Influence of biomass acclimation on the performance of a partial nitritation-anammox reactor treating industrial saline effluents
Introduction
The amount of saline wastewater that needs to be treated worldwide is rising due to the increase in industrial activities (petroleum, food, tannery, pharmaceuticals, etc.), the use of seawater for flushing toilets, the infiltrations of seawater in wastewater treatment plants (WWTPs) located in coastal regions, the separation of grey and black wastewaters with decentralized treatment in residential areas, etc.
One of the sectors that generates high salinity wastewaters is the fish canning industry (Cristóvão et al., 2016). This sector is very important in the region of Galicia (northwest Spain), which dominates the national market that places Spain as the leading fish and seafood canning county in the European Union (Taboada Gómez et al., 2016). The sector comprises approximately 65 companies distributed mainly along the coast. Similarly, Chile is an important fishing-aquaculture nation in Latin America, generating 48.5% of its aquaculture production and is the fifth country in the world in fishery production (Alfaro and Quintero, 2014). At the present time, the new stringent regulations and the need for preserving the quality of the marine environment in coastal areas make the development of efficient technologies to tackle fish canning wastewater treatment necessary.
According to the concept of “circular economy”, wastewater can be considered as a “source of materials” instead of as “waste”, to produce for example energy. It is known that the energy contained in the wastewater is enough to compensate for the energy required for its treatment (Gu et al., 2017). One of the alternatives to achieve the energy self-sufficiency of the WWTPs is the application of combined partial nitritation/anammox processes for autotrophic nitrogen removal, which enables the maximization of organic matter valorization via anaerobic digestion for biogas production (Morales et al., 2015b).
In particular, fish canning wastewater treatment normally consists of a physico-chemical process for the removal of solids and fats by dissolved air floatation. In some cases, an additional anaerobic digester is placed subsequently for organic matter valorization as biogas. More rarely, a coupled nitrification-denitrification system is added to remove nitrogen and fulfill the discharge requirements in terms of organic matter and nitrogen removal. However, the nitrification-denitrification processes present two main disadvantages that make the nitrogen removal inefficient: (1) the nitrification step consumes large amounts of oxygen, which involves high energy consumption and (2) the organic matter consumed for the denitrification process cannot be valorized as biogas in the anaerobic digestion step. Therefore, the application of the combined autotrophic partial nitritation/anammox processes is of great interest (Vazquez-Padin et al., 2014). This option allows a 50% saving in the energy needed for aeration, as only half of the ammonium contained in the wastewater is oxidized to nitrite (partial nitritation). Furthermore, all the organic matter previously used in the denitrification process can be used now to produce biogas in the anaerobic digester. This advantage relies on the fact that in the anammox process the ammonium is oxidized to nitrogen gas using the nitrite as an electron acceptor, without the need for an organic source. However, the anammox bacteria are very sensitive to different parameters and compounds, such as salinity (Jin et al., 2012). There are a significant number of studies that report on the inhibition of anammox bacteria by salinity and also their possible adaptation (Scaglione et al., 2017). However, there are no studies available that refer to the performance of the combined partial nitritation/anammox processes for saline industrial wastewater conditions. Furthermore, the research published to date used synthetic saline wastewater (Malovanyy et al., 2015, Wang et al., 2017). Therefore, specific studies with industrial wastewater are necessary to verify if a specific company can shift from an existing nitrification-denitrification treatment system to a partial nitritation/anammmox one.
Thus, the present study focuses on testing the feasibility of implementing a combined partial nitritation/anammox system to treat the effluents produced from an anaerobic digester in operation in a fish canning facility.
Section snippets
Reactor set-up
A pilot scale sequencing batch reactor (SBR) with a useful volume of 25 L was operated in 6 h cycles comprising: 5 min of feeding, 340 min of reaction with stirring and variable aeration, 5 min of sedimentation and 10 min of withdrawal. The exchange volume was 4.5 ± 0.3 L. The aeration was supplied from the bottom of the reactor by applying a controlled on/off strategy (Table 1) to guarantee an adequate balance between the activities of the partial nitritation and anammox processes. The oxygen
Partial nitritation-anammox processes performance with progressive NaCl concentration increase
In the first experiment (A) the wastewater collected in the fish cannery was characterized by a progressive and significant increase in the salt concentration, from 1.75 ± 0.26 to 17.40 ± 0.64 g-NaCl L−1, while the nitrogen concentration as ammonium slightly increased from 136 ± 14 to 215 ± 22 mg-TAN L−1. Thus, the fluctuations of the output parameters should be attributable mainly to the NaCl effect on the combined processes (Fig. 1).
In Stage A-I the high specific anammox activity of the
Conclusions
The removal of nitrogen from fish canning effluents with high salt content was accomplished in a partial nitritation/anammox reactor.
Percentages of 61.6 ± 7.2% of nitrogen removal efficiencies were obtained with effluents containing concentrations of up to 6.6 g-NaCl L−1; nitrite accumulation and the instability of the process were observed at higher salt levels.
Stable conditions were reached in the partial nitritation-anammox SBR after 154 days of progressive increase in salt concentration up
Acknowledgements
This research was funded by the Spanish Government (AEI) through GRANDSEA (CTM2014-55397-JIN) and FISHPOL (CTQ2014-55021-R) projects co-funded by FEDER. The authors from the USC belong to the Galician Competitive Research Group GRC/GPC2013-032 and to the CRETUS Strategic Partnership (AGRUP2015/02). All these programs are co-funded by FEDER (UE). The Chilean research internship was funded by CONICYT-PCHA/Doctorado Nacional/2014-21140373 and FONDECYT 1140491. Authors want to thank FCC Aqualia for
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