The present paper shows the results obtained through an experimental activity carried out on a pilot-scale plant using an innovative technology which couples the granular aerobic sludge with the sequencing batch process. Treatment efficiency and operation costs were evaluated in order to assess feasibility of this new technology for the upgrading of the existing continuous flow activated sludge treatment plant located in Casal Monastero, a decentralized area of the City of Rome. During start-up (about 3 months), the granular aerobic sludge was developed by controlling the dissolved oxygen concentration, the value of pH and the up-flow velocity. Besides, the influent organic loading was progressively increased starting from 0.1 kg/m3 d up to 0.9 kg/m3 d. In order to improve nitrogen removal, an anoxic phase was temporary added to the operative cycle. Complete development of the granular sludge determined an appreciable improvement of the denitrification process which allowed to eliminate the anoxic phase. At regime conditions, the plant was operated with 3 daily cycles, each one of 8 h. The new system showed a reduced sludge production (of about 20–35%) as compared to the existing plant, along with high removal efficiency of both Chemical Oxygen Demand (COD) and nitrogen. However, the operation was discontinuous and strictly related to the strength of the granular sludge. Therefore, a careful monitoring is recommended in order to control operation and performance of this new system.

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