Elsevier

Bioresource Technology

Volume 202, February 2016, Pages 101-106
Bioresource Technology

Simultaneous nitrification and denitrification by EPSs in aerobic granular sludge enhanced nitrogen removal of ammonium-nitrogen-rich wastewater

https://doi.org/10.1016/j.biortech.2015.11.088Get rights and content

Highlights

  • Nitrification and denitrification take place simultaneously.

  • Nitrogen in different forms was present in EPSs and underwent dynamic changes.

  • Biosorption affected the results of batch experiments.

  • Nitrosomonas eutropha and heterotrophic denitrifiers were identified of the AGS.

Abstract

In this study, role of extracellular polymeric substances (EPSs) in enhancing nitrogen-removal from ammonium-nitrogen-rich wastewater using aerobic granular sludge (AGS) technology were analyzed. AGS enabled ammonium oxidation and denitrification to occur simultaneously. Air stripping and simultaneous nitrification–denitrification contributed to total-nitrogen removal. Clone-library analysis revealed that close relatives of Nitrosomonas eutropha and heterotrophic denitrifiers were dominant in the AGS, whereas anammox bacteria were not detected. EPSs adsorption of ammonium, nitrite, and nitrate nitrogen results in improved removal of nitrogen in batch experiments.

Introduction

Aerobic granular sludge (AGS) is a promising wastewater-treatment technology that has many advantages, including good sludge settleability, high processing efficiency, and powerful resistance to impact load. Long sludge age promotes growth and reproduction of microorganisms with long generation time, such as nitrifying bacteria, to improve the removal efficiency of ammonium nitrogen. AGS is utilized from the initial treatment of organic wastewater to the treatment of ammonium-nitrogen-rich wastewater and poisonous and harmful substances (Adav and Lee, 2008). The hierarchical structure of granular sludge allows the AGS to remove organic matter and ammonium nitrogen. Moreover, the dissolved oxygen diffusion restriction allows the granular sludge to form anoxic and anaerobic zones. The anoxic condition inside creates the conditions for simultaneous nitrification and denitrification process (Gao et al., 2011). Thus, with the coexistence of nitrifying and denitrifying bacteria, simultaneous nitrification and denitrification is possible (Yang et al., 2003). Large granular sludge particle size is favorable for simultaneous nitrification and denitrification (Wang et al., 2007, Shi et al., 2011). Although simultaneous nitrification–denitrification has been observed (Wang et al., 2007, Shi et al., 2011, Wei et al., 2014, Yan et al., 2014), further study is needed to investigate the elimination of nitrogen in the processing system.

Batch experiments are often used to analyze microbial substrate degradation ability (Wang et al., 2007, Shi et al., 2011), such as the denitrification of denitrifying bacteria. However, adsorption is often ignored in this process. Neglecting ammonium adsorption can lead to underestimations of at least 10–25% of ammonium available for nitrification (Lin et al., 2012). Experiments on ammonium nitrogen adsorption by active sludge, biological membrane, and granular sludge have been carried out. Temmink et al. (2001) studied the adsorption of ammonium nitrogen by biological membrane. Schwitalla et al. (2007) examined the adsorption ability of ammonium nitrogen by activated sludge floc and found that the adsorption capacity of ammonium nitrogen by activated sludge floc was between 0.07 and 0.20 mg of NH4+-N/(g/VSS). Bassin et al. (2011) studied the adsorption capacity of ammonium nitrogen and the desorbing ability by AGS based on the small and middle test. However, during the study of ammonium nitrogen as wastewater treatment, and rarely described ammonium nitrogen adsorption process in the operation of bioreactor. Bassin et al. (2011) found that the adsorbed ammonium nitrogen will dissolve back into liquid. As a microbial cell secretion, EPSs contain abundant charged groups (e.g., –COOH, –NH, –OH, –CO–). These groups can react with cations (metal and ammonium ions) and anions (phosphate radical) in wastewater by electrostatic reaction and ion exchange reaction. EPSs of activated sludge can adsorb metal ions in wastewater (D’Abzac et al., 2010, Sheng et al., 2013, Wang et al., 2014, Yan et al., 2015), and its function in phosphorus removal system was analyzed (Lin et al., 2012, Chen et al., 2015, Wang et al., 2015). However, knowledge about how EPSs affect the ammonium nitrogen content in biological treatment systems is very limited (Lin et al., 2012, Chen et al., 2015). The adsorption characteristics of ammonium nitrogen by AGS have been studied, and EPSs are believed to play an important role in ammonium nitrogen adsorption (Bassin et al., 2011). Extended aeration was used to eliminate ammonium nitrogen absorbed by granular sludge by desorption and oxidation. However, Bassin et al. (2012) did not conduct a comprehensive analysis of the ammonium nitrogen, especially nitrite nitrogen and nitrate nitrogen in EPSs.

The adsorbed materials react with the functional groups of EPSs, completing the process of adsorption. If the pollutant content of the EPSs in the reactor sludge can be measured, the adsorption process of the sludge would be understood. The contribution of adsorption to the pollutant removal helps to accurately reflect the microbial activity and kinetics process. Hence, this study was conducted to evaluate the possible improvement of nitrogen removal from ammonium-nitrogen-rich wastewater using AGS technology incorporating EPSs.

Section snippets

Reactor set-up and operation

A SBR reactor connected by two organic glass cylinders was used. The diameter and height of the bottom cylinder was 80 mm and 645 mm, respectively, whereas the diameter and height of the upper cylinder was 100 mm and 50 mm, respectively. The height of the middle connection was 100 mm, the effective volume was 5.6 L, exchange volume ratio was 50%, and the operating temperature was room temperature. Each stage was controlled by a time controller and operated six cycles every day, with each cycle

Nitrogen removal performance in a typical cycle

AGS formed and lasted for 13 months. The changes in the concentrations of “three nitrogen” (ammonium, nitrite, and nitrate nitrogen), and total nitrogen in the typical liquid phase cycle and EPSs over time are shown in Fig. 1A and B, respectively.

Fig. 1A shows that AGS was effective for ammonium nitrogen removal. When the concentration of ammonium nitrogen in the reactor was 200.51 mg/L, the effluent ammonium nitrogen concentration was 6.47 mg/L and the removal rate of ammonium nitrogen was 98.11%.

Conclusion

AGS possessed exhibit high processing capacity of ammonium nitrogen and denitrification associated with EPSs. Simultaneous nitrification and denitrification had been achieved during AGS performed in this study. EPSs adsorption cannot be neglected in the dynamic process of biological nitrification/denitrification, ammonium, nitrite, and nitrate nitrogen of EPSs underwent dynamic changes with the reaction time and were found until the end of the aeration process. Total nitrogen adsorbed by EPSs

Acknowledgements

Lilong Yan and Shaoliang Zhang are co-first authors. This work was supported by National Natural Science Foundation of China (No. 51208084); Young Academic Backbone Support Project of Heilongjiang Province (No. 1254G010); Academic Backbone Support Project of Northeast Agricultural University (15XG07).

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