second National Workshop Constructed Wetlands for Animal Waste Management, May 15-18, 1996; Ft. Worth, Texas.

Production of Energy, Aquaculture Products and Cattle from an Integrated Feedlot System

Nick C. Parker, PhD; Texas Cooperative fish & Wildlife Research Unit 1; Texas Tech University Lubbock, TX 79409-2120

Clifford B. Fedler, PhD; Civil Engineering, Texas Tech University, Lubbock, TX 79409 1023

1Jointly supported by Texas Parks & Wildlife Department, Texas Tech University, the National Biological Service, and the Wildlife Management Institute


Abstract

About 5 million head of cattle are produced annually from about 200 feedlots in the Texas High Plains. At any time, there are about 3.5 million head standing in the feedlots for an average of about 17,500 head per lot. Most of the feed provided to these animals passes through the animals and is excreted as nitrogen-rich manure. Annually, the 3.5 million head of cattle produce about 61 billion Ibs of wet manure (88% water) containing 347 million Ibs of nitrogen. If anaerobically digested, this manure would yield about 50 million ft3 of biogas, or about 50 billion BTUs daily. Assuming a 30% conversion efficiency from biogas to electricity, the daily yield would be 4.4 million kWh/yr. At $0.0751kWh the value of electricity used on-site would be about $120 million annually. However, using cogeneration, 90/. of the energy in waste heat could be utilized to heat buildings, steam treat grain, etc. The value of this heat is about $45 million annually. Most of the 347 million Ibs of nitrogen would still be available as fertilizer and, valued at $ 1/lb of nitrogen, would be valued at $347 million. The sum of these revenue sources is ova $500 million annually and does not include the value of water, or other byproducts, such as fish and plants, produced from an integrated system.

A demonstration unit to treat the effluent from a 1000 head cattle feedlot is under construction at the Texas Tech University Animal Science Farm. This system employs a 20-ft deep anaerobic pit for production and capture of biogas, a shallow pond for production of aquatic plants, and a pond for production of fish or other aquatic species. At $0.075 per kWh, the electricity produced from the biogas and used on-site would be valued at about $22,000 annually. The energy from cogeneration to heat buildings, etc., would be valued at $14,600 annually. The value of the nitrogen in the anaerobic effluent would be $100,000 annually when priced at $1/lb Plants such as duckweed and knots grass will be used to extract nutrients from the water and recycled to cattle as feed. Additional crops include bait fish, sport fish and tropical fish produced in greenhouses. Similar systems expanded to treat the wastes from the 3.5 million head of cattle in feed1Ots on the Texas High Plains could yield revenues well over $500 million annually. These new agnbusinesses would not only produce revenues, but would also improve the environment though extraction of nitrogen compounds, capture of gaseous emissions, reduction of odor, and creation of wildlife habitat in constructed wetlands.

lntroduction

The bulk of grains produced in Texas are from farms located on the Southern High plains This intensive agricultural region overlies the Ogalalla Aquifer and relies on water from the aquifer for much of the agricultural production. The concentration of grains and other feeds on the High Plains, in addition to the climatic conditions, attracts the cattle feedlot industry. About 25% of the nation's 22 million cattle slaughtered annually are from the nearly 200 feedlots on the High Plains. Other confined animal units are now planned or are being built to house and annually produce up to 100,000 head of swine at a single location. The manure associated with these cattle and swine production units are a major source of nitrogenous compounds found in surface and ground water. The quantity of water available for irrigation has declined from 90% of all the fresh wata used in the world at the beginning of this century to 70% currently. By year - 2000, only 60% of the world's fresh water is expected to be available for irrigation (Bouwer, 1994). Treatment and reuse of water on-site will be essential if irrigation and animal production units are to meet the demands of the growing human population (Parker et al., 1991). This proposed demonstration unit will use existing technology to extract nutrients from non-point surface waters collected as runoff from animal production units, thereby improving quality of water reaching the playa lakes associated with feedlots.

Background

Our primary goal is to demonstrate an integrated solution to the environmental problems resulting from the hundreds of dairies and intensive cattle feeding operations in Texas. We intend to demonstrate conversion of livestock generated biomass into miao-organisms, aquatic plants and animals including the purple sulfur bacterium, Thiopedia (60 percent protein on a dry weight basis), microalgae and fish. The primary market for the single cell protein, microalgae and fish will be as a dietary ingredient in feeds for fish, livestock, and poultry. Methane produced in anaerobic lagoons will be collected and used as an energy source on-site for heating, drying and to produce electricity.

Contamination of water sources, especially for ground water, presents a critical problem in Texas. The Texas Water Commission has reported that 37 surface water bodies have been contaminated and another 70 water sources have been impacted to some degree by pollutants (TWC, 1990). The worst of the contamination problems in Texas has been caused by some of the 30 million Ib/week of dairy waste that has reaches the Upper North Bosque River (Jensen, 1991). In fact, pollution from cattle feeding operations is the single largest contributor to water pollution surpassing pesticides, which most citizens perceive as the mayor contributor (Aurelius, 1989; Sweeten and Melvin, 1985; Sweeten et al.., 1990; TWC, 1989). In Texas over 44 million tons of livestock and poultry waste is produced annually, which must be treated or recycled to avoid environmental contamination. This is a significant waste problem from an industry worth almost $11 billion in Texas alone, not accounting for the other business entities such as feeds that also depend on livestock and poultry production for sales.

Clearly, the environmental impact of animal waste is being felt throughout the nation and certainly in Texas. Poultry producers in Shelby county, dairy farmers in Erath beef producers in West Texas, and pork producers in central Texas are all economically affected by the problem of waste disposal. The Environmental Protection Agency has fined dairy farmers in Texas for ground water pollution. If no feasible answer is found to alleviate the waste handling situation the negative economic impact to the State will be enormous.

The demonstration project is an expansion of technology developed from an existing facility designed to culture the marine microalgae Spirulina using anaerobically digested biomass from cattle feedlots (Fedler et al., 1993; Fedler & Parker, 1993; Parker et al., 1992a; Parker et al., 1992b). Cattle feedlots located in the Texas High Plains are typically located on sloping ground - draining into a playa lake. In the Southern High Plains, playas serve as major recharge sources for the underlying Ogallala Aquifer. Nutrient loading into playas threatens ground water quality (Fedler and Parker, 1994a). An integrated treatment system to remove nutrients, produce on-site energy, improve water quality and produce aquacultural byproducts is possible using existing technology (Fedler & Parker, 1994b), but requires demonstration to promote acceptance. The objectives of this demonstration unit are as follows: (1) to demonstrate construction and operation of a membrane covered advanced facultative pond (AFP) anaerobic lagoon integrated as part of a four stage treatment system, (2) to monitor and model the cycling of nutrients throughout the waste treatment system, (3) to demonstrate the production of aquacultural products including aquatic plants and animals, and (4) to increase feedlot and other livestock and poultry system operators' awareness of NPS pollution prevention techniques.

A demonstration pilot plant (Figure 1) consisting of (1) an anaerobic lagoon for digestion of cattle waste and generation of methane gas (2) a facultative lagoon - a stratified digester with an aerobic surface and anaerobic bottom for first stage production of microalgae and the production of single-cell protein (3) a well mixed aerobic lagoon for production of microalgae to be harvested as protein and (4) and aerobic lagoon for culture of finfish is now under construction. Water will pass sequentially from unit 1 through unit 4 and be recycled back to the cattle operation. Data collected from this system will be shared with other agriculturists, developers, and managers for the purpose of advancing the development and use of lagoon systems by industry. In addition, the data will be used to further calculate and test production models already developed, but not completely verified.

Location

This demonstration unit is located at the Texas Tech University Animal Science Farm about 15 miles north of Lubbock near New Deal, Texas. The farm has a 1000 head cattle herd confined in either slotted-floor pens or in hard-surface pens (Figures 1 and 2). Runoff from these pens is now captured and pumped via a 2-foot diameter pipeline to a settling basin before discharging into a playa lake

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Figure 1. Approximate location proposed pending system in reference to the livestock operation at the Texas Tech University Animal Science Farm.

We designed the waste water treatment system calculating soil to be moved, slope of berms, and placement of all components within the space and elevations available at the site. Approximately 5000 yd3 of soil was moved to construct the ponds. We are installing a pump station connected to the existing 2-ft. pipeline and pump the collected wastewater to an anaerobic treatment pond. Water and waste pumped into the pond will be measured (by the pumping rate of the pump and the hours of operation). This treatment pond, an advanced facultative pond (AFP) (Figure 2), will discharge to two aquaculture ponds in series. The first aquaculture pond will produce aquatic plants, principally duckweed, for extraction of nutrients. The second pond will be used as a water source for production of (fish - principally tilapia These two ponds will be covered with a greenhouse structure to maintain heat during the winter months and provide year-round production.

The AFP will contain a plastic membrane, located over the deep anaerobic portion of the pond, for collection of biogas. The biogas will be used on-site to heat the AFP and the green houses. The gas will also be used to generate steam and fed into a turbine coupled to an electric generator. The exhaust gases and the heat from the turbine will be recycled to the AFP. Heating the AFP will increase rate of anaerobic digestion, the production of biogas, and improve water quality.

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Figure 2. The advanced pond ( ) showing the 40 x 40 anaerobic pit (upper view) and the biogas collection system located below the water surface of the pond (lower view). Note that the biogas is collected by a subsurface plastic membrane located above the deep portion of the anaerobic pit.

 

Subsurface water samples

The entire pond system has been constructed on the sandy-clay-loam soil. One half of the 20-ft deep anaerobic pit will be sealed with cattle manure, mixed and packed with the upper 6 inches of soil on the floor of the pit. The other half of the pit will be sealed only by the manure contained in the influent. Nutrient movement from the AFP will be monitored in a series of water sample collection devices (Figure 3) installed below the floor of the pit, the AFP pond and compared to levels adjacent to the pond.

These water samplers will be installed one foot below the floor of the AFP in a transect - running across the deepest portion of the anaerobic pit (Figure 4). Collecting devices will also be installed at similar elevations adjacent to the pond, but outside of the basin These collection devices will be connected to the surface via two polyethylene tubes run inside 1/2 " diameter polyvinylchloride (pvc) conduit. One tube will be pressurized to force water samples out of the other tube and to the surface for collection. water samples collected will be analyzed for nutrients, principally ammonia nitrogen, nitrite-nitrogen and nitrate-nitrogen.

The soil and water samples will be placed in the ground in three matrices—(1) sand, (2) soil excavated from the site and (3) in soil excavated from the site and then covered with a sheet of plastic placed as an umbrella above the samples Figure 5). These three placements will be used to determine if water moves from the AFP vertically down to the sampler through the sand surrounding sampler site number 1, or if the movement is laterally to the sampler covered with the plastic umbrella as in site number 3. Samples at site number 2 will provide a reference for the typical installation of sampling devices as previously used by others. This sampler will be placed in the hole and then back filled with soil excavated from the hole. The soil surrounding all samplers are packed in place.

Water samples collected from the devices at monthly intervals will be analyzed for nutrient content - principally nitrogen and phosphorous in accordance with standard Methods. Data will be collected and analyzed in triplicate to provide a statistical basis for analysis. Samples taken from the pond system will be analyzed to trace changes in quality as water moves through the treatment system.

A second sampling system, a TRASE system (manufactured by Soilmoisture Equipment Corporation, Goleta, California) based on time domain reflectometry will be used to monitor soil moisture content in non-saturated soils. We expect non-saturated conditions to exist outside of the basin of the AFP and perhaps even below the ALP once the manure effectively seals the pond.

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Figure 3. Sampling device to be used to collect leachate water from around and beneath the

Aquaculture production

This highly integrated system will produce an effluent that is expected to be suitable for sustaining aquatic plants, and especially duckweedminizing. The duckweed will be harvested and fed to cattle to recycle nutrients, minimizing loads flowing to the playa.

Finfish to be cultured will include blue tilapia, Tilapia aurea, Nile tilapia, T. nilotica, and flathead minnow, Pimephales promelas. Brood fish will be stocked into the aquaculture pond and monitored for reproductive success. Water quality, specifically dissolved oxygen, pH, ammonia-nitrogen, nitrite-nitrogen, nitrate-nitrogen, conductivity and temperature, will be monitored at least weekly until the system stabilizes.

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Figure 4. Layout of the 4- stage ponding system for treating livestock waste and integrating aquaculture production with location of subsurface water sample collection devices.

Methane production

Methane gas collected from the AFP will be used to fire a water heater from which water will be pumped through a closed coil back into the anaerobic pit and returned to the heater for recycling. Methane gas will also be fed to a gas combustion engine coupled to an electrical generator. Heat from the combustion engine and exhaust gases will be ducted through water jackets and delivered to the anaerobic pond. Electricity generated from this system will be used on-site to operate equipment or metered via a transfer switch into the lines of the South Plains Electric Cooperative Company.

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figure 5. Placement of the soil water collection devices below the manure and soil base used to seal the ponds. Note the three types of materials used to surround the collection devices and the plastic umbrella type cap above site 3.

Summary

The integrated confined animal feeding operations and aquaculture production has the potential to produce additional revernues in Texas valued at over $500 million. Aquatic plants and fishes can be recycled back to the animal production system or used as feed ingredients for other confined animal production operations. A new approach to treating the confined animal waste is through the use of an advanced facultative pond that integrates a deep anaerobic pit within a conventional facultative pond. The pit is protected from mixing caused by wind and the collected methane gas can be used to either produce electricity or heat the wastewater in the pit to increase the fermentation activity.

Acknowledgments

We thank Raymond Sims, Dr. Paul Medley, and Dr. Gene wilde for review of this manuscript. Direct funding for this project was provided by the Department of Energy (Western Regional Biomass Energy Program). Environmental Protection Agency, Texas State Soil and Water Conservation Board, Texas Tech University, College of Engineering and College of Agricultural Sciences and Natural Resources. Williams and Peters Construction Co., Inc., Lubbock, Texas and Environmental Spill Control, Inc., Hobbs, New Mexico donated equipment and operator time to complete the earth wore Publication No. T- 1 - 103 of the College of Agricultural Sciences and Natural Resources.

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