To evaluate the sludge reduction of three metabolic uncouplers (3,3',4',5-tetrachlorosalicylanilide (TCS), 2,4-dichlorophenol (DCP), and tetrakis (hydroxymethyl) phosphonium sulfate (THPS)), we conducted continuous experiments on laboratory-scale anaerobic-anoxic-oxic processes. The three metabolic uncouplers were separately added in each oxic tank of the three systems, and a system without uncoupler addition was used as control. During the 85-day operation, sludge production and observed growth yields decreased to 38.6% and 16.98%, 43.4% and 17.55%, and 39.3% and 17.04% by the addition of TCS, DCP, and THPS, respectively. The addition of metabolic uncouplers slightly reduced the wastewater treatment efficiencies of the system (about 1.1-8.7%) and increased sludge SVIs (about 69.9-80.6%). Meanwhile, the differences among three metabolic uncouplers were little. Besides metabolic uncoupling and maintenance metabolism, which exist in the TCS-and DCP-added systems, lysis-cryptic growth also exists in the THPS-added system. (C) 2016 Elsevier Ltd. All rights reserved.