Trace nutrients significantly affect the microbial metabolic activity within anaerobic digestion processes but always imply the risk of overdosing of heavy metals. In this study the applicability of a sequential extraction scheme established for soil and sediment samples on biogas slurries with different compositions was tested and compared to an adapted version of this extraction method. The analytical results proved the successful applicability of the developed analytical technique for the speciation of trace nutrients in anaerobic digestion systems. The procedure fulfills the basic requirements of reproducible data, a time-saving analytical approach and economic feasibility. Recovery rates of 90-110% were obtained for the most important trace elements Fe, Co, Cu, Mo, Ni and Zn. However, it was demonstrated that the adapted method provides more reliable information about the bioavailable fractions and it is considered the more appropriate approach. Data on fractionation indicated that up to 76% of these essential trace nutrients might be present in an insoluble state. Depending on the specific trace element a significant fraction, from 30% to more than 70%, is not directly bioavailable. This important aspect should be considered to guarantee sufficient supply of the microbial consortium with trace elements and at the same time to avoid overdosage. © 2014 Elsevier Ltd.

Management of municipal and commercial waste in Austria frequently involves mechanical-biological treatment (MBT) followed by incineration. A middle-caloric MBT output stream (lower heating value (LHV) = 9.90 MJ/kg WW, particle size = 20-80 mm) with a high proportion of inert material like stones, bricks, and metals (40.5 %m) is currently incinerated. Under favorable market conditions, it could be economically advantageous to split off a low-caloric heavy fraction (HF) that can be landfilled and to incinerate only the remaining, lighter fraction (LF) with a higher heating value. This study analyzes the specific global-warming potential (100-year GWP per tonne of input waste) of such an additional separation step and of the subsequent treatment processes. Four treatment alternatives were considered: a reference scenario without separation and three separation scenarios – a near-infrared (NIR) sensor-based scenario, an X-ray-transmission (XRT) sensor-based scenario, and a mechanical separation scenario using a diagonal sifter (DS). To calculate the specific GWP, the analysis applied techniques from life-cycle assessment (LCA). Primary data were obtained from pilot-scale and full-scale separation experiments, and from equipment manufacturers. Commercial databases provided secondary data. The results consist of separate LCA models for each scenario, including credits for fossil fuels replaced by LF incineration and HF landfill gas utilization. When only direct separation-related emissions are considered, the DS separation has by far the lowest specific GWP, followed by NIR-based separation, and by XRT-based separation. Overall specific GWP is strongly influenced by the choice of separation technology. It is lowest for the XRT scenario, followed closely by the reference scenario, while the DS and NIR scenarios show considerably higher results. Results are dominated by the net emissions from LF incineration. While incineration emissions are largely compensated by credits from replaced fossil fuels, credits for landfill gas utilization are much smaller than direct landfilling emissions. The ranking of the separation scenarios is largely determined by three waste stream characteristics: the ratio of biogenic to fossil carbon content and the LHV in the LF, and the degradable biogenic carbon content in the HF. Changes in important modeling assumptions leave the ranking between scenarios unchanged. It can be concluded that – given the right choice of
separation technology – a small positive effect of sorting on the overall specific GWP is feasible. This
work demonstrates that global warming effects of waste treatment decisions can be estimated and
considered early in the planning stage of treatment system design.

Catalytic systems integrated in firewood stoves represent a potential secondary measure for emission reduction. However, the evaluation of catalytic efficiency is challenging since measurements, especially for PM emissions, upstream an integrated catalyst are not possible. Therefore, a special test facility, called “DemoCat”, was constructed which enabled parallel measurements in catalytically treated and untreated flue gas. The catalytic efficiency for CO, OGC and PM emissions was investigated under real-life operating conditions including ignition and preheating. The results confirmed a significant emission reduction potential (CO: > 95%, OGC: > 60%, PM: ∼30%). The conversion rates of CO and OGC emissions correlated with the space velocity and the coated area of honeycomb carriers which represent key parameters for the integration design. A quick response of the catalytic effect of around 5–12 min after ignition was observed when reaching 250 °C flue gas temperature at the catalyst. Most effective CO and OGC emission conversion was evident during the start-up and burn-out phase of a firewood batch. This reveals an important synergy for primary optimization which focuses particularly on the stretched intermediate phase of a combustion batch. The catalytic effect on PM emissions, especially on chemical composition, needs further investigations.

The market offers a broad range of different combustion appliances dedicated to residential heating with biomass. The effect of fuel properties on the formation of slag and emissions varies and the technology influences the impact to a certain extent. The applicability of biomass fuels is not only determined by operational settings but also by the design of boiler components as grate area and combustion chamber. Aspects as the fuel load on the grate, residence time, geometry of grate and combustion chamber design, as well as feeding and de-ashing influence the extent of slag formation and emission release. The determination of characteristic numbers by means of constructional measures allows a systematic comparison and - in a further step - an assessment/categorization of combustion technologies. After conducting a boiler survey relevant parameters regarding grate, combustion chamber, feeding, and ash removal were gathered. Characteristic numbers were specified in order to compare technological aspects. The results of this study allow the investigation of the influence of the combustion technology on the performance. They will assist the systematic and targeted design of small-scale boilers and the optimization of combustion appliances in future, especially when it comes to fuel-flexibility.

Straw, Miscanthus, maize, and horse manure were reviewed in terms of fuel characteristics. They were tested in existing boilers, and the particulate and gaseous emissions were monitored. The ash was analyzed for the presence of sintered material. All the fuels showed problems with ash lumping and slag formation. Different boiler technologies showed different operational performances. Maize and horse manure are problematic fuels regarding NO_x and particulate emissions. Miscanthus was the best fuel tested. Due to the big variation of fuel properties and therefore combustion behavior of agricultural biomass, further R&D is required to adapt the existing boilers for these fuels.

Biomass boilers used for residential heating and hot water supply are typically combined with a buffer storage and solar collectors. However, the annual utilization rates typically achieved with such systems are far below those theoretically possible, which is mainly because of the often poor quality of both the individual control of the components as well as the high-level control of the entire system. The control strategies typically applied consist of simple decou-pled control circuits with linear controllers, which cannot deal with the mostly nonlinear and coupled behaviour of the components and thus do not ensure their reasonable interaction. The most appropriate approach to address these challenges is the application of model-based control techniques. Within the paper an overview of mathematical models suitable for control purposes, a simple to implement load forecasting method as well as control strate-gies for both the individual components and the entire system are presented. Future chal-lenges for a practical implementation of this novel approach are discussed in the outlook sec-tion.

This publication deals with the characterisation of Jatropha curcas seeds and the oil obtained hereof. The analyzed seeds have been harvested from hedges and plantations in the regions of Teriya Bugu and Bla in Mali in the years 2009 and 2010. The oil is obtained through solvent extraction. Parameters analyzed are those which are relevant for processing of the oil into fatty acid methyl ester (FAME, biodiesel), and include acid value, fatty acid profile and contents of S, P, K, Na, Ca and Mg. All oil samples are suitable for processing into biodiesel, but some of them require pre-treatment because of high contents of free fatty acids and phosphorous. The margin of deviation of acid value and element contents throughout the oil samples depends on the way of cultivation, harvest and storage of the Jatropha curcas plants and seeds. Despite high acid values, all oil samples show high oxidation stability. © 2012 Elsevier Ltd.

This study presents combustion behavior and emission results obtained for different fuels: poultry litter (PL) and its char (PLC), scrap tires (ST) and its char (STC) and blends of char/lignite (PLC/LIG and STC/LIG). The combustion parameters and emissions were investigated via a non-isothermal thermogravimetric method and experiments in a lab-scale reactor. Fuel indexes were used for the prediction of high temperature corrosion risks and slagging potentials of the fuels used. The addition of chars to lignite caused a lowering of the combustion reactivity (anti-synergistic effect). There was a linear correlation between the NO_x emissions and the N content of the fuel. The form of S and the concentrations of alkali metals in the fuel had a strong effect on the extent of SO₂ emissions. The use of PL and PLC in blends reduced SO₂ emissions and sulphur compounds in the fly ash. The 2S/Cl ratio in the fuel showed that only PLC and STC/PLC would show a risk of corrosion during combustion. The ratio of basic to acidic oxides in fuel indicated that ST, STC and STC/LIG have low slagging potential. The molar (Si + P + K)/(Ca + Mg) ratio, which was used for PL, PLC and PLC containing blends, showed that the ash melting temperatures of these fuels would be higher than 1000 °C.

Biochars produced from pelletized grape vine (GV) and sunflower husk (SFH) agricultural residues were studied by pyrolysis in a batch reactor at 400 and 500 °C. Chemical and physical evolution of the biomass under pyrolysis conditions was determined and the products were characterized, including the main gaseous organic components. Results showed a decrease in solid biochar yield with increasing temperature. Biochar is defined as a “porous carbonaceous solid” produced by thermochemical conversion of organic materials in an oxygen depleted atmosphere, which has physiochemical properties suitable for the safe and long-term storage of carbon in the environment and, potentially, soil improvement. The aim of this work is to improve the knowledge and acceptability of alternative use of the biochar gained from agro-forestry biomass residuals, such as grape vine and sunflower husks, by means of modern chemical and physical characterization tools.