Didier Oudart

Modelling nitrogen and carbon interactions in composting of animal manure in naturally aerated piles

Composting animal manure with natural aeration is a low-cost and low-energy process that can improve nitrogen recycling in millions of farms world-wide. Modelling can decrease the cost of choosing the best options for solid manure management in order to decrease the risk of loss of fertilizer value and ammonia emission. Semi-empirical models are suitable, considering the scarce data available in farm situations. Eleven static piles of pig or poultry manure were monitored to identify the main processes governing nitrogen transformations and losses. A new model was implemented to represent these processes in a pile considered as homogeneous. The model is based on four modules: biodegradation, nitrogen transformations and volatilization, thermal exchanges, and free air space evolution. When necessary, the parameters were calibrated with the data set. The results showed that microbial growth could reduce ammonia volatilization. Greatest nitrogen conservation is achieved when microbial growth was limited by nitrogen availability.

Modeling organic matter stabilization during windrow composting of livestock effluents

Composting is a complex bioprocess, requiring a lot of empirical experiments to optimize the process. A dynamical mathematical model for the biodegradation of the organic matter during the composting process has been developed. The initial organic matter expressed by chemical oxygen demand (COD) is decomposed into rapidly and slowly degraded compartments and an inert one. The biodegradable COD is hydrolysed and consumed by microorganisms and produces metabolic water and carbon dioxide. This model links a biochemical characterization of the organic matter by Van Soest fractionating with COD. The comparison of experimental and simulation results for carbon dioxide emission, dry matter and carbon content balance showed good correlation. The initial sizes of the biodegradable COD compartments are explained by the soluble, hemicellulose-like and lignin fraction. Their sizes influence the amplitude of the carbon dioxide emission peak. The initial biomass is a sensitive variable too, influencing the time at which the emission peak occurs.

Design of an integrated piggery system with recycled water, biomass production and water purification by vermiculture, macrophyte ponds and constructed wetlands

Since 2001 the swine experimental station of Guernévez has studied biological treatment plants for nutrient recovery and water recycling, suited to the fresh liquid manure coming out of flushing systems. An integrated system with continuous recycling was set up in 2007, associated with a piggery of 30 pregnant sows. It includes a screen, a vermifilter, and macrophyte ponds alternating with constructed wetlands. The screen and the vermifilter had a lower removal efficiency than in previous studies on finishing pigs. A settling tank was then added between the vermifilter and the first lagoon to collect the worm casts. A second vermifilter was added to recover this particulate organic matter. A storage lagoon was added to compensate for evaporative losses and complete pollution abatement, with goldfish as a bioindicator of water quality. The removal efficiency of the whole system was over 90% for COD and nitrogen, over 70% for phosphorus and potassium, and more than 4 logarithmic units for pathogens (E. coli, enterococci, C perfringens). Plant production was about 20 T DM ha(-1) y(-1). Floating macrophytes (Azolla caroliniana, Eichhornia crassipes, Hydrocotyle vulgaris) were more concentrated in nutrients than helophytes (Phragmites australis, Glyceria aquatica,…). Azolla caroliniana was successfully added to feed finishing pigs.

Extensive Treatment System For Recycling Water For Flushing Fresh Manure And Recovering Nutrients

From preliminary researches on a pilot scale, a complete demonstration plant was built to treat the effluents of a 30 pregnant sow’s piggery. It includes a screen, a vermifilter, a macrophyte lagooning, and a complementary water storage pond; the recycled water is used for flushing, and rainfall is collected to compensate for evapotranspiration. After functioning in 2008 and 2009, it was showed that, during the warm season, the whole plant produced an effluent suitable for flushing, where the concentration decrease was over 70% for the phosphorus and potassium, 95% for the COD and nitrogen, 99.8% for endocrine disruptors (estrogenic activity), and 99.99% for pathogenic micro‐organisms. During the cold season, the dilution by the rain water and the treatment effect of the constructed wetlands lead to similar results. Nevertheless, for this season, suitable floating macrophytes that will cover the lagoons remain to be settled.