The influence of dissolved oxygen on partial nitritation/anammox performance and microbial community of the 200,000 m3/d activated sludge process at the Changi water reclamation plant (2011 to 2016)

Abstract

Mainstream partial nitritation/anammox (PN/A), coupled with excess biological phosphorus removal, in a 200,000 m/d step-feed activated sludge process (Train 2) in the Changi Water Reclamation Plant (WRP), Singapore, has been studied and reported. This paper presents an overview of process performance and the microbial community during the period from 2011 to 2016. The site data showed that, along with the reduction of dissolved oxygen (DO) from 1.7 to 1.0 mg O/L in the aeration zones, the concentrations of ammonium and nitrate of the final effluent increased, while nitrite decreased, resulting in an increase of 2.4 mg N/L of total inorganic nitrogen. Autotrophic nitrogen removal was higher than heterotrophic biological nitrogen removal under higher DO concentration conditions, but decreased under low DO operating condition. These macro-scale changes were caused by shifts of the nitrogen-converting microbial community. The ammonia oxidizing bacteria (AOB) population abundance was reduced by 30 times, while the nitrite oxidizing bacteria (NOB) population abundance and specific activity increased significantly with a shift of dominant genus from Nitrobacter to Nitrospira. The ratio of AOB and NOB specific activities were reduced from 12.8 to 1.6, and the ex situ nitrite accumulation ratio reduced from 76% to 29%. Changes in the microbial community and overall process performance illustrated that, compared to the excellent NOB suppression under high DO conditions, NOB were more active after the DO concentration reduction despite still being partly suppressed. This case study demonstrated, for the first time, the influence of DO reduction on the nitrogen conversion microbial community and PN/A process performance for a suspended growth system. Its relevance to biofilm and hybrid PN/A processes is also discussed.

Overcoming Nitrite Oxidizing Bacteria Adaptation through Alternating Sludge Treatment with Free Nitrous Acid and Free Ammonia

“…For example, the adaptation of NOB to low DO was reportedly due to NOB community shift from Nitrobacter to Nitrospira 24,25 . This problem could potentially be dealt with by using FA treatment, which was shown selecting Nitrobacter against Nitrospira.…”

Improving wastewater management using free nitrous acid (FNA)

“…NOB adaptation is likely a universal problem for NOB suppression approaches. NOB resistances to low DO, free ammonia (FA) inhibition, have also been reported (Cao et al 2018, Liu and Wang 2013, Turk and Mavinic 1989, Wong-Chong and Loehr 1978. It is likely that not all NOB strains are equally susceptible to the same suppression, and consequently, the less susceptible strains could outcompete others and emerge as the dominating NOB population, leading to suppression failure.…”

Membrane aerated biofilm reactors for mainstream partial nitritation/anammox: Experiences using real municipal wastewater

“…In single stage processes, effective oxygen limitation usually protects anaerobic ammonium oxidizing bacteria (AnAOB) from oxygen inhibition ( Lotti et al., 2015 ). Successful implementation of PN/A, however, requires the combination of aerobic and anaerobic ammonium oxidation, AOB activity mostly being the limiting factor when operating systems under oxygen limitation ( Cao et al., 2018 ; Lotti et al., 2015 ). Joss et al.…”