Influence of carbon sources on nutrient removal in A2/O-MBRs: Availability assessment of internal carbon source

doi:10.1016/j.jes.2015.12.031

Journal of Environmental Sciences

Volume 48, October 2016, Pages 59-68

https://doi.org/10.1016/j.jes.2015.12.031 Get rights and content

Abstract

Both internal carbon source and some external carbon sources were used to improve the nutrient removal in Anaerobic-Anoxic-Oxic-Membrane Bioreactor (A²/O-MBRs), and their technical and cost analysis was investigated. The experimental results showed that the nutrient removals were improved by all the carbon source additions. The total nitrogen and phosphorus removal efficiency were higher in the experiments with external carbon source additions than that with internal carbon source addition. It was found that pathways of nitrogen and phosphorus transform were different dependent on different carbon source additions by the mass balance analysis. With external carbon source addition, the simultaneous nitrification and denitrification occurred in aerobic zone, and the P-uptake in aerobic phase was evident. Therefore, with addition of C-MHP (internal carbon source produced from sludge pretreatment by microwave-H₂O₂ process), the denitrification and phosphorus-uptake in anoxic zone was notable. Cost analysis showed that the unit nitrogen removal costs were 57.13 CNY/kg N of C-acetate addition and 54.48 CNY/kgN of C-MHP addition, respectively. The results indicated that the C-MHP has a good technical and economic feasibility to substitute external carbon sources partially for nutrient removal.

Graphical abstract

Introduction

Nowadays, the effluent standards are required to meet Standard A of “Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918–2002)” in China. As the effluent standards are getting more and more stringent, improvement of the nutrient removal efficiency in wastewater treatment plants (WWTPs) becomes an urgent issue. A significant factor in the success of the biological nutrient removal process is the availability of suitable carbon source, and some literatures suggested that the C/N ratio should be above 6 to achieve satisfactory effluent quality in biological wastewater treatment (Sun, S.-P., et al., 2010, Fu, Z., et al., 2009a). However, the domestic wastewater is always low in C/N ratio, sometimes lower than 3 in southern China (Wu, 2010). A most common method for increasing the C/N ratio is adding extra carbon. External carbon sources such as methanol, acetate, glucose and ethanol are used commercially as extra carbon to improve nutrient removal (Wang, D., et al., 2012, Wang, D., et al., 2013a, Kargi, F. and Uygur, A., 2003, Bracklow, U., et al., 2010). However, the external carbon source addition not only raise the operational cost but also increase the excess sludge production significantly (Mokhayeri et al., 2009), and the produced sludge increased further treatment cost (Metcalf and Eddy, 2004).

The readily biodegradable organic and volatile fatty acids (VFAs) are the preferred carbon source for nutrient removal microbes. There is an amount of organics in sludge, and VFA generation from sludge pretreatment has been suggested as alternative carbon source for nutrient removal. Various chemical, physical and biological methods are developed for sludge pretreatment, such as alkaline fermentation (Tong, J. and Chen, Y., 2009, Gao, Y., et al., 2011, Zhao, J., et al., 2015, Wang, D.B., et al., 2013b), thermochemical pretreatment (Rajesh Banu et al., 2009;, Galí, A., et al., 2006, Do, K., et al., 2009), ozonation pretreatment (Cui and Jahng, 2004), mechanical disintegration (Kampas et al., 2007) and microwave pretreatment (Wang, Y., et al., 2009, Wang, Y., 2009). Among these technologies, microwave irradiation has gained widespread popularity as an effective thermal method due to its rapid and selective heating and energy efficiency (Tyagi, V.K. and Lo, S.-L., 2013, Remya, N. and Lin, J., 2011).

In previous study, microwave-H₂O₂ process (MHP) was proved to be an efficient way for sludge breakage, by which some of biodegradable organics could be released from solid content to the bulk liquid phase of sludge (Wang, Y., et al., 2009, Xiao, Q., et al., 2012), and sludge reduction was significant in a pilot study based on microwave (Xiao, 2012). A subsequent research found that the organics released from sludge pretreated by MHP can be used as the internal carbon source to enhance the nutrient removal in an Anaerobic-Anoxic-Oxic-Membrane Bioreactor (A²/O-MBR) (Xu et al., 2014).

However, in the application of solubilized sludge as internal carbon source to improve the biological nutrient removal, it is important to note that the addition of internal carbon source includes not only VFAs, but also amount of nitrogenous and phosphorous compounds. Thus, it is necessary to analyze effect of carbon source on nitrogen and phosphorus transformation, and to evaluate the technical and economical availability of the internal carbon source for nutrient removal in A²/O-MBR.

In the present paper, the effects of the internal carbon source produced by MHP (C-MHP) and some common external carbon sources, as methanol and acetate, on the nutrient removal were studied in A²/O-MBRs. The influence of nitrogenous and phosphorous compounds in the internal carbon source on nutrient removal was analyzed and evaluated, and then the pathways of nitrogen and phosphorus removal were investigated by mass balance calculation. Finally, the cost assessment of internal and external carbon source was studied.

Section snippets

Experimental set-up

The A²/O-MBR experimental setup was made up of an anaerobic tank, an anoxic tank and an oxic tank with submerged membrane modules in (Fig. 1). The working volume was 58.3 L, including anaerobic tank 8.3 L, anoxic tank 16.7 L and aerobic tank 33.3 L, respectively. The Hydraulic Retention Time (HRT) of anaerobic, anoxic and aerobic basins were 2, 4 and 8 hr, respectively. There are two internal recycle (R). R1 (Q1 = Q) connected anoxic and anaerobic and R2 (Q2 = 2Q) was between aerobic and anoxic.

COD removal

Fig. 2 shows the COD removal during the operation period with different carbon source additions. The fluctuation of COD in influent was evident and sometimes very low COD concentration was detected. The low concentration of influent COD may drop the MLSS concentration and weaken nutrient removal. It was observed that the effluent COD was lower than 50 mg/L, fluctuations of the influent COD did not alter the effective removal of organics in the system. In the initial phase, the COD effluent of

Conclusions

Compared with nitrogen removal efficiency 47% and phosphorus removal efficiency 31% for the control, the nutrient removals were improved by both external and internal carbon source additions. The nitrogen removal efficiency was 57.08% for C-MHP addition, 68% for C-methanol addition and 70% for C-acetate addition, respectively. The phosphorus removal efficiency was 59% for C-MHP addition, 82% for C-methanol addition and 86% for C-acetate addition, respectively. By mass balance analysis, it was

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No. 51278483), the National Major Science & Technology Projects for Water Pollution Control and Management (No. 2012ZX07202-005) and the project of Watershed Ecosystem Health Assessment of Guangxi.

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Influence of carbon sources on nutrient removal in A2/O-MBRs: Availability assessment of internal carbon source

Abstract

Graphical abstract

Introduction

Section snippets

Experimental set-up

COD removal

Conclusions

Acknowledgments

Water Res.

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Renew. Sust. Energ. Rev.

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Influence of carbon sources on nutrient removal in A²/O-MBRs: Availability assessment of internal carbon source