Electricity and catholyte production from ceramic MFCs treating urine

Abstract

The use of ceramics as low cost membrane materials for Microbial Fuel Cells (MFCs) has gained increasing interest, due to improved performance levels in terms of power and catholyte production. The catholyte production in ceramic MFCs can be attributed to a combination of water or hydrogen peroxide formation from the oxygen reduction reaction in the cathode, water diffusion and electroosmotic drag through the ion exchange membrane. This study aims to evaluate, for the first time, the effect of ceramic wall/membrane thickness, in terms of power, as well as catholyte production from MFCs using urine as a feedstock. Cylindrical MFCs were assembled with fine fire clay of different thicknesses (2.5, 5 and 10 mm) as structural and membrane materials. The power generated increased when the membrane thickness decreased, reaching 2.1 ± 0.19 mW per single MFC (2.5 mm), which was 50% higher than that from the MFCs with the thickest membrane (10 mm). The amount of catholyte collected also decreased with the wall thickness, whereas the pH increased. Evidence shows that the catholyte composition varies with the wall thickness of the ceramic membrane. The possibility of producing different quality of catholyte from urine opens a new field of study in water reuse and resource recovery for practical implementation.

Keywords: Catholyte production; Ceramic membrane; Electroosmotic drag; Microbial Fuel Cell (MFC); Urine.

Fig. 1

Photo of the MFC setup.

Fig. 2

ESEM images of the fine fire clay of 2.5 mm; (a) and (b) are from the internal area, whereas (c) and (d) are side views of the ceramic cylinder at different magnifications.

Fig. 3

Polarisation curves obtained after 4 weeks of operation: a) Power and b) cell voltage versus current generated in the 3 different types of MFCs: MFC 1 2.5 mm FFC ceramic membrane, MFC 2 5 mm FFC ceramic membrane and MFC 3 10 mm FFC ceramic membrane. Error bars indicate SEM with n = 3.

Fig. 4

Anode voltage a) and cathode voltage b) versus SHE reference electrode as a function of the current generated in the MFCs.

Fig. 5

Comparison of the catholyte volume generated in 7 days of operation for the different types of MFC and the catholyte generated at the OCV.

Fig. 6

Measurements of the chemical analysis for the catholyte collected from the MFCs with different thickness under load (100 Ω) and under open circuit (OCV), in comparison with those measured from the urine used as the feedstock: A) pH, B) conductivity, C) dry weight.