Land Applications

Project 1

Long-Term Land Application of Municipal Wastewater-A
Case Study

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Abstract :

          With environmental regulatory agencies applying more stringent guidelines while also promoting the reuse of wastewater, we can expect slow-rate land application to become an integral part of more treatment systems in the future. Yet, as common as land application systems are in the United States, design of these systems is still less than optimum. Much of the problem is the lack of communication between the design engineers and the agriculturalists involved with the systems. Often the agricultural faction forgets that the purpose of the land application site is treating wastewater and not maximizing profits from the crop being produced. On the other hand, engineers forget that "good agricultural practices" are necessary for a long-term, effective land treatment system.

          The Lubbock, Texas Land Application Site (LAS) is one of the oldest (since 1925), continuously operating, slow-rate land application systems in the United States. Throughout its life, the LAS has provided an efficient method for disposal of secondary treated effluent. Yet, over the years some changes were required in order to implement new regulations required by the state’s regulatory agency. In 1988, a new design approach was developed to optimize the application of treated effluent to the LAS where minimal storage is provided. Since that time, the new operational design has been followed with only minor modifications needed to account for differing crops required by weather conditions or other external factors. In one area of the LAS prior to 1988, the owner/operator over applied effluent causing an increase in the groundwater nitrate concentration above that allowable for drinking water (10 mg/L NO3-N). Since the implementation of the new operating design and the inclusion of a groundwater pumping scheme, a reduction in nitrate concentration of about 11 percent per year has resulted.

          Design of land application systems is a complicated process that must include the principles of land limiting constituents, irrigation and the respective inefficiencies, water balance, evapotranspiration, and crop selection which include nutrient assimilation and leaching requirements. Each of the principles must be carefully analyzed both independently and collectively to provide the optimum design. The objective is to present a case study of the principles and procedures used to design effective land treatment systems for arid and semi-arid regions and to provide an analysis of one of the oldest land application sites in the U.S. based on 8 years of in-depth groundwater samples and 2 years of soil and plant nitrogen data. The groundwater analysis is provided for the entire 5,200 acre LAS where 2,950 acres of center pivot irrigation exist. Three plots from the LAS consisting of land that had been irrigated with effluent for as little as six years and up to 65 years were chosen for the detailed nitrogen analysis. Total nitrogen in the effluent applied to the soil varied from 10 to 25 ppm. The nitrate nitrogen in the top 2 ft of soil varied from 0 to 15 ppm with an average of about 3 ppm resulting in readily available nitrogen for plant uptake averaging about 38 lb/acre. These low values of available nitrogen illustrate that the plants are efficiently removing nitrogen, thus preventing the potential for groundwater contamination when the operators follow the schedule of irrigation as prescribe by the optimized design approach.

Project 2

Impact of Long-Term Application of Wastewater

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Abstract :

Environmental regulatory agencies are applying more stringent guidelines to the discharge of wastewater effluents while also promoting the reuse of treated wastewater. Therefore, we can expect slow-rate land application to become an integral part of more treatment systems in the future, especially for the arid and semiarid southwest region of the United States. Yet, as common as land application systems are in the United States, design of these systems is still less than optimum. Much of the problem is the lack of communication between the design engineers and the agriculturalists involved with the systems. Often the agriculturalists forget that the purpose of the land application site is treating wastewater and not maximizing profits from the crop being produced. On the other hand, engineers forget that "good agricultural practices" are necessary for a long-term, effective land treatment system. When a land application system for secondary treated municipal wastewater is properly designed, both from the standpoint of good engineering principles and good agricultural practices, the system can be operated successfully for many years without posing a threat to the environment.

Project 3

WasteWater

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Abstract :

One of the primary responsibilities of any municipal government is the removal, treatment, and final disposition of waste produced by its citizenry. Municipal solid waste (MSW) is recycled, taken to sanitary landfills, or used as fuel in large, energy producing facilities. In addition to MSW, each member of the community generates urine, feces, and other waste products that must be processed so that the health and welfare of the entire population is preserved. The aggregation of people into towns and cities occurred before the means to properly dispose of solid and human waste existed. During the period 500 to 1500 AD, people living in towns and cities threw their garbage and human waste into the streets or in spaces between buildings (Jewell and Seabrook, 1979). The filth accumulated until someone hauled it from the town, or until rainfall events washed it into nearby rivers and streams. The bubonic and pneumonic plagues were direct results of such egregious living conditions (Britannica, 2000a). The general requirements of sanitation were recognized by the middle of the nineteenth century. Potable water supplies and an arterial system for sewer drainage were either proposed or were being installed in some English cities by 1840, and by 1870, the treatment of municipal wastewater by land application was considered a proven technology (Jewell and Seabrook, 1979). Municipal wastewater was treated at sewage farms in Great Britain until about 1901. Land treatment of municipal wastewater was introduced in the United States in 1872, but by 1910, it was not considered to be an acceptable treatment alternative. Discharge of partially treated municipal wastewater into receiving waters was believed to be a safe and cost effective alternative to land application. By 1930, land treatment was considered to be an uncontrolled natural process, and was classified in the same area as the purification that occurs in discharges or disposal to streams (Jewell and Seabrook, 1979). Pollution of surface and groundwater in the United States became apparent during the 1950s. In 1972, the United States Congress enacted PL92-500, the "Clean Water Act," in an effort to improve the water quality in the U.S (Jewell and Seabrook, 1979). Municipal wastewater treatment facilities consisting of unit operations and unit processes were initially employed as the technology of choice. By the middle of the 1970s, it was apparent that mechanical methods were capital intensive, and that the quality of treated effluent was inferior to that produced by land treatment systems. In 1977, the EPA ruled that land treatment must be considered as an alternative, when new treatment facilities are planned (Appendix C).