The saying: "You can't judge a book by its cover" is being shunned by some producers who believe the cover they use for their lagoons may, in fact, be the measure by which it is measured. In other words, you won't smell a lagoon if it's covered.
Under pressure from government regulation and encroaching development, producers are experimenting with ways to "cover-up" the smell of their lagoons.
A new cover system, the Bio-Cap, is being marketed by Baumgartner Environics Inc. (BEI), an ag environmental consulting firm based in Olivia, MN. The Bio-Cap is a synthetic, permeable material that floats on top of a lagoon.
The textile matting material is most commonly used in construction under roadbeds. BEI found that by heat-welding sections of the matting material together, an effective lagoon cover can be economically fabricated on-site.
BEI's Wade Jager says the cover reduces the release of gas in two ways. First, he says, the fabric prevents large volumes of odor-causing gases from being stripped from open storage structures due to wind, wave action and rain.
The second manner of control comes from the permeable material allowing oxygen to diffuse from the atmosphere into the surface of the fabric. The presence of oxygen allows aerobic bacteria to flourish and to break down malodorous gases before they pass through the Bio-Cap to the atmosphere, says Jager. In this process, hydrogen sulfide and volatile organic compounds (two of the primary components of odor) are reduced.
BEI has experimented with a number of ideas for covers and began testing the Bio-Cap idea in September 1998. The cover was installed at a facility near Renville, MN, that houses 7,680 nursery pigs, 2,880 grower/feeder pigs and 4,800 finishing hogs. The primary stage of the lagoon measures 402 x 687 ft. A secondary stage measures 232 x 652 ft.
The site, owned by ValAdCo, a producer-owned cooperative, had generated odor complaints from neighbors and was being monitored by the Minnesota Pollution Control Agency (MPCA). The MPCA set up a continuous ambient monitor at the property boundary to record the concentration of hydrogen sulfide emissions. In Minnesota, a 30 parts per billion (ppb) ambient air quality standard cannot be exceeded twice within five days. Frequent spikes above this standard had the MPCA putting pressure on ValAdCo to find a solution.
Fortunately for ValAdCo, the Bio-Cap did the trick. Compliance has been maintained since the cover went on. ValAdCo has since installed Bio-Caps at four different sites.
Iowa State University ag engineer Dwaine Bundy evaluated the odors coming from the two-stage, earthen, anaerobic treatment lagoon system at one new site and at a ValAdCo site with no cover. The lagoons at the covered site are 202 x 252 ft., 17 ft. deep with manure from a three barn, 1,200-sow, breed-to-wean set-up. The "control" site is a four barn, 2,100-sow set-up with two lagoons, each measuring 322 x 427 ft., 17 ft. deep. Both sites are run with similar genetics and nutrition.
Bundy collected bagged samples to present to a trained panel of human sniffers. Data from that panel shows a five-fold reduction in odor for the covered compared to the non-covered lagoons. The hydrogen sulfide data shows a 10-fold reduction.
Using an on-site measurement, Bundy showed the odor downwind was non-detectable at 370 ft. with the covered lagoon. The uncovered lagoon still had an odor threshold of 1.9 at 950 ft., the farthest distance measured. (Odor threshold is defined as the number of volumes of fresh air needed to mix with one volume of odorous air to just be detectable.)
Jager says the idea of the Bio-Cap is to keep it simple and take advantage of natural processes. "We've eliminated the need for flares and incur virtually no operating costs," says Jager.
"The use of floating, porous covers on waste storage systems is a successful modification to the idea of biofiltration," says James Zahn, Livestock Emission Solutions, Indianapolis. Zahn, a microbiologist, researched lagoon management at Iowa State. He notes that the processes of anaerobic decomposition that occur in the stored waste and the aerobic treatment of the gaseous pollutants evolved from the anaerobic treatment are decoupled in two separate processes. Thus, odor reduction is done without severely reducing the nutrient value of the manure, says Zahn.
The cover also limits wave action and the resulting erosion of basin sidewalls, notes Jager. And, the Bio-Cap covers the sidewalls, controlling weeds, he says.
The synthetic material performed well throughout the Minnesota winter, accommodating the freezing and thawing process, says Jager.
Bundy suspects water will evaporate more quickly from a Bio-Cap-covered surface than from an open surface. The cover material is black and generates some heat, enhancing the process.
Jager thinks the biggest challenge to the Bio-Cap will be durability of the material under sunlight. Ultraviolet light will eventually break down the cover, says Jager, but he expects the life span of the cover to be three to five years. At that point, the cover would be removed and burned, if local law permits, or brought to a local landfill.
BEI will install the Bio-Cap cover system for about $1.25/sq. yd., with some variation on size of lagoon and travel requirements. Installation is relatively simple as no framework is required for suspending the Bio-Cap. A six-man crew can cover 3/4 of an acre of lagoon per day. Based on a three-year amortization of the cover and average manure production figures, the cost is about 15-45 cents/pig.
Another cover system is being tried a mile west of Williamsburg, IA. Gary Boland's family has raised livestock there for three generations. Boland knows that if another generation is to farm there, odor concerns will have to be addressed, especially as plans for a new school and golf course are moving Williamsburg ever closer.
Boland has a relatively small, 120 x 120 ft., 700,000-gallon storage lagoon. "We've never had complaints. It's a pretty ag-minded community and our family has maintained good relations."
But Boland thought it best to be pro-active and, working with Iowa State extension, decided to develop a lagoon cover. He called Reef Industries, Houston, which markets a non-permeable, synthetic material called Permalon.
Boland and Mark Moser, Resource Conservation Management Inc., Berkeley, CA, designed a lagoon cover using the synthetic Permalon material. Floating foam "logs" keep the cover buoyant, raising and lowering with the lagoon level. Boland dug a U-shaped trench around the berm of the lagoon and laid the edges of the cover through the trench, burying it to anchor the cover.
A slit in the material provides a "door" for agitation and pumping access. The slit is closed tight with grommets and rope. A layer of water on top helps keep the cover from flapping in the wind. Since the material is not permeable, Boland had to put together a burner system to flare off the gases that collect under the cover.
Boland says he spent about $14,000 on the cover. With a fence around the lagoon, the burner, and some tiling the entire project cost should total close to $20,000. As part of a demonstration project, he received some cost share funds.
"My neighbors never told me the smell was bad, but when I got done a number of them commented they sure appreciated what I had done," says Boland.
His wife also appreciates the project. "She puts the laundry on the line now; she was never willing to do that before we put up the cover," he commented.