Heloísa Fernandes

A decentralized full-scale sequencing batch reactor (SBR) system for treating wastewater was operated to assess their feasibility and the response of bacterial population dynamic and nutrient removal performance. The reactor was operated under low dissolved oxygen (DO) concentration (0.3–0.7 mgL⁻¹) and an average applied organic load of 0.5 g COD L⁻¹ d⁻¹. Removal efficiencies were higher than 70% for both soluble chemical oxygen demand and ammonium, with average effluent concentration of 51 ± 15 mg COD L⁻¹ and 16.0 mg NH₄⁺ L⁻¹. The mixed liquor volatile suspended solids/total suspended solids ratio was 0.9, and the average food/microorganism ratio was 0.3 g COD g VSS⁻¹ d⁻¹. The active biomass was composed of 94.9% heterotrophic and 5.1% autotrophic organisms. The most frequently identified were chemoorganoheterotrophic organisms affiliated with Bacteroidetes and Firmicutes, some of them with the capacity to denitrify and grow under low DO concentration. Temperature and sludge withdrawal were important factors in determining nitrification and phosphorus removal rates. The SBR was viable for domestic wastewater treatment and showed that the microbial community greatly influenced its performance. This work can also provide valuable insights into further applications in systems operated under low DO condition.

: This study describes the role of microorganisms in a full‐scale step‐feed sequencing batch reactor (SBR) system for urban wastewater treatment. Chemical profiles for three different cycle times were measured under low aeration conditions with a high carbon‐to‐nitrogen ratio. The applied organic load was above 1.0 g chemical oxygen demand (COD)/L·d. The removal efficiencies were higher than 81%, 93%, and 76% for soluble COD, N‐, and total Kjeldahl nitrogen, respectively. The ratio of volatile suspended solids (VSS) to total suspended solids was 78%, and the food‐to‐microorganism ratio was an average of 1.41 g COD/g VSS·d. The active biomass was comprised of 87.8% heterotrophic and 12.2% autotrophic organisms. Nitrifying organisms were found with a low amount of ammonia‐oxidizing bacteria (5%) and a much higher amount of nitrite‐oxidizing bacteria. Polyphosphate‐accumulating organisms (PAOs) were found at high amounts (25%) compared to glycogen‐accumulating organisms, even in a system with a high carbon to phosphorus ratio. The activity of denitrifying PAOs was 72%.