Long-term effect of acid and heat pretreatment of sludge from a sugarcane vinasse treatment plant on the microbial community and on thermophilic biohydrogen production

• A sludge from vinasse treatment served as inoculum for biohydrogen production.
• Heat- and acid-pretreated sludge promoted biohydrogen production at similar rates.
• The main metabolite in the heat-pretreated sludge was lactic acids.
• Lactic acid concentration diminished in the acid-pretreated sludge.
• Thermoanaerobacterium was the main Clostridiaceae found in the acid-treated sludge.

This work investigated how heat and acid pretreatment affected thermophilic biohydrogen production by a mixed culture present in the sludge of a sugarcane vinasse treatment plant. Heat- (80 °C for 15 min) or acid- (pH 3 for 24 h) treated sludge samples were employed to seed batch bioreactors along 36 days. The heat- and acid-treated sludge samples afforded H2 production rates (HPRs) of 8.4 and 9.5 mmol/L.d, respectively. The lactic acid concentration increased in the bioreactor seeded with heat-treated sludge, whilst the lactic acid concentration diminished in the bioreactor inoculated with the acid-treated sludge. Identification of the microbial community revealed that Clostridiaceae predominated in all the sludge samples. The most abundant Clostridiaceae in the heat- and acid-treated sludge samples were Clostridium and Thermoanaerobacterium, respectively. Acid pretreatment modified the microbial community and enhanced consumption of lactic acid, a metabolite that is normally associated with decreased H2 production.