Long-term continuous production of H2 in a microbial electrolysis cell (MEC) treating saline wastewater

A biofilm-based 4 L two chamber microbial electrolysis cell (MEC) was continuously fed with acetate under saline conditions (35 g/L NaCl) for more than 100 days. The MEC produced a biogas highly enriched in H2 (≥90%). Both current (10.6 ± 0.2 A/m2Anode or 199.1 ± 4.0 A/m3MEC) and H2 production (201.1 ± 7.5 LH2/m2Cathode·d or 0.9 ± 0.0 m3H2/m3MEC·d) rates were highly significant when considering the saline operating conditions. A microbial analysis revealed an important enrichment in the anodic biofilm with five main bacterial groups: 44% Proteobacteria, 32% Bacteroidetes, 18% Firmicutes and 5% Spirochaetes and 1% Actinobacteria. Of special interest is the emergence within the Proteobacteria phylum of the recently described halophilic anode-respiring bacteria Geoalkalibacter (unk. species), with a relative abundance up to 14%. These results provide for the first time a noteworthy alternative for the treatment of saline effluents and continuous production of H2

Challenges in microbial ecology: building predictive understanding of community function and dynamics.

The importance of microbial communities (MCs) cannot be overstated. MCs underpin the biogeochemical cycles of the earth's soil, oceans and the atmosphere, and perform ecosystem functions that impact plants, animals and humans. Yet our ability to predict and manage the function of these highly complex, dynamically changing communities is limited. Building predictive models that link MC composition to function is a key emerging challenge in microbial ecology. Here, we argue that addressing this challenge requires close coordination of experimental data collection and method development with mathematical model building. We discuss specific examples where model-experiment integration has already resulted in important insights into MC function and structure. We also highlight key research questions that still demand better integration of experiments and models. We argue that such integration is needed to achieve significant progress in our understanding of MC dynamics and function, and we make specific practical suggestions as to how this could be achieved

Engineered methanotrophic syntrophy in photogranule communities removes dissolved methane

The anaerobic treatment of wastewater leads to the loss of dissolved methane in the effluent of the treatment plant, especially when operated at low temperatures. The emission of this greenhouse gas may reduce or even offset the environmental gain from energy recovery through anaerobic treatment. We demonstrate here the removal and elimination of these comparably small methane concentrations using an ecologically engineered methanotrophic community harbored in oxygenic photogranules. We constructed a syntrophy between methanotrophs enriched from activated sludge and cyanobacteria residing in photogranules and maintained it over a two-month period in a continuously operated reactor. The novel community removed dissolved methane during stable reactor operation by on average 84.8±7.4% (±standard deviation) with an average effluent concentration of dissolved methane of 4.9±3.7 mg CH4∙l−1. The average methane removal rate was 26 mg CH4∙l−1∙d−1, with an observed combined biomass yield of 2.4 g VSS∙g CH4−1. The overall COD balance closed at around 91%. Small photogranules removed methane more efficiently than larger photogranule, likely because of a more favorable surface to volume ratio of the biomass. MiSeq amplicon sequencing of 16S and 23S rRNA revealed a potential syntrophic chain between methanotrophs, non-methanotrophic methylotrophs and filamentous cyanobacteria. The community composition between individual photogranules varied considerably, suggesting cross-feeding between photogranules of different community composition. Methanotrophic photogranules may be a viable option for dissolved methane removal as anaerobic effluent post-treatment.publishedVersio

Cyanobacterial abundance drives photogranulation

Oxygenic photogranules couple oxygen production through photosynthesis to heterotrophic respiration. They may be used in bioprocess engineering applications like wastewater treatment. We demonstrate that photogranulation does not require hydrodynamic shear and washout but also happens under static, batch conditions. Instead, it appears that the formation of these granules strongly depends on the initial presence and abundance of filamentous, motile cyanobacteria. In replicated augmentation experiments, we tested additions of cyanobacteria over a wide concentration gradient. The addition of small numbers of cyanobacteria statistically improved photogranulation, while too many added cyanobacteria led to the formation of microbial mats. Photogranulation is thus driven by entirely different factors than those typically postulated for anaerobic and aerobic granules

Anaerobic digester bioaugmentation influences quasi steady state performance and microbial community

Nine anaerobic digesters, each seeded with biomass from a different source, were operated identically and their quasi steady state function was compared. Subsequently, digesters were bioaugmented with a methanogenic culture previously shown to increase specific methanogenic activity. Before bioaugmentation, different seed biomass resulted in different quasi steady state function, with digesters clustering into three groups distinguished by methane (CH4) production. Digesters with similar functional performance contained similar archaeal communities based on clustering of Illumina sequence data of the V4V5 region of the 16S rRNA gene. High CH4 production correlated with neutral pH and high Methanosarcina abundance, whereas low CH4 production correlated to low pH as well as high Methanobacterium and DHVEG 6 family abundance. After bioaugmentation, CH4 production from the high CH4-producing digesters transiently increased by 11 ± 3% relative to non-bioaugmented controls (p < 0.05, n = 3), whereas no functional changes were observed for medium and low CH4 producing digesters that all had pH higher than 6.7. The CH4 production increase after bioaugmentation was correlated to increased relative abundance of Methanosaeta and Methaospirillum originating from the bioaugment culture. In conclusion, different anaerobic digester seed biomass can result in different quasi steady state CH4 production, SCOD removal, pH and effluent VFA concentration in the timeframe studied. The bioaugmentation employed can result in a period of increased methane production. Future research should address extending the period of increased CH4 production by employing pH and VFA control concomitant with bioaugmentation, developing improved bioaugments, or employing a membrane bioreactor to retain the bioaugment

Naturally occuring cyanobacteria can form oxygenic photogranules to treat wastewater

Oxygenic photogranules (OPGs) are roughly spherical aggregates with diameters of several millimeters containing a syntrophic community of heterotrophic bacteria and cyanobacteria, predominantly of the order Oscillatoriales [1]. OPGs may potentially be used in wastewater treatment because their in-situ produced oxygen can replace costly mechanical aeration for pollutant removal [2]. Toxin production could however nullify their application. OPGs can be produced from “activated sludge”, the aerobic microbial aggregates used for treating wastewater. This sludge is transferred into unagitated vials and exposed to light. Over the course of several weeks, the unconsolidated sludge transforms into one photogranule per vial. Curiously, in replicates using the same sludge, a granule does not always form: sometimes microbial mats result or the material remains unconsolidated. We therefore aim to better understand the initial conditions for photogranulation, specifically the role of filamentous cyanobacteria. We hypothesize that the behavior of Oscillatoriales is key to photogranulation and that cyanobacteria type and their relative abundance determine granulation success, i.e., OPG formation. We therefore investigate whether the formation of microbial mats, well-formed photogranules and intermediates, correlates to the presence of a specific microbial community. We performed nine granulation experiments which resulted in 135 qPCR corrected amplicons from both partial 16S (all bacteria) and 23S (cyanobacteria and algae) rRNA genes from samples on a gradient of granulation success. From sequence analysis we learnt that several Oscillatoriales species are able to form photogranules. For an application in wastewater treatment, we now need to evaluate whether operational conditions may lead to toxin production

Impact of hydrodynamic perturbations on physical structure and microbiological composition of biofilm

In natural environments as well as in industrial processes, microorganisms form biofilms. Hydrodynamic conditions are one of the key parameters influencing the microbiological and physical structures of a biofilm. In the present work, a method has been developed to count and characterize grazing population of a biofilm. We used hydrodynamic conditions to obtain biofilms having different microbiological compositions and superficial structures. We monitored two continuous bubbles columns, inoculated with aerobic activated sludge. One reactor was operated under a stable low hydrodynamic constraint while the second one was exposed to frequent high hydrodynamic perturbations. Microscopic images showed a very dense population of eukaryotic organisms such as rotifers, nematodes and ciliates. We developed an innovative approach to quantify the number of rotifers. The method is based on the analysis of microscopic images. Hydrodynamic perturbations modified both the morphological and microbiological structures: perturbations decreased the quantity of moving organisms, such as rotifers, whereas some streamers appeared

ENgineerInG interactions in Methanogenic communities at the Ecosystem level - ENIGME

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Invasibility of resident biofilms by allochthonous communities in bioreactors

Invasion of non-native species can drastically affect the community composition and diversity of engineered and natural ecosystems, biofilms included. In this study, a molecular community fingerprinting method was used to monitor the putative establishment and colonization of allochthonous consortia in resident multi-species biofilms. To do this, biofilms inoculated with tap water or activated sludge were grown for 10 days in bubble column reactors W1 and W2, and S, respectively, before being exposed to non-native microbial consortia. These consortia consisted of fresh activated sludge suspensions for the biofilms inoculated with tap water (reactors W1 and W2) and of transplanted mature tap water biofilm for the activated sludge biofilm (reactor S). The introduction of virgin, unoccupied coupons into W1 and W2 enabled us to additionally investigate the competition for new resources (space) among the resident biofilm and the allochthonous consortia. CE-SSCP revealed that after the invasion event changes were mostly observed in the abundance of the dominant species in the native biofilms rather than their composition. This suggests that the resident communities within a bioreactor immediately outcompete the allochthonous microbes and shape the microbial community assemblage on both new coupons and already colonized surfaces for the short term. However, with time, latent members of the allochthonous community might grow up affecting the diversity and composition of the original biofilms. (C) 2015 Elsevier Ltd. All rights reserved

Replication of experiments in anaerobic digestion: simpler, greater and easier than you had ever hoped

Reliability of results in science is done by replication of experiments, but it is often expensive and labour intensive. Indeed, operating anaerobic digesters in a continuous mode requires some experience and a lot of manpower. The number of anaerobic digesters that can be handled in parallel is therefore limited. In practice, experiments are often repeated several times, starting always with a fresh inoculum. One approach is to store and to restore the activity of the same inoculum, with no guarantee on the preservation of the functioning. Unfortunately, there is no consensus on any standardized strategy for the long-term preservation of complex ecosystems. Here, we present a multiplexed chemostat system that minimizes costs and manpower for operating several anaerobic digesters in parallel, and present a first application of the system. Up to thirty reactors may be operated by a single person. This system may unlock ecological studies as well as process optimization in the context of anaerobic digestion, where several conditions need to be tested in parallel. The vocation of this device is to make it available to the scientific community