Nitrite effect on the phosphorus uptake activity of phosphate accumulating organisms (PAOs) in pilot-scale SBR and MBR reactors

Gürkan Sin,Peter A Vanrolleghem,Kwinten Niville,Giulia Bachis,Stijn Van Hulle,Ingmar Nopens,Tao Jiang

doi:10.4314/wsa.v34i2.183646

Abstract

Batch tests were performed to investigate the nitrite effect on the P-uptake of biomass grown in pilot-scale SBR and MBR systems. The results showed that the nitrite has an inhibitory effect on the aerobic P-uptake of the SBR and the MBR biomasses. The degree of inhibition was observed to be 65 % and 37 % at 10 mg NO2-N/l for the SBR and the MBR respectively. Both biomasses were found capable of using nitrite as electron acceptor as effectively as nitrate. Moreover, for the SBR biomass the anoxic P-uptake rate using nitrite was found even higher (60%) than the P-uptake rate with nitrate. From a modelling point of view, the current models require appropriate extensions to describe these various effects of nitrite. Hence, an extension of the ASM2d model has been provided. Prevention of nitrite build-up in full-scale EBPRs will eliminate the nitrite inhibition problem. Alternatively one can adopt a proactive approach in which the aerobic P-uptake phase is replaced with an anoxic P-uptake phase using only nitrite as electron acceptor. Such an approach offers considerable cost savings and enhanced nitrogen and phosphorus removal. This, however, requires further research for experimental validation and testing.

Highlights

Microbiological investigation of the nitrite effect with a variety of physiological types of bacteria has shown that nitrite interferes with energy generation and growth mechanisms (Yarbrough et al, 1980; Rake and Eagon, 1980)
The nitrite effect on the aerobic and anoxic P-uptake activities of phosphorus accumulating organisms (PAOs) grown in an sequencing batch reactor (SBR) and an membrane bioreactor (MBR) system fed with the same synthetic wastewater was investigated experimentally, using batch phosphate uptake tests
The inhibitory effect was more pronounced on the SBR biomass than the MBR biomass, where the respective degree of inhibition for each biomass was 0.65 and 0.37 at 10 mg NO2-N/l

Summary

Introduction

Microbiological investigation of the nitrite effect with a variety of physiological types of bacteria (from aerobes to facultative anaerobes) has shown that nitrite interferes with energy generation (e.g. by inhibiting oxygen uptake, oxidative phosphorylation or proton-dependent active transport of substrate) and growth mechanisms (Yarbrough et al, 1980; Rake and Eagon, 1980). Nitrite has been experimentally observed to inhibit the activity of ordinary aerobic heterotrophic organisms (Musvoto et al, 1999). Nitrite was hypothesised to cause proliferation of filamentous bulking in activated sludge systems due to its interference with the aerobic respiratory mechanism (Casey et al, 1999). Several studies with phosphorus accumulating organisms (PAOs) have confirmed that elevated concentrations of nitrite negatively affect phosphorus uptake activities of PAOs under both aerobic and anoxic conditions (Meinhold et al, 1999; Saito et al, 2004). Note that denitrifying PAOs were shown to be able to utilise nitrite as an electron acceptor without any adverse affect within a certain concentration range

Methods

Results

Discussion

Conclusion