Generation of green electricity from sludge using photo-stimulated bacterial consortium as a sustainable technology

Abstract

Microbial fuel cell (MFC) is a bio-electrical energy generator that uses respiring microbes to transform organic matter present in sludge into electrical energy. The primary goal of this work was to introduce a new approach to the green electricity generation technology. In this context a total of 6 bacterial isolates were recovered from sludge samples collected from El-Sheikh Zayed water purification plant, Egypt, and screened for their electrogenic potential. The most promising isolates were identified according to 16S rRNA sequencing as Escherichia coli and Enterobacter cloacae, promising results were achieved on using them in consortium at optimized values of pH (7.5), temperature (30°C) and substrate (glucose/pyruvate 1%). Low level red laser (λ = 632.8nm, 8mW) was utilized to promote the electrogenic efficiency of the bacterial consortium, maximum growth was attained at 210 sec exposure interval. In an application of adding standard inoculum (10⁷ cfu/mL) of the photo-stimulated bacterial consortium to sludge based MFC a significant increase in the output potential difference values were recorded, the electricity generation was maintained by regular supply of external substrate. These results demonstrate the future development of the dual role of MFCs in renewable energy production and sludge recycling.

Keywords: Electrogenic Bacteria; Green Electricity; Microbial Fuel Cell (MFC); Sludge; Temperature; pH; photo-stimulation.

Fig. 1

Schematic diagram of the microbial fuel cell

Fig. 2

Total viable bacterial count (cfu/mL) in the collected sludge samples. One way Analysis of Variance test was performed for Mean ± SD & Multiple comparison between groups through Post Hoc test: Tukey’s test Letters A-D comparatively represent the descending order of results reflecting importance among means. p-value > 0.05 is insignificant; *p-value < 0.05 is significant; **p-value < 0.001 is highly significant

Fig. 3

Phylogenetic tree of E. coli and E. cloacae based on 16S rRNA constructed using the neighbor joining method.

Fig. 4

Total viable count (cfu/mL) at different ph and temperature values. Repeated-measures analysis of variance (ANOVA) & Multiple comparison between groups through Post Hoc test: Bonferroni-corrected. Letters A- E comparatively represent the descending order of results reflecting importance among means at the same value, p-value > 0.05 is insignificant; *p-value < 0.05 is significant; **p-value < 0.001 is highly significant

Fig. 5

Total viable count (cfu/mL) using different types of substrates. Repeated-measures analysis of variance (ANOVA) & Multiple comparison between groups through Post Hoc test: Bonferroni-corrected. Letters A-F comparatively represent the descending order of results reflecting importance among means at the same value, p-value > 0.05 is insignificant; *p-value < 0.05 is significant; **p-value < 0.001 is highly significant

Fig. 6

Pattern of potential difference output for E. cloacae, E. coli and their consortium. Paired Sample t-test. p-value > 0.05 is insignificant; *p-value < 0.05 is significant; **p-value < 0.001 is highly significant

Fig. 7

Effect of LLRL on the bacterial growth of the electrogenic bacterial consortium. Repeated-measures analysis of variance (ANOVA) & Multiple comparison between groups through Post Hoc test: Bonferroni-corrected, letters A-H comparatively represent the descending order of results reflecting importance among means at the same value. p-value > 0.05 is insignificant; *p-value < 0.05 is significant; **p-value < 0.001 is highly significant

Fig. 8

Pattern of potential difference using photo-stimulated bacterial consortium. Paired Sample t-test. p-value > 0.05 is insignificant; *p-value < 0.05 is significant; **p-value < 0.001 is highly significant