Gary A. BreitenbeckHazardous industrial wastes
Research at the LSU Agricultural Center and other landgrant universities has shown that nonhazardous industrial wastes can be used to enhance the productivity of crops, especially forage crops. When application rates are carefully monitored, land application offers a legitimate beneficial use that does not pose a hazard to health or environmental quality.
For example, scientists at the LSU Ag Center conducted a study in which an organic byproduct of grease-trap recycling was applied to a low-fertility, acid soil used for permanent bahia grass pasture. Results of this 1995 study are shown in Figure 1. Seasonal forage production was increased by as much as 350 percent, and forage crude protein content was increased from 4.6 percent to more than 10 percent.
Similar increases in yields of winter rye and bermudagrass have been obtained using other industrial wastes in Louisiana. A limited number of field trials suggest responses of sugarcane and other row crops are less compelling, but application of industrial organic wastes adequately supplied those crops with one or more essential nutrients and improved soil condition.
Problems may arise when developing a beneficial use program. In the study shown in Figure 1, for example, application techniques that minimized odors were necessary. The slurried mixture of hydrolyzed vegetable and animal matter developed a pungent, noxious odor during transport. Even in a remote setting, surface application was not feasible. Using special equipment, the slurry was injected about 6 inches below the surface with little disturbance to the soil. This eliminated the odor.
Beneficial use programs for hazardous industrial wastes are more of a challenge. Many of the petrochemical processors that line the banks of the Mississippi River from Baton Rouge to New Orleans generate wastewater streams that contain hazardous compounds. This material must be shipped to carefully regulated facilities for disposal.
Industrial wastes that contain toxic concentrations of organic or inorganic contaminants are typically sent to incinerators for disposal where they are burned under controlled conditions. Flue gases are monitored carefully to minimize contamination of surrounding neighborhoods. Costs of incineration are high.
Organic wastes that contain lower amounts of potentially hazardous contaminants are typically shipped to “landfarms.” At landfarms, organic wastes are injected or surface-applied and incorporated into the soil. Active fields, more commonly called cells, are frequently tilled to accelerate microbial decomposition of the wastes. Because cells repeatedly receive organic wastes, trace compounds that resist microbial attack can accumulate. If these contaminants become a health or safety hazard, special remediation techniques are required to lower their concentrations.
Accumulation of plant nutrients is also a significant concern of landfarms. Many of the organic wastes sent to these facilities contain high concentrations of nitrogen, potassium, phosphorus, sulfur and other elements commonly regarded as plant nutrients. Because landfarms do not produce crops, nutrients are not removed. Wells are required to monitor the accumulation of nutrients in subsurface water, but technologies for reducing nutrient concentrations are limited. Eventually, these accumulated nutrients may pose a pollution threat to surface and ground water. Beneficial use programs are an attractive alternative because the growing and harvesting of crops results in continuous nutrient removal.Allowable application rates
The amounts of crop nutrients removed by harvesting determine the waste application rate permitted, unless elevated concentrations of regulated contaminants are present Wastewater sludges typically contain high amounts of nitrogen and lower amounts of potassium, phosphorus and other nutrients. Therefore, nitrogen removal rates often establish the amount and frequency of safe waste application. Where slurries rather than solids are involved, the capacity of the soil to adsorb the liquid waste may determine maximum application rates.
A permit is required from the Solid Waste Division of the Louisiana Department of Environmental Quality before industrial wastes can be applied to land. A rigorous protocol has been implemented to protect public health and safety as well as to protect environmental quality. Two years or more of analysis and experimentation are commonly required before a beneficial use permit is issued. Initially, the Solid Waste Division will review the industrial processes that result in waste generation to determine if significant quantities of regulated metals or organic contaminants are likely to occur. These evaluations are supported by extensive chemical analyses of the waste by an approved laboratory.
If the waste does not appear to contain significant quantities of hazardous constituents, the LSU Agricultural Center or another independent party is contracted to assess the potential value of the waste as a soil amendment for crop production. An extensive battery of laboratory and greenhouse experiments are performed to identify potential benefits as well as limitations of the material. The capacity of the material to supply nutrients and to affect soil-water dynamics and other agronomic considerations are assessed, as well as the potential to cause problems such as noxious odors, surface runoff or poor crops. Field tests
Once preliminary tests have established the potential of an industrial organic waste for safe, beneficial use, a plan is devised to assess the benefits and limitations of the material in a field cropping system. This plan must include a detailed monitoring scheme to detect possible adverse impacts on environmental quality or health and safety. The plan is submitted to the state Department of Environmental Quality. If approved, a “permit exception” is granted to conduct a field trial.
Hay production is often ideal for industrial beneficial use programs because it offers high nutrient removal rates, and hay meadows allow access for waste application throughout the year. Most industrial facilities have a limited capacity to store waste, and therefore they require a program where wastes can be continuously applied.
In southern Louisiana, sugarcane production is another candidate for beneficial use because approximately 25 percent of cane land is set aside in fallow each year and available for land application. Much of that land is poorly drained, however, and equipment access during the wet, winter months is limited. Moreover, processed sugar is consumed directly by humans. The use of industrial wastes in sugarcane production may cause anxiety among consumers no matter how rigorous the monitoring procedures to ensure safety.
Beneficial use of industrial wastewater sludges and other organic wastes in Louisiana is in its infancy. Despite the demonstrated ability of some industrial wastes to enhance agricultural productivity, beneficial use is attractive primarily because it offers a sound, long-term disposal strategy for nutrient-rich industrial wastes that do not contain hazardous components. A few large petrochemical companies are evaluating beneficial use plans. If they are implemented, applications will be initially confined to lands owned by these companies to ensure appropriate oversight.
With the continued vigilance of our regulatory agencies, routine use of nonhazardous industrial wastes in agricultural production may offer a practical, safe and environmentally superior solution to disposal problems.
Gary A. Breitenbeck, Professor, Department of Agronomy, LSU Agricultural Center, Baton Rouge, La.
(This article was published in the spring 1999 issue of Louisiana Agriculture.)