Narcís Pous

Biocatalysed sulphate removal in a BES cathode.

Sulphate reduction in a biological cathode and physically separated from biological organic matter oxidation has been studied in this paper. The bioelectrochemical system was operated as microbial fuel cell (for bioelectricity production) to microbial electrolysis cell (with applied voltage). Sulphate reduction was not observed without applied voltage and only resulted when the cathodic potential was poised at -0.26V vs. SHE, with a minimum energy requirement of 0.7V, while maximum removal occurred at 1.4V applied. The reduction of sulphate led to sulphide production, which was entrapped in the ionic form thanks to the high biocathode pH (i.e. pH of 10) obtained during the process.

Anaerobic arsenite oxidation with an electrode serving as the sole electron acceptor: A novel approach to the bioremediation of arsenic-polluted groundwater

Arsenic contamination of soil and groundwater is a serious problem worldwide. Here we show that anaerobic oxidation of As(III) to As(V), a form which is more extensively and stably adsorbed onto metal-oxides, can be achieved by using a polarized (+497 mV vs. SHE) graphite anode serving as terminal electron acceptor in the microbial metabolism. The characterization of the microbial populations at the electrode, by using in situ detection methods, revealed the predominance of gammaproteobacteria. In principle, the proposed bioelectrochemical oxidation process would make it possible to provide As(III)-oxidizing microorganisms with a virtually unlimited, low-cost and low-maintenance electron acceptor as well as with a physical support for microbial attachment.

Microbiome characterization of MFCs used for the treatment of swine manure.

Conventional swine manure treatment is performed by anaerobic digestion, but nitrogen is not treated. Microbial Fuel Cells (MFCs) allow organic matter and nitrogen removal with concomitant electricity production. MFC microbiomes treating industrial wastewaters as swine manure have not been characterized. In this study, a multidisciplinary approach allowed microbiome relation with nutrient removal capacity and electricity production. Two different MFC configurations (C-1 and C-2) were used to treat swine manure. In C-1, the nitrification and denitrification processes took place in different compartments, while in C-2, simultaneous nitrification-denitrification occurred in the cathode. Clostridium disporicum and Geobacter sulfurreducens were identified in the anode compartments of both systems. C. disporicum was related to the degradation of complex organic matter compounds and G. sulfurreducens to electricity production. Different nitrifying bacteria populations were identified in both systems because of the different operational conditions. The highest microbial diversity was detected in cathode compartments of both configurations, including members of Bacteroidetes, Chloroflexiaceae and Proteobacteria. These communities allowed similar removal rates of organic matter (2.02-2.09 kg COD m(-3)d(-1)) and nitrogen (0.11-0.16 kg Nm(-3)d(-1)) in both systems. However, they differed in the generation of electric energy (20 and 2 mW m(-3) in C-1 and C-2, respectively).

Monitoring and engineering reactor microbiomes of denitrifying bioelectrochemical systems

Denitrifying bioelectrochemical systems (d-BES) are a promising technology for nitrate removal from wastewaters. Microbial community monitoring is required to pave the way to application. In this study, for the first time flow cytometry combined with molecular biology techniques is exploited to monitor and determine the structure–function relationship of the microbiome of a denitrifying biocathode. Stable cathode performance at poised potential (−0.32 V vs. Ag/AgCl) was monitored, and different stress-tests were applied (reactor leakage, nitrate concentration, buffer capacity). Stress-tests shifted the reactor microbiome and performance. The monitoring campaign covered a wide range of nitrate consumption rates (from 15 to 157 mg N LNCC−1 d−1), current densities (from 0 to 25 mA LNCC−1) and denitrification intermediates (nitrite and nitrous oxide consumption rates varied from 0 to 56 mg N LNCC−1 d−1). The reactor microbiome (composed of 21 subcommunities) was characterized and its structure–function relationship was revealed. A key role for Thiobacillus sp. in the bioelectrochemical reduction of nitrate was suggested, while a wider number of subcommunities were involved in NO2− and N2O reduction. It was demonstrated that different bacteria catalyze each denitrification step in a biocathode. This study contributed significantly to understanding denitrifying biocathodes, paving the way for their knowledge-driven engineering.

Bioelectroremediation of perchlorate and nitrate contaminated water: A review

Fresh water is a fundamental source for humans, hence the recent shrinkage in freshwater and increase in water pollution are imperative problems that vigorously affect the people and the environment worldwide. The breakneck industrialization contributes to the procreation of substantial abundance of wastewater and its treatment becomes highly indispensable. Perchlorate and nitrate containing wastewaters poses a serious threat to human health and environment. Conventional biological treatment methods are expensive and also not effective for treating wastewater effectively and incapable of in situ bioremediation. Bioelectrochemical systems are emerging as a new technology platform for a sustainable removal of such contaminants from wastewater streams. This article reviews the state of art of bioelectroremediation of contaminated waters with perchlorate and nitrate. Different aspects of this technology such as configuration and design, mode of operation and type of substrate are considered in detail.

Opportunities for groundwater microbial electro-remediation

Groundwater pollution is a serious worldwide concern. Aromatic compounds, chlorinated hydrocarbons, metals and nutrients among others can be widely found in different aquifers all over the world. However, there is a lack of sustainable technologies able to treat these kinds of compounds. Microbial electro‐remediation, by the means of microbial electrochemical technologies (MET), can become a promising alternative in the near future. MET can be applied for groundwater treatment in situ or ex situ, as well as for monitoring the chemical state or the microbiological activity. This document reviews the current knowledge achieved on microbial electro‐remediation of groundwater and its applications.

Employing Microbial Electrochemical Technology-driven electro-Fenton oxidation for the removal of recalcitrant organics from sanitary landfill leachate

The feasibility of employing Microbial Electrochemical Technology (MET)-driven electro-Fenton oxidation was evaluated as a post-treatment of an anammox system treating sanitary landfill leachate. Two different MET configuration systems were operated using effluent from partial nitrification-anammox reactor treating mature leachate. In spite of the low organic matter biodegradability of the anammoxs effluent (2401±562mgCODL-1; 237±57mgBOD5L-1), the technology was capable to reach COD removal rates of 1077-1244mgL-1d-1 with concomitant renewable electricity production (43.5±2.1Am-3NCC). The operation in continuous mode versus batch mode reinforced the removal capacity of the technology. The recirculation of acidic catholyte into anode chamber hindered the anodic efficiency due to pH stress on anodic electricigens. The obtained results demonstrated that the integrated system is a potentially applicable process to deal with bio-recalcitrant compounds present in mature landfill leachate.

Effect of hydraulic retention time and substrate availability in denitrifying bioelectrochemical systems

Denitrifying bioelectrochemical systems (BES) allow safe nitrate treatment in waters with low organic carbon content without chemical requirements and at a competitive cost. However, this technology should move towards scaling-up by improving removal rate capabilities. In this study, a novel tubular design was used to evaluate whether the hydraulic retention time and the influent nitrate concentration influence the nitrate removal rate of denitrifying BES. A nitrate consumption rate of up to 849 g N mNCC−3 d−1 was reached without accumulation of nitrites at a HRT of 28 minutes. Nitrate removal activity was evaluated under different nitrate influent concentrations and under different HRTs. Results suggested preeminence of HRT on modulating the denitrifying activity. Therefore, this study presents an innovative design for nitrate removal using denitrifying BES and it demonstrates that operation at low HRTs increases the nitrate removal rate. It suggests that an appropriate approximation of scaling-up denitrifying BES would be the implementation of compact reactors connected in series operated at low HRTs.

Denitrifying nirK-containing alphaproteobacteria exhibit different electrode driven nitrite reduction capacities

Abstract Biocathodic electrode-driven denitrification has been proved experimentally in complex biofilms. However, experimentation with isolated bacteria in pure culture is still limited. In this paper, six Alphaproteobacteria (Rhizobiales), found to be dominant in a denitrifying biocathode, have been characterized bioelectrochemically. Bacteria were isolated using strict autotrophic conditions in the presence of nitrate or nitrite. Six representative isolates were selected and proven able to denitrify under autotrophic and heterotrophic conditions in liquid media. Bioelectrochemical reduction of nitrate, nitrite and nitrous oxide was tested using cyclic voltammetry. Electrode-driven nitrite reduction was only detected in four of the six isolates. However, no electrode-driven nitrate or nitrous oxide reduction could be detected for any of them. In the presence of nitrite, estimated midpoint potentials for bioelectrocatalyzed reactions ranged from −500 to −534 mV vs. SHE. Two of the isolates exhibited midpoint potentials at −450 and −486 mV vs. SHE when incubated in the absence of any external nitrogenous electron acceptor. These redox peaks were attributed to electrode-driven hydrogen production in the biofilm. We have proven that electrode-driven nitrite reduction is feasible in monospecific biofilms. However, significant variability in relation to electrode-driven nitrogen reduction processes was observed in closely related species, confirming a strain-specific behavior.