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Title: Current and future outlook of dredged and sewage sludge materials in agriculture and environment

item Sigua, Gilbert

Submitted to: Journal of Soils and Sediments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2004
Publication Date: 2/4/2005
Citation: Sigua, G.C. 2005. Current and future outlook of dredged and sewage sludge materials in agriculture and environment. Journal of Soils and Sediments. 5(1):50-52.

Interpretive Summary: In the late 1960's there was an increasing realization in the U.S.A. and other parts of the world, especially in Europe of the potential problems associated with the disposal of spoil and sewage sludge materials. While insufficient information was available to determine potential adverse effects of disposal on land, many people including those in the scientific community had articulated their objections on the use of these materials in agriculture because data do not provide adequate environmental protection information. In many cases, site-specific geochemical and biological factors are typically excluded from the decision process. Because of continued studies and far-reaching research during the last 40 years on the environmental effects of dredged and sludge materials, the scientific community and regulatory agencies in the U.S.A. are now in a much better position to appraise the environmental and possible agricultural impacts connected with the disposal of dredged and sludge materials by diverse disposal methods. Land application of dredged materials may provide substantial benefits that will enhance the environment, community, and society. The trace metal contents of these materials were below the threshold effect levels. As such, the agricultural or livestock industry could utilize these dredged materials to produce forages. Successive land application of sewage sludge for at least three years followed by no sewage sludge application for at least two years may be a good practice economically and environmentally because it will enhance and/or maintain sustainable forage productivity and at the same time minimize probable accumulation of nutrients to a certain degree, especially heavy metals. Consecutive applications of sewage sludge may result in build up of toxic metals in soils in some other states with initial high metallic content of the sewage sludge, but our study suggested no detrimental effects on soil chemical properties and on plants. The possibilities for environmentally and economically sound application strategies are encouraging, but more and additional research is required to find optimal timing and rates that minimizes negative impacts on the environment. For proper utilization of sewage sludge, knowledge of the sewage sludges' composition, the crop receiving it, are crucial, so that satisfactory types and rates are applied in an environmentally safe manner. There is still much to be learned from this study and this investigation needs to continue to determine whether the environmental and ecological objectives are satisfied over the longer term.

Technical Abstract: Prohibition of dumping of dredged and sewage sludge materials in streams and oceans, diminishing landfill space, skyrocketing landfill costs and concerns over air pollution from incineration of waste have contributed to a strong public interest in finding alternative, environmentally sound solutions to dredged and sewage sludge disposal. Additional research on disposal options of dredged and sewage sludge materials are much needed to supply information on criteria testing and evaluation of the physical and chemical impacts of dredged and sludge materials at a disposal site. The ability to reuse dredged and sludge materials for agricultural purposes are important because it reduces the need for offshore disposal and provides an alternative to disposal of the materials in landfills that are already overtaxed. Often these materials can be obtained at little or no cost to the farmers or landowners. Thus, forage production offers an alternative to waste management since nutrients in the dredged and sludge materials are recycled into crops that are not directly consumed by humans. Results have shown the favorable influence that dredged materials had on bahiagrass during its early establishment in sandy subtropical beef cattle pasture areas. The dredged materials that were used in our study have high calcium carbonate content of 82%. Therefore, when these materials were incorporated into existing topsoil they would have the same favorable effects as liming the field. Application of sewage sludge materials gave better forage production than the unfertilized control during years with sewage sludge application (1997-2000) and during years with no sewage sludge application (2001-2002). The carry over effect of these sewage sludge over the long term can be especially significant in many areas of Florida where only 50% of the 1 million ha of bahiagrass pastures are given inorganic nitrogen yearly. Repeated applications of sewage sludge indicate no harmful environmental or plant effects on basis of the investigated components. Results suggested that excessive build up of plant nutrients (e.g. total N, total P, and trace metals) might not occur in beef cattle pastures that repeatedly received sewage sludge while favoring long-term increased forage yield of bahiagrass. Average soil test values in June 2002 exhibited: i) decrease in TIN (NO3-N + NH4-N), TP, K, Ca, Mg, Mn, and Fe; and ii) slight increase in Zn and Cu when compared with the June 1997 soil test results.