The performance of primary and secondary electroactive biofilms grown on layered corrugated carbon (LCC) electrodes was studied over a period of several months. With an average projected current density of 6.7 mA cm −2 , the studied secondary electroactive biofilms outperformed the primary biofilms (3.0 mA cm −2 ) over the entire experimental period. At the same time, both, primary and secondary biofilms, exhibited a constant Coulomb efficiency of about 89%. The study further illustrates that three-dimensional electrodes such as LCC allow a sustained long-term performance without significant decrease in electrode performance.
This study focuses on improving the treatment capacity and current output of electrochemically active microorganisms (EAM) during real wastewater treatment. A multi‐carbon‐source artificial wastewater consisting of several carbon sources, which represent typical fermentation and hydrolysis products derived from the otherwise myriad wastewater constituents, was developed as a more realistic simulation thereof. An electrochemically preselected inoculum was obtained by means of re‐suspension of a well‐established EAM biofilm, which was subsequently used to inoculate sterile electrodes. Repeating this procedure yielded increasingly enriched and conditioned biofilms with improved performance. After cultivation in the complex artificial medium, highly efficient fourth generation EAM biofilms were fed real wastewater (i. e. effluent after primary settling) and outperformed those cultivated using a single substrate (i. e. acetate) in terms of current output and chemical oxygen demand (COD) degradation rates.
In this study, electrochemically active microbial biofilms were cultivated and studied at continuously alternating electrode potentials. Compared to cultivation and operation at a single constant potential, this method enhanced microbial turnover and maximum current densities. Electrochemically active microbial biofilms were cultivated in a multi‐carbon source culture for several biofilm generations and were subsequently fed with real, domestic wastewater. Compared to constant potential cultivation, average (N=12) biofilm limiting current density at +0.2 V vs. Ag/AgCl increased from 0.350±0.101 to 0.508±0.099 mA cm−2 with a significant reduction in the time required until the maximum current output was reached from 2.01±0.79 to 1.36±0.71 d. The relative increase in maximum current density and decrease in the time required to reach it are similar. The relative differences of higher over lower values are both approximately 45 %. Biofilm community analysis showed a dominance of Geobacteraceae spp. in the electrochemically active biofilms, which is in accordance with the formal potentials derived from cyclic voltammetry. The overall increase in performance is related to the selection of electrochemically active microorganisms, which exhibit local maxima in their electron transfer kinetics between −0.3 and −0.2 V vs. Ag/AgCl.
The aim of the study was to provide experimental proof-of-concept that stand-alone power generation based on microbial fuel cells (MFCs) operated using human feces as the substrate can be achieved. A pit latrine that is typically employed for decentralized treatment of human feces e.g. in regions without access to centralized wastewater infrastructures was installed as sampling site. It was the philosophy that the components, i.e. anodes and cathodes, used in the MFCs had to be based on low-cost precursors. This was achieved by recycling common household materials or waste products and a low-tech/cost production method was developed to convert them into usable electrodes. It is demonstrated that i) pre-tests on using an equivalent to vent-air from ovens or fire-places allowed a low-tech carbonization of e.g. corrugated cardboard to electrode materials; ii) that anodes based on corrugated cardboard can be operated using real human feces as substrate, nevertheless, providing only low current densities (15.09 ± 5.18 μA cm −2 ) and iii) cathodes -with nitrogen functionalities derived from (artificial) urine -based on corrugated cardboard or as an alternative jeans cloth show a good oxygen reduction reaction (ORR) activity. Introducing nitrogen containing surface moieties to the cathode surface increased the ORR up to factor 5 (chronoamperometry at 0 V vs. Ag/AgCl sat. KCl) compared to the untreated reference. Most importantly, highly valuable lessons for exploiting real and highly heterogeneous and dense substrates like human feces in microbial electrochemical technologies were learned. In 2015 the United Nations proposed the 17 Sustainable Development Goals to be achieved by 2030.1 Among these are for instance "Good health and well-being", "Clean water and sanitation", "Affordable and clean energy" as well as "Sustainable cities and communities". Hence, sanitation and concurrently treat of waste is a key challenge, as it covers technical as well as socio-economic and health related issues.2,3 Wastewater treatment facilities and related infrastructure, e.g. as typically installed in the USA or Europe, can be a significant sink for energy and resources, 4-6 which are needed for construction, maintenance, especially of the sewer system, and operation. 7At the same time an estimated 2.4 billion people, or approx. 33 % of the world population, do not have access to such infrastructure. For this share of the world's population using simple solutions such as pit latrines can already be advantageous in terms of hygiene and security when compared to open defecation.2,3 Therefore decentralized sanitation systems seem advantageous in developing regions with no or only very little existing infrastructure.Waste and wastewaters have gradually become perceived not as sinks of chemicals and energy but as re-sources thereof. In this light microbial electrochemical technologies (MET) 8 and especially microbial fuel cells (MFCs) are considered to be a highly promising solution.6 MFCs are primary microbial electrochemical technologies...
In memory of Dr. Alessandra ColomboA cross-laboratory study on microbial fuel cells (MFC) which involved different institutions around the world is presented. The study aims to assess the development of autochthone microbial pools enriched from domestic wastewater, cultivated in identical single-chamber MFCs, operated in the same way, thereby approaching the idea of developing common standards for MFCs. The MFCs are inoculated with domestic wastewater in different geographic locations. The acclimation stage and, consequently, the startup time are longer or shorter depending on the inoculum, but all MFCs reach similar maximum power outputs (55 � 22 μW cm À 2 ) and COD removal efficiencies (87 � 9 %), despite the diversity of the bacterial communities. It is inferred that the MFC performance starts when the syntrophic interaction of fermentative and electrogenic bacteria stabilizes under anaerobic conditions at the anode. The generated power is mostly limited by electrolytic conductivity, electrode overpotentials, and an unbalanced external resistance. The enriched microbial consortia, although composed of different bacterial groups, share similar functions both on the anode and the cathode of the different MFCs, resulting in similar electrochemical output.
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