TYPES OF SPRAY IRRIGATION SYSTEMS: a) Infiltration type; b) Overland type
NITROGEN AND PHOSPHORUS REDUCTION: Up to 90%
BOD REDUCTION: About 99%
MAXIMUM ACCEPTABLE SODIUM CONTENT IN WASTEWATER.: 1000 ppm
REQUIRED WASTEWATER PUMPING PRESSURE: 60 to 100 psig
PRETREATMENT OF WASTEWATER: Screening and grease removal only
HYDRAULIC LOADING BY SPRAY IRRIGATION: 1 in/day (a), 3 in/week (b)
ORGANIC LOADING IN FOOD INDUSTRY: 100 to 250 lb BOD/acre/day is normal; 500 to 1000 is maximum.
TYPICAL INFLUENT AND EFFLUENT CONCENTRATIONS (MG/L): Wastewater BOD: 600 to 700; Underdrain effluent BOD: less than 10
Spray irrigation is a modification of the system used in agriculture for irrigating crops. However, the objective is the disposal of liquid waste rather than providing moisture and nutrients to harvestable crops.
The first operative spray irrigation system in the United States was located in Pennsylvania in 1947. Since 1947, spray irrigation systems have been used for the disposal of waste from paper mills, kraft and neutral sulfite semi-chemical pulp mills, vegetable and fruit canneries, straw-board mills, dairies, fine chemical fermentations, and milk bottling plants. The acceptance of this method of waste disposal is verified by its use in Indiana, Wisconsin, Michigan, Ohio, Illinois, Oregon, New Jersey, Texas, Ontario, Kentucky, Tennessee, Pennsylvania, Minnesota, and Iowa. The system is attractive because of its flexibility and total treatment of applied fluids.
Flexibility in expanding or contracting the capacity of the treatment facilities is especially beneficial with fer mentation waste because of the changing quantity and quality of this waste. Total treatment is a solid asset when highly concentrated waste, such as fermentation residue, is handled. Typical fermentation waste with 65,000 mg/l BOD after 98% treatment in a conventional, complete-treatment, biological facility still contains 1300 mg/l BOD, which is usually unacceptable for discharge.
After pretreatment and grease removal, this system sprays wastewater through a sprinkler system onto land that is planted with special grasses. The wastewater infiltrates the ground where soil microorganisms convert the organic waste into inorganic nutrients. The purified water is collected by an underground perforated pipe and sent to a final polishing pond.
The removal of soluble organic wastes by spray irrigation is a highly efficient process for treating industrial waste. Until recently, most of these systems required good soil infiltration characteristics. The system required a site where large volumes of water—as much as 1 in per day— could be applied and where the hydrological characteristics of the soil permitted water transfer underground and laterally out of the area of application. In many cases where the infiltration was adequate, the lack of sufficient lateral movement either limited the rate of application or created flooding. Usually, overcoming these problems involved installing artificial drainage similar to farm tile drainage except for extra precautions in the spacing and the means of avoiding siltation of the collection system because of the high application rates.
Techniques were also developed that use impervious soils for purification by overland flow. These systems are used with impervious clay-type soils in which significant infiltration is not possible.
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