Low-dissolved-oxygen nitrification in tropical sewage: an investigation on potential, performance and functional microbial community

Abstract

Intensive aeration for nitrification is a major energy consumer in sewage treatment plants (STPs). Low-dissolved-oxygen (low-DO) nitrification has the potential to lower the aeration demand. However, the applicability of low-DO nitrification in the tropical climate is not well-understood. In this study, the potential of low-DO nitrification in tropical setting was first examined using batch kinetic experiments. Subsequently, the performance of low-DO nitrification was investigated in a laboratory-scale sequential batch reactor (SBR) for 42 days using real tropical sewage. The batch kinetic experiments showed that the seed sludge has a relatively high oxygen affinity. Thus, the rate of nitrification was not significantly reduced at low DO concentrations (0.5 mg/L). During the operation of the low-DO nitrification SBR, 90% of NH-N was removed. The active low-DO nitrification was mainly attributed to the limited biodegradable organics in the sewage. Fluorescence in-situ hybridisation and 16S rRNA amplicon sequencing revealed the nitrifiers were related to Nitrospira genus and Nitrosomonadaceae family. Phylogenetic analysis suggests 47% of the operational taxonomic units in Nitrospira genus are closely related to a comammox bacteria. This study has demonstrated active low-DO nitrification in tropical setting, which is a more sustainable process that could significantly reduce the energy footprint of STPs.

Kinetic characterization of a low-dissolved‑oxygen oxic-anoxic process treating low COD/N tropical wastewater revealed selection of nitrifiers with high substrate affinity

“…Our modeling study provided a kinetic data to support the high proportional abundance of Nitrospira and comammox commonly observed in low-DO reactors below 1 mg O2 L -1 treating low-strength tropical wastewater [9,20]. Through the proliferation of K-strategist nitrifiers under low-DO condition (< 1 mg O2 L -1 ), WWTPs treating low COD/N wastewater may successfully operate a low-DO nitrification process to encourage energy saving between 23% and 25% [8,14].…”

“…To improve the existing process, How et al [8] and Cao et al [9] showed that efficient low-DO nitrification below 1 mg L -1 was feasible for tropical wastewater by capitalizing on the warm wastewater temperature (30 ± 1ºC) to promote the growth of slow-growing…”

“…The warm wastewater temperature may accelerate the hydrolysis of particulate matter to provide slowly-biodegradable COD (sbCOD), which could enhance the NO 3 removal in a post-anoxic denitrification stage [11,13]. Combining the low-DO nitrification and the post-anoxic denitrification in a low-DO oxic-anoxic (low-DO OA) process successfully produced effluent with low NH 4 + -N and NO 3 --N [13], while reducing the aeration energy by 23% to 25% when compared with the conventional AO process [8,14].…”

Ammonia-Nitrogen Reduction in Low Strength Domestic Wastewater by Polyvinyl Alcohol (PVA) Gel Beads

“…When DO concentrations are high, it may lead to low denitrification rates due to the reduction of anoxic zones. How et al (2018) reported low COD concentration in sewage may have contributed to active nitrification in low DO conditions by minimizing oxygen competition between heterotrophs and nitrifiers. At low DO concentrations, the microbial community structure of the nitrifying sludge is expected to be different from a standard high DO nitrifying community.…”

Influence of Deep-Treated Wastewater Discharge on Nitrification Activity in a Natural Reservoirs

“…The ability of nitrifying microorganisms to oxidize N-NH 4 and N-NO 2 has been widely used in biological wastewater treatment (Semenova et al, 2012, Gnida et al, 2016. Biological nitrification as a large-scale biotechnology is used as the final stage of wastewater treatment, when the treated water containing nitrates can be discharged into the reservoir, and in modern technologies for deep purification of nitrogen compounds -as an intermediate stage when it is combined with subsequent biological denitrification (Haandel et al, 2012, How et al, 2018. Modern urban wastewater treatment schemes use sludge liquid recycling in two-, three-, four-and five-stage processes that allow deep purification of not only nitrogen compounds but also other biogenic elements.…”