## 3 Results and Discussion  
### Monitoring of the Biological Thermophilic System  
As can be seen in Table 1, the loads of fed pollutants and performances of biological thermophilic process were reported. Biomass was able to treat high COD loads, with a concentration of two orders of magnitude higher, up to 50,000 mg L\({}^{-1}\), than conventional activated sludge (CAS) systems where the concentration of COD in input is almost 200-400 mg L\({}^{-1}\)[17; 18; 19; 20], with almost constant performance throughout 5 years of monitoring around 80%. As regards to nitrite and nitrate, removal of yields higher than 95% were granted for the entire monitoring period. Focusing on ammonia removal, a negative value was recorded. This result is confirmed in our previous study [11] where the enhancement of ammonia concentration during the thermophilic biological treatment was related to a strong ammonification phenomenon. If compared with the performance values of a CAS plant, the ability of the TAMR plant to obtain very high removal yields of nitrates is highly relevant [25]. The removal and production yields relating to nitrates and ammonia, respectively, are then reflected in the abatement yields of total nitrogen. In the five years of monitoring, the performances on total nitrogen were the most variable, going from a minimum value of 62% for 2019 to a maximum value of 76.7% recorded in 2021. Comparing the feed and the permeate, significant removal of phosphorus is pointed out at 82%. This result agrees with our previous study [13], in which the accumulation of phosphorus in the sludge in inorganic form was pointed out. The capacity of the TAMR plant, therefore, allows it to accumulate phosphorus inside the sludge making it rich in nutrients and, therefore, susceptible for possible recovery in agriculture. The specific oxygen consumption, C\({}_{\text{O2}}\) was influenced by the biodegradability of the organic matter fed. It remains constant for all years monitored and is equal to 1.42 kgO\({}_{\text{2}}\) CODrem\({}^{-1}\), this value represents a significant index of the operating conditions of the plant, in fact it allows to quantify the oxidizing agent necessary to degrade 1 kg of organic substance. TS in the TBR was 180.1-205.0 g L\({}^{-1}\) and the value of VS remained constant over the years of monitoring at around 47.1-52.0 g L\({}^{-1}\). These very high solids concentrations allow us to consider this operating reactor as a fluidized bed process [26]. Sludge load (Cf) and sludge age (\(\emptyset\)) provided an indication of the operating conditions of the thermophilic biological process. The sludge load remained almost constant for all monitoring years (0.02 kgBOD (kgSST d)\({}^{-1}\)). \(\emptyset\) indicates the number of days in which biomass remained in the biological system. The average value (221.7 \(\pm\) 11.9 d) was one order of magnitude higher than a traditional CAS plant (5-20d) [22]. This aspect was due to a lower production of VS typical of thermophilic system [9], which helped to produce a lower amount of excess sludge and more stabilized [27]. This aspect was extremely important for AW utility managers from an economic point of view since sludge production from biological systems represented one of the major cost items in plant management [28].