The objective of this study was to produce hydrogen and methane from cassava wastewater
using two steps of upflow anaerobic sludge blanket reactors (UASB), emphasizing
maximum hydrogen production. For the first hydrogen production stage, the UASB system
was operated at 37 C and pH 5.5 at different COD loading rates. A maximum specific H2
production rate of 0.39 l H2/l d and a maximum H2 yield of 39.83 l H2/kg COD removed were
found at a COD loading rate of 25 kg/m3d and the gas produced contained 36.4% H2, and
63.6% CO2 without methane. For the second methane production stage, the UASB was fed
by the effluent produced from the hydrogen production step operated at the optimum COD
loading rate. A maximumspecific CH4 production rate of 0.91 l CH4/l d and a maximum CH4
yield of 115.23 l CH4/kg COD removed were found at a COD loading rate of 8 kg/m3d. The
inhibition levels of organic acids to acidogens and methanogens were found to be 10,000
and 400 mg/l as acetic acid, respectively.
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