Land Application

Land Applied Sludges: Solution or Problem?

Aaron Shearer and Brad Shearer

Introduction

Land Application of biosolids is the "intimate mixing or dispersion of wastes into the upper zone of the soil-plant system with the objective of microbial stabilization and degradation, adsorption, immobilization, selective dispersion, perhaps with crop recovery, leading to an environmentally acceptable assimilation of the waste." The land application is as old as agriculture. The Chinese have used human waste as a fertilizer for thousands of years. In fact, the soil series "Plaggen" is classified as a soil whose structure is influenced by years of continual sludge application. Before the 1940s, land application of sludge was common in the United States. However, since synthetic fertilizers became affordable and available, sludge was seen as a disposal problem.

While the soils have been used primarily for food and fiber production to support mankind's existence, they have also been assimilating mankind's waste. As populations began to increase in the urban areas, wastewater collection and treatment systems became a necessity. The residuals generated during the retreatment of sewage were termed sewage sludge. Sewage sludge and other residuals that can be beneficially used are referred to as biosolids. This term was coined during the late eighties when land application became ever more prevalent in the United States. With residuals disposal options such as landfilling, incineration, and ocean dumping becoming increasing ly restricted, and with the public's interest in preserving natural resources through more recycling and beneficial reuse, application of biosolids to land remains one of the preferred options for biosolid management.

Based on information provided in the preamble to 40 CFR Part 503 -- Standards for the Use or Disposal of Sewage Sludge, one-third of the sewage sludges generated in the US are land applied. more than 65 percent of land applied sludges are placed on agricultural crop land. For the remaining sludge not land applied, 34 percent is landfilled, 16 percent incinerated, 10 percent disposed of on surface impoundments, and 6 percent disposed of by unknown means.

In the US, 12,750 publicly owned treatme nt works (POTWs) generate 5.4 million dry metric tons of sludge annually, or 47 dry pounds per US citizen. Sludge products come in a variety of forms. Sludges can be land applied as a liquid, spread as sludge cake, pelletized , sold in bags as fertilizer, used as topsoil, spread in forests or flower gardens, used as root zone coverage for landfills, or stabilized as structural fill.

Issues of Land Application

Types of Land Application
Agriculture
Forest
Reclamation
Nutrient Management
Nitrogen
Phosphates
Deficiencies/Imbalances
Trace Elements
Trace Organics
Soil Physics
Pathogens
Sociopolitical
Economics
Yuma Study
Chicago Study
References
Conclusions

Send comments and questions to Brad Shearer or Aaron Shearer

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