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Biosolids are nutrient-rich organic materials produced during the biological and physical treatment of Wastewater.
Biosolids can be beneficially used in farming and land reclamation, as they contribute to an improved soil structure, provide a source of plant nutrients, and assist in the establishment of microfauna and microflora.
Care is required in the utilization of biosolids as they may contain high levels of heavy metals and/or chemical residues. Nutrient contamination of waters is also a potential problem, as are enhanced weed growth, and public opposition to biosolids use. It may also be difficult to comply with the federal, state and, more often, local regulations applicable to biosolids utilization.
Not all land sites are suitable for the application of biosolids. Factors such as topography, soil characteristics, location of groundwater and surface waters, proximity to residences, operational accessibility, intended land use and economic viability need to be evaluated.
One of the major benefits of utilizing biosolids in crop production is that they act as a slow-release fertilizer, especially for nitrogen. Most nitrogen in biosolids applied to the land is in the organic form which must be converted to ammonium or nitrate forms in order to be utilized by plants. The rate of conversion or "mineralization" is dependent upon many factors such as the method of production of biosolids, the length of time in storage and the method of application to the land.
Another major benefit of biosolids is that the large amount of contained organic matter is capable of improving the physical soil structure of most land sites. The improved soil is less prone to hard setting, which in turn reduces soil erosion. The organic matter has an improved moisture holding capacity, which is important in drought-prone areas.
The quality of biosolids produced is improving as pretreatment authorities control the input of metals and pesticides into the collection systems. Care is required in the use of biosolids so that metal limits for soils, or plants grown on these soils, are not exceeded. It is very important that the quality of the biosolids applied to any site is accurately known and that metal limit guidelines are complied with.
Raw and untreated biosolids contain bacteria, viruses and eggs of parasites. When properly treated, the health risk from contact from such organisms in biosolids is low.