A high concentration of NH(4) (+) in piggery wastewater is major problem in Taiwan. Therefore, in our study, we isolated native heterotrophic nitrifiers for piggery wastewater treatment. Heterotrophic nitrifier AS-1 was isolated and characterized from the activated sludge of a piggery wastewater system. Sets of triplicate crimp-sealed serum bottles were used to demonstrate the heterotrophic nitrifying capability of strain AS-1 in an incubator at 30 degrees C. All serum bottles contained 80 mL medium, and the remainder of the bottle headspace was filled with pure oxygen. The experimental results showed that 2.5 +/- 0.2 mmol L(-1) NH(4) (+) was removed by 58 hours, and, eventually, 1.5 +/- 0.5 mmol L(-1) N(2) and 0.2 +/- 0.0 mmol L(-1) N(2)O were produced. The removal rate of NH(4) (+) by the strain AS-1 was 1.75 mmol NH(4) (+) g cell(-1) h(-1). This strain was then identified as Pseudomonas alcaligenes (97% identity) by sequencing its 16S rDNA and comparing it with other microorganisms. Thus, strain AS-1 displays high promise for future application for in situ NH(4) (+) removal from piggery wastewater.