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3.1 George Bekiaris – University of Copenhagen

ReUseWaste > Thesis abstracts > 3.1 George Bekiaris

Application of Fourier-transform infrared photoacoustic spectroscopy for characterisation of organic wastes and determination of their usefulness for bioenergy and soil amendment, George Bekiaris, UCPH

Organic wastes can be used as valuable fertiliser and this has a number of benefits for the soil compared to synthetic fertilisers, such as increase of organic matter content, improvement of soil structure and water holding capacity. Organic wastes can also be used for other purposes such as energy recovery through ethanol or biogas production. Laboratory assays that determine the usefulness of the organic wastes for these different purposes are already exciting. However, in most of the cases the assays are associated with high operational costs and times. Therefore, the main objective of this project was the development of less time-consuming and inexpensive techniques that can partially replace laboratory assays in the determination of the usefulness of organic wastes.

In this project the potential of a relatively new spectroscopic technique, i.e. Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS), for characterising the chemical composition and predicting the usefulness of organic wastes was tested. The working principle of FTIR-PAS allows the acquisition of detailed spectra of very dark and opaque samples (such as manure, biochars, soil etc.) without any pretreatment, which is not feasible with traditional transmittance FTIR techniques.

The work is reported in four papers. In the first paper, we investigated the ability of FTIR-PAS to predict the mineralisable fraction of carbon of a very diverse sample set of organic waste products. The spectra of the samples were recorded and characteristic peaks of each organic waste type as well as peaks-indicators of decomposition stage were identified. The correlation of these spectra with the carbon mineralisation values (obtained after the incubations for 91 days of soil-organic waste products mixtures) allowed calibration of a model that predicts the mineralisable carbon fraction. The predictions were similar to or better than predictions performed previously using near infrared spectroscopy (NIR), with R2 values of measured vs. predicted mineralisable C fraction ranging between 0.70 and 0.78. Compounds such as carboxylic acids, carboxylates and polysaccharides found to be positively associated with the mineralisable C fraction. FTIR-PAS can there be used to understand the role of the chemical composition and could predict, important properties of organic wastes, such as mineralisable C fraction, lignocellulosic fraction and organic matter content of organic waste products; biochemical methane potential of plant biomasses and sugar release. 

The second paper investigated the ability of FTIR-PAS for analysing phosphorus speciation of biochars produced from bone meal and the solid fraction of manure digestate. The advantage of the photoacoustic detector with very dark (black) samples was obvious and the FTIR-PAS spectra contained more information (features) compared to attenuated total reflection FTIR spectra of the same samples. The discrimination of phosphorus species, based on characteristic peaks of the most common phosphates that had previously been recorded with FTIR-PAS, was also feasible for biochars produced at 600 oC and above because the interference from organic components other than aromatic compounds was greatly reduced. The P speciation was significantly affected by the pyrolysis temperature for the biochars produced from the solid fraction of digestates (calcium phosphates existed at all temperatures in different forms, while there was a formation of iron phosphates, struvite and variscite at higher pyrolysis temperatures), while the speciation was only slightly affected for the biochars produced from bone meal which was mainly calcium phosphates to begin with.

  • Georgios Bekiaris, Clément Peltre, Lars S. Jensen, Sander Bruun. Using FTIR-photoacoustic spectroscopy for phosphorus speciation analysis of biochars. Submitted to Analytical Chemistry (2016).

The third and fourth paper investigated the usefulness of organic wastes for energy recovery. FTIRPAS was found able to calibrate a model that provides very good predictions of the biochemical methane potential (for biogas production) of various plant biomasses. Furthermore we were able to develop a model predicting the sugar release during bioethanol production from a large (1122 samples) sample set of winter wheat straw varieties. The predictive power and accuracy of the models was similar or greater than models calibrated using NIR. In addition the compounds that contributed to the biogas potential and sugar release were identified. In both cases the crystallinity of the cellulose was of major importance for the potential to recover energy, while lignin impeded the release of sugar and biogas.


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