Biostabilization of mechanically separated municipal solid waste fraction

Abstract

Municipal solid waste was processed by a mechanical-biological end composting process both in pilot and full-scale plants. The organic fraction obtained by mechanical treatment (fraction → < 50 mm) was processed at a high composting rate for 37 days followed by a curing phase of 79 days. Process parameters were registered and kept in an optimal range (oxygen > 140 ml 1^-1, temperature < 65°C, moisture > 500 g kg^-1 w.w.). After the high-rate phase, the products obtained showed a high degradation coefficient and good biological stability (ΔVS = - 54.75% and -35.35%, DRI = 300 and 500 mg O ₂ kg^-1 VS h^-1, respectively, for pilot and full-scale plants) especially for the pilot plant, indicating that it is not possible to obtain the same performance for a full-scale plant as obtained under laboratory conditions. Nevertheless, the successive curing phase showed less of a discrepancy between the two processes (ΔVS = - 66.33% and -56.87%, DRI = 280 and 360 mg O₂ kg^-1 VS h^-1, respectively, for pilot and full scale plants). The quality of the stabilized product was tested by biogas production tests. As expected, a sample processed in the pilot plant produced less biogas (26 1 kg TS^-1) than that obtained at full scale (40 1 kg TS^-1). An unprocessed sample produced less biogas owing to the production of organic acids, which, by lowering the pH, inhibit the generation of gas.