Study on Rapid Start-Up and Stable Nitrogen Removal Efficiency of Carrier Enhanced Continuous Flow Pd/A Granular Sludge System

Abstract

Anaerobic ammonia oxidation (anammox) has attracted much attention around the world, but the problems such as slow start-up and unstable operation remained unsolved. To address these issues and evaluate the carrier’s efficiency in improving the start-up and stable denitrification of the partial denitrification/anammox (PD/A) process under low nitrogen loading rate (NLR) (0.11-0.19 kg/(m3·d)). Two identically continuous flow carrier-based PD/A nitrogen removal system was constructed (self-immobilized granular sludge reactor(R1) and carrier based granular sludge reactor (R2)). The results revealed that the carrier facilitated a faster start-up of the PD/A process. Higher removal efficiencies of NH4+-N (90.95%) and TN (72.02%) were acheived in R2 than that in R1, with a start-up period 14 days shorter compared to R1. The settleability and structural stability of the carrier granular sludge were also superior to the self-immobilized granular sludge. The VSS/SS ratio of R2 (45.71%) was higher than R1 (25.56%), as was the PN/PS ratio (R2: 3.11, R1: 2.17). Furthermore, the abundance of the Anammox bacteria Candidatus_Kuenenia, a dominant bacterium involved in the PD/A process, was twice as high in R2 compared to R1. The hydrophilic porous biological carrier not only expedited the start-up period of the PD/A system in the USB reactor but also enhanced the interception and enrichment of effective functional microorganisms for stable anammox-driven nitrogen removal. Overall, this study highlighted the potential of hydrophilic porous biological carrier to improve the start-up efficiency and stability of anaerobic ammonia oxidation processes.

Keywords: granular sludge, partial denitrification(PD), anaerobic ammonia oxidation(anammox), biological carrier, Microbial community