Biomethane Yield Research Articles

Performance of sorghum cultivars for biomass quality and biomethane yield grown in semi-arid area of Pakistan.

Biomass is a promising renewable energy source and its significance is escalating in the context of climate change and depletion of fossil foils. This study was conducted for two consecutive years 2016 and 2017, using five sorghum cultivars, i.e., JS-263, Jawar-2011, Hagari, JS-2002, and YS-2016, in order to determine the best cultivars in terms of dry matter yield, chemical composition, and biomethane yield grown under semi-arid conditions in Pakistan. The results revealed that sorghum cultivars responded differently in terms of growth, biomass yield, chemical composition, and methane yield. Cultivars Jawar-2011 produced maximum leaf area index, leaf area duration, crop growth rate, plant height, and leaves per plant, however, they were comparable with Sorghum-2016, whereas cultivar JS-2002 performed poorly among the tested cultivars. Similarly, cultivar Jawar-2011 produced maximum dry matter yield (16.37tha-1) similar to that of YS-2016, further cultivar JS-2002 performed poorly and gave lower dry matter yield (12.87tha-1). The maximum protein concentration (10.95), neutral detergent fibers (61.20), and lignin contents (5.55) found in Jawar-2011 were comparable with those in YS-2016, while the lowest neutral detergent fiber and lignin contents were found in JS-2002. Although JS-2002 produced the highest specific methane yield per kilogram of volatile solids, it was overcompensated by Jawar-2011 owing to higher dry matter yield per hectare. These results suggested that cultivar Jawar-2011 can be grown successfully in semi-arid conditions of Pakistan in order to get good biomass yield along with higher methane yield.

Anaerobic digestion of waste activated sludge with incineration bottom ash: Enhanced methane production and CO2 sequestration

Development of anaerobic digestion (AD) technology in China for WWTP sludge treatment is hindered by low biomethane yield and costly biogas upgrading. This study investigated the feasibility of using a byproduct waste, sludge incineration bottom ash, as additive to promote AD performance. The effectiveness of ashes addition was investigated with varied dosages (0.6–1.5 g/g dry matter (DM) of sludge) to enhance thermophilic AD of sludge in batch experiments in terms of methane production and CO2 sequestration. The optimal dosage was 0.9 g/g DM, which increased the methane production by 26.6%, shortened the methanization lag phase by 32.4% and increased the maximum methane production rate by 36.0%. Kinetics modelling results show that ashes additive accelerated hydrolysis, acidogenesis and degradation of volatile fatty acids (VFAs) by up to 139.6%, 87.1% and 100.9%, respectively. High dosage at 1.5 g/g DM output the greatest sludge hydrolysis and VFAs production but inhibited methanogenesis. Moreover, the amount of sequestered CO2 resulting from basic cations (primarily Ca2+) leaching in ashes-amended digesters was linearly correlated (R2 > 0.99) with the dosage of ashes additive. This indicates that ashes addition facilitated in-situ carbonation in AD system and that Ca2+ leaching remains rate-limiting. The results demonstrated that sludge incineration bottom ash could be used as an effective additive material to improve AD of sludge, thus enhancing the technical and economic feasibility of AD technology for sludge treatment.

Sequential ethanol fermentation and anaerobic digestion increases bioenergy yields from duckweed

The potential for improving bioenergy yields from duckweed, a fast-growing, simple, floating aquatic plant, was evaluated by subjecting the dried biomass directly to anaerobic digestion, or sequentially to ethanol fermentation and then anaerobic digestion, after evaporating ethanol from the fermentation broth. Bioethanol yields of 0.41 ± 0.03 g/g and 0.50 ± 0.01 g/g (glucose) were achieved for duckweed harvested from the Penn State Living-Filter (Lemna obscura) and Eco-Machine™ (Lemna minor/japonica and Wolffia columbiana), respectively. The highest biomethane yield, 390 ± 0.1 ml CH4/g volatile solids added, was achieved in a reactor containing fermented duckweed from the Living-Filter at a substrate-to-inoculum (S/I) ratio (i.e., duckweed to microorganism ratio) of 1.0. This value was 51.2% higher than the biomethane yield of a replicate reactor with raw (non-fermented) duckweed. The combined bioethanol-biomethane process yielded 70.4% more bioenergy from duckweed, than if anaerobic digestion had been run alone.

Spent coffee enhanced biomethane potential via an integrated hydrothermal carbonization-anaerobic digestion process

This study reports the implications of using spent coffee hydrochar as substrate for anaerobic digestion (AD) processes. Three different spent coffee hydrochars produced at 180, 220 and 250 °C, 1 h residence time, were investigated for their biomethane potential in AD process inoculated with cow manure. Spent coffee hydrochars were characterized in terms of ultimate, proximate and higher heating value (HHV), and their theoretical bio-methane yield evaluated using Boyle-Buswell equation and compared to the experimental values. The results were then analyzed using the modified Gompertz equation to determine the main AD evolution parameters. Different hydrochar properties were related to AD process performances. AD of spent coffee hydrochars produced at 180 °C showed the highest biomethane production rate (46 mL CH4/gVS.d), a biomethane potential of 491 mL/gVS (AD lasting 25 days), and a biomethane gas daily composition of about 70%.

Mitigation of nitrogen in the poultry litter to enhance biomethane production

The objective of the study is to lower the nitrogen content in the substrate to mitigate the ammonia nitrogen generated in the anaerobic digestion of poultry litter using air stripping technique. The effect of nitrogen mitigation on the biomethane yield from poultry litter was studied in batch experiments with an organic load of 8 kg for a hydraulic retention time of 21 days in mesophilic ambiance. Air stripping results indicate that the free ammonia stripping is greatly influenced by the pH of the substrate and the aeration time. It is observed that the total Kjeldahl nitrogen content in the poultry litter substrate is reduced from 6.9% to 3.69% that is about a reduction of 53%. A significant improvement in the biomethane yield was noticed for poultry litter of which nitrogen content is lowered at a pH 11. The cumulative yield for air stripped substrate increased from 8.77 L/kg to 10.66 L/kg volatile solids. The biomethane production from air stripped poultry litter shows improvement of 18% compared to the control test. From this results, it is evident that the reduction in the nitrogen content of the substrate using air stripping at high pH value is a possible option for enhancing the biomethanisation of poultry litter.

Seasonal variation of elements composition and biomethane in brown macroalgae

To investigate the effect of seasonal variation on macroalgae biomass characteristics and its related energy content, four different algae species, two from the Fucales order (Fucus vesiculosus and Ascophyllum nodosum), and two from the Laminariales order (Saccharina latissima and Alaria esculenta), were harvested during spring, summer, autumn and winter over one year. The biomethane potential and the elemental composition were determined for all samples. Both Fucales species showed low biodegradability (<30%) with methane yields consistently below 20 Nm3 per wet tonne. Laminariales species, however, allowed up to 80% biodegradation efficiency, with methane yields varying between 20 and 70 Nm3 per wet tonne depending on the harvesting season. For each of the four algae the biomass concentrations of potassium, phosphorus, calcium, magnesium, sodium, sulphur, aluminium and iron was higher during spring/summer compared to autumn/winter. For heavy metals, variation was seen mainly for arsenic with higher values during autumn/winter. The highest values were observed for Laminariales (30–120 mg/kg total solids). Modelling the co-digestion of each algae with municipal wastewater sludge showed Laminariales species having the greatest potential as a profitable substrate for additional biomethane production generating up to 0.38 million Euro. However, seasonal variation could affect this expected income over 60% due to fluctuation in biomethane yields and biodegradability efficiency. Furthermore, the additional loading of cadmium and arsenic into the AD process suggested possible limitation for digestate utilisation in arable lands.

Carbon-to-nitrogen and substrate-to-inoculum ratio adjustments can improve co-digestion performance of microalgal biomass obtained from domestic wastewater treatment

ABSTRACTThis study comparatively evaluated the effect of co-substrates on anaerobic digestion (AD) and biochemical methane potential of wastewater-derived microalgal biomass, with an emphasis on carbon-to-nitrogen (C:N) and substrate-to-inoculum (S:I) ratios. A semi-continuous photobioreactor was inoculated with Chlorella vulgaris and the nutrient recovery potential was investigated. Derived microalgal slurry was subjected to AD in the absence and presence of co-substrates; model kitchen waste (MKW) and waste activated sludge (WAS). The results revealed that up to 99.6% of nitrogen and 91.2% of phosphorus could be removed from municipal wastewater using C. vulgaris. Biomethane yields were improved by co-digestion with both MKW and WAS. The maximum biomethane yield was observed as 523 ± 25.6 ml CH4 g VSadded−1, by microalgal biomass and MKW co-digestion in 50:50 ratio, at an initial chemical oxygen demand (COD) concentration of 14.0 ± 0.1 g l−1, C:N ratio of 22.0, and S:I ratio of 2.2. The observed biomethane yield was 80.7% higher than that of the mono-digestion. The highest improvement achieved by 50:50 co-digestion of microalgal biomass and WAS was 15.5%, with biomethane yield of 272 ± 11.3 ml CH4 g VSadded−1 at an initial COD concentration of 14.0 ± 0.1 g l−1, C:N ratio of 13.0, and S:I of 2.3.

Theoretical assessment of biomethane production from algal residues after biodiesel production

Energy shortage, global warming, and climate changes call for the creation and breakthroughs of renewable and sustainable energy technologies, and thus biofuels from microalgae have been the object of ever‐increasing interest. Microalgal biodiesel production presents as one of the promising options for biofuel production, since most microalgal species contain rich lipids. However, large amounts of residues are left behind after microalgal biodiesel production. In an effort to improve the potential economics of microalgal biofuels, it is essential to make full use of microalgal post‐extracts. This Focus Article determines the theoretical yields of microalgal biodiesel and biomethane together with the relevant calorific values during the continuous production. Based on the investigated species, the microalgal biodiesel and biomethane yields widely range from 6 to 134 g/kg‐VS and from 0.24 to 0.63 L/g‐VS, respectively, while the total calorific values experience the range of between 6.88 and 18.80 MJ/kg‐VS. Microalgal biodiesel production is not always required before anaerobic digestion, especially for those microalgal species with low lipid contents. Net energy ratio and cost‐effectiveness analysis are highlighted in order to evaluate the viability of the biorefinery process. Well‐funded research and development programs can help develop technologies and policies, thus driving the industry toward prosperity. WIREs Energy Environ 2018, 7:e273. doi: 10.1002/wene273.This article is categorized under: Bioenergy &gt; Science and Materials Bioenergy &gt; Systems and Infrastructure

Trace elements dosing and alkaline pretreatment in the anaerobic digestion of rice straw

The effect of trace elements (TEs) addition and NaOH pretreatment on the anaerobic digestion of rice straw was investigated in batch tests. Co, Ni and Se were added to the raw rice straw at different dosages. The NaOH pretreatment was applied to the rice straw both alone and in combination with the addition of TEs, in order to evaluate potential synergistic effects of the pretreatment and the TEs supplementation on the biogas production yields. The results obtained showed that the alkaline pretreatment was more effective than the TEs addition in increasing the cumulative biogas production, causing a 21.4% enhancement of the final biomethane yield, whereas the increase due to TEs dosing was not statistically significant. The analysis of volatile fatty acids (VFAs) confirmed that the NaOH pretreatment resulted in a higher production of VFAs, indicating an increased hydrolysis, while TEs addition did not cause significant changes in the VFA concentrations.

Mesophilic co-digestion of municipal solid waste and sewage sludge: Effect of mixing ratio, total solids, and alkaline pretreatment

A large number of biogas plants feeding with municipal solid waste (MSW) are installed throughout the world. However, researches are widely conducted with the aim of maximizing the process yield, in order to make it more comparable with fossil fuels. In the present paper, biomethane potential test (BMP) assays (37 °C) were conducted to maximize the biomethane production from anaerobic digestion (AD) of municipal solid waste (MSW) under different mixing ratios with sewage sludge (SS) (50:50, 60:40, 80:20, and 90:10), the total solid (TS) concentrations (5%, 10%, 15%, and 20%), and pretreatment with sodium hydroxide. Increase in SS ratio up to 40% led to a substantial increase in biomethane yield. After 18 days of retention time, 90% of the methane (280 NmL/g VS) was achieved. The results showed that the methane yield in liquid anaerobic digestion (L-AD) (5%-10% TS) was greater than high-solids anaerobic digestion (HS-AD) (15%-20% TS). Biomethane yield was increased up to 18% with sodium hydroxide pretreatment. The findings shows that such optimization framework can generally increase the biomethane yield up to 57%.

Effect of Harvest Time and Frequency on Biomass Quality and Biomethane Potential of Common Reed (Phragmites australis) Under Paludiculture Conditions

This study examined the effect of harvest time (from May to September) and dry matter partitioning on biomethane potential and methane yield per unit area of Phragmites australis cultivation under paludiculture conditions. The experimental site is part of a larger experimental platform (San Niccolo, Pisa) located within the Massaciuccoli Lake Basin in Central Italy (Tuscany, IT). The study also took into account the double cut strategy by evaluating the regrowth from June to September. Biomethane potentials ranged from 384 to 315 and from 412 to 283 NL CH4 kg VS−1 (normal liters of methane per kg of volatile solids) for leaves and stems, respectively. About digestion kinetics, maximum daily production rate (R max) was significantly affected by harvest time and not by plant partitioning. Along the harvest season, biomethane yield per unit area was mostly driven by the biomass yield showing an increasing trend from May (1659 Nm3 ha−1) to September (3817 Nm3 ha−1). The highest value was obtained with the double harvest option (4383 Nm3 ha−1), although it was not statistically different from the single harvest carried out in September. Owing to its remarkably lower yields, P. australis cannot be considered along the same lines as crops conventionally used for biogas production, but it may represent an interesting option for paludiculture cropping systems by coupling peatland restoration with bioenergy production. September harvest management seemed the most feasible option, although further investigation on crop lifespan is needed.

Comparison of pre-treatments to reduce salinity and enhance biomethane yields of Laminaria digitata harvested in different seasons

Pre-treatment can enhance anaerobic digestion of seaweed; however, seasonal variation in the biochemical composition of seaweed has a significant impact on the pre-treatment effect. In this study, various pre-treatments were employed for the brown seaweed Laminaria digitata harvested in March (with high ash content and low carbon to nitrogen (C:N) ratio) and September (with low ash content and high C:N ratio). Washing of L. digitata harvested in March with hot water (defined as 40 °C) removed 54% of the ash and improved the volatile solids (VS) content by 31% leading to an improved biomethane yield of 282 L CH4 kg VS−1. This pre-treatment affected a 16% increase in biodegradability, reduced salt accumulation in the digestate by 54%, and increased specific methane yield per wet weight by 25%. This level of effect was not noted for seaweed harvested in September, when the biodegradability is higher.

Direct hydrolysis of palm oil mill effluent by xylanase enzyme to enhance biogas production using two-steps thermophilic fermentation under non-sterile condition

Palm oil mill effluent (POME) is well known as the potential raw material for biogas production. However, the high hemicellulose and cellulose content (10–14% w/w in dry basis) of the palm fibre in POME are less accessible for biodegradable to sugars, therefore, limiting the carbon source for microorganisms for the biogas production. This study attempted to enhance the hydrolysis step of the biomass by enzymatic pretreatment of POME. The optimum temperature and hydrolysis time using the commercial xylanase (5 unit/mL) were at 50 °C for 12 h. Two-steps thermophilic process consisting of POME pretreatment by various concentrations of xylanase (5–20 unit/mL) under the optimum condition followed by biogas production at 60 °C for 45 days was carried out. In all cases, the substrate to inoculum volatile solids (VS) ratio and volume ratio were 1:1 and 4:1, respectively. The maximum biomethane (CH4) yield of 914 mL CH4/g VS was obtained from the fermentation of POME hydrolysed by 15 unit/mL of xylanase. However, it was not significantly different from those of the other three concentrations of xylanase (845, 870 and 851 mL CH4/g VS, respectively). They were about 2.5–3 folds higher than that of the control (POME without enzymatic hydrolysis) (297 mL CH4/g VS). Microbial community analysis revealed the presence of Clostridium sp. and Methanocaldococcus sp. as the dominant strains.

Anaerobic co-digestion of cattle manure and meadow grass: Effect of serial configurations of continuous stirred tank reactors (CSTRs)

In this study, anaerobic co-digestion of cattle manure (CM) and meadow grass (MG) with serial configurations of continuous stirred tank reactors (CSTRs) was investigated. Four laboratory-scale CSTRs were operated at thermophilic condition (55 °C), of which two CSTRs were connected serially with equal working volumes while the remaining two CSTRs were operated as single CSTRs as controls. Improvements on bio-methane yield, methane contents and solids reduction were observed with serial CSTR configurations. The results showed that co-digestion with 5% (w/w) MG with serial configurations of CSTRs produced 24% more bio-methane compared with single reactor, with the total hydraulic retention time (HRT) being the same. The volatile fatty acids (VFA) concentration was found higher in the 1st reactor, but was reduced by 40–50% in the 2nd reactor. The improved bio-methane yield with serial CSTR configuration with 100% CM was 8%, indicating that the serial CSTRs process is superior in a co-digestion set up with addition of MG.

Adaptation of continuous biogas reactors operating under wet fermentation conditions to dry conditions with corn stover as substrate

Corn stover (CS) is the agricultural by-product of maize cultivation. Due to its high abundance and high energy content it is a promising substrate for the bioenergy sector. However, it is currently neglected in industrial scale biogas plants, because of its slow decomposition and hydrophobic character.To assess the maximum biomethane potential of CS, long-term batch fermentations were carried out with various substrate concentrations and particle sizes for 72 days. In separate experiments we adapted the biogas producing microbial community in wet fermentation arrangement first to the lignocellulosic substrate, in Continuous Stirred Tank Reactor (CSTR), then subsequently, by continuously elevating the feed-in concentration, to dry conditions in solid state fermenters (SS-AD).In the batch tests, the <10 mm fraction of the grinded and sieved CS was amenable for biogasification, but it required 10% more time to produce 90% of the total biomethane yield than the <2 mm sized fraction, although in the total yields there was no significant difference between the two size ranges.We also observed that increasing amount of substrate added to the fermentation lowered the specific methane yield.In the CSTR experiment, the daily substrate loading was gradually increased from 1 to 2 gvs/L/day until the system produced signs of overloading.Then the biomass was transferred to SS-AD reactors and the adaptation process was studied. Although the specific methane yields were lower in the SS-AD arrangement (177 mL CH4/gvs in CSTR vs. 105 mL in SS-AD), the benefits of process operational parameters, i.e. lower energy consumption, smaller reactor volume, digestate amount generated and simpler configuration, may compensate the somewhat lower yield.

Enhanced biomethane production rate and yield from lignocellulosic ensiled forage ley by in situ anaerobic digestion treatment with endogenous cellulolytic enzymes

BackgroundEnzymatic treatment of lignocellulosic material for increased biogas production has so far focused on pretreatment methods. However, often combinations of enzymes and different physicochemical treatments are necessary to achieve a desired effect. This need for additional energy and chemicals compromises the rationale of using enzymes for low energy treatment to promote biogas production. Therefore, simpler and less energy intensive in situ anaerobic digester treatment with enzymes is desirable. However, investigations in which exogenous enzymes are added to treat the material in situ have shown mixed success, possibly because the enzymes used originated from organisms not evolutionarily adapted to the environment of anaerobic digesters. In this study, to examine the effect of enzymes endogenous to methanogenic microbial communities, cellulolytic enzymes were instead overproduced and collected from a dedicated methanogenic microbial community. By this approach, a solution with very high endogenous microbial cellulolytic activity was produced and tested for the effect on biogas production from lignocellulose by in situ anaerobic digester treatment.ResultsAddition of enzymes, endogenous to the environment of a mixed methanogenic microbial community, to the anaerobic digestion of ensiled forage ley resulted in significantly increased rate and yield of biomethane production. The enzyme solution had an instant effect on more readily available cellulosic material. More importantly, the induced enzyme solution also affected the biogas production rate from less accessible cellulosic material in a second slower phase of lignocellulose digestion. Notably, this effect was maintained throughout the experiment to completely digested lignocellulosic substrate.ConclusionsThe induced enzyme solution collected from a microbial methanogenic community contained enzymes that were apparently active and stable in the environment of anaerobic digestion. The enzymatic activity had a profound effect on the biogas production rate and yield, comparable with the results of many pretreatment methods. Thus, application of such enzymes could enable efficient low energy in situ anaerobic digester treatment for increased biomethane production from lignocellulosic material.

In-situ injection of potassium hydroxide into briquetted wheat straw and meadow grass – Effect on biomethane production

Alkaline pretreatment of lignocellulosic biomass has been intensively investigated but heavy water usage and environmental pollution from wastewater limits its industrial application. This study presents a pretreatment technique by in-situ injection of potassium hydroxide concentrations ranging from 0.8% to 10% (w/w) into the briquetting process of wheat straw and meadow grass. Results show that the biomethane yield and hydrolysis rate was improved significantly with a higher impact on wheat straw compared to meadow grass. The highest biomethane yield from wheat straw briquettes of 353mL.g−1 VS was obtained with 6.27% (w/w) potassium hydroxide injection, which was 14% higher than from untreated wheat straw. The hydrolysis rates of wheat straw and meadow grass increased from 4.27×10−2 to 5.32×10−2d−1 and 4.19×10−2 to 6.00×10−2d−1, respectively. The low water usage and no wastewater production make this a promising technology.

Boosting biomethane yield and production rate with graphene: The potential of direct interspecies electron transfer in anaerobic digestion

Interspecies electron transfer between bacteria and archaea plays a vital role in enhancing energy efficiency of anaerobic digestion (AD). Conductive carbon materials (i.e. graphene nanomaterial and activated charcoal) were assessed to enhance AD of ethanol (a key intermediate product after acidogenesis of algae). The addition of graphene (1.0g/L) resulted in the highest biomethane yield (695.0±9.1mL/g) and production rate (95.7±7.6mL/g/d), corresponding to an enhancement of 25.0% in biomethane yield and 19.5% in production rate. The ethanol degradation constant was accordingly improved by 29.1% in the presence of graphene. Microbial analyses revealed that electrogenic bacteria of Geobacter and Pseudomonas along with archaea Methanobacterium and Methanospirillum might participate in direct interspecies electron transfer (DIET). Theoretical calculations provided evidence that graphene-based DIET can sustained a much higher electron transfer flux than conventional hydrogen transfer.

The biomethane, silage and biomass yield obtainable from three accessions of Cynara cardunculus

In the light of the possible contribution of bioenergy to reducing the dependence on fossil fuel imports and to controlling greenhouse gas emission, a present priority is to develop crops which can be raised using minimal production inputs. The potential of the cardoon (Cynara cardunculus) has been investigated here by assessing the outcome of anaerobically digesting two cultivated forms and one wild one. Fermentation lab tests were performed on ensiled biomass, as in the real scale conditions, and they were aimed at measuring the biomethane production per unit of feedstock. The cultivated forms (‘Altilis 41’ and ‘Bianco avorio’) produced, respectively, 19.1 and 16.8t dry matter (DM) per hectare per year, from which, respectively 4074 and 4162Nm3 of biomethane was generated; the wild cardoon accession was less productive both in terms of biomass accumulation (11.8t DM per hectare per year) and estimated biomethane yield (2867Nm3). The yield of biomethane ranged from ∼200 (‘Altilis 41’) to 245 (‘Bianco avorio’ and wild cardoon) Nm3 per t DM, a level sufficiently high to justify considering C. cardunculus as a promising candidate bioenergy crop in the Mediterranean environment.

Effective bio-pretreatment of sawdust waste with a novel microbial consortium for enhanced biomethanation

Anaerobic digestion (AD) is considered an efficient cost-effective technology for sustainable biogas production from lignocellulosic wastes. A novel lignocellulosic degradation microbial consortium (LCDC) was isolated from rotten sawdust, and further used for sawdust pretreatment prior to AD. Results showed that pretreatment of sawdust for 10days led to significant reduction in cellulose, hemicelluloses, and lignin contents by 37.5%, 39.6%, and 56.7%, respectively, with respect to the control. In addition, the pretreatment enhanced cumulative biogas yield, which reached its maximum value of 312.0Lkg−1VS after 28days of AD (25.6% higher than the corresponding control). Moreover, the maximum significant cumulative methane yield was recorded after 28days of AD of the pretreated sawdust (155.2Lkg−1VS), which represented 72.6% higher than the corresponding control. Significantly higher biomethane yield from sawdust pretreated with LCDC confirms that this process is more economical than the previous reports.