Roasted coffee wastes as a substrate for Escherichia coli to grow and produce hydrogen

Abstract

After brewing roasted coffee, spent coffee grounds (SCGs) are generated being one of the daily wastes emerging in dominant countries with high rate and big quantity. Escherichia coli BW25113 wild-type strain, mutants with defects in hydrogen (H2)-producing/oxidizing four hydrogenases (Hyd) (ΔhyaB ΔhybC, ΔhycE, ΔhyfG) and septuple mutant (ΔhyaB ΔhybC ΔhycA ΔfdoG ΔldhA ΔfrdC ΔaceE) were investigated by measuring change of external pH, bacterial growth and H2 production during the utilization of SCG hydrolysate. In wild type, H2 was produced with rate of 1.28 mL H2 (g sugar)−1 h−1 yielding 30.7 mL H2 (g sugar)−1 or 2.75 L (kg SCG)−1 during 24 h. In septuple mutant, H2 production yield was 72 mL H2 (g sugar)−1 with rate of 3 mL H2 (g sugar)−1 h−1. H2 generation was absent in hycE single mutant showing the main role of Hyd-3 in H2 production. During utilization of SCG wild type, specific growth rate was 0.72 ± 0.01 h−1 with biomass yield of 0.3 g L−1. Genetic modifications and control of external parameters during growth could lead to prolonged and enhanced microbiological H2 production by organic wastes, which will aid more efficiently global sustainable energy needs resulting in diversification of mobile and fixed energy sources.

Coffee silverskin as a substrate for biobased production of biomass and hydrogen by Escherichia coli

“…Although, cumulative hydrogen production was 40 and 57 mL in wild type and septuple mutant, respectively (Table 4). High H 2 yields during 24 h were reported by using SCG, particularly 30.7 mL H 2 (g sugar) −1 and 72 mL H 2 (g sugar) −1 with application of septuple mutant 13 . Cumulative hydrogen production was determined while using 100 g L −1 and 200 g L −1 CS.…”

“…Currently, various studies were implemented for testing available lignocellulosic wastes as a substrate for biomass generation. 13 E. coli can utilize such carbon sources congregated either solely (glycerol as a biodiesel production waste) 40,41 or in combination with the mixture composing the biodegradable waste (lignocellulosic waste). 7,20,21 E. coli wild type and septuple mutant tested were able to utilize and grow in treated CS medium.…”

“…The pH of 2 to 10 times diluted samples was adjusted by using K 2 HPO 4 and sterilized for further assays. 13…”

“…The possibility of using solely glucose and xylose‐containing mediums by E. coli has been investigated previously, as well as the role of each Hyd enzyme 11 . Moreover, it was shown that H 2 production and the role of Hyd enzymes during the utilization of SCG 13 …”

“…However, rare studies have reported the valorization potential of CS as a sole carbon source to obtain bioenergy. Biohydrogen as an “eco‐friendly” biofuel has 3‐4‐time higher energy content compared to fossil fuels and advantageously can be produced in biological way with application of cost‐effective agricultural and industrial lignocellulosic wastes 13,20,21 …”