The feasibility of treating wastewater and excess sludge via simultaneous nitritation, anammox, denitrification and fermentation (SNADF) was investigated in three parallel sequencing batch reactors (SBRs). SBR2 and SBR3 received exogenous nitrification-denitrification sludge and thermal hydrolysis sludge, respectively. Nitrogen removal efficiencies of 92.8 ± 5.9%, 94.6 ± 4.1%, 93.4 ± 4.8% were achieved in SBR1, SBR2, and SBR3, respectively (influent ammonium: 56.0-74.0 mg N/L), with low observed sludge yield of 0.02-0.15, -0.06-0.11, -0.17-0.05 kg mixed liquor suspended solids (MLSS)/kg chemical oxygen demand (COD). Anammox bacterial abundances increased from 3.6 × 109 ± 2.8 × 108 to 8.1 × 109 ± 2.3 × 108, 1.5 × 1010 ± 1.1 × 108, and 1.4 × 1010 ± 2.9 × 108 copies/L in SBR1-SBR3, respectively. The abundances of Nitrosomonas, genes (amo, hao) for partial nitrification, and narGHI genes (nitrate → nitrite) in dominant partial denitrifying bacteria (Candidatus Competibacter) were higher in SBR2 and SBR3 than that in SBR1. These results suggested that adding excess sludge promoted sludge reduction, nitrite production and anammox bacterial enrichment. The SNADF system could treat excess sludge, meanwhile, achieve advanced nitrogen removal.
Keywords: Exogenous sludge; Mainstream anammox; Single reactor; Sludge reduction; Wastewater treatment.
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