Continuous Hydrogen Production from Agricultural Wastewaters at Thermophilic and Hyperthermophilic Temperatures.

Abstract

The objective of this study was to investigate the effects of hydraulic retention time (HRT) (8 to 0.5h) and temperature (55 to 75°C) in two anaerobic fluidized bed reactors (AFBR) using cheese whey (AFBR-CW=10,000mg sugars L-1) and vinasse (AFBR-V=10,000mg COD L-1) as substrates. Decreasing the HRT to 0.5h increased the hydrogen production rates in both reactors, with maximum values of 5.36±0.81L H2 h-1 L-1 in AFBR-CW and 0.71±0.16L H2 h-1 L-1 in AFBR-V. The optimal conditions for hydrogen production were the HRT of 4h and temperature of 65°C in AFBR-CW, observing maximum hydrogen yield (HY) of 5.51±0.37mmol H2 g COD-1. Still, the maximum HY in AFBR-V was 1.64±0.22mmol H2 g COD-1 at 4h and 55°C. However, increasing the temperature to 75°C reduced the hydrogen production in both reactors. Methanol and butyric, acetic, and lactic acids were the main metabolites at temperatures of 55 and 65°C, favoring the butyric and acetic metabolic pathways of hydrogen production. The increased productions of lactate, propionate, and methanol at 75°C indicate that the hydrogen-producing bacteria in the thermophilic inoculum were inhibited under hyperthermophilic conditions.