesis of methane. This combined process is termed as a single eponym "Biohythane" (hydrogen + methane). Several studies have demonstrated about the effectiveness of biofuel, and it is believed to have a greater energy recovery, environmental friendliness, and shorter fermentation time. Biohythane can serve as an alternative future green biofuel and solve the present energy crisis in India as well as the entire world.

Metaheuristic Algorithms to Optimal Parameters Estimation of a Model of Two-Stage Anaerobic Digestion of Corn Steep Liquor

Anaerobic Digestion (AD) of wastewater for hydrogen production is a promising technology resulting in the generation of value-added products and the reduction of the organic load of wastewater. The Two-Stage Anaerobic Digestion (TSAD) has several advantages over the conventional single-stage process due to the ability to control the acidification phase in the first bioreactor, preventing the overloading and/or the inhibition of the methanogenic population in the second bioreactor. To carry out any process research and process optimization, adequate mathematical models are required. To the best of our knowledge, no mathematical models of TSAD have been published in the literature so far. Therefore, the authors’ motivation is to present a high-quality model of the TSAD corn steeping process for the sequential production of H2 and CH4 considered in this paper. Four metaheuristics, namely Genetic Algorithm (GA), Firefly Algorithm (FA), Cuckoo Search Algorithm (CS), and Coyote Optimization Algorithm (COA), have been adapted and implemented for the first time for parameter identification of a new nonlinear mathematical model of TSAD of corn steep liquor proposed here. The superiority of some of the algorithms has been confirmed by a comparison of the observed numerical results, graphical results, and statistical analysis. The simulation results show that the four metaheuristics have achieved similar results in modelling the process dynamics in the first bioreactor. In the case of modelling the second bioreactor, a better description of the process dynamics trend has been obtained by FA, although GA has acquired the lowest value of the objective function.

Methanogenic consortia from thermophilic molasses-fed structured-bed reactors: microbial characterization and responses to varying food-to-microorganism ratios

The heterogeneous character of fixed-film reactors may create highly specialized zones with a stratified distribution of microbial groups and varying capabilities to withstand high organic loads in anaerobic digestion (AD) systems. The microbial distribution and methane-producing potential of biomass from different regions (feeding zone and structured bed) of two second-stage thermophilic (55 ºC) fixed-film reactors were assessed. Three levels of food-to-microorganism (F/M) ratio (0.4, 1.0 and 3.0 g-COD g−1VS) using fermented (two-stage AD) and fresh (single-stage AD) sugarcane molasses were tested in batch reactors, simulating low to high organic loads. Specific methane production rates increased as the F/M increased when using fermented molasses, maintaining efficient methanogenesis at substrate availability levels threefold higher than single-stage schemes (3.0 vs. 1.0 g-COD g−1VS). Success in methane production derived from the homogenous establishment (similar in both feeding zone and bed) of syntrophic associations between acetogens (Pelotomaculum, Syntrophothermus, Syntrophomonas and Thermodesulfovibrio), acetate oxidizers (Thermoacetogenium, Mesotoga and Pseudothermotoga) and hydrogenotrophic methogens (Methanothermobacter and Methanoculleus) replacing acetoclastic methanogens (Methanosaeta). Phase separation under thermophilic conditions was demonstrated to boost methane production from sugar-rich substrates, because the process depends on microbial groups (hydrogenotrophs) that grow faster and are less susceptible to low pH values compared to acetotrophs.

Dynamic modeling and parameter estimation of biomethane production from microalgae co-digestion.

This work proposes a dynamic modeling procedure applied to biomethane production from microalgae residual co-digestion. A two-stage anaerobic digestion representation is selected, considering acidogenesis and methanogenesis as main reaction pathways. Based on the experimental database generated in the University of Mons Laboratories, several candidate models, assuming the presence or absence of biomass dynamics, are suggested, and parametric structural and local identifiability studies are performed. An original parameter estimation procedure is applied to a data-set partition used for model direct validation. The remaining experiment data are dedicated to cross-validation. The results point out how these dynamic models may serve as advanced monitoring software tools such as digital twins, even in the presence of incomplete process data.

Comparative Study of Methane Production in a One-Stage vs. Two-Stage Anaerobic Digestion Process from Raw Tomato Plant Waste

An anaerobic digestion process performed in two stages has the advantages of the production of hydrogen in addition to methane, and of further degradation of the substrate over the conventional process. The effectiveness of the implementation of this system for the treatment of lignocellulosic waste has been demonstrated. In 2020, more than 180 million tons of organic waste were generated worldwide from tomato crop production, posing a serious environmental risk. In the present investigation, methane production was compared in a two-stage system versus one-stage system from non-pretreated tomato plant residues. For this, different temperature (37 and 55 °C) and initial pH (5.5 and 6.5) conditions were evaluated during hydrogenesis and a constant temperature (37 °C, without pH adjustment) during methanogenesis. At the same time, a one-stage treatment (37 °C, without pH adjustment) was run for comparison purposes. The two-stage treatment in which the highest production of hydrogen, 12.4 mL/g VS, and methane, 252.3 mL/g VS, was observed occurred under the conditions of pH 6.5 and at 37 °C. However, this energy production was statistically similar (p < 0.5) to the one-stage treatment (365.4 mL CH4/g VS). Furthermore, there were also no significant differences in the removal of volatile solids between the different treatments.

Optimization of Energy Production from Two-Stage Mesophilic–Thermophilic Anaerobic Digestion of Cheese Whey Using a Response Surface Methodology Approach

Spatial separation into acidogenic and methanogenic stages is considered a viable option to ensure process stability, energy efficiency and the better control of key anaerobic digestion (AD) parameters. The elucidation of the optimal modes of two-stage AD for the maximization of the recovery of biofuels (H2 and CH4) is still an urgent task, the main optimization criteria being the highest energy yield (EY) and energy production rate (EPR). In this work, a response surface methodology was used for an optimization of energy production from the two-stage mesophilic–thermophilic AD of cheese whey (CW). Three dilution rates of CW, providing values of 10.9, 14.53 and 21.8 g for the chemical oxygen demand (COD)/L in the influent and three hydraulic retention times (HRTs) (1, 2 and 3 days) in methanogenic biofilters at a constant HRT in an acidogenic biofilter of 0.42 days, were tested to optimize the EY and EPR. The desirability approach produced combined optimum conditions as follows: the dilution rate of the CW provided 17.58 g COD/L (corresponding to OLR of 6.5 g COD/(L·day)) in the influent and a HRT in the methanogenic biofilter of 2.28 days, both of which provided a maximum EPR of 80.263 kJ/(L·day) and EY of 9.56 kJ/g COD, with an overall desirability value of 0.883.

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.

Hydrogen and Methane Production by Single- and Two-Stage Anaerobic Digestion of Second Cheese Whey: Economic Performances and GHG Emissions Evaluation

This study aimed at evaluating the economic performances of and carbon footprint associated with innovative systems for the energetic valorization of second cheese whey (SCW), a by-product of whey cheese manufacture, through anaerobic digestion processes. Three systems were modeled: a conventional single-stage anaerobic digester (FAD), located at about 50 km from the dairy factory; an on-site conventional single-stage anaerobic digester (CAD), located at the dairy industry; and an on-site two-stage anaerobic digester (TAD). The TAD technology enables the simultaneous production of hydrogen and methane on site. The biogases produced were combusted in combined heat and power plants (CHP), but only the onsite systems provided process heat to the dairy factory. In the specific conditions assumed, TAD configuration exhibited a higher energy output, which led to a GHG emission reduction of about 60% compared to FAD, mostly thanks to the additional hydrogen (H2) production and the improved engine performances. A detailed cost analysis confirmed the results of the environmental analysis, pointing to the TAD solution as the most economically viable, with a payback period of 9 years, while the CAD had a payback time of 12 years. The results here presented aim at providing the dairy industry with a robust economic analysis on the opportunity of building an innovative system for SCW valorization, as well as providing policymakers with environmental reliable data to support the promotion of this technology.

Impact of pH in the first-stage of a two-stage anaerobic digestion on metabolic pathways and methane production

The present study focuses on the use of cow manure, slaughterhouse sludge, cheese whey and green beans in a two-stage batch anaerobic process. The effect of pH regulation (4.5 to 7) on metabolic pathways and microbial community involved was studied in the first-stage of the process under mesophilic condition. At a pH lower than 5, fermentation occurred and led to an accumulation of lactic acid with a dominance of Lactobacillus. A pH >5.5 led to dark fermentation. Temporarily lactic acid production was converted in volatile fatty acids. Streptococcus and Enterococcus were involved in lactic conversion at pH 5.5 and 7, respectively. A weak hydrogen production was monitored at these pH ranges. Regardless of fatty acids produced in the first-stage, dark or lactic fermentation did not lead to higher methane production in the second-stage. However, dark fermentation increased methane concentration in biogas from 63.1 % in a single-stage to 83.6 %.

Enhanced two-phase anaerobic digestion of waste activated sludge by combined free nitrous acid and manganese dioxide

Anaerobic digestion (AD) is a mature and reliable technology for sludge treatment, but it still faces many technical problems including slow hydrolysis rate and low methane yield. Free nitrous acid (FNA) pretreatment was previously confirmed in enhancing sludge hydrolysis and extracellular polymeric substances (EPS) disruption in anaerobic digestion. It was hypothesized that, due to the manganese dioxide (MnO2) addition during methanogenic stage, direct interspecies electron transfer (DIET) facilitated the biological activities, thus boosting the methane production in FNA-pretreated two-phase AD model. The results showed that the methane production of the combination of FNA pretreatment and MnO2 addition was improved by 18.64% and 22.23%, compared with reactors that solely treated by either MnO2 addition or FNA pretreatment. The changes of microbial metabolism activity were evaluated by measuring the coenzyme F420 and electron transfer system (ETS). The activities of coenzyme F420 and ETS were increased to 156.26% and 134.71% in two-phase AD model, respectively. Meanwhile, the obvious microbial community succession was found with the enrichment of methanogens such as Methanosarcina and Methanobacterium. Overall, the combination of FNA pretreatment and MnO2 addition avoided the inhibition of FNA pretreatment on methanogenesis in the early stage, and showed positively synergistic effect on methane production. The enhancement of microbial metabolism was responsible for, promoting methane production in the two-stage AD model. This research provides an alternative strategy for efficiency improvement of anaerobic sludge digestion as well as methane production.

Microbial communities and metabolic pathways involved in reductive decolorization of an azo dye in a two-stage AD system

Multiple stage anaerobic system was found to be an effective strategy for reductive decolorization of azo dyes in the presence of sulfate. Bulk color removal (56–90%) was achieved concomitant with acidogenic activity in the 1st-stage reactor (R1), while organic matter removal (≤100%) and sulfate reduction (≤100%) occurred predominantly in the 2nd-stage reactor (R2). However, azo dye reduction mechanism and metabolic routes involved remain unclear. The involved microbial communities and conditions affecting the azo dye removal in a two-stage anaerobic digestion (AD) system were elucidated using amplicon sequencing (16S rRNA, fhs, dsrB and mcrA) and correlation analysis. Reductive decolorization was found to be co-metabolic and mainly associated with hydrogen-producing pathways. We also found evidence of the involvement of an azoreductase from Lactococcus lactis. Bacterial community in R1 was sensitive and shifted in the presence of the azo dye, while microorganisms in R2 were more protected. Higher diversity of syntrophic-acetate oxidizers, sulfate reducers and methanogens in R2 highlights the role of the 2nd-stage in organic matter and sulfate removals, and these communities might be involved in further transformations of the azo dye reduction products. The results improve our understanding on the role of different microbial communities in anaerobic treatment of azo dyes and can help in the design of better solutions for the treatment of textile effluents.

Long term performance of pilot methanogenic digester filled with seashell wastes treating slaughterhouse wastes: Biogas production and environmental impact

High ammonia and organic acids contents of decomposed slaughterhouse waste (SHW) often result in the severe inhibition or even failure of the anaerobic digestion (AD). The two-stage AD system can alleviate the ammonia inhibition; however, addition of alkali is often needed to maintain the neutral condition. In this study, seashell wastes containing high percentage of calcium carbonate (CaCO3) were for the first time added in a pilot scale methanogenic digester treating chicken blood waste to retain the microorganisms and provide pH buffers for the substrate. A long-duration performance of this digester was conducted for 400 days under different organic loading rates (OLRs). The results show that methane yields of the digester were 244.8 and 224.9 mL g−1 CODadded at OLR of 0.4 and 0.6 g COD L−1 d−1, respectively, higher than the results of previous studies treating the similar feedstock. An AD system treating blood wastes of a typical poultry slaughterhouse was also proposed for which energy balance and carbon footprint analyses were conducted. The energy production of 0.35 MJ kg−1 blood and carbon emissions reduction of 0.05 kg CO2-eq kg−1 blood can be achieved from treating blood waste of the broiler chicken. This study reveals that using seashell wastes in an AD treating SHW can facilitate the reuse of aquaculture wastes and improve the sustainability of meat industry.

Considerations on bio-hydrogen production from organic waste in South African municipalities: A review

Organic waste disposal contributes to 3.8% of GHG emissions to the atmosphere, yet 68.8% of this putrescible waste fraction is still disposed of, untreated, to landfills in South Africa. The implementation of a ban on disposal of organic waste to landfills at provincial level opens up the need to research best technology pathways and waste minimisation strategies to valorise and promote the circularity of diverted waste streams. The SARChI Chair in Waste and Climate Change has developed the WROSETM (Waste Resource Optimization Scenario Evaluation) model to assist municipalities in selecting the most appropriate waste management solutions. A research gap has been identified in the lack of information on full-scale applications of two-stage anaerobic digestion (2-stage AD) for combined bio-hydrogen and bio-methane production from organic waste. waste. In this review, we explore drivers and barriers to the implementation of 2-stage AD in South Africa and propose possible scenarios using the WROSETM model for its insertion into an Integrated Waste Management System at municipal level. A literature analysis suggests that 2-stage AD is a potentially viable solution to recover the inherent value of organic waste and promote circularity using bio-hydrogen and bio-methane. However, the currently available organic fraction in the municipal solid waste streams is not a suitable feedstock, as it requires high levels of pre-treatment. Suitable scenarios using the WROSETM model are proposed for South African municipalities, paving the way for future research towards the scale-up of this technology.Significance: Organic waste is not managed adequately in South Africa, contributing to greenhouse gas emissions without recovering the intrinsic value of the material. 2-stage AD is a potentially viable solution to recover the inherent value of organic waste and promote circularity using bio-hydrogen and bio-methane. Several barriers must be overcome before carrying out the technology at full-scale. A 2-stage AD scenario can be implemented at full-scale into an Integrated Waste Management System using appropriate decision-making tools such as WROSETM.

Yak rumen fluid inoculum increases biogas production from sheep manure substrate

Hydrolytic bacteria are essential for the degradation of lignocellulose to produce biogas and organic fertilizers. In this study, sheep manure was used as substrate, and sheep manure slurry, yak rumen fluid and slurry from a biogas reactor (SBR) were used as inocula in single-stage anaerobic digestion. The SBR and rumen fluid inocula increased biogas production by 23% and 43%, respectively, when compared to solely sheep manure in the single-stage anaerobic digestion. The two-stage anaerobic digestion, with yak rumen fluid as inoculum in the hydrolytic reactor, increased the biogas production by 59, 86, and 58% compared with the control. Microbial analysis of the effluent revealed that yak rumen fluid contained hydrolytic bacteria such as Proteiniphilum, Jeotgalibaca, Fermentimonas, and Atopostipes to enhance the degradation of sheep manure and increase biogas production. It was concluded that yak rumen fluid, rich in hydrolytic bacteria, increases the degradability of sheep manure and improves production of volatile fatt acids and biogas.

Anaerobic digestion of organic fraction of municipal solid waste using a novel two-stage solid-liquid system

Organic fraction of municipal solid waste (OFMSW) has high volatile solid and moisture content, which is mainly treated via anaerobic digestion (AD). Since the composition of OFMSW is complicated and inconstant, it is difficult to maintain the AD process stable and effective. In this study, a novel two-stage AD system, including a tank-type acidogenic phase and a fixed-bed methanogenic phase, was implemented for OFMSW treatment to demonstrate the feasibility of the two-stage configuration. Results showed that 84% of potential CH4 yield was achieved and the methane content reached 77.83% on average in methanogenic phase. The acetoclastic methanogens, Methanosaeta and Methanosarcina, which can participate in direct interspecies electron transfer, were the dominant genera in solid digestate and the biofilm. The hydrogenotrophic methanogens, Methanospirillum and Methanoculleus, accounted for high proportions in liquid digestate. Our study provides a novel approach to treat OFMSW with less water consumption, high stability and efficiency.

Environmental and Economic Assessment of Alternative Food Waste Management Scenarios

The scope of this paper was to examine the environmental and economic performance of alternative household fermentable waste (HFW) management scenarios. In Greece, the business-as-usual scheme for the management of HFW is its disposal in landfills as part of mixed waste. Within a HORIZON2020 called Waste4think a series of alternative approaches based on the benefits of source separation was developed. Specifically, source separated HFW is led to a drying/shredding plant, located in the municipality, for the production of a high-quality biomass product, which is called FORBI (Food Residue Biomass). Alternative approaches have been examined for the exploitation of FORBI: a simple alternative consists of the transportation of food waste (without drying/shredding) to the landfill, composting and covering the landfill’s layers with the produced compost. On the other hand, a set of technological alternatives examined are: one- and two-stage anaerobic digestion for the production of biogenic compressed natural gas (bio-CNG) and bio-hythane, composting and utilization of compost in the municipality, bio-ethanol production and pelletization. The alternatives have been assessed using Life Cycle Assessment and Life Cycle Costing tools. The results show that both the simple and the innovative alternatives proposed perform better than the baseline scenario both in economic and environmental terms.

Continuous co-generation of biohydrogen and biomethane through two-stage anaerobic digestion of hydrothermally pretreated food waste

Increasing accumulation of food waste (FW) exerts pressure on resource conservation and environmental protection, while conventional anaerobic digestion (AD) of raw FW for bioenergy recovery and waste minimization often encounters limitations such as fast acidification and process failure. Herein, mild hydrothermal pretreatment (HTP: 140 °C, 20 min) of raw FW was employed to advance subsequent AD performances in a long-term continuous mode. With a decreased overall hydraulic retention time (HRT) from 30 to 18 days, the two-stage system digesting HTP-treated FW maintained very stable and robust biohydrogen (38.1 mL/gVS) and biomethane (439.6 mL/gVS) co-production, whereas both the two-stage system digesting raw FW and the one-stage system digesting HTP-treated FW exhibited deteriorating trends with significantly lower energy yields by 61.1% and 28.1%, respectively. Microbial community analyses revealed the less involvement of carbohydrate-fermenting and proteolytic microbes in the second-stage biomethane reactors as a result of the enhanced hydrolysis and acidogenesis of FW through HTP and first-stage biohydrogen fermentation. A proximate energy balance assessment indicated that the energy gain of increased biogas generation offset the extra heat requirement for the HTP of FW, while a significant treatment capacity enhancement of 66.7% was achieved given the HRT reduction from 30 to 18 days through this integrated system.

Post-hydrolysis ammonia stripping as a new approach to enhance the two-stage anaerobic digestion of poultry manure: Optimization and statistical modelling

Post-hydrolysis ammonia stripping was investigated as a new approach to enhance the methane potential of high ammonia substrates, such as poultry manure. The objective of the proposed approach is to address some of the noticeable disadvantages in the existing ammonia-stripping techniques i.e., treatment of raw samples and side-stream stripping. Poultry manure (PM) and a co-substrate (mixed wastes from a cheese factory and a coffee house, referred to as MS) characterized by a high carbon-to-nitrogen ratio were mixed at five different ratios: PM:MS of 100:0, 75:25, 50:50, 25:75, and 0:100. Samples were hydrolyzed for six days to promote ammonia conversion from organic nitrogen and then the samples with higher ammonia levels (>2000 mg NH3–N/L) were stripped with air at initial pH values of 9 and 10 and temperatures of 40 and 55 °C. Biochemical methane potential (BMP) test results showed that post-hydrolysis ammonia stripping had alleviated ammonia inhibition and improved methane potential up to 200% when compared with untreated samples. The ammonia removal efficiency was mostly affected by pH. On the other hand, methane potential was highest in the samples treated at a higher temperature as their biodegradability was enhanced when compared with the samples treated at lower temperatures. Post-BMP characterization showed that the proposed approach had also limited the increase of ammonia in the digestate which ensured proper growth of methanogenic microorganisms.

Environmental assessment of a two-stage high pressure anaerobic digestion process and biological upgrading as alternative processes for biomethane production

Biomethane plays a key role in achieving decarbonization and sustainable development goals. According to the objectives that arise, choosing the most suitable production system allows optimization of production, thereby reducing CO2 emissions. In this study, three biomethane production scenario life cycle assessments were compared to determine which would maintain the lowest CO2 emissions. Conventional anaerobic digestion and an innovative process called two-stage high pressure anaerobic digestion were considered. These methods were combined with two upgrading processes: water scrubbing and biological upgrading. Cattle manure and sugar beets were used as substrates for the process. Emissions were 805.6 gCO2eq/m3CH4 for the traditional biogas production process combined with water scrubbing and 450.3 gCO2eq/m3CH4 for the two-stage anaerobic digestion process combined with biological upgrading. Furthermore, the analysis demonstrated that these values would be reduced by 29.5 % and 48.0 % if electrical energy were produced using only renewable energy sources.