Bioreactor Performance and Quantitative Analysis of Methanogenic and Bacterial Community Dynamics in Microbial Electrolysis Cells during Large Temperature Fluctuations

The use of microbial electrolysis cells (MECs) for H₂ production generally finds H₂ sink by undesirable methanogenesis at mesophilic temperatures. Previously reported approaches failed to effectively inhibit methanogenesis without the addition of nongreen chemical inhibitors. Here, we demonstrated that the CH₄ production and the number of methanogens in single-chamber MECs could be restricted steadily to a negligible level by continuously operating reactors at the relatively low temperature of 15 °C. This resulted in a H₂ yield and production rate comparable to those obtained at 30 °C with less CH₄ production (CH₄% < 1%). However, this operation at 15 °C should be taken from the initial stage of anodic biofilm formation, when the methanogenic community has not yet been established sufficiently. Maintaining MECs operating at 20 °C was not effective for controlling methanogenesis. The varying degrees of methanogenesis observed in MECs at 30 °C could be completely inhibited at 4 and 9 °C, and the total number of methanogens (mainly hydrogenotrophic methanogens) could be reduced by 68–91% during 32–55 days of operation at the low temperatures. However, methanogens cannot be eliminated completely at these temperatures. After the temperature is returned to 30 °C, the CH₄ production and the number of total methanogens can rapidly rise to the prior levels. Analysis of bacterial communities using 454 pyrosequencing showed that changes in temperature had no a substantial impact on composition of dominant electricity-producing bacteria (Geobacter). The results of our study provide more information toward understanding the temperature-dependent control of methanogenesis in MECs

Data_Sheet_1.pdf

<p>p-Nitrophenol (PNP) is common in the wastewater from many chemical industries. In this study, we investigated the effect of initial concentrations of PNP and glucose and applied voltage on PNP reduction in biocathode BESs and open-circuit biocathode BESs (OC-BES). The PNP degradation efficiency of a biocathode BES with 0.5 V (Bioc-0.5) reached 99.5 ± 0.8%, which was higher than the degradation efficiency of the BES with 0 V (Bioc-0) (62.4 ± 4.5%) and the OC-BES (59.2 ± 12.5%). The PNP degradation rate constant (k_PNP) of Bioc-0.5 was 0.13 ± 0.01 h^-1, which was higher than the k_PNP of Bioc-0 (0.024 ± 0.002 h^-1) and OC-BES (0.013 ± 0.0005 h^-1). PNP degradation depended on the initial concentrations of glucose and PNP. A glucose concentration of 0.5 g L^-1 was best for PNP degradation. The initial PNP increased from 50 to 130 mg L^-1 and the k_PNP decreased from 0.093 ± 0.008 to 0.027 ± 0.001 h^-1. High-throughput sequencing of 16S rRNA gene amplicons indicated differences in microbial community structure between BESs with different voltages and the OC-BES. The predominant populations were affiliated with Streptococcus (42.7%) and Citrobacter (54.1%) in biocathode biofilms of BESs, and Dysgonomonas were the predominant microorganisms in biocathode biofilms of OC-BESs. The predominant populations were different among the cathode biofilms and the suspensions. These results demonstrated that applied voltage and biocathode biofilms play important roles in PNP degradation.</p

MOESM1 of Multiple syntrophic interactions drive biohythane production from waste sludge in microbial electrolysis cells

Additional file 1: Table. S1. Similarity-based OTUs and species richness and diversity estimates of bacteria in different systems. Figure. S1. Current density of MEC fed with raw sludge (RS-MEC) and alkali-pretreated waste sludge (AS-MEC). Figure. S2. Variations of SCOD (A), soluble protein (B) and carbohydrates concentration (C) of raw sludge open-circuit MEC (RS-OCMEC), MEC fed with raw sludge (RS-MEC) or alkali-pretreated sludge (AS-MEC)

Molecular-Weight-Dependent Degradation of Plastics: Deciphering Host–Microbiome Synergy Biodegradation of High-Purity Polypropylene Microplastics by Mealworms

The biodegradation of polypropylene (PP), a highly persistent nonhydrolyzable polymer, by Tenebrio molitor has been confirmed using commercial PP microplastics (MPs) (Mn 26.59 and Mw 187.12 kDa). This confirmation was based on the reduction of the PP mass, change in molecular weight (MW), and a positive Δδ13C in the residual PP. A MW-dependent biodegradation mechanism was investigated using five high-purity PP MPs, classified into low (0.83 and 6.20 kDa), medium (50.40 and 108.0 kDa), and high (575.0 kDa) MW categories to access the impact of MW on the depolymerization pattern and associated gene expression of gut bacteria and the larval host. The larvae can depolymerize/biodegrade PP polymers with high MW although the consumption rate and weight losses increased, and survival rates declined with increasing PP MW. This pattern is similar to observations with polystyrene (PS) and polyethylene (PE), i.e., both Mn and Mw decreased after being fed low MW PP, while Mn and/or Mw increased after high MW PP was fed. The gut microbiota exhibited specific bacteria associations, such as Kluyvera sp. and Pediococcus sp. for high MW PP degradation, Acinetobacter sp. for medium MW PP, and Bacillus sp. alongside three other bacteria for low MW PP metabolism. In the host transcriptome, digestive enzymes and plastic degradation-related bacterial enzymes were up-regulated after feeding on PP depending on different MWs. The T. molitor host exhibited both defensive function and degradation capability during the biodegradation of plastics, with high MW PP showing a relatively negative impact on the larvae