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Treatment of the fibre/solid fraction

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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Short description

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.

Best Available Technique: Not indicated
Objective

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.

Level of complexity

Usual scale

Innovation stage

General diagram

Applied to







Typical technology combinations Adding bulking agent, composting
Pictures

Illustration of on farm composting (first to third columns) and centralized composting of solid cattle manure, Juncosa, Spain (fourth column).

Theroetical fundamentals and process description

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.

Environmental effects

Effects on air (emissions):

  • Possible emissions of NH3, COVs and CH4
  • CH4 is produced when the composting matrix has anaerobic zones
  • The use of close systems (tunnels), or semi-permeable membranes, as well as efficient aeration, can reduce emissions.
Expected emissions CH4-C N2O-N
g/kg VS degraded 8.1 - 13 0.047 - 0.176
CO2eq (g/kg VS degraded) 271 - 418 22 - 83

 

Effects on water/soil (and management):

  • Production of an organic fertilizer (compost) with part of the original nitrogen and most of the P, K, etc. Its application to soil makes nutrients recycling possible to soil and field crops. When the system is open, up to 30-50% N is lost during composting of pig manure and straw.

Other effects:

  • Organic matter stabilization, pathogens and seeds removal, and odour abatement (during the thermophilic phase).
Biosecurity aspects Not indicated
Technical indicators

Conversion efficiency:


  • Volume and weigh reduction: 40-50%
  • Conversion of ammonia to NO3 and organic nitrogen (40 – 70%)
  • Concentration of nutrients and heavy metals (due to water evaporation)
  • Organic matter stabilization, pathogens and seeds removal, and odour abatement.
  • Net energy consumption - explanation:

    The guidance consumptions of the possible machineries used in a composting plant are:

     

    Energy consumption (KWhel/t)

    Trommel  3.0
    Magnet separator  0.5 
    Shredding and crushing 2.6
    Container composting (11 days) 10  
    Waste gas purification of 11 days intensive composting  8.1
    Conversion of the secondary maturing stage windrows in door composting, every 14 days for 8 weeks  10
    Waste gas purification (8 weeks) 19.3 

     

  • Reagent 1 - explanation:

    • Bulking agent in different proportions
    • Water: 250-650 L/t manure
    • Possible use of inoculum to start up the process, or chemical agents to reduce odour emission
Observations

Composting can be applied at farm scale (exists many experiences), but composting in centralized plants could benefit of scale economy.

Economic indicators (Economic figures are rough indications, which cannot be used for individual project planning)
  • Investment cost:

    Equipment:

    • Turner machinery (windrow composting): 30,000 € (100 m3/h) / 100,000 € (1,000 – 1,500 m3/h)/ 180,000 (2,500 m3/h)
    • Tractor: 50,000 €
    • Mixers: 20,000- 50,000 € (10-100 m3/h)
    • Drum sieve: 70,000 (100 m3/h)

    Full plant (investment cost):

    • Turned windrow composting plant (2,000 t/y manure + 1,360 t/y sawdust): 35,000 – 100,000 € (depending on the buildings or covers constructed)
  • 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.

Literature references
  • Ahn, H.K., Mulbry, W., White, JH.W., Kondrar, S.L. (2011) Pile mixing increases greenhouse gas emissions during composting of dairy manure. Bioresource Technology 102: 2904-2909.
  • Barrington, S. Choinière, D., Trigui, M., Knight, W. (2002). Effect of carbon source on compost nitrogen and carbon losses. Bioresource Technology 83: 189-194.
  • CBMI (2010). Best available Technologies for manure treatment- For intensive rearing of pigs in batic sea region EU member states. Baltic Sea 2020. pp. 103
  • de Guardia, A., Mallard, P., Teglia, C., Marin, A., Le Pape, C., Launay, M., Benoist, J.C., Petiot, C. (2010). Comparison of five organic wastes regarding their behaviour during composting: Part 2, nitrogen dynamic. Waste Management 30: 415 – 425
  • Hao, X., Chang, C., Larney, F. J., Travis, G.R. (2001) Greenhouse gas emissions during cattle feedlot manure composting. J. Environ. Qual. 30: 376-386
  • Levasseur P. (2004) Traitement des effluents porcins. Guide Pratique des Procédés. Institut Technique du Porc. pp.36
  • Zhu, N. (2007). Effect of low initial C/N ratio on aerobic composting of swine manure with rice straw. Bioresource Technology 98: 9-13
Real scale installation references

Many full scale plants at farm level as well as centralized plants. E.g.:

  • Composting Plant Juncosa de les Garrigues (Catalunya, Spain)
Examples of suppliers