Herout M., Malaťák J., Kučera L., Dlabaja T., 2011. Biogas composition depending on the type of plant biomass used. Res. Agr. Eng., 57: 137-143.The aim of the work is to determine and analyse concentrations of individual biogas components according to the used raw materials based on plant biomass. The measurement is focused on biogas production depending on input raw materials like maize silage, grass haylage and rye grain. The total amount of plant biomass entering the fermenter during the measurement varies at around 40% w/w, the rest is liquid beef manure. The measured values are statistically evaluated and optimised for the subsequent effective operation of the biogas plant. A biogas plant operating on the principle of wet anaerobic fermentation process is used for the measurement. The biogas production takes place during the wet fermentation process in the mesophile operation at an average temperature of 40°C. The technology of the biogas plant is based on the principle of using two fermenters. It follows from the measured results that maize silage with liquid beef manure in the ratio of 40:60 can produce biogas with a high content of methane; this performance is not stable. At this concentration of input raw material, the formation of undesirable high concentrations of hydrogen sulphide occurs as well. It is shown from the results that the process of biogas production is stabilised by the addition of other components of plant biomass like grass haylage and rye grain and a limitation of the formation of hydrogen sulphide occurs. It follows from the results that the maize silage should form about 80% w/w from the total amount of the plant biomass used.

Malaťák J., Dlabaja T. (2016): Hydrothermal carbonization of kitchen waste. Res. Agr. Eng., 62: 64-72.Hydrothermal carbonization is a suitable method for energy and material recovery of wet heterogeneous kitchen waste. The paper examines the ability of the process to produce stable, energy-rich material without harmful by-products from lunch leftovers, raw potatoes, creamy yogurt and raw onions. Results of the batch experiments confirm the hypothesis that waste processing results in homogenous energy-rich (> 24 MJ/kg) and carbon-rich (> 63 % wt.) material. The biochar of creamy yogurt reaches the highest lower-heating value of 31.75 MJ/kg. In terms of energy use and emission concentrations, all samples meet legal requirements for incineration in combustion devices. Phytotoxicity tests prove the harmlessness of the liquid by-product for agricultural purposes.

Dlabaja T., Malaťák J., 2013. Optimization of anaerobic fermentation of kitchen waste. Res. Agr. Eng., 59: 1-8.Anaerobic fermentation is a suitable method of energetic and material utilisation of waste coming from restaurants and canteens. Laboratory experiments of wet anaerobic fermentation were performed in a continuous reactor and in batch reactors under mesophilic conditions. Effects of hydraulic retention time, organic loading rate, period of feeding and recirculation of digestate were examined in the continuous reactor. Effects of substrate pre-treatment (crushing, heating, freezing) were examined in the batch reactors. Degree of substrate degradation ranged between 83-85% within hydraulic retention time of 2-30 days. Appropriate organic loading rate was found in the range 2-3 kg of volatile solids per m 3 /day. Recirculation of digestate (both an inoculum for fresh substrate and replacement of fresh water supply)caused an increase in ammonia concentration and led to immediate inhibition of the process. The results further showed a positive effect of substrate pre-treatment in the initial phase of fermentation. However, degree of degradation did not show a significant increase for the period of 20 days of fermentation.

Malaťák J., Dlabaja T. (2015): Hydrothermal carbonization of stabilized sludge and meat and bone meal. Res. Agr. Eng., 61: 21-28.Hydrothermal carbonization is one of suitable methods for energy recovery of sewage sludge and meat and bone meal. The task of the article is to determine appropriate hydrothermal carbonization process conditions and their impact on the quality of the final product -so called biochar or hydrochar. Parameters of the two main phases -initiation and polymerization -were monitored. The basic fuel properties of the final solid products of hydrothermal carbonization were determined. To produce biochar by hydrothermal carbonization, multifunctional pressure vessel with accessories was used -a batch reactor BR-300. Process parameters of hydrothermal carbonization confirm the effect of increasing temperature to increase the lower heating value (LHV). Neither calorific values of meat and bone meal (17.22 MJ/kg), nor calorific values of digested stabilized sludge (12.14 MJ/kg) showed a significant increase after undergoing processing. The effect of reaction temperature on the LHV of the final product is significantly higher than that of residence time. The results show that the main factor affecting LHV of the fuel sample is the final amount of ash. Unlike the meat and bone the hydrothermal carbonization of the stabilized wastewater sludge is one of the effective processing methods for subsequent energy use.