Abstract
Methods for the enrichment of an anaerobic sludge with H 2 -producing bacteria have been compared by using cassava processing wastewater as substrate. The sludge was submitted to three different pretreatments: 1) heat pretreatment by boiling at 98 °C for 15 min ., 2) heat pretreatment followed by sludge washout in a Continuous Stirring Tank Reactor ( CSTR ) operated at a dilution rate ( D) of 0.021 h - 1 , and 3) sludge washout as the sole enrichment method. The pretreated sludge and the sludge without pretreatment (control) were employed in the seeding of 4 batch bioreactors, in order to verify the volume and composition of the generated biogas. M aximum H 2 production rates ( R m ) from the pretreated sludges, were estimated by the modified Gompertz model. Compared to the control, H 2 production was ca. 4 times higher for the sludge submitted to the heat pretreatment only and for the sludge subjected to heat pretreatment combined with washout, and 10 times higher for washout . These findings demonstrated that the use of sludge washout as the sole sludge pretreatment method was the most effective in terms of H 2 production , as compared to the heat and to the combined heat and washout pretreatments .
Highlights
Brazil is one of the largest world producers of cassava, whose processing for the production of flour and starch generates about 7 m3 wastewater per kg processed root
The seed sludge and the heatpretreated sludge were submitted to sludge washout using a continuous process and a dilution rate (D) high enough to promote the washout of non-H2producing bacteria and methanogens
The sludge was not adapted to this kind of substrate, so the growth rate was very poor compared with the growth rate in other substrates
Summary
Brazil is one of the largest world producers of cassava, whose processing for the production of flour and starch generates about 7 m3 wastewater per kg processed root. This wastewater is rich in carbohydrates, with about 5-15 and 20-50 g L-1 of Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD), respectively (CEREDA, 2001). This wastewater can be treated by anaerobic. Hydrogen production is more advantageous, because H2 combustion produces only water as byproduct, which classifies H2 as a clean fuel
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