S. Marzorati*, A. Goglio*, D. Mombelli**, C. Mapelli**, S.P. Trasatti***, P. Cristiani****, A. Schievano*
*e-Bio Center, via Celoria 2 - 20133 Milano (Italy)
** Sezione Materiale per Applicazioni Meccaniche, Dipartimento di Meccanica - Politecnico di Milano, via La Masa 1 - 20156 Milano, (Italy) ***Department of Environmental Science and Policy, via Celoria 2 - 20133 Milano (Italy)
**** RSE – Ricerca sul Sistema Energetico S.p.A., via Rubattino, 54, 20100 Milano, (Italy)
Abstract - Novel solutions for cylindrical Microbial Fuel Cells
(MFCs) design are hereby proposed, starting from a ligno- cellulosic material: Giant Cane. Giant Cane is cylindrical, porous and can be used (as it is) as separator or (pyrolized) as cathode in low-cost MFCs architectures.
First, Giant Cane was used as tubular separator for MFC modules. This system yielded 30-40 mWm-2, relatively low compared to state-of-the-art. However, the generated electric field was enough to sustain electro-osmotic drag. Over 70 days of operation, deposition phenomena of valuable elements (Ca, Mg, Mn, K and others) were observed.
Secondly, pyrolized Giant Cane was set as the cathode. The as- obtained MFC, equipped with the pyrolized cathode, underwent remarkable deposition phenomena of micro and macronutrients.
By these solutions, the MFC modules are almost completely built by biogenic/low-cost materials. At the end of MFCs life cycle, MFCs impregnated by micro and macronutrients, can be reused as bio-fertilizers in agriculture.
Index Terms – Bio-fertilizers, ligno-cellulosic biomass,
microbial fuel cells, nutrients recovery.
I. NOMENCLATURE
GC: Giant Cane
MFC: Microbial Fuel Cell MPL: Microporous Layer OCP: Open Circuit Potential ORR: Oxygen Reduction Reaction
II. INTRODUCTION
Research in the field of MFCs has been tremendously expanding over the last decades, due to their appealing ability to treat different kind of wastewater, producing electricity through bioelectrochemical reactions [1]. However, materials costs of electrodes, architecture and membranes have been severely affecting the full-scale applications of this
biotechnology. Costs and architecture should be strongly optimized. In order to eliminate expensive commercial membranes, some researchers recently introduced cylindrical separators made of ‘terracotta’ [2]. Others developed similar systems by means of natural rubber [3] or earthen pot [4]. These low cost MFCs showed performance comparable to many sophisticated systems employing expensive membranes.
On the side of the electrodes’ costs, the hindered kinetics for ORR is a well-known and discussed topic in the fuel cells and MFCs field. Efforts towards the possibility of reducing costs of catalysts for ORR represent an evergreen scientific focus [5].
A ligno-cellulosic biomass, Giant Cane (Arundo Donax L.), was selected in this work as the porous matrix to be used as a separator or (if pyrolized) as a cathode in MFCs architectures. The aim of this work is to investigate Giant Cane (as it is) as separator and (pyrolized) as the cathode in cylindrical MFCs. To date, this concept has never been presented in literature. An explorative experiment to test the properties and performance of cylindrical air-cathode MFCs based on this ligno-cellulosic material is here presented.
III. MATERIALSANDMETHODS
A. MFCs equipped with Giant Cane-based separator and a standard cathode.
Fig. 1 (GC-A) shows a schematic of the first experimental setup, GC-A. A carbon cloth anode was fixed around the external face of the Giant Cane cylinder, set as the separator. A carbon cloth cathode (added with an activated carbon MPL) was positioned in the inner part of the cane.
B. MFCs without separator and equipped with pyrolysed Giant Cane as cathode
Copyright © 2017 setup, GC-B. A carbon cloth anode was fixed around the
external face of the Giant Cane cylinder. A 900°C pyrolized Giant Cane was set as the cathode, wrapped by some felt to avoid the short circuit.
Fig. 1. Schematic of GC-A and GC-B experimental setup.
C. MFCs operation
GC-A and GC-B were positioned in glass jars, immersed in swine manure, run in batch mode at (25 ± 1) °C and cyclically fed with sodium acetate. Cell potential difference was recorded across external loads of 100 Ω by a data logger.
IV. RESULTSANDDISCUSSION
A. Power production and deposition phenomena
Fig. 2. Power density curves.
Under 3 g l-1 sodium acetate feeding and 100 Ω external load, GC-A and GC-B yielded 40 and 20 mW m-2, respectively, relatively low if compared to state-of-the-art MFCs, oriented to electricity harvesting [6]. However, the generated electric field was enough to sustain electro-osmotic ions mobility and to establish high pH conditions (pH 11-12) at the cathode. The generated potential difference induces ion movement within the reactor. Cations in the anolyte are attracted to the cathode. Once they approach the vicinity of the cathode, increased pH, due to ORR occurring, is known to favor the precipitation of a variety of salts. For instance, the solubility of many carbonates (like MgCO3 and CaCO3) decreases as the pH increases.
Over 70 days of operation, electro-migration and deposition phenomena of valuable elements (Na, Ca, Mg, Mn, K, etc.) were observed, both inside the separator (in the case of GC-A) and on the cathode (both in GC-A and GC-B).
Simultaneously, partial biodegradation of the ligno-cellulosic biomass, drove partial release of organic carbon, nitrogen, phosphorous and other elements in the anodic chamber of GC- A. The biodegradation phenomenon deserves to be carefully considered, when the aim of MFCs is wastewater treatment together with nutrients recovery.
V. CONCLUSION
By the proposed solutions, the MFC modules are almost completely built by biogenic/low-cost materials. Both the configurations demonstrated good conductivity, allowing the MFCs to operate with a relative low internal resistance. These results address towards the possibility of using cylindrical- shaped biomass as separators and/or cathode to fabricate low- tech MFC modules. At the end of their life, resulting enriched by valuable macro and micronutrients, such MFCs could be completely re-used as bio-fertilizers to agricultural production.
ACKNOWLEDGMENT
This work was financed by the SIR 2014 Grant (PROJECT RBSI14JKU3, BiofuelcellAPP), Italian Ministry of University and Research (MIUR) and by the Research Fund for the Italian Electrical System in compliance with the Decree of March, 19th 2009.
REFERENCES
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December 12-15, 2017, Naples, Italy