Effect of Temperature on Nitrogen Removal Performance and the Extracellular Polymeric Substance (EPS) in a Sequencing Batch Reactor (SBR)

Abstract

In this paper, the long-term effects of temperature on the nitrogen removal performance and the extracellular polymeric substance (EPS) in a sequencing batch reactor (SBR) treating synthetic wastewater was investigated under three temperature conditions (15℃, 25℃, 35℃). The results showed that high temperatures (35℃) could promote the establishment of short-cut nitrification processes and improve nitrogen removal performance greatly. Temperature had a significant impact on the EPS and its composition. With an increased temperature, the EPS and tightly bound EPS (TB-EPS) content decreased, while, loosely bound EPS (LB-EPS) increased slowly. TB-EPS became dominant in the EPS (the percentage of TB-EPS/EPS was 69.0%-79.5%), however, the ratio of TB-EPS/LB-EPS decreased from 3.8 (15℃) to 3.6 (25℃), and then to 2.2 (35℃) with a gradual increase in temperature. Moreover, protein (PN) and DNA in the EPS, TB-EPS, and LB-EPS decreased with an increasing temperature. Carbohydrates (PS) in the EPS and LB-EPS increased as temperature increased, nevertheless, PS in TB-EPS decreased. Furthermore, 25℃ was identified as the breaking-point temperature in the variation of PN, DNA and PS concentrations. At 15℃ and 25℃, PN was the main component in TB-EPS and LB-EPS. PS has the second highest concentration and DNA the least. However, PS were the dominant component at 35℃, with PN having the second highest concentration, and DNA having a subtle concentration. Moreover, at 15℃ and 25℃, the EPS content increased in the nitrification process and reduced in the denitrification process.