Effects of the Food-to-Microorganism (F/M) Ratio on N 2 O Emissions in Aerobic Granular Sludge Sequencing Batch Airlift Reactors

摘要

The present study investigated the effect of the food-to-microorganism (F/M) ratio on nitrous oxide (N 2 O) emissions in aerobic granular sludge sequencing batch airlift reactors. Three identical sequencing batch airlift reactors were fed with sodium acetate-based wastewater at different chemical oxygen demand (COD) concentrations, resulting in F/M ratios from 0.2 to 0.67 g COD/g SS. The results indicated that N 2 O emissions increased with an increase of the F/M ratio. N 2 O emissions at the high F/M ratio of 0.67 g COD/g SS were the highest (4.4 ± 0.94 mg/d). The main source of the high N 2 O emissions at the F/M ratio of 0.67 g COD/g SS was nitrifier denitrification, rather than heterotrophic denitrification, confirmed by the qPCR (quantitative real-time PCR) results. The heterotrophic denitrification was destroyed by the DO (dissolved oxygen) diffusing into the sludge particles with porous structures. This study offers theoretical support to study the N 2 O emissions in aerobic granular sludge, and can provide guidance for conducting risk assessment and enhancing our ability to predict N 2 O production in aerobic granular sludge at different F/M ratios.