Maximising municipal solid waste - Legume trimming residue mixture degradation in composting by control parameters optimization

Composting is one of the most successful biological processes for the treatment of the residues enriched in putrescible materials. The optimization of parameters which have an influence on the stability of the products is necessary in order to maximize recycling and recovery of waste components. The influence of the composting process parameters (aeration, moisture, C/N ratio, and time) on the stability parameters (organic matter, N-losses, chemical oxygen demand, nitrate, biodegradability coefficient) of the compost was studied. The composting experiment was carried out using Municipal Solid Waste (MSW) and Legume Trimming Residues (LTR) in 200L isolated acrylic barrels following a Box-Behnken central composite experimental design. Second-order polynomial models were found for each of the studied compost stability parameter, which accurately described the relationship between the parameters. The differences among the experimental values and those estimated by using the equations never exceeded 10% of the former. Results of the modelling showed that excluding the time, the C/N ratio is the strongest variable influencing almost all the stability parameters studied in this case, with the exception of N-losses which is strongly dependent on moisture. Moreover, an optimized ratio MSW/LTR of 1/1 (w/w), moisture content in the range of 40-55% and moderate to low aeration rate (0.05-0.175Lairkg-1min-1) is recommended to maximise degradation and to obtain a stable product during co-composting of MSW and LTR.

The authors acknowledge financial support from the CICYT (Science, Technology Inter Ministerial Commission, Spanish Government-cofinanced FEDER), project number CTM2007-62117/TECNO. Special thanks to the European Social fund (ESR), the Ministry of Economy and Competitiveness of Spain for funding the Cabeza I.O PhD grant.

Peer Reviewed