Nitrogen oxidation consortia dynamics influence the performance of full-scale rotating biological contactors

D Freeman,Y Bajón Fernández,A Wilson,B.A Mckew,C Whitby,D.R Clark,B Jefferson,F Coulon,F Hassard

doi:10.1016/j.envint.2019.105354

Abstract

Ammonia oxidising microorganisms (AOM) play an important role in ammonia removal in wastewater treatment works (WWTW) including rotating biological contactors (RBCs). Environmental factors within RBCs are known to impact the performance of key AOM, such that only some operational RBCs have shown ability for elevated ammonia removal. In this work, long-term treatment performance of seven full-scale RBC systems along with the structure and abundance of the ammonia oxidising bacteria (AOB) and archaea (AOA) communities within microbial biofilms were examined. Long term data showed the dominance of AOB in most RBCs, although two RBCs had demonstrable shift toward an AOA dominated AOM community. Next Generation Sequencing of the 16S rRNA gene revealed diverse evolutionary ancestry of AOB from RBC biofilms while nitrite-oxidising bacteria (NOBs) were similar to reference databases. AOA were more abundant in the biofilms subject to lower organic loading and higher oxygen concentration found at the distal end of RBC systems. Modelling revealed a distinct nitrogen cycling community present within high performing RBCs, linked to efficient control of RBC process variables (retention time, organic loading and oxygen concentration). We present a novel template for enhancing the resilience of RBC systems through microbial community analysis which can guide future strategies for more effective ammonia removal. To best of the author’s knowledge, this is the first comparative study reporting the use of next generation sequencing data on microbial biofilms from RBCs to inform effluent quality of small WWTW.

Highlights

The removal of ammonia remains essential for purification of wastewater prior to discharge which is difficult to achieve at small wastewater treatment works (WWTWs) (e.g. < 2000–10,000 population equivalents) due to conflicting requirements for low energy and maintenance, land, capital expenditure and need for decentralised rural networks compared to conventional activated sludge processes (ASP) (Dutta et al, 2007; Hassard et al, 2015)
A decline in performance from a peak of 85.1% ammonia removal (WWTW 1) occurred at a temperature of 17.5 °C compared to a low of 68% ammonia removal (WWTW 2) which occurred at a temperature of 8 °C (Fig. 2A)
Effluent ammonia concentrations were relatively stable over the 7.5 years sampling with characteristic elevated ammonia levels in effluent which typically occurred in winter months

Summary

Introduction

The removal of ammonia remains essential for purification of wastewater prior to discharge which is difficult to achieve at small wastewater treatment works (WWTWs) (e.g. < 2000–10,000 population equivalents) due to conflicting requirements for low energy and maintenance, land, capital expenditure and need for decentralised rural networks compared to conventional activated sludge processes (ASP) (Dutta et al, 2007; Hassard et al, 2015). Ammonia-oxidizing bacteria (AOB) and ammonia oxidising archaea (AOA), which together are known as ammonia oxidising microorganisms (AOM) along with nitrite-oxidizing bacteria (NOB) are involved in nitrification processes (Bollmann et al, 2014; Daims et al, 2015). These chemolithoautotrophs obtain energy for growth by oxidizing either ammonia to nitrite (AOM) or nitrite to nitrate (NOM) using oxygen as a terminal electron acceptor.

Methods

Results

Conclusion