Biomethane Yield Research Articles

Biogas upgrading using membrane contactor process: Pressure-cascaded stripping configuration

Abstract In this paper, we present a novel pressure-cascaded stripping configuration for membrane contactor biogas upgrading processes. The work clearly illustrates that optimizing the stripping unit for the biogas upgrading process is crucial to maximize the plant productivity. Employing polypropylene (PP) hollow fiber membrane modules and water as physical absorbent, the effects of absorption pressure, gas-liquid flowrate, and vacuum mode were systematically studied. In addition, exploiting the solubility difference between CO 2 and CH 4 , as well as the preferential absorption of CO 2 in water, a pressure-cascaded stripping tank was implemented to recover and recycle the absorbed CH 4 in high purity. The proposed configuration simultaneously enhanced the biomethane yield (90%) and purity (97%), high enough to be linked to the natural gas pipeline. A preliminary analysis showed that the proposed configuration offers cost benefits for large-scale biogas upgrading plants, and a significant reduction of global warming potential (GWP) compared to conventional configuration. The process developed in this work will be implemented in a biogas pilot-plant site to assess its overall feasibility.

WITHDRAWN: Biomethane production from lignocellulosic biomass enhanced by bioaugmentation with anaerobic rumen fungi

Abstract The aim of this study was to reveal the effect of bioaugmentation with anaerobic rumen fungi on biogas production from lignocellulosic biomass, such as manure and macroalgae. Anaerobic rumen fungi Orpinomyces sp. , Piromyces sp. , Anaeromyces sp. and Neocallimastix frontalis, which received groups of genes that originated in bacteria by way of horizontal gene transfer, were used in the study to enhance biomethane yield. Rumen fungi at a concentration of 15% achieved greater production of biogas (3500 mL/d) and methane (+54.7%) in the digesters fed with the macroalgae Ulva lactuca and manure. Microbial community dynamics and quantification of rumen fungi in anaerobic digesters were also detected by next-generation sequencing and real-time quantitative PCR to control the effect of fungal augmentation. Diversity of bacterial and archaeal communities and quantities of anaerobic rumen fungi showed the increased performance of anaerobic digesters fed with Ulva lactuca thanks to the addition of anaerobic rumen fungi. The results also indicated that concentrations of rumen fungi and anaerobic microorganisms should be balanced for sufficient biomethane yield. Because of their nonspecific extracellular enzyme systems, anaerobic rumen fungi may be a promising alternative to improve biogas production from different types of algae and lignocellulosic compounds.

Effect of structural carbohydrates and lignin content on the anaerobic digestion of paper and paper board materials by anaerobic granular sludge.

Anaerobic digestion (AD) of lignocellulosic materials is commonly limited by the hydrolysis step. Unlike unprocessed lignocellulosic materials, paper and paper board (PPB) are processed for their fabrication. Such modifications may affect their methane yields and methane production rates. Previous studies have investigated the correlation between lignin and biomethane yields of unprocessed lignocellulosic materials; nevertheless, there is limited knowledge regarding the relationship between the AD kinetic parameters and composition of PPB. This study evaluated correlations of methane yields and Monod and Gompertz kinetic parameters with structural carbohydrates, lignin, and ash concentration of five types of PPBs. All components were used as single and combined independent variables in linear regressions to predict methane yield, maximum specific methanogenic activity (SMAmax ), saturation constant (Ks ), and lag phase (λ). Additionally, microbial community profiles were obtained for each PPB assay. Results showed methane yields ranging from 69.2 ± 8.61 to 97.2 ± 2.29% of PPB substrates provided. The highest correlation coefficients were obtained for SMAmax as function of hemicellulose/(lignin + ash) (R2 = 0.86) and for λ as a function of lignin + cellulose (R2 = 0.85). All other parameters exhibited weaker correlations (R2 ≤ 0.77). Relative abundance analyses revealed no major changes in the community profile for each of the substrates evaluated. The overall findings of this study are: (i) combinations of structural carbohydrates, lignin, and ash used as ratios of degradable to either non-degradable or slowly degradable fractions predict AD kinetic parameters of PPB materials better than single independent variables; and (ii) other components added during their fabrication may also influence both methane yield and kinetic parameters. Biotechnol. Bioeng. 2017;114: 951-960. © 2016 Wiley Periodicals, Inc.

Effect of N-methylmorpholine-N-oxide Pretreatment on Biogas Production from Rice Straw, Cocoa Shell, and Hazelnut Skin

Abstract This study investigated effects of chemical pretreatment with N-methylmorpholine-N-oxide (NMMO) on methane yields of rice straw, cocoa bean shell, and hazelnut skin. Three lignocellulosic materials were separately pretreated with NMMO at 120°C for 3 h. Subsequently, batch biomethane production tests were performed under mesophilic (37°C ± 2°C) conditions, also with the untreated feedstocks, to provide methane production baseline data. Pretreatment was particularly effective for rice straw, with an 82% increased biomethane production yield from 206 mL CH4/g volatile solids (VS) obtained with the untreated substrate. A lower enhancement of the biomethane yield from 199 to 226 mL CH4/g VS (i.e., 14% increase) was observed for cocoa shell. For hazelnut skin, NMMO pretreatment resulted in a faster digestion rate in the initial 7 days, increasing the biomethane yield from 17 to 27 mL CH4/g VS·day. However, the cumulative biomethane yield after 40 days was not affected by NMMO pretreatment.

Ensilage suitability and bio-methane yield of Arundo donax and Miscanthus × giganteus

Biogas production is a key technology for the sustainable use of agricultural biomass as a renewable energy source and maize (Zea mays L.) is the most commonly used energy crop in Italy. However, maize as an energy crop shows several negative aspects such as high environmental impact and a possible adverse effect on the price of food and feed commodities. For these reasons several perennial crops, and in particular miscanthus (Miscanthus×giganteus Greef et Deu.) and giant reed (Arundo donax L.), have recently generated wide interest because they are considered positive for environmental loads and footprint and already recognized as very high-yielding crops for Mediterranean environments. In order to evaluate the biogas yield potential of these crops, local accessions of arundo and miscanthus were cultivated, at very low inputs, in a northeastern area of Italy, harvested in summer and fall and submitted to an ensilage process, in comparison with maize. All ensiled biomasses were then submitted to anaerobic digestion, utilizing a 2:1 inoculum to substrate ratio (I:S) of volatile solids, through a laboratory Methane Test System. The perennial species can be stored as traditional silage with no need for additives, assuring a suitable biomass dry matter content at silage time (no more than 43%). Although arundo and miscanthus showed a significantly higher biomass yield at the fall harvest time with respect to maize, the latter gave an about 30% higher methane yield per hectare due to the very low biochemical methane potential (BMP) of both perennial species. Efforts have to be made to improve biodegradability and, consequently, the BMP of these perennial species in order to bridge the methane yield gap with respect to maize. In fact, the adoption of the perennial crops as energy crops for bio-methane production, could avoid the negative impact on environmental sustainability and depletion of limited resources (water), shortcomings evidenced by maize as an energy crop.

Utilization of Organosolv Waste Waters as Liquid Phase for Hydrothermal Carbonization of Chaff

Organosolv wastewater was used as the liquid source during the hydrothermal carbonization (HTC) of chaff at 200 °C for 4 h and compared to a control HTC of chaff in water. The produced hydrochars had a carbon content of 58 wt % and a higher heating value (HHV) of 23 MJ kg–1 independently of the employed liquid source. Concentrations of inorganic elements were analyzed as well as organic acids in the process water. The use of organosolv wastewater had no negative effects on the HTC process and hydrochar properties. Subsequently, the HTC process waters were used for biomethane production. Performing HTC in organosolv water led to a doubling of the biomethane yield as compared to water as liquid source. The use of this industrial wastewater in combination with the solid agricultural waste chaff has the potential of increasing the sustainability of the HTC process by the disposal of two waste stream sources at the same time as well as by reducing the amount of contaminated waters that would eventually have to...

Effect of Lipase Hydrolysis on Biomethane Production from Swine Slaughterhouse Waste in China

The purpose of this study was to evaluate biomethane production in anaerobic digestion of swine slaughterhouse waste (SSW) and the effect of lipase pretreatment on biomethane yield. Lipase extracted from porcine pancreas was employed to hydrolyze SSW at 37 °C for 24 h. Three different lipase concentrations of 0.04, 0.2, and 0.4% (w/v) were adopted. Anaerobic digestion was carried out in batch style for 50 days. The results showed that the highest experimental biomethane yield (EMY) of 851.6 mL/g of VSadded was achieved when the lipase concentration of 0.2% (w/v) was used, which was significantly higher (18.4%; α < 0.05) than that of the untreated group. Furthermore, the highest biodegradability (Bd) of 72.7% was also achieved at 0.2% (w/v) lipase-pretreated group. Results proved that the conversion of SSW to biomethane was improved through pretreatment of lipase hydrolysis and offered a promising method for disposal of SSW.

Effects of pungency degree on mesophilic anaerobic digestion of kitchen waste

This study investigated the influence of pungency degrees (PDs) on mesophilic anaerobic digestion of kitchen waste (KW). Batch tests were performed to evaluate the methane potential and production rate and the effect of PDs on organics degradation efficiency (in terms of volatile solids, protein and ether extract) at mesophilic temperature. Koch and Drewes model and modified Gompertz model were applied to assess the effects of PDs on the hydrolysis rate constant, biomethane yield rate and lag time. The results revealed that with the increasing contributions of PDs, the methane yield, organics degradation efficiency and hydrolysis rate of KW decreased while the pH values and concentrations of total ammonia nitrogen and free ammonia nitrogen were increased. Additionally, PDs lower than PD3 presented better digestion performance, and according to results of organics degradation and kinetics study, it could be suggested that appropriate range of PD in KW beneficial for AD is PD5–PD4.

Selective digestion of industrial potato wastes for efficient biomethanation: a sustainable solution for safe environmental disposal

Potato being the staple vegetable in India is widely cultivated and processed for different value additions. During processing of potato, a huge amount of waste is generated in the form of peel and meat (mash). These wastes constitute a potential feedstock for biogas generation. The present study is focused on mitigation of acidogenesis that occurs during early stages of anaerobic digestion (AD) of potato waste which eventually inhibits the process of methanogenesis. A novel strategy of selective digestion was adopted in which the leachate and solid slurry resulting from the first stage digestion were further subjected to second stage by separating the solid and liquid phases. The obtained results indicated that stepwise digestion enhanced biomethane yield with an increase in methane percent from 46.47 to 60.4 % and reduction in total COD to about 94 %. Another novel strategy adopted in this study was the use of specifically developed microbial consortia for AD of potato wastes instead of conventional inoculum for production of biogas. The obtained yield is at par with the conventional inoculums which suggests that the developed consortia could act as potential substitute. The present study paves the way for sustainable utilization of industrial potato wastes for bioenergy production by overcoming the problems associated with conventional processes.

Study on the bio-methane yield and microbial community structure in enzyme enhanced anaerobic co-digestion of cow manure and corn straw

The use of enzymes to improve anaerobic co-digestion (AcoD) of cow manure and corn straw was explored in this study, including cellulase pretreatment and direct additions of amylase and protease. The effects of enzymes on microbial community structure were investigated though PCR-DGGE method. Results showed that AcoD with amylase achieved the highest methane yield of 377.63ml·CH4/g·VS, which was an increase of 110.79%. The methane increment consumed the amylase of 4.18×10−5g/ml·CH4. Enzymes mainly affected the bacteria in the hydrolysis stage rather than the bacteria in the hydrogenesis and acetogenesis stage and the archaea in the methanogenesis stage. However, the experimental results demonstrated that enzymes had no negative influence on microbial communities; the predominant microbial communities were similar. Therefore, AcoD with amylase was an effective way to improve the bio-methane yield of cow manure and corn straw.

Enzymatic pretreatment of activated sludge, food waste and their mixture for enhanced bioenergy recovery and waste volume reduction via anaerobic digestion

In the present study, the in-situ produced fungal mash rich in hydrolytic enzymes was used for the pretreatment of activated sludge, food waste and their mixture prior to anaerobic digestion. The enzymatic pretreatment of activated sludge mixed with food waste resulted in the production of 3.72g/L glucose and 51mg/L free amino nitrogen, equivalent to 7.65g/L soluble chemical oxygen demand (SCOD) within 24h, accompanied with 19.9% of volatile solids (VS) reduction. After pretreatment of activated sludge and food waste by fungal mash, 19.1% and 21.4% of VS reduction were achieved respectively. Furthermore, the bio-methane yield of mixed waste pretreated with fungal mash was found to be 2.5 times higher than activated sludge without pretreatment, with a further VS reduction of 34.5%. These suggest a total VS reduction of 54.3% in the proposed anaerobic system with the pretreatment by fungal mash. Theoretical estimation further revealed that about 678millionkWh of electrical energy could be potentially recovered annually through the co-digestion of mixed waste activated sludge and food waste after the pretreatment with fungal mash in Singapore. In this case, the energy produced was higher than energy consumed by wastewater treatment. It was demonstrated in this study that the pretreatment of mixed activated sludge and food waste by in-situ produced fungal mash would be a promising option for enhancing biomethane production as well as for maximizing volume reduction of mixed waste via anaerobic co-digestion.

Studies on Bio-Pretreatment of Pine Needles for Sustainable Energy thereby Preventing Wild Forest Fires

Deforestation, forest fire hazard and exploitation of forest have been warning threats to our environment and ecosystem globally. In the present study an attempt has been made to enhance the biodegradability and biomethanation potential of treated pine needles, the leaves of a coniferous tree ( Pinus roxburghii ) by using Trichoderma spp. and Pseudomonas spp. thereby, utilizing the pine needles for green energy. Studies were carried out in four litre capacity polymer reagent bottles as anaerobic bioreactor at mesophilic conditions (35 ± 1°C) for 80 days. The experiments were replicated thrice and the results compared with untreated ground pine needles substrate (control). The results showed a specific biomethane production of 0.269 l/g VS destroyed from bio-pretreated substrates whereas it was 0.133 l/g VS destroyed for untreated substrate with a biodegradability of 10.41% and 4.78% respectively. Results indicate that bio-pretreated substrate produced a cumulative biomethane yield of 21.3 l/kg pine needles which was 285% higher as compared to the untreated pine needles substrate (5.53 l/kg). The present study may promote utilization of forest litter as natural resource, thereby preventing the wild forest fires which destruct local ecology.

Giant cane (Arundo donax L.) for biogas production: The effect of two ensilage methods on biomass characteristics and biogas potential

Arundo donax L. is a perennial plant that can substitute for traditional energy crops to produce biogas, reducing costs because of its high biogas yield per Ha cultivated and low agronomic and energetic inputs. Nevertheless, Arundo donax biomass needs to be ensiled to be preserved and used. Because no full-scale data exist about A. donax ensilage and the effect of this process on potential biogas production, in this work two different ensiling techniques, i.e. trench and silo-bag ensiling, were performed at full scale, and the processes studied for 200 days. Results obtained indicated that A. donax could be successful ensiled by using the two approaches. Ensilage proceeded by fermentation of organic acids already present in the biomass, i.e. malic and oxalic acids that were degraded, giving volatile fatty acid accumulation. This was different from corn ensiling characterized by starch fermentation to lactic acids. Biological processes determined a loss of the potential biomethane production, namely −20.1% and −7.6% for trench and silo-bag, respectively. Taking into consideration biomethane yield per Ha and ensilage losses, potential biomethane losses of 5000 Nm3 CH4 Ha−1 for trench silage and of 2000 Nm3 CH4 Ha−1 for silo bag, were estimated, respectively. Nevertheless, taking into consideration the higher biomass and biomethane yields Ha−1 in comparison with the other energy crops, A. donax still remained more efficient and cheaper than traditional energy crops in producing biogas.

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.

Enhancement of animal waste biomethanation using fruit waste as co-substrate and chicken rumen as inoculums

ABSTRACTThis work investigated the effects of co-substrates (orange, mango, and pineapple wastes) and inoculums (chicken rumen), pH, and total solid (TS) content on animal waste (cow dung, pig dung, poultry droppings) for efficient and high biomethane production. The biomethanation experiments were carried out in five different 1.5 L anaerobic digesters and incubated for 10 weeks. The results showed that co-digestion of animal wastes with fruit wastes and inoculums (additives) increased biomethane yield and reduced the startup time for biomethane generation as compared to animal wastes alone. In addition, cumulative biomethane yield increased with increase in pH while it decreased with increase in TS content.

Does the C/N ratio really affect the bio-methane yield? a three years investigation of buffalo manure digestion

Does the C/N ratio really affect the bio-methane yield? a three years investigation of buffalo manure digestion

A biorefinery concept using the green macroalgae Chaetomorpha linum for the coproduction of bioethanol and biogas

An innovative integrated biorefinery approach using the green macroalgae Chaetomorpha linum was investigated in the present study for the co-production of bioethanol and biogas. Among three pretreatments of C. linum biomass, consisting of acidic, neutral and alkali ones, 3% NaOH pretreatment gave the best result in terms of thallus disintegration, biomass recovery and enzymatic digestibility as demonstrated by scanning electron microscopy and saccharification tests. The hydrolysis of C. linum feedstock with a crude specific enzyme preparation, locally produced from fermentation of Aspergillus awamori, at 45°C, pH 5 for 30h gave the maximum yield of fermentable sugar of 0.22±0.02g/g dry substrate. An ethanol yield of 0.41g/g reducing sugar corresponding to about 0.093g/g pretreated algae was obtained after alcoholic fermentation by Saccharomyces cerevisiae. In the integrated proposed process, mycelium issued from the fungal fermentation, liquid issued from alkali pretreatment, residual from the non-hydrolysable biomass and all effluents and co-products represent a heterogeneous substrate that feed an anaerobic digester for biogas production. GC-analysis of this later showed that the biomethane yield reached 0.26±0.045L/gVS. This study presents therefore an eco-friendly biorefining process, which efficiently coproduce bioethanol and biomethane and generate only a single waste (0.3±0.01g/g) allowing an almost complete conversion of the algal biomass.

Biomethane potential evaluation of co-digestion of sewage sludge and organic wastes

Co-digestion of organic rich wastes and wastewater sludge to enhance biogas production has become an attractive economic possibility for water utilities. The suitability of the organic rich waste depends on its ability to produce biogas as well as its influence on the overall anaerobic digestion process. Biomethane potential evaluation was conducted to screen seven organic wastes and dehydrated algae. All co-substrates increased the bio-methane yield by three to six times compared with conventional anaerobic digestion of sewage sludge. Maximum co-digestion ratios were identifiable for most solid co-substrates including algae (6% wt/wt), undiluted food waste (5% wt/wt), bakery waste (5% wt/wt), and diluted commercial food waste (10% wt/wt). On the other hand, the maximum co-digestions ratio of beverage reject and sewage sludge was 10% (wt/wt). With the exception of fat-oil-grease, all solids free liquid co-substrates evaluated in this study showed a notable synergistic effect, to enhanced removals of total solids, volatile solids (VS) and chemical oxygen demand (COD) during anaerobic digestion. The increase in COD removal when co-digesting wastewater sludge and liquid waste was from 2 to 41%. Conversely, the co-digestion of most solid co-substrates resulted in additional VS and COD residuals in the final biosolids. Elevated concentrations of sulphur and phosphorous in all food waste co-substrates suggest that control measures to address H2S in biogas and the accumulation of phosphorus in sludge centrate may be necessary during full scale operation. Data presented here provide the basis for subsequent pilot scale evaluation of anaerobic digestion of these organic rich wastes and wastewater sludge.

Effects of thermal pretreatment on the biomethane yield and hydrolysis rate of kitchen waste

In this study, batch tests were performed to evaluate the effects of different thermal pretreatment temperatures (55–160°C) and durations (15–120min) on the anaerobic digestion of kitchen waste (KW). Two commonly used approaches, namely the modified Gompertz model and the approach developed by Koch and Drewes, were applied to assess the effects of the different pretreatment parameters on the biomethane yield, lag time and hydrolysis rate constant via data fitting. The subsequent anaerobic digestion of KW pretreated at 55–120°C presented greater efficiency, and longer treatment durations resulted in increased methane production and higher hydrolysis rate constants. These findings were obtained due to the lower nutrient loss observed in KW treated at lower temperature treatments compared with that found with higher temperature treatments. In general, the effects of thermal pretreatment on the lag phase and hydrolysis rate differed depending on the treatment parameters leading to the variations in the KW compositions. The soundness of the two model results was evaluated, and higher statistical indicators (R2) were found with the modified Gompertz model than with the approach developed by Koch and Drewes.

Production of bio-coal, bio-methane and fertilizer from seaweed via hydrothermal carbonisation

Macroalgae have emerged as a potential future source of feedstock for the production of chemicals and biofuels. The main drawbacks of macroalgae in terms of a biofuel feedstock are its low heating value (HHV), high halogen content, high ash content and high slagging and fouling propensity. In this investigation, three species of kelps; (i) Laminaria digitata (ii) Laminaria hyperborea and (iii) Alaria esculenta have been processed by hydrothermal carbonisation (HTC) in a batch reactor at two temperatures (200°C and 250°C). The yields and properties of the resulting hydrochars including their HHV, CHNS, mineral content and ash fusibility properties have been determined and compared to the starting material. Significant improvement in fuel quality is observed resulting in an increase in energy density from 10MJ/kg to typically 25MJ/kg, which is comparable to that of a low rank coal. The results indicate significant demineralisation of the fuel, in particular a significant removal of alkali salts and chlorine. This results in improved combustion properties due to a reduction in the slagging and fouling properties of the fuel. Analysis of the HTC water phase indicates the presence of high levels of soluble organic carbon consisting of sugars and organic acids, and high levels of potassium, magnesium and phosphorous. The potential for production of bio-methane and recovery of nutrients following anaerobic treatment of the water phase is assessed. A prediction of the bio-methane yields for the different seaweeds has been calculated. Processing of biomass collected throughout the growth season indicates the influence of seasonal variation on energy and nutrient recovery.