No abstract

This paper deals with the design, operation, modeling, and grid integration of bioelectrochemical systems (BES) for power-to-gas application, through an electromethanogenesis process. The paper objective is to show that BES-based power-to-gas energy storage is feasible on a large scale, showing a first approximation that goes from the BES design and operation to the electrical grid integration. It is the first study attempting to cover all aspects of a BES-based power-to-gas technology, on authors’ knowledge. Designed BES reactors were based on a modular architecture, suitable for a future scaling-up. They were operated in steady state for eight months, and continuously monitored in terms of power consumption, water treatment, and biomethane production, in order to obtain data for the following modeling activity. A black box linear model of the BES was computed by using least-square methods, and validated through comparison with collected experimental data. Afterwards, a BES stack was simulated through several series and parallel connections of reactors, in order to obtain higher power consumption and test the grid integration of a real application system. The renewable energy surplus and energy price variability were evaluated for the grid integration of the BES stack. The BES stack was then simulated as energy storage system during low energy price periods, and tested experimentally with a real time system.

No abstract

No abstract

Microbial Desalination Cell (MDC) represents an innovative technology which accomplishes simultaneous desalination and wastewater treatment without external energy input. MDC technology could be employed to provide freshwater with low-energy input, for example, in remote areas where organic wastes (i.e., urban or industrial) are available. In addition, MDC technology has been proposed as pre-treatment in conventional reverse osmosis plants, with the aim of saving energy and avoiding greenhouse gases related to conventional desalination processes. The use of oxygen reduction (i.e. O 2 + 2H 2 O + 4e − → 4 OH − , E 0 ′ = 0.815 V, pH = 7) was usually implemented as cathodic reaction in most of the MDCs reported in literature, whereas other strategies based on liquid catholytes have been also proposed, for example, ferroferricyanide redox couple (i.e. Fe(CN) 3− 6 + 1e − → Fe(CN) 4− 6 , E 0 = 0.37 V). As the MDC designs in the literature and operation modes (i.e., batch, continuous, semi-continuous, etc.) are quite different, the available MDC studies are not directly comparable. For this reason, the main objective of this work was to have a proper comparison of two similar MDCs operating with two different catholyte strategies, and compare performance and desalination efficiencies. In this sense, this study compares the desalination performance of two laboratory-scale MDCs located in two different locations for brackish water and sea water using two different strategies. The first strategy consisted of an air cathode for efficient oxygen reduction, while the second strategy was based on a liquid catholyte with Fe 3+ /Fe 2+ solution (i.e., ferro-ferricyanide complex). Both strategies achieved desalination efficiency above 90% for brackish water. Nominal desalination rates (NDR) were in the range of 0.17-0.14 L•m −2 •h −1 for brackish and seawater with air diffusion cathode MDC, respectively, and 1.5-0.7 L•m −2 •h −1 when using ferro-ferricyanide redox MDC. Organic matter present in wastewater was effectively removed at 0.9 and 1.1 kg COD•m −3 •day −1 using the air diffusion cathode MDC for brackish and Ramírez-Moreno et al.Comparative Performance of Microbial Desalination Cells sea water, respectively, and 7.1 and 19.7 kg COD•m −3 •day −1 with a ferro-ferricyanide redox MDC. Both approaches used a laboratory MDC prototype without any energy supply (excluding pumping energy). Pros and cons of both strategies are discussed for subsequent upscaling of MDC technology.

In dye-sensitised solar cells developed to-date, ultraviolet blocking layers (UV-BL) is employed to avoid photocatalysis effects on the dye and consequent reduction in PV energy output over time due to UV exposure in outdoor conditions. Use of a UV-BL increases stability but, power conversion efficiency decreases as incident UV photons are not converted. The organolanthanide complex Eu(tta) 3 phen is examined for inclusion in large Stokes shift downshifting (LSS DS) layers. It is shown that such LSS DS layers can be used as a UV blocking layer in DSSCs. A ray-trace numerical model is used to optimise the thickness and concentration of the LSS DS layers for the specific N719 DSSC. EQE is significantly increased in the UV spectral region compared to DSSCs utilizing a passive, non-luminescent, UV-BL. High Eu(tta) 3 phen film transparency in the visible range minimises DSSC EQE losses at visible wavelengths. The photostability of the blended LSS DS polymer films is not sufficient to be useful for medium-long term outdoor PV applications. However, the results demonstrate that significant efficiency enhancement can be realized. Short circuit current enhancement due to downshifting is demonstrated (~1%) in small scale LSS DS polymer films prepared and attached to DSSC devices, where the specific geometry limits the photon collection efficiency and overall enhancement. Model predictions indicate that 2-3% enhancement is realizable in DSSC minimodules, compared to minimodules using passive, non-luminescent, UV-BL. Predicted enhancement in energy produced in outdoor conditions is 3-5%.

Anaerobic digestion of sewage sludge produces large amounts of CO2 which contribute to global CO2 emissions. Capture and conversion of CO2 into valuable products is a novel way to reduce CO2 emissions and valorize it. Membrane contactors can be used for CO2 capture in liquid media, while bioelectrochemical systems (BES) can valorize dissolved CO2 converting it to CH4, through electromethanogenesis (EMG). At the same time, EMG process, which requires electricity to drive the conversion, can be utilized to store electrical energy (eventually coming from renewables surplus) as methane. The study aims integrating the two technologies at a laboratory scale, using for the first time real wastewater as CO2 capture medium. Five replicate EMG-BES cells were built and operated individually at 0.7 V. They were fed with both synthetic and real wastewater, saturated with CO2 by membrane contactors. In a subsequent experimental step, four EMG-BES cells were electrical stacked in series while one was kept as reference. CH4 production reached 4.6 L CH4 m−2 d−1, in line with available literature data, at a specific energy consumption of 16–18 kWh m−3 CH4 (65% energy efficiency). Organic matter was removed from wastewater at approximately 80% efficiency. CO2 conversion efficiency was limited (0.3–3.7%), depending on the amount of CO2 injected in wastewater. Even though achieved performances are not yet competitive with other mature methanation technologies, key knowledge was gained on the integrated operation of membrane contactors and EMG-BES cells, setting the base for upscaling and future implementation of the technology.

No abstract