Hydrogen sulphide in a fattening pig barn operated with inhouse acidification

With in-house acidification treatments, the pH value of slurry is reduced to a target level of approximately 5.5. It is a promising option for ammonia emission abatement since an emission reduction can be achieved over the entire manure chain which includes housing, manure storage and application. Acidification is done through addition of sulfuric acid (H₂SO₄) to slurry in a reactor outside of the livestock housing. The acidified slurry is returned to the channels in the house. The excretions of the animals immediately end up in an acidified environment where the equilibrium between NH₄⁺ and NH_3,l is shifted towards NH₄⁺. Through the addition of H₂SO₄, further sulphur is available which can be potentially converted to H₂S. This induces concerns for enhanced formation of H₂S that is highly toxic to humans and animals. Long-term workplace exposure limits given as 8-h time-weighted averages is 5 ppm with a 15 min exposure threshold of 10 ppm in the EU. The aim of this study is to present data from H₂S concentration measurements in a fattening pig housing with 400 animal places in 16 pens littered with straw pellets with a partly slatted floor before and after installation of an in-house acidification method.

In 2021, H₂S concentrations were measured in the barn using portable gas detectors "PAC 6500 and Multiwarn II" from Dräger and with electrochemical sensors (range of 0.1 - 100 ppm). Four measurement campaigns were conducted. One of them was conducted before the acidification was operative and three campaigns with acidification in summer and winter with and without ventilation of the slurry channels. The number of measurement periods was 5 for the reference measurement and 6 to 14 for the measurement with acidification. The duration of a measurement period was 10 to 104 min, with less than 20 min occurring only in the summer campaign with 14 measurement periods.

H₂S was exclusively detected when channels were flushed. Outside of periods with flushing, H₂S concentrations were below the detection limit of 0.1 ppm. The maximum average over 15 minutes value was 20.2 ppm which was obtained without acidification. With slurry acidification, no exceedance of the 15 Min threshold of 10 ppm occurred, as the maximum H₂S concentration was 4.8 ppm. Overall, the mean H₂S concentrations with slurry acidification (0.14 ppm) were lower than without acidification (1.44 ppm). The mean values of measured H₂S concentrations in winter (0.16 ppm) were higher than in summer (0.06 ppm) due to higher barn ventilation rate in summer. The use of the ventilation system in slurry channels reduced H₂S concentrations to 0.16 ppm compared to 0.30 ppm without ventilation. This can be explained by the inhibition of sulfate reduction by microorganisms at a pH of 5.5.

Overall, in-house slurry acidification did not enhance H₂S concentrations in the investigated pig barn which agrees with previous studies.