Sonia Campbell

Charcoal ash and volatile matter effects on soil properties and plant growth in an acid ultisol.

There is a growing interest in converting organic wastes to charcoal for use as a sustainable soil amendment with a potential to improve soil productivity and sequester C. Three consecutive greenhouse experiments were conducted to investigate the effects of charcoal with different ash and volatile matter (VM) contents on soil properties and maize (Zea mays) growth and to evaluate the effect of time on charcoal performance. Five charcoal amendments (high-VM corncob, low-VM corncob, Kiawe, Binchotan, and a gasification charcoal of Leucaena leucocephala) applied at a 2.5% (wt/wt) rate were compared with a zero-charcoal control with and without fertilization. Only the gasification charcoal significantly increased maize growth without fertilization. The low-VM corncob charcoal with fertilization significantly increased maize growth by 164% compared with the fertilized control in the first planting cycle. Maize growth in the high-VM corncob charcoal supplemented with fertilizer treatment was significantly lower than that of the fertilizer-alone treatment in the first planting cycle. The negative effect of the high-VM charcoal on the fertilizer was caused by bioavailable carbon in the charcoal, which increased soil microbial activity and could have caused N immobilization. Both the beneficial and detrimental effects of charcoal did not persist beyond the first planting cycle, suggesting that charcoal impacts are temporary. Whereas charcoal ash and VM content seem to be important parameters for predicting charcoal behavior in the short-term, more research is needed to examine a broader spectrum of feedstocks exposed to varying thermal treatments.

Bench-Scale Phytoremediation of Polycyclic Aromatic Hydrocarbon-Contaminated Marine Sediment with Tropical Plants

ABSTRACT Elevated levels of polycyclic aromatic hydrocarbons (PAHs) were found in dredged marine sediment from Pearl Harbor. The degradation of PAHs was investigated with soil-sediment systems (washed and unwashed) and 20 plant species. Marine sediment was diluted with native soil in the first experiment. Sediment was washed with gypsum solution and water in the second and third experiments, respectively, prior to soil dilution. Soil dilution ratios were 0, 6, 16, and 37% by weight in the first experiment, 0, 37, 64, and 100% in the second and 0, 18, 64, and 100% in the third. Seven tree, nine shrub, and four grass species were grown for 12 weeks in a glasshouse. A “no plant” control was used in all the experiments. Several plant species yielded up to 90% PAH degradation in the first experiment when compared with no plant control. In the second planting, dwarf hau (Hibiscus tiliaceus) and vetiver (Vetiver zizanoides) appeared to cause the greatest PAH reduction, while paspalum (Paspalum vaginatum) and naupaka (Scaevola sericea) did not. The greatest difference between control and planted soil for both benzo[a]pyrene and total PAH occurred at the highest sediment ratios.

Remediation of benzo[a]pyrene and chrysene-contaminated soil with industrial hemp (Cannabis sativa).

ABSTRACT The phytoremediation, with industrial hemp (Cannabis sativa), of a Hawaiian silty clay soil contaminated with two polycyclic aromatic hydrocarbons (PAHs), chrysene and benzo[a]pyrene, was studied. Hemp showed a very high tolerance to the contaminants. The growth rates of hemp, compared with control, in soils fortified with chrysene and benzo[a]pyrene at concentrations of each varying from 25 to 200 μg/g were consistently above 100%. The plants grew from seed for 45 days in soil fortified with PAHs at concentrations of 25, 50, and 75 μg/g. Controls were pots with contaminated soil but no plant. PAHs levels were significantly reduced in all pots (control and seeded pots), except for one set at a high concentration of chrysene, which may be due to uneven spiking. A time course study over 28 days was done to monitor changes of microbial count and levels of chrysene. Little changes were observed for the total microbial count in the soil, and the concentration of chrysene in the soil decreased slightly in the pots containing plants. However, the chrysene levels in those pots were consistently lower than those in the pots without plants.