## 3 Results
### Oxygen Uptake Rate Tests
#### 3.2.1 Batch Tests
Furthermore, it can be observed that biomass B2 showed exogenous sOUR values lower than those of the endogenous one, except for the sample that did not contain any AOX, demonstrating a possible inhibitory effect due to the presence of an AOX. Table 6 shows the results obtained from the batch tests carried out with the thermophilic biomass (B5). On days \"A\" and \"B\", tests were carried out with the same aqueous waste that had an AOX concentration of 1.81 mg\({}_{\text{AOX}}\) L\({}^{-1}\) and a pH of 7.80. Originally, it was decided to evaluate the exogenous OUR using the substrate as is and with two different DFs, i.e., 1:2 and 1:5. Since the results obtained with DF 1:2 and DF 1:5 were similar, on day \"B\", the tests were only carried out with the aqueous waste diluted 1:5. On day \"C\", aqueous waste characterized by an AOX concentration of 30.80 mg\({}_{\text{AOX}}\) L\({}^{-1}\) and a pH of 8.00 was tested as is and with a DF equal to 1:5. It can be observed that as the dilution increased, the sOUR value increased on day \"A\", decreased on day \"B\", and remained almost the same on day \"C\". Comparing the results obtained from the tests carried out on days \"B\" and \"C\", it can be concluded that the higher the concentration of AOXs in the original aqueous waste (i.e., 30.80 mg\({}_{\text{AOX}}\) L\({}^{-1}\) vs. 1.81 mg\({}_{\text{AOX}}\) L\({}^{-1}\)), the lower the sOUR value. Thus, thermophilic aerobic systems are particularly suited for the treatment of wastewaters with toxicity concerns resulting from high salinity levels or the presence of hazardous compounds [32]. The energy content of high-strength wastewaters is sufficient to allow for autothermal operation, avoiding the need for exogenous heat input: the release of significant energy from the microbial metabolism of the organic substrate allows for the maintenance of autothermal thermophilic conditions [32]. On the other hand, biomass separation is often difficult due to poor flocculation and the settling characteristics of thermophilic biomasses [32]. Figure 5: Effect of AOX type. * By lowering the pH from values of about 10 to around 8, the oxygen consumption increases. * Industrial biomass B1, which was already acclimated to industrial wastewaters, showed a higher oxygen consumption than the civil biomass. * Under the same substrate conditions--same AOX concentration and same pH--the thermophilic biomass (B5) showed a lower oxygen consumption with respect to the industrial biomass (B1). Table 8 shows that as the concentration decreased (from 30.80 to 2.00 and finally to 0.40 mg L\({}^{-1}\)), the oxygen consumption increased. However, as the concentration decreased from 0.40 to 0.20 mg L\({}^{-1}\), the oxygen consumption decreased because the substrate was too diluted. Regarding the test in which the industrial biomass B1 was put in contact with a synthetic solution containing 80 mg L\({}^{-1}\) dichlorophenol for 5 days, no medium-term toxicity effect was observed. All the evidence shows that there was no inhibition of the aerobic biomasses tested, even in the medium term; however, low oxygen consumption was observed. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Test-Day**} & \multirow{2}{*}{**AOX Concentration in the Aqueous**} & \multicolumn{3}{c}{**sOUR [mg\({}_{\text{DO}}\) gvss\({}^{-1}\) h\({}^{-1}\)]**} \\ \cline{3-6}  & & **Waste Tested [mg\({}_{\text{AOX}}\) L\({}^{-1}\)]** & **Endogenous** & **DF 1:1** & **DF 1:2** & **DF 1:5** \\ \hline A & 1.81 & 0.30 & 0.29 & 0.36 & 0.44 \\ B & 1.81 & 0.29 & 0.79 & - & 0.51 \\ C & 30.80 & 0.29 & 0.42 & - & 0.41 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Results obtained from batch tests carried out with thermophilic biomass (biomass B5). “-” indicates unmeasured values.