Land Application of
Historically, sewage sludge has been considered a waste and has been dumped in municipal and commercial land fills or the ocean - such practices were easy and cheap. But times have changed and so too, have our attitudes of sludge management. We have come to recognize, that like animal wastes, wastewater residuals are a part of the natural life cycle. They have nutrient and soil-enhancing properties that make them a practical choice for a variety of beneficial uses.
Traditionally, liquid or dewatered
biosolids have been applied successfully to agricultural lands, forests,
or reclaimed lands. More recently, there has been greater emphasis on
such markets as landscaping projects, nurseries, sod farms, and direct
use by homeowners.
Biosolids contain many of the same constituents as commercial fertilizers, including invaluable organic matter, nitrogen and phosphorous. While not a complete replacement for chemical fertilizers in terms of nutrient ratios, biosolids do some things that chemical fertilizers can't do. They're composed of organic matter that promotes necessary bacterial activity and improves the structure, texture, and water retention characteristics of the soil. These properties stimulate the growth of vegetation, which helps reduce soil erosion and improve crop yields. Biosolids also provide trace metals and nutrients that commercial fertilizers do not have.
Biosolids are generally land applied using one of several techniques. The biosolids may be sprayed or spread on the soil surfaces and left on the surface. They may be tilled (incorporated) into the soil after being surface applied or injected directly below the surface for producing row crops or other vegetation and for establishing lawns.
Biosolids in a liquid state can be applied using tractors, tank wagons, irrigation systems, or special application vehicles. Dewatered biosolids are typically applied to land using similar equipment to that used for applying limestone, animal manure, or commercial fertilizer. Both liquid and dewatered biosolids are applied to land with or without subsequent incorporation into the soil.
Operational standards to control disease causing organisms called pathogens and to reduce the attraction of vectors (e.g., flies, mosquitoes, and other potential disease-carrying organisms) to the biosolids must also be met. In addition there are general requirements, management practices, and frequency of monitoring, record keeping, and reporting requirements that must be met.
AGRICULTURAL LANDS - Agricultural use accounts for approximately 77 percent of the biosolids that are land applied in the United States. This includes land that is used to grow both food crops and feed crops and pasture land. As with commercial fertilizers, farmers must follow best management practices when applying biosolids. The material must be applied at the correct agronomic rate for the plant being grown and must be monitored. Biosolids may need to be supplemented with other fertilizers to balance crop needs.
FORESTS - Biosolids are used in civil culture to increase forest productivity for certain tree species. The application of biosolids to forest land can shorten pulp wood and lumber production cycles, especially on marginally productive soils.
LAND RECLAMATION SITES - Biosolids are used to help reclaim barren lands such as mines, quarries, gravel pits, and construction sites. Biosolids provide nutrients and condition the soil so that vegetation can be established. Vegetation reduces soil erosion and helps make the land productive again.
RECREATION AND OTHER USES - Biosolids are applied to areas of land to condition the soil and enhance the growth of vegetation. Example of such sites include parks, ball fields, golf courses, cemeteries, plant nurseries, and highway media strips.