The Pilot Study of the Influence of Free Ammonia on Membrane Fouling during the Partial Nitrosation of Pig Farm Anaerobic Digestion Liquid.

Hanxiao Bian,Zhiping Zhu,Shunli Wang,Qianwen Sui

doi:10.3390/membranes11110894

Abstract

The problem of membrane fouling is a key factor restricting the application of the membrane bioreactor (MBR) in the partial nitrosation (PN) and anaerobic ammonia oxidation (anammox) processes. In this study, the pilot-scale continuous flow MBR was used to start up the partial nitrosation process in order to investigate the change trend of mid-transmembrane pressure (TMP) in the process of start-up, which was further explored to clarify the membrane fouling mechanism in the pilot-scale reactor. The results showed that the MBR system was in a stable operating condition during the partial nitrosation operation and that the online automatic backwash operation mode is beneficial in alleviating membrane fouling and reducing the cost of membrane washing. Particular attention was paid to the influence trend of free ammonia (FA)on membrane fouling, and it was found that the increase in FA concentration plays the most critical role in membrane fouling. The increase in FA concentration led to an increase in the extracellular polymer (EPS), dissolved microorganism product (SMP) and soluble chemical oxygen demand (SCOD) concentration. FA was extremely significantly correlated with EPS and SCOD, and the FA concentration was approximately 20.7 mg/L. The SCODeff (effluent SCOD concentration) concentration was approximately 147 mg/L higher than the SCODinf (influent SCOD concentration) concentration. FA mainly affects membrane fouling by affecting the concentration of EPS and SCOD.

Highlights

Anaerobic ammonium oxidation is an important nitrogen removal process and has many advantages, including no organic carbon consumption, less oxygen consumption and less sludge production, compared to the traditional nitrogen removal treatment [1]
Some factors have been found to be able to influence the start-up of the partial nitrosation (PN) process, including the hydraulic retention time (HRT), temperature, dissolved oxygen (DO), wastewater composition and nitrogen compound concentration [5,6]
It has been found that membrane fouling of the membrane bioreactor (MBR) during the reactor operation period plays a crucial role in the instability and low efficiency of the PN and anammox process [12]

Summary

Introduction

Anaerobic ammonium oxidation (anammox) is an important nitrogen removal process and has many advantages, including no organic carbon consumption, less oxygen consumption and less sludge production, compared to the traditional nitrogen removal treatment [1]. Due to these benefits, it has been applied to the removal of the nitrogen of pig farm anaerobic digested liquid with high ammonia nitrogen (NH4+-N) and a low carbon–nitrogen ratio [2]. Studies that investigated membrane fouling during the start-up of partial nitrification by using the MBR are very limited, and the impact of FA in the membrane fouling of MBR reactors for the partial nitrosation process is rarely investigated

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Conclusion