Processing methods particularly suitable for solid manures or solid fractions obtained after separation. The descriptions of these livestock manure processing technologies were based on 'Flotats, Xavier, Henning Lyngsø Foged, August Bonmati Blasi, Jordi Palatsi, Albert Magri and Karl Martin Schelde. 2011. Manure processing technologies. Technical Report No. II concerning “Manure Processing Activities in Europe” to the European Commission, Directorate-General Environment. 184 pp."
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Aerobic biological decomposition and stabilization under conditions which allow development of thermophilic temperatures as a result of biological heat, with a final product sufficiently stable for storage and beneficial soil application.
The main objective is to obtain a stable product with low moisture content and most of the initial nutrients, free of pathogens and seeds, called compost. The significant reduction of mass (water evaporation) reduces substantially transport costs.
Illustration of on farm composting (first to third columns) and centralized composting of solid cattle manure, Juncosa, Spain (fourth column).
Compost is obtained through a thermophilic aerobic degradation process of the organic matter, followed by a curing phase where temperature slowly decreases and complex organic macromolecules are produced (fulvic and humic acids).
In the first stage (decomposition), exothermic reactions produce an increase of temperature of the composting matrix above 50ºC (55-70ºC). Aerobic conditions must be assured in order to enable the reaction. Mechanical turning of the piles, as well as forced aeration are commonly used. The high temperatures, together with aeration, leads to a high rate of water evaporation. Water must be provided and maintained to a certain level to avoid microbes inhibition. In a second stage, curing is produced. Complex organic matter is degraded and humic and fluvic acids are produced. Temperature slowly decreases till room temperature. The whole process lasted between 8 to 16 weeks.
Adequate initial conditions of the composting matrix: Moisture content: 40-65%, C/N ratio: 25-35. Porosity (AFP: Air Filled Porosity): 30-60%.
Solid manures usually need the addition of bulking agent (e.g. well-chopped straw) in order to have appropriate C/N ratio, structure and porosity. When applied to slurries a previous mechanical separation is necessary.
Composting of liquid manures requires abundant bulking agent, in order to absorb the water and have an adequate C/N ratio.
Effects on air (emissions):
Effects on water/soil (and management):
Net energy consumption - explanation:
The guidance consumptions of the possible machineries used in a composting plant are:
Energy consumption (KWhel/t)
Reagent 1 - explanation:
Composting can be applied at farm scale (exists many experiences), but composting in centralized plants could benefit of scale economy.
Full plant (investment cost):
Operational costs - explanation:
As a guidance: 20€/ton
Quantifiable income - text:
Sales of compost (guidance price): 15 - 30 €/t
Non economically quantifiable benefits:
Favours closing the nutrient cycle, consequently the consumption of fossil fuels used to synthesize chemical fertilizers is reduced.
Many full scale plants at farm level as well as centralized plants. E.g.: