# Nitrogen Removal Using a Membrane Bioreactor with Rubber Particles as the Fouling Reducer
## 3 Results & Discussion  
### Performance of the MBR with Intermittent Aeration  
Figure 2 shows the changes in the TMP of the MBR over time with intermittent aeration (30 min air on/30 min air off) at a constant flux of 20 L/m\({}^{2}\)/h. For comparison, TMP was also monitored under continuous aeration mode. During the experiments, the MBR with intermittent aeration produced higher TMPs than the MBR with continuous aeration. The TMP for the MBR with intermittent aeration promptly rose to around 0.7 bar after the operation started, which resulted in a reduced flux (flow rate of the effluent) of less than 10 mL/min. On the other hand, the flux of the MBR with continuous aeration was constant during the experiment with no changes to the TMP. The changes of TMP in the MBR with intermittent aeration led to significant fouling on the membrane. These results indicate that including a non-aeration period during MBR operation leads to a crucial obstacle for the widespread application of intermittently aerated single membrane reactors. Earlier studies [16; 17] reported that extracellular polymeric substances (EPS) and soluble microbial products (SMP) are two important factors that affect the membrane fouling propensity. The fouling problems observed in this experiment were possibly due to EPS and SMP. \begin{table}
\begin{tabular}{c c} \hline \hline
**Compound** & **Concentration (mg/L)** \\ \hline Glucose (as COD) & 220 \\ NH\({}_{4}\)Cl (as N) & 25 \\ KNO\({}_{3}\) (as N) & 5 \\ KH\({}_{2}\)PO\({}_{4}\) (as P) & 2.5 \\ K\({}_{2}\)HPO\({}_{4}\) (as P) & 2.5 \\ KHCO\({}_{3}\) (as HCO\({}_{3}\) ) & 366 \\ Nutrient solution * & 1 mL \\ \hline \hline \end{tabular}  
*: The nutrient solution contains per liter: 90 g MgSO\({}_{4}\)7H\({}_{2}\)O, 6 g CaCl\({}_{2}\)-2H\({}_{2}\)O, 1.5 g FeCl\({}_{5}\)-6H\({}_{2}\)O, 6.5 g MnCl\({}_{2}\)-4H\({}_{2}\)O, 1.7 g ZnSO\({}_{4}\)-7H\({}_{2}\)O, 0.1 g CuCl\({}_{2}\)-2H\({}_{2}\)O, 1.9 g CoCl\({}_{2}\)-6H\({}_{2}\)O, 6.5 g NiSO\({}_{4}\)-6H\({}_{2}\)O, 0.1 g H\({}_{3}\)BO\({}_{3}\), 0.6 g (NH\({}_{4}\))\({}_{6}\)Mo\({}_{7}\)O\({}_{2}\)-4H\({}_{2}\)O, 1 g yeast extract.  
\end{table} 
Table 1: Compositions of the compounds in the synthetic wastewater. Several studies [7; 9; 18] have shown that the addition of a bio-fouling reducer can reduce the fouling problem in MBRs. Activated carbon is one of the most effective bio-fouling reducers, and it can both improve flux and remove organic submerged anaerobic material by the MBR. Figure 3 shows the changes in the TMP of the intermittently aerated single membrane reactor over time at a constant flux in the experiment after the addition of 0.5% (V/V) granule activated carbon (GAC). The increase in TMP took place gradually up to 0.7 bar during the experiment, indicating significant fouling on the membrane. At 70 h after the first addition of GAC, the TMP had dramatically decreased to 0.3 bar. However, the MBR could not even sustain this TMP for 20 h, then the TMP gradually increased with time back up to 0.7 bar. At 180 h, a second addition of GAC was made, and the TMP decreased back to 0.45 bar. After the second addition of GAC, the TMP increased back to 0.8 bar over time. These results indicate that the addition of GAC as a fouling reducer can reduce TMP for a short time. However, after initial improvement, the TMP in the MBR gradually increases back to previous levels. It could also be noted that the granules of activated carbon were breaking down to activated carbon powder by the end of the experiment, resulting in less friction between the activated carbon and EPS or SMP on the surface of the membrane. This result differs from previous results showing that the addition of activated carbon could reduce TMP in submerged MBRs [19]. Figure 3: Transmembrane pressure (TMP) profiles of an intermittently aerated single membrane reactor with the addition of 0.5% (V/V) GAC. Figure 2: Trans-membrane pressure (TMP) profiles and flow rates of effluent under continuous aeration or intermittent aeration in MBRs.