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Effect of composted sewage sludge on heavy metal Content of the soil and plants

A good way for utilizing municipal sewage sludge is its use on agriculture lands after composting. The fate of sewagesludge is unsolved, its large quantity is cumulated on the territories of sewage cleaning plants. We can solve seriousenvironmental problems with sewage sludge treatment, however there are some risks, since sewage sludge may containheavy metals in high rate.In the Nyírség region of Hungary there are mostly acidic sandy soils with low humus content. Because of the decreasingquantity of livestock manure, the subsequent delivery of organic matter into the soils could be problematic.

Further Author:
Gy. Füleky - Szent István University

Applicationof sewage sludge (compost) in agriculture is very difficult, because the possible great toxic elements content of sludgesand the farmers have to proceed according to stringent lows.Sandy soils are poor in organic and mineral colloids. Long-term use of organic fertilizers could improve this problem,but in a short-term period only the macro- and micro-element content could be supplied. Due to these properties sandysoils have low fertility. To improve all these characteristics we can use composted sewage sludge.Experiment was established in spring, 2003 at the Research Institute of University of Debrecen, in Nyíregyháza city,located at NE part of Hungary and was re-treated in 2006 and 2009. The compost was applied at 9, 18, 27 t ha-1 doses,ploughed into the soil before sowing. Beside the toxic element content of soil, we studied the effect of the appliedcompost on triticale, maize and pea in a small-plot experiment in five replicates. The pH of this light textured sandy soilis 4.58, its humus content is 0.31%. In the composting process some additives such as bentonite, rhyolite and wheatstraw were used, because these materials have good effects on light textured sandy soils, especially with organicmaterial. In this way, the compost contains 40% sewage sludge, 25% straw, 30% rhyolite and 5% bentonite. Ourcompost fills the requirements of the Agricultural Ministry Order of 36/2006 (V.18.).The observed parameters were the followings:
􀂃 toxic element content (As, Cr, Cu),
􀂃 the quantity of the yield,
􀂃 the development of plants.
In the 2008 and 2009 years of the experiment, soil samples were collected twice a year, in April and after harvesting.Samples were sieved to <2 mm, dried at 105 oC and the Cr and Cu concentrations analyses were done after a HNO3-H2O2 digestion by ICP-OES (VARIAN VISTA PRO) and the As concentrations analyses was done by GF-AASequipments. Plant samples were dried at 105oC and were ground before digestion. The measured elements were arsenic(As), chromium (Cr), and copper (Cu).One-way analysis of variance and Tukey’s test were used to determine the effects of treatments on crop yield and onmetal content of plants and soil.Pea accumulated heavy metals in its root but the heavy metal content of seeds was not increased in the treatments andthe values were in the concentration range of crops growing on unpolluted soils. In the case of the other crops treated,there was no or very little increase of the heavy metal content. The results of the metal content stayed under the levelsset in the 50/2001 (IV.3.) Goverment Statute. Any significant effect of sewage sludge compost treatments on Cu, As and Cd content of the soil was not found.

Copyright:	© European Compost Network ECN e.V.
Quelle:	Orbit 2012 (Juni 2012)
Seiten:	8
Preis:	€ 8,00
Autor:	Attila Tomócsik Marianna Makádi V. Orosz Tibor Aranyos J. Mészáros
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