Methanogenic Activity in Neotropical Lacustrine Systems at Different Altitudes

This study evaluated the methane (CH4) production capacity of microbial consortia from three neotropical lakes at different altitudes: Mojanda (4,263 m.a.s.l., 10°C), Papallacta (3,250 m.a.s.l., 14°C), and Caimanes (510 m.a.s.l., 25°C). Specific methanogenic activity (SMA) and biochemical methane potential (BMP) from cellulose were assessed at two temperatures (the original lake temperature and 37°C) and three different inoculum-to-substrate ratios (ISR of 1, 2, and 4). The highest SMA values were observed at 37°C, being 0.021, 0.011, and 0.009 g COD/gVS·d for Caimanes, Papallacta, and Mojanda, respectively. At their original temperatures, only Mojanda and Caimanes showed activity (0.007 and 0.014 COD/gVS·d), which was significantly lower. Methane yields from cellulose were also highly temperature-dependent. The highest yield was achieved by the Caimanes consortium at 37°C (409 NmL CH4/gVS), while at its native 25°C, the yield was 147 NmL CH4/g VS. The Mojanda consortium, from the highest altitude, produced methane even at 10°C (26 NmL CH4/gVS), while at 37°C was 137 NmL CH4/gVS. No activity was detected for Papallacta at its original temperature (14°C) but 203 NmL CH4/gVS for 37°C. These results demonstrate the strong temperature dependence of these consortia and classify them as psychrotrophic rather than psychrophilic. This sensitivity suggests a potential for increased greenhouse gas emissions from these lakes under climate warming scenarios. Furthermore, the resilience and cellulolytic activity at low temperatures exhibited by these consortia highlight their potential for specialized applications in anaerobic digestion, such as bioaugmentation for the treatment of complex wastes.