Adding the metabolic inhibitor molybdate to swine manure significantly reduces hydrogen sulfide emissions.
Tests over a six-month monitoring period compared a scale-model, open-manure holding system and in-room scale tests where the average concentration of hydrogen sulfide measured just above the surface of agitated fresh manure slurry was 831 and 88.4 ppm., respectively.
The addition of molybdate at 16 to 160 ppm levels reduced the emission of hydrogen sulfide to about 18 and 2.5 ppm, respectively.
A cost analysis for application of the molybdate treatment in the grow-finish stage of production of a 300-sow operation showed that total material and labor costs would amount to less than 1% of the overall production cost for each market hog.
The effect of manure age on control of hydrogen sulfide and the level of nitrite and molybdate required to control these emissions was studied using fresh, one-, three- and six-month-old manure. Laboratory tests were conducted in closed systems with 3.75-oz. bottles containing 0.9 oz. of manure, capped with a rubber septum. Different concentrations were tested.
Because results from the closed-system tests could possibly overestimate the required treatment level, experiments were conducted in semi-pilot scale with open-top containers in order to simulate practical conditions. These tests were conducted with six, open-top cylindrical containers, each filled with about 66 gal. of manure collected from the manure pit of a grow-finish barn. The molybdate solution was sprayed on the surface of the manure using a conventional hand pump sprayer. Sampling for hydrogen sulfide gas emissions was done on Days 10, 20 and 30 following the addition of molybdate.
In the room scale tests, a solution of molybdate was sprayed on 18-day-old manure slurry in a collection tub in a manure pit to achieve a final concentration of 16 ppm.
Figure 1  shows the hydrogen sulfide concentration levels of sealed serum bottles containing different ages of manure and the relative decrease in emission levels as the manure ages. With six-month-old manure, gas concentrations in the control bottles were below detectable levels.
For all treatment levels and regardless of manure age, the addition of molybdate caused an immediate decrease in the concentration of hydrogen sulfide gas emissions, which was maintained or decreased further during the 30-day monitoring period.
Higher levels of molybdate and increases in manure age both led to lower levels of hydrogen sulfide gas levels. All cases of treated manure recorded lower gas concentrations than the control cases.
Figure 2  shows concentrations of hydrogen sulfide gas from the open-top containers treated with various amounts of molybdate and the control group. Gas concentrations collected from the containers treated with molybdate were significantly lower than that of the control system. Increasing the amount of molybdate led to lower gas levels.
Room-scale chamber experiments also led to much lower hydrogen sulfide gas concentrations compared to laboratory and semi-pilot, open-top experiments.
Researchers: B. Predicala, Prairie Swine Centre; and L. Moreno and M. Nemati, University of Saskatchewan. For more information, contact Predicala by phone (306) 667-7444, fax (306) 955-2510 or e-mail [email protected] .