Currently in Slovenia, all biogas on agricultural biogas plants is used in cogeneration units for the production of electricity and heat, but only a small number of biogas plants distribute heat energy to other end users (because of technical and economic barriers), therefore the efficiency of cogeneration is relatively low. Biogas is relatively easy to store and can then be used anywhere and at any time. The possibility of storage of biogas represents its specific value (with storage and its use it is possible to compensate fluctuations, which have other renewable energy sources, such as wind and solar energy). Biogas offers us another possibility, for example, cleaning and its upgrading to phase of biomethane. With the injection of biomethane in the future it will be possible to take advantage of the existing network of natural gas and the gas can be transported over long distances, which will be accessible to users which are not achievable due to its location. With the injection of biomethane into the natural gas network will be possible to improve efficiency of existing agricultural and other biogas plants. By cleaning the biogas and upgrading to biomethane phase also will increase the number of potential biogas users. A review of potential technologies that will enable better use of biogas in the future is presented. Included are technologies for micro and other biogas plants and the potential for the introduction of biomethane technology in Slovenia.
COBISS.SI-ID: 4236136
The aim of the research was to examine the effect of extended storage and procedures between storage on microbial and chemical composition of cattle slurry. Effect of extended storage was examined in practical conditions with 100 m3 flexible storing tank for slurry and in laboratory conditions at different temperatures where the effect of aeration and mixing between extended storage were tested. In both trials with flexible storing tank for slurry it was established that with this kind of storage number of E. coli can be reduced in 2 months for 100-times, number of Enterococcus and C. perfringens for 10-times. During the storage of slurry in flexible storing tank changes in chemical composition typical for anaerobic fermentation were observed. During extended storage in laboratory trial at 30°C number of E. coli and Enterococcus were reduced for 400 and 200-times. Except for Enterococcus no additional decrease in the number of microorganisms was obtained with the effect of aeration and mixing. Because of the high temperature, aeration and mixing major changes in chemical composition were measured. With extended storage in laboratory trial at 10 and 15°C number of E. coli was reduced for 100-times and Enterococcus and C. perfringens for 10-times. At 10 and 15°C reduction of E. coli was achieved in 25 and 45 days. Changes in chemical composition were larger at 15°C but at both temperatures lower than in laboratory trial at 30°C. Slurry samples from farms with extensive production contained lower number of unwanted microorganisms than slurry samples from farms with intensive production.
COBISS.SI-ID: 4589160
Emissions of greenhouse gases in milk and beef production for the period 2007-2011 were quantified for farms participating to measures Organic farming (ORG), Sustainable rearing of domestic animals (SRDA) and for farms aside from these measures but receiving payments from Rural Development Programme (RDPothers). Emissions were assessed on the basis of data on milk production, longevity and reproduction parameters in dairy cows, on the basis of intensity of heifer rearing and daily gains in fattening cattle and by taking into account the differences in rearing systems. Emissions in milk production were on farms in ORG, SRDA and RDPothers 1.21, 1.11 in 1.07 kg of CO2 equivalent per kg of milk and in beef production 10.73, 10.14 and 10.01 kg CO2 equivalent per kg of carcass. Higher emissions in measures ORG and SRDA were mainly due to lower milk production and slower growth rate in fattening bulls and therewith related higher expenditure of energy for maintenance. Advantage of cattle production in measures ORG and SRDA is better adaptation to natural conditions which is expressed through lower quantities of concentrates and maize silage in diets. It was concluded that due to limited availability of concentrates on ORG farms it would be wise to pay more attention to production of high quality grassland forage with the aim to mitigate emissions of greenhouse gases.
COBISS.SI-ID: 3954792
On the basis of the results of published and unpublished trials and on the basis of analyzes of silages from Slovenian farms some of the factors that affected the energy value of grass silages were identified and quantified. It was established that the main reason for the low energy value of grass silages in Slovenia is low energy value of forage at the cutting time. The energy value of grassland forage depends on the species of meadow plants. In the period from the last days of April until the end of May, on average, the lowest energy value among the grasses was reached by orchard grass (5.54 MJ NEL per kg dry matter) and the highest by the perennial ryegrass (6.83 MJ NEL per kg of dry matter). Red clover had better net energy value than alfalfa (6.40 vs. 5.74 MJ per kg dry matter). In non-leguminous forbs the net energy value ranged from 5.62 MJ in broad leaved dock to 7.09 MJ NEL per kg of dry matter in creeping buttercup. Differences between species within the botanical groups were greater than differences between botanical groups (grasses, legumes and non-leguminous forbs 6.23, 6.07 and 6.10 MJ NEL per kg of dry matter respectively). There were also differences among varieties within individual species of grasses and legumes. The differences between the worst and the best variety ranged from 0.32 MJ NEL for meadow fescue to 0.84 MJ NEL per kg of dry matter in Italian ryegrass. The rate of the energy value reduction during the forage maturation depended on the plant species. In non-leguminous forbs the reduction of the energy value was slower (from -0.11 to -0.30 MJ NEL per 10 days) than in grasses (from -0.29 to -0.63 MJ NEL per 10 days) and legumes (from - 0.41 to - 0.52 MJ NEL per 10 days). In grasses, the slowest decline of NEL content was observed in perennial ryegrass and the fastest in orchard grass and Italian ryegrass. The energy value of grass silages was also affected by the soil contamination of forages. Based on samples of silages from Slovenian farms it was estimated that severe contamination of forage with soil reduces the net energy value of silage by 0.5 MJ per kg of dry matter.
COBISS.SI-ID: 4590952