TECHNOLOGY UPDATE Ryegrass used in soil remediation test Results obtained from a year-long greenhouse study conducted by Phytokinetics, Inc., of Logan, Utah, indicate that planting perennial ryegrasses accelerates removal of polyaromatic hydrocarbons and pentachlorophenol (PCP) from contaminated soils. The study was funded by EPA's Superfund Innovative Technology Evaluation Emerging Technology program. Well-mixed samples of contaminated soils taken from a Superfund site in Portland, Oreg., were incorporated into three test systems: planted soil columns amended with nutrients and dolomite; unplanted amended columns; and unplanted, unamended columns. These were periodically examined to determine the extent of any contaminant removal. It was found that during the first two-month period, biodegradation rates depended on the addition of amendments. Moreover, in the planted columns, the root system provided additional stimulation of biodegradation rates. Ryegrass accelerated the removal rate of PCP, pyrene, and chrysene; and nutrients stimulated removal of PCP fluoranthene, pyrene, chrysene, and benzofluoranthene. No contaminants were found in the plant shoot tissue. By the end of the one-year study period, which began in March 1996, incremental decreases in contaminant levels were no longer observed; there was no further statistically significant effect of plants or nutrients regarding contaminant removal. Ari Ferro of Phytokinetics believes the residual hydrophobic contaminants are tightly bound in soil organic matter. Phytokinetics is investigating use of phytogenic surfactants to help solubilize the contaminants and make them more accessible to soil microbes. Phytokinetics has begun the second phase of the project, during which ryegrasses will be planted at the Portland site. Although contami-
Soil columns are being used to test the effectiveness of perennial ryegrasses in accelerating the removal of organic compounds from contaminated soils. (Courtesy Ari Ferro, Phytokinetics, Inc.)
nant removal occurred in unplanted, unamended soils in the greenhouse study, this occurs very slowly in the field. Whereas natural attenuation is stimulated by adequate soil moisture, the waxy creosote contaminants at the Superfund site retard water percolation. This problem is surmounted by planting ryegrass, allowing moisture to percolate into the soil and facilitate contaminant removal.—KELLYN S. BETTS
New chemical reactor design cuts waste SRI International of Menlo Park, Calif., has built a prototype chemical reactor, significantly reducing waste production compared with the reduction achieved with conventional technologies. Based on an old approach to chemical mixing, and enhanced with new materials from computer modeling insights, the patented technique is the impetus for this materials-saving development process. According to William J. Asher, SRI's principle chemical engineer, a challenge in the industry is to minimize waste products while conducting highly exothermic reactions. Asher used a computer model to modify an existing method for adding reactants along the length of a
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reactor, facilitating volumetric mixing and reducing concentration gradients and hot spots. The study was supported with funds from the Center for Waste Reduction Technologies, the Department of Energy's Office of Industrial Technologies, and five major chemical companies. The model used by Asher predicted that byproduct waste production could be minimized by using a reactant-reactor interface with a flow resistance 10 times higher than that of conventionally used materials. Asher selected a sintered, porous, metal flow-through interface to introduce reactants into the reactor. A slurry of particles was filtered into the interface, partially blocking reactant flow and controlling flow resistivity and reactor performance; reduced interface permeability limited thermal runaway at the reactor exit. Packing materials within the reactor enhanced mixing. The computer model was used to predict waste minimization during liquid sulfur trioxide sulfonation of toluene. In a bench-scale technology demonstration performed by SRI in 1996, the ratio of product to waste effluent increased by a factor of 20 compared with conventional technology performance. SRI is refining the model to further evaluate reactor performance because design parameters are varied. The model will also allow SRI to predict pilot-scale performance by using the modeling technique in conjunction with process development in the bench-scale apparatus. SRI is testing and evaluating the performance of the enhanced model. Candidate reactions for process improvement include alkylations, carbonylations, carbamylations, chlorination, direct oxidations, ethoxylations, hydroformylations, hydrogenations, nitration, and sulfonations. The company estimates a cost of $250,000 to retrofit an existing reactor and three to four times that amount to install a new reactor.—K.S.B.
VOL.31, NO. 10, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 4 4 9 A
