| Summary: | The purpose of the study was to determine the suitability of wastes from herbal industry for biogas production. Wastes of lemon balm (Melissa officinalis L.) and alder buckthorn (Frangula alnus Mill.) were used for biomethane potential test (BMP). The following properties were determined in the tested material: total solids content (TS), volatile solids content (VS), total Kjeldahl nitrogen content (TKN), total organic carbon content (TOC), total phosphorus content (P) and total potassium content (K). Biogas yield was monitored on the basis of the liquid displacement method. The examined wastes differed in terms of basic properties affecting the biogas production. Alder buckthorn contained more VS, TKN and TOC, while lemon balm had a narrower C/N ratio and higher P and K content. Tested wastes were also different in terms of biogas production kinetics. In case of lemon balm, the highest production was observed at the beginning of the experiment, while the anaerobic digestion of alder buckthorn waste was only noticeable in the third week of the experiment. This delay caused higher cumulative methane yield of lemon balm waste by about 60% than that of alder buckthorn. Despite those differences, wastes from both plants were suitable for biogas production, mainly as co-substrates. Co-digestion resolves problem of utilization of such wastes and decreases the demand for energy crops such as maize which should be used as fodder and food in the first place. In addition, clear differences in the kinetics of anaerobic digestion may cause that simultaneous use of both tested wastes will ensure continuous biogas production at a relatively high level.
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