Linda F. Benedict, Theegala, Chandra
Louisiana’s abundance of public water bodies and plentiful rainfall makes the state’s waters particularly susceptible to runoff from manure-enriched soils and overflow from concentrated animal-rearing facilities. According to a U.S. Environmental Protection Agency estimate, more than two-thirds of lakes and streams monitored in Louisiana are impaired by metal and excess nutrient contamination. Based on historical records at the Louisiana Department of Environmental Quality, fecal contamination is one of the most frequently cited, suspected causes of river impairment, followed by excess nutrient contamination.
Although it is difficult to quantify the actual impact waste manure contamination has on the state’s economy, one has to keep in perspective that tourism is one of Louisiana’s largest industries. Contamination can lead to beach closures and increased prevalence of diseases. Fisheries losses are also difficult to evaluate because of year-to-year variability in fish populations and differences in species and harvesting techniques. From a human health and environmental perspective, despite not having a clear dollar figure tied to economic losses resulting from animal wastes, it is critically important to lower the contamination from concentrated animal-rearing facilities.
The Louisiana poultry industry produces approximately a billion pounds of broiler meat each year. According to the 2009 LSU AgCenter Ag Summary, the state has 468 broiler producers, 156 breeder-flock producers and 836 table-egg producers. Poultry litter primarily comprises bird droppings and bedding material. A typical broiler house generates approximately 150 tons of litter per year from seven grow-outs. With little commercial value and costs associated with hauling the waste material over long distances, poultry litter is often over-applied to producer-owned and adjacent lands. Repeated land application of wastes leads to excess nutrients and pathogens in runoff water.
Unlike the wastes generated by poultry operations, waste from dairy and beef facilities is often directly deposited by the animals on pastures; therefore, it is difficult to collect, contain or treat. Depending on the mode of operation, however, some dairy facilities keep cows on concrete floors anywhere from four to 24 hours per day. According to Louisiana law, the portion of the waste collected on concrete floors or in milking parlors has to be pumped, usually as a slurry, to a no-discharge, single-stage, anaerobic lagoon for treatment and containment. Fine bedding sand or other cow bedding material, such as sawdust or rice husks, also gets flushed along with manure. A typical 1,400-pound dairy cow produces approximately 10 percent of its body weight as waste daily. Because of these enormous quantities of waste and bedding material entering the lagoon, the dairy operator is forced to clean out or dredge the lagoon every three to five years.
Waste treatment in a lagoon that is not emptied (Figure 1) gets seriously undermined, thereby leading to contamination of neighboring water bodies with nutrients and pathogens. Depending on the size of the lagoon, the cleanout or dredging costs can be as high as $20,000. Because the dairy industry in Louisiana is in decline, these dredging costs can further cripple this ailing industry.
Historically, some dairy producers have emptied their lagoons with financial and technical support from the Lake Pontchartrain Basin Foundation and the LSU AgCenter Southeast Research Station in Franklinton, La. Dairy operators also exercise the option of land application of manure and wastewater from the lagoon. However, excessive loads of manure spread onto the land or improperly incorporated into deeper soil depths can lead to contamination of public waters caused by runoff following a major storm.
To address these manure-related problems and to help dairy and poultry operators, LSU AgCenter researchers have been looking into treatment alternatives that have revenue-generating potential. For dairy waste, the first step involves separating the solid portions from the liquid slurry pumped into the lagoon. After constructing and testing several prototypes, a low-cost, self-cleaning, inclined gravity screen with a sand-separation feature was developed (Figure 2). This unit, which is ready for commercialization, is constructed of stainless steel and aluminum and is anticipated to yield decades of trouble-free service at a dairy farm. This unit separates into two piles the larger organic particles in the manure (about 50-60 percent) and more than 80 percent of the sand in the waste slurry.
Installation of this self-cleaning manure/sand separator on a lagoon levee will directly lead to reducing waste into the lagoon. The sand/manure separator, which is projected to cost less than the cost of one lagoon cleanout, is anticipated to eliminate the need for frequent and expensive cleanouts or dredging. The separated manure, which resembles chopped up wet hay rather than fresh manure, can be used for generating other value-added products. The separated sand, which has small quantities of manure, can be reused as a bedding material or for other applications.
Screen-separated dairy manure or poultry litter has high nutritive value and can be used as a fertilizer or soil amendment. The products, however, have high moisture content – up to 90 percent – and are contaminated with fecal coliforms and other pathogens. To address these problems, LSU AgCenter researchers have been working on developing solar stills for drying wet manure and eliminating bacterial contamination. Solar radiation heats the still to extremely high temperatures, above 210 degrees during a midsummer day. Results from the final prototype indicate that the solar still can dry wet biomass with 80-90 percent moisture to less than 5 percent moisture in three summer days. In winter, manure drying occurs within seven to eight sunny days. A unique drying protocol simultaneously dries the manure and eliminates bacterial populations. This drying protocol is critical because traditional drying induced development of heat-tolerant bacterial strains that remained viable for months in dried manure.
Once the dairy manure or poultry litter is dried and rendered pathogen- or coliform-free, it can be used as a soil amendment or organic fertilizer. Bacterial testing of manure subjected to the unique drying protocol indicates bacteria populations can be totally eliminated, beating the approved threshold bacterial concentrations of less than 1,000 colony-forming units per gram for use as organic fertilizer. It is anticipated that pelletizing pathogen-free manure will enhance its economic value (Figure 3).
An on-farm price of $2 for a 40-pound bag of dry material will yield an income of approximately $110 per cow per year, assuming a 50-percent manure collection efficiency. Higher returns are anticipated from poultry litter because all the litter can be collected. Assuming the same per-bag price, a poultry operator could anticipate earning approximately $95,000 per 100,000 birds each year. Higher per-bag prices can be expected if the pellets can be certified as "organic soil amendment" or "organic fertilizer."
Although the projected numbers appear attractive – sometimes appearing to generate more revenue from waste than from the broiler meat or milk – market flooding will eventually limit the revenues to sustainable levels. Apart from the waste-generated revenue, which will improve the profitability for dairy and poultry farmers, the biggest benefit is anticipated to be contaminant mitigation. Using the manure to generate value-added products helps reduce nutrient and bacteriological contaminants in Louisiana water bodies.
Chandra Theegala, Associate Professor, Department of Biological & Agricultural Engineering, LSU AgCenter, Baton Rouge, La.
(This article was published in the spring 2010 issue of Louisiana Agriculture.)