Heat partition during composting
process of cattle manure
P. Robin
(2), S. Hacala
(1), J.M. Paillat
(2)(1)Bâtiments Fourrages Environnement Institut de l'Elevage B.P. 646
-14 avenue Jean Joxé - 49006 Angers cedex 01 (France) - tel: 02 41 96 77 37 - fax: 02 41 96 77 33
(2)INRAUMR Sol Agronomie Spatialisation de RennesQuimper
-65 rue de Saint-Brieuc – CS 84215 - 35042 Rennes cedex (France)
Introduction
Most of the literature deduce the heat production of the composting process from combustion heat of initial and final compost. There are few data on the heat partition during the composting of livestock manure.
Results and Discussion
Material and Methods
• continuous measurements during six weeks in controlled conditions;
• cattle manure from a commercial dairy cow housing; • one ton homogenised, and disposed in two small cells.
One heap was turned twice and the other not;
• measurements of sensible heat, water vapour and carbon dioxide lost by the cell;
• compost heat capacity estimated from the literature (Mears et al, 1975).
Air speed (TSI, 8450)
inside air: controlled temperature;
measurements : dry bulb, wet bulb,
CO2 compost temperature 3 cross-sections 3 distances to the heap bottom (20, 35, 45cm) Cell walls (wood+polystyrene +
plastic sheet inside)
outside air: controlled temperature;
measurements : dry bulb, wet bulb, CO2 heating inputs 500 kg cattle manure air inlet air outlet
TABLE 1 : MASS AND VOLUME OF THE TURNED OR NOT TURNED HEAP
not turned Turned
0 46 0 18 32 46
Volume(l) 1351 974 1346 999 814 616
Mass(kg) 548 302 555 359 269 221
Water (kg) 429 220 433 266 192 159
Moisture (kg water/kg mass) 78% 73% 78% 74% 71% 72%
• Increase in mass reduction (table) and heat production (graphs) by the turnings • Most of the heat production is water evaporation
• Heat stored represents about half heat production after turning until the maximum temperature is reached • Sensible heat ranges between 100 and 500 W per ton
• Both heaps keep warm whatever the turning
• These results suggest that cattle manure can supply significant heat on a farm even with extensive heat retrieval and without turning -100 0 100 200 300 400 500 600 700 0 10 20 30 40 Day Heat (W) heat stored latent heat em itted sensible heat em itted
TURNING TURNING -100 0 100 200 300 400 500 600 700 0 10 20 30 40 Day Heat (W) heat stored latent heat emitted sensible heat emitted
NOT TURNED 25 30 35 40 45 50 55 60 65 70 75 0 10 20 30 40 Day Temperature (°C)
not turned heap turned heap
