Physical, chemical and biological characterization of six biochars produced for the remediation of contaminated sites

Nutrient alterations following biochar application to a Cd-contaminated solution and soil

Biochars, when applied to contaminated solutions or soils, may sequester potentially toxic elements while releasing necessary plant nutrients. This purpose of this study focused on quantifying both phenomenon following wheat straw (Triticum aestivum L.) biochar application (0, 5, and 15% by wt) to a Cd containing solution and a Cd-contaminated paddy soil using 240-day laboratory batch experiments. Following both experiments, solid phases were analyzed for elemental associations using a combination of wet chemical sequential extractions and synchrotron-based X-ray absorption spectroscopy (XAS). When wheat straw biochar was applied at 15% to Cd containing solutions, Cd and Zn concentrations decreased to below detection in some instances, Ca and Mg concentrations increased by up to 290%, and solution pH increased as compared to the 5% biochar application rate. Similar responses were observed when biochar was added to the Cd-contaminated paddy soil, suggesting that this particular biochar has the ability to sequester potentially toxic elements while releasing necessary plant nutrients to the soil solution. When significant, positive correlations existed between nutrient release over time, while negative correlations were present between biochar application rate, potentially toxic element sorption and pH. The latter suggests that potentially toxic elements were sorbed by a combination of organic functional groups or mineral precipitation based on whether pH was above or below ~ 7. In support of this contention, the wet chemical sequential extraction procedure in conjunction with previously observed Cd or current Zn XAS showed that biochar application promoted the formation of layered double hydroxides, sorption to (oxy)hydroxides, and organically bound to biochar as Zn species. As a multifunctional material, biochar appears to play an important role in sequestering Cd while releasing essential plant nutrients. These findings suggest that biochar may be a 'win-win' for improving environmental quality in potentially toxic element contaminated agroecosystems.

Economic and Environmental Optimization of the Forest Supply Chain for Timber and Bioenergy Production from Beetle-Killed Forests in Northern Colorado

Harvesting mountain pine beetle-infested forest stands in the northern Colorado Rocky Mountains provides an opportunity to utilize otherwise wasted resources, generate net revenues, and minimize greenhouse gas (GHG) emissions. Timber and bioenergy production are commonly managed separately, and their integration is seldom considered. Yet, degraded wood and logging residues can provide a feedstock for bioenergy, while the sound wood from beetle-killed stands can still be used for traditional timber products. In addition, beneficial greenhouse gas emission (GHG) savings are often realized only by compromising net revenues during salvage harvest where beetle-killed wood has a relatively low market value and high harvesting cost. In this study we compared Sequential and Integrated decision-making scenarios for managing the supply chain from beetle-killed forest salvage operations. In the Sequential scenario, timber and bioenergy production was managed sequentially in two separate processes, where salvage harvest was conducted without considering influences on or from bioenergy production. Biomass availability was assessed next as an outcome from timber production managed to produce bioenergy products. In the Integrated scenario, timber and bioenergy production were managed jointly, where collective decisions were made regarding tree salvage harvest, residue treatment, and bioenergy product selection and production. We applied a multi-objective optimization approach to integrate the economic and environmental objectives of producing timber and bioenergy, and measured results by total net revenues and total net GHG emission savings, respectively. The optimization model results show that distinctively different decisions are made in selecting the harvesting system and residue treatment under the two scenarios. When the optimization is fully economic-oriented, 49.6% more forest areas are harvested under the Integrated scenario than the Sequential scenario, generating 12.3% more net revenues and 50.5% more net GHG emission savings. Comparison of modelled Pareto fronts also indicate the Integrated decision scenario provides more efficient trade-offs between the two objectives and performs better than the Sequential scenario in both objectives.