A case study of two dairy manure management systems
April 29, 2009 by By Patrick Nortz C.P.G. P.E.; Timothy Krause P.E.; and Thomas Menke
As the world economy drives livestock farmers to produce more food at
less cost per animal, larger livestock operations become more
prevalent. Many modern farms house hundreds to sometimes tens of
thousands of livestock on site. These livestock operations produce a
more concentrated volume of manure.
As the world economy drives livestock farmers to produce more food at less cost per animal, larger livestock operations become more prevalent. Many modern farms house hundreds to sometimes tens of thousands of livestock on site. These livestock operations
|Photo 1: Sand lane, vertical concrete wall, access ramp, and solid stacking slab at Burdock Hill Dairy|
produce a moreconcentrated volume of manure. In turn, the operations seek increasingly better ways of laying out the farm operation to: maintain animal health; improve manure transfer, treatment, and utilization; and minimize costs and labor. This article presents basic concepts for wastewater treatment systems for dairy operations that utilize available resources on the farm to maximize treatment. We follow that explanation with examples of systems that incorporate these concepts. The examples provided here will help show how selection and proper operation of manure management system (MMS) can increase the profit of the business, take full advantage of the nutrient value of the wastewater in crop production, and improve environmental protection.
The Decision-Making Process
It stands to reason that farmers want, or even expect, their MMS to help realize a return on their investment. The challenge is to design and operate a MMS that will provide a return on investment within an agreeable timeframe. Each farm is different, thereby requiring a different MMS. To help recognize a return, farm managers need to make decisions on what benefits given by the MMS will be the most beneficial to the farm. During the decision-making process, farm managers should leverage their assets. For example, a farm’s assets could include: that there is nobody around for miles (in other words, odor complaints may not be their primary concern); they have personnel who likes to tinker with systems and would make a good treatment-system operator; or a nearby landscape operation that can use the manure byproducts for compost.
|Figure 1 – Flush-Flume/Sand-Lane System flow diagram|
An important consideration is the variability of the waste stream produced on the farm. Variability is most often a function of weather. Depending on whether the climate is arid or moist, the manure waste stream can operate with a “fresh” supply of water or be drier (i.e., thicker). Weather can also impact the volume of contaminated storm water that comes in contact with stored feeds and outside feedlots, thereby affecting the waste stream. Variability in a waste stream makes it essential to choose a system that is robust enough to handle changes in consistency of the waste stream. If you select components that require a consistent waste stream to function properly, there is a good chance you will end up with something that works about half the time.
In almost every case, the two commonly overlooked farm assets are time and space. Many of the traditional wastewater-treatment technologies being transferred to MMS were designed to quickly treat the manure waste stream in an area similar to typical municipal wastewater treatment systems. Quick treatment comes with increased costs for maintenance, operation, and energy. These are all costs that the farm pays for directly. If a MMS is designed properly from an ideal storage and operation perspective, it should cost a farm virtually nothing for treatment to occur. Typically, a larger land footprint is required for “passive” manure treatment components. These treatment components take longer to treat the manure but use less energy and have less operation and maintenance needs. Fortunately, most farms have available land to accommodate manure treatment components with a larger footprint.
|Photo 2 – Separated fibrous solids using a screw press.|
Considering System Benefits
Aside from leveraging assets, several potential benefits need to be considered. Most farmers understand the benefits of various treatment components. But an in-depth analysis may help determine what MMS component or system makes the most economic sense for their farm. A dollar value can be assigned to some benefits while others are harder to measure.
Potential benefits of an engineered MMS can be determined by measuring the cost of labor, energy inputs, maintenance, fuel, and by-product reuse. Some less measurable benefits of a MMS are odor control, environmental protection through pathogen and nutrient removal, and avoiding conflict with the government agencies or the community. The remainder of this article presents the benefits two dairies recognized by installing engineered MMSs that utilize the farm’s assets.
Flush-Flume and Sand-Lane System
Burdock Hill, located in Hastings, Michigan, is a 550-head dairy. As part of an expansion in 2008, they constructed a flush-flume/sand-lane system. The farm uses sand bedding and has automated alley scrapers. Prior to the expansion of the farm, the parlor wash water and silage runoff was stored in one pond while the sand-laden manure was stored in pits at the ends of each barn. The capacity of the storage units was limited, thereby requiring frequent spreading of sand-laden manure.
Dan and Chris Javor, the owners of Burdock Hill, did their homework prior to selecting a new MMS. After deciding on a flush-flume/sand-lane system, they visited other farms that had similar systems. The Javors observed the other systems in operation and talked with the owners and operators of those systems. They wanted a design that took advantage of the 30-foot elevation change across their farm. They identified specific system components that would increase the efficiency of treating the sand-laden manure waste stream and improve the overall farm operation.
|Photo 3 – Constructed slurry pond at Vreba-Hoff Dairy|
Burdock Hill retained NTH Consultants, Ltd., of Grand Rapids, Michigan to assist with the design and installation of the system. One floating pump charges the entire system by pumping up to the flush flume starting at the parlor holding area. The flush flume transfers manure from each of the free-stall barns, incorporating the previously existing automated scrapers. The scrapers deposit sand-laden manure into the flush flume through drop chutes located at the ends of the barns. To collect manure at the end of each barn, the flush flume is laid out with six 90-degree turns. The sand-laden manure flows from the flush flume into the sand lane. The sand lane has a vertical concrete wall along one side and a concrete access ramp along the other side. A sloped stacking area is located along the same side as the access ramp.
The sand that settles out in the sand lane is recovered and “stacked” on the solid stacking slab. The water content in the sand seeps out and the sand is eventually reused as bedding. The sand lane is connected to a series of three settling basins. The basins are designed to allow for the finer sand particles and fibrous organic solids to settle out. The manure in the settling basins has the highest fertilizer nutrient value. The accumulated solids slurry is removed from the first settling basin around every three months. The solids slurry is spread on cropland via a tanker. The liquid slurry in the second and third settling basins is applied via a drag hose. The third settling basin empties into an earthen storage structure where the liquid is stored until it can be irrigated onto growing crops. Approximately half of the liquid in the storage structure is permanent and is used for recirculation in the flush-flume system.
Recognized Benefits of a Flush-Flume/Sand-Lane System
The Javors identified several benefits with the new system, including achieving their original goal of having an efficient MMS using only one pump. They also reported system benefits with respect to reduced labor, maintenance, and fuel. Prior to installing the flush-flume/sand lane system, Burdock Hill was rebuilding tanker pumps every few months and paying approximately $3,000 in equipment fees each time. Since Burdock Hill installed the system in early 2008, the farm has not needed to rebuild a pump. In summary, Burdock reports reductions in:
- fuel use;
- tire wear/purchase;
- pump repair/maintenance (no pump rebuild since early 2008);
- labor (nearly 80 percent less); and
- sand purchase (up to 80 percent is reused).
The benefits of the flush-flume/sand-lane system have exceeded the Javor’s expectations. They recognize this system may not be a perfect option for each farm but are satisfied with the results of combining transfer and treatment. This MMS did not come with an owner’s manual. Therefore, some trial and error was necessary. Some of the disadvantages of the system:
- the sand cannot be reclaimed when the temperature falls below approximately 25 degrees Fahrenheit;
- the reclaimed sand is not as clean as purchased sand (use of the reclaimed sand has not created problems when properly managed);
- and the system requires ample clean water to properly transfer and remove the sand.
Burdock Hill Dairy has a long history of managing the manure in an environmentally sustainable manner. Even before installing the flush-flume/sand- lane system, community relations were not a problem for Burdock Hill. As such, when Burdock Hill selected this MMS, environmental benefits like odor and pathogen reduction were not as critical as they may be with some larger farms.
Two Vreba-Hoff dairies located in Hudson, Michigan, were challenged with proper manure treatment as the dairies grew from several hundred head to more than 7,000 cows over a four-year period. The dairy expansions and a desire to use sand bedding prompted management to convert to a new system and replace the mechanically intensive Press Treatment System (PTS) that was in place before the expansion. The proprietary EarthMentor® manure management system (EMS) by Envirolytic Technologies, LLC was selected to help address an environmental mandate from the Michigan Department of Environmental Quality (MDEQ). The mandated standards required treating the manure for specific pathogenic-indicator bacteria (fecal coliform) prior to land application.
|Figure 2 – EarthMentor® Manure-Wastewater Treatment System|
The EMS takes advantage of various components of treatment and recycling. If sand bedding is used, the sand can be hydraulically separated to be reused as bedding. Fibrous solids are then removed by a screen separator or screw press. Fibrous solids may be: composted for re-use as bedding; or sold as an additive for compost or as a soil amendment. Composting provides pathogen control where required. After removal of inorganic and coarse solids (sand and fiber), additional fine solids (and the majority of the phosphorus) are removed through one settling basin or, preferably, two alternating settling basins. The settled fine solids are removed, as needed, from the settling basins and land applied as nutrient-rich slurry. The slurry contains a high concentration of phosphorus from the manure stream and is utilized as concentrated fertilizer source. Retention time of up to six months provides a measured reduction of fecal coliform bacteria in the slurry.
The wastewater is directed from the settling basins to a specifically engineered and sized anaerobic treatment cell, recognized by the U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS) and the U.S. Environmental Protection Agency (EPA) as an effective treatment component for pathogens, nutrients, and odors. By removing the majority of the solids prior to the treatment cell, the overall size of the anaerobic cell is reduced to efficiently treat the remaining organic portion of the wastewater. Similar results can also be achieved with EarthMentor® using aerobic treatments. Aerobic treatment generally requires less space but more energy, equipment, operation, and maintenance.
The top water from the anaerobic treatment cell is decanted into a storage structure. Within the storage structure the waste stream undergoes one final “polishing” treatment step. The water within the storage structure is irrigated onto growing crops at relatively high application rates and recycled as wash water for solids separation or other on-farm uses.
Envirolytic Technologies, LLC reports the EarthMentor® system, when properly operated, will treat water better than simple treatment lagoons by: removing pathogens that, if present, are concerns for human and accidental runoff impacts; reducing odors; and reducing nutrients to allow a greater degree of irrigation. The company also reports the system has several advantages over “single-stage lagoon” anaerobic treatment systems without solids pre-separation including: up to 80 percent less area is required for the treatment cells and cropland irrigation; fewer mechanical parts must be maintained (a well engineered system can be primarily gravity flow); and an estimated savings of manure handling of approximately $75 per cow per year over conventional manure-handling systems. The separated solids are reportedly easier to store and transport than un-treated liquid manure; distinct by-products (i.e., coarse solids, slurry, and treated water) are each used to the advantage of crop farmers; a smaller odor footprint; and a lower potential to cause adverse water-quality impact. The Earthmentor® system can be adapted to allow for aerobic treatment, which can be sized according to the pretreatment of manure prior to aeration.
The system is very forgiving and resilient with lots of backups (Michigan Farm News, June 15, 2007). Although the EarthMentor® system is designed for simple operation and low maintenance, the EMS requires increased management skills over traditional systems. Specifically, management must understand the system’s design and how to monitor benchmarks. If building the EarthMentor® system from scratch, the capital costs are greater than simplistic long-term holding pits. With prudent management of operation (e.g., not overloading the system), the payback for the upfront costs can be achieved by: sand (and/or coarse organic solids) recycling, more efficient treatment, replacing manufactured fertilizer purchase by full utilization of the partitioned nutrient by-products, and the potential to defend your operation against neighbors and regulators that may be unhappy with the odors and potential pathogen and water-quality impacts of conventional operations. Envirolytic Technologies, LLC reports that financial payback of the system can be achieved in less than two years, with ongoing return on investment opportunities after the initial payback period.
Recognized Benefits of EarthMentor®
Bob Gildea, environmental manager and operator of the EarthMentor® system at the Vreba-Hoff dairies, generally agrees with the EarthMentor® functions as claimed by Envirolytic Technologies, LLC. Bob could not validate the “$75 per cow per year” savings or payback period on the system, although he did agree with Envirolytic Technologies' claim of lower operational costs than conventional treatment systems that have greater reliance on mechanical features. Bob indicated the Vreba-Hoff dairies face ongoing challenges in achieving the water-quality standards mandated by the Michigan Department of Environmental Quality (MDEQ). He suggested that after the system has more time to catch-up in treating old stored waste, the water-quality criteria will be routinely achievable. The nutrient-containing treated water is now used for center-pivot irrigation onto adjoining crop fields. Because the treated water is more dilute than it was prior to Vreba-Hoff’s use of the EarthMentor® system, the water can be applied at greater quantities without causing water-quality impacts. In fact, Bob indicates that the system has continually met the biosolids “pathogen reduction standard.” The coarse solids captured at the front end of the system are applied to cropland as an organic soil conditioner. Bob reports routine contact from area crop farmers requesting these coarse solids. Piping the water to the adjoining fields reduces impact to pavement on area roads and greatly reduces fuel consumption associated with truck transport. One impressive statistic Bob shared is the irrigated treated water helped realize a 50-percent increase in crop yields.
The presented treatment systems take advantage of the farm’s land base and time, which are generally available to most livestock operations. By minimizing the costs, whether up-front or operational, and maximizing the benefits of the components of the waste stream, the featured wastewater treatment systems can be economically feasible. Though the systems are designed to be relatively simple in operation and maintenance, they are not self-operating. The desired returns on the investments will require the farm operators to increase the level of management and maintenance over conventional pump-and-haul systems.
Patrick Nortz, C.P.G., P.E., is a principal engineer with NTH Consultants in Michigan; Timothy Krause, P.E. is also with NTH Consultants; and Thomas Menke is with Menke Consulting of Greenville, Ohio, and a managing member of Envirolytic Technologies.