This paper aims to investigate the enhancement effect of low intensity intermittent ultrasound irradiation on the efficiency of anaerobic ammonium oxidation (ANAMMOX) process at ambient temperature. With intermittently irradiated (ultrasound intensity of 0.7 w/cm(2), exposure time of 0.19 min), the reactor (R-U) had a nitrogen removal rate (NRR) of 5.49 kg TN/m(3)/d at 14.8 degrees C, while the NRR was 1.53 kg TN/m(3)/d in the control reactor (R-C). At the end of operation, the contents of polysaccharide, protein, TTC-dehydrogenase and VSS were 6.82 mg/mgVSS, 26.79 mg/mgVSS, 0.58 mg TF/L/H and 10.11 gVSS/L in R-U, higher than the levels in the R-C. These results demonstrated that it is possible to achieve stable and highly efficient operation in an ANAMMOX reactor at low ambient temperature by implementation of ultrasonication. (C) 2013 Elsevier Ltd. All rights reserved.