Insights into the efficient electricity production performance using acid-treated straw in MFCs

Abstract

In this study, a mixed electrogenic culture (RS) was successfully enriched from cow rumen fluid which produced the maximum current density of 634 ± 58 μA cm−2 using carboxymethyl cellulose (CMC) as the substrate in a three-electrode system. Furthermore, in the microbial fuel cells (MFCs) system the RS as the inocula can generate electricity using treated corn straw instead of CMC as substrates. The 550 ± 25 mW m−2 from the alkali-treated straw, 842 ± 35 mW m−2 from neutral-treated straw, and 1377 ± 20 mW m−2 from acid-treated straw for RS has been obtained, respectively, which are all much higher than that of 110 ± 15 mW m−2 using untreated straw as the substrate. It can be found that MFCs electricity generation performance of RS using the straw via treated different methods will be significantly different. Among them, the power density of RS using acid-treated straw was 1.64 and 2.50 times higher than that using neutral-treated and alkali-treated straw, respectively. Meanwhile, the power density of RS using acid-treated straw was also respective 1.36 times and 1.58 times higher than that of RS using CMC and that of G. sulfurreducens PCA using small molecule acetic acid as the substrate. On the other hand, the analysis of microbial community composition of the RS enriched using differently treated straw revealed that the relative abundances of 47.1 % for Geobacter and 14.7 % for Wolinella were dominant in the acid-treated straw RS by comparison of 1.9 %, 11.3 % and 14.0 %, 4.2 % for RS using alkali-treated and neutral-treated straw, respectively. In addition, the metabolite analysis of RS during generating electricity was also analyzed. It showed that the RS enriched from acid-treated straw contained a higher acetic acid amount of 9.3 ± 0.4 mmol/L as the carbon source for electrochemically active bacteria (EAB) to utilize such as Geobacter, which is higher than the values of 4.3 ± 0.4 mmol/L (alkali-treated) and 0.34 ± 0.04 mmol/L (neutral-treated) using the other treated methods. Therefore, these results implied that the degraded organic matters in the acid-treated straw contained more acetic acid accessible to RS for being utilized and produced more electricity current by enriching more efficient EAB. It can be seen that the acid-treated method for straw can effectively degrade the straw to low molecules (more acetic acid) which will improve the microbial community composition to produce higher electricity current. This study offers a promising practical method for recovery energy using straw in MFCs system in the future.