Johannes Tintner

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.

Scrutinizing compost properties and their impact on methane oxidation efficiency

Methane emissions from active or closed landfills can be reduced by means of microbial methane oxidation enhanced by properly designed landfill covers and engineered biocovers. Composts produced using different waste materials have already been proven to support methane oxidation, and may represent a low-cost alternative to other suitable substrates such as sandy or humic-rich soils, which are frequently not available in sufficient amounts or are too costly. In the present study a data set of 30 different compost materials (different age and input materials) and mixtures, as well as seven soils and mineral substrates were tested to assess methane oxidation rate under similar conditions in a laboratory column set-up. Multivariate data analysis (discriminant analysis) was applied to predict the influence of 21 different parameters (chemical, maturation and physical) on methane oxidation rate in a PLS-DA model. The results show that bulk density, total nutrient content (nitrogen and phosphorus), as well as the quantity and quality (with respect to maturity) of organic matter determined methane oxidation rate in this data set. The model explained 50% of the data variation, indicating how characterisation of oxidation rate by single, even diverse conventional parameters was limited. Thus for the first time, Fourier Transform Infrared (FTIR) spectroscopy was applied to a series of samples to better determine the characteristics of methane-oxidising materials. The initial data obtained in this study appear to be most promising. The prediction of specific methane oxidation rate of a potential biocover material from FTIR spectra and multivariate data analyses is a target to be focused on in the future.

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.

Determination of Humic Acids Content in Composts by Means of Near- and Mid-Infrared Spectroscopy and Partial Least Squares Regression Models

Humic acids are part of the stable organic matter fraction in soils and composts. Due to their favorable properties for soils and plants, and their role in carbon sequestration, they are considered a quality criterion of composts. Time-consuming chemical extraction of humic acids and the inherent source of errors require alternative approaches for humic acids quantification. Different measurement techniques in the mid-infrared (MIR: KBr pellet technique) and near-infrared (NIR: fiber probe as well as an integrating sphere with a sample rotator) regions were applied. Partial least squares regression (PLSR) models based on infrared spectra were developed to determine humic acids contents in composts. As the wavenumber regions used (NIR: 6105–5380 cm−1 and 4360–4220 cm−1, MIR: 1745–1685 cm−1 and 1610–1567 cm−1) represent different molecular vibrations, the importance of the methylene-group-derived vibrations for the NIR models is discussed. The correlation coefficients obtained for the KBr pellet technique, the NIR fiber probe technique, and the NIR integrating sphere (r = 0.94, 0.93, and 0.94) and the root mean square errors of cross-validation (RMSECV = 2.2% organic dry matter (ODM), 2.5% ODM, and 2.2% ODM) make the models appropriate for application in composting practice.

How to enhance humification during composting of separately collected biowaste: impact of feedstock and processing

Conventional parameters (loss on ignition, total organic carbon, total nitrogen, C/N-ratio, respiration activity (RA4), compost status (= ‘Rottegrad’), NH4-N and NO3-N) are not correlated to humification. At best, they provide information on the biological stability (status of degradation) of composts. Humic substances which are a source of stable organic matter and nutrients are discussed as a parameter describing compost quality. Thus, in the present research project a photometric method evaluating humic acids was used to characterize the quality of 211 Austrian and foreign composts made from source-separated collected biowaste or sewage sludge. Furthermore, parameters influencing the formation of humic acids during the rotting process were investigated by implementing rotting experiments in the laboratory as well as in composting plants. The analysed composts showed humic acid contents between 2.5 and 47 %, calculated on a organic dry matter (oDM) basis. In addition to the duration of treatment the main influence on humification was the feedstock used. Stabilized sewage sludge, biowaste after intensive anaerobic pre-treatment or biowaste with low reactivity (RA4) or uniform composition (e.g. mainly grass) showed a low formation of humic acids. For optimum humification the feedstock needed to contain components that are well balanced from scarcely to easily degradable compounds. Processing also influenced humification. Open windrow systems and reactor systems allow the same quality to be produced when operated well, but optimizing mineralization (e.g. very intensive aeration) showed negative effects. The positive condition required for humification is an unhurried (not too intense) degradation with long-lasting biological activity in which microbes have enough time to use the metabolic products of degradation for humification.

Reproducibility of Fourier transform infrared spectra of compost, municipal solid waste, and landfill material.

The reproducibility of infrared spectra from different waste materials such as compost, mechanically-biologically treated (MBT) municipal solid waste, and landfill materials was investigated. Reproducibility tests focused mainly on infrared spectra and parameter prediction from the spectrum developed for composts and MBT-waste, as well as band height ratio measurement for landfill materials in terms of practical applications. Compared to compost and landfill material, the reproducibility of infrared spectra from MBT-waste was considerably lower. Accordingly, sample preparation was modified and maximum mean deviation was minimized from 8.3% to 4.2%. The number of required spectra replicates was determined in consideration of practical aspects such as parameter prediction for composts and MBT-waste and the measurement of band height ratios (2925/1630 cm−1) of landfill materials. For composts two-fold measurements and for MBT-waste and landfill materials three-fold measurements were considered appropriate.

Risk assessment of an old landfill regarding the potential of gaseous emissions – A case study based on bioindication, FT-IR spectroscopy and thermal analysis

Risk assessment of two sections (I and II) of an old landfill (ALH) in Styria (Austria) in terms of reactivity of waste organic matter and the related potential of gaseous emissions was performed using conventional parameters and innovative tools to verify their effectiveness in practice. The ecological survey of the established vegetation at the landfill surface (plant sociological relevés) indicated no relevant emissions over a longer period of time. Statistical evaluation of conventional parameters reveals that dissolved organic carbon (DOC), respiration activity (RA(4)), loss of ignition (LOI) and total inorganic carbon (TIC) mostly influence the variability of the gas generation sum (GS(21)). According to Fourier Transform Infrared (FT-IR) spectral data and the results of the classification model the reactivity potential of the investigated sections is very low which is in accordance with the results of plant sociological relevés and biological tests. The interpretation of specific regions in the FT-IR spectra was changed and adapted to material characteristics. Contrary to mechanically-biologically treated (MBT) materials, where strong aliphatic methylene bands indicate reactivity, they are rather assigned to the C-H vibrations of plastics in old landfill materials. This assumption was confirmed by thermal analysis and the characteristic heat flow profile of plastics containing landfill samples. Therefore organic carbon contents are relatively high compared to other stable landfills as shown by a prediction model for TOC contents based on heat flow profiles and partial least squares regression (PLS-R). The stability of the landfill samples, expressed by the relation of CO(2) release and enthalpies, was compared to unreactive landfills, archeological samples, earthlike materials and hardly degradable organic matter. Due to the material composition and the aging process the landfill samples are located between hardly degradable, but easily combustible materials and thermally resistant materials with acquired stability.

Modelled on Nature – Biological Processes in Waste Management

Biological degradation and transformation of organic substances under aerobic or anaerobic conditions are key processes within the natural metabolism of an equilibrated circulation system in order to handle the accumulating biomass. These fundamental processes are the basis for management strategies focusing on the biological treatment of organic waste materials. They are subjected to the biochemical metabolism using the capability of microbial populations to degrade, transform and stabilise organic matter. Stabilisation comprises biological as well as abiotic chemical and physical processes and their interaction. Avoiding greenhouse gases and shortening the after care period stabilisation is the key target for safe waste disposal in landfills. Biogenic waste materials are a source of secondary products: biogas obtained by anaerobic digestion and composts produced under aerobic conditions. For composts stabilisation is a relevant process to achieve plant compatibility and persistent organic substances for soil amelioration. Biological processes additionally contribute to landfill remediation, e.g. by methane oxidation. Nevertheless, biological degradation of waste materials is ambivalent and can lead to harmful effects if microbial activities take place under uncontrolled conditions in imbalanced systems. Abandoned landfills from the past demonstrate this fact. Anthropogenic organic wastes differ from “natural” organic waste by their amount, their heterogeneity and the content of xenobiotics. Therefore it is necessary to support and optimise biological degradation of waste organic matter by adequate process operation and technical devices. The equilibrium of necessary mineralisation and accessible humification is a topic of high interest in the context of carbon fixation. “Optimisation” is no aspect in the context with natural degradation processes. Additionally they are not harmless a priori. They take place under the current conditions, but it can be assumed that an equilibrium is reached over longer periods of time. Changes of environmental conditions by anthropogenic activities can accelerate biological degradation. Peat bogs that were drained and amended with carbonates lose organic matter due to mineralisation (Kuster, 1990). The pH value, water and air supply and temperature mainly influence the transformation rate. This fact indicates that biodegradability is not only an inherent property that depends on chemical and physical features of the material. The behaviour of biodegradable substances is affected by the interaction of both material characteristics and environmental conditions.

Development of Mechanically Biologically Treated Municipal Solid Waste under Different Vegetation Types

The use of mechanically biologically treated (MBT) waste as cover material for landfills during the aftercare period has gained in importance since the previous decade. The question arises how such materials change their properties under open field conditions. For field experiments, two MBT plants in Austria with related landfills were selected. A cover layer consisting of MBT material was applied on the surface and planted with grass and rape. The development without any vegetation served as a reference. Leaching, mineralization, and humification of waste organic matter were quantified. The impact of time, sampling depth, respective oxygen supply, and vegetation on the material was investigated. Intensive grass vegetation promoted mineralization and humification. Leaching of salts and the transformation of nitrogen were mainly influenced by time and depth. Aerobic conditions advanced degradation of still-reactive material. Under aerobic conditions, the remaining respiration activity was about two times lower than in the anaerobic zones. It was proven that well stabilized MBT material can be used as a cover layer with adequate vegetation.