DOI: 10.5061/dryad.pvmcvdnm7
title: Rainwater-driven microbial fuel cells for power generation in the remote areas' raw data

description: The possibility of utilizing rainwater as a sustainable anolyte in an
 air-cathode microbial fuel cell is investigated in this study. The results
 indicate that the proposed microbial fuel cell can work within a wide
 temperature range (from 0 to 30 oC), and under aerobic or anaerobic
 conditions. However, the rainwater season has a distinct impact. Under
 anaerobic conditions, the summer rainwater achieves a promised open
 circuit potential of 553±2 mV without addition of nutrients at the ambient
 temperature, while addition of nutrients leads to increase the cell
 voltage to 763±3 and 588±2 mV at 30 oC and ambient temperature,
 respectively. The maximum open circuit potential for the winter rainwater
 (492±1.5 mV) is obtained when the reactor is exposed to the air (aerobic
 conditions) at ambient temperature. Furthermore, the winter rainwater
 microbial fuel cell generates a maximum power output of 7±0.1 mWm-2 at a
 corresponding current density value of 44±0.7 mAm-2 at 30 oC. While, at
 the ambient temperature, the maximum output power is obtained with the
 summer rainwater (7.2±0.1 mWm-2 at 26±0.5 mAm-2). Moreover, investigation
 of the bacterial diversity indicates that lactobacillus sp. is the
 dominant electroactive genus in the summer rainwater, while in the winter
 rainwater, Staphylococcus sp. is the main electroactive bacteria. The
 cyclic voltammetry analysis confirms that the electrons are delivered
 directly from the bacterial biofilm to the anode surface and without
 mediators. Overall, the study opens a new avenue for utilizing a novel
 sustainable type of microbial fuel cell derived by rainwater.
description: 2.1. Rainwater samples The samples were
 collected in April and December for summer and winter rainwater samples,
 respectively. A 500 ml of each rainwater sample was collected in a
 sterilised glass bottle at elevation of 59 meters above sea level in
 Jeonju, Jeollabuk-do province, Republic of Korea. A 200 ml from each
 sample (immediately after collecting) was transferred to 1 L sterilised
 bottle for chemical and microbiological analyses. These samples were
 transported in a chilled-cold box to the laboratory and processed within 8
 h of collection. The average corresponding electrical conductivities of
 the collecting samples were 61 and 24 µS for the summer and winter
 rainwaters, respectively. 2.2. Anolyte
 preparation The rainwater (without pretreatment) was
 used as anolyte without additives, and with Nutrient Broth media (1:1
 ratio v/v) which contains (for 1 L), 15g of peptone (Samchun Pure Chemical
 Co., Ltd.), 3g of yeast extract (Samchun Pure Chemical Co., Ltd.), 1g of
 glucose (Junsei Chemical Co., Ltd.) and 6g of sodium chloride (Samchun
 Pure Chemical Co., Ltd.), for comparison purposes. 2.3.
 MFC Construction and operation A single chamber
 air-cathode MFC made of transparent polyacrylic was used. 4 cm between the
 anode and the cathode was maintained. An Ag/AgCl reference electrode is
 placed in the anode compartment to measure the potential of the
 electrodes. Cation exchange membrane (CEM, CMI-7000, Membrane
 International Inc., NJ, USA) was used for ions exchange. The membrane was
 firstly treated by dipping in a H2SO4 solution (0.5 M) for 18 h, and then
 kept in a distilled water. The cathode was 2.4 cm × 2.4 cm Pt-loaded (0.5
 mgcm-2) carbon cloth (EC-20-5, Electro Chem, Inc., USA). The cathode
 material was in a direct contact with the natural air. A carbon felt (2.4
 cm × 2.4 cm, 3.18 mm, Alfa Aesar) was used as an anode. The power
 calculation was normalized for the anode projected surface area (6.25
 cm2). The current collectors were two 0.1cm-thick high corrosion
 resistance stainless steel plates. The cell was assembled as described in
 our previous work 25 (add yours) as follows: the anode was attached to
 anode current collector, this assembly was placed at one side of the cell.
 Then, at the other side, the cathode was sandwiched between the cation
 exchange membrane and cathode current collector. The assembled MFC was
 sterilised by UV (CHC LAB Co., Ltd, Korea), while the culture media and
 the glassware adopted in this study were autoclaved at 121 °C for 20 min
 before operation with a steam steriliser (Autoclave, AC-60, Hanyang
 Scientific Equipment Co. Ltd, Korea). To evaluate the
 performance, the RMFC was driven with pure rainwater as anolyte, and with
 mixture of rainwater and Nutrient broth media (1:1 ratio v/v).
 Furthermore, the aerobic and anaerobic conditions were examined, the
 bacteria was cultivated under anaerobic conditions by blocking the access
 of oxygen 26. For the aerobic conditions, the MFC was in direct contact to
 the ambient air through an open access of 10 mm 27. Moreover, the
 temperature effect was investigated, where the RMFC was operated at the
 ambient temperature (with lowest temperature degree around 0 to 5 oC, from
 10 to 31 of January) and at 30 oC for comparison purposes.
 2.4. Electrochemical Characterization The MFCs
 electrochemical performances were evaluated using HA-151A potentiostat
 (HA-151A POTENTIO STAT/GALVANOSTAT, Japan). The cyclic voltammetry
 analysis (CV) was carried out on the assembled cell using a
 three-electrode setup in which the anode was assigned as a working
 electrode (WE), and the cathode and Ag/AgCl as a counter (CE) and
 reference (RE) electrodes, respectively. The used potential window was
 from 1.0 to -0.4 V at a scan rate of 1 mVs-1. The open circuit potential
 (OCP) values were recorded using GL220 midi-logger.  After OCP
 stabilisation, the cell circuit was closed and the power curves were
 obtained by a linear sweep voltammetry from the maximum OCP to a
 zero-voltage at a scan rate of 1 mVs-1 with a two-electrode mode, where
 the cathode was connected as WE and the anode as both CE and RE 28, 29.
 The power (P) was obtained as P =IV. The morphology of the used anodes was
 investigated by the scanning electron microscopy (SEM Hitachi S-7400,
 Japan). The electrodes were dried at room temperature (20 ± 2 oC) in
 sterilised Petri dishes and then used for the analysis.
 2.5. Microbial Community Analyses At the end
 of the experiment (after 22 days of operation), the RMFC was dismantled,
 and the anode was abstracted from the MFC in a sterilized laminar cabinet
 (CHC LAB Co., Ltd, Korea). The biofilm was sampled from both anode surface
 and anolyte, and then cultured in Nutrient Agar media (Sigma-Aldrich,
 Inc.). The bacterial growth was subsequent isolated in a separate culture
 using the same media according to the growth morphology characteristic.
 Finally, the strains were grown overnight and processed to extract the
 total genomic DNA. The total genomic DNA was isolated using DNA extraction
 kit protocol (QIAGene, Hilden, Germany) with a little modifications as
 described previously 30. Briefly, a 1 ml from all isolated cells were
 harvested in a 1.5 ml microcentrifuge tube, after centrifuging for 5 min
 at 8000 g. Then, the bacterial pellet re-suspended in 180 µl buffer T1 and
 mixing well, following by adding 25 µl proteinase K and vigorously
 homogenized by vortex and incubated at 56 oC for 1-3 h with shaking during
 incubation. The samples after that were vortexed and a volume of 200 µl of
 buffer B3 was added and totally mixed by vigorous vortexing. A 210 µl of
 ethanol (100%) was added to the samples and vigorously mixed with vortex
 and then each sample was applied to the Nucleospin Tissue Column and
 placed into a collection tube and centrifuged for 1 min at 11000 g. After
 discarding the flow-through from the previous step, a 500 µl of buffer BW
 was added following by centrifuge for 1 min at 11000 g. The Nucleospin
 Tissue Columns were placed in a new collection tube, 600-µl buffer B5 were
 added and centrifuged for 1 min at 11000 g. The samples were centrifuged
 again for 1 min at 11000 g. After that, the Nucleospin Tissue Columns were
 shifted to a 1.5 ml microcentrifuge tube and incubated for 1 min at room
 temperature after a 100 µl of prewarmed buffer BE (70 oC) was added.
 Finally, the previous tubes were centrifuged for 1 min at 11000 g and the
 flow-through was kept at -4 oC for the following analysis. The DNA purity
 ratio was determined using 260 and 280 nm absorbance ratio. The 16S rRNA
 gene was amplified using forward primer 27f (5′-AGAGTTTGATCCTGGCTCAG-3′)
 and reverse primer 1492r (5′-GGTTACCTTGTTACGACTT-3′) by polymerase chain
 reaction (PCR) as previously described 31. Besides that, the total
 bacterial count was carried out using Nutrient agar media (Sigma-Aldrich,
 Inc.) 32 before as well as after utilization in the MFC for a comparison
 purpose.
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