Nitrogen removal and microbial community for the treatment of rural domestic sewage with low C/N ratio by A/O biofilter with Arundo donax as carbon source and filter media

Nitrogen removal from the rural domestic sewage with low pollutant concentration and low chemical oxygen demand (COD) to total nitrogen (TN) ratio (C/N) by biological process is quite difficult. Raw broken Arundo donax (A. donax) pieces were supplied as anoxic column filter media and carbon source in the anoxic/oxic biofilter (hereinafter referred to as A.-A/O-BF) for the nitrogen removal from rural domestic sewage, while gravel was served as the anoxic column filter media in the control A/O biofilter (hereinafter referred to as G-A/O-BF). Under the condition of 3.34 m/d (anoxic column) and 1.35 m/d (oxic column) filtration rate, 4:1 air/water ratio (oxic column) and 150 % nitrate recycling ratio, the average NH4+-N and TN removal efficiency of A.-A/O-BF were 99.0 % and 68.8 %, which were much higher than those (91.4 % and 39.8 %) of G-A/O-BF. The class Nitrospira affiliated with the phylum Nitrospirae were the most widely distributed nitrifying bacteria in the oxic column of A.-A/O-BF, which rarely existed in the oxic column of G-A/O-BF. Dechloromonas and Chlorobium genera were the main denitrificans in the anoxic column of A.-A/O-BF, while SM1A02 and Denitratisoma were dominant in the anoxic column of G-A/O-BF. The abundance of the main nitrification functional genes (amoA and Nitrospira 16S rDNA) in the oxic column of A.-A/O-BF was two orders of magnitude higher than that of G-A/O-BF, and the denitrification functional genes (narG, nosZ, nirS, and nirK) and anaerobic ammonium oxidation functional gene (Anammox) in the anoxic column of A.-A/O-BF were also remarkably higher than those of G-A/O-BF.