Preliminary results of a new surface aeration system pilot-tested at a 4,800-head, grow-finish operation show it provides an effective and affordable means of handling odors in lagoons.
The aerator module (Figure 1) features six venturi air injectors, which significantly increases aeration efficiency without altering power consumption.
Increased efficiency results in the establishment of an aerated layer in top lagoon liquid with a constant level of dissolved oxygen of greater than 0.3 mg./L at a depth of 6 in. from the lagoon's surface. This layer functions as a biological cover that prevents odorous compounds from escaping from the liquid, enhancing odor reduction.
In limited trials, the odor detection threshold (ODT) was reduced from around 3,000 to 1,200 in less than 10 days of continuous operation, according to the olfactometry analysis of air samples collected from the lagoon used in the experiment.
Surface lagoon aeration is not new technology. However, unlike earlier systems, the innovative engineering design developed by the University of Minnesota offers an economical alternative. Based on a 4.5-hp motor driving the system 24 hours/day, 365 days/year (with a definitely shorter period in cold climates), the total annual power usage will be 29,565 kWh (kilowatt hours) [24 hour/day × 365 days/year × 4.5 hp × 0.75 kW/hp]. In the equation, 0.75 kH/hp represents both horsepower and kilowatt hours, which are power consumption units.
The relationship between these two units is 0.75 kWh, which is equal to 1 hp. Based on $0.07/kWh and 2.5 production cycles/year, the cost/pig for this treatment is $0.17. As a rule of thumb, the cost for odor treatment should be below $1/pig.
The cost of the whole aeration system is expected to be very affordable to the vast majority of pork producers.
The project is being funded by a research grant from the USDA National Research Initiatives Air Quality Program.
Researcher: Jun Zhu, University of Minnesota Southern Research and Outreach Center at Waseca, MN. Contact Zhu by phone (507) 837-5625, fax (507) 835-3622 or e-mail [email protected].
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