Studies on the Chemical Stabilisation of Digestate from Mechanically Recovered Organic Fraction of Municipal Solid Waste

Abstract

This study aims to explore an innovative approach consisting of the Fenton's process to stabilise organic wastes as an alternative to the traditional aerobic decomposition (composting). Digestate from the anaerobic digestion of the organic fraction of municipal solid wastes was taken from a mechanical-biological treatment plant and was thoroughly characterised regarding physical, chemical and biological properties. This sludge contained around 7.8 g Fe kg TS-1, which can be beneficial to the chemical oxidation. However, the use of zero-valent iron nanoparticles or iron(II) salt revealed treatment can be improved by adding extra iron into the system. The response surface methodology determined that the best peroxidation conditions were 35.6 g H2O2 kg TS-1 and 33.1 g Fe2+ kg TS-1, while maintaining constant pH 3, L/S 5 and room temperature. The chemical treatment enhanced the stability, reducing the oxygen uptake rate from 4.63 to 2.57 g O-2 kg VS-1 h(-1). Moreover, the germination index increased from 37 to 99.9 %, which means the treatment yielded a non-phytotoxic product. The outcomes of the present study are promising and open a new pathway for the Fenton peroxidation in semi-solid processes since this fast method can be very competitive when compared with the slow composting technology.