Researchers at the University of Minnesota are continuing research on reducing odor, hydrogen sulfide (H2S) and ammonia (NH3) emissions from manure storage with straw and geotextile covers.
In a controlled study at the university, researchers found that a 0.3 mm geotextile (permeable and floats) membrane topped with either 8 or 12 in. of straw reduced manure odor, H2S and NH3 emissions by more than 70%. The on-campus research followed field trials and tested both hog and dairy manure. The study used 32 PVC columns (4.6 ft. deep and 15-in. internal diameter) to represent deep pit systems. Manure was added at a rate of 1 gal. every two weeks, and increased the depth by 1 in. with each addition. The columns were covered with straw and/or a geotextile material. Straw thickness was 4, 8 and 12 in. and geotextile thickness were 0.3, 1.1 and 2.4 mm. A total of 16 cover combinations were tested with each type of manure, including a control column with no cover. Researchers took a total of 320 air samples and measured for odor, H2S and NH3.
The geotextile cover reduced odor from 10% to 45%, depending on the thickness of the material. H2S was reduced by 10% to 35% and NH3 emissions dropped from 8% to 27%.
The tests on a 4-in. layer of straw alone revealed 60, 69 and 61% reductions in odor, H2S and NH3, respectively. Odor and gas emissions were reduced 80% with a 12-in. layer of straw.
The combination of a geotextile membrane covered with straw resulted in lower percent reduction in odor and emissions than straw alone.
The researchers hypothesize that the smoother geotextiles allow more gases to move sideways. In a storage lagoon, the gases would need to move longer distances to escape from under the cover and may be trapped, thus improving the odor and gas emissions.
With straw alone, the surface is rougher and more gas moves up into the straw layer instead of moving sideways. The gases get trapped in the straw, oxidized by microorganisms and, therefore, result in less odor emissions.
The researchers found support for the concept that a reduction of odor and gas emissions involves both a liquid-to-air interface exchange and biofilter effect. They also note that the biofilter effect of straw could be more significant than the physical barrier effect, as shown by greater reductions of odor and gas than the geotextile covers.
The geotextile may also serve a practical purpose as a barrier between the manure and the straw and may keep the straw layer from sinking in the lagoon under some specific conditions (from early spring until late fall or until snow starts falling).
The researchers suggest that more data should be collected from field units, possibly with improved methodology to accurately access performance. Larger tanks (375 gal.) will be used to evaluate the covers in wet/dry conditions and during freeze/thaw cycles.
Researchers: Jose Bicudo, David Schmidt, Larry Jacobson and Kevin Janni, University of Minnesota. Phone Jacobson at (612) 625-8288 or e-mail [email protected]