Temporal evolution of polycyclic aromatic hydrocarbons (PAHs) in sludge from wastewater treatment plants: comparison between PAHs and heavy metals

This paper presents results on the presence and temporal variability of the 16 PAHs recommended by the EPA in primary, secondary and digested sewage sludge over a year. The sewage sludges originated from the Guadalete wastewater treatment plant (WWTP) site in Jerez de la Frontera (Cádiz, Spain). These organic pollutants have been extracted from the sewage sludge by microwave energy. High performance liquid chromatography coupled with diode array (HPLC-DAD) or fluorescence (HPLC-FL) detectors have been used. The results showed that total PAHs concentration varied between 1,945 ng g(-1) dry matter (DM) for primary sludges collected in March and 10,100 ng g(-1) DM for primary sludge collected in June. Generally, concentrations of PAHs were higher in compost and digested sludge than in fresh one. On the other hand, the highest concentration of PAHs were found on summer. This thing is associated to the traffic increase from inland zones to the coast (Jerez de la Frontera is very near to beaches). Finally, this paper present a comparative study of the American an European legislation concluding that the limits of concentrations established are not exceeded. In addition heavy metals were analysed. The origin of PAHs and heavy metals seems to be different.     

Alleviation of Cd toxicity by composted sewage sludge in Cd-treated Schmidt birch (Betula schmidtii) seedlings

We investigated alleviation of Cd toxicity and changes in the physiological characteristics of Betula schmidtii seedlings following application of composted sewage sludge to Cd-treated plants. Plants were grown under four test conditions: control, Cd treatment, sludge amendment, and Cd treatment with sludge amendment. B. schmidtii treated with Cd only accumulated the greatest amount of Cd in the leaves, but absorbed Cd was also highly concentrated in the roots. In contrast, Cd concentrations in the Cd and sludge amendment treated seedlings were the lowest in the roots. Since sludge amendment increased the growth of seedlings, it may have alleviated toxicity by dilution of Cd. Additionally, the absorbed Cd was more widely distributed since it was transported from the roots and accumulated in the stems and leaves of Cd and sludge treated plants. Cd treatment inhibited the growth and physiological functions of B. schmidtii seedlings, but sludge amendment compensated for these effects and improved growth and physiological functions in both Cd-treated and control plants. SOD activity in the leaves of seedlings was increased in the Cd-treated plants, but not in the Cd and sludge amendment treated seedlings. In conclusion, alleviation of Cd toxicity in response to sludge amendment may be related to a dilution effect, in which the Cd concentration in the tissues was effectively lowered by the improved growth performance of the seedlings.     

Short-term exposure to ozone altered the relative feed value of an alfalfa cultivar

Biomonitors are organisms that provide quantitative information on environmental quality. There are some constraints and limitations for the use of plants as biomonitors of soil pollution, as pointed out recently by some authors in this journal. However, we defend the use of plants as biomonitors, and argue that they have important advantages over soil analyses as indicators of soil quality, particularly when investigations are made on a large scale.     

Mechanisms of NOx removal from flue gas by zero valent iron

Chemical reaction between nitric oxide (NO) andzero valent iron (ZVI) was studied in a packed-bed column process with high temperatures based on ZVI strong reducing abilities. For six controlled temperatures of 523-773 K and 400 ppm of NO (typical flue gas temperature and concentration), under short empty bed contacttime ([EBCT] 0.0226-0.0679 sec), NO was completely removed for temperature of 573-773 K but not for 523 K. Break-through curves were conducted for the five working temperatures, and the results indicated that NO reductions by ZVI were varied from 2 to 26.7 mg NO/g ZVI. Higher temperature and longer EBCT achieved better NO removal efficiency. X-ray diffraction (XRD) and electron spectroscopy for chemical analysis (ESCA) were conducted to analyze the crystal structure and oxidation state of the reacted ZVI. Three layers of iron species were detected by XRD: ZVI, Fe3O4, and Fe2O3. ZVI was the most prevalent species, and Fe3O4 and Fe2O3 were less from the XRD analysis. By ESCA, the oxidation state on the reacted ZVI surface was determined, and the species was identifled as Fe2O3, which is the most oxidizing species for iron. Therefore, three layers from the ZVI core to the ZVI surface can be identified: ZVI, Fe3O4, and Fe2O3. Combining the results from XRD and ESCA, the mechanisms for ZVI and NO can be proposed as two consecutive reactions from lower oxidation state (ZVI) in the core to higher oxidation state on the iron surface (Fe2O3): 3Fe + 4NO<--(high temperature)-->Fe3O4 + 2N2 (A1), 4Fe3O4 + 2NO<--(high temperature)-->6Fe2O3 + N2* (A2) Because there was only <5% ZVI used to remove NO comparing to theoretical ZVI used based on the proposed stoichiometry, it can be concluded that the heterogeneous reaction only occurred on the ZVI surface instead of on bulk of the ZVI.     

A survey of light-vehicle driver education curriculum on sharing the road with heavy vehicles

IntroductionLight-vehicle driver education programs that contain content about sharing the road with heavy vehicles may be helpful in reducing future light-vehicle/heavy-vehicle interactions. However, the extent of curricula in the United States including such content is unclear.MethodResearchers developed an online survey targeted at instructors/administrators of state driver education programs to identify curricula addressing heavy vehicles and to determine perceived effectiveness.ResultsNinety-one percent of respondents indicated that the light-vehicle driver education curriculum they teach/administer included a component covering how to safely share the road with heavy vehicles (82% perceived this component to be effective).DiscussionAlthough a large proportion of these programs included a component on how to safely share the road with heavy vehicles, participants indicated there may be room for improvement.Impact on IndustryParticipants recommended that future improvements to driver education programs include updated materials and student hands-on experience with heavy vehicles.     

Design and performance characterization strategy using modeling for biofiltration control of odorous hydrogen sulfide

Biofilter, dynamic modeling software characterizing contaminant removal via biofiltration, was used in the preliminary design of a biofilter to treat odorous hydrogen sulfide (H2S). Steady-state model simulations were run to generate performance plots for various influent concentrations, loadings, residence times, media sizes, and temperatures. Although elimination capacity and removal efficiency frequently are used to characterize biofilter performance, effluent concentration can be used to characterize performance when treating to a target effluent concentration. Model simulations illustrate that, at a given temperature, a biofilter cannot reduce H2S emissions below a minimum value, no matter how large the biofilter or how long the residence time. However, a higher biofilter temperature results in lower effluent H2S concentrations. Because dynamic model simulations show that shock loading can significantly increase the effluent concentration above values predicted by the steady-state model simulations, it is recommended that, to consistently meet treatment objectives, dynamic feed conditions should be considered. This study illustrates that modeling can serve as a valuable tool in the design and performance optimization of biofilters.