# Nitrogen Removal Using a Membrane Bioreactor with Rubber Particles as the Fouling Reducer
## 1 Introduction  
Membrane bioreactors (MBRs) are among the most promising domestic wastewater treatment technologies due to their high efficiency [1, 2, 3]. However, several challenges impede the wide application of MBRs such as low nitrogen removal efficiency and a tendency for membrane fouling. To achieve high nitrogen removal through the MBR process, it is essential to provide contrasting conditions in two separate reactors that hold either nitririving or denitrifying bacteria. Effluent from aerobic units containing nitrites and nitrutes should be recycled in the anoxic unit to achieve denitrification. However, these additional processes increase the operational complexity and cost [4].  
The use of a single reactor under time division operation is one of the approaches for nitrification-denitrification applied in MBR. Intermittent aeration in a single-reactor MBR has been reported as an attractive way to create an anoxic environment; this approach results in greater operating flexibility, process simplicity, and lower energy consumption. However, its wide application is limited by membrane fouling. Although intermittent aeration is beneficial for nitrogen removal in MBRs, it may aggravate membrane fouling due to the decreased shear force acting on the membrane surface during non-aeration periods [5]. Membrane fouling leads to increased operation and maintenance costs, thus gradually decreasing MBR treatment capacity, as well as shortened membrane lifetime. Several studies have shown that the addition of a bio-fouling reducer is an effective strategy to reduce the fouling propensity in the MBR process. The direct addition of adsorbents or granule activated carbon into submerged MBRs could enhance organic removal efficiency without the need for a membrane chemical cleaning step and therefore reduced operating time. For instance, it has been reported that the addition of the use of zeolite as bio-fouling reducer has been reported to stabilize the operation process of the membrane bioreactor, and also reduces membrane fouling [6, 7, 8, 9, 10]. In addition, the use of bio-fouling reducers could be a key mechanism in increasing MBRs retention time. However, this approach has not yet been tested on single-reactor MBRs with intermittent aeration; this is crucial especially during the important non-aerated period. In addition to bio-fouling reducers,quorum quenching has also been reported as a promising solution to the fouling problem, but it has not been tested widely enough to be considered for practical application in MBRs [11].  
The objective of this study is to evaluate the performance of an intermittently aerated single membrane reactor with and without the addition of a bio-fouling reducer. Chemical oxygen demand (COD), nitrogen removal efficiency, and fouling reduction were monitored in all our tests. In addition, the effects of important influencing factors, such as the aerobic/anoxic time ratio, on system performance were also investigated. The PCR-amplified v3 region of 16s rDNA was analyzed using denaturing gradient gel electrophoresis (DGGE) to evaluate the microbial diversity involved in intermittently aerated MBRs.