Carbon sources derived from corncobs enhanced nitrogen removal in SBBR treating low C/N domestic sewage

Abstract

Domestic sewage has the characteristics of low carbon to nitrogen ratio (C/N), so an external carbon source is required to increase the denitrification performance of the system. Agricultural waste carbon sources have attracted much attention due to their wide range of sources and low cost. Therefore, this study investigated the corncob pretreated with acid and alkali as the external carbon source. Then the effect on nitrogen removal was further determined by sequencing batch biofilm reactor (SBBR). The results showed that the alkali pre-treated corncob had a higher carbon release capacity; the COD cumulative release amount was 123.5 mg/g·L within 16 days. It had an excellent denitrification rate, with a total nitrogen removal rate of 90.1%. In addition, the denitrification rate of alkali pre-treated corncob (100 g) as a carbon source was equivalent to that of sodium acetate (influent C/N ratio: 15). At this time, the total nitrogen removal rate reached a maximum of more than 90%. Microbial community analysis discovered that microbial abundance and diversity increased after adding corncob carbon sources. Among them, the contents of Firmicutes, Macellibacteroides, and Hydrogenophaga were significantly increased, which played a decisive role in degrading cellulose and using cellulose as a carbon source for denitrification. Besides, denitrifying bacteria such as Proteobacteria, Thauera, and Gemmatimonas were also abundantly aggregated, indicating that the denitrification in SBBR was enhanced. These findings collectively suggest that alkali pre-treatment of corncob as a carbon source could effectively improve the denitrification performance of low C/N ratio wastewater.