Biotechnological potential of spent coffee grounds for biohydrogen production by Escherichia coli

The impact of varying initial pH levels of coffee waste hydrolysate on bacterial growth, redox potential changes, and enhanced hydrogen production in 5 L vessels were investigated. Escherichia coli wild-type and septuple mutant ( ΔhyaB ΔhybC ΔhycA ΔfdoG ΔldhA ΔfrdC ΔaceE ) were used. Bacteria were grown in spent coffee grounds (SCG) medium (40 g L −1 SCG hydrolysed with diluted sulphuric acid) at pH 6.0 to pH 8.0 with addition of 13.6 g L −1 glycerol. In wild type and mutant strain without the presence of glycerol, the cumulative H 2 yield was ∼4 L and∼5.3 L, respectively. During glycerol co-fermentation, the cumulative amount of H 2 in the wild type was ∼5.2 L, accumulating 0.2 L of H 2 per day, while the septuple mutant produced 15 L of H 2 , accumulating 0.5 L of H 2 per day. Thus, H 2 gas equal to 33 kWh of energy was produced during batch culturing of 200 g SCG and glycerol. • In engineered mutant during waste utilization the cumulative H 2 yield was 5.3 L. • During glycerol co-fermentation, the cumulative H 2 yield was 15 L. • H 2 gas equal to 33 kWh of energy was produced from 200 g SCG in mixture with glycerol.