| dc.description.abstract | Considering the increasing global demand for energy, the reduction of nonrenewable energy resources and
concern for the environmental quality, hydrogen (H2) emerges as a clean, renewable and promising
alternative, since its combustion results only in water and energy. Among the biological methods for H2
production, anaerobic fermentation is considered the most viable technology, since it does not require an
external source of energy and several types of biomass can be used as carbon source by the
microorganisms. Therefore, the aim of this work was to select an agroindustrial residue and to evaluate the
production of H2 from anaerobic fermentation of its hydrolysate under different experimental conditions.
The raw materials used were rice husk (CA), rice bran (FA), brewers’ spent grain (BC), soybean waste
(RS) and wheat waste (RT). All materials were characterized, prepared and submitted to the acid hydrolysis
process for the carbohydrate’s conversion into fermentable sugars under different conditions of temperature
(104.4-127.0°C), time (20-60 min), acid concentration (5-15% H3PO4), and moisture (60-90%). The best
experimental condition and the raw material to be used for H2 production were selected by total reducing
sugars (ART) of obtained hydrolysates. Selected hydrolysate was then used as a source of substrate in the
anaerobic fermentation process for H2 production, using anaerobic sludge as inoculum. Fermentation tests
were conducted according to the factorial experimental design, evaluating the effect of temperature (35-
45°C), initial pH (5.5-7.5) and inoculum ratio (10-30%) in H2 production and maximum H2 production rate.
All experiments were monitored for 20 h. The composition of the medium was analyzed before and after
each assay in terms of sugars, inhibitors, and acetic acid. The final pH of each experiment was also
determined. The experimental condition of acid hydrolysis that resulted in the highest concentration of
ART in the hydrolysates of rice husk and rice bran was assay 3 (127°C, 60 min, 15% (w/w) H3PO4 and
60% moisture). In this condition, the concentration of ART was 118.16 g kg CA
-1 and 170.38 g kg FA
-1. On
the other hand, the assay 1 (127°C, 20 min, 5% (w/w) H3PO4 and 90% moisture) resulted in higher ART
concentration in brewers’ spent grain, soybean waste and wheat waste hydrolysates. The concentration of
ART was 600.97 g kg BC
-1, 80.37 g kg RS
-1 and 228.04 g kg RT
-1. From the results of hydrolysis, brewers’
spent grain was the raw material chosen for the H2 production process, as it resulted in the highest ART
concentration. In addition, the BC will be available in large quantity during all over the year. The highest
H2 yield (4160 mL L-1) and maximum H2 production rate (760 mL L-1 h-1) were found in assays 7 (35°C,
pH 7.5 and 30% inoculum) and 8 (45°C, pH 7.5 and 30% inoculum), respectively. In some assays, glucose
consumption of the BC hydrolysate reached 100%, while xylose was consumed up to 91.56%. The
concentration of inhibitors (furfural and 5-HMF) before and after the fermentation process did not have
significant alteration and did not show negative interference in H2 production. On the other hand, the
concentration of acetic acid had an expressive increase from a range of 0.1392-0.3001 g L-1 to 1.1490-
5.8392 g L-1, which explains the drop in pH in the fermentation medium at the end of the tests. Finally, it
was concluded that brewers’ spent grain hydrolysate presented appropriate characteristics for H2 production
by anaerobic fermentation, leading to promising results when compared to the literature. | |
