A novel process of salt tolerance partial denitrification and anammox (ST-PDA) for treating saline wastewater
Graphical abstract
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.
References: (31)
- et al.
Nitrate and nitrite bacterial reduction at alkaline pH and high nitrate concentrations, comparison of acetate versus dihydrogen as electron donors
J. Environ. Manage.
(2021) - et al.
Performance and microbial structure of partial denitrification in response to salt stress: Achieving stable nitrite accumulation with municipal wastewater
Bioresour. Technol.
(2020) - et al.
Nitrite production from partial-denitrification process fed with low carbon/nitrogen (C/N) domestic wastewater: performance, kinetics and microbial community
Chem. Eng. J.
(2017) - et al.
Comparison of nitrite accumulation performance and microbial community structure in endogenous partial denitrification process with acetate and glucose served as carbon source
Bioresour. Technol.
(2021) - et al.
From freshwater anammox bacteria (FAB) to marine anammox bacteria (MAB): A stepwise salinity acclimation process
Sci. Total Environ.
(2021) - et al.
Combined Partial Denitrification (PD)-Anammox: A method for high nitrate wastewater treatment
Environ. Int.
(2019) - et al.
Advanced nitrogen removal from wastewater by combining anammox with partial denitrification
Bioresour. Technol.
(2015) - et al.
Effects of salinity build-up on the performance and microbial community of partial-denitrification granular sludge with high nitrite accumulation
Chemosphere
(2018) - et al.
Enrichment and retention of key functional bacteria of partial denitrification-Anammox (PD/A) process via cell immobilization: A novel strategy for fast PD/A application
Bioresour. Technol.
(2021) - et al.
Effect of self-alkalization on nitrite accumulation in a high-rate denitrification system: Performance, microflora and enzymatic activities
Water Res.
(2016)
A novel strategy for accelerating the recovery of a Fe(II)-inhibited anammox reactor by intermittent addition of betaine: Performance, kinetics and statistical analysis
Chemosphere
The variation on nitrogen removal mechanisms and the succession of ammonia oxidizing archaea and ammonia oxidizing bacteria with temperature in biofilm reactors treating saline wastewater - ScienceDirect
Bioresour. Technol.
A novel control strategy for the partial nitrification and anammox process (PN/A) of immobilized particles: Using salinity as a factor
Bioresour. Technol.
Effect of free nitrous acid as inhibitors on nitrate reduction by a biological nutrient removal sludge
J. Hazard. Mater.
Effects of carbon source on denitrification efficiency and microbial community structure in a saline wastewater treatment process
Water Res.
Cited by (32)
Anammox-based technologies: A review of recent advances, mechanism, and bottlenecks
2024, Journal of Environmental Sciences (China)Nitrite production mechanism and microbial evolution characteristic influenced by pH during partial denitrification (PD) process
2023, Journal of Environmental Chemical Engineering