The aim of this study was to analyse the effect of different nitrogen increase rates in feedstock on the process stability and conversion efficiency in anaerobic digestion (AD). The research was conducted in continuously stirred tank reactors (CSTR), initially filled with two different inocula: inocula #1 with low and #2 with high nitrogen (N) concentrations. Three N feeding regimes were investigated: the “0-increase” feeding regime with a constant N amount in feeding and the regimes “0.25-increase” and “0.5-increase” where the N concentrations in feedstock were raised by 0.25 and 0.5 g·kg−1, respectively, related to fresh matter (FM) every second week. The N concentration inside the reactors increased according to the feeding regimes. The levels of inhibition (Inhibition) in specific methane yields (SMY), related to the conversion efficiency of the substrates, were quantified. At the N concentration in digestate of 10.82 ± 0.52 g·kg−1 FM measured in the reactors with inoculum #2 and “0.5-increase” feeding regime, the level of inhibition was equal to 38.99% ± 14.99%. The results show that high nitrogen increase rates in feeding regime are negatively related to the efficiency of the AD process, even if low volatile fatty acid (VFA) concentrations indicate a stable process.

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To design biogas plants, it is necessary to have accurate data about the properties and biogas productivity of the available substrates. Reference data should not be used because the performance of the same substrate can vary significantly. In this research,chicken, horse, sheep and rabbit manure from one of the farms inthe Belgorod region of Russia were analyzed, and the parameters of a biogas station for the processing of this raw material were calculated.The biogas yield of the substrates was determined using the Hohenheim Biogas Yield Test. It was found that the specific biogas yield from the droppings of broilers, laying hens, rabbits, sheep, and horses, and from corn silage were, respectively, 456, 363, 390, 189, 116 and 618 ml/g оDM. The methane content in the biogas was 58.00, 58.50, 57.00, 62.00, 65.00 and 53.60%, respectively. In most cases, the obtained results differed significantly from the data presented in publications of other researchers and reference books.The biogas plant parameter calculations were made according to generally accepted equations, taking into account the characteristics of the studied substrates. Based on the results, it can be concluded that to dispose of the animal excrement of this farm, it is necessary to build a biogas plant with a bioreactor of volume 102.2 m3 and an engine with a power of 12 to 31 kW. The planned output of electric and thermal energy would be 246.19 and 410.27 kWh/day, respectively. Keywords: Hohenheim Biogas Yield Test, rabbit manure, horse dung, sheep manure, chicken droppings, biogas yield of substrates

The influence of the probiotic product Amylocin in the diet of laying hens on the biogas production potential of their droppings has been studied. A laboratory batch experiment on litter anaerobic fermentation was carried out. The total and specific biogas and methane yields from poultry droppings in the control and experimental groups were determined. It was found that the use of the probiotic Amylocin in the diet of laying hens reduced the biogas productivity of their dung; the average specific biogas and methane yields from the droppings of hens that received the probiotic was 73.90 and 19.52 ml/g of organic matter, respectively; the corresponding values for hens the diet of which did not contain Amylocin was 120.97 and 46.69 ml/g of organic matter, respectively. At the same time, the litter of the poultry group with the highest productivity was characterized by the lowest yield of biogas and methane (51.56 and 14.05 ml/g organic material, respectively), which may be due to the better conversion of feed nutrients in the poultry body, as well as to the inhibitory effect of probiotic microflora on the methane-forming consortium in the droppings. The methane concentration in the biogas from poultry litter averaged 29.75% in the experimental groups and 38.60% in the control. Only biogas from droppings of poultry that received the lowest dose of the additive contained 46.71% methane and was combustible. The addition of carbon-rich co-substrates can potentially increase the efficiency of converting into biogas of droppings of laying hens fed with Amylocin. biogas, methane, poultry litter, laying hens, Amylocin, Bacillus subtilis, Bacillus amyloliquefaciens The work was funded by the Russian Foundation for Basic Research, project no. 18-47-310008 р_а.