Is aerobic composting capable of degrading pharmaceuticals and other xenobiotics in sewage sludge?

There is a growing interest in EU in finding environmental sustainable ways of using the enormous amounts of sewage sludge produced by the wastewater treatments plants. The sewage sludge contains both inorganic and organic compounds of which many inorganic salts are derived from the farmland soil and transported to the sewage sludge via food and feed crops to the human end uses and finally ends in the wastewater and the sewage sludge.

Ideally the inorganic compounds such as phosphorus (P), nitrogen (N), potassium (K) should be brought back to the farmland from where it is derived. The organic compounds derived from the plants, such as organic fibres and microbiological biomass could be a good additive to the humus content in the soil and bind carbon. Direct use of the sewage sludge on the farmland is the most simple and most direct way of using it, but it has the disadvantage, that pathogenic microorganisms and pests can be transferred to the soil together with environmental unfriendly organic compounds such as pharmaceuticals, plasticizers etc. The finding of high concentrations of unwanted chemical compounds, such as pharmaceuticals and the biocide Triclosan® in sewage sludge from several sewage treatment plants resulted in renewed interest for incineration of the sewage sludge. Incineration in power plants is an obvious way of treating the sewage sludge. In this way all organic compounds are degraded and converted to CO2 and other oxidized compounds. The inorganic compounds (N, P, K) etc. will be found in the ashes and can be used in cement production or as fertilizer if the content of heavy metals are low. This utilisation adds CO2 to the atmosphere and removes carbon from the soil, but also removes unwanted organic compounds. Four Danish composting plants decided to join forces in investigation on whether unwanted chemical compounds still would be present after aerobic composting in open windrows. Looking at biocides, e.g. Triclosan®, environmental unfamiliar organic compounds, e.g. LAS, DEHP, NPE and PAH it has already been shown, that composting reduces these compounds and often dramatically. Concerning pharmaceuticals very little information is available about degradation and mobility in sewage treatment plants and soil, but a preliminary screening has shown, that out of 15 pharmaceuticals found in wastewater, 13 was also found in the outlet from the sewage treatment plant. On the basis of the chemical composition of the pharmaceuticals we found it probable that composting will degrade many of these. Life cycle analyses (LCA) was carried out on fresh and anaerobic digested sewage sludge, treated by aerobic composting and compared to direct use on farmland and incineration in power plants. The conclusion is that composting is a more favourable solution concerning climatic effects, whereas incineration is a better option concerning degradation of unwanted organic compounds.

Copyright: © European Compost Network ECN e.V.
Quelle: Orbit 2008 (Oktober 2008)
Seiten: 8
Preis inkl. MwSt.: € 7,00
Autor: Margrethe M. Andersen
L. Clowes
P.H. Petersen
J. Kirkeby

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