RESEARCH WATCH
AIR QUALITY
Cutting down on wastewater sludge volume
Smoke-free tavern air
Reducing sludge volume from domestic water treatment requires better understanding of the behavior of Ca2+ and Mg2* during precipitation of Fe(lll) salts. Fe(lll) salts are being used as substitutes for alum because of concerns about a link between soluble aluminum and Alzheimer's disease. K. A. Baltpurvins and co-workers reported that rapid hydrolysis of Fe(IN) forms ferrihydrite and then goethite and hematite, with a reduction in total hydroxide sludge volume. Ca2+ adsorbed on the Fe(lll) hydroxide surface and prevented transformation to goethite, favoring formation of the smaller volume hematite phase. The authors found that conditions favoring hematite over goethite reduce sludge volume. (Environ. Sci. Techno!., this issue. pp. 1024-32)
The contribution of cigarette smoking relative to other sources of indoor air pollution in public places is controversial. Some pollutants associated with cigarettes are also generated by cooking and other sources. Distinguishing sources can be difficult. W. Ott and colleagues took advantage of a smoking ban in California to measure changes in indoor air quality in a sports tavern. Respirable suspended particles (RSP) levels declined from age of 57 u e / m 3 above outdoor levels to 13 ug/m 3 above outdoor levels after the smoking ban The ban did not affect overall tavern attendance The authors have developed an indoor air quality model for predicting RSP levels from smoking that can be used to estimate RSP levels in similar SDorts taverns (T Air Wastp Manaep Awnr 1199 46 1120-341
BIOREMEDIATION Vinyl chloride degradation Groundwater bioremediation of trichloroethylene (TCE) and tetrachloroethylene (PCE) results in formation of vinyl chloride, which poses greater risks than TCE or PCE. Degradation of the vinyl chloride in these systems often results in the formation of environmentally benign ethane and ethylene. D. L. Freedman and S. D. Herz investigated a bioremediation strategy involving use of ethylene and ethane as primary substrates for aerobic cometabolism of vinyl chloride. Combinations of ethane ethylene and vinyl chloride were inoculated into enrichment cultures grown on either ethane or ethylene Results indicated that ethane and ethylene enrichment cultures could reduce the concentration of vinyl chloride
below current drinking water standards. (Water Environ. Res. 1996, 68, 320-28)
GREEN CHEMISTRY Enhanced PHB yields High production costs remain a major barrier to wide use of microbially produced biodegradable polymers such as poly-3-hydroxybutyrate (PHB). Costs could be reduced through use of microbes that produce large quantities of PHB on inexpensive substrates. T Yamane and co-workers describe the growth of Alcaligenes latus on sucrose in a pHstat fed-batch culture to attain increased PHB productivity. High concentrations of cells and PHB were obtained in a short (18 h) culture time. PHB productivity was 4 0 g PHB/(Lh), which is the highest reported value to date The authors report that pH-stat control can be enhanced through careful control of the feed rate of the pH-control substrate in relation to cell growth (Biotprhnnl Binpne 1996 TO 197-2021
Thermoplastic starch Natural macromolecules such as starch are biodegradable and have potential application as substitutes for plastics. But starch-based biodegradable polymers are thermally unstable and difficult to process into packaging products. When heated,
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they degrade before reaching the melting point. J. Yu and colleagues have reported production of a thermoplastic starch that has been chemically modified so that it can be heat processed. They conducted tensile strength tests on plastic rods produced in the laboratory. The authors found that the mechanical properties of the material depended on reaction temperature, water content, and additives in the thermoplastic starch composite. Addition of polyhydric alcohols caused significant changes in mechanical properties, destroying the crystalline structure during extrusion and decreasing the crystallinitv glass transition and softening temperature (/ Awl Polym Sci 1996 62 1491-94)
Microbial polyester degradation Microbial polyesters such as poly(3hydroxybutyrate) and its copolymers have attracted attention as potential new biodegradable thermoplastics. They degrade in the environment with relative ease by enzymatic action, hydrolysis, or heat. But little is known about the mechanism of degradation. J-S. Yoon and co-workers report development of a theoretical random chain scission model of the hydrolytic degradation of microbial polyesters. The theoretical model was then applied to experimental hydrolytic degradation results They found that three conditions must be met to confirm that hydrolytic deg-
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