Experiments were conducted as biomethane potential experiments (BMP), performed in mesophilic (37 °C) conditions using automated testing equipment (Bioprocess Control Ltd, Sweden). The assays were mechanically mixed (84 rpm) for one minute per hour. The biowaste/inoculum volatile solids (VS):VS ratio and the amount of ash added varied depending on the experiment: In Experiment 1 the VS ratio was 0.25 and ash dosages were 0, 10, 16.7 and 23.3 g/kgww. In experiment 2 VS ratio was 0.34 and ash dosages were 0, 2.5, 5 and 7.5 g/kgww. In experiment 1 the fly ash used was from combined heat and power (CHP) plant in Kuopio, Finland, using different wood-based materials (56%) and peat (44%) (WP). In experiment 2 three different types of fly ashes from CHP plant in Saarijärvi, Finland was used: ash from peat (P), wood (W) and mix of wood (75%) and peat (25%) (WP).
Distilled water was added to the bottles after the sample and the inoculum to achieve the desired liquid mass. All bottles were buffered with NaHCO3 (3 g/L) and flushed with N2 to obtain anaerobic conditions. The CO2 of the produced biogas was absorbed in a 3M NaOH solution, and the cumulative volume (mL) of methane was determined with water displacement. Methane yields were converted into normal conditions (0 °C, 101.32 kPa) according to the ideal gas law.
In Experiment 1 triplicate bottles were used for inocula only assay and five bottles for sample assays. The used liquid volume was 300 mL. The added amount of inoculum in each assay was 24.29gVS/bottle (276 gww) and added amount of biowaste 6.07 gVS/bottle (24.07 gww).
In experiment 2 triplicate bottles were used for all samples and inocula only assays. One of the inoculum only assays the mixing was broken during the experiment, so only two bottles were used for the result calculation. The used liquid volume was 400 mL. The added amount of inoculum in each assay was 8.04 gVS/bottle (375 gww) and added amount of biowaste 2.71 gVS/bottle (12.05 gww).
Project and Funding
Circular economy ecosystem (CECO): raw materials from waste and side streams
European Regional Development Fund and the state (project number 2014/11264/09 02 01 01/2021/PL)
