Saturday, 15 July 2006

Effect of applying sewage sludge and Mitilus galloprovincialis Lam. shells on degraded mine soil.

P. Marcet, J. Rey, and S. Gonzalez. Universidad de Vigo. Escuela de Ingeniería Técnica Forestal., . Escuela de Ingeniería Técnica Forestal. Campus a Xunqueira s/n,, Pontevedra, 36005, Spain

The properties of mined soils make them a poor medium for plant growth and natural recolonization on these soils is slow (Sengupta 1993). Unvegetated mine spoils are devoid of vegetation and prone to erosion, resulting in further environmental degradation (Tennessee Valley Authority 1963). Reclaiming these highly disturbed soils is an important process in returning land to a stable state. The objetives of this study were to investigate the effect of applying sewage sludge and Mitilus galloprovincialis Lam. crushed shell on selected chemical properties and availability of metals in degradated mine soil. Land application of sludge forest and disturbed lands represents one of the better options for utilization of this material by recycling plant nutrients and organic matter to soil for crop production. Unfortunately, pollutants such as heavy metals, toxic organic compounds and pathogens might be accumulated during conventional sewage treatment process, which limited their use for land application (Wong et al., 2001). Heavy metal content is one of the major factors limiting the application of sewage sludge (Sims and Kline, 1991). How to reduce the availability of heavy metals is a major concern in land application of sewage sludge. Many authors have reported the relationship between solubility of heavy metals in sludge amended soil and soil pH ( Hamon et al., 1995; Otte et al., 1995).The lowered pH of mine soils also increases the solubility of toxic metals allow leaching of essential nutrients. For that reason, in this study it is tried to increase soil pH with the application of a mixture of sewage sludge and crushed shell, and hypothesized to decrease toxic metals biodisponibility. Mitilus shell application has like purpose of correcting soil pH. In a nineteen days laboratory experiment, two mine soils were amended with a rate of 25 and 50 Mg ha-1 of municipal sewage sludges and crushed shell and incubated to study organic matter, nitrogen dynamic, and heavy metal availability under controlled conditions of moisture and temperature. Samples with a mixtura of sewage sludge and shell crushed were compared to samples where the application consisted only of sewage sludge. The study have an important conclusion: the soil treated with 50 Mg.ha-1of residual sludge and crushed shell is the most effective treatment. At the end of incubation a pH increase and significant effects on the organic matter content had been produced. The nitrate and ammonium content increases during incubation, the highest nitrate values are reached at 45 days of incubation period. The highest mineralization rate was produced in the soil at 45 days. The aplication of residual sludge and crushed shell increased organic-N mineralized . The available metals content present a significant decreased at the end of the experiment. The results suggest that the sewage sludge and crushed shell application had a positive effect on mine soils.

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