Influence of sequencing batch reactor configuration on aerobic granules growth: Engineering and microbiological aspects

Abstract

This work evaluated the effect of two sequencing batch reactor (SBR) configurations used for aerobic granular sludge (AGS) cultivation (conventional and constant-volume) on the physical and microbiological characteristics of the granules, as well as on the systems’ performance. In the conventional SBR (R1), the filling, reaction, settling and decanting phases occurred sequentially, while, in the SBR operated at constant volume (R2), the filling and decanting phases occurred simultaneously followed by the reaction and settling phases. A faster formation of granules (about 30 days) with a larger size (∅ > 1 mm) and better settleability (SVI 30 ≈ 44.8 mL/g) was observed in R1. On the other hand, R2 presented a slower formation of granules (about 50 days) with a smaller diameter (∅ ≈ 0.8 mm) and a worse settleability (SVI 30 ≈ 70.7 mL/g). Although R2 presented smaller granules (and longer time for biomass formation), this configuration presented several advantages, such as better system stability during the entire operation (125 days), higher solids retention, and granules with better physical resistance. In terms of performance, both systems presented high values of COD (>90%), NH 4 + (>90%) and TN (>50%) removals after stabilization. However, the phosphorus removal in R2 was higher (≈50%) than in R1 (≈25%). The results justify the use of SBRs operated at constant volume in most full-scale AGS wastewater treatment plants, such as Nereda®. Therefore, the SBR configuration has a direct influence on the granule formation and its physical and microbiological characteristics as well as on the system performance in terms of efficiency and operational stability. • Conventional (R1) and constant-volume (R2) SBR configurations were tested on AGS. • In R1, the granulation was faster (30 d), and the granules were larger (1.2 mm). • In R2, the higher solids content (7 g VSS/L) favored a better P removal (48%). • R1 and R2 obtained similar N removals (55%), but the mechanisms were different. • The settling time decrease played a key role in the filaments removal only in R1.