Physical and chemical characterization of waste wood derived biochars

Biochar, a solid byproduct generated during waste biomass pyrolysis or gasification in the absence (or near-absence) of oxygen, has recently garnered interest for both agricultural and environmental management purposes owing to its unique physicochemical properties. Favorable properties of biochar include its high surface area and porosity, and ability to adsorb a variety of compounds, including nutrients, organic contaminants, and some gases. Physical and chemical properties of biochars are dictated by the feedstock and production processes (pyrolysis or gasification temperature, conversion technology and pre- and post-treatment processes, if any), which vary widely across commercially produced biochars. In this study, several commercially available biochars derived from waste wood are characterized for physical and chemical properties that can signify their relevant environmental applications. Parameters characterized include: physical properties (particle size distribution, specific gravity, density, porosity, surface area), hydraulic properties (hydraulic conductivity and water holding capacity), and chemical and electrochemical properties (organic matter and organic carbon contents, pH, oxidation-reduction potential and electrical conductivity, zeta potential, carbon, nitrogen and hydrogen (CHN) elemental composition, polycyclic aromatic hydrocarbons (PAHs), heavy metals, and leachable PAHs and heavy metals). A wide range of fixed carbon (0-47.8%), volatile matter (28-74.1%), and ash contents (1.5-65.7%) were observed among tested biochars. A high variability in surface area (0.1-155.1g/m(2)) and PAH and heavy metal contents of the solid phase among commercially available biochars was also observed (0.7-83 mg kg(-1)), underscoring the importance of pre-screening biochars prior to application. Production conditions appear to dictate PAH content--with the highest PAHs observed in biochar produced via fast pyrolysis and lowest among the gasification-produced biochars.

State-of-the-art of waste wood supply chain in Germany and selected European countries

According to the statistic office of the European Union (Eurostat), Germany is the main producer of waste wood in Europe followed by France, United Kingdom, Italy and Finland. Based on the characteristics of the waste wood, it can be classified in four (4) categories: A I, A II, A III and A IV. This paper focuses in the A I waste wood since is the only category able to be used directly for both material and energy purposes without a previously pre-treatment. Currently, most of this waste wood is used for direct energy production due to the previous government legislation that promoted its use directly in incineration facilities. However, the newest Renewable Energy Act (EEG 2017) may promote the cascade-use of A I waste wood prior to be intended for energy purposes. Nonetheless, the government incentives to the energy sector is not the only bottleneck that the use of A I waste wood as raw material in the wood-based industry has to overcome. The peak availability, collection logistics (collection centers and transportation) and recycling facility location are some of the parameters that must be considered in order to design the "best" supply chain network for A I waste wood. This work presents a detailed description of the effect of the hierarchical strategic decision in the proper design of the waste wood supply chain. Additionally, the global picture of waste wood recycling in different European countries (UK, Italy and Finland) is briefly presented.

Assessment of chemical and material contamination in waste wood fuels--A case study ranging over nine years

The increased demand for waste wood (WW) as fuel in Swedish co-combustion facilities during the last years has increased the import of this material. Each country has different laws governing the use of chemicals and therefore the composition of the fuel will likely change when combining WW from different origins. To cope with this, enhanced knowledge is needed on WW composition and the performance of pre-treatment techniques for reduction of its contaminants. In this study, the chemical and physical characteristics of 500 WW samples collected at a co-combustion facility in Sweden between 2004 and 2013 were investigated to determine the variation of contaminant content over time. Multivariate data analysis was used for the interpretation of the data. The concentrations of all the studied contaminants varied widely between sampling occasions, demonstrating the highly variable composition of WW fuels. The efficiency of sieving as a pre-treatment measure to reduce the levels of contaminants was not sufficient, revealing that sieving should be used in combination with other pre-treatment methods. The results from this case study provide knowledge on waste wood composition that may benefit its management. This knowledge can be applied for selection of the most suitable pre-treatments to obtain high quality sustainable WW fuels.

Pyrolysis kinetic evaluation by single-step for waste wood from reforestation

The objective of this study was to evaluate the kinetic parameters of pyrolysis of waste wood from reforestation: Eucalyptus benthamii (EB), Eucalyptus dunnii (ED) and Pinus elliottii (PN). The kinetic study was performed using the Friedman, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Starink, and Vyazovkin methods from the experimental data at four heating rates (5, 10, 20 and 30 °C min^-1). The Friedman method presented higher activation energy values (E_a) when compared to the other methods (E_aEB = 142.98 kJ mol^-1, E_aED = 147.71 kJ mol^-1, E_aPN = 155.46 kJ mol^-1). The KAS, Starink and Vyazovkin methods resulted in approximate values of activation energy (E_aEB = 132.83-133.31 kJ mol^-1, E_aED = 137.51-137.98 kJ mol^-1, E_aPN = 145.24-145.70 kJ mol^-1) due to the approximation equations with lowest relative errors. The simulation of curves using the kinetic parameters obtained with the Vyazovkin method showed that the decomposition process of EB and ED occurs as a multi-step process resulting in an unsatisfactory result for the simulation. On the other hand, for PN a satisfactory fit to the experimental data was obtained, which demonstrates its suitability for application to the modeling of thermochemical systems.

Effects of pyrolysis parameters on physicochemical properties of biochar and bio-oil and application in asphalt

Adoption of renewable energy sources such as biomass has been increasing worldwide. In this study, fast pyrolysis as an acceptable and viable method to get renewable bio-oil and biochar is used. Different temperatures and N₂ flow velocities were used in the fast pyrolysis process to evaluate the pyrolysis yield of biochar and bio-oil. The waste wood and pig manure were utilized to prepare biochar and bio-oil. X-ray fluorescence, X-ray diffraction, high-pressure liquid chromatograph, Micro confocal laser Raman spectrometer, Fourier transform infrared spectrometer, and dynamic shear rheometer were used to measure the chemical compositions, structure, and pyrolysis yield of biochar and bio-oil. The obtained results indicate that pyrolysis temperature increases the purity of inorganic oxide in biochar and N₂ flow velocity promotes the yield of carbon in biochar. The increase of N₂ flow velocity would increase the acid property of bio-oil and damage the products yield of bio-oil. It was also observed that biochar could remarkably alter the fundamental performances of petroleum asphalt including penetration, softening point, ductility, viscosity, and complex modulus. The most important is that the upgraded bio-oil can be used to replace partly or fully the petroleum asphalt which is a promising biomass application.

LCA-based optimization of wood utilization under special consideration of a cascading use of wood

Cascading, the use of the same unit of a resource in multiple successional applications, is considered as a viable means to improve the efficiency of resource utilization and to decrease environmental impacts. Wood, as a regrowing but nevertheless limited and increasingly in demand resource, can be used in cascades, thereby increasing the potential efficiency per unit of wood. This study aims to assess the influence of cascading wood utilization on optimizing the overall environmental impact of wood utilization. By combining a material flow model of existing wood applications - both for materials provision and energy production - with an algebraic optimization tool, the effects of the use of wood in cascades can be modelled and quantified based on life cycle impact assessment results for all production processes. To identify the most efficient wood allocation, the effects of a potential substitution of non-wood products were taken into account in a part of the model runs. The considered environmental indicators were global warming potential, particulate matter formation, land occupation and an aggregated single score indicator. We found that optimizing either the overall global warming potential or the value of the single score indicator of the system leads to a simultaneous relative decrease of all other considered environmental impacts. The relative differences between the impacts of the model run with and without the possibility of a cascading use of wood were 7% for global warming potential and the single score indicator, despite cascading only influencing a small part of the overall system, namely wood panel production. Cascading led to savings of up to 14% of the annual primary wood supply of the study area. We conclude that cascading can improve the overall performance of a wood utilization system.

Sulfur dioxide-ethanol-water fractionation platform for conversion of recycled wood to sugars, lignin and lignosulfonates

Recycled wood of two grades (A and B) and spruce were converted on bench (100 o.d. g) and pilot (100 o.d. kg) scales to monosugars, lignin and lignosulfonates using SO₂-Ethanol-Water (AVAP®) technology. After digestion, C6 and C5 sugars were recovered at 98-100% and 87-99% for Wood A and Spruce, respectively, while the values for Wood B were 92% and 74-87%. Cellulose was hydrolysed to glucose at 90% or higher using enzyme charge of 7.1 FPU/g glucan. Hemicellulosic sugars were autohydrolyzed to 95-100% monosugars. At bench scale, monosaccharide yield was 609, 561 and 688 kg (hydrous) per BDT biomass for Wood A, Wood B and Spruce, respectively. Corresponding water insoluble lignin yield was 157, 148 and 189 kg per BDT biomass. The preliminary techno-economic evaluation revealed that conversion of recycled wood to sugars using AVAP® fractionation platform results in higher profitability in comparison to virgin wood.

A new way to discriminate polluted wood by vibrational spectroscopies

In this work, two sets of samples were considered: field samples collected from local waste wood and synthetic samples made by mixing clean wood (including oak, beech, poplar) with typical organic pollutants: creosote, polychlorinated byphenils (PCBs), pentachlorophenol (PCP), cypermethrin, dodecyl dimethyl ammonium chloride (DDAC). Vibrational spectroscopy techniques were tested to detect organic pollutants in wood items. Raman and infrared spectroscopies were showed as fast, non-destructive and non-invasive fingerprint techniques for detection of organic molecules. Associated with principal component analysis, we have shown the evidence of quick detection of and discrimination of polluted wood items by kinds and versus concentration.

Quality assessment of recycled wood with and without non-wooden materials from selected recycling companies in Europe

Recycled wood is becoming an important material source for production of new materials and chemicals. Predominantly clean recycled wood should be used for the products with high added value. However, contamination of the recycled wood defines the potential end uses. Thus, it is of the huge commercial and environmental importance to monitor the contamination of the respective material. In the present research, we focused on concentrations of non-wooden materials in recycled wood and the presence of indicative inorganic pollutants, namely: chlorine (Cl), chromium (Cr), copper (Cu), zinc (Zn), lead (Pb), iron (Fe) and bromine (Br). Sampling of various qualities of commercially available recycled wood was performed for one year in recycling companies from Germany, Slovenia, Finland and UK. In addition to the above-mentioned long term monitoring, fraction analysis was also performed on selected batches. For nine different fractions, the water soluble part and lignin content were additionally determined. The results showed that high quality recycled wood had low shares of non-wooden materials and only a few samples exceeded the limit values for inorganic pollutants prescribed by German ordinance Altholzverordnung or EPF standard. On the other hand, mixed recycled wood, of lower quality contained a significantly higher portion of non-wooden material (up to 3%). These mixtures also had higher concentrations of inorganic pollutants. More than 85% of samples exceeded the limit concentration prescribed by the German ordinance Altholzverordnung for recovered wood for at least one of the analysed chemicals. The concentration of chemical elements in samples from nine different size fractions negatively correlated with the particle size in the fractions. The same trend was also observed for the soluble part and the lignin content. In general, it can be concluded that recycled wood deriving from larger annual process capacity volumes with sophisticated sorting systems, contains less non-wooden material and can provide clean wood. On the other hand, the mixed recycled wood contained high concentrations of inorganic elements, regardless of the origin or sorting system.

Waste wood as bioenergy feedstock. Climate change impacts and related emission uncertainties from waste wood based energy systems in the UK

Considering the urgent need to shift to low carbon energy carriers, waste wood resources could provide an alternative energy feedstock and at the same time reduce emissions from landfill. This research examines the climate change impacts and related emission uncertainties of waste wood based energy. For this, different grades of waste wood and energy application have been investigated using lifecycle assessment. Sensitivity analysis has then been applied for supply chain processes and feedstock properties for the main emission contributing categories: transport, processing, pelletizing, urea resin fraction and related N₂O formation. The results show, depending on the waste wood grade, the conversion option, scale and the related reference case, that emission reductions of up to 91% are possible for non-treated wood waste. Compared to this, energy from treated wood waste with low contamination can achieve up to 83% emission savings, similar to untreated waste wood pellets, but in some cases emissions from waste wood based energy can exceed the ones of the fossil fuel reference - in the worst case by 126%. Emission reductions from highly contaminated feedstocks are largest when replacing electricity from large-scale coal and landfill. The highest emission uncertainties are related to the wood's resin fraction and N₂O formation during combustion and, pelletizing. Comparing wood processing with diesel and electricity powered equipment also generated high variations in the results, while emission variations related to transport are relatively small. Using treated waste wood as a bioenergy feedstock can be a valid option to reduce emissions from energy production but this is only realisable if coal and landfill gas are replaced. To achieve meaningful emission reduction in line with national and international climate change targets, pre-treatment of waste wood would be required to reduce components that form N₂O during the energy conversion.

Pilot scale sulfur dioxide-ethanol-water fractionation of recycled wood to sugars, bioethanol, lignin and lignosulfonates: Carbohydrate balance

Two grades of recycled wood (Waste Wood A and Waste Wood B) were fractionated on a pilot scale (800 BD kg) to monomeric sugars, lignin and lignosulfonates using SO₂-Ethanol-Water (AVAP®) technology, including pretreatment, separation of cellulosic and hemicellulosic streams, and saccharification. Carbohydrate mass balance was obtained through determination of poly-, oligo- and monosaccharides as well as sugar degradation products in process streams. High monosaccharide yields were obtained confirming laboratory scale findings. Fermentability of mixed cellulosic and hemicellulosic sugar stream was confirmed on bench scale (25 kg).

Methods to estimate the transfer of contaminants into recycling products - A case study from Austria

Recycling of waste materials is desirable to reduce the consumption of limited primary resources, but also includes the risk of recycling unwanted, hazardous substances. In Austria, the legal framework demands secondary products must not present a higher risk than comparable products derived from primary resources. However, the act provides no definition on how to assess this risk potential. This paper describes the development of different quantitative and qualitative methods to estimate the transfer of contaminants in recycling processes. The quantitative methods comprise the comparison of concentrations of harmful substances in recycling products to corresponding primary products and to existing limit values. The developed evaluation matrix, which considers further aspects, allows for the assessment of the qualitative risk potential. The results show that, depending on the assessed waste fraction, particular contaminants can be critical. Their concentrations were higher than in comparable primary materials and did not comply with existing limit values. On the other hand, the results show that a long-term, well-established quality control system can assure compliance with the limit values. The results of the qualitative assessment obtained with the evaluation matrix support the results of the quantitative assessment. Therefore, the evaluation matrix can be suitable to quickly screen waste streams used for recycling to estimate their potential environmental and health risks. To prevent the transfer of contaminants into product cycles, improved data of relevant substances in secondary resources are necessary. In addition, regulations for material recycling are required to assure adequate quality control measures, including limit values.

Detailed estimation of generated woody biomass ash for use as fertilizer material

The physical and chemical characteristics of woody biomass ash (WBA) are highly dependent on the ash type, fuel, and furnace type. WBA recycling requires knowledge of its amount and characteristics. In this study, the amount of WBA recoverable as fertilizer in Japan was estimated considering the ash type, furnace type, and fuel type, using data obtained in a questionnaire-based survey of 105 of the 220 biomass power plants in Japan. The results showed that the amount of ash was > 1.5 times larger than that calculated according to fuel type. The discharged ash contained moisture, sand, and impurities. The slopes of the estimation model of the actual versus calculated amount were larger for gasification power generation, followed by stoker furnaces and fluidized bed furnaces. The bottom ash ratio in WBA from all furnace types was 0.37. With an estimated biomass combustion by the 220 biomass power plants in Japan of 3.4 × 107 t in 2026, the amount of generated ash would be 6.9-12 × 105 t. Bottom ash accounted for 2.7-4.7 × 105 t, with circulated fluidized bed furnace-derived ash comprising > 60 % of the total. The estimated annual amount of ash suitable for fertilizer use was 6.2-11 × 105 t. The K content of WBA in 2026 was estimated to be 1.8 times larger than that in annually imported fertilizer. This K resource should be fully exploited and the efficient use of K extraction residue should be pursued to achieve an effective circular economy.