Improving aerobic stability and biogas production of maize silage using silage additives

The effects of air stress during storage, exposure to air at feed-out, and treatment with silage additives to enhance aerobic stability on methane production from maize silage were investigated at laboratory scale. Up to 17% of the methane potential of maize without additive was lost during seven days exposure to air on feed-out. Air stress during storage reduced aerobic stability and further increased methane losses. A chemical additive containing salts of benzoate and propionate, and inoculants containing heterofermentative lactic acid bacteria were effective to increase aerobic stability and resulted in up to 29% higher methane yields after exposure to air. Exclusion of air to the best possible extent and high aerobic stabilities should be primary objectives when ensiling biogas feedstocks

Improving aerobic stability and biogas production of maize silage using silage additives

The effects of air stress during storage, exposure to air at feed-out, and treatment with silage additives to enhance aerobic stability on methane production from maize silage were investigated at laboratory scale. Up to 17% of the methane potential of maize without additive was lost during seven days exposure to air on feed-out. Air stress during storage reduced aerobic stability and further increased methane losses. A chemical additive containing salts of benzoate and propionate, and inoculants containing heterofermentative lactic acid bacteria were effective to increase aerobic stability and resulted in up to 29% higher methane yields after exposure to air. Exclusion of air to the best possible extent and high aerobic stabilities should be primary objectives when ensiling biogas feedstocks

Energy Demand and Economy of Nutrient Supply through Distillers Grains with Solubles from Bioethanol Production

Two different distillers grains with solubles are analysed for its contents of nitrogen and phosphorus in untreated and processed fraction. Processing includes decanting, heating and anaerobic digestion. Untreated DGS contains approx. 3.3 to 8 g N·l-1 and 0.2 to 0.5 g P·l-1. These concentrations can be increased by one order of magnitude through processing. Anaerobic digestion shifts the availability of nutrients from organic fixed forms to inorganic one. Furthermore, anaerobic digestion delivers energy from methane formed rather than the consumption of energy immanent with the other ways of processing

Biogas crops grown in energy crop rotations: Linking chemical composition and methane production characteristics

Methane production characteristics and chemical composition of 405 silages from 43 different crop species were examined using uniform laboratory methods, with the aim to characterise a wide range of crop feedstocks from energy crop rotations and to identify main parameters that influence biomass quality for biogas production. Methane formation was analysed from chopped and over 90 days ensiled crop biomass in batch anaerobic digestion tests without further pre-treatment. Lignin content of crop biomass was found to be the most significant explanatory variable for specific methane yields while the methane content and methane production rates were mainly affected by the content of nitrogen-free extracts and neutral detergent fibre, respectively. The accumulation of butyric acid and alcohols during the ensiling process had significant impact on specific methane yields and methane contents of crop silages. It is proposed that products of silage fermentation should be considered when evaluating crop silages for biogas production

Biogas Crops – Part II: Balance of Greenhouse Gas Emissions and Energy from Using Field Crops for Anaerobic Digestion

Several field crops, cultivated under north-eastern German conditions, are analysed for their ecological benefit if used for anaerobic digestion. The analyses is based on the assessment of cumulated energy demand necessary for the cultivation at different fertilisation levels, transport and storage of these crops as well as on the assessment of greenhouse gas emissions deriving from these processes. Although the values obtained are quite similar to each other this picture completely changes if considering the methane formation potential and hence the electricity available from these renewable energy sources. Cereals like rye, triticale, barley and maize as well as alfalfa show relatively low values of GHG emissions, and cumulated energy demand whereas hemp and Jerusalem artichoke have a considerable worse balance. In the case of high fertiliser input during cultivation the value of GHG emissions for Jerusalem artichoke even approaches the value for electricity produced within the German power-mix. Open-top tanks for digested energy crops may be a serious source of additional methane emissions

Installation of a Feed-and-Turn Dryer: An Option to improve Heat Utilization and Economy of an existing Biogas Plant

Feed-and-turn dryers may be installed in order to use excess heat from biogas CHPs especially in agricultural enterprises with otherwise low heat utilization. These dryers can be used for drying a manifold of agricultural produce. In this case draff, maize silage and saw dust were investigated. The focus was on drying effectiveness, economic benefits and probable changes in chemical composition of the materials investigated. Results demonstrate that the installation of the feed-and-turn dryer is a substantial improvement of the biogas plant. In the case investigated it significantly improves the energy efficiency by increasing heat utilization from 6,669 GJ·a-1 in 2007 to more than 27,542 GJ·a-1 in 2009. It provides, in addition, the agricultural enterprise with valuable equipment for producing high quality and high valuable feed and other products.  Finally, on-farm drying generates an additional income compared to purchasing equivalent products or to external drying

Results of batch anaerobic digestion test – effect of enzyme addition

The hydrolysis of lignocellulose is assumed to be the rate-limiting step in the anaerobic fermentation process. A fungal hydrolytic enzyme mixture was used to assess the enzymatic impact on different feedstocks for biogas production. The optimal conditions for enzymatic hydrolysis of rye grain silage, maize silage, grass silage, feed residues and solid cattle manure were determined in lab-scale experiments. Finally, the effects of enhanced hydrolysis on anaerobic digestion were investigated in batch digestion tests. Enzyme treatment of substrate showed Michaelis-Menten-like behavior and reached maximum values after 3 hours for reduced sugars as a product of hydrolysis. Methane production potential was determined for specific feedstock mixtures without enzyme, with inactivated enzyme and with active enzyme (with and without buffer). The results obtained show a clear increase in methane production after enzyme application for solid cattle manure (165 LN CH4∙kgODM-1  to 340 LN CH4∙kgODM-1 ), grass silage (307 LN CH4∙kgODM-1 to 388 LN CH4∙kgODM-1; enzyme plus buffer), feed residue (303 LN CH4∙kgODM-1 to 467 LN CH4∙kgODM-1), maize silage (370 LN CH4∙kgODM-1 to 480 LN CH4∙kgODM- 1)and a lower increase for rye grain silage (355 LN CH4∙kgODM-1 to 413 LN CH4∙kgODM-1). The ratios of heating values from methane yields to heating values from the dry materials ranged between 0.3 and 0.7 for the untreated feedstock and increased to levels between 0.6 and 0.9 after the different forms of enzyme application

Influence of silage additives on methane yield and economic performance of selected feedstock

Ensiling is an appropriate way of preserving feedstock for anaerobic digestion. Biological and chemical silage additives were used to improve silage quality and to prevent silage losses due to aerobic instability. Lab-scale experiments were conducted using alfalfa, grass and maize. Silages without additives and with chemical and biological additives were compared to the fresh material as well. The effect of silage additives was investigated using batch anaerobic digestion tests and comparing the results on an organic dry matter basis as well as on a hectare basis. In an economic assessment the costs of silage additives were compared to the additional proceeds which can be achieved from improving digestability and preventing silage losses. There seems to be some evidence that there is a correlation between organic acid content of silages and methane yield on organic dry matter basis. Considering aerobic instability of opened silos the additional income can over-compensate the costs of the application of chemical additives

Biogas Crops - Part I: Specifications and Suitability of Field Crops for Anaerobic Digestion

In Germany, the growing number of agricultural biogas plants causes an increasing demand for crops as a feedstock in both mono‑ and co‑digestion processes. Laboratory scale batch anaerobic digestion tests under mesophilic conditions according to the German Standard Procedure VDI 4630 were conducted to investigate the suitability of different plant species like barley (Hordeum vulgare), rye (Secale cereale), triticale (X Triticosecale), alfalfa (Medicago sativa), hemp (Cannabis sativa), Jerusalem artichoke (Helianthus tuberosus) and maize (Zea mays) for biogas production. Emphasis was placed on growing stage and maturity, respectively as well as on whole crop silage preparation without additives as a preservation method for biogas crops. Results presented indicate that biogas yield is clearly influenced by plant species and harvest stage. Ensiled matter shows a positive effect on biomethanation with higher biogas yields and methane contents than fresh matter investigated. Hence, storage as silages can be considered as pre‑treatment which has also potential to improve methane production from plant matter. Analyses of digested materials reveal considerable reduction of organic matter of all crops investigated

Energy balance, greenhouse gas emissions, and profitability of thermobarical pretreatment of cattle waste in anaerobic digestion

In this study modeled full scale application of thermobarical hydrolysis of less degradable feedstock for biomethanation was assessed in terms of energy balance, greenhouse gas emissions, and economy. Data were provided whether the substitution of maize silage as feedstock for biogas production by pretreated cattle wastes is beneficial in full-scale application or not. A model device for thermobarical treatment has been suggested for and theoretically integrated in a biogas plant. The assessment considered the replacement of maize silage as feedstock with liquid and/or solid cattle waste (feces, litter, and feed residues from animal husbandry of high-performance dairy cattle, dry cows, and heifers). The integration of thermobarical pretreatment is beneficial for raw material with high contents of organic dry matter and ligno-cellulose: Solid cattle waste revealed very short payback times, e.g. 9 months for energy, 3 months for greenhouse gases, and 3 years 3 months for economic amortization, whereas, in contrast, liquid cattle waste did not perform positive replacement effects in this analysis