A dewatering system that uses
geotextiles developed from a joint research project with the US Army
Corps of Engineers Ten Cate Geotube—and given a try-out at the
University of Georgia dairy farm—offers farms the opportunity to reduce
manure transportation costs.
A dewatering system that uses geotextiles developed from a joint research project with the US Army Corps of Engineers Ten Cate Geotube—and given a try-out at the University of Georgia dairy farm—offers farms the opportunity to reduce manure transportation costs.
Farm operations that are faced with the problems associated with additional manure generation that could limit their growth or government regulations that are causing them to transport manure effluent greater distances at a higher cost now have a new option. A manure dewatering technology is available that could make hauling of manure solids greater distances less expensive than the traditional method of pumping, hauling, and applying manure effluent with tanker trucks.
The Geotube Nutrient Recovery System can be installed between a manure gathering system at the barn and the lagoon, or to remove and store solids from an existing lagoon for land application at some future date at the farm’s convenience.
Agri-Waste Technology Inc (AWT) headquartered in Raleigh, North Carolina, is one of several companies that have partnered with the Geotube technology designer, Ten Cate Nicolon, to introduce and market the technology to the agriculture industry. “It’s still in its early stages as far as market penetration into the agricultural industry,” says AWT senior project manager, Kevin Davidson. “We’re seeing increased interest as more pressure is put on different producers to manage the solid level and sludge accumulation in their lagoons.”
AWT is confident there will be a growing market for Geotube technology. It believes that producers are well aware of the problem of solids build-up in lagoons and that it is going to become an issue. Also, with a greater emphasis on phosphorus in farmland Nutrient Management Plans—because of concerns over potential groundwater contamination—farmers will be required to take more corrective action to limit the amount of organic phosphorus they apply to farmland.
The first step in the Geotube system is to conduct a rapid dewatering test or a cone test using a small lagoon sample to determine the amount of chemicals needed, if any, to optimize the dewatering process. Next, a larger scale evaluation is conducted using a Geotube hanging bag test. It evaluates between 20 and 40 gallons of waste material to accurately estimate the cost and efficiency of implementing this technology.
Once implemented, the manure—either directly from the barn or from a storage lagoon—is agitated and pumped into the patented Geotube bag. With smaller lagoons, this can be accomplished with a tractor-powered agitating pump. With larger lagoons, it may require a floating dredge.
The Geotube bag’s fibrous material and construction is part of the technology that resulted from a Construction Productivity Advancement Research program between Ten Cate Nicolon and the US Army Corp of Engineers. The partnership spent two years and committed several million dollars for research and actual field application to prove the feasibility and benefits of this geocontainment technology, which uses specially developed high strength geotextiles with unique filtration and retention properties. When field-tested, it proved to have immediate environmental and economic benefits for both government and industry.
The bag can be filled with fine grain sludge, hazardous contaminated soils, or dredged waste materials. The geotextile’s unique weave and fabrication creates small pores that contain the fine grains of the contained material. Effluent water drains from the Geotube bag through the small pores in the geotextile. In the case of agricultural applications, the effluent flows onto a drainage media over an impermeable ground cover that drains the effluent water by gravity flow into a storage facility, such as a lagoon.
|Manure is agitated and pumped—either directly from the barn or from a storage lagoon— into the patented Geotube bag. Water within the effluent drains from the bag through the small pores in the geotextile, and solids are retained. Once the bag is full, it is cut open.|
Water within the effluent drains from the Geotube bag through the small pores in the geotextile, and in the case of agricultural application, onto an impermeable ground cover that drains by gravity flow into a storage facility, such as a lagoon. The filtered effluent can be used, for example, to irrigate land as needed.
Davidson says it is extremely important to place the bag on a flat surface with only a small slope to assist with drainage. In the event of the system being located in line between the barn and lagoon, the owner will need to use a sump pump to transport the water to a holding facility such as a storage lagoon or tank.The removal of the water significantly reduces the volume of the sludge. The volume reduction allows for the repeated filling of the Geotube bag until it is completely filled with dewatered solids.As the retained solid material is stored in the bag, the bag contents continue to consolidate because much of the remaining water will evaporate. Once the bag is full, it is cut open. The farmer is left with solid nutrients that can then be applied as natural fertilizer to farmland. The bag itself can be landfilled or used in the farm operation for erosion control.
“If you can get the effluent to a more condensed state, that means you are not going to be hauling as much water,” says Davidson. “Then your costs are going to come down from a trucking standpoint and also from a time standpoint.” That’s because in the case of existing lagoons, the sludge can be dewatered at any time and the solids stored in the bag. Therefore, this job can be done during non-peak crop management periods. Storage and recovery of the solid material for fertilizer can also be planned so that it is available for application as a natural fertilizer at the appropriate time during the crop rotation cycle.
The recommended bag size depends on the amount of waste being generated by the operation and how often the farm owner wants to access the solids for use as fertilizer. Producers can do some of the work themselves to help bring the Geotube system cost down so that it is more comparable to pumping, transportation, and applying the manure with tankers. For example, they can do the site preparation, agitate the lagoon and pump the sludge into the bag themselves, and even take training so that eventually they can manage the chemical application on their own. Davidson recommends that they use the services of a professional chemical management company to start with.
The Biological and Agricultural Engineering Department at the University of Georgia saw an opportunity to test the technology in an agricultural application on its own dairy farm facility. The dairy farm lagoon had become overloaded with solids and the university was looking for a way to clean it out. After hearing about the Geotube technology, it appeared to represent a win-win situation where the university could solve its problem and provide valuable information to the agricultural industry. According to John Worley at the University of Georgia, sludge application at the source can be a challenge in many areas.
“We’ve got a lot of cases where the fields right around the lagoon are saturated with nutrients, and farmers can’t apply a lot more nutrients to them,” he says. There are also a number of existing old lagoons that have been closed where the land around the lagoon has been sold. So there is no longer access to this land to dispose of the lagoon solids.
|The removal of water significantly reduces the volume of the sludge. The volume reduction allows for the repeated filling of the Geotube bag until it is completely filled with dewatered solids. The farm is left with solid nutrients that can then be applied as natural fertilizer to the farmland.|
“Using the Geotube technology would allow the lagoon owner to get the effluent down to a dry form so that it can be hauled greater distances,” he says.
The university tested the Geotube system for two years, the first year without any chemical additives. It filled three Geotube bags in that year and Worley says, “it worked fairly well.”
The second year, the university filled three more bags but used the chemical additives, including alum and a polymer. “That worked better, but it added to the cost,” he comments.
While the university found the Geotube system to have potential in specific applications, it did require fairly close monitoring of the chemical additives to ensure that more wasn’t being used than was required. “What we were pumping was constantly changing,” he says. “Sometimes it was thicker than at other times, therefore we were having to adjust the chemicals we were adding. We pulled samples of effluent periodically into a beaker and inspected it to see what it looked like, and adjusted the chemical additives based on that.”
When asked about the environmental friendliness of the chemicals that aid in the separation process, he says the polymer is an organic compound that breaks down and is absorbed into the natural environment without cause for concern. In terms of the alum, he says farmers need to ensure that their cash crop is not sensitive to aluminum. Because so little is actually used, “I can’t see that as being much of a problem.”
Worley says he could see where this dewatering technology would offer some advantages to farmers facing specific challenges. “The advantage is that you get the solids separated out from the liquid and you can store them in a bag and apply them when it is to your advantage, rather than while you are pumping, as in the case of a conventional system. You can also haul the solids longer distances.”
Ten Cate Nicolon claims that with proper use, more than 90 percent of effluent solids can be removed from the liquid, farmers can achieve over 90 percent phosphorus and heavy metal removal, and achieve a 50 percent nitrogen reduction. It also claims to create a measure of odor control from the effluent.
While the technology is new to the agriculture industry, it has been successfully used in a variety of other applications, such as managing sludge residue from municipal waste systems, the pulp and paper industry, and a variety of other industrial installations. The Army Corps of Engineers is now specifying the Geotube system as the best management practice for dewatering contaminated marine dredge materials. The contaminated sediments are removed from rivers, bays, harbors, marinas, ports and dock facilities, and then pumped directly into Geotube containers for containment and dewatering.
The Geotube system is also designated as a Practice Standard (632) by the United States Department of Agriculture Natural Resource Conservation Service. Therefore, it can qualify for up to 75 percent matching funds under the Environmental Quality Incentives Program.