Mainstream-sidestream wastewater switching promotes anammox nitrogen removal rate in organic-rich, low-temperature streams

The main issues with mainstream anammox application are loss of bacterial activity by low temperatures and by a high organic content of wastewater. We demonstrate a novel switching method between sidestream and mainstream wastewater. The wastewater flow was switched between sidestream (reject water at >22 degrees C) and mainstream (municipal wastewater at 16.5 degrees C), so that the anammox biomass activity and biomass growth could benefit from sidestream conditions. Real sidestream wastewater (biogas plant effluent) (approximate to 1000 mg NH+ (4)-N L-1) and synthetic mainstream (municipal wastewater-like source) (approximate to 100 mg NH+ (4)-N) wastewater were used for 20 L biofilm reactor feeding. The highest total nitrogen removal rate (TNRR) of 527 g N m(-3) d(-1) (average TNRR 180 (+/- 140) g N m(-3) d(-1)) was achieved with sidestream wastewater at a low chemical oxygen demand (COD)/TN ratio of 1.1/1. For reactor feeding with mainstream, the highest TNRR achieved was 61 g N m(-3) d(-1). Average TNRR for mainstream of 20 (+/- 15) g N m(-3) d(-1) was low due to a higher COD/N ratio of 3.2/1. The highest TNRR in a batch test was achieved at the COD concentration of 480 mg L-1, reflecting a TNRR of approximate to 5 mg N g(-1) TSS h(-1). With a high COD concentration of 2600 mg L-1 (TOC/TN = 8/1), TNRR decreased similarly in both feeds to 1.6 mg N g(-1) TSS h(-1). The anammox microorganism's genus Candidatus Brocadia enrichment in deammonification biofilm reactor was higher in the mainstream operation (7.6% of all bacteria) than in sidestream operation period (<0.7% of all bacteria).

Automated summary

The research demonstrates a novel approach for wastewater treatment by switching between sidestream and mainstream wastewater, optimizing the activity and growth of anammox biomass. This method provides a new perspective for improving total nitrogen removal rate.