Abstract
Fixed-bed reactors are good alternatives for hydrogen production due of their simple construction and increase in retention cellular. In this work, upflow anaerobic fixed-bed reactors using three support arrangements: recycled low-density polyethylene scraps (R1), recycled low-density polyethylene cylinders (R3) and bamboo stems (R2 and R4) were tested using cassava starch wastewater as the substrate. In reactors R1 and R2 the pH initial was adjusted for 6.0, with hydraulic retention time (HRT) of 4 h and organic load rate (OLR) of 9.5 g/L.d. Assays R3 and R4 were conducted in pH initial of 4.5, HRT of 4 h and OLR of 13.5 g/L.d. The hydrogen production was favored by bamboo stems arrangement and adjustment of the pH for 6.0 (248 mLH2/d.L). The reactor with polyethylene cylinders (229 mLH2/d.L), at pH 4.5, obtained better performance than polyethylene scraps (175 mLH2/d.L) at pH 6.0, due to maintenance of higher porosities in bed. Great concentrations of butanol and ethanol were verified in the reactors with bamboo stems, principally, in pH initial of 4.5, leading to decrease in hydrogen production due to occurrence of solventogenesis.
Highlights
The increase in global demand for energy, reduction in fossil fuel reserves and environmental impacts has motivated the search for alternative fuels
This study employed upflow anaerobic fixed-bed reactors made of 5 mm of thickness transparent plexiglass, with 75 cm of height, 8 cm of inner diameter and 3.6 L of total volume (PEIXOTO et al, 2011)
The hydrogen yield from cassava wastewater was favored for bamboo stems arrangement (0.86 and 0.31 mmol H2.mol Carb in R2 and R4, respectively), followed by polyethylene cylinders(0.2mmol H2.mol Carb) and polyethylene scraps(0.15 mmol H2.mol Carb) in the anaerobic fixed-bed reactor
Summary
The increase in global demand for energy, reduction in fossil fuel reserves and environmental impacts has motivated the search for alternative fuels. In this context, hydrogen is a promising substitute, a clean and efficient source, because it is its burning results in zero emissions of greenhouse gases and with energy potential three times higher than that of gasoline (141.8 kJ.g-1) (SRIRANGAN et al, 2012; ARIMI et al, 2015). The biological production includes bio-photolysis, photo fermentation and electrochemical processes (AZWAR et al, 2014). The use of cheaper substrates and the application of technologies that require lower energy expenditure are some of the advantages of biological processes
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