Is Anoxic Operation Effective to Control Nitrate Build-Up and Sludge Loss for the Combined Partial Nitritation and Anammox (CPNA) Process?

Hongyan Wang,Yuansong Wei,Fumin Zuo,Dazhou Hu,Junya Zhang,Yuanyue Wang,Qianwen Sui

doi:10.3390/pr8091053

Abstract

There were three main issues of long start-up period, nitrate build-up and sludge loss during the operation of combined partial-nitritation anammox (CPNA). To fully start up the CPNA reactor, the fast achievement of partial-nitritation (PN) was the first step. Firstly, the PN process was successfully achieved within 22 days by 2 mg·L−1 hydroxylamine (NH2OH) addition and online intermittent aeration control at 0.2~0.3 mg·L−1 dissolved oxygen (DO). Then, a novel strategy of adding anoxic stirring phase between feeding and aeration period during CPNA operation was applied. It was shown effective to control nitrate build-up since the mole ratio of NO3−-N production and NH4+-N removed (MNRR) was mostly below 15%. Also, the procedure adjustment was proven useful to alleviate sludge loss by sustaining filamentous bacteria that could act as biomass framework and reduce nitrate substrate. The filamentous denitrifying bacteria could cause sludge bulking. The total nitrogen removal rate (TNRR) varied from 0.20 to 0.45 kg·m−3·d−1 during CPNA operation. In Stage III, after adding anoxic stirring phase, the abundance of nitrogen transformation functional microorganism’s nitrite oxidizing bacteria (NOB) was below 1.6%, which was one order of magnitude lower than Anammox and ammonia oxidizing bacteria (AOB).

Highlights

Since the first discovery of autotrophic anaerobic ammonium oxidation in early1990s [1], the research and application of anammox–based technologies have been widely reported [2].The single–stage anammox systems such as combined partial–nitritation anammox (CPNA) require much lower investment costs and skips of adjusting two reactors, making it the most frequently adopted anammox process
2 mg·L−1 NH2 OH on Day 6–10, the produced nitrate declined and more ammonia was oxidized to nitrite, indicating the inhibition of nitrite oxidizing bacteria (NOB) and promotion of ammonia oxidizing bacteria (AOB)
A start-up of PN, its transition to anammox and the stable operation of CPNA process were studied in an sequencing batch reactor (SBR)

Summary

Introduction

Since the first discovery of autotrophic anaerobic ammonium oxidation (anammox) in early. The single–stage anammox systems such as combined partial–nitritation anammox (CPNA) require much lower investment costs and skips of adjusting two reactors, making it the most frequently adopted anammox process. There were three main issues during the operation of CPNA, namely long start-up period, nitrate build–up and sludge loss. The slow-growth physiological characteristics of anammox bacteria makes the anammox inocula scarce, affecting the start-up duration. Lackner et al [1] investigated the practical engineering of Anammox installations and found that 50% of wastewater treatment plants (WWTPs) had experienced nitrate build-up which lasted up to several weeks. Some of them even confronted nitrate build-up repeatedly [3].

Methods

Results

Conclusion