## 3 Results
### Changes in Influent and Effluent Wastewater Characteristics
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Initial Wastewater**} & \multicolumn{2}{c}{**Acidic Reactor**} & \multicolumn{2}{c}{**Alkaline Reactor**} \\ \hline \multirow{2}{*}{**Parameters**} & **Average** & \multirow{2}{*}{\(\pm\)**sd**} & **Average** & \multirow{2}{*}{\(\pm\)**sd**} & **Average** & \multirow{2}{*}{\(\pm\)**sd**} \\  & **Value** & & & **Value** & & **Value** & \\ \hline pH & 7.4 & 0.1 & 6.6 & 0.1 & 8.4 & 0.1 \\ \hline EC & 1417 & 94 & 1593 & 107 & 1571 & 148 \\ \hline T, \({}^{\circ}\)C & 21.9 & 1.1 & 22.2 & 0.6 & 22.0 & 1.0 \\ \hline TN, mg/L & 60 & 7 & 57 & 5 & 58 & 8 \\ \hline NH4-N, mg/L & 53 & 7 & 54 & 5 & 55 & 7 \\ \hline NO3-N, mg/L & 5.2 & 0.8 & 3.2 & 0.7 & 3.1 & 1.6 \\ \hline NO2-N, mg/L & 0.020 & 0.004 & 0.016 & 0.003 & 0.007 & 0.001 \\ \hline TP, mg/L & 23.4 & 3.0 & 23.4 & 2.6 & 21.9 & 1.6 \\ \hline PO4-P, mg/L & 19.3 & 2.5 & 18.7 & 3.2 & 17.2 & 2.8 \\ \hline COD, mg/L & 287 & 72 & 249 & 67 & 243 & 81 \\ \hline TOC, mg/L & 54.2 & 18.5 & 64.9 & 8.8 & 66.1 & 13.7 \\ \hline IC, mg/L & 106.4 & 8.0 & 70.2 & 6.7 & 123.9 & 12.0 \\ \hline TC, mg/L & 160.6 & 25.4 & 135.1 & 14.2 & 190.0 & 24.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Changes in composition of influent wastewater before and after pH regulations (n = 3). The results showed that the nitrification process in the reactors before inhibitor addition demonstrated high-quality ammonium nitrogen removal of up to 96-97%. Further, when analyzing the inhibition influence, NH\({}_{4}\)-N concentration in the effluent from the reactor with alkaline pH stayed up to 1.92 \(\pm\) 2.18 mg/L (Figure 1a). Low NH\({}_{4}\)-N concentration after 72 h in the alkaline reactor effluent denotes that ammonium oxidizing bacteria (AOB) have not been inhibited, and ammonium was converted to nitrites with the initial efficiency. However, in the acidic reactor, effluent NH\({}_{4}\)-N concentration increased from 1.44 \(\pm\) 0.90 to 10.50 \(\pm\) 4.25 mg/L within 72 h (Figure 1a). Nitrite concentration decreased in the effluent of both reactors (Figure 1b) during the 48 h; thus, NO\({}_{2}\)-N was successfully converted to NO\({}_{3}\)-N by NOB. Then, an increase in the acidic reactor effluent was observed after 72 h (up to 0.96 \(\pm\) 1.41 mg/L). These changes indicate a possible risk of NOB inhibition due to long FA influence. The nitrate concentration decreased from 26.27 \(\pm\) 8.96 mg/L to 18.98 \(\pm\) 2.12 mg/L in acidic reactor effluent after 72 h and from 28.97 \(\pm\) 13.53 mg/L to 25.03 \(\pm\) 3.44 mg/L in alkaline reactor effluent after 72 h (Figure 1d). As suggested [22], NOB bacteria can be sensitive to the toxicity of free ammonia, and the impact occurs progressively. NOB has a long augmentation time; hence, a slight decrease NO\({}_{3}\)-N production is observed due to the NOB biomass fraction death after the inhibitor addition and sufficient biomass deficiency for the efficient second-step nitrification process. The formation of high concentrations of the FA leads to strong microbial activity inhibition [22]. It was found that under the alkaline pH conditions, the concentration of FA is 8.82 mg/L (calculated according to [PERSON] et al. [23]), indicating an impact on the nitrification process. In influent wastewater with acidic pH, the predictable formation of FA is low, but the level of FNA reach 0.228 mg/L shows the toxicity towards both AOB and NOB. However, nitrification ratio (NIT) was high (80% in acidic and 96% in alkaline reactors), and nitrite accumulation ratio (NAR) was only 4% in acidic and 0.3% in alkaline reactors (calculated according to [PERSON] et al. [24]). Thus, AOB was significantly affected by the inhibition. However, NOB and nitrite accumulation in the sludge was not affected.