Rémy Gourdon

Phase partition of organic pollutants between coal tar and water under variable experimental conditions.

On some abandoned manufactured-gas plant sites the presence of a particular non-aqueous phase liquid (NAPL), namely coal tar, represents a potential source of groundwater pollution. The aim of this study was to characterise the phase partition of aromatic pollutants between coal tar and water. Batch trials have been carried out in order to evaluate the state of phase partition equilibrium of pollutants between coal tar and water, under variable experimental conditions (temperature, pH, ionic strength, coal tar composition). The experimental results clearly show that coal tar cannot be considered as an ideal solution with regards to phase partition of pollutants with water. The main identified mechanisms of phase partition are the quasi instantaneous solubilization of pollutants near the coal tar/water interphase, and the diffusion of pollutants within the organic phase or at the interphase which controls the transfer kinetics of pollutants towards the aqueous phase. The dissolution kinetics experimentally observed were therefore correlated to a diffusional model of mass transfer. The formation of a film which increased resistance to mass transfer was also observed at the coal tar/water interphase. This ageing phenomenon of the coal tar/water interphase was found to be an important aspect which can have a significant influence on the long term fate of coal tar in soils or subsoils, as well as on soil remediation techniques.

Effect of leachate injection modes on municipal solid waste degradation in anaerobic bioreactor

Three pilots simulated landfill bioreactors were used to investigate the effect of leachate injection modes on anaerobic digestion and biogas production from municipal solid waste. The technical modes used to increase waste moisture consisted of an initial saturation of the waste by flushing with leachate followed by a quick drainage, or weekly leachate injections with two different rates. The results confirmed that increasing moisture content is a key parameter to boost the biological reactions. Weekly leachate injection with high flow rate led to better results than the initial saturation of the waste in terms of biogas production kinetics. Water percolation was found to be an important factor to accelerate the degradation of solid waste. However, a modelling of the collected data by Gompertz model clearly showed that the intrinsic biogas potential determined on the initial solid waste was not reached with any of the progressive leachate injection modes.

Effect of microbial activity on the mobility of chromium in soils.

The effect of microbial activity on the chemical state of chromium, in a contaminated soil located in the Rhĵne-Alpes region (France), has been investigated. This soil contained 4,700 mg kg(-1) Cr, with about 40% present in the soluble hexavalent form. Indigenous microbial activity was found to significantly reduce Cr(VI) to the less mobile form (III) when the soil was incubated at 30 degrees C in an aqueous medium containing glucose and nutrients. A Cr(VI)-reducing strain of Streptomyces thermocarboxydus was isolated from the contaminated soil. The strain was found to metabolize Cr(VI) in a similar manner as an exogenous inoculum of Pseudomonas fluorescens LB300, and to precipitate chromium as a Cr oxyhydroxide with a gammaCrOOH-like local structure. The Cr(VI)-reducing activity of S. thermocarboxydus was induced, or significantly accelerated, by the aggregation of bacterial cells or their adhesion to suspended solid particles, and was stimulated in pure culture by glycerol and chromate.

Assessment of the effectiveness of an industrial unit of mechanical–biological treatment of municipal solid waste

An assessment of the French municipal solid waste (MSW) mechanical-biological treatment (MBT) unit of Mende was performed in terms of mass reduction, biogas emissions reduction and biostability of the biologically treated waste. The MBT unit consists of mechanical sorting operations, an aerobic rotating bioreactor, forced-aeration process in open-air tunnels (stabilization), ripening platforms and a sanitary landfill site for waste disposal in separated cells. On the overall plant, results showed a dry matter reduction of 18.9% and an oxidative organic matter reduction of 39.0%. A 46.2% biogas production decrease could also be observed. Concerning the biotreatment steps, high reductions were observed: 88.1% decrease of biogas potential and 57.7% decrease of oxidative organic matter content. Nevertheless, the usually considered stabilization indices (biogas potential, respirometric index) remained higher than recommended by the German or Austrian regulation for landfilling. Mass balance performed on each step of the treatment line showed that several stages needed improvement (especially mechanical sorting operations) as several waste fractions containing potentially biodegradable matter were landfilled with very few or no biological treatment.

Life cycle assessment as a tool for controlling the development of technical activities: application to the remediation of a site contaminated by sulfur

Abstract The objective of this study is to show how a life cycle assessment approach can be used to direct the development of technical activities according to environmental considerations. The case study deals with the remediation of a soil contaminated by sulfur in an industrial context. The environmental merits of four treatment techniques are compared by taking into account the raw materials and energy consumption, air and water emissions and waste production. First results are discussed criterion by criterion. It is shown that bio-leaching is the most energy-consuming technique, whereas liming requires the highest quantity of materials. Furthermore, results related to atmospheric emissions highlight the importance of transportation operations in the environmental balance especially in the case of offsite landfilling. As regards waste production, treatment techniques may be divided into two groups: on the one hand, liming and onsite containment which lead to great quantities stored onsite, on the other hand, offsite landfilling and bio-leaching for which waste is transported out of the site. Then, a multicriteria analysis enables to aggregate inventory results, avoiding compensation phenomena. Based on this analysis, onsite containment appears to be the most environmentally-friendly technique, whereas bio-leaching and offsite landfilling result in the most important environmental burdens.

Study of the VOC emissions from a municipal solid waste storage pilot-scale cell: comparison with biogases from municipal waste landfill site.

The emission of volatile organic compounds (VOCs) from municipal solid waste stored in a pilot-scale cell containing 6.4 tonnes of waste (storage facility which is left open during the first period (40 days) and then closed with recirculation of leachates during a second period (100 days)) was followed by dynamic sampling on activated carbon and analysed by GC-MS after solvent extraction. This was done in order to know the VOC emissions before the installation of a methanogenesis process for the entire waste mass. The results, expressed in reference to toluene, were exploited during the whole study on all the analyzable VOCs: alcohols, ketones and esters, alkanes, benzenic and cyclic compounds, chlorinated compounds, terpene, and organic sulphides. The results of this study on the pilot-scale cell are then compared with those concerning three biogases from a municipal waste landfill: biogas (1) coming from waste cells being filled or recently closed, biogas (2) from all the waste storage cells on site, and biogas (3) which is a residual gas from old storage cells without aspiration of the gas. The analysis of the results obtained revealed: (i) a high emission of VOCs, principally alcohols, ketones and esters during the acidogenesis; (ii) a decrease in the alkane content and an increase in the terpene content were observed in the VOCs emitted during the production of methane; (iii) the production of heavier alkanes and an increase in the average number of carbon atoms per molecule of alkane with the progression of the stabilisation/maturation process were also observed. Previous studies have concentrated almost on the analysis of biogases from landfills. Our research aimed at gaining a more complete understanding of the decomposition/degradation of municipal solid waste by measuring the VOCs emitted from the very start of the landfill process i.e. during the acidogenesis and acetogenesis phases.

Qualification of soils through microbial activities measurements influence of the storage period on int-reductase, phosphatase and respiration

Abstract The storage of soils occurring before microbial activities measurements is liable to cause pronounced changes in their microbial populations. The bias thus introduced in not often taken into account during contaminated soils studies. The study of the influence of time and temperature of the storage period on three microbial activities and for three different soils shows that, in less structured ones certain activities decrease very quickly with the time of storage. Measurement of microbial activities for soil diagnosis must take place quickly after sampling, and storage is preferable at 4°C. Comparison of the results obtained from different soils is not possible as physico-chemical characteristics have a strong influence on the response levels of microbial activities.

Effect of baling on the behaviour of domestic wastes: laboratory study on the role of pH in biodegradation

Abstract This study was carried out using real domestic waste, which was fractioned and then reconstituted. It was incubated after having been compacted or not in airtight containers placed in a room thermoregulated at 28°C. In one series of experiments the waste was initially incubated at 40% humidity to simulate the average moisture of real domestic waste bales. Some of these assays were not modified over 16 months of incubation, whereas others were saturated with water after several weeks of incubation to allow pH measurements and neutralization of the waste. In another series of experiments, the waste was incubated under watersaturated conditions from the beginning. The results show very low biodegradation for the assays carried out under non-saturated conditions simulating the actual moisture of domestic wastes in real bales. Acidoic biodegradation, which was limited by the small amount of O2 in the containers, was insignificant as shown by the absence of heat production in the containers, the temperature of the wastes never being higher than the room temperature. Anaerobic biodegradation was also very low as shown by the low gas production (between 8 and 16 1 of gas/kg of dry organic matter) and the absence of methane and H2S in the biogas. The observed inhibition of biological activity under unsaturated conditions was caused by acidification of the medium. This acidification was due to production of volatile fatty acids during the first days of incubation by facultative anaerobic micro-organisms, under anoxic conditions. The biological evolution was, therefore, inhibited at the acid production phase. The biodegradation was very significantly increased when the waste was saturated with water and the pH adjusted above 6.5 whether the waste was compacted or not. In this case, the total production of biogas was between 250 (compacted waste) and 290 (non-compacted waste) litres of gas/kg of dry organic matter, with a methane concentration of 60%. A complete anaerobic biodegradation of the organic matter would have led to a biogas production of about 1000 1 of gas/kg of dry organic matter.

Pilot-scale anaerobic digestion of screenings from wastewater treatment plants

The anaerobic digestion of screenings from a municipal wastewater treatment plant was studied in a 90 L pilot-scale digester operated at 35 degrees C under semi-continuous conditions. In the first 4 weeks, a dry solids residence time of 28 days was applied, but the installation of inhibitory conditions was observed. Feeding was therefore suspended for 4 weeks to allow the digester to recover from inhibition, and then progressively increased up to a constant load of 6 kg of raw waste per week, corresponding to an average residence time of about 35 days of dry solids. At this stage, biogas production stabilized between 513 and 618 Nl/kg VS(added) per week, with methane contents around 61% v/v. The results of this work thereby supported the feasibility of (co-)digestion as a potential alternative treatment of screenings from municipal wastewater treatment plants.

Long-term behaviour of baled household waste

This study was carried out at the laboratory scale (approximately 15 l) and using real baled waste of industrial dimensions (about 1m 3 ), in order to assess the long-term behaviour of baled household waste. The laboratory assays were carried out with real household waste which was fractioned on site, reconstituted in the laboratory and then compacted into 15 l airtight containers (unless stated otherwise). These containers were incubated under diAerent experimental conditions at a constant temperature (28∞C). Three assays were conducted over 34 months and two others over 27 months. For the assays incubated in conditions simulating those of real baled waste (confined medium, with no aeration or water flow), a very low microbial activity was observed. The assay incubated in the same conditions but with slight aeration during the first three months in order to simulate imperfectly airtight wrapping, revealed biodegradation which started in a significant manner after 800 days of incubation. The evolution of two real wrapped bales each containing 900 kg of household waste was monitored over 8 months. These bales were produced industrially, one in July 97 and the other in July 98 at the incinerator plant at Agde (France). The bales were then stored outside at the laboratory location and their evolution was monitored mainly by biogas analysis and temperature measurement. No methane formation was observed, revealing the absence of anaerobic biodegradation, thus confirming the laboratory assays. ” 1999 Elsevier Science Ltd. All rights reserved.