To date, only a handful of studies have described application of organic materials as carriers (nuclei) in the aerobic granular sludge (AGS) system, compared to inorganic materials.

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In this study, we evaluated the relative abundance of nitrogen functional genes (amoA, nirK and nirS) involved in ammonia oxidation and denitrification bacteria in laboratory-scale bioretention columns in response to the environmental factors (e.g., moisture content, pH, soil organic matter, soil nitrogen) under different antecedent dry days (ADDs). We observed a decrease tendency of the relative abundance of ammonia-oxidizing bacteria at first and then increase when increasing ADDs from 1 to 22 day, while the relative abundance of denitrifying bacteria shown a downward trend. The abundance of bacteria genes amoA was positively associated with soil ammonia nitrogen concentration (r2 = 0.389, p < 0.05) and soil organic matter concentration (r2 = 0.334, p < 0.05), while the abundance of bacteria genes nirS was positively correlated with soil ammonia nitrogen (r2 = 0.730, p < 0.01), soil organic matter (r2 = 0.901, p < 0.01) and soil total nitrogen (r2 = 0.779, p < 0.01). Furthermore, Gene counts for bacteria genes nirS was correlated negatively with plant root length (r2 = 0.364, p < 0.05) and plant biomass (r2 = 0.381, p < 0.05). Taken together, these results suggest that both nitrification and denitrification can occur in bioretention system, which can be affected by environmental factors.