## 3 Results  
### First Stage: Testing Ammonium Volatilisation  
The initial mean concentrations between 165 to 173 mgNH4+-N/L in comparison to the mean concentrations determined on the fifth day of the test between 165 to 168 mgNH4+-/L, indicate that no significant decrease (\(p>0.05\) based on Wilcoxon rank sum test) was evident in the ammonium concentrations. The ammonium concentrations recorded for treatment A showed more variability than the other treatments, most probably due to the constant aeration in the system. However, the pH values of 6.8-7.5 indicate that only approximately 1% of NH3 is present, thus no significant NH4+ removal could be expected according to pKa (NH4+/NH3) = 9.25 at 25 \({}^{\circ}\)C.  
Figures 2 and 3 show the mean ammonium concentrations and pH values determined at each IBC during the five-day period of this stage. Figure 2: The mean of NH4+-N concentrations (mgNH4+-N/L) recorded during the ammonium volatilisation test. Treatment A (constant aeration), Treatment B (intermittent aeration 4h AA:4h no-AA), Treatment C (intermittent aeration 6h AA:4h no-AA), Treatment D (no aeration), AA = aeration. Second Stage: Evolution of Physicochemical Parameters, Organic and Nitrogen Compound Concentrations under Different Aeration Regimes  
The initial and final value of each physicochemical parameter, organic and nitrogen compound concentrations are presented in Appendix A Table A1. Based on these records, the removal percentages of organic and nitrogen compounds were estimated considering the different aeration regimes. The evolution of recorded values was assessed based on Figures 4 and 5. Their statistical relevance was evaluated through the estimates derived from the mixed model procedure. For a better graphical interpretation of the results, Figure 4 shows the evolution of pH, EC, DO, BOD, and COD, whereas, Figure 5 indicates the evolution of nitrogen compounds (NH\({}_{4}\)+-N, NO\({}_{3}\)-N and TN) set against the sampling date. Figure 3: The mean pH values recorded during the ammonium volatilisation test. Treatment A (constant aeration), Treatment B (intermittent aeration 4h AA:4h no-AA), Treatment C (intermittent aeration 6h AA:4h no-AA), Treatment D (no aeration), AA = aeration. Figure 4: Evolution of (**a**) pH, (**b**) conductivity, (**c**) dissolved oxygen, (**d**) biological oxygen demand, (**e**) chemical oxygen demand in each IRC exposed to different aeration periods. Treatment A (constant aeration), Treatment B (intermittent aeration 4h AA:4h no-AA), Treatment C (intermittent aeration 6h AA:4h no-AA), Treatment D (no aeration), AA = aeration. The evolution of the three different nitrogen-compounds per treatment was compared in single graphs due to the link in their removal processes. Figure 4a indicates that pH values decreased over time in the IBCs where constant and intermittent aeration was provided. Relatively similar pH values were registered in treatment A (from 7.2 to 5.2), treatment B (from 7.3 to 5.4) and treatment C (from 7.3 to 5.4) after 60 days. An opposite effect was identified in the IBC without aeration where pH increased from 7.1 to 8.1 in the same period. The initial conductivity values 13.6 mS/cm shown in Figure 4b remained relatively stable throughout the whole testing period. On the last testing day of the two-month period, the water samples representing treatment B (13.2 mS/cm), followed by the ones of treatment D (13.6 mS/cm) showed a slight decrease in comparison with the water samples from treatment A and C (14.1 and 14 mS/cm respectively). The DO concentrations (Figure 4c) in treatments A, B, and C increased over time. Again, relatively similar values were recorded among these treatments. Treatment A (from 7.2 to 9.3 mg/L), treatment B (from 7.4 to 9.3 mg/L), treatment C (from 7.5 to 9.3 mg/L) clearly show the effect of aeration provided to each IBC. However, the DO concentrations in treatment D lowered and stayed below the initial 5 mg/L since no air was supplied to the system.