Single chamber air-cathode microbial fuel cells as biosensors for determination of biodegradable organics

Single chamber air cathode microbial fuel cells (MFCs) were investigated with sodium-acetate and peptone as test substrates to assess the potential for application as biosensor to determine the concentration of biodegradable organics in water/wastewater samples.

MFCs provided well-reproducible performance at high (> 2000 mg COD l^-1-Chemical Oxygen Demand) acetate concentration values. Current in the cells proved to be steady from 25 to 35 °C, significant decrease was, however, revealed in the current below 20 °C. Direct calculation of non-toxic biodegradable substrate concentration in water/wastewater from the current in MFCs is possible only in the non-saturated substrate concentration range due to the Monod-like dependence of the current. This range was determined by a fitted and verified Monod-based kinetic model. Half saturation constant (K_S) values were calculated at 30 °C applying different external resistance values (100 Ω, 600 Ω and 1000 Ω, respectively). In each case K_S remained below 10 mg COD l^-1.

Biosensors with this particular MFC design and operation are potentially applicable for detecting as low as 5 mg COD l^-1 readily biodegradable substrates, and measuring the concentration of these substances up to ~ 50-70 mg COD l^-1.