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学生の研究活動報告−国内学会大会・国際会議参加記 25

Applicability of Iron Chelate
Compounds as An Electron
Acceptor for A DoubleChamber Microbial Fuel Cell

2.2 Material and Methods

──IWA World Water Congress &Exhibition 2016──

trickling filter-type iron oxidation column. A ferrous-

2.2.1 Oxidation characteristics
We explored an easily oxidizable ferrous-chelate andan optimal hydraulic loading of the catholyte on achelate solution used contained 5 or 10 mM of ferrous
sulfate and the same concentration of a chelating agent.

𠮷田英人

Hideto YOSHIDA
環境ソリューション工学専攻修士課程

2年

1. PrefaceThe solution pH was set at 7 by the addition of 1.0 Mof sodium hydroxide solution. Chelating agents examined were ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid, and triethylenetetra-I addressed a research topic of “Applicability of ironminehexaacetic acid. We tested the validity that a ferricchelate compounds as an electron acceptor for a double-chelate compound changed a ferrous-chelate compound-chamber microbial fuel cell” at the IWA conference inby atmospheric oxygen. A trickling filter-type oxidation

Brisbane, Queensland, Australia from 9 to 14 Octo-column was an acrylic pipe with 30 mm in diameterber 2016.

and 500 mm in height, in which cylindrical high den-ththsity polyethylene carriers with 5 mm in diameter and 5

2. Summary and Presentation

mm in height were packed. The bulk volume of the fil-

2.1 Introduction

ter bed was 314 cm3. We calculated oxidation rates by

A microbial fuel cell (MFC) is defined as a system
in which microorganisms function as catalysts to con-measured absorbance of iron-chelate solutions.
2.2.2 MFC operation

vert chemical energy into electrical energy. Thus, theFigure 1 illustrates the experimental set up of MFC.

MFC is expected to become an organic wastewater

The cathodic flow cell had a spacer made of polyvinyl

treatment system with an energy recovery function. An-chloride, which was sandwiched between a pair of car-aerobic oxidation of organic matter at the anode and re-bon cloths (Torayca CO 6151 B, Toray, Japan) as cath-duction of electron acceptors at the cathode constituteodes. The outside of each carbon cloth adhered to athe oxidation-reduction reactions in the MFC. Oxygen

cation-exchange membrane (Nafion N 117, DuPont,is often used as an electron acceptor because it is richUSA) and the other side of the cation-exchange mem-in the air and a reaction product of oxygen is harmless.

brane adhered to a carbon cloth as an anode. The effec-

When a double-chamber MFC is used, it is importanttive electrode area was 200 cm2 for both cathodes andhow to promote the cathodic reaction. In this study, weanodes. The wastewater in a sanitary chamber insearch for safe chelating agents easily re-oxidized by

Ryukoku University was pumped up to a sedimentation

oxygen and use ferric ions as electron acceptors. Ferrictank. The hydraulic retention time was 8 h. The threeions are reduced into ferrous ions at cathodes of thesets of MFCs were prepared for the experimental runs.

MFC. Then, the ferrous ions are oxidized into ferric

The one of them was a control and received a tap waterions in a trickling filter-type oxidation column and areas the catholyte. The rest of them received the catholyte

reused.

containing 5 or 10 mM of ferric-EDTA chelates. Thecatholyte pH was regulated to pH 7 by addition of sul― ４３ ―

Fig. 1Fig. 2 Changes in generated currents during
the MFC operations. Ferric-EDTA chelates (5 or10 mM) were used as catholytes. In the control atap water substituted for the ferric-EDTAchelate solution.

The experimental setup

furic acid using a pH controller (FD-02, TGK, Japan).

0.266 mM at 25℃. In this research 5 or 10 mM ofThe hydraulic loading of a trickling filter-type oxida-ferric-EDTA chelate solution was used as the catholyte.

tion column was 6.6-6.9 m md . The ferric-EDTA

Therefore, the equivalent density of electron acceptor ofchelates were prepared by mixing an adequate amountthe ferric-EDTA chelate solution was 4.7-9.4-timesof ferric nitrate and EDTA.

higher than that of the oxygen-saturated water. Conse-3−3−1

quently, it was considered to promote the cathodic reac2.3 Results and Discussion

tion and to enhance the generated current. However,

2.3.1 Oxidation characteristics of ferrous-chelatedissolved CODCr removal efficiencies were 71.3±11.4

The observed oxidation rate of ferrous-chelate% (average±sample standard deviation) for the 5 mMstrongly depended on the chelating agent used, namely

ferric-EDTA chelate solution, 67.0±11.3% for the 10the highest in EDTA (date not shown). The oxidationmM ferric-EDTA chelate solution, and 67.0±11.8% for

efficiency can be approximated to a constant in thethe control. There was no significant difference of therange of hydraulic loadings less than 10 m m d .

three. It was indicated that anaerobic bacteria except

2.3.2 Applicability of EDTA as a ligand of iron for

exoelectrogenic bacteria were responsible for the or-3−3−1

ganic removal in this system.

MFCFigure 2 shows changes in the generated currents
over time. As can be seen from this figure, the gener-

3. Acknowledgement

ated current was enhanced using the ferric-EDTA

Advice and comments given by Prof. N. Kishimotochelate solution as a catholyte. When tap water washave been grateful in this research. I would like toused as a catholyte, dissolved oxygen played the elec-

show my greatest appreciation to him.

tron acceptor. The solubility of oxygen to water is― ４４ ―