K. Thomas Klasson

Screening biochars for heavy metal retention in soil: Role of oxygen functional groups

Oxygen-containing carboxyl, hydroxyl, and phenolic surface functional groups of soil organic and mineral components play central roles in binding metal ions, and biochar amendment can provide means of increasing these surface ligands in soil. In this study, positive matrix factorization (PMF) was first employed to fingerprint the principal components responsible for the stabilization of heavy metals (Cu, Ni, Cd, Pb) and the release of selected elements (Na, Ca, K, Mg, S, Al, P, Zn) and the pH change in biochar amended soils. The PMF analysis indicated that effective heavy metal stabilization occurred concurrently with the release of Na, Ca, S, K, and Mg originating from soil and biochar, resulting in as much as an order or magnitude greater equilibrium concentrations relative to the soil-only control. In weathered acidic soil, the heavy metal (especially Pb and Cu) stabilization ability of biochar directly correlated with the amount of oxygen functional groups revealed by the O/C ratio, pH(pzc), total acidity, and by the (1)H NMR analysis. Equilibrium speciation calculation showed minor influence of hydrolysis on the total soluble metal concentration, further suggesting the importance of binding by surface ligands of biochar that is likely to be promoted by biochar-induced pH increase.

Contaminant immobilization and nutrient release by biochar soil amendment: Roles of natural organic matter

Contamination of soil interstitial waters by labile heavy metals such as Cu(II), Cd(II), and Ni(II) is of worldwide concern. Carbonaceous materials such as char and activated carbon have received considerable attention in recent years as soil amendment for both sequestering heavy metal contaminants and releasing essential nutrients like sulfur. Information is currently lacking in how aging impacts the integrity of biochars as soil amendment for both agricultural and environmental remediation purposes. Major contributors to biochar aging in soils are: sorption of environmental constituents, especially natural organic matter (NOM), and oxidation. To investigate the impact of NOM and organic fractions of chars, we employed broiler litter-derived chars and steam-activated carbons that underwent varying degrees of carbonization, in the presence and absence of NOM having known carboxyl contents. For aging by oxidation, we employed phosphoric acid activated carbons that underwent varying degrees of oxidation during activation. The results suggest that the organic fractions of biochars, and NOM having high carboxyl contents can mobilize Cu(II) retained by alkaline soil. Base treatment of broiler litter-derived char formed at low pyrolysis temperature (350 degrees C) improved the immobilization of all heavy metals investigated, and the extent of immobilization was similar to, or slightly greater than pecan shell-derived phosphoric acid activated carbons. Portions of total sulfur were released in soluble form in soil amended with broiler litter-derived carbons, but not pecan shell-derived phosphoric acid activated carbons.

Influence of soil properties on heavy metal sequestration by biochar amendment: 1. Copper sorption isotherms and the release of cations.

The amendment of carbonaceous materials such as biochars and activated carbons is a promising in situ remediation strategy for both organic and inorganic contaminants in soils and sediments. Mechanistic understandings in sorption of heavy metals on amended soil are necessary for appropriate selection and application of carbonaceous materials for heavy metal sequestration in specific soil types. In this study, copper sorption isotherms were obtained for soils having distinct characteristics: clay-rich, alkaline San Joaquin soil with significant heavy metal sorption capacity, and eroded, acidic Norfolk sandy loam soil having low capacity to retain copper. The amendment of acidic pecan shell-derived activated carbon and basic broiler litter biochar lead to a greater enhancement of copper sorption in Norfolk soil than in San Joaquin soil. In Norfolk soil, the amendment of acidic activated carbon enhanced copper sorption primarily via cation exchange mechanism, i.e., release of proton, calcium, and aluminum, while acid dissolution of aluminum cannot be ruled out. For San Joaquin soil, enhanced copper retention by biochar amendment likely resulted from the following additional mechanisms: electrostatic interactions between copper and negatively charged soil and biochar surfaces, sorption on mineral (ash) components, complexation of copper by surface functional groups and delocalized π electrons of carbonaceous materials, and precipitation. Influence of biochar on the release of additional elements (e.g., Al, Ca) must be carefully considered when used as a soil amendment to sequester heavy metals.

Influence of soil properties on heavy metal sequestration by biochar amendment: 2. Copper desorption isotherms.

Contaminant desorption constrains the long-term effectiveness of remediation technologies, and is strongly influenced by dynamic non-equilibrium states of environmental and biological media. Information is currently lacking in the influence of biochar and activated carbon amendments on desorption of heavy metal contaminants from soil components. In this study, copper sorption-desorption isotherms were obtained for clay-rich, alkaline San Joaquin soil with significant heavy metal sorption capacity, and eroded, acidic Norfolk sandy loam soil having low capacity to retain copper. Acidic pecan shell-derived activated carbon and basic broiler litter biochar were employed in desorption experiments designed to address both leaching by rainfall and toxicity characteristics. For desorption in synthetic rain water, broiler litter biochar amendment diminished sorption-desorption hysteresis. In acetate buffer (pH 4.9), significant copper leaching was observed, unless acidic activated carbon (pH(pzc)=3.07) was present. Trends observed in soluble phosphorus and zinc concentrations for sorption and desorption equilibria suggested acid dissolution of particulate phases that can result in a concurrent release of copper and other sorbed elements. In contrast, sulfur and potassium became depleted as a result of supernatant replacements only when amended carbon (broiler litter biochar) or soil (San Joaquin) contained appreciable amounts. A positive correlation was observed between the equilibrium aluminum concentration and initial copper concentration in soils amended with acidic activated carbon but not basic biochar, suggesting the importance of cation exchange mechanism, while dissolution of aluminum oxides cannot be ruled out.

Influence of post-treatment strategies on the properties of activated chars from broiler manure☆

There are a myriad of carbonaceous precursors that can be used advantageously to produce activated carbons or chars, due to their low cost, availability and intrinsic properties. Because of the nature of the raw material, production of granular activated chars from broiler manure results in a significant ash fraction. This study was conducted to determine the influence of several pre- and post-treatment strategies in various physicochemical and adsorptive properties of the resulting activated chars. Pelletized samples of broiler litter and cake were pyrolyzed at 700 °C for 1h followed by a 45 min steam activation at 800 °C at different water flow rates from 1 to 5 mL min(-1). For each activation strategy, samples were either water-rinsed or acid-washed and rinsed or used as is (no acid wash/rinse). Activated chars physicochemical and adsorptive properties towards copper ions were selectively affected by both pre- and post-treatments. Percent ash reduction after either rinsing or acid washing ranged from 1.1 to 15.1% but washed activated chars were still alkaline with pH ranging from 8.4 to 9.1. Acid washing or water rinsing had no significant effect in the ability of the activated char to adsorb copper ions, however it significantly affected surface area, pH, ash content and carbon content. Instead, manure type (litter versus cake) and the activation water flow rate were determining factors in copper ion adsorption which ranged from 38 mg g(-1) to 104 mg g(-1) of activated char. Moreover, strong positive correlations were found between copper uptake and concentration of certain elements in the activated char such as phosphorous, sulfur, calcium and sodium. Rinsing could suffice as a post treatment strategy for ash reduction since no significant differences in the carbon properties were observed between rinsed and acid wash treatments.

Activated biochar removes 100 % dibromochloropropane from field well water

Dibromochloropropane was one of the primary chemical soil fumigants used to control nematodes. As a consequence, dibromochloropropane is now occurring widely in groundwater. This situation requires treating drinking water before human consumption because exposures to dibromochloropropane have shown linkage to infertility and circulatory system diseases. Here, activated biochar was produced from almond shells and used in the field to remove dibromochloropropane from a municipal water well. Results show that activated biochar removed 100xa0% of the dibromochloropropane for approximately 3xa0months and continued to remove it to below treatment standards for an additional 3xa0months. The breakthrough was modeled by a liquid film mass transfer model that described the experimental data very well. This manuscript reports on the efficient use of local resources such as almond shells to address local environmental needs.

Impact of Potential Fermentation Inhibitors Present in Sweet Sorghum Sugar Solutions

In this work, the fermentation of the sweet sorghum sugars such as sucrose, glucose, and fructose to ethanol was studied in the presence of acetic acid, lactic acid, and aconitic acid, which are present in the juice or produced by microorganisms during prolonged storage of harvested materials or juice. An industrial strain of distiller’s yeast was used to produce ethanol from 100xa0g/L (83xa0g/L after inoculum) of total sugars. The fermentation time ranged from 12 to 140xa0h, with the longer fermentation time corresponding to clear inhibition of yeast growth and product accumulation in the presence of 8xa0g/L of initial acetic acid. Among the acids, only acetic acid showed a negative impact on the fermentation rates and only at levels greater than 2xa0g/L. Lower levels of acetic acid and all levels of lactic acid and aconitic acid (1–5xa0g/L) either showed an improvement in fermentation rates or in final ethanol concentration. The acidity was not controlled during the fermentation but was initially adjusted, and it is presumed that the pH buffering effect on the organic acids contributed to the higher fermentation rates and prevented the pH from naturally dropping as the fermentation progressed.

The Inhibitory Effects of Aconitic Acid on Bioethanol Production

The fermentation of the sweet sorghum sugars, glucose, fructose, and sucrose to ethanol was studied in the presence of aconitic acid. In the past, aconitic acid has been identified as potential fermentation inhibitor, but very limited information exists about its inhibitory effects. As aconitic acid is naturally present in sweet sorghum (and its juice) and the fact that this plant has been proposed as a bioenergy crop, it was necessary to quantify the inhibition. Distiller’s yeast was used to produce ethanol from 83xa0g/L of total sugars in the presence of 0 to 13xa0g/L of aconitic acid. In some experiments, the pH of the fermentation was initially adjusted and allowed to drop as the fermentation progressed. In other experiments, the level of aconitic acid was held constant, while the pH was controlled at different set points between 2 and 4.5. In a final set of experiments, the pH was controlled to 2.9 and the initial concentration of aconitic acid was varied. It was conclusively shown that aconitic acid negatively impacts fermentation rate of distiller’s yeast and that the impact was pH dependent. At below pH 3.5, the impact was clearly observed and it became more influential at lower pH. The impact of aconitic acid on the fermentation rate was linked to the presence of undissociated aconitic acid which occurs at below pH 4.5. The level of undissociated aconitic acid that can be tolerated by the yeast depends on the pH. Thus, the most reasonable approach to improve fermentation rates in the presence of aconitic acid is to increase the pH of the fermentation. Both the ethanol yield (on sugar) and the final ethanol concentration (titer) were higher in the presence of aconitic acid but at a very small level (i.e., 4 and 3%, respectively). Thus, if the pH of the fermentation is increased, the presence of aconitic acid can be seen as advantageous.

High solid fed-batch butanol fermentation with simultaneous product recovery: Part II-process integration

In these studies, liquid hot water (LHW) pretreated and enzymatically hydrolyzed Sweet Sorghum Bagasse (SSB) hydrolyzates were fermented in a fed‐batch reactor. As reported in the preceding paper, the culture was not able to ferment the hydrolyzate I in a batch process due to presence of high level of toxic chemicals, in particular acetic acid released from SSB during the hydrolytic process. To be able to ferment the hydrolyzate I obtained from 250 g L−1 SSB hydrolysis, a fed‐batch reactor with in situ butanol recovery was devised. The process was started with the hydrolyzate II and when good cell growth and vigorous fermentation were observed, the hydrolyzate I was slowly fed to the reactor. In this manner the culture was able to ferment all the sugars present in both the hydrolyzates to acetone butanol ethanol (ABE). In a control batch reactor in which ABE was produced from glucose, ABE productivity and yield of 0.42 g L−1 h−1 and 0.36 were obtained, respectively. In the fed‐batch reactor fed with SSB hydrolyzates, these productivity and yield values were 0.44 g L−1 h−1 and 0.45, respectively. ABE yield in the integrated system was high due to utilization of acetic acid to convert to ABE. In summary we were able to utilize both the hydrolyzates obtained from LHW pretreated and enzymatically hydrolyzed SSB (250 g L−1) and convert them to ABE. Complete fermentation was possible due to simultaneous recovery of ABE by vacuum.

129Xe NMR Studies of Pecan Shell-Based Biochar and Structure-Process Correlations

Pecan shell-based biochar is utilized as a filtration medium, sequestrant for metallic ions, soil conditioner, and other applications. One process for creating the biochar involves the use of phosphoric acid at high temperature in a partial oxygen atmosphere to produce a highly porous carbonaceous material. In this work, we found 129Xe NMR to be an excellent technique to study micropores in biochar. Thus, the 129Xe chemical shift in biochar was found to vary linearly with the xenon pressure; from the data an estimate of about 8–9 Å could be proposed for the average pore diameter in pecan shell-based biochar. Through saturation recovery and 2-D NMR exchange experiments, information on the exchange between free versus bound xenon was obtained. Furthermore, correlations of 129Xe NMR data with the carbonization process conditions were made.