A pilot-scale (300 L) evaluation of waste-activated sludge digestion by a cyclical aerobic–anoxic mode of operation was undertaken at ambient liquid temperatures (14–17 °C). Three experimental runs were conducted over a 2-year period. The first run compared the aerobic–anoxic process to a conventional, continuously aerated, digestion process. During the second run, the aerobic–anoxic digester was compared to a lime-supplemented conventional aerobic process. The third run compared two aerobic–anoxic digester units, operating at reduced (50 and 25% of normal) aeration rates during the aerobic period. In addition, basic data from batch tests are outlined and discussed. Results from the various experimental runs indicated numerous potential advantages for the aerobic–anoxic mode of digester operation. The main advantage was that turning the air on and off resulted in volatile solids reduction efficiencies similar to that in the continuously aerated systems. In addition to the potential for significant savings in aeration costs, another benefit of the intermittent aeration mode of operation involved improved supernatant quality of the final, settled effluent.Key words: aerobic digestion, anoxic, intermittent aeration, lime, pilot-scale, Redox potential, sludge, solids reduction.