Limits of the anammox process in granular systems to remove nitrogen at low temperature and nitrogen concentration
Graphical abstract
Introduction
The implementation of partial nitritation-anammox (PN-AMX) processes to remove nitrogen from the mainstream of the wastewater treatment plants (WWTPs) arises as one of the most promising options to increase the energy efficiency of these facilities (Morales et al., 2015). So far, several studies have been carried out operating PN-AMX systems at mainstream conditions, low ammonia concentration and low temperature using a one-stage configuration (Jiang et al., 2018; Lotti et al., 2014). These research works revealed two main drawbacks. On the one hand, the achieved volumetric nitrogen removal rates were below 10–30 g N/(m3·d) at 15 °C (Akaboci et al., 2018; Laureni et al., 2016; Pedrouso et al., 2018) mainly due to the oxygen limiting conditions imposed in order to maintain the balance between the activities of both ammonia-oxidizing (AOB) and anammox bacteria. On the other hand, the operational stability lost as a consequence of the development of the nitrite-oxidizing bacteria (NOB) activity (Han et al., 2016; Li et al., 2019). Both factors are responsible for the deterioration of the effluent quality, which does not meet the European discharge requirements, in sensitive areas, of 10 g/m3 of total nitrogen (TN) (Council Directive, 1991).
Since the bottleneck to apply the PN-AMX process at mainstream conditions is the stability of the PN process, efforts have been recently focused on the evaluation of the two-stage configuration systems to carry out the PN and anammox processes separately (Jin et al., 2019; Kowalski et al., 2019). Using this approach, stable long-term PN was achieved by inhibiting NOB activity due to the presence of free nitrous acid (HNO2) (Cui et al., 2019; Pedrouso et al., 2017. At this point, the performance of the subsequent anammox process needs to be further optimized to produce an effluent suitable for discharge.
The anammox process stability at mainstream conditions was demonstrated using enriched anammox biomass as inoculum and starting-up the reactors at temperatures close to 30 °C that were, then, stepwise decreased to 15 °C in a long-term acclimation period (De Cocker et al., 2018; Dosta et al., 2008; Hoekstra et al., 2018; Li et al., 2018). Another used alternative is the enrichment of anammox bacteria from activated sludge directly at low temperature (Hendrickx et al., 2014). However, although both strategies were successful, they required long start-up periods that are not useful for their implementation at full-scale WWTPs.
In the present study, a completely stirred tank reactor (CSTR), inoculated with anammox-enriched granular biomass coming from a reactor operated at 30 °C, was started-up directly at mainstream conditions (50 g TN/m3 and 15 °C). The objective was to evaluate the process stability and produced effluent quality in order to asses the anammox process feasibility at the operational conditions. Biomass mass transfer limitations and oxygen transfer from air were also considered to identify the operational considerations regarding those aspects limiting its full-scale application.
Section snippets
Set-up
The anammox process was carried out in a CSTR jacketed cylinder reactor with a useful volume of 1 L and a height to diameter (H/D) ratio of 1. The reactor temperature was maintained at 15 °C using a cryostat bath. A mechanical stirrer (58 rpm) provided a complete mixture inside the system. pH was not controlled and remained at 7.8 ± 0.2. A continuous peristaltic pump supplied the feeding while the effluent discharge took place by overflow. The reactor was inoculated with 2.8 kg VSS/m3 of anammox
Reactor performance
During the start-up period (Stage I), the applied NLR was approximately 33 g N/(m3⋅d) (Table 1). On day 7, a sudden increase in the effluent nitrate concentration was measured (Fig. 1). However, this nitrate production was not justified by the anammox process activity since ammonium concentration did not decrease proportionally. Thus, this nitrate rise was due to nitrite oxidation. Although this effect was associated with air entry into the reactor, dissolved oxygen concentration measured in the
Conclusions
When anammox biomass grows as biofilm, nitrogen mass transfer limitations reduce the reactor efficiency, which hinders compliance with discharge limits. Thus, on the one hand, the composition of the produced effluent in a PN-AMX system mainly depends on the treated wastewater nitrogen content and on the other hand, the removal efficiency depends on the NOB activity.
To reach the required low TN concentrations in the produced effluent, it is crucial to minimize the presence of dissolved oxygen in
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
This work was funded by the Chilean Government through the projects FONDECYT 1150285 and ANID/FONDAP/15130015. Anuska Mosquera-Corral wants to thank the MEC-CONICYT project 80180081 for its financial support in the short stay in the UAI, UdeC and UPLA (Chile) to collaborate in the elaboration of this paper. The authors from the USC belong to CRETUS Strategic Partnership (ED431E 2018/01) and to the Galician Competitive Research Group (GRC-ED431C 2017/29). All these programs are co-funded by
References (40)
- et al.
Assessment of operational conditions towards mainstream partial nitritation-anammox stability at moderate to low temperature: reactor performance and bacterial community
Chem. Eng. J.
(2018) - et al.
Kinetic characteristics and microbial community of Anammox-EGSB reactor
J. Hazard. Mater.
(2011) - et al.
Stable partial nitrification of domestic sewage achieved through activated sludge on exposure to nitrite
Bioresour. Technol. Rep.
(2019) - et al.
Evaluation of activity and inhibition effects on Anammox process by batch tests based on the nitrogen gas production
Enzyme Microb. Technol.
(2007) - et al.
Enrichment and adaptation yield high anammox conversion rates under low temperatures
Bioresour. Technol. Rep.
(2018) - et al.
Kinetic models for nitrogen inhibition in ANAMMOX and nitrification process on deammonification system at room temperature
Bioresour. Technol. Rep.
(2016) - et al.
Short- and long-term effects of temperature on the Anammox process
J. Hazard. Mater.
(2008) - et al.
Uncoupling the solids retention times of flocs and granules in mainstream deammonification: a screen as effective out-selection tool for nitrite oxidizing bacteria
Bioresour. Technol.
(2016) - et al.
High specific activity for anammox bacteria enriched from activated sludge at 10 °C
Bioresour. Technol.
(2014) - et al.
A pilot-scale study on start-up and stable operation of mainstream partial nitrification-anammox biofilter process based on online pH-DO linkage control
Chem. Eng. J.
(2018)
High-efficient nitrogen removal from municipal wastewater via two-stage nitritation/anammox process: Long-term stability assessment and mechanism analysis
Bioresour. Technol.
Effective nitrogen removal in a two-stage partial nitritation-anammox reactor treating municipal wastewater – piloting PN-MBBR/AMX-IFAS configuration
Bioresour. Technol.
Mainstream partial nitritation and anammox: long-term process stability and effluent quality at low temperatures
Water Res.
Influence of temperature on an Anammox sequencing batch reactor (SBR) system under lower nitrogen load
Bioresour. Technol.
NOB suppression in partial nitritation-anammox (PNA) process by discharging aged flocs: Performance and microbial community dynamics
Chemosphere
Simultaneous partial nitritation and anammox at low temperature with granular sludge
Water Res.
Performance of anammox UASB reactor treating low strength wastewater under moderate and low temperatures
Bioresour. Technol.
Mainstream wastewater treatment in integrated fixed film activated sludge (IFAS) reactor by partial nitritation/anammox process
Bioresour. Technol.
The granular biomass properties and the acclimation period affect the partial nitritation/anammox process stability at a low temperature and ammonium concentration
Process Biochem.
Nitrite oxidizing bacteria suppression based on in-situ free nitrous aid production at mainstream conditions
Sep. Purif. Technol.
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