Tropical storm threatens wastewater lagoons in eastern US

An article in the News & Observer, North Carolina, US, describes impacts of tropical storm Ernesto on animal feeding operations that manage wastes in liquid form. After more than a foot of rain in some regions and with more on the way, many wastewater storage lagoons are filled to the brim and in danger of overflowing or breaching, although no spills have yet been reported. To prevent catastrophe, poultry and hog producers particularly are faced with the expensive options of temporarily moving animals to drier locations or trucking wastes to off-site facilities with excess capacity. The alternative is untenable: pumping wastewater onto saturated ground and polluting water sources.

Water-based waste handling, treatment and storage systems have been attractive to producers because they allow dilution, gravity flow and pumping through conventional pipelines and irrigation equipment. But because better treatment efficiency is in part a function of larger lagoon surface area, and because every manured lot and alley open to the sky produces contaminated runoff from rainfall, the storage and treatment ponds must be designed to hold enormous quantities of precipitation in addition to animal wastes. Designs must also allow for the storage of unusually heavy rainfalls coming at the most unfortunate times, particularly at the end of the storage season or when crops are nearing harvest. Keeping excess rainfall and uncontaminated runoff out of the system can be very expensive, requiring the roofing-over of outdoor lots and alleys, tanks and lagoons, and diverting roof runoff and upstream overland flows.

Handling more wastes as solids can present management challenges, but with the challenges come opportunities to extract value from the operation. The most significant aspect of lagoon treatment systems is the biological transformation of nitrates and nitrites to atmospheric nitrogen, and the off-gassing of ammonia nitrogen. All that nitrogen was captured at a large energy cost, particularly so with the conversion of natural gas to nitrogen fertilizers used to grow animal feed, and cannot be recycled as crop nutrient. Solid waste storage, composting and similar low-water processes can retain much more of the nitrogen, and in forms that are less volatile and fugitive in the environment, that is, more likely to stay where it's put until used by a growing plant. Enterprises such as manure trading and the production of commercial soil amendments then become possible. Less dilute liquid wastes have the potential for anaerobic digestion for renewable natural gas energy production.

It's all a matter of treating what happens beyond the back end of an animal to be just as important as what comes before; it's not a complete farming operation if resource management is not a fully integrated consideration.
© 2006 Livestock & Ag Waste Intelligence