Methane Content In Biogas Research Articles

Simultaneous biogas upgrading and acetic acid production by homoacetogens consortium enriched from peatland soil

Homoacetogens consortium was enriched from peatland soil, digested sludge, and rumen fluid for simultaneous carbon dioxide (CO2) consumption and acetic acid production in the biogas upgrading process. The homoacetogens consortium enriched from peatland soil (PL3) has a maximum CO2 consumption and acetic acid production of 95% and 120 mg/L, respectively. The methane content in upgraded biogas and acetic acid production of 98% and 543 mg/L was obtained at optimum hydrogen (H2) to CO2 at a ratio of 2:1, pH 8, and temperature 30 °C. The upgraded biogas (CH4 > 95%) can be used as vehicle fuel or injected into the natural gas grid. The homoacetogens consortium PL3 was dominated by Clostridium sp., Proteiniclasticum sp., and Petrimonas sp. Clostridium species are the main homoacetogens responsible for CO2 reduction using H2 as an energy source. The homoacetogens consortium PL3 could provide an opportunity for simultaneous biogas upgrading to biomethane and acetic acid production.

Can portable analyzers be reliable for biogas characterization?

Anaerobic digestion for treatment of swine wastewater is an attractive alternative, among other aspects, for the generation of biogas. This gas is composed predominantly of methane and can be converted into electrical and thermal energy. However, the knowledge of the biogas composition is of paramount importance, especially regarding the methane content due to its energetic properties. The alternatives for this determination usually require high cost and specialized technicians. Therefore, the search for simple and low cost alternative solutions and techniques can improve the biogas use as an energy source and favor energy sustainability in pig farming. The present study aimed to compare the results of the methane composition of a portable analyzer with that of a Gasboard gas analyzer. The biogas was collected and characterized in a full cycle swine farm from January to December 2019 in the municipality of Teixeiras (MG), Brazil. The methane composition values did not differ statistically for a 5% significance level between the evaluated methods. The use of the portable kit is a simple and low cost alternative in determining the methane content in biogas and can be used reliably.

Влияние коэффициента рециркуляции эффлюента метантенка на выход биоводорода в двухстадийном процессе анаэробной биоконверсии жидких органических отходов

This paper considers the production of biohydrogen in a two-stage process of anaerobic bioconversion of organic matter (OM) of liquid waste with recirculation of digester effluent into an anaerobic bioreactor for dark fermentation (ARDF). The values of the average biohydrogen specific yield (BSY) and the average volumetric biohydrogen production rate (VBPR) were obtained at 4 recirculation ratios (RR) of the digester effluent (1, 1.1, 1.18, 1.25) and 2 hydraulic retention times (HRT) ( 1 and 2.5) in ARDF. Organic loading rate (olr) varied from 7.96 to 21.6 g OM / (l ∙ day). The pH value in ARDF practically did not depend on RR and HRT, and ranged from 3.8 to 4.16. The maximum BSY was 0.108 l / (day ∙ g OMin) with a RR of 1.11 and a HRT of 2.5 days. The maximum VBPR was observed at RR 1 and HRT 1 day and amounted to 1.67 l / (l ∙ day). The methane content in biohydrogen-containing biogas at modes providing maximum BSY and VBPR was no more than 0.01%, but it increased sharply at higher values of RR and HRT. The hydrogen content in biogas averaged 50-52% for all combinations of RR and HRT, but it sharply decreased to 46.7% with HRT 2.5 and RR 1.25. In general, with RR 1.11 and HRT 1 day, an increase in BSY by 9.05% was observed, while the VBPR decreased by 1.04% (compared with RR 1.0 and HRT 1 day). In general, the experi- mental data obtained allow us to speak of a RR equal to 1.11 as the most effective for both HRTs in the studied range of RR.

Treatment of the Supernatant of Anaerobically Digested Organic Fraction of Municipal Solid Waste in a Demo-Scale Mesophilic External Anaerobic Membrane Bioreactor.

Conventional aerobic biological treatments of digested organic fraction of municipal solid waste (OFMSW) slurries–usually conventional activated sludge or aerobic membrane bioreactor (AeMBR)–are inefficient in terms of energy and economically costly because of the high aeration requirements and the high amount of produced sludge. In this study, the supernatant obtained after the anaerobic digestion of OFMSW was treated in a mesophilic demo-scale anaerobic membrane bioreactor (AnMBR) at cross flow velocities (CFVs) between 1 and 3.5 m⋅s–1. The aim was to determine the process performance of the system with an external ultrafiltration unit, in terms of organic matter removal and sludge filterability. In previous anaerobic continuous stirred tank reactor (CSTR) tests, without ultrafiltration, specific gas production between 40 and 83 NL CH4⋅kg–1 chemical oxygen demand (COD) fed and removals in the range of 10–20% total COD (tCOD) or 59–77% soluble COD (sCOD) were obtained, for organic loading rates (OLR) between 1.7 and 4.4 kg COD⋅m–3reactor d–1. Data helped to identify a simplified model with the aim of understanding and expressing the process performance. Methane content in biogas was in the range of 74–77% v:v. In the AnMBR configuration, the COD removal has been in the ranges of 15.6–38.5 and 61.3–70.4% for total and sCOD, respectively, with a positive correlation between solids retention time (SRT, ranging from 7.3 to 24.3 days) and tCOD removal. The constant used in the model expressing inhibition, attributable to the high nitrogen content (3.6 ± 1.0 g N-NH4+⋅L–1), indicated that this inhibition decreased when SRT increased, explaining values measured for volatile fatty acids concentration, which decreased when SRT increased and OLR, measured per unit of volatile suspended solids in the reactor, decreased. The alkalinity was high enough to allow a stable process throughout the experiments. Constant CFV operation resulted in excessive fouling and sudden trans-membrane pressure (TMP) increases. Nevertheless, an ultrafiltration regime based on alternation of CFV (20 min with a certain CFVi and then 5 min at CFVi + 1 m⋅s–1) allowed the membranes to filter at a flux (standardized at 20°C temperature) ranging from 2.8 to 7.3 L⋅m–2⋅h–1, over 331 days of operation, even at very high suspended solids concentrations (>30 g total suspended solids⋅L–1) in the reactor sludge. This flux range confirms that fouling is the main issue that can limit the spread of AnMBR potential for the studied stream. No clear correlation was found between CFV or SRT vs. fouling rate, in terms of either TMP⋅time–1 or permeability⋅time–1. As part of the demo-scale study, other operational limitations were observed: irreversible fouling, scaling (in the form of struvite deposition), ragging, and sludging. Because ragging and sludging were also observed in the existing AeMBR, it can be stated that both are attributable to the stream and to the difficulty of removing existing fibers. All the mentioned phenomena could have contributed to the high data dispersion of experimental results.

In-situ methane enrichment of biogas from anaerobic digestion of palm oil mill effluent by addition of zero valent iron (ZVI)

Palm oil mill effluent (POME) is a wastewater effluent that is generated from palm oil milling. Treatment of POME, especially using biological treatment methods, is a challenge as it contains high amounts of organic and sulfur compounds, and it is highly acidic. In this research, the effects of zero-valent iron (ZVI) on the enhancement of methane production from POME via anaerobic digestion were investigated. Furthermore, to identify the reactor operation modes that were suitable for the addition of ZVI, anaerobic digestion of POME was tested in three reaction configurations: batch reactor, fed-batch reactor, and continuous stirred-tank reactor (CSTR). In the batch mode, where acidic POME was fed with 16 g/L of ZVI dose just once, methane production increased by 74%. However, as the oxidation of ZVI under anaerobic conditions led to the production of hydroxyl ions, the pH of the medium continuously increased from approximately 7 to 9, which is not suitable for methanogenesis. In the fed-batch mode that involved intermittent feeding of acidic POME, the pH of the culture media was maintained at 6.8. This is because the extra hydroxyl ions generated from the oxidation reaction of ZVI tended to neutralize the acids in the feeding substrate. In addition, ZVI promoted the production of methane from POME and increased the average methane content in biogas from 62% to 76%. In the CSTR mode, which involved continuous feeding of acidic POME, ZVI increased methane production by 86% (from 1.79 to 3.32 L/day), methane content in biogas from 60 to 75%, and total chemical oxygen demand (tCOD) removal efficiency from 78 to 89 to 88–95%. Thus, the addition of ZVI can be a potential strategy for in-situ methane enrichment of biogas by anaerobic digestion of POME. This is because ZVI acts as a buffer for acid generation and provides extra electrons, ferrous ions, and ferric ions, which promote key microbial activities in the anaerobic digestion process.

A comparative analysis of biogas production from tomato bio-waste in mesophilic batch and continuous anaerobic digestion systems

Annually, agricultural activity produces an enormous amount of plant biomass by-product. Many studies have reported the biomethane potential of agro-industrial wastes, but only a few studies have investigated applying the substrates in both batch and continuous mode. Tomato is one of the most popular vegetables globally; its processing releases a substantial amount of by-product, such as stems and leaves. This study examined the BMP of tomato plant (Solanum lycopersicum Mill. L. cv. Alfred) waste. A comparative test revealed that the BMPs of corn stover, tomato waste,and their combination were approximately the same, around 280 mL methane/g Volatile Solid. In contrast, the relative biogas production decreased in the presence of tomato waste in a continuous mesophilic anaerobic digestion system; the daily biogas productions were 860 ± 80, 290 ± 50, and 570 ± 70 mL biogas/gVolatile Solid/day in the case of corn stover, tomato waste, and their mixture, respectively. The methane content of biogas was around 46–48%. The fermentation parameters of the continuous AD experiments were optimal in all cases; thus, TW might have an inhibitory effect on the microbial community. Tomato plant materials contain e.g. flavonoids, glycoalkaloids (such as tomatine and tomatidine), etc. known as antimicrobial and antifungal agents. The negative effect of tomatine on the biogas yield was confirmed in batch fermentation experiments. Metagenomic analysis revealed that the tomato plant waste caused significant rearrangements in the microbial communities in the continuously operated reactors. The results demonstrated that tomato waste could be a good mono-substrate in batch fermentations or a co-substrate with corn stover in a proper ratio in continuous anaerobic fermentations for biogas production. These results also point to the importance of running long-term continuous fermentations to test the suitability of a novel biomass substrate for industrial biogas production.

High efficiency in-situ biogas upgrading in a bioelectrochemical system with low energy input

Biogas produced from anaerobic digestion usually contains 30%-50% CO2, much of which must be removed, before utilization. Bioelectrochemical biogas upgrading approaches show promise, however, they have not yet been optimized for practical applications. In this study, a bioelectrochemical system with low energy input (applied cathode potential of -0.5 V vs. standard hydrogen electrode, SHE) was used for in-situ biogas upgrading. High efficiency CO2 conversion (318.5 mol/d/m2) was achieved when the system was operated with an organic load of 1.7 kgCOD/(m3 d). Methane content in the upgraded biogas was 97.0% and CO2 concentrations stayed below 3%, which is comparable to biogas upgraded with more expensive and less sustainable physiochemical approaches. The high efficiency of this approach could likely be attributed to a significant enrichment of Methanothrix (92.7%) species on the cathode surface that were expressing genes involved in both acetogenic methanogenesis and direct electron transfer (DET). Electromethanogenesis by these organisms also increased proton consumption and created a higher pH that increased the solubility of CO2 in the bioreactor. In addition, CO2 removal from the biogas was likely further enhanced by an enrichment of Actinobacillus species known to be capable of CO2 fixation. Artificial neural network (ANN) models were also used to estimate CH4 production under different loading conditions. The ANN architecture with 10 neurons at hidden layers fit best with a mean square error of 6.06 × 10−3 and R2 of 0.99.

Analysis of biogas content influence on the flame properties

The paper has examined the combustion of gas with variable methane content where it was supplied separately from the air. The analytical one-dimensional model of the diffusion straight-flow flame in the unrestricted and restricted space and a numerical three-dimensional model of the turbulent flame in a swirled airflow were used in this research. It has been established that in furnaces (in a restricted space) the maximum flame temperature depends only on the methane content in fuel and in average lower than the temperature of clean methane combustion by 20-70°C for conventional biogas and by 100-200°C for biogas with low methane content. The methane content decrease in gas leads to the diffusion flame length decrease in comparison with clean methane combustion by approximately two-fold for conventional biogas and fourfold for combustion of biogas with low methane content. For the turbulent flame in a swirled air flow, the flame length decrease is insignificant and is around 10% for conventional biogas and around 40% for biogas with low methane content. It can be concluded that by changing the methane content in biogas the heating plant operating mode can be stable on the condition that the biogas flow rate is controlled to ensure constant heat production during its combustion and turbulent flame with a swirled airflow. Combustion, in this case, can be done using the same burner.

BIOMETHANE POTENTIAL OF INVASIVE AQUATIC WEED WATER PRIMROSE

This study aims to examine the perspective of feedstock for producing biomethane from invasive aquatic weed water primroses (Ludwigia Hyssopifolia). The methane yield and methane content of biogas were analyzed and studied. The calculating methods of theoretical methane yield based on the elemental application or the theoretical chemical oxygen demand (COD) number were showed. The percentage of element chemicals, carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S) of raw materials were analyzed, and results were 40.2%, 5.03%, 22.13%, 1.8% and 0.24%, respectively. The plant biomass was contained moisture content, volatile carbon, fixed carbon and ash were 7.28%, 63.07%, 1.28% and 28.37%, respectively. From the water primroses calculated yield of methane (CH4), carbon dioxide (CO2) and ammonia (NH3) results were 54.90%, 41.40% and 3.70%, respectively. Therefore, the aquatic weed water primroses biomass are suitable feedstock for biogas production as well as future scale-up studies.

Effects of mixing ratios on anaerobic co-digestion of swine manure and rice straw: methane production and kinetics

The effects of seven mixing ratios (1:0, 3:1, 2:1, 1:1, 1:2, 1:3, and 0:1, swine manure (SM)/rice straw (RS), based on total solid) on anaerobic co-digestion (co-AD) of SM and RS mixtures were investigated in batch tests. The results showed that the highest methane yield (188.79 mL/g VSadded) was obtained at the ratio of 1:1, which was higher than that of the mono-digestion of RS or SM by 178.77% and 18.94%, respectively. For the remained six ratios, the methane yield increased with the increase of SM proportion. The highest organic matter degradation rates were also observed at the ratio of 1:1. The methane content of biogas and the pH, total alkalinity, and total ammonia nitrogen of the digestate all decreased with the increase of RS proportion and decrease of SM proportion. Additionally, the kinetic results of each anaerobic digestion (AD) step suggested that the co-AD of SM and RS at the ratio of 1:1 significantly improved the reaction rates of the four AD steps. Meanwhile, the methane production time was prolonged and the lag time of methanogenesis was shortened at the ratio of 1:1.

Perspectives of anaerobic decomposition of biomass for sustainable biogas production: A Review

Biogas production from biomass is an eco-friendly approach that offers renewable energy generation, waste recycling, biofertilizer production along with maintaining environmental quality. Anaerobic decomposition is a familiar practice used for biogas production in worldwide, whereas only few substrates were convenient for attaining desired methane concentration in biogas. Hence, further advancements are necessary for the exploration and utilization of various complex organic materials for the purpose. This article gives a clear outlook on potential of various biomass for biogas production, necessity of pretreatment, applicability of microbial/enzyme addition, maintenance of various process parameters, formulation of suitable digester designs and future scope of this area. The livestock wastes and agricultural wastes possess high energy generation potential (71%) and sustainable utilization of such wastes are admirable to commercialize biogas production in future. Hence, selection of biomass through biochemical methane potential (BMP) analysis and biomass pretreatment prior to anaerobic decomposition is adequate to improve the quality and quantity of generated biogas. Addition of effective microorganisms or respective enzymes along with the employment of suitable bioreactors, are other perspectives to enhance decomposition. The single-stage and multi-stage systems possess much attention than other types of reactors since that offers accurate process management at four different stages of decomposition. Moreover, the maintenances of optimum pH, temperature, volatile fatty acids, carbon/nitrogen ratio, etc. are crucial to evade system unsteadiness during decomposition. Since comprehensive mathematical models are appropriate to make the anaerobic decomposition process economically feasible and advancement with these forecasts are adequate to commercialize this technology in the future.

Optimisation of methane fermentation as a valorisation method for food waste products

The aim of the study was to optimize methane fermentation of food waste products based on the composition of substrates mixture and technical parameters of anaerobic digestion to obtain the highest biogas and methane production. The study was conducted in the laboratory scale in the mesophilic (37°C) and thermophilic (55°C) conditions. Also the effects of the organic loading rates (OLRs) on the biogas productivity and composition were analysed. The highest biogas yield was obtained in mesophilic digestion of the substrates mixture containing 50% of meat, 40% dairy products, 10% fruit and vegetables. It amounted to 740.4 ± 19.9 cm3·g ODM−1 of biogas with 68.6 ± 1.8% of methane. Biogas potential in thermophilic digestion was from 2.1 to 2.8 times lower for analogical feedstock. It was caused by high concentration of volatile fatty acids (VFAs) in the reactor chamber. The ratio of VFAs to alkalinity was on the level from 0.5 ± 0.1 to 0.8 ± 0.1. In continuous experiments, the average biogas production rate was from 2646.9 ± 117.3 cm3·d−1 for OLR of 2 g ODM·dm−3·d−1 to 9893.4 ± 362.0 cm3·d−1 for OLR amounting to 8 g ODM·dm−3·d−1. Methane content in biogas was between 65.6 ± 2.5 and 65.5 ± 1.9%, respectively. It was confirmed that applying OLR above 6 g ODM·dm−3·d−1 causes inhibition of methane fermentation.

Исследование влияние состава биогаза на свойства факела

The goal of this paper was the study flame lengths dependence on biogas composition to decide if the boiler`s furnaces using natural gas need reconstruction for biogas usage or it is possible to use the already existing equipment. The analytical one-dimensional model of a diffusion straight-flow flame in unrestricted and restricted space and the numerical three-dimensional model of a turbulent flame in a swirled airflow have been applied in this research. The research has analyzed the flame length for methane content of 20 to 100% in biogas. It has been concluded that by changing the methane content in biogas the heating plant1s operating mode can be stable on the condition that the biogas flow rate is controlled to ensure constant heat production during its combustion and turbulent flame with a swirled airflow. Combustion, in this case, can be done by using the same burner and without changing the size of the furnace.

Расчет совместного сжигания биогаза и RDF топлива

The paper suggests the calculation method of combustion when solid and gaseous fuels are cofired. The calculation is suggested to carry out per unit of heat output released during combustion but not per unit of mass or volume of fuel. The method has been tested for evaluation of greenhouse gas emissions during combustion of different fuel types and during waste and landfill gas cofiring. During coal and waste combustion, the CO2 content in products of combustion is around 0,05 m3/MW, for natural gas combustion - 0,028 m3/MW which is 1,8 times lower than for coal firing. During biogas combustion, the carbon dioxide content in the combustion products depends on the methane concentration in biogas and is around 0,04...0,06 m3/MW. The increased CO2 emission during biogas combustion in comparison to natural gas is explained by a high carbon dioxide content in biogas itself. Having in mind that biogas creates a significant greenhouse effect due to methane presence in it the landfill gas utilization, which would have been released into the atmosphere anyway, leads to greenhouse gas emissions decrease by 0,6...1,9 m3/MW of CO2 equivalent.

Effective pretreatment of lignocellulosic co-substrates using barley straw-adapted microbial consortia to enhanced biomethanation by anaerobic digestion

Microbial pretreatments have been identified as a compatible and sustainable process with anaerobic digestion compared to energy-intensive physicochemical pretreatments. In this study, barley straw and hay co-substrate was pretreated with a microaerobic barley straw-adapted microbial (BSAM) consortium prior to anaerobic digestion. The improved digestibility was investigated through 16S rRNA gene sequencing, microbial counts and C:N ratios. BSAM pretreatment resulted in 15.2 L kg−1 TS of methane yield after 35 days, almost 40 times more than the control. The methane content in total biogas produced were 58% (v/v) and 10% (v/v) in BSAM and control, respectively. This research demonstrated that BSAM-based pretreatment significantly increased the digestibility and surface area of the lignocellulosic material and considerably enhanced biomethanation. This study generates new potential bio-research opportunities in the emerging field of lignocellulosic anaerobic digestion-biorefineries.

Study on interchangeability of seed based feedstocks for biogas production in multi-feeding mode

Biogas is an excellent renewable fuel providing gas for clean energy applications and fertilizers for organic farming. In the present study, seeds from four tree species of Acacia nilotica , Albizia lebbeck , Prosopis juliflora , and Leucaena leucocephala have been utilized for biogas production as alternative feedstocks. They have been investigated in a mixed-feeding mode in a single digester to tackle the feedstock availability and seasonality challenges. The investigations were conducted in a 300 ​L anaerobic digester for 120 days under daily feeding mode. The average specific biogas yield and specific methane yield was found to be 0.425 ​m 3 /kg of volatile solids and 0.228 ​m 3 /kg of volatile solids, respectively. The average volumetric methane content in biogas was 54.7%. This paper presents a unique study on anaerobic digestion of selected seeds in a mixed-feeding mode to provide broad opportunities for their efficient and sustainable utilization. • Interchangeability of tree species seeds explored for 120 days in the mixed-feeding mode for biogas production. • Anaerobic digestion parameters for the utilization of these seeds are investigated in detail. • An amount of 3.0–3.5 ​kg of seeds is required to produce one cubic metre of biogas. • Specific biogas yield of 0.425 ​m 3 /kg VS with methane of 54.7% and TVSMRE as 46.0% were found.

Evaluation of biogas production potential of trace element-contaminated plants via anaerobic digestion

Within the domain of phytoremediation research, the proper disposal of harvestable plant parts, that remove pollutants from contaminated soil, has been attracted extensive attention. Here, the bioenergy generation capability of trace metals (Cu, Pb, Zn, Cd, Mn, and As) polluted plants was assessed. The biogas production potential of accumulators or hyperaccumulator plants, Elsholtzia haichowensis, Sedum alfredii, Solanum nigrum, Phytolacca americana and Pteris vittata were 259.2 ± 1.9, 238.7 ± 4.2, 135.9 ± 0.9, 129.5 ± 2.9 and 106.8 ± 2.1 mL/g, respectively. The presence of Cu (at approximately 1000 mg/kg) increased the cumulative biogas production, the daily methane production and the methane yield of E. haichowensis. For S. alfredii, the presence of Zn (≥500 mg/kg) showed a significant negative impact on the methane content in biogas, and the daily methane production, which decreased the biogas and methane yield. The biogas production potential increased when the content of Mn was at 5 000–10,000 mg/kg, subsequently, decreased when the value of Mn at 20,000 mg/kg. However, Cd (1–200 mg/kg), Pb (125–2000 mg/kg) and As (1250–10,000 mg/kg) showed no distinctive change in the cumulative biogas production of S. nigrum, S. alfredii and P. vittata, respectively. The methane yield showed a strong positive correlation (R2 =0.9704) with cumulative biogas production, and the energy potential of the plant residues were at 415–985 kWh/ton. Thus, the anaerobic digestion has bright potential for the disposal of trace metal contaminated plants, and has promising prospects for the use in energy production.

Anaerobic digestion of sewage sludge pretreated by high pressure homogenization using expanded granular sludge blanket reactor: Feasibility, operation optimization and microbial community

Biogas production via anaerobic digestion from sewage sludge have been investigated in different reactors. However, the efficient conversion of sewage sludge into biogas via continuous operational reactor with short retention time, have been overlooked. Considering the liquid-like property of sewage sludge pretreated by high pressure homogenization (HPH), in this study, the biogas production from HPH-pretreated sewage sludge was investigated in an expanded granular sludge blanket (EGSB) reactor for 219 d. Under optimized hydraulic retention time (HRT) of 6 d, upflow velocity of 4 m/h and organic loading rate (OLR) of 1.66 kg total chemical oxygen demand (TCOD)/(m3·d), the raw sludge was digested with a biogas production, methane content in biogas, TCOD and volatile solid (VS) removal of 215 mL/(gTCOD)·d, 52 %, 43 % and 35 %, respectively. After sludge HPH pretreatment, the HRT was shortened to 5 d due to the sludge disintegration of 24 % and enhanced growth of acetolastic Methanosaeta and hydrogenotrophic Methanolinea, subsequently, the biogas production, methane content in biogas, TCOD and VS removal increased to 240 mL/(gTCOD)·d, 57 %, and 58 % and 43 %, respectively. Abundance of dominant bacterial phylum Chloroflexi and archaeal genera Methanosaeta significantly increased for the improvement of organic biodegradation and methane production, respectively, reflecting the successful EGSB operation. Due to the good performances of EGSB reactor for the anaerobic digestion of HPH-pretreated sewage sludge, the combined HPH-pretreatment and EGSB reactor is promising to be applied in sustainable wastewater treatment plants.

Effect of silage maize plant density and plant parts on biogas production and composition

Higher maize plant density represents a possible tool for biomass yield improvement but the effect on biogas production and quality has not been intensively investigated so far. The aim of the study was to compare two different plant densities (90 000 and 130 000 plants ha−1) and their effects on yield and biogas production. Experiments were carried out at two sites in Central Bohemia in 2014 and 2015. Specific biogas yield of maize ears and stover was evaluated in batch tests. In both years, there were significantly higher dry matter yield, volatile solids (VS) degradation, and methane content in biogas from ears in comparison with stover. Stover produced on average 90% of biogas per weight unit (625–719 L kg−1 VS) compared to ears (721–801 L kg−1 VS) depending on locality and year. During the batch tests, ears produced more biogas than stover with the exception of the period from the 4th to 11th day when specific biogas yield of stover was higher. Biogas hectare yield of ears (5039–8962 m3 ha−1) was 1.3–1.8 times higher than biogas hectare yield of stover (3943–4865 m3 ha−1). The influence of plant density on dry matter yield and biogas hectare yield was not significant, but higher plant density supported faster dynamics of specific biogas yield of ears in both years and higher volatile solids degradation of ears in 2014.

Green Dairy Plant: Process Simulation and Economic Analysis of Biogas Use in Milk Drying

A project of a new milk drying unit processing 4800 kg/h of fresh milk into milk powder with expected steam consumption of 1000 kg/h (equivalent to ca. 2.6 GJ/h) was assessed. In this paper, investment profitability of this project was analyzed combining mathematical modeling, market analysis, and parametric sensitivity study. Aspen Plus was used as the simulation environment to determine values of key process variables—major streams, mass flows, and energy consumption. Co-digestion of cattle manure in an adjacent biogas plant was considered to provide biogas to partially or completely substitute natural gas as an energy source. As biogas composition from potential co-digestion was unknown, variable methane content from 45 to 60 mol.% was considered. In the next step, thorough economic analysis was conducted. Diverse effects of biogas addition depending on market prices, biogas treatment costs, and biogas methane content were simulated and evaluated. In a market situation closest to reality, biogas mixing to boiler fuel decreased simple payback period from 11.2 years to 5.1 years. However, if biogas treatment costs were high (final biogas price equal to or above 0.175 EUR/m3), the simple payback period was increased two- to sixfold, making the analyzed project practically unfeasible.