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.

Methane mass balance at three landfill sites: what is the efficiency of capture by gas collection systems?

Many developed countries have targeted landfill methane recovery among greenhouse gas mitigation strategies, since methane is the second most important greenhouse gas after carbon dioxide. Major questions remain with respect to actual methane production rates in field settings and the relative mass of methane that is recovered, emitted, oxidized by methanotrophic bacteria, laterally migrated, or temporarily stored within the landfill volume. This paper presents the results of extensive field campaigns at three landfill sites to elucidate the total methane balance and provide field measurements to quantify these pathways. We assessed the overall methane mass balance in field cells with a variety of designs, cover materials, and gas management strategies. Sites included different cell configurations, including temporary clay cover, final clay cover, geosynthetic clay liners, and geomembrane composite covers, and cells with and without gas collection systems. Methane emission rates ranged from -2.2 to >10,000 mg CH(4) m(-2) d(-1). Total methane oxidation rates ranged from 4% to 50% of the methane flux through the cover at sites with positive emissions. Oxidation of atmospheric methane was occurring in vegetated soils above a geomembrane. The results of these studies were used as the basis for guidelines by the French environment agency (ADEME) for default values for percent recovery: 35% for an operating cell with an active landfill gas (LFG) recovery system, 65% for a temporary covered cell with an active LFG recovery system, 85% for a cell with clay final cover and active LFG recovery, and 90% for a cell with a geomembrane final cover and active LFG recovery.

Enumeration and characterization of cellulolytic bacteria from refuse of a landfill.

Enumeration and phenotypic characterization of aerobic cellulolytic bacteria were performed on fresh, 1 year old and 5 years old refuse samples of a French landfill site. Numbers of cellulolytic bacteria ranged from 1.1x10(6) to 2.3x10(8) c.f.u. (g dry wt.)(-1) and were lower in 5 years old refuse samples. A numerical analysis of phenotypic data based on 80 biochemical tests and performed on 321 Gram-positive isolates from refuse, revealed a high phenotypic diversity of cellulolytic bacteria which were distributed into 21 clusters. Based on the phenotypic analysis and the sequencing of 16S rDNA of five representative strains of major clusters, the predominant cellulolytic groups could be assigned to the family of Bacillaceae and to the genera Cellulomonas, Microbacterium and Lactobacillus. Furthermore, chemical parameters such as pH, carbohydrates and volatile solid contents influenced the composition of the cellulolytic bacterial groups which were reduced essentially to the family of Bacillaceae in the oldest refuse samples.

Detection of a whitening fluorescent agent as an indicator of white paper biodegradation: a new approach to study the kinetics of cellulose hydrolysis by mixed cultures.

A simple and reliable method to estimate paper degradation by cellulolytic bacteria is described. This method is based on the detection in the culture medium of a fluorescent whitening agent (FWA) added to white paper during the manufacturing process. Preliminary results using a Cellulomonas strain cultivated in a liquid medium containing FWA, indicated that this component is non-toxic at a final concentration of 0.01 per thousand (v/v) and that the fluorescence decreased during the first 24 h of incubation, i.e. during exponential growth phase, suggesting an adsorption of FWA on bacterial cells. Consequently, all experiments have been performed with a liquid medium containing FWA (0.01 per thousand v/v) and white paper (8.0 g/l) as cellulose source. Mixed bacterial populations (MBPs) were prepared from refuse samples. These MBPs, which mainly consisted of bacterial rod cells, were used as inocula and fluorescence was measured after 30 h of incubation, i.e. after the stationary phase was reached. A high linear correlation (R(2) = 0.979) was found between the percentages of degraded paper (%P) deduced from residual paper weight and the fluorescence values (F) of the culture medium and the following equation between %P and F was determined: %P = 8.71x10(-5) x F. An additional experiment using a second MBP showed a strong correlation (R(2) = 0.990) between the measured %P and the %P estimated from F values, confirming the reproducibility of the method. Moreover, the time course of paper degradation by five replicate flasks from a unique MBP was set up. Paper degradation was detected 3 to 5 days after the beginning of the stationary phase. The average degradation rate between the 7th and the 11th day of incubation was 11.4% per day. Rates of paper degradation ranged from 31 to 60% after 10 days and from 77 to 88% after 3 weeks of incubation, depending on the inoculum.