Microbial fuel cells for direct electrical energy recovery from urban wastewaters

Abstract

Application of microbial fuel cells (MFCs) to wastewater treatment for direct recovery of electric energy appears to provide a potentially attractive alternative to traditional treatment processes, in an optic of costs reduction, and tapping of sustainable energy sources that characterizes current trends in technology. This work focuses on a laboratory-scale, air-cathode, and single-chamber MFC, with internal volume of 6.9 L, operating in batch mode. The MFC was fed with different types of substrates. This study evaluates the MFC behaviour, in terms of organic matter removal efficiency, which reached 86% (on average) with a hydraulic retention time of 150 hours. The MFC produced an average power density of 13.2 mW/m(3), with a Coulombic efficiency ranging from 0.8 to 1.9%. The amount of data collected allowed an accurate analysis of the repeatability of MFC electrochemical behaviour, with regards to both COD removal kinetics and electric energy production.

Figure 1

MFC prototype used in laboratory: (1) active section of the plant, where electrodes are situated; (2) sampling port; (3) discharge tap, equipped with thermostat; (4) recycle pump; (5) volumetric flow meter; (6) spectrophotometric probe; (7) ball valve for flux tuning.

Figure 2

Working principle of MFC prototype.

Figure 3

Electrodes polarization during treatment cycle 1. Filled points represent polarization curves, empty points the power curves.

Figure 4

Continuous monitoring of treatment cycle 1. Grey bars are placed in correspondence of polarization curve measurements.

Figure 5

Anodic biomass growing throughout three consecutive treatment cycles with SW2, without emptying the cell. Filled points represent polarization curves, empty points the power curves.