Cédric Francou

Influence of green waste, biowaste and paper–cardboard initial ratios on organic matter transformations during composting

The influence of green waste, biowaste and paper-cardboard proportions in initial mixtures on organic matter (OM) evolution during composting in pilot-scale reactors was studied using respirometric procedure, humic substance extraction, crude fiber analysis and Fourier transform infrared spectroscopy. The stabilisation of OM during composting resulted from the degradation of easily biodegradable organic fraction as cellulose and hemicellulose, the relative increase of resistant compounds as lignin, the microbial synthesis of resistant biomolecules, and from humification processes. Little stabilisation of green waste OM during composting was observed, in relation with their large lignin content. With moderate contents of paper-cardboard in initial mixtures (20-40%), cellulose proportion remained favorable to fast OM stabilisation. Larger proportions of paper-cardboard (more than 50%) affected OM stabilisation, probably due to a lack of nitrogen. The influence of biowastes only appeared at the very beginning of composting, because of their large proportions of easily biodegradable OM.

Stabilization of Organic Matter During Composting: Influence of Process and Feedstocks

Information on compost organic matter stability is necessary to anticipate the effects of compost application on soil properties. Such information will soon be required by French legislation. The main objectives of the present work were: (1) to study the influence of the composting process and the composted waste on the kinetics of stabilization of organic matter during the composting process; (2) to validate physicochemical indicators of compost stabilization and also rapid tests used by the compost producers on the composting plants in order to be able to follow compost stabilization during the process. Ten compost windrows were sampled after 3, 4 and 6 months of composting at plants where green wastes (GW), biowastes (BIO), sludge (SG) or municipal solid wastes (MSW) were composted. In some plants, the composting process was accelerated by enforced aeration. The stability of the organic matter was assessed by laboratory incubations during which organic matter mineralization was followed. Maturity tests were run on compost samples which were then analyzed. For the GW, BIO and SG composts, the stabilization of organic matter occurred more rapidly than for the MSW composts and 3 to 4 months were enough for satisfying organic matter stabilization. For the MSW composts, 6 months were necessary to reach stabilization similar to the GW or BIO composts. The self-heating test was highly significantly correlated with the compost organic matter stability as evaluated from the incubation results and should be recommended to the compost producers rather than the Solvita test. Among the physicochemical characteristics of the composts, total organic C (TOC) appeared to be well correlated with organic matter stability of the composts and a better indicator than the C/N ratio, pH, electrical conductivity and N-NO3−/N-NH4+ ratio. The humic and fulvic acids (C-HA + C-FA) represented 9 to 27 percent of TOC and the humification index (C-HA/C-FA) was also well-correlated with organic matter stability.

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

ABSTRACT 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.

Agronomic Value and Environmental Impacts of Urban Composts Used in Agriculture

Agronomic value and environmental impacts of three composts (a biowaste compost, BIO; a municipal solid waste compost, MSW and a compost made from green wastes co-composted with sewage sludge, GWS) are compared to those of farmyard manure (FYM) in a long-term field experiment located in Feucherolles (Yvelines, France) and initiated in 1998. The first compost spreading occurred in October 1998 and maize was sown in spring 1999.

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

In 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, we determined 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 waste compost (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 soil characteristics were measured during 77-day incubations in microcosms. The impact of composts input on hydrological behaviour related to erodibility was estimated by measuring runoff, retention and percolation (i.e. infiltration) of water using a rainfall simulator under laboratory conditions. Input of composts increased organic matter and soil nutrient content, and enhanced C and N mineralisation and total 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 significant effect compared to the control. Composts mixed with soil weakly limited runoff and infiltration whereas composts laid at the soil surface significantly reduced runoff and increased percolation and retention, particularly with the MWC.