Surface modifications of anode materials are important for enhancing power generation of microbial fuel cell (MFC). Membrane free single-chamber air-cathode MFCs, MFC-A and MFC-N, were constructed using activated carbon fiber felt (ACF) anodes treated by nitric acid and ethylenediamine (EDA), respectively. Experimental results showed that the start-up time to achieve the maximum voltages for the MFC-A and MFC-N was shortened by 45% and 51%, respectively as compared to that for MFC-AT equipped with an unmodified anode. Moreover, the power output of MFCs with modified anodes was significantly improved. In comparison with MFC-AT which had a maximum power density of 1304 mW/m(2), the MFC-N achieved a maximum power density of 1641 mW/m(2). The nitric acid-treated anode in MFC-A increased the power density by 58% reaching 2066 mW/m(2). XPS analysis of the treated and untreated anode materials indicated that the power enhancement was attributable to the changes of surface functional groups. (C) 2010 Elsevier Ltd. All rights reserved.