Article
Bioaugmentation of two-stage aerobic sequencing batch reactor with mixed strains for high nitrate nitrogen wastewater treatment

https://doi.org/10.1016/j.cjche.2020.08.014Get rights and content

Abstract

Mixed strains Delftia sp.YH01 and Acidovorax sp.YH02, with capability of heterotrophic nitrification-aerobic denitrification, were introduced into a two-stage aerobic sequencing batch reactor to enhance NO3-N removal. With optimal C/N of 8, efficient NO3-N removal was achieved at initial NO3-N concentration of 2000 mg·L−1. Meanwhile, the massive accumulation of NO2-N was avoided during the long operation. Compared to the one-stage aerobic sequencing batch reactor, the removal efficiency of NO3-N and TN in the two-stage aerobic sequencing batch reactor was increased by 36.5% and 42.7%, which respectively was 93.8% and 88.4%. Microbial community study showed that the mixed strains have the stronger viability and can synergistically denitrify with the indigenous microorganisms in system, such as Azoarcus, Uncultured Saprospiraceae, Thauera, Paracocccus, which could be major contributors for aerobic denitrification. The proposed technology was shown to achieve high-efficiency treatment of high NO3-N wastewater through aerobic denitrification.

Introduction

High concentration nitrate-nitrogen (NO3-N) wastewater was discharged from various pollutant sources including the fertilizer, uranium, nuclear, metal finishing, cellophane, and explosives industries [1]. High NO3-N wastewater could result in water eutrophication and had a potential hazard to human health [2]. Most studies about high NO3-N wastewater (> 2000 mg·L−1) treatment relied on anaerobic denitrification [[3], [4], [5]]. Traditional biological nitrogen removal includes aerobic nitrification and anaerobic denitrification,which need separated reactors and different operating conditions. Fortunately, simultaneous nitrification denitrification has been achieved with the discovery of heterotrophic nitrification-aerobic denitrification (HNAD) strains, such as Alcaligenes faecalis C16 [6], Diaphorobacter sp. PD-7 [7], Acinetobacter sp. T1 [8], Pseudomonas tolaasii strain Y-11 [9]. Simultaneous nitrification denitrification could be a better alternative because nitrification and denitrification could occur concurrently in one reactor, which could greatly reduce reactor volumes and construction costs [10]. However, most aerobic denitrification studies were carried out in shake flasks with low concentrations of NO3-N(< 200 mg·L−1) [8,11,12]. Studies of treating high NO3-N wastewater in aerobic denitrification reactor were limited. Hence, how to achieve efficient treatment of high NO3-N wastewater in aerobic denitrification reactor is worth studying.

Bioaugmentation was an effective strategy to enhance the treatment of target contaminants by adding microorganisms to activated sludge processes [13]. Some HNAD strains have been added to the reactor to enhance nitrogen removal. HNAD bacteria Bacillus sp. K5 was applied into a sequencing batch reactor (SBR) to enhance ammonium-nitrogen (NH4+-N) removal [14]. P. stutzeri strain XL-2 was applied to a sequencing batch biofilm reactor to treat ammonium-rich wastewater [15]. However, not all bioaugmentation was successful [16,17]. There was a competition between introduced strains with indigenous strains [18]. If introduced strains did not have a strong competitive ability, bioaugmentation would be invalid because introduced strains did not have enough biomass. The choice of biofortifiers would be important.

In the present study, Mixed HNAD strains (Delftia sp. YH01 and Acidovorax sp. YH02) was used as biofortifier to achieve the success of bioaugmentation. In previous studies, Delftia could possess nitrification and denitrification simultaneously so that it has better adaptability to the environment [19], even in complex wastewater [20]. Acidovorax specifically has efficient denitrification capacity [21,22]. YH01 and YH02, isolated in our laboratory, had a strong capability of heterotrophic nitrification-aerobic denitrification [23]. Mixed HNAD strains (YH01 + YH02) have better performances on nitrogen removal than single strain (YH01, YH02) [23]. The main reason may be that interspecific cooperation between YH01 and YH02 could promote biofilm formation [24]. So, mixed strains had a stronger viability in the bioreactor.

In the present study, mixed strains (YH01 + YH02) were used to enhance the treatment effect of a two-stage aerobic SBR on high NO3-N wastewater. Meanwhile, the microbial community of SBR was systematically studied by using high-throughput sequencing technology. The main purposes of this study were: (i) to assess the performance of NO3-N removal in the two-stage aerobic SBR process bioaugmented by mixed HNAD strains for high NO3-N wastewater treatment; (ii) to confirm whether mixed HNAD strains can synergistically denitrify with microorganisms in the system by studying microbial community.

Section snippets

Bacterial strains and seed sludge

HNAD strains Delftia sp. YH01 (GenBank No. KY419588) and Acidovorax sp. YH02 (GenBank No. KY419589) were used as a biofortifier [23]. YH01 and YH02 were isolated in our laboratory at the early stage, and they were both Gram-negative bacteria. YH01 has a thin rod shape and YH02 has a thick rod shape. Fig. 1 shows mixed HNAD strains (YH01 + YH02) had good performances of heterotrophic nitrification and aerobic denitrification. As shown in Fig. 1A, NH4+-N could be efficiently removed by the mixed

Performance of the two-stage aerobic SBR process in start-up

The concentration of NO3-N and COD was periodically raised in the start-up of R1 and R2 to examine the high nitrogen resistance and avoid high shock loading. Fig. 3A shows that R1 was successfully started after 51 days of operation. The performance of NO3-N, TN, and COD removal achieved a stable state. The average removal efficiency of NO3-N, TN, and COD was 57.3%, 45.7%, and 62.5%. R1 was the one-stage aerobic SBR. Obviously, the treatment efficiency of the one-stage SBR for high

Conclusions

With optimal C/N of 8, the two-stage aerobic SBR bioaugmented by the mixed HNAD strains achieved high efficiency nitrogen removal for high NO3-N wastewater treatment. Compared to the one-stage aerobic SBR, the removal efficiency of NO3-N and TN in the two-stage aerobic SBR was greatly increased. The two-stage aerobic SBR will provide a reference value for practical aerobic denitrification for high NO3-N wastewater treatment.

Microbial community study showed that indigenous microorganisms,

Acknowledgements

This work was supported by grants from the Science and Technology Planning Project of Guangzhou City, China (201903010031) and the Natural Science Foundation Research Team Project of Guangdong Province, China (2016A030312009).

References (39)

Cited by (22)

View all citing articles on Scopus
View full text