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A new-two, phase "decanter" (able to centrifuge the oily pastes without previous addition of hot water) was compared with a three-phase one, processing homogeneous lots of three olive varieties (Coratina, Nebbio and Grossa di Cassano) at an industrial level. The results showed that the integral centrifuge frequently yielded higher oil outputs. Furthermore, as the vegetation water was not separated from the husk, the amount liquid effluent produced was much lower (about 10 Kg/q olives, on average). This goes towards solving the age-old and very difficult problems connected with the production of this highly polluting outflow. However, the olive cake obtained semi-liquid (with about 55-60% of moisture), making the industrial recovery of the residual oil difficult and expensive. Furthermore, the solid by-product was characterized by higher percentage values of the oil amount, higher values of the pulp/stone ratio, as well as the greater weight produced. The effluent produced in small quantities, besides being more concentrated and thus richer in fat, dry residue, phenols and o-diphenols. The COD and turbidity values were also higher. Finally, as will be referred to in detail in the second part of this work, the oils obtained were of a far higher quality, mainly for their lower oxidizability and better organoleptic characteristic, so that they are wholly comparable to those extracted by pressing or filtering. In addition, the significant reduction of processing costs, as well as the lower consumption of hot water and electrical energy, must also be emphasized.