You can do everything in your power to properly manage hog manure to cut odor before it reaches the lagoon, but if you treat your lagoon like a waste basin, instead of a treatment system, all of your effort could be wasted.
"A lagoon has a permanent volume that is designed to continue treating the incoming manure and biologically stabilize that manure," stresses Terry Feldmann, consulting agricultural engineer from Peoria, IL.
In contrast, with an earthen manure storage basin, the goal is to pump it down as far as you can. Feldmann says, "You should pump it empty as often as necessary but usually once or twice a year."
With a lagoon system, you want to stop pumping when you reach the treatment level, he explains (Figure 1). This layer and the sludge layer comprise the bottom two layers of your lagoon.
The sludge volume consists of two layers of sludge. But Feldmann views them as separate layers.
"The bottom one is thicker, more inert sludge, not very active biologically. The majority of the sludge, particularly in a newer lagoon, I call the active sludge layer because it does support some biological stabilization."
Over time, the inactive, lower sludge level builds up and starts to intrude on the treatment volume.
"When you don't have enough treatment volume, common in older lagoons, you start to see them become more odorous," says Feldmann.
Most lagoons are designed for a 10- to 20-year sludge volume and life span.
How do you properly manage and extend the life of your lagoon?
Feldmann explains: "It depends on how a producer pumps their lagoon down. I like to recommend that producers do some agitation of that lagoon so that they get some of the sludge stirred up in the bottom and get more of the solids and sludge out." Do this on an annual basis, he suggests, and consider having a professional custom manure applicator do the job. They have the equipment and the know-how, he stresses.
The other problem is many producers will just pump out the top of their lagoons, which consists of waste and wash water, net precipitation and dilution water (Figure 1). "Just pumping out the top can be a real problem, over time, because your sludge volume will accumulate at a faster rate," he explains.
Many lagoon odor problems also occur with improper lagoon startup. This happens during the first year or two, while the lagoon is still maturing and establishing its bacterial populations.
Feldmann believes the best startup procedure is to pump some manure from an existing lagoon, which already has active bacterial development, to the new lagoon. That gets the odor-reducing, methanogenic bacteria going. That's the "good" bacteria that forms methane gas. As an alternative, precharge your lagoon with fresh water. Whether using effluent from an existing lagoon or fresh water, you should bring the level up to the top of the treatment level.
Once going, monitor your lagoon and periodically add some dilution water to minimize buildup of salts, minerals and toxic compounds like high levels of ammonia. Ammonia, combined with low temperatures, inhibits the growth of methanogens, bacteria that digest odorous volatile fattyacids compounds.
Lagoon recharge can be especially critical if you live in a dry climate where evaporation exceeds rainfall much of the year, Feldmann cautions.
The other key lagoon management tip is "feed" your lagoon regularly. "Bacteria are living organisms just like we are and they like to be fed regularly," he says. Daily is best. Less regular feedings cause surges and declines in microbial populations. The resulting imbalance will tip the scales to favor the odorous compounds.
Also, don't skip feeding and then try to make up for it by "slug loading" or over-feeding your lagoon. It will increase odor levels, warns Feldmann.
To establish the correct loading rates and pumping rates for your lagoon, contact an agricultural engineer or environmental specialist.
Walk the berms of your lagoons regularly, he suggests. Check for wet spots, burrow holes, sloughing and other signs of berm degradation. Record the level of freeboard. Mow right up to the freeboard so you can inspect the condition of the side slopes easily.