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°C) and mainstream (municipal wastewater at 16.5°C), so that the anammox biomass activity and biomass growth could benefit from sidestream conditions. Real sidestream wastewater (biogas plant effluent) (≈1000 mg NH+ 4-N L−1) and synthetic mainstream (municipal wastewater-like source) (≈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 ≈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).