The simultaneous partial nitrification and anammox (PN/A) granular sludge process in a plug-flow reactor has been difficult to achieve. This study provides a novel way to enhance granulation using biofilm detachment. In a plug-flow reactor, a fixed carrier was added to the activated sludge, and a PN/A biofilm gradually formed during the operation. Mature biofilm detachment appeared and caused the emergence of micro-granule. Then the fixed carriers were removed from the reactor, but the nitrogen removal rate (NRR) of the reactor was barely affected. This result suggests granular sludge is a feasible replacement for biofilm. Moreover, the particle size of the granule increased from 212 to 425 μm, and the NRR was 1.63 kg N/(m3·d), with a maximum nitrogen removal efficiency of 86.5%. Overall, this study implies that it is feasible to maintain granular sludge in a plug-flow PN/A reactor, and biofilm detachment significantly favors the granulation process.
Keywords: Granulation; Granule enlargement; Partial nitrification and anammox; Plug-flow reactor.
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