Chemical changes in peat as a result of self-heating: analysing peat suitability for growing media use Päivi Picken, Jaakko Lehtovaara & Jaakko Soikkeli, Vapo Oy Introduction Background Raw material safety = good practices and regular storage monitoring…. Despite this sometimes a laboratory evaluation of the peat’s suitability is needed. Introduction Motivation for this paper • A significant part of the chemically detailed self- heating research is done from the energy peat perspective. • Due to this background the relationship between known chemical changes and phytotoxicity has been poorly defined. • Also the analytical recognization of self-heated material has been less relevant as focus has been quite purely in understanding of the self-heating ending to self-ignition and preventing the self- heating process. Self-heating, simplified version from horticultural point of view Micro-organism activity: hydrolysis of polysaccharides (hemicellulose) Temperature raises => monosaccharides (simple sugars) Monosaccharides react Monosaccharides other with amino acids, => reactions, producing melanoidines carboxylic acids (humic acid –like like compounds) further decomposition of carboxylic Decomposition products, e.g. ammonia acids and volatile compounds (smell) up to 60-70 °C Introduction • Examples of known results of hemicellulose=> self-heating of biomass: monosaccharides carboxylic acids like formic acid, acetic acid, linoleic acid, monosaccharides =>carboxylic acids phospholipid fatty acids, aldehydes like hexanal. • For example formic and acetic acid are considered as phytotoxic compounds. • Many prevent nutrient uptake due to lower pH Introduction • Self-heating also releases nutrients into more available (water-soluble) form etc. • Organic acid content (created by self- heating) decreases in later stages of self-heating due to further reactions (resulting different salts). • The impact on plants is likely to vary due to the phase of the self-heating process (incl. temperature). Introduction • The impact on plants varies also due to the plant and growing culture. For example flushing the growing media through is likely to remove most problem sources. Harmful compounds are mainly water-soluble. Introduction • Immature (still composting) bio- waste materials and self-heated peat share largely the same chemical characteristics. Maturation improves both. • Same type of processes happen in all biomass materials (including also harvested wood and wood residues and products like pellets). Analytical methods and recognizing self- heated peat Self-heating does not perform miracles: • Self-heating does not produce or add new chemical elements into peat. • Only relative quantity (%) may change due to decrease of other elements - some elements leave peat in form of gas (for example CO2 and H2S) resulting losses of dry matter. • Mainly only the forms, the compounds in which the elements appear, do change. => in analysis selective extraction methods should be prioritized. Analytical methods and recognizing self- heated peat • Most of the commonly used analysis methods for evaluation self-heating status are currently based on water soluble concentrations chemical elements. This works, if reference concentration of exactly same peat* is available. *) same peat = same peatland, same depth • BUT: This may lead to false interpretation, if reference concentrations of exactly same peat are not available. Analytical methods and recognizing self- heated peat • Considering total and water soluble concentrations of different elements, natural variation in peat is very large (often larger than the change-range due to self-heating). • Mainly related to the geo- and biological formation history of the peatland and to the geochemical characteristics of the mineral subsoil, underlying bedrock and groundwater feed. Analytical methods and recognizing self- heated peat • Water extraction does not separate different compounds or oxidation stages. Even forms bound to minerals are part of the analysis result. For example clay minerals are commonly present in peat and a large part of clay passes average filters due to its very fine particle size. Analytical methods and recognizing self- heated peat Other interpretation challenges: • All organic materials change as a result of exposure to different environmental factors including normal storage conditions. • Many of these changes (like hydrophobic development) can be confused with changes related to self-heating – how to distinguish them? Different methods and related problems X = problem relevant to parameter EC pH (water-soluble) Mn, Al, B Fe, Ca, Mg, Fe3+/Fe2+ NH4-N P CODCr Water abs. Germination Smell (water-sol.) Natural variation too large compared to X X X (x) change in self- heating More dependent on anaerobic status (x) X than actual heating Natural presence of clay particles in X (x) peat may give a false positive result Different methods and related problems X = problem relevant to parameter EC pH (water-soluble) Mn, Al, B Fe, Ca, Mg, Fe3+/Fe2+ NH4-N P CODCr Water abs. Germination Smell (water-sol.) Drying and UV- exposure => same X (x) impact as heating * Flushing of the test growing media may X give a false negative result *) Changes in organic compound level, e.g. auto-oxidation of fatty acid compounds. Lack of water in dry peat alone causes a “polar - non-polar conflict” X = apparent benefit Different methods, benefits relevant to parameter EC pH (water-soluble) Mn, Al, B Fe, Ca, Mg, Fe3+/Fe2+ NH4-N P CODCr Water abs. Germination Smell (water sol.) Origin in peat biological – not dependent on X X X geochem. factors Selective method X Shows the seriousness of the problem (x) (x) (x) X Peaks around the most phytotoxic stage of self- X X X X heating * ** *) Negative peak. **) Reflects the increase of hydrolysis of polysaccharides (water-soluble results). Estimating different methods Own data-set, bivariate correlations (Pearson) Significant correlations with self-heating: NH4-N 0.74 CODCr (in water filtration) 0.61 EC 0.60 pH -0.48 P (water-soluble) 0.36 Moisture -0.27 No significant correlations with other elements than P. Analysis: mainly EN-methods Conclusions • Parameters selected for identifying self-heated peat should represent factors that have small natural variation, but large variation due to self-heating. • Selective extraction methods should be prioritized. • Examples of suitable parameters: NH4-N, CODCr (in water filtration), P (water-soluble), germination. • Other possible parameters: EC as a quick-test, if reference concentration of the same peat is known. • Water-soluble/exchangeable elements, if reference concentration of the same peat is known. • Future: • Organic marker compounds? • New analytical techniques? (IR, NIR, others) ? Literature cited 1. Komppula, Jarmo, 1983. Turpeen hiilihydraatit ja niiden suhde jyrsinturpeen itsekuumenemisherkkyyteen. Turvetutkimusseminaari (peat research seminar), Jyväskylä 28.-29. April. 1983. 2. Lappi, Maija, 1986. Osaraportti: Turpeen orgaaniset aineosat, hydrolysoituva aine ja itsekuumenemisominaisuudet (Projekti Swe-Fin Torv). 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