Long-term starvation and subsequent reactivation of a high-rate partial nitrification activated sludge pilot plant

The starvation process of a high-rate partial nitrification system during 30days and its controlled recovery were studied in an activated sludge pilot plant. Four ammonium-starved reactors under anoxic, aerobic and two different alternating aerobic/anoxic conditions were evaluated. The highest and the lowest decay rates of ammonia oxidizing bacteria (AOB) were obtained under full aerobic (0.24d -1) and full anoxic (0.11d -1) conditions, respectively. The evolution of biomass activity correlated well with the AOB quantification using FISH technique. AOB fractions lower than 1% were measured in the four reactors after 23days of starvation. The recovery of the system was achieved in only 5days using a nitrogen loading rate (NLR) control loop, obtaining the same conditions than before the long-term starvation period with a NLR of 1.2gNL -1d -1 and 98% of nitrite accumulation in the effluent. © 2011 Elsevier Ltd.