INTEGRATED WASTE TREATMENT SYSTEMS 1
Clifford B. Fedler
Nick C. Parker
1Research support was provided by the Water Resources Center, Texas Tech University and the Texas Higher Education Coordinating Board Advanced Technology Program Project No. 003644-064.
2Jointly sponsored by Texas Tech University, Texas Parks and Wildlife Department, the National Biological Survey, and the Wildlife Management Institute.
The Southern High Plains produces about 25%, or over 5 million head, of the cattle slaughtered annually in the United States. Most of these cattle are processed through about 200 feedlots, of which 87 have standing herds of over 5,000 head (Sweeten et al. 1991). Considering an average gain of 600 lb/head while in the feedlots and a feed conversion ratio of 9:1, then approximately 13.5 million tons of feed are moved into these 200 feedlots annually. Manure produced in the feedlots at the annual rate of 9 tons/1000 lbs of animal weight (wet weight) totals about 45 million tons and contains 0.31 million (0.57%) tons of total nitrogen (MWPS-18 1985). Nitrogen from this manure and urine can be either volatilized as ammonia gas, microbially converted into nitrites and nitrates as potential water pollutants, or removed from the feedlots as organic fertilizer or compost for assimilation into plants.
The increasingly stringent county, state and federal regulations are forcing all industries to become better stewards of natural resources. The Agricultural Summit (Nelson and Jones 1994) held in College Station, Texas in October 1993 and the mini-Summit held at Texas Tech University on 16 May 1994 were attempts to develop agricultural strategies acceptable to consumers, environmentalists and regulators.
As the human population has grown, ecologists have begun to develop global models to predict the carrying capacity of the world based on renewable resources. The first such model "The Limits of Growth. was published in 1972, Beyond the Limits. in 1993, and, most recently, "Toward Global Equilibrium " and "Dynamic of Growth in a Finite World (Perelman 1976, Roberts 1978, and Pestel, 1989).. " Computer models are now available to simulate agriculture production, nutrient cycling and population growth. These models were instrumental in debates held during the 1993 Earth Summit in Rio. The parties that now express interest in agriculture and natural resources issues extend well beyond the traditional farm community (Speth 1992). In response to constituents, the 103rd U.S. Congress considered 571 bills in 27 broad topic areas affecting food, environment and renewable resources during the first session of 1993 alone. It is likely that this focus on agriculture by consumers, environmentalists and regulators will increase. Agriculturists will benefit by aggressively addressing the real and perceived problems associated with the production of food and fiber and develop environmentally sensitive methods of on-site reuse and recycling. Examples of some of the real and perceived problems are reflected in the study sites selected by the U.S. Geological Survey of the National Water-Quality Assessment Program (Hamilton and Shedlock 1992). Concern for agriculture systems and national water quality extends to the cattle feedlots in the High Plains. Our objectives are 1) to determine the real or perceived problem for ground water contamination as caused by cattle feedlots in the Texas High Plains, 2) to identify potential integrated wastewater treatment systems for on-site reuse and recycling of resources, and 3) to identify new potential products resulting from the recycling of current resources and their potential as revenue sources.
When looking at the potential sources of surface and ground water pollution, non-point sources such as agricultural applications are often targeted. Playa lakes that are a natural part of nearly all farming and cattle feedlots operations in the Texas High Plains are known recharge sites for the underlying Ogallala aquifer (Richter and Scanlon 1992). Nitrate data published by the High Plains Underground Water Conservation District Tables 1 and 2) were analyzed for 12 counties - 8 containing cattle feedlots (Figures 1-8). When nitrogen levels are elevated in ground water, the most visible sources of nutrients, such as those found in cattle waste stored in area playas, are often identified as the contributing source in the absence of firm data proving otherwise. However, feedlots are not the only source of nitrogen. For example, the annual nitrogen fertilizer usage on U.S. farms increased from 14 million tons in 1950 to 145 million tons in 1990 (Brown 1991). Sweeten and Wolfe (1993) twice sampled wells on 11 dairy farms and reported average nitrate-nitrogen (NO3-N) concentrations of 1.2 + 1.6 mg/L with a range of 0.0 to 4.35 mg/L - well below the 10 mg/L nitrate-nitrogen level permitted by the U.S. Environmental Protection Agency Standard for drinking water. However, data from the High Plains Underground Water District indicates nitrate levels ranging from not detectible to 83 mg/L (0 to 18 mg/L as NO3-N; Table 1).
TABLE 1. Minimum and maximum nitrate concentrations in Texas High Plains ground water collected from eight counties with cattle feedlots and four counties without feedlots.
|Number of Feedlots||Number of Obs. Wells||1 Maximum NO3 Conc., mg/L||1Minimum NO3 Conc., mg/L|
1Source: High Plains Underground Water Conservation District
1ND - Not Detectable
Nitrate-nitrogen (NO3-N) equals nitrate concentration times 0.226
TABLE 2.Alphabetical listing of Texas High Plains counties used in this study.
The nutrient rich runoff and solid wastes from cattle feedlotscan be processed through integrated wastewater treatment systems to recover nutrients for conversion into additional farm products (Parker et al. 1992a; Parker et al. 1992b; Staminathan 1992; and Fedler and Parker 1993). Wastewater treatment systems can be integrated will cattle feedlots to produce hydroponic and aquaculture products. These new products, or on-site resources, include biogas (methane) for energy, aquatic plants (microalgae, duckweed, and water lilies), fish (bait, ornamental, and forage) and invertebrate products (crawfish, clams, and worms). Additional benefits of integrated wastewater treatment systems include odor control, aesthetic value, maintenance of habitat for migratory waterfowl and resident wildlifeattributes which may have environmental and public relations values far greater than their commercial value.
|Figure 1. Plot of contour lines of nitrate concentration and location of feedlots for Bailey County. Solid square indicates location of cattle feedlots.||Figure 2. Plot of contour lines of nitrate concentration and location of feedlots for Castro County. Solid square indicates location of cattle feedlots.||Figure 3. Plot of contour lines of nitrate concentration and location of feedlots for Cochran County. Solid square indicates location of cattle feedlots.|
|Figure 4. Plot of contour lines of nitrate concentration and location of feedlots for Deaf Smith County. Solid square indicates location of cattle feedlots.||Figure 5. Plot of contour lines of nitrate concentration and location of feedlots for Floyd County. Solid square indicates location of cattle feedlots.||Figure 6. Plot of contour lines of nitrate concentration and location of feedlots for Bailey County. Solid square indicates location of cattle feedlots.|
|Figure 7. Plot of contour lines of nitrate concentration and location of feedlots for Parmer County. Solid square indicates location of cattle feedlots.||Figure 8. Plot of contour lines of nitrate concentration and location of feedlots for Lubbock County. Solid square indicates location of cattle feedlots.||Figure 9. Schematic of an integrated wastewater treatment system for livestock waste with three options for the third stage of the process (not to scale).|
INEGRATED WASTEWATER TREATMENT SYSTEMS
We have incorporated elements of wastewater treatment systems of Oswald (1988) and Hammer (1989) to develop an integrated system to treat effluent from cattle feedlots while producing biomass-based energy and agricultural products. This treatment system consisted of a 4-stage system beginning with an anaerobic lagoon followed by a facultative pond, a high-rate algal production pond (for production of duckweeds and macr~phytes) and a final aerobic maturation pond. The final effluent could then be used to raise fish. A second system is being designed to reduce the nutrient discharge from a secondary treated municipal wastewater. This system will consist of constructed wetlands with the option of producing native macrophytes, duckweed, microalgae, ornamental plants or alternately flooded and dried grasslands. Components of these two systems are scheduled for construction at the Texas Tech University cattle feedlot demonstration site near New Deal, Texas. This system provides three options for the third stage of the process - production of algae, duckweeds or macrophytes (Figure 9) of which only one or two may be constructed at the demonstration site.
The demonstration treatment system will accept both swine and cattle waste that is screened to separate some of the heavy solid material in the waste. This system is an expansion of technology developed from an existing facility designed to culture marine microalgae using anaerobically digested biomass from cattle feedlots (Fedler and Parker 1993). The demonstration pilot plant will consist of (1) an advanced facultative lagoon (figure 10) a stratified digester with an aerobic surface and anaerobic bottom for digestion of the waste biomass, production of single cell protein, and generation of methane gas, (2) a pond for the production of rnicroalgae, and (3) a well mixed lagoon for culture of Finnish.. Water will pass sequentially from unit 1 through unit 3 and be recycled back to the swine and cattle operations for flush water or discharged as water for irrigation of crops.
Figure 10. Schematic of the advanced facultative pond used in the integrated wastewater treatment system (not to scale).
|Based on preliminary data, this project will have the potential to not only utilize animal waste and alleviate a major environmental problem for Texas, but to create a new industry in Texas with the production of single cell protein and protein from aquatic plants (duckweed), which can be produced and used in Texas or exported. This protein source can be combined with corn, cottonseed, soybean meal or wheat by-products, which are also produced in Texas and processed into rations for fish, livestock, and poultry. Production of single cell protein and aquatic plant in could provide new regional and nationwide markets for Texas commodities. Maximum annual production of marine microalgae is around 74 tons/A on a dry weight basis annually. Typically, microalgae raised on the farm-scale produce between 3 and 18 tons/A (Richmond 1986), indicating the need for improved efficiency in production. Taking an average production rate of 12 tons/A, nearly 2 million tons of microalgae could be produced from the waste generated by the cattle produced on the Texas High Plains. If this algae (from 50 to 7096 protein) were sold at a price compared to that of soya protein it would generate annual sales of approximately $240 million. Clearly, more economic value is possible when you consider that several high-valued products (Cohen 1986) can be extracted from the algae reducing the value of the protein (Fedler et al. 1991). Duckweed, containing up to 45 % protein, has been produced at about 34 tons (dry weight)/A and could serve as feed for cattle (Culley et at. 1981 and Sldllicorn et at. 1993). In addition to this potential new industry, other existing industries wilt be impacted through sales of the necessary equipment required to harvest and process the single cell protein (bacteria), microalgae, duckweed, and macrophytes into feeds and feed ingredients.|
Production and sale of fish will generate additional funds. Bait fish commonly sell for $10 - 15/lb and other high-value fish include fingerlings of sport fish such as bass and bluegill; fingerlings of foodfish such as red drum and channel catfish to be stocked and reared in other facilities; and ornamental fish such as swordtails and mollies. Lower value fish, such as carp, can be processed as fish meal or incorporated into feeds for swine and poultry.
Along with the glamour of producing nearly 25 % of the nations cattle in the concentrated area of the Texas High Plains comes the spotlight of being the cause of many real and perceived problems, such as contamination of the Ogallala with nutrients produced by such a large quantity of cattle. Whether surface or ground water contamination problems are viewed as real or perceived by the public, it is in the best interest of the producers to address these issues. One method is to develop and adopt new technologies that reduce or eliminates the potential of surface and ground water contamination by integrating waste treatment with development of new products. By integrating known technologies, new revenue sources can be produced to stimulate the economy of Texas and to meet the food production needs of the growing world population.
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