from ASHBACK, midterm report
October, 2015
Results of work
WP1 Ash handling
Task 1 Ash analysis
 Because of the high temperature of burning at the energy plants the remaining material is quite inaccessible.
 Combustion in nitric acid plus hydrofluoric acid mean full destruction and whereas nitric acid gives a fraction.
 We assessed heavy metals in 13 biofuel ashes from 10 energy plants with full and partial destruction.
 For Cd and Zn the partial destruction gave 3/4 of the heavy metals (Cd, Zn) assessed with full destruction.
 The measurements done at two of our laboratories show high correlation (R2 = 0.9); we find this very satisfactory.
Task 2 Heavy metals in and out from an energy plant
 Variation in heavy metal content in wood chips fuel was analyzed at the Herningværket during 13 weeks in 2014.
 The fly ash contained on average 9.6 µg Cd g-1 ash, 100 times above the fuel; a value within acceptable limits.
 Cd content in ash varied on average 10% at consecutive samplings whereas 27% variation occurred in wood chips.
 This difference is governed by the ease of making a representative sample of ash and wood chips, respectively.
WP2 Field experiment, model studies
Task 1 Field experiment established
 At Gedhus plantation with treatments of 0, 3, 4.5 and 6 t ash/ha each in three replicates; start April 2014.
 Suction cups for collecting soil water were installed in 15 and 60 cm depth in replicates of three in all 12 plots.
 Water through fall samplers, rain fall samplers as well as TDR poles was likewise installed.
Task 2 Field experiment sampled
 Soil water collected monthly is continuously analyzed for pH, salts, nutrients and heavy metals.
 Overall water balance for the area and water content of the soil is assessed at same frequency.
 All data will be analyzed collectively in winter/spring 2017.
Task 3: Formulation of improved ashes
 Due to low content of heavy metals and lack of toxic effects, encapsulation of harmful metals have been left out.
Task 4: Model experiments on heavy metal movement in soil
 The results show long term release of alkaline compounds, confirming the suitability of ash for liming purposes.
 Fast dissolution of nutrients like K and Na takes place when the ash is spread on forest soil.
 Nutrients like P and Al are stronger bound to the ash matrix and may only be released in small quantities.
 The release of Cd was pH-dependent, presenting negligible releases (< 0.5 µg/l) for pH values above 7.
 The effect of ash amendment is very local; pH was only affected to one cm depth during first year after amendment.
WP3 Ecotoxicology
Task 3 Soil animals
 We tested how bio-ash affected reproduction and survival in two collembolan species with ash doses up to 15 t/ha.
 In the coniferous soil (Gedhus) there was no negative effect of ash addition, actually both species were stimulated.
 In the agricultural soil (Foulum) both species were affected negatively by ash.
 Parallel experiments with Ca(OH)2 indicated that the negative effect was due to a pH-increase.
Task 4 Fungal growth
 With ash amendment up to 15 t/ha no change was observed in fungal growth.
WP4. Food webs and bioaccumulation of Cd
Task 1. Ash effects on food web structure.
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In Gedhus we have seen a consistent positive effect of ash on bacterial and bacterial-feeding organisms.
This effect is evident even at the lowest dose of 3 t/ha.
No significant effects were found for the fungal-feeding nematodes.
So far we have not detected any effects on other components of the soil food web at doses up to 6 t/ha.
Results are consistent with our hypothesis that ash may stimulate bacteria and the bacterial-feeding soil fauna.
Omnivorous nematodes were negatively affected by ash application.
This is in accordance with the general notion that larger animals with longer generation times are most sensitive.
Task 2. Cd accumulation and food web complexity.
 Pot experiments with grass indicated increased Cd levels in plant tissues at ash application rates above 11 t/ha.
WP5 Ecosystem services
Task 1 Carbon sequestration
 We assessed release of CO2 from the soil in the Gedhus plantation added different amounts of ash.
 Even a dose of 90 t ash/ha did not alter the release of CO2 from the forest floor throughout a 15 month period.
 The strong ash effects on soil carbon turnover does not affect carbon sequestration in spruce plantation at Gedhus.
 Same lack of ash effect found in agricultural soil (Foulum).
Task 2 Greenhouse gasses
 No exchange of N2O up to 9 t ash/ha, but larger additions resulted in release of the gas in Gedhus.
 The exchange of CH4 mainly involved absorption by the soil and this was not affected by ash in Gedhus.
 In agricultural soil (Foulum) similar lack of effect of lower ash amounts on N2O emission.
What does this mean to society/industry?
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Until now we have not identified any toxic effects of ash amendments that can be related to compounds in the
ash at doses up to five times above presently allowed amounts.
The effects observed hitherto can be ascribed to the change in pH of the environment.
Even though marked shifts occur in the soil community with ash, also at low doses, no indication of changes in
nutrient leaching, carbon sequestration or greenhouse gas emission have been observed.
Final conclusion if more ash amendment should be allowed awaits ongoing studies on changes in soil
community, and if these mean marked changes in ecosystem functioning or can be ascribed to toxic effects.
Researcher education
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The project has seven ongoing ph.d. projects.
Cross institutional, interdisciplinary, international cooperation
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We have project participants from industry (Hede Danmark) environmental management (ÅU Environment),
engineering (DTU environment), and biology (ÅU Biosystems, KU Bioilogical institute) actively involved in the
project.
Our ph.d. students benefit from the longer term experience with ash handling in Sweden and Finland.