Development of a Photo-baffled Reactor for Microalgae-Nitrifying Bacteria Consortia: Achieving Long-term, Stable Partial Nitrification

The ammonia removal of microalgal-nitrifying bacteria consortia in a photo-baffled reactor from synthetic wastewater to concentrations of 150 mg-N·L-1 was investigated. The photo-baffled reactor had an ammonia removal efficiency of 66.7 ± 11.1% under a nitrogen loading rate of 0.083 ± 0.011 kg-N·m-3·day-1. Moreover, long-term, stable partial nitrification was achieved with nitrite concentration in the effluent of 60 ± 26 mg-N ·L-1. The low dissolved oxygen and the free ammonia concentration on day 200 of 10 to 16 mg-N·L-1 and on day 365 of 14 to 24 mg-N·L-1 in each column might have been inhibited by nitrite-oxidizing bacteria (NOB) activity. Moreover, the specific reactor configuration of the photo-baffled reactor created a competitive environment between Chlorella vulgaris and nitrifying bacteria. The microbial community structure of the retained sludge in the photo-baffled reactor indicated that the abundance of ammonia-oxidizing bacteria Nitrosomonas europaea was low at 2 and 3% upstream of the reactor, and increased downstream. In contrast, the detection rate of NOB was less than 0.05% in each column, and quantitative polymerase chain reaction analysis showed that the growth of NOB was inhibited. This microalgae-nitrifying bacteria consortia photo-baffled reactor has the potential to be a novel partial nitrification process for post-treatment using the anammox process.