# Nitrogen Removal Using a Membrane Bioreactor with Rubber Particles as the Fouling Reducer
## 2 Experimental Method  
For this study, a 20 L laboratory-scale MBR system (Figure 1) was used and operated at room temperature (approximately 25 \({}^{\circ}\)C). Initially, a polypropylene flat sheet membrane module (Pure-Envitech, Korea) with a pore size of 0.4 \(\upmu\)m and an area of 0.07 m\({}^{2}\) was immersed in the MBR. This provided a flux of 20 L/m\({}^{2}\)/h. Air was then introduced 10 cm below the membrane module through a diffuser with an air rate set at 2 L/min, corresponding to an air to water ratio (defined as the air rate divided by the liquid rate through the membrane) of about 500 [12]. Either granule activated carbon (GAC) or rubber particles roughly 2 mm in diameter were added as fouling reducers to the reactor, and they were circulated by aeration or by an internal circulation pump below the reactor during non-aeration periods. The effluent pump of the reactor was operated in an alternating fashion with a filtration time of 8 min followed by 2 min of idle time.  
The MBRs were seeded with activated sludge from the Ujeongbu wastewater treatment plant, Korea. The hydraulic retention time of the reactor was set to 18 h. The mixed liquor suspended solids (MLSS) concentration of the sludge was maintained in the range of 3200-3400 mg/L. The aeration/non-aeration periods of the reactor for nitrogen removal were set to either 20 min/40 min, 30 min/30 min, 20 min/40 min, or 10 min/50 min. A glucose-based synthetic feed with a COD concentration of 220 mg/L was prepared by adding nutrients and other ingredients to tap water. Table 1 lists the compositions of the compounds in the synthetic wastewater.  
Figure 1: Configuration of MBR system. P: pump, P: pump for internal circulation, B: blower for air supply, T: timer.  
The levels of MLSS, COD, total suspended solids (TSS), total nitrogen (TN), NH\({}_{4}\)+-N, NO\({}_{2}\)\({}^{-}\)-N, and NO\({}_{3}\)\({}^{-}\)-N were measured following the Standard Method [13]. The dissolved oxygen content and pH levels, respectively, were measured using a YSI 52 dissolved oxygen meter (YSI, Inc., Yellow Springs, OH, USA) and an Accumet Ap62 pH meter (Fisher Scientific Co., Pittsburgh, PA, USA).  
The rubber particles that were used as fouling reducers were produced from waste tires, and they were added to decrease the TMP in the MBR. The GAC and rubber particles were first dried and shifted with sieves No. 10 and 20 to achieve a fraction between 2.00 and 0.85 mm. The obtained particles were then washed and dried before being used in the experiment. The GAC and rubber particles had bulk densities of 0.45 and 0.85 g/cm\({}^{3}\), respectively.  
To analyze the complexity of the microbial community in the MBR, the DNA of the microorganism was extracted from the samples. The eluted DNA from the microorganisms in the samples was reamplified by PCR with forward primer 341f and reverse primer 518r [14]. The quality of the DNA sample was analyzed by DGGE. The sequencing analyses of the bands on the gradient gel and their closest reference microorganisms in the GenBank database were found using the BLAST program [15].  
Analysis of the experimental results was done using the average values obtained from repeated experiments.