Improvement of Anammox Particle Size Distribution in a Reactor Fed with Real Effluent Using Flow Rate as a Strategy for Loading Rate Increase

Abstract

In this study, anammox granulation was studied using the feed flow rate as a strategy to increase loading rate, without using effluent recirculation. A bench-scale upflow reactor with a volume of 1 L was inoculated with 300 mL of anammox sludge, coming from a pilot system previously in operation for 250 days. The reactor was fed with 200 mg N L⁻¹ of total nitrogen being 100 mg L⁻¹ of NH₄ ⁺-N coming from digestate from an upflow anaerobic sludge blanket bioreactor fed with swine manure and 100 mg L⁻¹ of NO₂ ^–N supplemented with NaNO₂ solution. The reactor was operated for 50 days, divided into two phases, adjusting the hydraulic retention time based on the feed flow rate (Qin), starting at 4.0 L d⁻¹, and nitrogen loading rate (NLR) of 0.8 kg N m^-3 d⁻¹. The NLR range was 0.8 to 1.6 g L⁻¹d⁻¹. The anammox process was established in 20 days, achieving 100% efficiency of N removal during the second phase of operation. The results of volatile suspended solids (VSS) obtained during the experimental period corroborate the improvement in particle size distribution inside the reactor. The VSS/TSS ratio increased from 67% to 80% after 50 days, reflecting an increase in average granule size from 0.30 to 1.4 mm during this period.