Specific Methane Research Articles

Enhancement of sewage sludge thickening and energy self-sufficiency with advanced process control tools in a full-scale wastewater treatment plant

On their path to becoming sustainable facilities, it is required that wastewater treatment plants reduce their energy demand, sludge production, and chemical consumption, as well as increase on-site power generation. This study describes the results obtained from upgrading the sludge line of a full-scale wastewater treatment plant over 6 years (2015–2021) using three advanced process control strategies. The advanced process control tools were designed with the aim of (i) enhancing primary and secondary sludge thickening, (ii) improving anaerobic digestion performance, and (iii) reducing chemical consumption in the sludge line. The results obtained show that the use of advanced process control tools allows for optimising sludge thickening (increasing solids content by 9.5%) and anaerobic digestion (increasing both the removal of volatile solids and specific methane yield by 10%, respectively), while reducing iron chloride and antifoam consumption (by 75% and 53%, respectively). With the strategies implemented, the plant increased its potential energy self-sufficiency from 43% to 51% and reduced de-watered sludge production by 11%. Furthermore, the upgrade required a low investment, with a return of capital expense (CAPEX) in 1.98 years, which presents a promising and affordable alternative for upgrading existing wastewater treatment plants.

Methane production of banana plant: Yield, kinetics and prediction models influenced by morphological parts, cultivars and ripening stages

Banana trees and fruits with three ripening stages, including green, ripe, and overripe, of two cultivars, namely Nam wa and Hom were separated into different morphological parts for biogas yield determination. Specific methane yields (SMY) were significant different among banana parts (p ≤ 0.05). High non-structural carbohydrates and high non-lignocellulosic residual in substrates promoted high SMY. Pseudostem showed the highest share of energy yields among farm wastes which Nam wa cultivar provided higher energy potential than Hom. Peel presented the major energy source from fruit wastes which ripening stages did not have a significant effect on its SMY. Modified Gompertz model presented the best fit for methane production of most substrates. The SMY prediction models based on chemical constituents were developed to obtain conveniently used methane estimating tool which showed that a combination of lignin, hemicellulose, non-lignocellulosic residual, and crude fiber contents presented the highest performance for banana substrates.

Effect of low temperature and municipal wastewater organic loading on anaerobic granule reactor performance

Biogas production and municipal wastewater COD removal at low temperatures by granulated anaerobic biomass were investigated. Two anaerobic granule reactors were operated continuously for 1025 days by stepwise increase of organic loading from 1.3 to 15.2 g CODdissolved·l−1·d−1 at 25, 16, 12, 8.5, 5.5, and 2.5 °C. The sustained reactor performance was evaluated by COD removal efficiency, methane production, and microbial community analysis. Stable COD removal of 50–70% were achieved at 25–8.5 °C and up to 15 g CODdissolved·l−1·d−1, and no significant temperature effect was observed on specific methane production rate and yield. Below 8.5 °C, COD removal and methane yields reduced, but still significant methane formation was observed even at 2.5 °C. More than 90% of COD removed was converted to methane. Methanogenic archaea communities showed that temperature changes affected the major methane formation pathways, which explains temperature adaptability of the granules.

Strategy to enhance semi-continuous anaerobic digestion of food waste by combined use of calcium peroxide and magnetite

Optimizing methane production from food waste (FW) efficiently is always a hot topic in the field of anaerobic digestion (AD). In this study we aimed to improve the conversion of organics to methane by using CaO2 and magnetite to enhance the semi-continuous AD of food waste. Under the organic load of 2.5 g VS/L·d−1, the specific methane yield was increased from 333.9 mL CH4/g·VS to 423.4 mL CH4/g·VS by adding 0.01 g/L CaO2 with 0.4 g/L magnetite, improving the production of methane from FW. We assessed reactor performance, ORP changes, mass balance, enzyme activities and characterized the metagenomic profile of microorganisms involved in digestion. These microorganisms showed rapid conversion of volatile fatty acids and increased expression of genes related to hydrolysis and acid production. Thus, the addition of CaO2 and magnetite optimized the relationship between fermentation bacteria and methanogenic archaea to enhance the overall production of methane. Microorganisms evolved unique adaptive mechanisms in the co-operative environment of CaO2 and magnetite, as their energy metabolism patterns combined those controlled by individual CaO2 and magnetite addition. This method of combining a micro-aeration environment with conductive materials provides a new perspective for optimizing the AD of FW.

Methanosarcina thermophila bioaugmentation and its synergy with biochar growth support particles versus polypropylene microplastics in thermophilic food waste anaerobic digestion

Both biochar supplementation as well as bioaugmentation have been shown in literature to improve the methane yield of anaerobic digestion. In this study, the combination of both are evaluated by growing Methanosarcina thermophila on biochar support particles prior to augmentation of thermophilic food waste anaerobic digestion. Biochar stand alone, bioaugmentation solely, a combination of both added separately or grown together, and utilizing polypropylene (PP) microplastics as growth support instead were all tested when starting up a thermophilic process from mesophilic inoculum. Methanosarcina thermophila and biochar supplementation displayed synergy, with 5% M. thermophila on 1 g/L biochar presenting a 32% increase in specific methane yield over the control. Double the bioaugmentation dosage/concentration was also trialled with a thermophilic inoculum, and 10% M. thermophila grown on 2 g/L biochar displayed the best results with a 20% increase specific methane yield from its control standard.

Alleviating “inhibited steady-state” in anaerobic digestion of poultry manure by bentonite amendment: Performance evaluation and microbial mechanism

This study systematically evaluated the effects of bentonite as a possible additive to alleviate the “inhibited steady-state” induced by ammonia and acid accumulation during anaerobic digestion. Continuous stirred tank reactors fed with poultry manure were operated at 35 ± 1 °C either with bentonite or not. The results demonstrate that bentonite amendment increased average specific methane production by 35% as suffered from steady-state at an organic loading rate of 6.25 g VS/L·d. 16S rRNA gene amplicon sequencing revealed that the relative abundance of electron-donating Sedimentibacter and Syntrophomonas, and electrophilic Methanosarcina was increased by 110%, 91%, and 49%, respectively. The genera were identified as crucial for alleviating “inhibited steady-state”, through establishment of a more robust syntrophic pathway of methanogenic acetate degradation. The enhancement might result from the accelerated electron transfer by bentonite, which is qualified for serving as an exogenetic electron mediator due to containing abundant redox-active metal elements.

Evaluation of triticale anaerobic digestion in a double cropping system: Relation between biomass yield, chemical composition, and biomethane production

AbstractFor sustainable biomethane production, energy crops should not compete for land against feed and food. In response to this requirement, a set of practices for an innovative way to produce food and biomethane was developed in Italy with the Biogasdoneright™ model, which introduces the double‐cropping system along with digestate fertilization and minimum tillage. Triticale is a promising feedstock as energy crop in such systems. Ninteen varieties of triticale harvested at milk and dough development stages were evaluated. Principal component analysis showed that cellulose content positively affects methane production whereas starch content has only a very weak relation with specific methane yield and methane formation rate. Despite these relations, triticale chemical composition did not influence the profitability of bioenergy production as much as the total biomass solids yields, the total solids concentration at harvest, and the timing of growth. Triticale can be considered a suitable energy crop for biomethane targeting at least 4600 Nm3 CH4 per hectare. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Methane Production Potential from Apple Pomace, Cabbage Leaves, Pumpkin Residue and Walnut Husks

Circular economy aims to eliminate organic waste through its transformation, composting and processing into other products or energy. The main aim of the study was to determine the specific methane yield (SMY) of anaerobic digestion (AD) of four different fruit and vegetable residues (FVR). In addition, the reduction in greenhouse gas (GHG) emissions was calculated based on the assumption that maize will be replaced by the FVR as a feedstock for biogas production. The SMY of four residues (apple pomace, cabbage leaves, pumpkin peels and fibrous strands and walnut husks) was measured in the biomethane potential test (BMP) in wet anaerobic digestion technology. The highest SMY (297.81 ± 0.65 NL kgVS−1) was observed for cabbage leaves while the lowest SMY (131.07 ± 1.30 kgVS−1) was found for walnut husks. The concentrations of two inhibitory gasses (NH3 and H2S) in biogas were low and did not affect the AD process. Only biogas produced from cabbage leaves was characterised by higher NH3 and H2S concentrations resulting from the highest protein concentration in this waste. FVR used as feedstock in biogas production may decrease the area of maize cultivation. Therefore, the GHG emissions from maize cultivation will be reduced. In Poland only, the use of four studied FVR as feedstock for biogas production would contribute to the reduction of GHG emissions by 43,682 t CO2 eq.

Activated Carbon Facilitates Anaerobic Digestion of Furfural Wastewater: Effect of Direct Interspecies Electron Transfer

Anaerobic digestion of furfural wastewater suffers from toxicity to microbes, which reduces its performance. The toxic effects may be eliminated by a sustainable way of conductive material supplementation. In this study, the effect on anaerobic digestion of furfural (0.5–4 g/L) was investigated by adding 0–40 g/L granular activated carbon (GAC) in batch tests. The innovation of this current study is to explore the potential direct interspecies electron transfer (DIET) for the first time in furfural degradation as the sole substrate in anaerobic digestion. The results demonstrated that when furfural was the sole substrate, in the presence of GAC, the peak methane production rate was increased by 46.0%, while the specific methane yield was improved by 24.7%, compared with the control. Additionally, the electroactive Geobacter sulfurreducens abundance in biofilms attached to the surface of GAC was 19.0 folds higher than that in the control. The abundances of the related genes of methane metabolism and furfural degradation in biofilms were 1.1 and 5.8 folds higher than the control by metagenomic analysis, respectively. These lines of evidence suggested that the pathway of furfural metabolism to methane among Moorella species, G. sulfurreducens, and Methanothrix species based on DIET was likely established.

Bioelectrochemical enhancement of methane production from exhausted vine shoot fermentation broth by integration of MEC with anaerobic digestion

A microbial electrolysis cell integrated in an anaerobic digestion system (MEC-AD) is an efficient configuration to produce methane from an exhausted vine shoot fermentation broth (EVS). The cell worked in a single-chamber two-electrode configuration at an applied potential of 1 V with a feeding ratio of 30/70 (30% EVS to 70% synthetic medium). In addition, an identical cell operated in an open circuit was used as a control reactor. Experimental results showed similar behavior in terms of carbon removal (70–76%), while the specific averaged methane production from cycle 7 was more stable and higher in the connected cell (MECAD) compared with the unpolarized one (OCAD) accounting for 403.7 ± 33.6 L CH4·kg VS−1 and 121.3 ± 49.7 L CH4·kg VS−1, respectively. In addition, electrochemical impedance spectroscopy revealed that the electrical capacitance of the bioanode in MECAD was twice the capacitance shown by OCAD. The bacterial community in both cells was similar but a clear adaptation of Methanosarcina Archaea was exhibited in MECAD, which could explain the increased yields in CH4 production. In summary, the results reported here confirm the advantages of integrating MEC-AD for the treatment of real organic liquid waste instead of traditional AD treatment.

Influence of the substrate to inoculum ratio on the methane yield from the batch anaerobic digestion of river tamarind (Leucaena leucocephala) and Guinea grass (Panicum maximum)

AbstractThe substrate to inoculum ratio (SIR) is an often overlooked parameter in the determination of the methane potential of a substrate.In this article we highlight the importance of the SIR, in the determination of the biochemical methane potential of two substrates, Guinea grass (Panicum maximum) and river tamarind (Leucaena leucocephala). Additionally, the results of this method not only give the specific methane potential, but also the optimum substrate to inoculum ratio, which is an important parameter for bioreactor start‐up.The specific methane volumes of the two substrates are, 148 mL/gDM and 250 mL/gDM for the river tamarind and Guinea grass, respectively, with optimum substrate to inoculum ratios of 0.055 and 0.035, respectively. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Promoting direct interspecies electron transfer for methane production in bioelectrochemical anaerobic digestion: Impact of electrode surface area and switching circuit

The bioelectrochemical enhancement of direct interspecies electron transfer (DIET) for methane production was investigated in a UASB reactor under different electrode surface areas. The specific methane production rate is stabilized at 316.7 mL/g COD in the bioelectrochemical UASB (BUASB) reactor with an electrode surface area of 10 m2/m3, which is significantly higher than the 216.8 mL/g COD of the UASB reactor. The electroactive bacteria, involved in the DIET for methane production, is signifianctly increased in the BUASB reactor. When the electrode surface area is expanded to (20 and 30) m2/m3, the specific methane production rates in the BUASB reactor are further increased to (358.4 and 361.0) mL/g COD, respectively (p-value > 0.05). The theoretical methane production from the electrode surface is approximate 3.1% of the total methane production in all BUASB reactors, and the bioelectrochemical methane production is mainly attributed to the biological DIET pathway (54%) in the bulk solution. The BUASB reactor at the electrode surface area of 20 m2/m3 showes better performance according to the methane production, process stability, and enrichment of electroactive microorganisms. The bioelectrochemical system provides a new platform that can dramatically improve the performance of UASB process for treating brewery wastewater.

Enhancement mechanisms of iron powder on co-digestion of kitchen waste and Pennisetum hybrid

To investigate iron enhanced anaerobic digestion performance, a survey was conducted to examine how iron powder (IP) affected the stability of a co-digestion reactor for kitchen waste and Pennisetum hybrid in a semi-continuous mode. In addition, the mechanisms underlying this process were analyzed according to various parameters and microbial communities. The results showed that the maximum stable operational organic loading rate (OLR) for the IP reactor increased by 50% compared to that of the control reactor, while the specific methane yields and volumetric methane yields increased by 4.8%− 106.8% and 6.3%− 105.9%, respectively, when OLRs were 1.0–3.0 g VS/(L·d). Meanwhile, selective enrichment of propionate-utilizing bacteria and hydrogenotrophic methanogens may have promoted the conversion of volatile fatty acids while increasing gene abundance via a methane-forming pathway. The addition of IP changed the dominant microorganisms related to the methanogenesis pathway. Additionally, the occurrence of interspecies formate transfer promoted anaerobic digestion stability in the IP reactor.

Inoculum production from pig slurry for potential use in agricultural biogas plants

Biogas production may benefit from the use of specialized microbial consortia (inocula) to increase biogas yields in anaerobic digesters. For this study, a specialized inoculum was obtained from raw pig slurry by applying an innovative procedure. The aims of this research were: i) to compare the performance of this inoculum in the anaerobic digestion (AD) of four agricultural feedstocks with that of digestates commonly used for bioaugmentation of agricultural biogas plants; ii) to assess the duration of the methanogenic activity of this inoculum. The nutrient content of the residual liquid from inoculum production for its potential re-use as fertilizer was also assessed. Specific methanogenic activity and specific methane yield of the inoculum from pig slurry were higher (+28% and + 39% on average) than those of the two digestates. The inoculum successfully maintained its AD performance, almost unchanged, for a prolonged storage period (up to one year). The residual clarified liquid from inoculum preparation contains nutrients and mineral salts at very low concentrations. A possible way to recycle it could be fertigation. Inoculum production from pig slurry represents an additional possibility of valorisation of animal waste, from the storage tank to land spreading, in a context of biorefinery.

Biogas production from winery wastewater: Effect of the substrate-inoculum ratio on fly ash addition and iron availability

The effect of substrate-inoculum ratio and fly ash (FA) concentration on the anaerobic digestion of winery wastewater was studied. Two substrate-inoculum ratios (0.50 and 1 g soluble COD/g VSS) and five fly ash concentrations (25, 50, 75, 100 and 150 mg/L) were tested under mesophilic conditions. The results showed that 0.50 g soluble COD/g VSS was the best substrate-inoculum ratio. Regarding the FA, 100 mg/L improved the specific methane production by 79% compared to the control assay. In comparison, 150 mg/L produced an inhibition of methane production, with a 55% decrease in specific methane production with respect to the control assay. According to the bioavailability study, FA had a similar effect to a system with Fe-EDTA on anaerobic digestion, which could indicate that the Fe present in FA was present in the solution and bioavailable to microorganisms. Therefore, a possible mechanism for the action of FA on anaerobic digestion was proposed. Finally, the kinetic analysis showed that FA improved the maximum specific methane production rate and decreased the lag phase.

Biogas Production Enhancement through Chicken Manure Co-Digestion with Pig Fat

Chicken manure and pig fat are found abundantly around the globe, and there is a challenge to get rid of them. This waste has considerable energy potential to be recovered into fuel, but extracting this energy from some by-products, especially fat, isn’t an easy task. When anaerobic digestion technology stepped to the level of anaerobic co-digestion, the utilisation of hardly degradable waste became feasible. Our research was conducted on anaerobic co-digestion of chicken manure as the primary substrate with pig fat as a fat reach supplement in a semi-continuous mode at different organic load rates. The influence of fat waste on the process of biogas production from chicken manure and the composition of the obtained products was determined using an organic load rate of 3.0–4.5 kg VS·(m3·day)−1. A sturdy and continuously growing biogas production was observed at all organic load rates, implying the synergetic effect on chicken manure and pig fat co-digestion. The highest specific methane yield, 441.3 ± 7.6 L·kg VS−1, was observed at an organic load rate of 4.5 kg VS·(m3·day)−1. The research results showed that co-digestion of chicken manure with pig fat is an appropriate measure for fat utilisation and contributes to the increase in biogas yield, methane concentration, and overall methane yield at investigated organic load rates.

Effectiveness of layered inoculation in solid-state anaerobic co-digestion of pig manure and corn straw: Focus on macro-, micro-, and genetic-levels

Layered inoculation can achieve rapid start-up and promote methanation performance of anaerobic digesters. Daily specific methane yield (SMY) rapidly increased to 2.93 mL/g VS/d during 0–13 days, and cumulative SMY reached 212 mL/g VS in the solid-state anaerobic co-digestion (SS-AcoD) of pig manure and corn straw. Data were collected at macro-, micro-, and genetic-levels of each substrate layer. The results showed that layered inoculation could improve volatile fatty acids utilization and prevent adverse effects of high total ammonium nitrogen concentrations. Layered inoculation accelerated hydrolysis, acidification, and methanogenesis of substrates, as evidenced by the efficient inoculation of Bacteroidetes, Anaerolineales, Methanosphaerula, and Methanothrix, which were primarily from inocula. The various stages of SS-AcoD were synergistically initiated during the first 13 days, and acetoclastic pathway was boosted. These results further explain why layered inoculation is an efficient method for improving methanation performance of SS-AcoD and achieving efficient utilization of organic solid waste.

Co-production of Biohydrogen and Biomethane from Chicken Manure and Food Waste in a Two-Stage Anaerobic Fermentation Process.

Batch experiments were performed to evaluate the biohydrogen and biomethane production by co-digestion of chicken manure and food waste in a two-stage mesophilic fermentation process. Results showed that no hydrogen was produced in the first stage of sole chicken manure fermentation, while methane yield was 247.3 mL·g-1-VS. By comparison, the co-digestion process with food waste proportions of 50-85% obtained hydrogen yields of 15.5-57.5 mL·g-1-VS, and the methane yields and maximum specific methane production rates were also improved by 7.0-16.7% and 80%, respectively. Moreover, the highest hydrogen and methane yields were achieved during sole food waste fermentation process. The acetate was the main volatile fatty acid (VFA) produced during sole chicken manure fermentation process in the first stage. Statistical analysis revealed that hydrogen production from co-digestion process and sole food waste fermentation process followed the n-butyrate-type pathway. Meanwhile, it should be noticed that the co-fermentation of chicken manure and food waste had antagonistic effects on the hydrogen fermentation, implying that there might be some inhibition factors existing in chicken manure or produced during the co-fermentation process. At the beginning of methane fermentation, the VFA profiles were similar to those at the end of hydrogen fermentation, and the main VFA compositions changed to acetate and propionate in the latter period of methane production. The volatile solid removal efficiencies were also promoted in co-digestion process compared with sole chicken manure digestion, which were increased by 9.7-14.4% with food waste proportions of 50-80%.

Towards green whiskey production: Anaerobic digestion of distillery by-products and the effects of pretreatment

Using renewable biogas from the anaerobic digestion of distillery by-products as a low-carbon heat source can decarbonize the distillery process and support the distillery industry to transition to a more sustainable production process. This study investigated the anaerobic digestion performance of different types of whiskey by-products and the effects of acid pretreatment on the digestion of solid by-products. Results of biomethane potential assays showed that the methane yield from the unprocessed by-products was 330 mL/g volatile solids (VS) from draff, 495 mL/g VS from thin stillage, and 503 mL/g VS from thick stillage. For the processed by-products the specific methane yield was 370 mL/g VS from cake maize, 382 mL/g VS from wet distillers’ grains with solubles (WDGS), and 545 mL/g VS from syrup. Acid pretreatment (1% H2SO4 at 135 °C for 15 min) did not significantly improve the methane yield from solid by-products (such as draff and WDGS) but reduced the digestion time by 54.5% for cake maize. The microbial community analysis revealed that methane production from the untreated and acid-pretreated solid by-products (draff and WDGS) was mainly through the hydrogenotrophic methanogenesis pathway. The gross thermal energy in the form of methane produced from 100 tonnes of mixed unprocessed by-products (draff, thin stillage, and thick stillage) was calculated as 24.4 MWthh equivalent to 60.6% of the thermal energy consumed in whiskey production, which effected the same percentage of CO2 emissions reduction.

Co-digestion of two-phase olive-mill waste and cattle manure: Influence of solids content on process performance

The solids content is a key parameter in the development of anaerobic digestion as it can determine the proper operation and performance of the process. The influence of the total solids content on the mesophilic anaerobic co-digestion of two-phase olive-mill waste (2POMW) and cattle manure (CM) was investigated. Four different total solids (TS) concentrations, in a 75:25 mixture of 2POMW:CM, were studied in batch reactors of 2 L capacity: 10%TS (R10), 15%TS (R15), 20%TS (R20) and 28.6%TS (Reactor non-diluted). The methane yields and the organic matter removal efficiency for the reactor with 10 and 15% TS were significantly higher than in the reactors with a higher solids content (R20 and Rnd). The hydrolytic and acidogenic phases were not adversely affected by the total solid content since the concentration of volatile fatty acids (VFAs) increased as TS percentage increased. However, a clear effect on the methanogenic phase was observed, which led to the accumulation of VFAs in the reactors R15, R20 and Rnd. Experimental results have shown that the best conditions correspond to the reactor containing 10% TS. The volatile solids and VFA removal in reactor R10 were 57.5% and 93.7% respectively. Moreover, the methane yield and the specific methane production were 35.80 LCH4/kgVSadded and 82.51 LCH4/kgVSremoved respectively.