TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Device: The apparatus comprises at least one electrolytic cell associated to the tank and having: at least one pair of electrodes extending internally of a volume defined by the tank and configured such as to at least partially contact the sewage, at least one electrical energy generator connected to the pair of electrodes, the electrolytic cell being configured such as to energize at least one part of the sewage present internally of the tank and promote oxidation and/or reduction of the organic material of the sewage by electrolysis. The microwave generator comprises at least one magnetron configured such as to irradiate the sewage present in the tank by at least partially carrying out the heat raising treatment. It is configured to irradiate the fluid with electromagnetic waves having a frequency greater than 1 GHz, in particular comprised between 1 and 3 GHz, still more in particular comprised between 2.3 and 2.6 GHz. The tank has internally at least one choke able to define at least one forced passage of the sewage circulating in the tank, in particular where the tank comprises chokes, each chokes defining a respective forced passage of the sewage circulating in the auxiliary tank. The microwave generator is externally engaged to the tank, substantially at least at a forced passage, and configured such as to generate electromagnetic waves in a direction of the forced passage, and where the tank comprises, at the forced passage, at least one window that is radio-transparent to the frequencies of the electromagnetic radiation. Gas blown internally of the tank by the blowing device comprises air, in particular oxygen and/or ozone. The apparatus comprises at least one bypass branch hydraulically connected to the inlet branch and the outlet branch, at least one discharge outlet able to place the internal volume of the tank in fluid communication with the bypass branch, and at least one intercepting element operatively active on the discharge and configured such as to be arranged in a first operating condition in which the intercepting element prevents passage of the sewage through the discharge outlet, the intercepting element being further configured such as to be arranged in a second operating condition where the intercepting element enables the sewage to passage through the discharge outlet. It comprises at least one sensor that is operatively active on the tank and at least one control unit connected to the sensor, the control unit being configured such as: to receive at least one signal from the sensor, and to process the signal for determining at least one parameter linked to the sewage circulating internally of the tank, for example the pressure and/or the temperature of the sewage, and where the control unit is configured to establish, after having received the signal from the sensor, the presence of a clogged condition of the tank, the control unit being connected with the intercepting element and being configured such as to send a command signal for commanding the first or second condition, the control unit being configured such as to arrange the intercepting element in the second operating condition after it has been determined the clogged condition of the tank in order to enable sewage to outflow from the bypass branch. Preferred Parameter: The forced passages have a height, measured perpendicularly to the advancement direction of the sewage, comprised between 15 mm and 60 mm, in particular comprised between 20 mm and 50 mm, still more in particular comprised between 25 mm and 45 mm, and where at least one between the microwave generator and the electrolytic cell is engaged at the forced passage and configured such as to energize the sewage crossing the forced passage.