Effect of biological pretreatment of coarse MSW on landfill behaviour: laboratory study.

Mechanical and biological pre-treatment (MBT) of residual Municipal Solid Waste (MSW) is considered as a promising technical option prior to landfilling. The aim of MBT is to control the biological landfill activity to minimize biogas and leachate production. Laboratory-scale bioreactors were set up to study the behaviour of untreated and pre-treated residues. The bioreactors were designed to simulate the anaerobic condition of sanitary landfill. Initial water addition has been performed to ensure optimal condition of biological degradation. The incubation time was 400 days to achieve the biodegradation. Experiments have been carried out with untreated or treated waste collected from a mechanical-aerobic biological treatment plant located in middle south of France. Chemical and biological analyses have been performed to characterise the waste samples before and after the incubation. Results showed that a residual anaerobic activity does exist for the pre-treated waste when incubated in optimal moisture condition: biogas production does still exist even after a long period of aerobic hot fermentation and maturation.

Mass balance to assess the efficiency of a mechanical-biological treatment.

Using mechanical-biological treatment of residual municipal solid waste, it is possible to significantly lower landfill volume and gas and leachate emissions. Moreover, the landfill characteristics are improved. The performance of the Mende (France) mechanical-biological treatment plant is assessed via mass balances coupled with manual sorting according to the MODECOM methodology and biochemical methane potential after 90 days of incubation. The site includes mechanical sorting operations, a rotary sequential bioreactor, controlled aerobic stabilisation corridors, maturation platforms, and a sanitary landfill site for waste disposal in separated cells. Results showed that several steps could be improved: after a first sieving step, about 12% of the potentially biodegradable matter is landfilled directly without any treatment; mechanical disintegration of papers and cardboards in the rotary sequential bioreactor is insufficient and leads to a high proportion of papers and cardboards being landfilled without further treatment. Two fine fractions go through stabilisation and maturation steps. At the end of the maturation step, about 54% of the potentially biodegradable matter is degraded. The biochemical methane potential after 90 days of incubation is reduced by 81% for one of the two fine fractions and reduced by 88% for the other one. Considering the whole plant, there is a reduction of nearly 20% DM of the entering residual municipal solid waste.