Elsevier

Bioresource Technology

Volume 345, February 2022, 126472
Bioresource Technology

A novel process of salt tolerance partial denitrification and anammox (ST-PDA) for treating saline wastewater

https://doi.org/10.1016/j.biortech.2021.126472Get rights and content

Highlights

  • ST-PDA process was established for dealing with saline wastewater.

  • Stable nitrogen removal of PD and Anammox was achieved under 10 g·L-1 salinity.

  • Inhibition of NO3-N and FNA was verified and FNA inhibition could be eliminated with self-alkalization.

  • The TN of effluent from ST-PDA process was average 17.8 mg·L-1.

  • Thauera showed a high tolerance to fluctuating salinity levels.

Abstract

In the study, the salt-tolerant partial denitrification and Anammox (ST-PDA) process was established, meanwhile, the feasibility of salinity inhibition model as the boundary control method and the subsequent operation performance were studied. Study indicated that the performance of salt-tolerant PD sludge was the optimum under the 10 g·L-1 salinity, and AnAOB also maintained high activity at the salinity. Haldane and Aiba models verified that NO3-N (substrate) and FNA (product) would have negative consequences for performance of ST-PDA system. However, the effect of FNA would be eliminated by self-alkalization in the denitrification process. A 90% nitrogen removal rate was achieved and the average effluent total nitrogen of 17.8 mg·L-1 was maintained in the system. The high throughput sequencing revealed that the species richness decreased with the salinity increased, while Thauera played a major role in nitrogen removal in saline environment. The study provides a novel insights for salt-containing industrial wastewater.

Introduction

Many industrial wastewater with high nitrate (NO3-N) is generally accompanied by a large number of inorganic salts, such as metal refineries, landfill leachate, fertilizer and fishery processing plants (Osaka et al., 2008, Banihani et al., 2009, Bi et al., 2020, Zhang et al., 2021), how to remove NO3-N from these wastewater economically and effectively has become an urgent issue to be solved. If physical or chemical means (such as membrane separation) are used for eliminating NO3-N from these industrial wastewater, they are expensive and will generate secondary pollution (Du et al., 2015, Du et al., 2019). Comparatively, biological removal of NO3-N become the optimum decision on account of energy-efficient and pro-environment. However, Salinity will bring about inactivation of cells or enzymes in the biological nitrogen removal process, especially under high-salinity or instantaneous variation in salinity conditions (Jiang et al., 2021). It's worth noting that microorganisms have a strong adaption ability to the external environment changes. Liu et al., (2020) had found that the 80% nitrogen removal rate could be realized through the salinity-adapted partial nitrification and Anammox (PN/A) process under the salinity of 10 g·L-1, due to halotolerant bacteria reproduction. Recently, a novel partial denitrification and Anammox (PD/A) process was proposed for NO3-N removal in saline environment. Du et al., (2019) reported that PD/A was used to treat high NO3-N wastewater, 95% NO3-N removal rate could be achieved, and 92% NH4+-N could be removed by subsequent anammox. She et al., (2016) found that salinity promoted nitrite (NO2-N) accumulation in the process of partial denitrification for treating saline wastewater. Park et al., (2021) have demonstrated that the moderate salinity (1.0–2.0%) could enhance the anammox reaction and minimize heterotrophic denitrification in anammox reactors. Importantly, the process can maintain excellent total nitrogen (TN) removal efficiency (Wang et al., 2020). However, if PD/A was applied to the treatment of saline wastewater directly, inorganic salts would have a strong inhibition on microbial activity (Ji et al., 2018). Therefore, for target stable and efficient NO3-N removal in saline wastewater, the salinity boundary conditions that most suitable for PD and anammox could maintain high activity were found by means of inhibition kinetics model, a new salt tolerance-partial denitrification and anammox (ST-PDA) process was established.

In the process, anammox belongs to the post-processing, thus, PD stable operation was crucial. The PD adaptation in saline wastewater had been studied by many scholars. Bi et al., (2020) had found that 80% nitrate-nitrite transformation rate (NTR) could be obtained by using municipal wastewater to provide organics for PD at the salinity of 12.5 g·L-1; Ji et al., (2018) found that undomesticated PD sludge was completely inhibited when salinity increased to 15 g·L-1. However, the kinetic characteristics of salinity on PD have been rarely reported until now. The parameters obtained from the inhibition kinetic model were often used as important foundation for process design. Therefore, it was necessary to conduct inhibition kinetics experiments before PD salinity acclimation. In addition, partial denitrification systems were also affected by substrate ((NO3-N) and production (FNA, free nitrite acid). Albina et al., (2021) found that NO3-N reduction rate decreased by 50% with NO3-N concentration reached 400 mg·L-1 in the denitrification process; Ma et al., (2010) reported that when pH was 6.5 and FNA concentration was 0.2 mg·L-1, the activity of denitrifying bacteria was almost completely inhibited. Therefore, if these factors were not appreciated, the stability of ST-PDA would be affected seriously.

Kim et al., (1997) found that the inhibitory kinetics model of chlorophenol anaerobic degradation of acetic acid could effectively simulate the inhibitory process of toxic substances (substances adverse to microbial growth) on microorganisms. Since there were few kinetic models that could be directly used to study the effects of salinity on PD system, this kinetic model can be used as a salinity inhibition model. Haldane model (Qi et al., 2018) and Aiba model (Li et al., 2020) were generally used to simulate the effects of substrates and products on PD and anammox processes, providing important theoretical foundation and parameter guidance for PD and anammox coupling process and PD/A performance optimization (Cao et al., 2017). Therefore, it is necessary to utilize these kinetics to establishment and rationalization of the ST-PDA process.

In this study, a maximum salinity of inhibition PD activity that utilizing kinetics of chlorophenol anaerobic degradation acetic acid to fit was obtained. Subsequently, salinity was acclimated to the PD process and the validity of the kinetic parameters was verified. In addition, in order to enable anammox accept partial denitrifying effluent, appropriate salinity adaption was also carried out for anammox. Then, Haldane and Aiba kinetics model were used to simulate the inhibition of NO3-N and FNA on PD in salt environment respectively. Finally, the microbial community structure of PD was analyzed by high-throughput sequencing technology, revealed that the changes of PD microbial community under the increasing salinity. Consequently, a new ST-PDA process with inhibition kinetics as regulation method was established. More importantly, it provided an important theoretical basis for a PN + PD + Anammox process that could effective nitrogen removal in saline wastewater.

Section snippets

Salinity inhibition kinetics

To determine the maximum salinity that PD system could endure, kinetics batch experiments were carried out in six 500 mL conical flask. Partial denitrifying activated sludge was obtained from the SBR reactor (Fig. 1A), which ran 12 cycles per day for 51 consecutive days in the laboratory. The operation details of each cycle are 5 min for feeding, 60 min for anaerobic reaction, 30 min for precipitation, 5 min for drainage and 20 min for idle (Fig. 1B). After the sludge was taken out, it is

Analysis of salinity inhibition kinetics fitting results

Research showed that salinity had an inhibition effect on denitrifying bacterial community activity in activated sludge system, but, to some extent, control of the PD could be achieved. Therefore, in this experiment, through setting salinity gradient, the inhibition model of salinity on PD process was established using inhibitory kinetics model of chlorophenol anaerobic degradation of acetic acid. Experimental values β = 36,641 mg·L-1, n = 0.54 and m = 1.6816 were obtained by fitting with the

Research advances in ST-PDA process and future perspectives

Many scholars had carried out relevant studies about PD and Anammox performance by taking salinity as an important influencing factor. Ji et al., (2018) reported that PD could maintain about 90% NTR at 30 g·L-1 salinity by setting an appropriate salinity gradient, nevertheless, the highest salinity that PD could withstand was not be acquired. Bi et al., (2020) found that PD could achieve excellent performance at the salinity of of 12.5 g·L-1 through using municipal wastewater as carbon source,

Conclusions

In the present study, the kinetic characteristics of PD process during salinity elevation were simulated and verified. Accordingly, a ST-PDA process for nitrogen removal was established at the salinity of 10 g·L-1. Haldane and Aiba models fitting results showed that PD would be influenced with NO3-N concentration exceeded 200 mg·L-1 in the salt environment; the influence of FNA would be eliminated with the self-alkalization process. High-throughput results revealed that the functional bacteria

CRediT authorship contribution statement

Ao Xu: Writing – original draft. Deshuang Yu: Supervision, Funding acquisition. Yanling Qiu: Investigation. Guanghui Chen: Supervision, Project administration. Yuan Tian: Investigation, Software, Validation. Yanyan Wang: Funding acquisition, Writing – review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The work was supported by the National Natural Science Foundation of China (grant number 51978348), Shandong Key Research and Development Program (grant number 2019GSF110014), the National Natural Science Foundation of China (grant number 51878363). Here, I would like to express my special thanks to my supervisor Guanghui Chen for his outstanding contribution to the research and Yuan Tian for her constant support and help.

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