Effects of operational models (batch, continuous and CFID modes) on the performance of a single A₂O airlift bioreactor for treatment of milk processing wastewater

This study surveys the effect of different operational models, batch, continuous, and continuous feeding with intermittent discharge (CFID), on the performance of an air lift reactor (ALR) and a stirred tank reactor (STR) in terms of simultaneous removal of CNP from milk processing wastewater. The experimental data were recorded under similar operating conditions with HRT of 10 h, air flow rate of 2 l/min, and biomass concentration of 5–6 g/l. The obtained results indicated that the CFID mode was a promising regime which ensured the occurrence of anaerobic, anoxic, and aerobic conditions in the air lift bioreactor. This gave favorable conditions for simultaneous COD and nutrient removal processes in one compartment. At the optimum condition obtained, 170 mg/l (79%) of total nitrogen (TN) and 25 mg/l (63%) phosphorus (TP) were removed in the CFID-ALR, while, batch and continuous operational conditions did not create anaerobic and efficient anoxic zones in the air lift bioreactor. The ALR was more effective to remove nutrients when compared to the STR at all different operational modes studied. The microbial community at different experimental conditions was also investigated to detect Candidatus Accumulibactor as a common species of phosphate accumulating organism (PAOs) through PCR method. From the PCR results, Candidate Accumulibactor was detected in the CFID-ALR, underpinning the observed TP removal.