Low temperature BMP tests using fish waste from invasive Round goby of the Baltic Sea
Riga Technical University, Institute of Energy Systems and Environment, Azenes street 12-K1, LV-1048 Riga, Latvia
Round goby (Neogobius melanostomus) is an invasive fish species in the Baltic Sea. While meat can be used for human consumption, fish processing residues are considered as a waste. Within circular economy and bio-economy perspectives fish waste could be used as a valuable feedstock for biogas production. However, the research is mostly focused on evaluating biogas yield at mesophilic conditions (i.e. 37 °C). In this study the impact of low temperature on Biochemical Methane Potential (BMP) tests has been investigated. Round goby’s processing leftovers – heads, intestines and skin/bone mixture were tested in codigestion with sewage sludge. Anaerobic digestion (AD) was carried out in 100 mL batch tests at low temperature 23 °C and 37 °C conditions, over an incubation period of 31 days. The results show that AD at low temperature occurs twice as slowly as under 37 °C conditions. However, after 31 days the BMP values for 23 °C samples were only 2% lower than for high temperature samples. Heads and skins showed similar BMP values reaching on average 502 L CH4 kgVS-1 and 556 L CH4 kgVS-1 respectively. BMP for fish intestines was higher, reaching on average 870 L CH4 kgVS-1. Average BMP for mixes of fish heads, skins, intestines and bones was 660 L CH4 kgVS-1. Acquired BMPs were further compared with the theoretical BMPs from Buswell’s formula. Research results suggests that anaerobic digestion of fish waste under low temperature conditions could be feasible as the process still efficiently occurs, in fact opening a new opportunity to explore the overall sustainability of technologies based on these conversion processes.