Interaction effect of high feed to inoculum ratio (F/I) and temperature on the biomethanation kinetics of water hyacinth

Abstract

The anaerobic digestion of the invasive water hyacinth (Pontederia crassipes Mart.) from eutrophic water bodies could contribute to the sustainability of communities that have insecure energy sources. The optimization of critical process parameters, e.g., feed to inoculum ratio (F/I), temperature, supplementation, and inoculum acclimatization is important for large-scale applications. In the present work, water hyacinth was anaerobically digested at different F/I (1.0, 5.0, 10.0, and 30.0), mesophilic temperatures (30 and 40 °C), and supplementation settings using non-acclimatized and acclimatized inoculum to determine the process’s optimal conditions through kinetics (modified Gompertz, Chen and Hashimoto, and first-order) and energy analyses. The F/I ratio had a directly proportional effect on the methane yield [N mL·CH4/g·VS], which ranged from 416.8 ± 6.2 (F/I = 1.0) to 263.8 ± 26.9 (F/I = 30.0). The methane production rate [N mL·CH4/g·VS·day] was highest at 40 °C (9.0 ± 0.8) and lowest at F/I = 30 (5.6 ± 2.8). The biomethanation of water hyacinth followed the modified Gompertz and Chen and Hashimoto models when using the non-acclimatized and acclimatized inoculum, respectively. A 30-day pseudo-lag phase was observed at the highest F/I (30) and low temperature (30 °C) but was negligible at higher temperature (40 °C). For a 5.0 m3 biodigester, the highest estimated net energy occurred at F/I = 30 (370.5 ± 22.6 MJ). The doubling times at 40 °C (16.9 ± 0.3 days) were lower than that at 30 °C (49.6 ± 2.5 days). The anaerobic digestion of water hyacinth in batch mode was optimal at higher F/I ratio and high mesophilic temperatures.