Analysis of the biodrying and biostabilization efficiency of a continuous flow full-scale facility

The technological solution adopted for aerobic treatment of Waste Organic Fraction (WOF) can influence the evolution of the physical parameters of the process making the facility acting as a biostabilization or a biodrying system. In the present study, the continuous flow biological section of the full-scale mechanical biological treatment plant was experimentally investigated by means of evolution, during treatment period (day), of temperature (T) (° C), volatile solids (VS) (%TS) and oxygen uptake of the WOF under treatment. Oxygen uptake was measured by the Dynamic Respirometer Index Potential (DRIP) (mgO2/kgVSh). Main findings were that T (° C) and VS %TS remained quite constant among inlets and outlets of the biological treatment sections, about 70° C and 50 (%TS), respectively. DRIP (mgO2/kgVSh) values measured by several samples withdrawn along the basin width increased significantly in the first half portion of the basin of the aerobic section, remaining quite constant in the second half. This was mainly caused by the strong moisture reduction that rapidly achieved values lower than 40% causing inhibition to microbial activity. The simulation model developed in this work showed that the mean retention time (day) of the WOF inside the aerobic basin was about 14-16 days, this parameter being strongly influenced by the WOF inlet rate (tonnes/day). Finally, experimental evidence pointed out that the reduction of WOF DRIP (mgO2/kgVSh) stopped after the first days of treatment indicating that the facility operates mainly as biodrying system. Based on simulations, biostabilization can also be pursued by maintaining the moisture of WOF to proper values not lower than 40 (% w/w).