Improving Stabilization or Mass Reduction Effect for an Existing MBT Plant

The aerobic stabilization process performed in the Biological Treatment (BT) section of an existing Mechanical Biological Treatment (MBT) facility, operating since 1994, has been analyzed. It consists of an aerobic continuous flow basin, in which the waste is straddled by screws moved by a crane bridge, with an aerated floor through which process air is supplied by electrical fans. The experimental investigation performed on several samples withdrawn from the continuous flow BT basin at different Retention Time (RT) periods shows a strong Humidity (H) loss of the Waste Organic Fraction (WOF) from the inlet to the outlet section. This strong H reduction produces positive effect on the WOF weight loss, more than 40%, but inhibits stabilization process. The Dynamic Respirometer Index Potential (DRIP) shows that the main stabilization effect occurs in the first half part of BT basin length. Further Volatile Solids (VS) reduction results negligible showing that the BT operates mainly a bio drying of the WOF. For removing the stabilization inhibition effects it is necessary to add water to the WOF under treatment for maintaining the H > than 40-45% w/w. On the basis of a simulation model developed by the aid of the experimental analysis results, the increase in H content is able to increase significantly the DRIP reduction increasing the stability of the WOF at BT section outlet. On the other hand, even if the VS concentration results also reduced, the increase in the H content of the WOF at BT outlet causes a reduction of the weight loss that results about of 20%.