Development and long-term operation of aerobic granular system for simultaneous removal of COD, nitrogen, and phosphorous in a conical SBR

Abstract

This study evaluates the performance of a simple sequencing batch reactor (SBR) with conical geometric configuration in terms of aerobic granulation and simultaneous removal of COD, nitrogen, and phosphorous from synthetic wastewater. The reactor was operated for 328 days in 3 different phases. Stable granules measuring around 0.9±0.3 mm with good settling properties were formed in phase III of operation. Optimum removals of COD (90%), NH4+-N (91%), total nitrogen (87%), and PO43--P (83%) were achieved in phase III, while the influent concentrations were COD (640±32 mg/L), NH4+-N (53±2.5 mg/L), and PO43--P (9±0.6 mg/L). Mixed liquor suspended solids increased from 0.26 g/L to 2.3 g/L while sludge volume index (SVI30) decreased from 380 mL/g to 65 mL/g during start-up to end of the study, respectively. The conical geometry induces an effective velocity gradient along with aeration in the reactor for better flocculation of biomass which has a good impact on the formation of stable and resistant aerobic granules. This system in conical SBR is advantageous as it attains simultaneous nutrient removal (CNP) with effective biomass retention without automatic process control. This treatment system has the potential to employ in low volume wastewater treatment in many decentralized applications.