Microbial response of nitrifying biofilms to cold-shock

Abstract

The purpose of this study is to investigate the effects of cold-shock events on attached growth nitrification kinetics and the nitrifying biofilm between the temperatures of 10 °C and 1 °C. A comparison between acclimatized moving bed biofilm reactors (MBBR) in-series system and a cold-shocked MBBR in-series system resulted in 17.28% lower removal rates of the cold-shocked system. Increases in biofilm thickness and decreases in density are observed in both the acclimatized and cold-shocked biofilms. The fraction of viable cells in the acclimatized biofilm is shown to increase at 1 °C, while the viability of embedded cells of the cold-shocked biofilm remains unchanged immediately following the cold-shock and with extended exposure time at 1 °C. β-Diversity analysis indicates a greater community shift in the acclimatized biofilm during acclimatization from 10 °C to 1 °C, while the cold-shocked system underwent a significant microbiome shift following during operation at 1 °C. Although the cold-shock affected the system's performance, the biofilm's characteristics, the viability of the embedded biomass and the microbiome, the cold-shocked system maintained significant nitrification kinetics during an extended operation at 1 °C following the shock event.