Achievement and microbial profiles of non-aerated partial nitrification in photo sequencing batch and continuous flow reactors

Nitrite accumulation could be achieved in algal-bacterial consortia without energy-intensive aeration, which could be a sustainable alternative for wastewater treatment. However, few studies focused on the achievement of partial nitrification in different non-aerated algal-bacterial systems and the related microbial mechanisms are still unclear. Here two different algal-bacterial systems (photo-sequencing batch reactor (PSBR) and up-flow sludge blanket bioreactor (PUSB)) were operated for anaerobic effluent treatment and the non-aerated partial nitrification was evaluated. Results showed that the nitrite accumulation rates in the PSBR and PUSB were 92.70 +/- 7.81 % and 81.44 +/- 11.28 %, respectively, which was constant with microbial activities. Denser algal-bacterial granules were observed in the PSBR, whereas looser algal-bacterial flocs were in the PUSB. Phormidium and Leptolyngbya (i.e., two filamentous cyanobacteria) were enriched in the PSBR and PUSB, respectively, and the higher enrichment of Nitrosomonas and complete inhibition of Nitrospira contributed to better partial nitrification of PSBR. The PUSB had more intensive interspecific interactions and more cooperative behavior in microbial network. Metagenomic analysis revealed that partial denitrification might partially contribute to the nitrite accumulation in the PUSB owing to higher nitrate reductase gene expressions. Overall, this study advances our understandings of the partial nitrification process and nitrite accumulation by algal-bacterial consortia.

Automated summary

Nitrite accumulation in algal-bacterial consortia without aeration was evaluated in this study. Two different algal-bacterial systems (PSBR and PUSB) were operated and non-aerated partial nitrification was observed. Higher nitrite accumulation was achieved in PSBR due to enrichment of Phormidium and Leptolyngbya and inhibition of Nitrospira. PUSB showed more intensive interspecific interactions and potential contribution of partial denitrification to nitrite accumulation. This study advances our understanding of the partial nitrification process and nitrite accumulation by algal-bacterial consortia.