In this study, purification of the wastewater from corn stover-based bioethanol production process with simultaneous biogas production was investigated in a combined system, which was based on thermophilic anaerobic digestion in a fluidized bed reactor (AFBR), an aerobic airlift loop reactor (ALR), and a biological aerated filter (BAF). High strength distillery wastewater and high ammonia nitrogen content pretreatment wastewater were used as the influents. In the thermophilic anaerobic process (54-55°C), the methane yield of 280 ± 10.
Anaerobic
dark fermentation biohydrogen production from xylose was investigated
under mesophilic (35 °C) and thermophilic (55 °C) conditions
at various initial pH (5.0–10.0) and substrate concentrations
(2.5–12.5 g/L). In addition, the microbial community structure
variations under different temperatures were analyzed. It was demonstrated
that the maximum hydrogen yield (1.24 mol-H2/mol-xylose)
was obtained with substrate concentration of 7.5 g/L and initial cultivation,
pH 7.0, at 35 °C, with butyrate, acetate, and ethanol as the
major byproducts. The increase of substrate concentration resulted
in accumulation of volatile fatty acids (VFAs), especially propionate,
and a decrease in final pH under mesophilic conditions. However, the
hydrogen yield increased along with the increase of substrate concentration
at 55 °C with butyrate and ethanol as the main metabolite. Stable
pH of the system could be maintained even at high xylose concentration
up to 12.5 g/L due to a low level of VFAs accumulation. A lower hydrogen
yield of 1.14 mol-H2/mol-xylose was obtained at thermophilic
condition, while a stable operation condition could be achieved and
maintained more easily. Polymerase chain reaction-denaturing gradient
gel electrophoresis (PCR-DGGE) analysis showed that microbial community
structures of both systems were dominated with bacterial species related
to Clostridium, while the thermophilic system had
fewer hydrogen-producing microbial species than that at mesothermal
condition.
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