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LEACHABILITY OF DENITRIFYING BIOREACTOR FILLINGS
Abstract
Denitrifying bioreactors can be used to reduce high nitrate concentrations in agricultural runoff in situ. They operate on the basis of the flow of nitrate-rich water through a filtration medium containing biodegradable organic matter that serves as an organic carbon source for denitrification bacteria. However, undesirable excessive leaching of organic compounds from the bioreactor fillings can occur, especially in the start-up phase. The paper presents the results of static leaching tests conducted on six different wood materials potentially applicable as denitrifying bioreactor fillings, namely a mixture of pine and larch bark, and chips made from oak, poplar, beech, acacia, and spruce wood. The chemical properties of aqueous extracts from wood materials were determined and ecotoxicological bioassays were performed. The results indicate significant differences among the woods of different tree species, mainly in terms of the leaching of organic substances and ecotoxicity. The best results were achieved with the mixture of pine and larch bark, and with poplar chips. In contrast, acacia and oak chips emerged as the least suitable due to their excessive leaching of organic substances and the ecotoxicity of the resulting leachates. Storage of nitrification bioreactor fillings in moist conditions during a dry period led to lower leachability than storage submerged in water. The pretreatment of materials by drying was shown to be somewhat inadvisable.
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