RESEARCH WATCH

BIODEGRADATION

Bioavailability study The availability of persistent organic compounds in soils for biodegrada-tion declines over time. The parti­tioning of organic compounds into organic solids or the movement of organic compounds into nanopores are two mechanisms that might explain this. P. B. Hatzinger and M. Alexander evaluated the biodegrad-ability of phenanthrene and 4-nitro-phenol sequestered in porous silica nanopores and in nonporous or~ ganic solids. Rates of biodegradation decreased as the amount of silica and the amount of substrate in silica pores increased When phenan­threne was sequestered in solid al-kanes waxes and low molecular weight polymers rates markedly de­creased Results suggest but cannot prove that diffusion into nanopores or partitioning into solid organic mat­ter can limit biodeeradation in soils (Fnviran Taxirnl Chem 1997 7,(111 2215-2221)

Carbon tetrachloride removal The biodegradation of carbon tetra­chloride (CT), a groundwater con­taminant resistant to spontaneous degradation, can be facilitated by optimizing prevailing environmental conditions. G. Jin and A. J. Englande, Jr., performed laboratory studies to investigate biodegradation kinetics of CT by Escherichia coli K-12 under varying oxidation-reduction poten­tial conditions. By using titanium(III) citrate as a reducing agent, signifi­cant compound degradation was observed when bacterial cultures experienced low initial oxidation-reduction potential conditions By optimizing conditions >80% re­moval of carbon tetrachloride was achieved in 300 hours The results of this study can be used to develop an in situ system for biodegradation of chloroorganic compounds {Water Environ Res 1997 69(6) 1100-1105)

BIOREMEDIATION

Industrial effluent cleanup The ability of microorganisms to re­move heavy metals from aqueous solutions by various mechanisms has generated interest in their po­tential for treating industrial efflu­ents. P. Yong and L. E. Macaskie studied the effect of increased sub­strate concentration on a Citrobacter species (sp.) that accumulates heavy metals as cell-bound metal phos­phates in stirred-tank and plug-flow reactors (STR and PFR, respectively). A significant increase in metal re~ moval was observed for Citrobacter sp. cells in the PFR but not in the STR. Inhibition of Citrobacter phos­phatase by nitrate interferes with remediation of effluents and was found to be concentration-dependent and reversible The authors developed a model to predict the decrease in flow rate needed to compensate for nitrate interference {Biotechnol Bio-em 1997 55(6) 821-830)

Phosphorus removal Biological treatment systems for the removal of phosphorus can be used more effectively if rates of volatile fatty acid (VFA) production and up­take processes by different groups of bacteria are known. S. Danesh and

J. A. Oleszkiewicz isolated and char­acterized two processes using a bench-scale, anaerobic sequencing batch reactor and a biological, nutri­ent-removal sequencing batch reac­tor. Reaction conditions were varied, and VFA production and uptake were evaluated. Results indicate that biological removal of phosphorus can be improved by prefermentation of degritted wastewater before nutri­ent removal. (Water Environ. Res. 1997,69, 1106-1101)

GREEN CHEMISTRY Composting degradable polymers The behavior of degradable poly­mers disposed of in waste streams has been studied, but their behavior in compost has not been well char­acterized. M. Day and co-workers examined degradable polymer be­havior in a laboratory-scale com­posting system, a thermal hydrolytic environment consisting of water at 60 °C, and a thermal-oxidative dry oven environment. Results indicate that physical reorganization of poly­meric structures can occur at com­posting environment temperatures. However, although polyethylene-based samples (compost bags)

Mobility of copper in soils Knowledge of metal adsorption and complexation processes in soils is needed to predict metal solubility, speciation, and transport. P. Romkens and J. Dolfing studied the distribution of copper among low molecular weight and high molecular weight fractions of soil organic matter. Results indicate that low molecular weight, more soluble organic matter components had a greater capacity for copper binding than did the high molecular weight, less soluble fraction, which exhibited a greater af­finity for copper. Addition of calcium, simulating the liming of soils, caused floccula-tion of most of the high molecular weight fraction and associated copper, whereas the low molecular weight components remained dissolved and bound to copper. These findings highlight the potential importance of low molecular weight organic matter components in controlling the mobility of trace metals in soils. (Environ. Sci. Technol., ,his iisue, pp. 366-369)

0013-936X/98/0932-99A$15.00/0 © 1998 American Chemical Society FEB. 1, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 9 9 A