Judy A. Libra

Hydrothermal carbonization of biomass residuals: a comparative review of the chemistry, processes and applications of wet and dry pyrolysis

The carbonization of biomass residuals to char has strong potential to become an environmentally sound conversion process for the production of a wide variety of products. In addition to its traditional use for the production of charcoal and other energy vectors, pyrolysis can produce products for environmental, catalytic, electronic and agricultural applications. As an alternative to dry pyrolysis, the wet pyrolysis process, also known as hydrothermal carbonization, opens up the field of potential feedstocks for char production to a range of nontraditional renewable and plentiful wet agricultural residues and municipal wastes. Its chemistry offers huge potential to influence product characteristics on demand, and produce designer carbon materials. Future uses of these hydrochars may range from innovative materials to soil amelioration, nutrient conservation via intelligent waste stream management and the increase of carbon stock in degraded soils.

Effects of Biomass Types and Carbonization Conditions on the Chemical Characteristics of Hydrochars

Effects of biomass types (bark mulch versus sugar beet pulp) and carbonization processing conditions (temperature, residence time, and phase of reaction medium) on the chemical characteristics of hydrochars were examined by elemental analysis, solid-state ¹³C NMR, and chemical and biochemical oxygen demand measurements. Bark hydrochars were more aromatic than sugar beet hydrochars produced under the same processing conditions. The presence of lignin in bark led to a much lower biochemical oxygen demand (BOD) of bark than sugar beet and increasing trends of BOD after carbonization. Compared with those prepared at 200 °C, 250 °C hydrochars were more aromatic and depleted of carbohydrates. Longer residence time (20 versus 3 h) at 250 °C resulted in the enrichment of nonprotonated aromatic carbons. Both bark and sugar beet pulp underwent deeper carbonization during water hydrothermal carbonization than during steam hydrothermal carbonization (200 °C, 3 h) in terms of more abundant aromatic C but less carbohydrate C in water hydrochars.

Sorption of four hydrophobic organic contaminants by biochars derived from maize straw, wood dust and swine manure at different pyrolytic temperatures.

Sorption behavior of acetochlor (ACE), dibutyl phthalate (DBP), 17α-Ethynyl estradiol (EE2) and phenanthrene (PHE) with biochars produced from three feedstocks (maize straw (MABs), pine wood dust (WDBs) and swine manure (SWBs)) at seven heat treatment temperatures (HTTs) was evaluated. The bulk polarity of these biochars declined with increasing HTT while the aromaticity and CO2-surface area (CO2-SA) rose. The surface OC contents of biochars were generally higher than bulk OC contents. The organic carbon (OC)-normalized CO2-SA (CO2-SA/OC) of biochars significantly correlated with the sorption coefficients (n and logK(oc)), suggesting that pore filling could dominate the sorption of tested sorbates. SWBs had higher logK(oc) values compared to MABs and WDBs, due to their higher ash contents. Additionally, the logK(oc) values for MABs was relatively greater than that for WDBs at low HTTs (≤400 °C), probably resulting from the higher CO2-SA/OC, ash contents and aromaticity of MABs. Surface polarity and the aliphatic C may dominate the sorption of WDBs obtained at relatively low HTTs (≤400 °C), while aromatic C affects the sorption of biochars at high HTTs. Results of this work aid to deepen our understanding of the sorption mechanisms, which is pivotal to wise utilization of biochars as sorbents for hazardous organic compounds.

Removal of antimony (III) and cadmium (II) from aqueous solution using animal manure-derived hydrochars and pyrochars

In this study, hydrochars and pyrochars prepared from animal manures were characterized and were used to remove Sb (III) and Cd (II) from aqueous solution. Fourier transform infrared spectroscopy (FTIR) analysis revealed the interaction between Cd (II) and CO and CO groups within biochars and between Sb (III) and CO, CO and OH groups, respectively. Additionally, the lower absolute value of zeta potential of biochar after loading Sb (III) and Cd (II) suggested the occurrence of surface complexation. Existing primarily in the form of Sb (OH)3, the maximum adsorption capacities (Qmax) for Sb (III) were lower than those for Cd (II). Due to the lower contents of surface polar functional groups and less negative surface charge, hydrochars exhibited lower Qmax for Sb (III) and Cd (II) than pyrochars. However, hydrochars in this study had higher sorption capacities for Cd (II) than most of plant-based pyrochars reported by other literature.

Variation in sorption of propiconazole with biochars: The effect of temperature, mineral, molecular structure, and nano-porosity.

Sorption behavior of propiconazole (PROPI) by plant-residue derived biochars (PLABs) and animal waste-derived biochars (ANIBs) obtained at three heating treatment temperatures (HTTs) (300, 450 and 600 °C) (e.g., BCs300, BCs450, and BCs600) and their corresponding de-ashed BCs450 was investigated. PLABs belonged to high- or medium-C biochars and ANIBs were low-C biochars. Surface C concentrations of the tested biochars were generally higher than their corresponding bulk C. Surface polar groups were mainly composed of O-containing groups of minerals within biochars. The nonlinearity coefficients (n) of propiconazole (PROPI) sorption isotherms ranged from 0.23 to 0.64, which was significantly and negatively related to organic carbon (OC)-normalized CO2-surface area (CO2-SA/OC) of biochars. This correlation along with the positive relationship between CO2-SA/OC and aromaticity indicates that pore-filling in nanopores within aromatic C dominate nonlinear PROPI sorption. HTTs or C contents do not necessarily regulate PROPI sorption. Removal of minerals from BCs450 elevated PROPI sorption because minerals may exert certain influence on sorption via impacting spatial arrangement of polar groups and/or organic matter (OM)-mineral interactions. This study helps to better understand sorption behavior of PROPI to biochars and evaluate the potential role of biochar in water treatment systems.

Leachate water quality of soils amended with different swine manure-based amendments

In the face of the rising level of manure production from concentrated animal feeding operations (CAFOs), management options are being sought that can provide nutrient recycling for plant growth and improved soil conditions with minimal environmental impacts. Alternatives to direct manure application are composting and thermochemical conversion which can destroy pathogens and improve handling and storage. The effect of four forms of swine manure-based soil amendments (raw, compost, hydrochar, and pyrochar) on soil fertility and leachate water quality characteristics of a sandy soil were investigated in soil incubation experiments. All four amendments significantly increased soil carbon, cation exchange capacity and available nutrient contents of the soil. However, hydrochar amended soil leached lower amounts of N, P, and K compared to the other amendments including the control. On the other hand, pyrochar amended soil leached higher concentrations of P and K. Subsequent tests on the hydrochar for K and N adsorption isotherms and surface analysis via XPS suggested that these nutrients were not sorbed directly to the hydrochar surface. Although it is still not clear how these nutrients were retained in the soil amended with hydrochar, it suggests a great potential for hydrochar as an alternative manure management option as the hydrochar can be soil applied while minimizing potential environmental issues from the leaching of high nutrient concentrations to water bodies.

Oxidation resistance of biochars as a function of feedstock and pyrolysis condition

Assessing biochars ability to resist oxidation is fundamental to understanding its potential to sequester carbon. Chemical oxidation exhibits good performance in estimating the oxidation resistance of biochar. Herein, oxidation resistance of 14 types of biochars produced from four feedstocks at different pyrolysis conditions (hydrothermal versus thermal carbonization) was investigated via hydrogen peroxide oxidation with varying concentrations. The oxidation resistance of organic carbon (C) of hydrochars was relatively higher than that of 250°C pyrochars (P250) but was comparable to that of 450°C pyrochars (P450). Both hydrochars and P450 from ash-rich feedstocks contained at least three different C pools (5.9-18.3% labile, 43.2-56.5% semi-labile and 26.9-45.9% stable C). Part (<33%) of aromatic C within 600°C pyrochars (P600) was easily oxidizable, which consisted of amorphous C. The influence of pyrolysis temperature upon oxidation resistance of biochars depended on the feedstock. For ash-rich feedstock (rice straw, swine manure and poultry litter), the oxidation resistance of biochars was determined by both aromaticity and mineral components, and mineral protection was regulated by pyrolysis conditions. The amorphous silicon within hydrochars and P450 could interact with C, preventing C from being oxidized, to some extent. Nevertheless, this type of protection did not occur for P250 and P600.

Relationship between irrigation water demand and yield of selected crops in Germany between 1902 and 2010: a modeling study

The demand for irrigation water is increasing worldwide, including regions in Germany with low precipitation and water-demanding crops. In this study, history of irrigation water demand (IWD) in the German nation states in relation to the yield of four crops (1) potato, (2) spring barley, (3) oat, and (4) winter wheat, during droughts between 1902 and 2010 was analyzed. The difficulties caused by the shifting borders of the German nation state over the past century were dealt with by dividing the data for the region into four time periods for the analysis. Low precipitation during droughts influenced crop yield in the German nation states. Analyses of droughts resulted in no clear conclusions; however, it appeared that after 1950, German nation states droughts had a negative influence on the yield of the four crops despite the important role irrigation played in German agriculture since 1960 in the German nation state. Lower yield because of weather conditions since 1950 was primarily attributable to the high-yield potential of improved crop varieties, for which yield potential is only reached under optimal growing conditions. In this study, the analysis of the modeled historical IWD in agriculture revealed the urgency with which the German crop production systems must adapt to extremes in a changing climate not only by improving irrigation systems via irrigation scheduling but also by greater higher diversification of crops.

Wassernutzung und Wassereffizienz in Landschaften

Wasser ist ein naturlicher Bestandteil unseres Lebens. Wir trinken es, waschen und kochen damit, wassern unsere Pflanzen und nutzen es auch sonst auf vielfaltige Weise als Roh- und Werkstoff. In Deutschland sind rund 99 Prozent der Bevolkerung an das Trinkwassernetz angeschlossen (UBA 2010a), sodass die jederzeitige und ausreichende Verfugbarkeit von Wasser selbstverstandlich geworden ist. Auserhalb der Stadte jedoch, an den land- und forstwirtschaftlichen Standorten und den Naturschutzflachen, zeigt sich ein anderes Bild. Hier entscheidet die naturliche Verfugbarkeit von Wasser unter anderem uber Ernteertrage, das Futterangebot fur Weidetiere, uber die Grundwassererneuerung und uber den Zustand der okosysteme. Kommt es zum Ungleichgewicht durch nicht nachhaltige Nutzung, Flachenversiegelung oder aufgrund unausgewogener Niederschlage, kann dies regional nachdruckliche und unerwunschte Folgen haben. Mehr als 80 Prozent der Flache Deutschlands sind landwirtschaftliche Flachen oder Wald (Destatis 2011).