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					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). VTT, Polttoainejalostus- ja
    voitelutekniikan laboratorio.
3. Lappi, Maija, 1983. Jyrsinturpeen itsekuumeneminen. VTT. 99 p.
4. Paasivirta, J., Ruokokoski, V. & Nyrönen, T. 1978. On the qualitative analysis of the volatile
    compounds escaping from the peat stockpiles during the self-heating process. proceedings
    of the symposium of commission II. Kouvola.
5. Pankratov, N.S. (toim.) 1972. Jyrsinturve ja sen ainesosat varastoinnin
    itsekuumenemisprosessissa. Valkovenäjän tiedeakatemia, 320 p.
6. Jing Quan Yu &Yoshihisa Matsui: Effects of Root Exudates of Cucumber (Cucumis sativus)
    and Allelochemicals on Ion Uptake by Cucumber Seedlings. Journal of Chemical Ecology
    23/3: 817-827.
7. Jensen, P. & Adalsteinsson, S. 1991. Organiska syror i näringslösningen kräver god pH
    kontroll vid odling av växthuskulturer. Trädgård 944. Sveriges Lantbruksuniversitet.
8. Ranneklev, S.B. and Bååth, E., 2003. Use of Phospholipid Fatty Acids to Detect Previous Self-
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9. Ludwig, B., Schmilewski, G. and Terhoeven-Urselmans, T. 2006. Use of near infrared
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10. Zevenhoven, M., Hupa, M., Lehtovaara, J. & Storholm, S. 2008. Ash forming matter in peat-
    the role of iron, SNCI, 22-24. October 2008, Göteborg, Sweden.
11. Järvinen, S., Lehtovaara, J., Sirén, P., Pakkanen, H., Salo, M. and Alén. R., 2009, Self-heating
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    2009, Jyväskylä, Finland.

				
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