Biohydrogen and biomethane from water hyacinth (Eichhornia crassipes) fermentation: Effects of substrate concentration and incubation temperature

The effects of substrate concentration and temperature on fermentative hydrogen production from Eichhornia crassipes using pig slurry microflora were studied, and the optimal values for maximum biohydrogen production were determined in batch experiments. Hydrogen and methane yield (HY and MY) and production rate (HPR and MPR) were evaluated at various E. crassipes concentrations (10-80 g/L) and incubation temperatures (25, 35, 45, 55, and 65 °C). Hydrogen and methane production were observed during the E. crassipes fermentation without any nutrients addition, and were dependent on E. crassipes concentrations. Maximum HPR (38.2 mmol H₂/L/d) and MPR (29.0 mmol CH₄/L/d) were obtained at E. crassipes concentration of 40 g/L and 80 g/L, respectively. Monod model and modified Andrew model were used to fit the hydrogen production rate data. Modified Andrew model could describe better the effects of substrate concentration on hydrogen production rate (greater R ² value). Maximum HPR (221.3 mmol H₂/L/d) and MPR (24.4 mmol CH₄/L/d) were obtained at 45 and 55 °C, respectively. These values were ca. 1105 and 18 folds higher than the HPR (0.2 mmol H ₂/L/d) and MPR (7.3 mmol CH₄/L/d) at 25 °C, probably due to increased hydrolysis of E. crassipes at higher temperatures. Ratkowsky model could best describe the progress of hydrogen and methane production potential and rate (R² > 0.9). The optimum E. crassipes concentration and incubation temperature were determined as 47.8 g/L and 62.5 °C, respectively for maximum hydrogen and methane production. Biohydrogen and biomethane yields from E. crassipes were 31.3 GJ/ha/y and 853.9 GJ/ha/y, respectively, with a total CO₂ emission reduction from 15.2 to 23.7 tons.