# Nitrogen Removal Using a Membrane Bioreactor with Rubber Particles as the Fouling Reducer
## 3 Results & Discussion
### Performance of the MBR with Intermittent Aeration
To reduce TMP in intermittently aerated single membrane reactors, rubber particles produced from waste tires were added to the MBR instead of activated carbon. Figure 4 illustrates the fouling behavior of TMP under a constant flux of 20 L/m\({}^{2}\)/h in the experiments with the addition of 0.01 to 0.5% (V/V) rubber particles to the MBR. The TMP slope (dP/dt) was measured by examining the initial pressure drop rate with time over the first 25 h. Membrane fouling after the addition of rubber particles reduced substantially compared to that without the addition of rubber particles. The addition of over 0.2% rubber particles substantially enhanced the reduction in the TMP of the MBR. In contrast to GAC, the rubber particles did not break down with internal circulation during the non-aeration periods. This allowed the rubber particles to work as a scouring agent causing additional shear forces near the membrane surface, thus helping remove deposits from the membrane. Figure 5 shows changes in TMP over time with 0.5% (V/V) rubber particles. Based on a flux of 20 L/m\({}^{2}\)/h, the TMP stabilized at around 0.1 bar, indicating less membrane fouling with rubber particles. These results indicate the possibility of operating the MBR for some time at constant flux. The result suggests that using rubber particles as a scouring agent is effective in reducing internal fouling. In contrast to our study, [PERSON] and [PERSON] concluded that a larger surface area of powdered activated carbon (PAC), compared to that of GAC, improves operating flux and critical flux in MBRs [20]. In this experiment, the addition of GAC did not lead to satisfactory results in maintaining the desired TMP, due to the breakage of GAC into PAC during internal circulation. However, the addition of rubber fouling reducing agents greatly enhanced the effective operating period and helped maintain the membrane's permeability. Figure 4: TMP increment ratio (dP/dt) versus waste rubber particle addition to MBR. Regression was conducted using the exponential equation [dP/dt = dp\({}_{0}\)/dt\(\cdot\) EXP (-k\(\cdot\)r)]. The pressure drop coefficient, k, was 19.76, while r represents the proportion of rubber particles (%, V/V) in the reactor. The _R-square_ and _p-_value of the regression line were 0.97 and 0.0005, respectively. The results indicate that EPS, SMP, and colloids are the main contributors to increasing the TMP in MBRs, and this conclusion is supported by visual examinations of the membrane. After using an MBR for over 40 days without backwash, the membrane was extracted and observed. As shown in Figure 6, when no fouling reducer was used, a significant amount of deposit was found on the surface of the membrane. However, the existence of these kinds of deposits was slightly reduced when using GAC, and minimal deposits were detected when using rubber particles (the membrane had a white appearance). Although membrane surface damages were not visually observed for over 40 days as shown in Figure 6, friction due to long-term use of the fouling reducer may damage the surface of the membrane. Considering the importance of a stable fouling reducer, it is recommended that follow-up research should be conducted.