Thickened sludge are put in an acid reactor (pH between 2 and 3). During 30 minutes, sludge are in contact with nitrite ions (NO2-) powerful reagent in acid condition to destroy the reduced "osmophore components" (H2S, mercaptans), responsible of bad odors, and to inactivate the germ achieving the organic matters removal.
This process is similar to a stabilization phase, and according to the pH of the reaction, this stabilization meets the hygienisation standard of either Class A EPA (pH around 2) or Class B EPA (pH around 3). Therefore the sludge can be stored during several months without odors. In the reactor, the amount of nitrite injected is controlled by checking the pH level.
