Lab-scale assessment of gaseous emissions from laying-hen manure storage as affected by physical and environmental factors.

摘要

Manure-belt (MB) and high-rise (HR) laying-hen houses are the two predominant housing types in the U.S. Compared with HR houses, MB houses have better indoor air quality and lower aerial emissions as a result of frequent (every 1 to 4 d) manure removal from the hen houses into separate manure storage. However, emissions from on-farm manure storage are integral parts of the whole-farm emissions and need to be quantified. This series of lab-scale studies assesses emission rates (ER) of ammonia (NH₃) and greenhouse gases (CH₄, CO₂, and N₂O) from stored laying-hen manure as affected by the following physical and environmental factors: air exchange rate (10 or 20 air changes per hour, or ACH), manure stacking configuration expressed as surface area to stack volume ratio (SVR at 2.5, 5, 10, or 20 m-1), air temperature (constant at 25 degrees C or diurnal cyclic from 21 degrees C to 32 degrees C), manure moisture content (MC, 50% or 77%), and periodic addition of new manure to the existing stack. Results of the studies showed the following: (1) air exchange rate of 10 or 20 ACH had no apparent effects on the gaseous emissions; (2) SVR significantly affected emissions, with larger SVR leading to higher NH₃ and CO₂ ERs but lower CH₄ ER on per kg manure basis; (3) emissions were positively related to air temperature; and (4) laying-hen manure with 77% MC had higher emissions than that with 50% MC. At the storage condition of 25 degrees C air temperature, 20 ACH, every 2 d addition of 120 kg (5 cm thick layer) manure at 75% MC (equivalent to 2 d manure production of 682 laying hens) to the flat base area of 2.8 m2, the daily gaseous ERs per hen were 0.06 to 0.22 g NH₃, 1.6 to 4.8 g CO₂, and 7.4 to 32 mg CH₄ (0.18 to 0.8 g CO_2e). N₂O concentrations from the stored manure were below the detection limit (0.03 ppm) of the measurement instrument; hence, N₂O emission was omitted from the presentation.