Experimental Investigation of Substrate Shock and Environmental Ammonium Concentration on the Stability of Ammonia-Oxidizing Bacteria (AOB)

Hareef Ahmed Keerio,Wookeun Bae

doi:10.3390/w12010223

Abstract

A wastewater treatment plant (WWTP) frequently encounters fluctuation in ammonium concentration or flow rate (Q), which may affect the stability of ammonium oxidizing bacteria (AOB). In this study, two continuous stirred tank reactors (CSTRs) were operated for 588 days and ammonium concentration was varied at various steady-state conditions. There was no inhibition observed in CSTR operation and AOB acclimated once at a certain ammonium concentration. Cells at an acclimated steady-state concentration (200 mgTAN/L from R(A) and 1000 mgTAN/L from R(B)) were extracted to perform a batch test at operating conditions, and self-inhibition behavior was observed in the batch reaction. In CSTR operation, the environmental ammonium concentration was varied and the specific oxygen uptake rate (SOUR) value was estimated from daily profile data and compared with batch reaction. In the CSTR operation as a substitute for self-inhibition, the SOUR was shifted towards the maximum specific oxygen uptake rate (SOURmax) and no self-inhibition was observed. For further justification of the CSTR’s stability, several total ammonium nitrogen (TAN) concentrations (range from ~−106 to ~+2550 mgTAN/L) were directly added to interrupt the stability of the process. As a substitute for any effect on the SOUR, the CSTRs were recovered back to the original stable steady-state conditions without varying the operational conditions.

Highlights

Ammonium oxidizing bacteria (AOB) is the most common species that relies on the ionic ammonium (AOB activate its ammonium transport mechanism) or free ammonia, which depends on the choice and accessibility of the substrate [1,2,3]
The specific oxygen uptake rate (SOUR) was estimated using daily profile data and the batch test was performed at an acclimated concentration (~200 mgTAN/L for R(A) and ~1000 mgTAN/L for R(B))
The self-inhibition model was fitted in batch test data and the Monod model was fitted in the SOUR estimated from daily profile data

Summary

Introduction

Ammonium oxidizing bacteria (AOB) is the most common species that relies on the ionic ammonium (AOB activate its ammonium transport mechanism) or free ammonia (passive diffusion), which depends on the choice and accessibility of the substrate [1,2,3]. ‘Inhibition’ is a degradation of a substrate that is slowed down by the substrate itself when environmental substrate concentration surpasses the maximum specific substrate utilization rate (q) [4]. [5] applied the critical substrate concentration to decide the stability of AOB. If substrate concentration changes from the critical substrate concentration rate AOB slows down its substrate degradation rate (self-inhibition) [6]. Incidental variations in the environmental substrate concentration affects specific substrate utilization rate (q) and the reactor regains the previous steady-state conditions [5,7]. Due to the self-inhibition behavior of AOB, several researchers [7,8,9,10] operated reactors at steady-state conditions utilizing various control tactics (substrate feedback control and dissolved oxygen (DO) control [10]

Methods

Results

Conclusion