Evaluation of sludge discharge methodologies in aerobic granular sludge reactors

Abstract

We performed a comparison of different aerobic granular sludge (AGS) discharge methodologies in sequencing batch reactors (SBRs), evaluating the system efficiency, physical and microbiological characteristics of granules, and resource recovery of the discharged biomass. In R1, there was a selective discharge (30% top sludge and 70% bottom sludge, based on biomass weight) with SRT control (10–20 days). The same selective discharge was applied to R2, but with control of food to microorganisms (F/M) ratio (0.22–0.44 gCOD/gVSS·day). In R3, the discharge was conventional (similar to activated sludge reactors), i.e., mixed liquor during the aerobic period. Additionally, the best protocol of the lab-scale studies was used in a pilot-scale reactor (R4) treating municipal wastewater. R1 protocol was the best strategy for AGS formation, maintenance, and performance, achieving better removal efficiencies of COD (95%), total nitrogen (85%), and phosphorus (80%). Sludge discharge improved the system's performance and resource recovery, especially alginate-like exopolysaccharides (ALE).