In-vitro method and model to estimate methane emissions from liquid manure management on pig and dairy farms in four countries.

Methane (CH4) emissions from manure management on livestock farms are a key source of greenhouse gas emissions in some regions and for some production systems, and the opportunities for mitigation may be significant if emissions can be adequately documented. We investigated a method for estimating CH4 emissions from liquid manure (slurry) that is based on anaerobic incubation of slurry collected from commercial farms. Methane production rates were used to derive a parameter of the Arrhenius temperature response function, lnA', representing the CH4 production potential of the slurry at the time of sampling. Results were used for parameterization of an empirical model to estimate annual emissions with daily time steps, where CH4 emissions from individual sources (barns, outside storage tanks) can be calculated separately. A monitoring program was conducted in four countries, i.e., Denmark, Sweden, Germany and the Netherlands, during a 12-month period where slurry was sampled to represent barn and outside storage on finishing pig and dairy farms. Across the four countries, lnA' was higher in pig slurry compared to cattle slurry (p < 0.01), and higher in slurry from barns compared to outside storage (p < 0.01). In a separate evaluation of the incubation method, in-vitro CH4 production rates were comparable with in-situ emissions. The results indicate that lnA' in barns increases with slurry age, probably due to growth or adaptation of the methanogenic microbial community. Using lnA' values determined experimentally, empirical models with daily time steps were constructed for finishing pig and dairy farms and used for scenario analyses. Annual emissions from pig slurry were predicted to be 2.5 times higher than those from cattle slurry. Changing the frequency of slurry export from the barn on the model pig farm from 40 to 7 d intervals reduced total annual CH4 emissions by 46 %; this effect would be much less on cattle farms with natural ventilation. In a scenario with cattle slurry, the empirical model was compared with the current IPCC methodology. The seasonal dynamics were less pronounced, and annual CH4 emissions were lower than with the current methodology, which calls for further investigations. Country-specific models for individual animal categories and point sources could be a tool for assessing CH4 emissions and mitigation potentials at farm level.

Assessment of the biochemical methane potential of in-house and outdoor stored pig and dairy cow manure by evaluating chemical composition and storage conditions.

Biogas production is a suitable option for producing energy from dairy and pig manure types. During manure storage, organic matter degradation results in methane emissions decreasing the potential biogas yield. The present research advances the understanding of the biochemical methane potential (BMP) and the chemical characteristics of manure collected year-round from sequential stages of the liquid manure management chain of commercial dairy cow and pig farms. To this end, manure samples from six livestock farms in Germany were analyzed. The results showed that changes in chemical composition during storage led to a 20.5% decrease in the BMP of dairy manure from the barn to outdoor storage. For fattening pig manure samples, there was a 39.5% decrease in the BMP from intermediate to outdoor storage. An analysis of BMP according to manure age showed that pig manure degrades faster than dairy manure; the importance of promptly feeding manure to the biogas plant in order to avoid significant CH4 emission losses and reduction in energy producing capacity was highlighted. The best BMP predictors for dairy manure were the contents of dry matter, volatile solids and lignin, whereas best BMP predictors for pig manure were dry matter and volatile fatty acid (VFA) content. Prediction models performed well for samples from outdoor storages; refinements for predicting BMP of less aged samples presenting lower chemical variability would be necessary.

Comparative effect of biochar and activated carbon addition on the mesophilic anaerobic digestion of piggery waste in batch mode.

A comparative study of the batch mesophilic anaerobic digestion of piggery waste was carried out with the addition of 5% biochar and 5% activated carbon. The results obtained showed that the bioreactors amended with biochar increased cumulative methane production, the kinetic constant for methane production and the COD removal efficiency compared to the control reactors and reactors with activated carbon addition. The maximum methane production and the kinetic constant were 6.9% higher in the reactors with biochar addition compared to the controls; while the COD removal efficiency was 3% higher in the case of biochar addition. In the case of activated carbon, only a slight improvement in anaerobic digestion performance was observed compared to the control.

Effect of organic loading rate on the anaerobic digestion of swine waste with biochar addition.

The aim of this study was to investigate the impact of biochar addition on the mesophilic semi-continuous anaerobic digestion of swine waste with a focus on the effects of the organic loading rate (OLR) on biogas production, methane yield, total volatile fatty acids (TVFA), alkalinity, ammonium, volatile solids (VS) removal efficiency and process stability. Four reactors, two with amended biochar (R1 and R2) and two without biochar addition as controls (R3 and R4), were operated at OLRs in the range of 2-7 g VS/(L d), which corresponded to hydraulic retention times (HRTs) in the range of 7-2 days, respectively. The addition of biochar initially caused an increase in the generation of biogas and methane when compared to the control reactors when the process operated at OLRs of 2 and 3 g VS/(L d). This behaviour could be attributed to the presence of several trace elements (such as Fe, Co, Ni and Mn) in the biochar, which are involved in the action of acetyl-CoA synthase and methyl coenzyme M reductase to catalyse key metabolic steps, especially the methanogenic stage. The pH, alkalinity, TVFA and TVFA/Alkalinity ratio values for the effluents remained within the optimal ranges for the anaerobic digestion process. It was also found that the increase in OLR in the range of 2-5 g VS/(L d) determined a proportional increase in the VS removal rate. However, when the OLR increased up to 7 g VS/(L d), a drastic decrease in the VS removal rate was found for the control reactors. Biochar amendment contributed to a more balanced state of the anaerobic process, preventing biomass washout.

Methane emissions from the storage of liquid dairy manure: Influences of season, temperature and storage duration.

Methane emissions from livestock manure are primary contributors to GHG emissions from agriculture and options for their mitigation must be found. This paper presents the results of a study on methane emissions from stored liquid dairy cow manure during summer and winter storage periods. Manure from the summer and winter season was stored under controlled conditions in barrels at ambient temperature to simulate manure storage conditions. Methane emissions from the manure samples from the winter season were measured in two time periods: 0 to 69 and 0 to 139 days. For the summer storage period, the experiments covered four time periods: from 0 to 70, 0 to 138, 0 to 209, and 0 to 279 continuous days, with probing every 10 weeks. Additionally, at the end of all storage experiments, samples were placed into eudiometer batch digesters, and their methane emissions were measured at 20 °C for another 60 days to investigate the potential effect of the aging of the liquid manure on its methane emissions. The experiment showed that the methane emissions from manure stored in summer were considerably higher than those from manure stored in winter. CH4 production started after approximately one month, reaching values of 0.061 kg CH4 kg-1 Volatile Solid (VS) and achieving high total emissions of 0.148 kg CH4 kg-1 VS (40 weeks). In winter, the highest emissions level was 0.0011 kg CH4 kg-1 VS (20 weeks). The outcomes of these experimental measurements can be used to suggest strategies for mitigating methane emissions from manure storage.

Inactivation of ESBL-/AmpC-producing Escherichia coli during mesophilic and thermophilic anaerobic digestion of chicken manure.

The high prevalence of extended-spectrum-ß-lactamase (ESBL)-/AmpC-producing Escherichia (E.) coli in European broiler farms leads to the possible dissemination of antibiotic-resistant strains into the environment using contaminated feces as organic fertilizer. The aim of the present study was to determine the influence of temperature on the reduction kinetics of two artificially added ESBL-/AmpC-producing E. coli strains during lab-scale mesophilic (37 °C, 42 °C) and thermophilic (55 °C) anaerobic digestion of chicken manure. The decimal reduction times (D-value) were approximately 3-6 days at 37 °C, 1.5 days at 42 °C and 48 min at 55 °C. Starting with initial E. coli counts of 7 log10 colony forming units (CFU) per milliliter, both E. coli strains were below the detection limit after 35 days at all temperatures; however, at 37 °C and 42 °C, ESBL-producing E. coli were still partially detectable by enrichment. Temperature and retention time were the main inactivation factors. No direct correlation could be found between pH, volatile fatty acids (VFA) or ammonia (NH3) and E. coli reduction. D-values were predicted for several temperatures between 37 °C and 55 °C and may help define time-temperature guidelines. Thermophilic digestion is an adequate method to rapidly inactivate ESBL-producing E. coli in chicken manure. At mesophilic temperatures, however, strict compliance of retention times and the prevention of short-circuiting become essential to gain an ESBL-producing E. coli free digestate.

Demand-driven biogas production from sugar beet silage in a novel fixed bed disc reactor under mesophilic and thermophilic conditions.

A newly developed fixed bed disc reactor (FBDR) which combines biofilm formation on biofilm carriers and reactor agitation in one single system was assessed for its applicability to demand-driven biogas production by variable feeding of sugar beet silage. Five different feeding patterns were studied at an organic loading of 4gVSL-1d-1 under mesophilic and thermophilic conditions. High methane yields of 449-462LNkgVS were reached. Feeding variable punctual loadings caused immediate response with 1.2- to 3.5-fold increase in biogas production rates within 15min. Although variable feeding did not induce process instability, a temporary decrease in pH-value and methane concentration below 40% occurred. Thermophilic temperature was advantageous as it resulted in a more rapid, higher methane production and less pronounced decrease in methane content after feeding. The FBDR was demonstrated to be well-suited for flexible biogas production, but further research and comparison with traditional reactor systems are required.

Optimised biogas production from microalgae through co-digestion with carbon-rich co-substrates.

Microalgae can be used to upgrade biogas to biomethane and subsequently be digested for biogas production. However, the low C:N ratio of species such as Arthrospira platensis may cause ammonia inhibition and low process stability during anaerobic digestion. This study investigates co-fermentation of A. platensis with carbon-rich co-substrates (barley straw, beet silage and brown seaweed) at a C:N ratio of 25 to enhance biomass conversion. No synergistic effects on biomethane potential could be proven in batch fermentation tests. However continuous digestion trials showed significantly improved process stability. Mono-digestion of A. platensis was stable only at an organic loading of 1.0gVSL(-1)d(-1). The optimum process co-digested A. platensis with seaweed and achieved stable operation at an organic loading of 4.0gVSL(-1)d(-1). Co-digestion of microalgae and seaweed can be effectively applied to integrated coastal biomethane systems.

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.

Production of hydrogen, ethanol and volatile fatty acids through co-fermentation of macro- and micro-algae.

Algae may be fermented to produce hydrogen. However micro-algae (such as Arthrospira platensis) are rich in proteins and have a low carbon/nitrogen (C/N) ratio, which is not ideal for hydrogen fermentation. Co-fermentation with macro-algae (such as Laminaria digitata), which are rich in carbohydrates with a high (C/N) ratio, improves the performance of hydrogen production. Algal biomass, pre-treated with 2.5% dilute H2SO4 at 135°C for 15min, effected a total yield of carbohydrate monomers (CMs) of 0.268g/g volatile solids (VS). The CMs were dominating by glucose and mannitol and most (ca. 95%) were consumed by anaerobic fermentative micro-organisms during subsequent fermentation. An optimal specific hydrogen yield (SHY) of 85.0mL/g VS was obtained at an algal C/N ratio of 26.2 and an algal concentration of 20g VS/L. The overall energy conversion efficiency increased from 31.3% to 54.5% with decreasing algal concentration from 40 to 5 VS g/L.

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.

Ensiling of seaweed for a seaweed biofuel industry.

Effective biogas production from seaweed necessitates harvest at times of peak quality of biomass and low-loss preservation for year-around supply. Ensiling of five seaweed species and storage up to 90days was investigated as a method to preserve the methane yield potential. Adequate acidification by natural lactic acid fermentation was difficult due to low rapidly fermentable carbohydrate contents, high buffering capacities and low initial numbers of lactic acid bacteria. Nevertheless, products of silage fermentation increased methane yields by up to 28% and compensated for volatile solid losses during ensiling. Preservation of the original methane yield potential was achieved for four of five seaweed species, provided that silage effluent is collected and utilised. 10-28% of the ensiled biomass was released as effluent with methane yields of 218-423LNkg(-1) VS. If further optimised, ensiling represents an effective method of preservation crucial for an efficient seaweed biofuel industry.

Production of hydrogen, ethanol and volatile fatty acids from the seaweed carbohydrate mannitol.

Fermentative hydrogen from seaweed is a potential biofuel of the future. Mannitol, which is a typical carbohydrate component of seaweed, was used as a substrate for hydrogen fermentation. The theoretical specific hydrogen yield (SHY) of mannitol was calculated as 5 mol H2/mol mannitol (615.4 mL H2/g mannitol) for acetic acid pathway, 3 mol H2/mol mannitol (369.2 mL H2/g mannitol) for butyric acid pathway and 1 mol H2/mol mannitol (123.1 mL H2/g mannitol) for lactic acid and ethanol pathways. An optimal SHY of 1.82 mol H2/mol mannitol (224.2 mL H2/g mannitol) was obtained by heat pre-treated anaerobic digestion sludge under an initial pH of 8.0, NH4Cl concentration of 25 mM, NaCl concentration of 50mM and mannitol concentration of 10 g/L. The overall energy conversion efficiency achieved was 96.1%. The energy was contained in the end products, hydrogen (17.2%), butyric acid (38.3%) and ethanol (34.2%).

Investigation of the optimal percentage of green seaweed that may be co-digested with dairy slurry to produce gaseous biofuel.

Ulva lactuca, a green seaweed, accumulates on beaches and shallow estuaries subject to eutrophication. As a residue, and a macro-algae, it is a source of sustainable third generation biofuel. Production of biomethane from mono-digestion of U. lactuca, however is problematic due to high levels of sulphur and low ratios of carbon to nitrogen. Fresh and dried U. lactuca were continuously co-digested with dairy slurry at ratios of 25%, 50% and 75% (by volatile solid content) in 6 number 5L reactors for 9months. The reactors digesting a mix with 75% U. lactuca struggled to reach stable conditions. Volatile fatty acid levels of 14,000mgl(-1) were experienced. The levels of ammonia increased with percentage U. lactuca in the mix. Optimum conditions were observed with a mix of 25% fresh U. lactuca and 75% slurry. A yield of 170LCH4kg(-1)VS was achieved at an organic loading rate of 2.5kgVSm(-3)d(-1).

Effects of ensiling, silage additives and storage period on methane formation of biogas crops.

Effects of the ensiling process, storage periods of up to 1 year and several chemical and biological silage additives on biomethanation were assessed for maize, sorghum, forage rye and triticale with the aim to identify optimised conditions for silage production of crops used as feedstock in biogas plants. Ensiling, prolonged storage and biological silage additives showed positive effects on methane yield of up to 11%. These could be attributed to increases in organic acids and alcohols during ensiling. A regression model including acetic acid, butyric acid and ethanol accounts for 75-96% of the variation in methane yield. Storage periods of up to 1 year for properly ensiled crops could be possible without losses in methane production, considering the increase in methane yield and the losses of dry matter during this period. However, taking storage losses into account silage additives showed little effect on methane production.