Starch/polylactic acid (SPLA9) was prepared and used as electron donor for biological nitrate removal. The denitrification performance and microbial diversity were investigated and compared with that of ethanol supported denitrification system. The results showed that the SPLA9 system had richer microbial diversity by analyzing Shannon's diversity index, but the ethanol system showed higher denitrification rate. The formation of NH3-N was observed during denitrification for both systems, but its concentration in the SPLA9 system was lower than that in the ethanol system. The quick release and accumulation of dissolved organic carbon (DOC) were observed in SPLA9 system during the start-up period. Fortunately it decreased to about 5 mg/L. Proteobacteria was the major phylum and Alicycliphilus and Thauera were the most abundant genera for both systems. Organisms from the genus Desulfovibrio were identified in both systems, which probably contributed to the dissimilatory nitrate reduction to ammonia (DNRA) reaction. (C) 2012 Elsevier Ltd. All rights reserved.