Effect of HRT and BDPs types on nitrogen removal and microbial community of solid carbon source SND process treating low carbon/nitrogen domestic wastewater

A novel simultaneous nitrification and denitrification (SND) process using biodegradable polymers (BDPs) as the biofilm carrier and carbon source was developed to remove nitrogen from low-carbon sewage. The effects of BDPs types and hydraulic retention time (HRT) on nitrogen removal and microbial community composition were investigated. The results suggested that HRT parameters were tested in a range from 40h to 3h, and nitrogen removal performance was significantly worse with short HRT (13h to 3h). The NH4+-N and total nitrogen (TN) removal rates of the polycaprolactone (PCL) reactor reached to 98.40 % and 89.14 % at the optimal HRT (13h), respectively, and polybutylene succinate (PBS) reactor reached to 85.73 % and 81.64 %, respectively. When HRT was decreased from 13h to 3h, the NH4-N removal rate of the PCL and PBS reactors were reduced to the lowest values of 55.43 % and 33.47 %, and the removal rate of TN also reduced to 55.53 % and 44.88 %. According to Illumina MiSeq sequencing and correlation analyses, the genera Methyloversatilis, Bdellovibrio, and Zoogloea were significantly, positively correlated with nitrogen removal rate and short HRT, and short HRT impacted TN removal through increasing the abundance of these genera. LEfSe analysis revealed that the differences observed between PCL and PBS reactors were dependent on differences in Methyloversatilis, ultimately resulting in differences in microbial communities related to nitrogen removal. KEGG analysis suggested that nitrification-related functional genes (amoA, amoB, amoC, and hao) had the greatest abundance in the 13h HRT condition, and denitrification-related functional genes (napA, napB, nasA, nirS, and nosZ) were generally more abundant in the PBS system than the PCL system.