Heated and insulated sample tubes
of PTFE (outer diameter: 8 mm, inner diameter: 6 mm, Mikrolab A/S,
Aarhus Denmark) for the venting outlet in each section and the common
fresh air supply were flushed continuously (ca. 5 L min
–1) by a pump with a PTFE membrane (Capex L2, Charles Austen Pumps Ltd.,
Byfleet, UK) placed in an insulated room next to the sections. The
concentrations of methane, carbon dioxide, and ammonia was measured
by cavity-ring down spectroscopy (CRDS) using G2201-i, G4301, and
G2103 analyzer models (Picarro Inc., Santa Clara, CA, USA). The VOCs
and hydrogen sulfide were measured by proton-transfer reaction mass
spectrometry (HS-PTR-MS, Ionicon Analytik, Innsbruck, Austria) during
periods 1 and 4. The CRDS analyzers were connected to the outlet from
the Teflon pump using a 10-way PEEK valve (VICI, Houston, TX, USA)
and PTR-MS with a five-way PEEK valve (Bio-Chem Valve Incorporated,
Boonton, NJ). Measurements were performed in a continuous cycle with
two measurements per hour for each outlet for methane, carbon dioxide,
and ammonia and one measurement per hour for VOCs and hydrogen sulfide.
The VOCs measured were methanethiol, trimethylamine, acetic acid,
propanoic acid, butanoic acid, pentanoic acid, 4-methylphenol, and
skatole. These VOCs together with hydrogen sulfide were chosen as
they are found in high concentrations in air from pig sections and/or
have low odor threshold values.
15 (link)−17 (link) The PTR-MS was operated with
standard drift tube conditions: a voltage of 600 V, a pressure between
2.1 and 2.2 mbar, and a temperature of 75 °C. The inlet temperature
was 75 °C. The rate constants used were based on previously reported
values,
15 (link),18 (link) and the hydrogen sulfide concentration was
corrected for humidity dependence.
15 (link)Temperature, relative humidity, airflow rate in each section, and
the temperature outside were recorded every minute by a log system
(VengSystem A/S, Roslev, Denmark). Calibrated measuring fans were
used to estimate the airflow rate (Reventa, Horstmar, Germany). In-house
air temperature was measured 1.7 m above the floor over the pen partitioning
and ca. 1/3 from the back end of the section using a calibrated temperature
sensor of the ventilation control. Slurry temperature (PT100, Campell
Scientific, Logan, UT, USA) was measured in sections C and WF in the
bottom of the slurry pits.
Dalby F.R., Hansen M.J., Guldberg L.B., Hafner S.D, & Feilberg A. (2023). Simple Management Changes Drastically Reduce Pig House Methane Emission in Combined Experimental and Modeling Study. Environmental Science & Technology, 57(9), 3990-4002.