Recovery Effects of the Long-Term Frozen Anammox Sludge by Adjusting the Sludge Amount

Abstract

This paper proffers in-depth research on the anaerobic ammonia oxidation (Anammox) process, which attracts significant study due to its superior denitrification performance and operational benefits, mainly the avoidance of organic carbon sources or aeration. However, the process has instability factors as anaerobic ammonia oxidation bacteria (AAOB) prove sensitive to the environment, leading to potential disruptions during startup and operation. We used two MBR reactors to examine the recovery of Anammox sludge post extended freezing storage. In R1, the Anammox sludge was primarily recovered under conditions of low ammonia nitrogen concentration, through sludge discharge, after undergoing pre-treatment with low-substrate simulated wastewater before the lengthy freezing period. This led to TNRE and TNRR achieving 77% and 0.264 kg/(m3·d) respectively. R2 implemented a fast startup under low ammonia nitrogen concentration using Anammox sludge pre-treated with low-substrate simulated wastewater prior to the protracted freezing. When inhibited by high ammonia nitrogen concentration, recovery was predominantly via sludge addition, resulting in TNRE and TNRR of 86% and 0.618 kg/(m3·d) respectively. Through enzyme activity comparison and high-throughput sequencing, conclusions drawn show that in low ammonia nitrogen concentration the restoration of Anammox denitrification performance merely necessitates sludge discharge. In contrast, under high ammonia nitrogen concentration inhibition, Anammox sludge addition is requisite for fast denitrification performance restoration of the reactor.

Keywords: Denitrification, Recovery of Anammox, Inhibition by High Ammonia Nitrogen Concentration, start-up