Abstract
The present study investigated the effect of the food-to-microorganism (F/M) ratio on nitrous oxide (N2O) 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 N2O emissions increased with an increase of the F/M ratio. N2O 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 N2O 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 N2O emissions in aerobic granular sludge, and can provide guidance for conducting risk assessment and enhancing our ability to predict N2O production in aerobic granular sludge at different F/M ratios.
Highlights
Aerobic granular sludge technology is a promising new environmental biotechnological process [1,2,3]
The hydraulic retention time (HRT) was 12 h, the air supply was provided by virtue of an aeration pump at the bottom of the reactor at an aeration rate of around 3 L/min during the aeration stage, and the dissolved oxygen (DO) concentration in the reactors was measured throughout the 6 h cycle
It was found that the F/M ratio had an important effect on the nitrous oxide (N2 O) emissions in aerobic granular sludge sequencing batch airlift reactors (SBARs)
Summary
Aerobic granular sludge technology is a promising new environmental biotechnological process [1,2,3]. Aerobic granular sludge technology is increasingly drawing the interest of researchers committed to biological wastewater treatment technology. It is generally accepted that the biological treatment process of wastewater occupies an important position among the main sources of nitrous oxide (N2 O) [4,5]. N2 O is one kind of greenhouse gas, and its half-life is as long as 114 years in the atmosphere. The global warming potential of N2 O is 310 times higher than for carbon dioxide, and the doubling volume of N2 O in the atmosphere will make the average global temperature rise by 0.4 ◦ C [6]. It is of great importance to study the mechanism of N2 O emissions in wastewater treatment processes
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