Enhanced solubilization and anaerobic biodegradability of source-separated kitchen waste by microwave pre-treatment

Abstract

Results from an investigation of the effect of high temperature and pressure microwave (MW) pre-treatment of source-separated kitchen waste (SSKW) are presented. MW pre-treatment to a temperature of 175 °C (1 min holding time) at a heating rate of 7.9 °C min(-1), enhanced SSKW solubilization by 40% in comparison with control; yielding higher soluble chemical oxygen demand (sCOD), total sugars and proteins concentrations in the soluble phase (<45 μm). Batch biochemical methane potential tests (BMP) at 33 °C, indicated an enhanced anaerobic biodegradability compared to non-pretreated samples. However, the comparative analysis of semi-continuous anaerobic digesters performance for pre-treated and non-treated SSKW, indicated that MW pre-treatment was successful at solids retention times (SRT) higher than 25 days, showing not only a robust performance in terms of volatile solids (VS) and total chemical oxygen demand (TCOD) removals (6 and 5% gain, respectively, in comparison with control). Effluent dewaterability was also enhanced by MW pre-treatment, showing a 20% increase for the best operation conditions. The study of biomass activity revealed the production of difficult to degrade compounds during pre-treatment conditions and also served as a tool to monitor reactor performance deterioration.