Simultaneous biological organic matter and nutrient removal in an anaerobic/anoxic/oxic (A2O) moving bed biofilm reactor (MBBR) integrated system

Abstract

In the present study, the performance of three moving bed biofilm reactors (MBBRs) has been evaluated in series with anaerobic/anoxic/oxic (A2O) units for simultaneous removal of organic matter and nutrients (nitrogen and phosphorous) from a synthetic wastewater with characteristics similar to those of a typical municipal wastewater. Response surface methodology based on central composite design was used to investigate the effects of nitrate recycle ratio, hydraulic retention time (HRT), and influent chemical oxygen demand (COD) on the organic and nutrient removal and optimization process. The optimized values of influent COD, HRT, and R were 462 mg/L, 10 h, and 3.52, respectively. The predicted and observed values at optimized conditions were 92.8% and 93 ± 1.3%, 84.3% and 84 ± 1.3%, 71.7% and 68 ± 1.6% for COD, TN, and TP removals and 100 and 97 ± 1.2 mL/g for sludge volume index, respectively. After that, the influent COD, TN, and TP were increased to 550, 48, and 12 mg/L, respectively, to partly simulate the organics and nutrient variations of real wastewater treatment plants. The COD, TN, and TP removals were 91 ± 1.3, 82 ± 1.1, and 71 ± 0.8%, respectively. The influent COD, TN, and TP were increased again to 650, 56, and 14 mg/L, respectively. After this phase, the COD, TN, and TP removals were 90 ± 0.8, 80 ± 1.2, and 70 ± 1.0%, respectively. Obtained results indicated the good stability of the optimized system and the ability of MBBRs to remain stable at influent organics and nutrient variations. The ratio of attached volatile solids to mixed liquor volatile suspended solids was 1.90 ± 0.10, 2.07 ± 0.09, and 2.25 ± 0.14 in phases 1, 2, and 3, respectively. These high ratios indicate that the microorganisms had favored the attached growth to the suspended growth within the whole operation time.