Performance and inhibition recovery of anammox reactors seeded with different types of sludge

In order to study the performance, inhibition and recovery processes of different types of anammox sludge, three up-flow anaerobic sludge blanket reactors were inoculated with flocculent sludge, granular sludge, and cultured inactive methanogenic granules. During stable period, with nitrogen loading rates of 0.9–1.1 kg/m³/d, the total nitrogen removal efficiencies of these reactors averaged at 86.5%, 90.8% and 93.5%, respectively. The kinetics study indicated that the reactor seeded with cultured inactive methanogenic granules possessed the highest nitrogen removal potential, followed by the granular anammox reactor and the flocculent anammox reactor. The study suggested that a concentration as high as 988.3 mg NH₄⁺-N/L and 484.4 mg NO₂⁻-N/L could totally inhibit granular anammox bacteria and result in a inhibition of 50% flocculent anammox activity. In addition, reactors seeded with flocculent sludge and anammox granules could be fully recovered by decreasing their influent substrate concentrations. However, the decrease of influent substrate concentration for the reactor with cultured inactive methanogenic granules could only restore about 75% of its bacterial activity. In this study, anammox bacteria purity was the major factor to evaluate the recovery ability in comparison with sludge type. Free ammonia was a more appropriate indicator for the anammox recovery process compared to free nitric acid.