Philipp Aschenbrenner

Heavy metal removal from municipal solid waste fly ash by chlorination and thermal treatment

Municipal solid waste (MSW) fly ash is classified as a hazardous material because it contains high amounts of heavy metals. For decontamination, MSW fly ash is first mixed with alkali or alkaline earth metal chlorides (e.g. calcium chloride) and water, and then the mixture is pelletized and treated in a rotary reactor at about 1000 degrees C. Volatile heavy metal compounds are formed and evaporate. In this paper, the effect of calcium chloride addition, gas velocity, temperature and residence time on the separation of heavy metals are studied. The fly ash was sampled at the waste-to-energy plant Fernwärme Wien/Spittelau (Vienna, Austria). The results were obtained from batch tests performed in an indirectly heated laboratory-scale rotary reactor. More than 90% of Cd and Pb and about 60% of Cu and 80% of Zn could be removed in the experiments.

Limitations for heavy metal release during thermo-chemical treatment of sewage sludge ash

Phosphate recycling from sewage sludge can be achieved by heavy metal removal from sewage sludge ash (SSA) producing a fertilizer product: mixing SSA with chloride and treating this mixture (eventually after granulation) in a rotary kiln at 1000 ± 100°C leads to the formation of volatile heavy metal compounds that evaporate and to P-phases with high bio-availability. Due to economical and ecological reasons, it is necessary to reduce the energy consumption of this technology. Generally, fluidized bed reactors are characterized by high heat and mass transfer and thus promise the saving of energy. Therefore, a rotary reactor and a fluidized bed reactor (both laboratory-scale and operated in batch mode) are used for the treatment of granulates containing SSA and CaCl(2). Treatment temperature, residence time and - in case of the fluidized bed reactor - superficial velocity are varied between 800 and 900°C, 10 and 30 min and 3.4 and 4.6 ms(-1). Cd and Pb can be removed well (>95 %) in all experiments. Cu removal ranges from 25% to 84%, for Zn 75-90% are realized. The amount of heavy metals removed increases with increasing temperature and residence time which is most pronounced for Cu. In the pellet, three major reactions occur: formation of HCl and Cl(2) from CaCl(2); diffusion and reaction of these gases with heavy metal compounds; side reactions from heavy metal compounds with matrix material. Although, heat and mass transfer are higher in the fluidized bed reactor, Pb and Zn removal is slightly better in the rotary reactor. This is due the accelerated migration of formed HCl and Cl(2) out of the pellets into the reactor atmosphere. Cu is apparently limited by the diffusion of its chloride thus the removal is higher in the fluidized bed unit.

A method for determining buildings’ material composition prior to demolition

A prerequisite of the efficient recycling of demolition waste and its evaluation in terms of the material specific recycling rates is information on the composition of the building material stock (as the source of future demolition waste). A practical method is presented that characterizes the material composition of buildings prior to their demolition. The characterization method is based on the analysis of available construction documents and different approaches of on-site investigation. The method is tested in different buildings and the results from four case studies indicate that the documents are useful to quantify bulk materials (e.g. bricks, concrete, sand/gravel, iron/steel and timber). However, on-site investigations are necessary to locate and determine the trace materials such as metals (e.g. copper and aluminium), or different types of plastics. The overall material intensity of the investigated buildings ranges from 270 to 470 kg/m³ gross volume. With ongoing surveys about the composition of different buildings, the collected data will be used to establish a building-specific database about the amount of materials contained in Viennas building stock.

Sewage sludge ash to phosphate fertilizer by chlorination and thermal treatment: residence time requirements for heavy metal removal

Heavy metal removal from sewage sludge ash can be performed by mixing the ash with environmentally compatible chlorides (e.g. CaCl2 or MgCl2) and water, pelletizing the mixture and treating the pellets in a rotary reactor at about 1000 °C. Thermogravimetry–mass spectroscopy, muffle oven tests (500–1150 °C) and investigations in a laboratory-scale rotary reactor (950–1050 °C, residence time 1–25 min) were carried out. In the rotary reactor, up to 97% of Cu, 95% Pb and 95% Zn can be removed at 1050 °C. As Cl release starts from 400 °C (obtained from thermogravimetry–mass spectrometry experiments), heavy metals are already removed partially within the heating period. This heavy metal removal can be described as being similar to a first-order rate law. To meet the limit values specified in the Austrian and German fertilizer ordinances, residence times of the order of minutes are sufficient at 950 °C.

Sample preparation and biomass determination of SRF model mixture using cryogenic milling and the adapted balance method

The biogenic fraction of a simple solid recovered fuel (SRF) mixture (80 wt% printer paper/20 wt% high density polyethylene) is analyzed with the in-house developed adapted balance method (aBM). This fairly new approach is a combination of combustion elemental analysis (CHNS) and a data reconciliation algorithm based on successive linearisation for evaluation of the analysis results. This method shows a great potential as an alternative way to determine the biomass content in SRF. However, the employed analytical technique (CHNS elemental analysis) restricts the probed sample mass to low amounts in the range of a few hundred milligrams. This requires sample comminution to small grain sizes (<200 μm) to generate representative SRF specimen. This is not easily accomplished for certain material mixtures (e.g. SRF with rubber content) by conventional means of sample size reduction. This paper presents a proof of principle investigation of the sample preparation and analysis of an SRF model mixture with the use of cryogenic impact milling (final sample comminution) and the adapted balance method (determination of biomass content). The so derived sample preparation methodology (cutting mills and cryogenic impact milling) shows a better performance in accuracy and precision for the determination of the biomass content than one solely based on cutting mills. The results for the determination of the biogenic fraction are within 1-5% of the data obtained by the reference methods, selective dissolution method (SDM) and (14)C-method ((14)C-M).

Sample preparation and determination of biomass content in solid recovered fuels: A comparison of methods

The biomass content of material from pulp and paper production (a mixture of waste and paper and thin layer packaging plastics) is determined by the adapted balance method. This novel approach is a combination of combustion elemental analysis (CHNSO) and a data reconciliation algorithm based on successive linearisation for evaluation of the analysis results. It also involves less effort and expense than conventional procedures. However, the CHNSO technique only handles small mass amounts (few hundred milligrams), so cryogenic impact milling was applied for particle size reduction below 200 µm in order to generate homogeneous, representative analysis samples. The investigation focuses on the parameters biogenic content as a percentage of the total mass xB and xBTC, which is the biomass stated as a fraction of the total carbon value. The results are within 1%–5% of the data obtained by the reference methods, namely the selective dissolution method and 14C- method. Additionally, advantages and drawbacks of the adapted balance method in comparison with standard methods are discussed, showing that the adapted balance method is a method to be considered for the determination of biomass content in solid recovered fuels or similar materials.

Analysis of total copper, cadmium and lead in refuse-derived fuels (RDF): study on analytical errors using synthetic samples.

Components with extraordinarily high analyte contents, for example copper metal from wires or plastics stabilized with heavy metal compounds, are presumed to be a crucial source of errors in refuse-derived fuel (RDF) analysis. In order to study the error generation of those ‘analyte carrier components’, synthetic samples spiked with defined amounts of carrier materials were mixed, milled in a high speed rotor mill to particle sizes <1 mm, <0.5 mm and <0.2 mm, respectively, and analyzed repeatedly. Copper (Cu) metal and brass were used as Cu carriers, three kinds of polyvinylchloride (PVC) materials as lead (Pb) and cadmium (Cd) carriers, and paper and polyethylene as bulk components. In most cases, samples <0.2 mm delivered good recovery rates (rec), and low or moderate relative standard deviations (rsd), i.e. metallic Cu 87–91% rec, 14–35% rsd, Cd from flexible PVC yellow 90–92% rec, 8–10% rsd and Pb from rigid PVC 92–96% rec, 3–4% rsd. Cu from brass was overestimated (138–150% rec, 13–42% rsd), Cd from flexible PVC grey underestimated (72–75% rec, 4–7% rsd) in <0.2 mm samples. Samples <0.5 mm and <1 mm spiked with Cu or brass produced errors of up to 220% rsd (<0.5 mm) and 370% rsd (<1 mm). In the case of Pb from rigid PVC, poor recoveries (54–75%) were observed in spite of moderate variations (rsd 11–29%). In conclusion, time-consuming milling to <0.2 mm can reduce variation to acceptable levels, even given the presence of analyte carrier materials. Yet, the sources of systematic errors observed (likely segregation effects) remain uncertain.

DETERMINING THE CLIMATE RELEVANCE OF REFUSE-DERIVED FUELS – VALIDITY OF LITERATURE-DERIVED VALUES IN COMPARISON TO ANALYSIS-DERIVED VALUES

The adapted Balance Method (aBM) represents a cost efficient method for determining the fossil share in solid refuse-derived fuels (RDF). The method requires data on the elemental composition of the RDF on water-and-ash-free basis (TOXRDF) and on the elemental composition of biogenic and fossil organic matter on water-and-ash-free basis present in the RDF (TOXBio and TOXFos). TOXBio and TOXFos generally need to be defined only once (e.g., before a routine application). After these data are known, only TOXRDF needs to be determined analytically for any RDF sample in order to apply the aBM. As TOXBio and TOXFos are crucial input parameter for the aBM, the presented paper aims to assess the most suitable and practical way for their reliable determination. Within this study, 6 different solid RDFs are investigated and the aBM is applied, whereby the suitability of literature values is compared to own analysis data for TOXBio and TOXFos. The potential utilization of literature data could save the initial workload when applying the aBM and could make the method even more economical and practical compared to other methods. Altogether, seven aBM results are compared utilizing seven different methods for generating input values of TOXBio and TOXFos: using generic values, literature values only, analyses results only, or combinations of literature and analyses data. The study results suggest that the usage of analysis data together with information from literature is the best option to derive reliable input data (TOXBio and TOXFos) for the aBM (mean deviation from standardized methods of below 2%). The findings further suggest that there is a typical composition of the biogenic and fossil organic matter present in RDFs produced out of commercial and industrial waste. Thus, the initial workload for conducting RDF-specific analyses could be significantly reduced when some more data about different types of RDFs are collected (e.g in a database).