Performance of a low cost MBT prior to landfilling: study of the biological treatment of size reduced MSW without mechanical sorting.

In France, the interest in Mechanical Biological Treatment (MBT) prior to landfilling is actually growing. In the absence of acceptance criteria for the waste to be landfilled, an alternative to the intensive, high-technology MBT can only find its place in the French context if it shows substantial benefits from an environmental, economic or operational point of view. This paper presents an experiment of low-cost MBT of size reduced MSW without material splitting. The performance of an experimental, pilot-scale mechanical and biological treatment process has been studied on 37.5 Mg of raw municipal solid waste. The mechanical process has been kept simple with only coarse shredding and no material recovery. The biological treatment, which was a low-cost forced aeration process, was monitored for 25 weeks. The biogas production potential of the waste was reduced by 90% to 19 NL kgDM(-1). The initial AT4 index of 82.9 mg O2 gDM(-1) decreased to 16.0 mg O2 gDM(-1). After 25 weeks of aerobic treatment, the dry mass loss reached 37%, while the mass of waste going to landfill was reduced by 28%. The average performances of the process were explained by the biological process itself, which was not optimal, and also by the characteristics of the input waste. The high particle size of the treated waste and the high content of slowly biodegradable matter (such as paper and cardboard) may both be significant drawbacks for the biological stabilisation of waste.

Leachate recirculation effects on waste degradation: study on columns.

The purpose of this study is to determine the impact of leachate recirculation on the degradation of municipal solid wastes (bioreactor concept). The study was carried out using columns containing approximately 50 kg of waste, in order to follow waste degradation over a limited time. Three types of waste were studied: fresh waste of standard composition, fresh waste of fermentable composition and some 8-yr-old waste extracted from a site in France. Measurement of the global parameters, such as chemical oxygen demand (COD), volatile acidity, alkalinity, leachate conductivity, methane potential of the wastes and biogas production monitoring (volume of CO2 and CH4 produced), were carried out. The quantity of oxydizable matter and biogas production was increased by the leachate recirculation, and the duration of the first degradation phases was reduced in all cases. Chloride, ammonium and organic pollution accumulation was observed according to the duration of recirculation. After 400 days of degradation, waste stabilization seemed to be reached for all of the recirculated columns (COD<300 mg/L O2, and methane potential reached).

Indicating the parameters of the state of degradation of municipal solid waste.

This study related to the analysis of the physical (granulometry and composition) and chemical (organic matter, organic carbon and nitrogen contents) characteristics, as well as those relating to release (leaching tests and determining the methanogene potential) of several domestic wastes, with an aim of evaluating stabilization indicators. Values thresholds for a known stabilized waste were thus deduced by correlation (% paper-cardboard = 0-1; % volatile solid (VS) = 18-19; % OC = 5-6; % fines = 44-45; % degraded components = 75-76, COD of leachate = 141-155 mg O2/L; DOC from leachate = 45-49 mg C/L and 0.9-1 m3 CH4/t of dry waste). However, these values thresholds remain specific to the method employed for the analyses. The results obtained represent a considerable advance in the definition of a waste stabilized state and propose the importance of certain parameters, such as the paper-cardboard content and the measurement of leachates by using the SUVA index for determining a stabilization state.