 |
| Titel |
What happens with the nitrogen in sewage sludge once this material is pyrolyzed? |
| VerfasserIn |
Marina Paneque, José María De la Rosa, Jürgen Kern, Heike Knicker |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250152780
|
| Publikation (Nr.) |
 EGU/EGU2017-17662.pdf |
|
|
|
|
|
| Zusammenfassung |
| The transformation of sewage sludge (SS) into char by pyrolysis achieves sludge
hygienization, a necessary step prior to a possible application on agricultural soils. Former
studies indicated that during this process part of the organic nitrogen (No) of this material is
incorporated into the aromatic network of the charred product and forms the so called black
N (BN). De la Rosa and Knicker (2011) showed further that at least some of the BN is
bioavailable. However, neither the pathways of BN formation nor its chemical structure is
well understood.
Therefore, we studied the production of inorganic N (Ni) and the forms of No after
subjecting two types of SS to hydrothermal carbonization (HTC) and dry pyrolysis
(Dry-Py). The samples were collected at two different stages of the wastewater
treatment (hereafter A_SS and T_SS) at the Experimental Wastewater Treatment plant
CENTA, located in Carrion de los Céspedes (Southern Spain). Four chars were
produced by HTC at 200∘C and 260∘C, and with residence times of 30 min and
3 hours. Dry pyrolysis char was obtained after heating at 600∘C for 1 hour. The
organic N forms were revealed by solid-state 15N nuclear magnetic resonance (NMR)
spectroscopy.
All pyrolysis conditions resulted in a decrease of the amount of total N (Nt). Whereas
HTC preserved between 83-59% of original N, only 2% were recovered in the char after
Dry-Py. With respect to Ni, the amounts of ammonium and nitrite increased between 2 and 4
times compared to the non-treated SS after HTC. After Dry-Py no Ni was detected in the
solid residue. The solid-state 15N NMR spectra of the non-treated SS are dominated by the
signals assignable to amide-N. With increasing temperature and residence time applied
during HTC, a shift of the signal intensity toward the region of pyrrole-N was evidenced.
The largest contribution of pyrrole-N was identified in the sample obtained after
heating at 260∘C for 3h although the 15N-intensity in the chemical shift region of
amide/carbazole N dominated the spectrum. In contrast, Dry-Py resulted in a dominance of
pyrrole-N.
In conclusion, our study demonstrated the impact of the pyrolysis conditions on the quantity
and quality of N-forms in chars of SS. Considering the N fertilization potential, HTC chars
may be more suitable than chars produced by Dry-Py if fast fertilization is needed due to the
presence of Ni. On the other hand, the binding of N in heterocyclic structures retards
its bioavailability. Thus Dry-Py chars will be a better choise, if slow N-release is
wanted. However, deeper and specific researchers are necessary to confirm this
hypothesis.
De la Rosa JM, Knicker H (2011) Bioavailability of N released from N-rich
pyrogenic organic matter: An incubation study. Soil Biology and Biogeochemistry 43:
2368-2373 |
|
|
|
|
|
|