Ena Smidt

Characterization of different decomposition stages of biowaste using FT-IR spectroscopy and pyrolysis-field ionization mass spectrometry

The decomposition stage and stabilization of organic matter in biowaste (mixture of yard waste and kitchen waste), originating from an open windrow process, were investigated using Fourier transform infrared (FT-IR) spectroscopy and pyrolysis-field ionization mass spectrometry (Py-FIMS). These investigations provided detailed information about chemical constituents and their behavior during the composting process. The chemical compounds were classified by their molecular signals in Py-FIMS. Multivariate statistical analysis revealed, that during the composting process, the group containing lipids, fatty acids and other chemical compounds with aliphatic skeletons changed the most. Corresponding with Py-FIMS findings changes were observed in absorbance bands of infrared spectra that reflect this group of organic compounds: the aliphatic methylene bands at 2925 and 2850 cm-1, the band of C=O vibrations of carboxylates at 1640 cm-1, the O=H in-plane bend of carboxylic acids, the CO2 stretch of carboxylates and the CH2 group of alkanes at around 1430 cm-1. During decomposition these bands decreased up to a steady level that indicated stabilization. The band at 1260–1240 cm-1 that can be assigned to the C=O stretch of carboxylic acids or to the C=N stretch of amides and the band of aromatic amines at 1320 cm-1 disappeared completely. The nitrate band at 1384 cm-1 appeared at a later stage of the composting process. The relative increase of chemical compounds like moieties of lignin, humic acids and tannins in the composted material contributed to the aromatic C=C band at around 1640 cm-1.

Characterization of waste organic matter by FT-IR spectroscopy: Application in waste science

A series of experiments has shown that FT-IR (Fourier transform infrared) spectroscopy is a helpful tool for characterizing waste organic matter, its decomposition, and stabilization in rotting processes. A specific set of differently treated input materials, originating from various composting plants, was chosen to reflect a wide range of spectroscopic properties. The approach to FT-IR spectra interpretation is presented. Changes of relative absorbances of the band at 2925 cm−1 (methylene groups of aliphatics) reflect the progress and dynamics of composting processes. Different processes can be compared by the specific development of their 2925 cm−1 band. Nitrate was quantified by calibrating nitrate band heights with added amounts of KNO3. The concentrations and band heights (absorbances) were linearly correlated (R2 = 0.9968, SD = 0.001). Bands of inorganic components are useful to assess the decomposition process because they also indicate the development of organic matter. Different wastes can be distinguished by their fingerprint region (1500–900 cm−1). This region also reveals fresh and undecomposed materials. The presence or absence of specific bands provides information about the decomposition status of materials.

Prediction of humic acid content and respiration activity of biogenic waste by means of Fourier transform infrared (FTIR) spectra and partial least squares regression (PLS-R) models

Fourier transform infrared (FTIR) spectroscopy has been proven to be an appropriate analytical method for the qualitative assessment of compost stability. This study focuses on quantitative determination of two time-consuming parameters: humic acid (HA) contents and respiration activity. Reactivity/stability and humification were quantified by respiration activities (oxygen uptake) and humic acid contents. These features are also reflected by a specific infrared spectroscopic pattern. Based on this relationship partial least squares regression (PLS-R) models for the prediction of respiration activities and humic acid contents were calculated. Characteristic wavenumber regions that are assigned to the biological/chemical parameter were selected for multivariate data analysis. The coefficient of determination (R(2)) obtained for the humic acid prediction model from infrared spectra was 87% with a root mean square error of cross-validation (RMSECV) of 2.6% organic dry matter (ODM). The prediction model for respiration activity resulted in a R(2) of 94% and a RMSECV for oxygen uptake of 2.9mgg(-1) dry matter (DM).

Characterization of waste materials using FTIR spectroscopy: Process monitoring and quality assessment

Abstract Stages of organic matter decomposition in waste materials are reflected by their IR spectral pattern. Indicator bands undergo changes during the biological treatment of the waste material. Based on the alteration of band intensities, process control can be carried out. Different spectral patterns of yard‐waste composting processes were related to divergent compost features. Mechanical–biological treatment of municipal solid waste results in a final product that can be disposed in a land fill. Several missing bands that indicate metabolic activities reveal final product quality. Identification of unknown materials can be carried out by comparison with pure substances or landfill components. The assessment of waste organic matter in abandoned landfills is based on the spectral pattern that is assigned to a specific stage of decomposition. Maturity and stability, which are considered important properties of waste organic matter, are reflected by their spectroscopic characteristics. This paper was by special invitation as a contribution to a special issue of the journal entitled “Application of Spectroscopic Methods to Environmental Problems”. The special issue was organized by Professor Peter A. Tanner, Professor in the Department of Biology and Chemistry at City University of Hong Kong.

Potential emissions from two mechanically–biologically pretreated (MBT) wastes

The interaction of parameters determining the potential emissions of two different mechanically-biologically pretreated municipal solid wastes (MBT wastes) is elucidated in this work. The origins of the wastes are Germany and Sweden. By means of lab-scale experiments, increased stabilisation through composting is preferably determined by a decrease in respiration activity. Concurrently, the stabilisation is verified for the leachates by a decrease in COD, DOC, and BOD(5). Total organic carbon content reflects stabilisation less accurately. FT-IR and thermal analytical methods add valuable information about the state of degradation, especially when several distinct thermal parameters are taken into account. Mobility of Cr, Ni, Pb, and Zn produced by a batch leaching test with deionized water is reduced by the pretreatment of both materials. Mobility of copper unambiguously increased. A principle component analysis (PCA) of membrane fractionated leachates indicates an affinity of Cu to mobile humic acids or dissolved organic carbon. High Cr, Zn, and Ni contents in the solid co-occur with high contents of solid humic acids. To a lesser extent, this is also true for solid Cd, Cu, and Pb contents. Due to differences in required landfilling conditions, actual emissions and after-care phase length will depend on whether each waste is landfilled in Germany or Sweden.

Effect of sewage sludge treatment and additional aerobic post-stabilization revealed by infrared spectroscopy and multivariate data analysis.

Sewage sludge samples representing different stages during waste water and sewage sludge treatment were collected at four Austrian municipal waste water treatment plants. Changes of sludge composition are reflected by a specific infrared spectroscopic pattern. Anaerobically digested sludge was subjected to aeration in lab-scale reactors in order to find out if post-aeration after anaerobic digestion provides enhanced organic matter degradation and stabilization. Spectral data were evaluated by means of multivariate statistics. Similar spectral characteristics of sludge degradation stages were visualized by principal component analysis. The effect of additional aerobic treatment of anaerobically stabilized sludge was revealed by discriminant analysis that distinguishes additionally aerated sludge from all the other degradation stages of sludge because of changes in the spectral pattern by increasing stabilization. Based on partial least squares regression (PLSR) a correlation coefficient of R(2)=0.91 was found between spectral characteristics and the chemical oxygen demand (COD).

Investigations of biological processes in Austrian MBT plants.

Mechanical biological treatment (MBT) of municipal solid waste (MSW) has become an important technology in waste management during the last decade. The paper compiles investigations of mechanical biological processes in Austrian MBT plants. Samples from all plants representing different stages of degradation were included in this study. The range of the relevant parameters characterizing the materials and their behavior, e.g. total organic carbon, total nitrogen, respiration activity and gas generation sum, was determined. The evolution of total carbon and nitrogen containing compounds was compared and related to process operation. The respiration activity decreases in most of the plants by about 90% of the initial values whereas the ammonium release is still ongoing at the end of the biological treatment. If the biogenic waste fraction is not separated, it favors humification in MBT materials that is not observed to such extent in MSW. The amount of organic carbon is about 15% dry matter at the end of the biological treatment.

The Application of FT-IR Spectroscopy in Waste Management

This synopsis of FT-IR spectroscopic applications in waste management covers relevant issues regarding monitoring, process and quality control. Quality in this context means low reactivity, low gas forming potential and compliance with limit values of materials to be landfilled, appropriate compost ingredients and improvement of the stable carbon pool by humification of compost organic matter. The division into sections was carried out according to specific materials and processes and the related questions to be answered. Waste materials have not posed a problem in the past, as long as they were returned to the natural cycle. The higher degree of utilisation, the long lasting life cycle of goods and their re-use caused minor waste amounts and contributed to the balance of input and output streams. As natural materials were the basis for good production, waste was integrated in the natural cycle. Organic waste materials only escaped degradation if they were preserved under particular conditions. Inorganic residues from ore mining have led to local contamination by heavy metals. In contrast, fragments of ancient pottery or ruins have gained in importance as historical witnesses. The economical and social increase in prosperity and urban development has been paralleled by strongly rising amounts of organic and inorganic waste and the acceleration of turnover rates. These have led primarily to sanitation problems, especially in expanding urban areas. Disposal of these wastes by spreading them over the surrounding countryside or filling dumps were only temporary “solutions”. Natural waste such as foliage falling in autumn can be considered as an intermediate product in a closed circle. Except for natural disasters, turnover rates and the related contents of substances are subjected to regulations. Anthropogenic waste is in most cases the end of a one-way street that causes system imbalances. Therefore new approaches and waste management strategies aim at copying natural cycles. The amount, changes in the chemical composition of our goods, the use of hazardous substances and the careless landfilling of waste in dumps have caused serious environmental problems and demonstrated the need for action. The awareness of this issue emerged when soils and groundwater were contaminated by leachate emissions. Due to the missing separation of hazardous waste, landfill remediation has often implied a complete excavation of the landfilled material. Discussions on climate change, the role of waste management in the global carbon cycle and its contribution to the carbon budget have drawn attention to relevant gaseous emissions from landfills with a global warming potential, especially of methane.

Determination of MBT-waste reactivity - An infrared spectroscopic and multivariate statistical approach to identify and avoid failures of biological tests

The Austrian Landfill Ordinance provides limit values regarding the reactivity for the disposal of mechanically biologically treated (MBT) waste before landfilling. The potential reactivity determined by biological tests according to the Austrian Standards (OENORM S 2027 1-2) can be underestimated if the microbial community is affected by environmental conditions. New analytical tools have been developed as an alternative to error-prone and time-consuming biological tests. Fourier Transform Infrared (FT-IR) spectroscopy in association with Partial Least Squares Regression (PLS-R) was used to predict the reactivity parameters respiration activity (RA(4)) and gas generation sum (GS(21)) as well as to detect errors resulting from inhibiting effects on biological tests. For this purpose 250 MBT-waste samples from different Austrian MBT-plants were investigated using FT-IR spectroscopy in the mid (MIR) and near infrared (NIR) area and biological tests. Spectroscopic results were compared with those from biological tests. Arising problems caused by interferences of RA(4) and GS(21) are discussed. It is shown that FT-IR spectroscopy predicts RA(4) and GS(21) reliably to assess stability of MBT-waste materials and to detect errors.

Investigation of 15-year-old municipal solid waste deposit profiles by means of FTIR spectroscopy and thermal analysis

Five profiles of a 15-year-old bank containing over three weeks composted municipal solid waste were characterized by means of different parameters habitually applied in waste management (loss on ignition, total organic carbon, total nitrogen, NH(4)-N, pH), and in addition by humic acid determination, FTIR spectroscopy and thermal analysis. Stabilization processes are revealed by humic acid contents. Over the 15 year period organic matter had developed in various ways. Highest humic acid contents were found at 0.5 m below the surface. Below 1.0-1.5 m anaerobic conditions dominated causing a strong decline of humic acid concentrations. Despite similar contents of organic matter at 0.5 m and at 3.0 m organic matter quality differed. These differences were verified by infrared spectroscopic investigations and thermal analyses (differential scanning calorimetry DSC). The spectral pattern of 15-year-old profile samples (municipal solid waste including the biogenic fraction) was compared to current municipal solid waste and abandoned landfill materials. Current municipal solid waste samples comprised different degradation stages from fresh materials to stabilized waste, suitable for landfilling according to Austrian standards. Municipal solid waste originating from abandoned landfills closed in the seventies represented stable material. Principal component analysis was performed to detect similarities and differences. It is evident that the profile samples constitute a particular group in between municipal solid waste and abandoned landfill material. Some differences can be attributed to the divergent composition of municipal solid waste in the eighties when the organic fraction was not separated. Otherwise, landfill materials from the seventies with the same composition regarding the organic fraction were deposited together with construction waste. Heat flow curves (DSC profiles) of municipal solid waste, representing different decomposition stages, illustrate the development of enthalpies and reveal the status of the profile samples. It is evident that mechanical-biological pretreatment leads to a faster stabilization of waste organic matter.