Effect of Salt on the Metabolism of 'Candidatus Accumulibacter' Clade I and II.

Zhongwei Wang,Pascal E Saikaly,Aislinn Dunne,Mark C M Van Loosdrecht

doi:10.3389/fmicb.2018.00479

Abstract

Saline wastewater is known to affect the performance of phosphate-accumulating organisms (PAOs) in enhanced biological phosphorus removal (EBPR) process. However, studies comparing the effect of salinity on different PAO clades are lacking. In this study, ‘Candidatus Accumulibacter phosphatis’ Clade I and II (hereafter referred to as PAOI and PAOII) were highly enriched (∼90% in relative abundance as determined by quantitative FISH) in the form of granules in two sequencing batch reactors. Anaerobic and aerobic batch experiments were conducted to evaluate the effect of salinity on the kinetics and stoichiometry of PAOI and PAOII. PAOI and PAOII communities showed different priority in using polyphosphate (poly-P) and glycogen to generate ATP in the anaerobic phase when exposed to salt, with PAOI depending more on intracellular poly-P degradation (e.g., the proportion of calculated ATP derived from poly-P increased by 5–6% at 0.256 mol/L NaCl or KCl) while PAOII on glycolysis of intracellularly stored glycogen (e.g., the proportion of calculated ATP derived from glycogen increased by 29–30% at 0.256 mol/L NaCl or KCl). In the aerobic phase, the loss of phosphate uptake capability was more pronounced in PAOII due to the higher energy cost to synthesize their larger glycogen pool compared to PAOI. For both PAOI and PAOII, aerobic conversion rates were more sensitive to salt than anaerobic conversion rates. Potassium (K+) and sodium (Na+) ions exhibited different effect regardless of the enriched PAO culture, suggesting that the composition of salt is an important factor to consider when studying the effect of salt on EBPR performance.

Highlights

Application of saline water as secondary quality water for non-potable use such as toilet flushing is a cost-effective and environmentally friendly alternative to mitigate shortage of fresh water in coastline cities and inland areas where brackish ground water is available (WSD, 2009; Leung et al, 2012; Wu et al, 2016)
SBR1 and SBR2 were fed with the same synthetic wastewater and operated under the same condition except they were inoculated with a different biomass (51% PAOI and 23% Glycogen accumulating organism (GAO) in SBR1 and 35% PAOII and 7% GAO in SBR2)
The results showed that PAOI and PAOII had intrinsic differences in response to salt inhibition

Summary

Introduction

Application of saline water (seawater or brackish) as secondary quality water for non-potable use such as toilet flushing is a cost-effective and environmentally friendly alternative to mitigate shortage of fresh water in coastline cities and inland areas where brackish ground water is available (WSD, 2009; Leung et al, 2012; Wu et al, 2016). This practice will introduce a significant amount of inorganic salt (>1% salinity, considering up to 30% of the fresh water use can be replaced by seawater with the typical salinity of 3.4%) to wastewater treatment plant (Lazarova et al, 2003). In Pronk et al (2014), all PAOs belonged to ‘Candidatus Accumulibacter phosphatis’ Clade I (hereafter PAOI), while in Wang et al (2017), the granules were enriched by ‘Candidatus Accumulibacter phosphatis’ Clade II (hereafter PAOII)

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