CMS4SMWJ

3086

8 avril 2021 10:12

8 avril 2021 10:12

Animal production increased regularly since some decades, in developed countries at first, and now in developing countries. Industrial systems have been developed to increase rapidly the productivity of animal farms and to supply the food consumed by the towns. They are efficient in terms of biosecurity and of feed conversion efficiency but they have severe environmental impacts such as the odor emissions, the ammonia or greenhouse gas emissions, or the water pollution. The sustainability of these systems depends on their ability to limit their impact on resource depletion and to limit their leakages so that the wild environment and the biodiversity can be preserved beside the producing areas. Expensive treatment systems can not be used because of economical reasons. Ecological engineering provides concepts that can help finding solutions more efficient economically and ecologically. Our work began with the starting up of a new system of animal production that associates a pig house with manure flushing and screening, a vermifilter, lagooning, and constructed wetlands. This system was designed to increases the recycling efficiency of water and to produce biomass for animal feed, fertilization, biogas, etc. The system combines high manure dilution, which allows a decrease in polluting emissions, to the reuse of water and nutrients. Water is reused for excretion flushing. The nutrients are either reused within the farm or exported. The needed surface is around 50 times less than for manure spreading. The fundamental objective of the present work was to improve the understanding of the system to define more precisely its advantages and its limits. The applied objective was to study if this new knowledge was useful to improve the design and the management of this system. Specific methods were developed to study from the process or from a systemic point of view a recycling system that was too large to be reproduced in a laboratory. They were applied to the gaseous emissions of the vermifilter and to the treatment efficiency of the combination of lagoons and constructed wetlands. The results show that an "optimal transfer" of liquid can be defined that will maximize the earthworm population (preferendum). Above this input the earthworms die because of anoxic conditions. When earthworm population is maximal, the ammonia and the greenhouse gases are minimized as related to the input flux. Therefore, the earthworm abundance can be used as a bioindicator of low energy and low emissions in manure transforming systems. The effect on gaseous emissions is mostly indirect, through the influence of earthworms on the structure of the organic layer, its free air space, transfer of organic particles and its microbial population. This "optimal transfer" between two successive levels also exists for the vegetation production of lagoons and constructed wetlands. If we compare "recycling" to "open" system, the water recycling will induces a change in the stoechiometry of nutrients, because of the various treatment efficiencies of elements: for example, potassium abatement rate is less than nitrogen abatement rate; this case induces an increase in potassium concentration in the water compared to nitrogen. Potassium concentration reaches a stable level when the retention by all subsystems corresponds to a mass decrease equivalent to the potassium excreted by the animals. This case shows that the stoechiometry of nutrients should change in agricultural systems with increased recycling efficiency. Calculating the mass balance of the system shows that ammonia and greenhouse gas emissions were low, regarding the nitrogen fluxes, and that the organic products (worm casts and sludge from lagoons) were the major contributors to the removal of nutrients. Recommendations for the design and management of systems that improve manure recycling are proposed, based on this knowledge. Our results were and can be further used for socio-economical purposes.

None

• AB - Modalité bio
• earthworms
• FREDO durabilité
• FREDO effluents et litière
• FREDO environnement
• ammonia
• biodiversité
• boue
• eau
• lagunage
• lombrifiltration
• nutrient
• recyclage
• élevage

2011/06/21

21 juin 2011