• Energy Research

AbstractUnderstanding the abundance change of certain bacterial taxa is quite important for the study of soil microbiology. However, the observed differences of relative abundances by high-throughput techniques may not accurately reflect those of the actual taxon abundances. This study investigated whether soil microbial abundances coupling with microbial quantities can be more informative in describing the microbial population distribution under different locations. We analyzed relative abundances of the major species in soil microbial communities from Beijing and Tibet grasslands by using 16 S rRNA high-throughput sequencing technique, and quantified the absolute bacterial cell numbers directly or indirectly by multiple culture-independent measurements, including adenosine tri-phosphate (ATP), flow cytometry (FCM), quantitative real-time PCR (qPCR), phospholipid fatty acids (PLFA) and microbial biomass Carbon (MBC). By comparison of the relative abundance and the estimated absolute abundances (EAA) of the major components in soil microbial communities, several dominant phyla, including Actinobacteria, Bacteroidetes, Verrucomicrobia, Chloroflexi, Gemmatimonates and Planctomycetes, showed significantly different trends. These results indicated that the change in EAA might be more informative in describing the dynamics of a population in a community. Further studies of soil microbes should combine the quantification and relative abundances of the microbial communities for the comparisons among various locations.

Methane production was tested in membrane-less microbial electrolysis cells (MECs) under closed-circuit (RCC) and open-circuit (ROC) conditions, using glucose as a substrate, to understand the regulatory effects of bioelectrochemistry in anaerobic digestion systems. A dynamic model was built to simulate methane productions and microbial dynamics of functional populations, which were colonized in groups RCC and ROC during the start-up stage. The experiment results showed significantly greater methane production in RCC than ROC, the average methane production of RCC was 0.131 m3/m3/d, which was 1.4 times higher than that of ROC (0.055 m3/m3/d). The simulation results revealed that bioelectrochemistry had a significant influence on the abundance of microorganisms involved in acidogenesis and methanogenesis. The abundance of glucose-uptaking microorganisms was 87% of the total biomass in ROC without applied voltage, which was 20% higher than that in RCC (67%) when external voltages were applied between the anode and cathode. The abundance of hydrogenotrophic methanogens in RCC was 6% higher than that in ROC. The simulation results were verified through 16S rDNA high-throughput sequencing analysis. An electron balance analysis revealed that alteration of the acidogenesis type led to more acetate and hydrogen production from glucose fermentation, compared with the situation without bioelectrochemistry. An additional pathway from acetate to hydrogen was introduced by bioelectrolysis. These two factors resulted in significant enhancement of methane production in RCC. Bioelectrolysis process directly contributed to 26% of the total methane production after the start-up stage. When the applied voltages were cut down or decreased, RCC could maintain considerable methane productions, because the microbial communities and electron transfer pathways were already formed. Starting-up with high voltage, but operating under low voltage, could be an energy-favorable strategy for accelerating biogas production in bioelectro-anaerobic bioreactors.

AbstractThe relationship between biodiversity and ecosystem stability is poorly understood in microbial communities. Biofilm communities in small bioreactors called microbial electrolysis cells (MEC) contain moderate species numbers and easy tractable functional traits, thus providing an ideal platform for verifying ecological theories in microbial ecosystems. Here, we investigated the resilience of biofilm communities with a gradient of diversity, and explored the relationship between biodiversity and stability in response to a pH shock. The results showed that all bioreactors could recover to stable performance after pH disturbance, exhibiting a great resilience ability. A further analysis of microbial composition showed that the rebound of Geobacter and other exoelectrogens contributed to the resilient effectiveness, and that the presence of Methanobrevibacter might delay the functional recovery of biofilms. The microbial communities with higher diversity tended to be recovered faster, implying biofilms with high biodiversity showed better resilience in response to environmental disturbance. Network analysis revealed that the negative interactions between the two dominant genera of Geobacter and Methanobrevibacter increased when the recovery time became longer, implying the internal resource or spatial competition of key functional taxa might fundamentally impact the resilience performances of biofilm communities. This study provides new insights into our understanding of the relationship between diversity and ecosystem functioning.

Low electrode resistance is crucial for achieving efficient reactions in bio-electrochemical system (BES), especially considering the factors of BES scaling-up and microbial effects. Graphene has revealed a cornucopia of potential applications due to its high conductivity and extraordinary electrochemical properties. Here, significant reduction of electrode resistance and increment of electrochemical activity were achieved by fabricating the three-dimensional carbon brush using reduced graphene oxide (rGO/carbon brush) through one-step electro-deposition without any binder. The rGO/carbon brush was employed as cathode in BES equipped with bio-anode for azo compound (AO7) removal. The charge transfer resistances of cathode part and whole cell were decreased by 89% and 65%, respectively. The reactor showed quickly start-up within 48 h with peak cycle current six fold increase relative to the control. AO7 decolorization efficiency reached 91.1 ± 0.1% at 4 h and 97.6 ± 0.4% at 6 h. Effective decolorization of AO7 was at rate up to 650.7 g AO7/m3·h. The results indicated that the advantages of graphene and three-dimensional carbon brush successfully improved the overall performance of BES and enhanced refractory pollutants removal when applied to specific wastewater.

It is controversial to introduce oxygen into anode chamber as oxygen would decrease the CE (Coulombic efficiency) while it could also enhance the degradation of aromatics in microbial fuel cell (MFCs). Therefore, it is important to balance the pros and cons of oxygen in aromatics driven MFCs. A RMO (micro-oxygen bioanode MFC) was designed to determine the effect of oxygen on electricity output and phenol degradation. The RMO showed 6-fold higher phenol removal efficiency, 4-fold higher current generation than the RAN (anaerobic bioanode MFC) at a cost of 26.9% decline in CE. The Zoogloea and Geobacter, which account for phenol degradation and current generation, respectively, were dominated in the RMO bioanode biofilm. The biomass also showed great difference between RMO and RAN (114.3 ± 14.1 vs. 2.2 ± 0.5 nmol/g). Therefore, different microbial community, higher biomass as well as the different degradation pathway were suggested as reasons for the better performance in RMO.

We investigated the short-term dynamics of microbial composition and function in bioreactors with inocula collected from full-scale and laboratory-based anaerobic digestion (AD) systems. The Bray-Curtis dissimilarity of both inocula was approximately 10% of the predicted Kyoto Encyclopedia of Genes and Genomes pathway and 40% of the taxonomic composition and yet resulted in a similar performance in methane production, implying that the variation of community composition may be decoupled from performance. However, the significant correlation of volatile fatty acids with taxonomic variation suggested that the pathways of AD could be different because of the varying genus. The predicted function of the significantly varying genus was mostly related to fermentation, which strengthened the conclusion that most microbial variation occurred within the fermentative species and led to alternative routes to result in similar methane production in methanogenic bioreactors. This finding sheds some light on the understanding of AD community regulation, which depends on the aims to recover intermediates or methane.

Abstract Methane production rate (MPR) in waste activated sludge (WAS) digestion processes is typically limited by the initial steps of complex organic matter degradation, leading to a limited MPR due to sludge fermentation speed of solid particles. In this study, a novel microbial electrolysis AD reactor (ME-AD) was used to accelerate methane production for energy recovery from WAS. Carbon bioconversion was accelerated by ME producing H2 at the cathode. MPR was enhanced to 91.8 gCH4/m3 reactor/d in the microbial electrolysis ME-AD reactor, thus improving the rate by 3 times compared to control conditions (30.6 gCH4/m3 reactor/d in AD). The methane production yield reached 116.2 mg/g VSS in the ME-AD reactor. According to balance calculation on electron transfer and methane yield, the increased methane production was mostly dependent on electron contribution through the ME system. Thus, the use of the novel ME-AD reactor allowed to significantly enhance carbon degradation and methane production from WAS.

Abstract Due to the crucial role of the cathodic catalyst in the electron-transfer rate and hydrogen recovery in bioelectrochemical systems, coupling nickel and earth-abundant transition metal phosphides with high catalysis efficiency and low cost could provide a promising alternative to Pt/C catalysts. Herein, we fabricated a three-dimensional (3D) biphasic Ni5P4-NiP2 nanosheet matrix to act as a cathodic tunnel for electron transfer for hydrogen coupled with a microbially catalyzed bioanode. Benefiting from the “ensemble effect” of P, the Tafel slope obtained from voltammetry reflected the improved catalytic performance (83.9 mV/dec vs. 113.6 mV/dec) and contributed to a higher hydrogen production rate of 9.78 ± 0.38 mL d−1 cm−2 that was 1.5 times faster than that of NF, which was even faster than that reported for commercial Pt/C. The impedance resistance obtained using electrochemical impedance spectroscopy (EIS) showed that the NF-P simultaneously exhibited