Compositional variation and hazards of wood ash in Ireland

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Jagodzinski, Lucas S.
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University College Cork
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The lack of physico-chemical as well as ecotoxicological data on wood energy ash in Ireland hampers its development as a secondary raw material. This study compiled the first compositional account of the energy wastes and leachates as they accrue from ten untreated wood-fired power plants in Ireland. Bottom and fly ash as well as their leachates, were distinguished for five boilers that allowed for separate sampling. Composition of separate wood bottom and fly ash over time was investigated in a case study on a combined heat and power (CHP) model power plant. Samples of these ashes were examined for their quality as plant nutrient sources and their toxicological properties in an aquatic test battery. The MICROTOX test, Pseudokirchneriella subspicata growth inhibition test, Daphnia magna immobilization assay, Lemna minor growth inhibition and Oncorhynchus mykiss acute and prolonged survival tests comprised the ecotoxicological test battery. Further to this, the two ash types from the case study site were sieve fractionated and tested with MICROTOX and L. minor. Leachates were more variable in composition than their parent solid ashes. A large part of the variability and chemical hazards observed in the wood energy waste stemmed from the fly ash portion therein. Segregation of bottom and fly ash allows for higher compositional consistency and thus better predictability of the materials’ properties. The case study site ashes were variable over time, but some compositional consistency is given. Ecotoxicological assessment revealed fly ash from the case study site to be more toxic than bottom ash. Single cell organisms within the test battery were most likely to be adversely affected. Measurable effects of ash on aquatic species were affected by the test regime (native leachates were more toxic than pH neutralized counterparts). Given the observed variability, a case-by-case evaluation of ashes from distinct boilers (over-time) is recommended.
Wood ash , Wood energy , Ecotoxicology , Chemical composition , Wood ash fertilization , Waste acceptance criteria
Jagodzinski, L. S. 2016. Compositional variation and hazards of wood ash in Ireland. PhD Thesis, University College Cork.
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