Stabilisation de la matière organique au cours du compostage de déchets urbains : influence de la nature des déchets et du procédé de compostage - recherche d'indicateurs pertinents

Composting is a process of biological treatment of organic wastes which reproduces the natural process of organic matter humification in soil. Today in France, only 7 % of the urban wastes are composted, although the organic part represents 50 % of the 47 million tons produced annually. Composts are mainly used in agriculture to increase or to maintain soil organic matter concentration. Their behavior after soil incorporation depends on the stability of their organic matter (OM). In this work, we studied the evolution of compost OM characteristics during composting, in relation with their origin (nature of the composted wastes and process of composting) and evaluated the potential storage of OM in soil with their use. The relation between the residual biodegradability of compost OM and the potential availability of nitrogen in soil was also studied. Ten urban composts made from municipal solid wastes, biowastes, green wastes or sewage sludge, coming from industrial composting plants were sampled after three, four and six months of composting. To avoid the influence of composting process, eight composts elaborated in laboratory reactors from variable proportions of green wastes, biowastes, and papers-cardboards, were followed during three months. A range of five classes of compost OM stability was defined on the basis of mineralization kinetics of compost carbon during incubations in a reference soil. Compost OM was characterized by chemical (humic substances) and biochemical (lignin, cellulose, hemicellulose and soluble fraction) fractionation and by analysis in infrared spectrometry (FTIR). The degree of compost maturity was defined from the level of compost OM stability and the range of stability previously defined was used as reference for the validation of various indicators of maturity. During the composting process, all composts evolved towards products with similar characteristics and independent from the composted waste and process that only influenced the rates of stabilization. In most cases, the cellulose fraction rapidly decreased when nitrogen was not limiting. The slower degradation of lignin as compared to total organic matter led to its relative enrichment in compost OM. The IR spectra confirmed the increase of aromaticity during composting. When greenwastes were dominant in the composted wastes, their initial high lignin concentration explained the fast stabilization of OM during composting and little evolution was observed between three and six months of composting. On the contrary, composts made from municipal solid wastes, initially richer in cellulose materials (papers-cardboards) with a relative lack of nitrogen, were not stabilised after three months of composting, and required at least six months of composting, with turning, to be stabilized. The influence of biowastes on compost OM stabilization was not pointed out, probably because they only represent a weak proportion of the dry mass of the initial mixtures. From the biochemical fractionation results, an indicator of the proportion of stable OM in compost was calculated (Biological Stability Index, BSI). This stable fraction of compost OM contributes to soil OM upkeep or increase after compost application. For greenwaste composts, BSI little increased during maturation and the simultaneous decrease of total compost OM made lightly decreased their efficiency to soil OM upkeep. The reverse was observed for municipal solid waste composts. Their important stabilization during maturation made increase their BSI. Of this important stabilization resulted a relative increase of their efficiency for soil OM upkeeping between three and six months of composting. A small potential availability of compost nitrogen was estimated from incubations of soil-compost mixtures. The organic fraction of nitrogen of stabilized compost mineralized slowly. On the contrary, a strong immobilization of soil nitrogen occurred after incorporation of unstable compost, followed by a faster mineralization than observed with stable compost. Among the tested indicators of maturity, the humification ratio (RH=CHA / CFA) was the more reliable chemical indicator. RH values smaller than 1 indicated a lack of maturity, and RH larger than 1.3 corresponded to stabilized composts with high maturity levels. The self-heating test was the most relevant to be used on composting platforms. These two indicators allowed a correct estimation of compost OM stabilization level, from which recommendations could be made on the optimal period for soil incorporation, taking into account the risks of nitrogen immoblization.Le compostage est un procédé de traitement et de valorisation des déchets organiques qui reproduit en accéléré le processus d'humification de la matière organique (Mo) dans les sols. Actuellement en France, seulement 7 % des déchets urbains sont compostés, alors que la part organique représente 50 % des 47 millions de tonnes produites annuellement. Les composts sont avant tout utilisés en agriculture pour augmenter ou entretenir les teneurs en MO des sols, et le niveau de stabilité de leur MO conditionne leur comportement après incorporation au sol. Notre projet se proposait d'étudier l'évolution des caractéristiques de la MO de composts au cours du compostage, en la reliant à leur origine (nature des déchets compostés et procédé de compostage), et d'en déduire leur aptitude à entretenir le stock de MO d'un sol (valeur amendante). Les conséquences de la biodégradabilité résiduelle des composts sur la disponibilité potentielle de l'azote ont été également étudiées. Une dizaine de composts issus de plates-formes de compostage industrielles, comprenant des composts de déchets verts. des co-composts de déchets verts et boues, des composts de biodéchets (fraction fermentescible des ordures ménagères collectée sélectivement), et des composts d'ordures ménagères résiduelles (après collecte sélective des emballages propres et secs), ont été échantillonnés après trois, quatre et six mois de compostage. Afin de s'affranchir de la variable procédé de compostage, des composts ont également été élaborés en réacteurs de laboratoire à partir d'un procédé unique de compostage d'une durée de 3 mois et des proportions variables de déchets verts, biodéchets, et papiers-cartons. Une gamme de cinq classes de stabilité de la MO des composts a été définie sur la base de la minéralisation résiduelle du carbone des composts étudiés au cours d'incubations dans un sol de référence. La caractérisation de la Mo des composts a été réalisée à partir de fractionnement chimique (extraction des acides humiques et fulviques) et biochimique (composition en lignine, cellulose, hémicellulose, substances solubles), et par analyse en spectrométrie infrarouge à transformée de Fourier (IRTF), et a permis d'interpréter les différences de vitesse de stabilisation. Le degré de maturité étant défini par le niveau de stabilisation de la MO des composts, le classement de stabilité défini précédemment a servi de référence pour la validation d'indicateurs de maturité. Au cours du compostage, les composts évoluent vers des produits aux caractéristiques de plus en plus proches, indépendantes de leur origine, mais les vitesses de stabilisation dépendent de l'origine des composts. On observe généralement une disparition rapide de la cellulose quand l'azote n'est pas facteur limitant. La dégradation plus lente de la lignine par rapport à la MO totale conduit à son enrichissement relatif au cours du compostage. Les mesures IRTF confirment l'augmentation du rapport d'aromaticité au cours du compostage. La prédominance dans les déchets initiaux, de déchets verts par nature riches en lignine, entraîne la stabilisation rapide de la MO des composts, que le procédé soit accéléré ou non. Les caractéristiques de la MO de ces composts évoluent peu entre trois et six mois de compostage. A l'opposé, la prédominance dans les déchets initiaux, de papiers par nature riches en cellulose, requiert une durée de compostage plus longue pour arriver à des composts stabilisés, sans doute en raison d'un déficit en azote. De ce fait, les composts d'ordures ménagères, plus riches en papiers -cartons, sont encore instables au bout de trois mois, et nécessitent au moins six mois de compostage, avec retournements réguliers, pour se stabiliser. L'influence des biodéchets sur la vitesse de stabilisation des composts n'a pas pu être mise en évidence, car ils ne représentent qu'une faible proportion de la masse sèche des mélanges initiaux. A partir du fractionnement biochimique, on définit l'indice de stabilité biologique (ISB) des composts, indicateur de la proportion de matière organique susceptible d'entretenir la MO des sols. Pour les composts de déchets verts, la faible augmentation de leur ISB couplée à la minéralisation de leur MO au cours du compostage, se traduit par une légère diminution de leur valeur amendante en fin de compostage. En revanche, l'importante stabilisation de la MO des composts d'ordures ménagères au cours du compostage entraîne une augmentation de leur valeur amendante entre trois et six mois qui reste toutefois plus faible que celle des composts de déchets verts. La biodisponibilité potentielle de l'azote des composts, évaluée à partir d'incubations de mélanges sol-compost apparaît faible. L'azote des composts stabilisés se minéralise lentement. L'incorporation au sol des composts instables provoque une forte immobilisation de l'azote du sol, suivi d'une phase de minéralisation à des vitesses supérieures à celles observées avec les composts stables. Parmi les indicateurs de maturité étudiés, le rapport d'humidification (RH=CAH/CAF) est le seul indicateur chimique fiable, un RH inférieur à 1 désignant un degré de maturité faible, et un RH supérieur à 1.3 désignant un degré de maturité élevé. Le test d'auto-échauffement est le test de terrain le plus pertinent. Ces deux indicateurs permettent d'évaluer de façon fiable le degré de stabilisation des composts, et d'en déduire des conseils sur leur période d'apport, en tenant compte des risques d'immobilisation de l'azote dans les sols liés à leur utilisatio

STABILISATION DE LA MATIERE ORGANIQUE AU COURS DU COMPOSTAGE DE DECHETS URBAINS : Influence de la nature des déchets et du procédé

Composting is a process of biological treatment of organic wastes which reproduces the natural process of organic matter humification in soil. Today in France, only 7 % of the urban wastes are composted, although the organic part represents 50 % of the 47 million tons produced annually. Composts are mainly used in agriculture to increase or to maintain soil organic matter concentration. Their behavior after soil incorporation depends on the stability of their organic matter (OM).In this work, we studied the evolution of compost OM characteristics during composting, in relation with their origin (nature of the composted wastes and process of composting) and evaluated the potential storage of OM in soil with their use. The relation between the residual biodegradability of compost OM and the potential availability of nitrogen in soil was also studied.Ten urban composts made from municipal solid wastes, biowastes, green wastes or sewage sludge, coming from industrial composting plants were sampled after three, four and six months of composting. To avoid the influence of composting process, eight composts elaborated in laboratory reactors from variable proportions of green wastes, biowastes, and papers-cardboards, were followed during three months. A range of five classes of compost OM stability was defined on the basis of mineralization kinetics of compost carbon during incubations in a reference soil. Compost OM was characterized by chemical (humic substances) and biochemical (lignin, cellulose, hemicellulose and soluble fraction) fractionation and by analysis in infrared spectrometry (FTIR). The degree of compost maturity was defined from the level of compost OM stability and the range of stability previously defined was used as reference for the validation of various indicators of maturity.During the composting process, all composts evolved towards products with similar characteristics and independent from the composted waste and process that only influenced the rates of stabilization. In most cases, the cellulose fraction rapidly decreased when nitrogen was not limiting. The slower degradation of lignin as compared to total organic matter led to its relative enrichment in compost OM. The IR spectra confirmed the increase of aromaticity during composting.When greenwastes were dominant in the composted wastes, their initial high lignin concentration explained the fast stabilization of OM during composting and little evolution was observed between three and six months of composting. On the contrary, composts made from municipal solid wastes, initially richer in cellulose materials (papers-cardboards) with a relative lack of nitrogen, were not stabilised after three months of composting, and required at least six months of composting, with turning, to be stabilized. The influence of biowastes on compost OM stabilization was not pointed out, probably because they only represent a weak proportion of the dry mass of the initial mixtures.From the biochemical fractionation results, an indicator of the proportion of stable OM in compost was calculated (Biological Stability Index, BSI). This stable fraction of compost OM contributes to soil OM upkeep or increase after compost application. For greenwaste composts, BSI little increased during maturation and the simultaneous decrease of total compost OM made lightly decreased their efficiency to soil OM upkeep. The reverse was observed for municipal solid waste composts. Their important stabilization during maturation made increase their BSI. Of this important stabilization resulted a relative increase of their efficiency for soil OM upkeeping between three and six months of composting.A small potential availability of compost nitrogen was estimated from incubations of soil-compost mixtures. The organic fraction of nitrogen of stabilized compost mineralized slowly. On the contrary, a strong immobilization of soil nitrogen occurred after incorporation of unstable compost, followed by a faster mineralization than observed with stable compost.Among the tested indicators of maturity, the humification ratio (RH=CHA / CFA) was the more reliable chemical indicator. RH values smaller than 1 indicated a lack of maturity, and RH larger than 1.3 corresponded to stabilized composts with high maturity levels. The self-heating test was the most relevant to be used on composting platforms. These two indicators allowed a correct estimation of compost OM stabilization level, from which recommendations could be made on the optimal period for soil incorporation, taking into account the risks of nitrogen immoblization.Le compostage des déchets organiques reproduit le processus naturel de transformation dans le sol, des matières organiques fraîches, d'origine animale et végétale, en matière organique humifiée, communément appelée humus. C'est une pratique ancienne, dont on trouve des témoignages dans les lointaines civilisations romaine et même égyptienne. Mais l'évolution des déchets suit étroitement celle des sociétés, et les déchets du passé qui étaient essentiellement organiques (effluents d'élevages, déchets alimentaires, résidus végétaux...) renferment aujourd'hui une gamme très hétérogène de produits (déchets verts, déchets alimentaires, effluents d'élevages et industriels, papiers, emballages plastiques et métalliques,...). Aux composts « artisanaux » destinés à un usage très local se sont ajoutés les composts industriels visant à digérer les déchets des collectivités et des industries agro-alimentaires, pour les valoriser en agriculture. Cette diversité des déchets, accentuée par la diversité des procédés de compostage conduit à une grande variabilité des composts produits

Stabilisation de la matière organique au cours du compostage de déchets urbains (influence de la nature des déchets et du procédé de compostage - recherche d'indicateurs pertinents)

PARIS-AgroParisTech Centre Paris (751052302) / SudocSudocFranceF

Use of urban composts for the regeneration of a burnt Mediterranean soil: A laboratory approach

Supplement : "Environmental Risks and Problems, Strategies to reduce them through Biotechnology and Engineering"International audienceIn Mediterranean region, forest fires are a major problem leading to the desertification of the environment.Use of composts is considered as a solution for soil and vegetation rehabilitation. In this study, wedetermined under laboratory conditions the effects of three urban composts and their mode of application(laid on the soil surface or mixed into the soil) on soil restoration after fire: a municipal wastecompost (MWC), a compost of sewage sludge mixed with green waste (SSC) and a green waste compost(GWC). Carbon (C) and nitrogen (N) mineralisation, total microbial biomass, fungal biomass and soilcharacteristics were measured during 77-day incubations in microcosms. The impact of composts inputon hydrological behaviour related to erodibility was estimated by measuring runoff, retention andpercolation (i.e. infiltration) of water using a rainfall simulator under laboratory conditions. Input ofcomposts increased organic matter and soil nutrient content, and enhanced C and N mineralisation andtotal microbial biomass throughout the incubations, whereas it increased sporadically fungal biomass.For all these parameters, the MWC induced the highest improvement while GWC input had no significanteffect compared to the control. Composts mixed with soil weakly limited runoff and infiltration whereascomposts laid at the soil surface significantly reduced runoff and increased percolation and retention,particularly with the MWC

Long-Term Survival of Pathogenic and Sanitation Indicator Bacteria in Experimental Biowaste Composts

For economic, agricultural, and environmental reasons, composting is frequently used for organic waste recycling. One approach to limiting the potential risk from bacterial food-borne illnesses is to ensure that soil amendments and organic fertilizers are disinfected. However, more knowledge concerning the microbiological safety of composted substrates other than sludge and manure is necessary. Experimental in-vessel biowaste composts were used to study the survival of seeded Listeria monocytogenes, Salmonella enterica subsp. enterica serotype Enteritidis, and Escherichia coli. Four organic waste mixtures, containing various proportions of paper and cardboard, fruits and vegetables, and green waste, were composted in laboratory reactors with forced aeration. The physicochemical and microbiological parameters were monitored for 12 weeks during composting. The survival of bacteria over a 3-month period at 25°C was assessed with samples collected after different experimental composting times. Strain survival was also monitored in mature sterilized composts. Nonsterile composts did not support pathogen growth, but survival of seeded pathogens was observed. Salmonella serovar Enteritidis survived in all composts, and longer survival (3 months) was observed in mature composts (8 and 12 weeks of composting). Mature biowaste composts may support long-term survival of Salmonella serovar Enteritidis during storage at room temperature. E. coli and L. monocytogenes survival was observed only in 4-week-old composts and never in older composts. Proper composting may prevent long-term survival of E. coli and L. monocytogenes. These results suggest that like composted sewage sludge or manure, domestic waste composts may support pathogen survival. Survival was not related to the physicochemical characteristics of the composts

bioindicateurs d'impact du recyclage de produits résiduaires organiques en sols cultivés: lien avec la disponibilité de micropolluants organiques et métalliques

National audienc