Role of soluble microbial product as an intermediate electron station linking C/N and nitrogen removal performance in sequencing batch reactor

Abstract

The C/N ratio in wastewater differs in place and time and affects the nitrogen removal performance of wastewater treatment. However, studies have focused only on the direct relationship between C/N and nitrogen removal efficiency but disregarded the significant role of soluble microbial products (SMPs) as an intermediate electron station. In this work, the contribution of SMPs to TN removal for treating wastewater with different C/N in a sequencing batch reactor (SBR) was investigated to extend relevance from C/N-TN removal to C/N-SMP-TN removal. TN removal efficiency was improved by increasing the influent C/N. The relative contribution of SMPs increased from 15% (C/N = 2) to 54% (C/N = 8), including 25.5% via utilization-associated product (UAP)-dependent denitrification and 28.5% via biomass-associated product (BAP)-dependent denitrification. The direct contribution of influent organic substrates dramatically decreased from 85.1% to 46%. In addition, providing an anoxic phase effectively enhanced BAP-dependent denitrification and achieved an increment of the SMP absolute contribution from 20.3% to 43% at C/N = 8 with 6.7 mg/L of TN additionally removed. This work clarified the significant contribution of SMPs to the nitrogen removal process, particularly in treating wastewater with high C/N. It also presented a new strategy for improving nitrogen removal performance via SMP reclamation.

Keywords: C/N; Denitrification; Nitrogen removal; Sequencing batch reactor; Soluble microbial products.