Wastewater treatment


cern. Results showed that maximum concentrations occurred early in the day, before customer traffic through doors increased ventilation or opera tors ...
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RESEARCH WATCH

ASSESSMENT Recycled post leachability A. M. Kells and K. R. Solomon re­ port the first study of pesticide leachability from fence posts made of recycled plastic pesticide con­ tainers. Two groups of commercial posts were leached with well water, simulated acid rain, and simulated alkaline rain, some just after manu­ facture and some after one year of outdoor weathering. Only one pesti­ cide, trifluralin, was detected in the leachates, and its concentration de­ creased about 20-fold after weather­ ing. Concentrations of trifluralin in leachate did not exceed Canadian guidelines for protection of water used by humans, livestock, or ter­ restrial plants; however, concentra­ tions did exceed guidelines for the protection of aquatic life. (Environ. Toxicol. Chem. 1995, 14(3), 383-88)

Dioxins form on collected particles Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF) are far more likely to form on particles collected by emission control sys­ tems than on uncollected fly ash particles, R. Addink and K. Olie found in a review of surface-catalyzed for­ mation and destruction of PCDD/ PCDF during combustion. Collected particles spend several hours at 300350 °C, temperatures appropriate for formation of dioxin from macromolecular carbon structures. Ring con­ densation and chlorination reactions, important in forming PCDD/PCDF from precursor molecules, can be catalyzed with copper compounds. But, the authors stress, more re­ search is needed about dioxin forma­ tion on uncollected particles to pro­ vide more data on the reactivity of precursors in the postcombustion zone. (Environ. Sci. Techno!., Ms issue, 1425)

BIODEGRATlON Degrading olive mill wastes

Soil mineralization

Removing phenolic-based pollution has become necessary in the Mediter­ ranean area, where olive mill waste­ waters contain high concentrations of phenolics and other aromatic com­ pounds. S. Sayadi and R. Ellouz stud­ ied lignin and manganese peroxidases produced by Phanerochaete chrysosporium for degrading pollutants in olive mill wastewaters. Wastewater exposed to high Mn(II) concentrations and high levels of manganese peroxi­ dase (0.65 μΜ) experienced about 25% decolorization, which indicated aromatic compound degradation. Greater than 70% decolorization oc­ curred in wastewater with low Mn(II) concentrations and high levels of lig­ nin peroxidase activity (0.3 μΜ). The results are significant for application and design of treatment processes for wastewater containing aromatics and phenolics. (Appl. Environ. Microbiol. 1995, 61(3), 1098-1103)

Remediation technologies are needed for sites polluted with polycyclic aromatic hydrocarbons (PAHs) and Λί-heterocyclic aromat­ ics (NHAs), two groups of common environmental contaminants. R. J. Grosser, D. Warshawsky, and J. R. Vestal studied PAH and NHA miner­ alization in five soils taken from a coal tar-contaminated site. Within 64 days, two of the five soils studied had higher mineralization rates for five of the eight compounds. Results did not correlate with total biomass, indicating that mineralization de­ pended on individual soil chemistry and biological characteristics. Bioremediation success depends on de­ termination of these parameters. Microorganisms isolated from soils with higher degradation rates en­ hanced degradation in lower rate soils. (Environ. Toxicol. Chem. 1995, 14(3), 375-82)

2 4 0 A • VOL. 29, NO. 6, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

BIOREMEDIATION Wastewater treatment Biological suspended-growth sys­ tems are becoming attractive for removing nitrogen at wastewater treatment facilities because they eliminate the need for a clarifier. Β. Rusten, L. J. Hem, and H. ©degaard evaluated nitrification rates of a moving-bed bioreactor process that operates at low temper­ atures and is less complicated than traditional systems. It uses biofilm grown on small plastic elements with a large surface area and nomi­ nal density. This design eliminates the need for recycling biomass and minimizes reactor head loss. Biofilm surface area can be adjusted by add­ ing more plastic elements. Two de­ signs were evaluated, and both dem­ onstrated acceptable nitrification rates. Temperature, between 7 and 18 °C, was not significant in reducing nitrification rates because increased dissolved oxygen levels were attain­ able at lower temperatures. (Water Environ. Res. 1995, 67(1), 75-86)

INDOOR AIR Reducing fugitive vapors Redesign of dry cleaning machines has reduced the direct emission of perchloroethylene (PERC) vapors, but fugitive emissions also must be reduced. D. J. Moschandreas and D. S. O'Dea measured indoor air PERC concentrations at six dry cleaning facilities. They measured maximum indoor air PERC concen­ trations of 50 ppm, with average concentrations ranging from 5 to 16 ppm, sufficiently high to cause con­ cern. Results showed that maximum concentrations occurred early in the day, before customer traffic through doors increased ventilation or opera­ tors turned on ventilation system. (J. Air Waste Manage. Assoc. 1995, 45, 111-15)