Short-term effects of temperature and COD in a microbial fuel cell

In this work, chemical oxygen demand (COD) and temperature stress-tests on a microbial fuel cell (MFC) were studied. Regarding the temperature stress-test, its value was cyclically modified between 20 and 40 degrees C with stepwise increments of 5 degrees C. The main result was an exponentially increase in the current intensity generated. In these tests, no hysteresis was observed, indicating that the temperature stress-test did not modify the behaviour of the MFC used in this work. To study the response of the system under COD stress conditions, the influent COD concentration was stepwise modified from the steady-state value, 100 mg COD L-1, to 3000 mg COD L-1 and later was reduced stepwise again to 100 mg COD L-1. In these test, it was observed that the higher the COD concentration, the higher the intensity generated. The electricity yield was an almost constant value of 6.7 x 10(-6) A mg(-1) COD removed per hour. In these tests, hysteresis was observed for the reverse scan, and a hysteresis loop was traced. To study how long the hysteresis lasts, several stress-tests were carried out during one week, and it was observed that the hysteresis was maintained for only 2 days. After that, the system recovered the initial behaviour. (C) 2012 Elsevier Ltd. All rights reserved.