Stabilizing Feedlots Using Coal Ash
Debra Pflughoeft-Hassett, EERC
Tera Berland, EERC
Preliminary results of one of the largest, most comprehensive, and definitive studies confirm that coal ash effectively stabilizes soils in feedlots. The three-year project, being conducted by the University of North Dakota Energy & Environmental Research Center and the North Dakota State University Carrington Research Extension Center, demonstrates the engineering and environmental performance of coal ash, a by-product of combustion in coal-burning power plants. This utilization technique offers feedlot operators a low-cost method to improve feedlot conditions, animal health, animal weight gain, and odor control.
The objective of this project was to demonstrate the use of coal ash in feedlot surfacing and to provide feedlot operators with an environmentally safe, low-cost option to improve feedlot conditions, animal health, animal weight gain, and odor control.
Criteria being evaluated in the demonstration include placement techniques, engineering performance, environmental performance, and economics. The research team is comprised of the Energy & Environmental Research Center (EERC), Carrington Research Extension Center (CREC), and Power Products Engineering, Inc. Financial partners for this effort include Great River Energy, Otter Tail Power Company, the North Dakota Industrial Commission Lignite Energy Council, the North Dakota State Board of Agricultural Research and Education, and the U.S. Department of Energy National Energy Technology Laboratory.
Twelve pens (60 х 70 ft) were surfaced with three different regional ashes, and four pens were left untreated for comparative purposes. Coal ash was delivered in both pneumatic and bottom-dump trucks; however, it is recommend to use a bottom-dump truck to control dusting. Over 140 tons of coal ash was placed at the CREC pens on moist soil and was incorporated at a 6–8” depth using conventional farm equipment. Fly ash additions ranging from 12–28 percent were used to aid in determining the optimum level of fly ash.
The concrete aprons were constructed with a mixture of cement, bottom ash, and fly ash and placed using a cement truck.
As illustrated in Table 1, postplacement engineering monitoring included density testing, moisture content, and sampling for permeability. From an engineering standpoint, the treated pens are performing extremely well when measured against the control pens and have achieved the desired strength and durability. Strength tests indicated soil blended with coal ash was 3 to 6 times stronger than soil without ash. It is important to note that these results are dependent on the source of ash and amounts used and this figure is an average. Nuclear density testing indicated compaction levels of 89 percent to over 100 percent of maximum. Preliminary permeability results of the treated pens were low and ranged from 1.7 х 10-7 to 8.3 х 10-7 cm/s. In some pens, this number is approaching the U.S. Environmental Protection Agency recommended value of 1 х 10-7 cm/s for waste containment facilities.
Table 1: Engineering Performance Results
On-site visual evaluations are valuable and provide the best information on the engineering performance of the placed surfaces. Results indicate that when conditions are dry, control and treated pens look and perform similarly; however, during spring breakup, the treated pens performed much better than the control. This comparison is illustrated in Figure 1. In addition, during rainfall events throughout the summer, pen conditions were notably improved in the treated pens. Muddy conditions were reduced by as much as 2 to 3 days in the treated pens as compared to the untreated pens.
It was also noted that there was far less wear around the fence lines and concrete aprons in treated pens. At the time of pen cleaning, the untreated pens yielded a much higher volume of material that needed to be removed than treated pens.
Figure 1: Comparison of Treated vs. Control Pens
Postplacement environmental monitoring included four groundwater-sampling events and four runoff- sampling events. Groundwater analytical results for 38 samples collected indicate that the overall elemental concentration and physical parameters for individual monitoring wells are very stable and do not exhibit significant trends that would exceed typical elemental variability. Runoff results indicate that pens treated with coal ash meet North Dakota surface water standards, with the exception of boron, which is not a toxin to animals or humans. The pH levels were also measured. Data for the treated vs. untreated pens were similar and near neutral pH, with a range from 7.40–8.23.
A formal economic evaluation has not yet been completed; however, it is generally known that this type of utilization is an economical option for both utilities and livestock producers. In this study, animal performance monitoring revealed a significant cost savings for livestock producers. Results indicate that bison in the treated pens gained an average of .15 pounds per day more than bison in the control pens, saving producers $.06 per day per head for feed. It is anticipated that these figures will be even more significant for beef cattle.
It is anticipated that the positive environmental and engineering information generated as a result of this project will bring the North Dakota Department of Health closer to writing a beneficial use rule to place coal ash in feedlots. Currently, a permit is required to place coal ash in feedlots in North Dakota. A few states have adopted laws governing coal ash use in feedlot settings, but requirements vary widely among states. Applications for permission to use coal ash are frequently handled on a case-by-case basis or under generic state recycling regulations. States that do specify acceptable use applications for coal ash are the states where the most progress has been made regarding ash utilization.
It is predicted that over 200,000 tons of coal ash will be utilized per year in the northern Great Plains as a result of this demonstration. At the present time, only about 8% of the coal ash produced each year in the northern Great Plains is used, leaving nearly 3 million tons to be disposed of annually.