Degradation of rizazole in water–sediment systems

This study investigated the degradation of rizazole in water-sediment systems (West Lake system, WL; Beijing–Hangzhou Grand Canal system, BG) with two different types of sediments under aerobic and anaerobic conditions. The half-lives of rizazole in the WL water phase (14.59–15.13 d) were similar to those in the BG water phase (15.90–16.46 d). Within 3–7 d, the rizazole concentration in the sediments reached the maximum values, i.e., equilibrium. Rizazole dissipation was faster in the WL sediment phase with higher organic matter content (T_1/2 = 18.99–19.09 d) compared with the BG sediment phase (T_1/2 = 31.08–33.32 d). Rizazole degradation was slightly faster in the West Lake water-sediment system (WL system) (T_1/2 = 17.11–18.05 d) than in the Beijing–Hangzhou Grand Canal water—sediment system (BG system) (T_1/2 = 20.51–25.02 d). The aerobic degradation of rizazole was similar to its anaerobic degradation in the water-sediment system. The findings are useful to understand the behavior of pesticide in environment.     

The Autothermal Pyrolysis of Waste Tires

Abstract

The growing amount of rubber waste, such as that from tires and cables, has resulted in serious environmental problems. Since rubber waste is not easily biodegradable even after a long period of landfill treatment, material and energy recovery is the preferable alternative to disposal. The potential offered by waste tire pyrolysis for solving both energy and waste treatment problems is widely recognized. Pyrolysis is one method of inducing thermal decomposition without using any oxidizing agent, or using such a limited supply of the agent that oxidization does not proceed to an appreciable extent. The latter may be described as autothermal pyrolysis and will be studied in the present work.

The main objective of this research was to study the operating parameters of autothermal pyrolysis of scrap tires in a laboratory-scale fluidized bed reactor with a 100-cm bed height (10 cm I.D.) and a 100-cm freeboard (25 cm I.D.). Scrap tires were pyrolyzed in a limited oxygen supply, so that the heat for pyrolysis of the scrap tires was provided by combustion of some portion of the scrap tires. The operating parameters evaluated included the effect on the pyrolysis oil products and their relative proportions of (1) the air factor (O.O7–O35); (2) the pyrolysis temperature (370–570 °C); and (3) the catalyst added (zeolite and calcium carbonate). The results show that: (1) the composition of the liquid hydrocarbon obtained is affected significantly by the air factor; (2) the higher operating temperature caused a higher yield of gasoline and diesel; (3) the yield of gasoline increased due to the catalyst zeolite added, and the yield of diesel increased due to the addition of the catalyst calcium carbonate; (4) the principal constituents of gasoline included dipentene and diprene.     

The Adsorptive Capacity of Vapor-Phase Mercury Chloride onto Powdered Activated Carbon Derived from Waste Tires

Abstract

Injection of powdered activated carbon (PAC) upstream of particulate removal devices (such as electrostatic precipitator and baghouses) has been used effectively to remove hazardous air pollutants, particularly mercury-containing pollutants, emitted from combustors and incinerators. Compared with commercial PACs (CPACs), an alternative PAC derived from waste tires (WPAC) was prepared for this study. The equilibrium adsorptive capacity of mercury chloride (HgCl₂) vapor onto the WPAC was further evaluated with a self-designed bench-scale adsorption column system. The adsorption temperatures investigated in the adsorption column were controlled at 25 and 150 °C. The superficial velocity and residence time of the flow were 0.01 m/sec and 4 sec, respectively. The adsorption column tests were run under nitrogen gas flow. Experimental results showed that WPAC with higher Brunauer–Emmett–Teller (BET) surface area could adsorb more HgCl₂ at room temperature. The equilibrium adsorptive capacity of HgCl₂ for WPAC measured in this study was 1.49 × 10^?1 mg HgCl₂/g PAC at 25 °C with an initial HgCl₂ concentration of 25 μg/m³. With the increase of adsorption temperature ≤150 °C, the equilibrium adsorptive capacity of HgCl₂ for WPAC was decreased to 1.×34 10^?1 mg HgCl₂/g PA≤C. Furthermore,WPAC with higher sulfur contents could adsorb even more HgCl₂ because of the reactions between sulfur and Hg²⁺ at 150 °C. It was demonstrated that the mechanisms for adsorbing HgCl₂ onto WPAC were physical adsorption and chemisorption at 25 and 150 °C, respectively. Experimental results also indicated that the apparent overall driving force model appeared to have the good correlation with correlation coefficients (r) >0.998 for HgCl₂ adsorption at 25 and 150 °C. Moreover, the equilibrium adsorptive capacity of HgCl₂ for virgin WPAC was similar to that for CPAC at 25 °C, whereas it was slightly higher for sulfurized WPAC than for CPAC at 150 °C.     

Application and Evaluation of Two Air Quality Models for Particulate Matter for a Southeastern U.S. Episode

Abstract

The Models-3 Community Multiscale Air Quality (CMAQ) Modeling System and the Particulate Matter Comprehensive Air Quality Model with extensions (PMCAMx) were applied to simulate the period June 29–July 10, 1999, of the Southern Oxidants Study episode with two nested horizontal grid sizes: a coarse resolution of 32 km and a fine resolution of 8 km. The predicted spatial variations of ozone (O₃), particulate matter with an aerodynamic diameter less than or equal to 2.5 μm (PM_2.5), and particulate matter with an aerodynamic diameter less than or equal to 10 μm (PM₁₀) by both models are similar in rural areas but differ from one another significantly over some urban/suburban areas in the eastern and southern United States, where PMCAMx tends to predict higher values of O₃ and PM than CMAQ. Both models tend to predict O₃ values that are higher than those observed. For observed O₃ values above 60 ppb, O₃ performance meets the U.S. Environmental Protection Agency's criteria for CMAQ with both grids and for PMCAMx with the fine grid only. It becomes unsatisfactory for PMCAMx and marginally satisfactory for CMAQ for observed O₃ values above 40 ppb.

Both models predict similar amounts of sulfate (SO₄ ^2?) and organic matter, and both predict SO₄ ^2? to be the largest contributor to PM_2.5. PMCAMx generally predicts higher amounts of ammonium (NH₄ ⁺), nitrate (NO₃ ^?), and black carbon (BC) than does CMAQ. PM performance for CMAQ is generally consistent with that of other PM models, whereas PMCAMx predicts higher concentrations of NO₃ ^?,NH₄ ⁺, and BC than observed, which degrades its performance. For PM₁₀ and PM_2.5 predictions over the southeastern U.S. domain, the ranges of mean normalized gross errors (MNGEs) and mean normalized bias are 37–43% and –33–4% for CMAQ and 50–59% and 7–30% for PMCAMx. Both models predict the largest MNGEs for NO₃ ^? (98–104% for CMAQ, 138–338% for PMCAMx). The inaccurate NO₃ ^? predictions by both models may be caused by the inaccuracies in the ammonia emission inventory and the uncertainties in the gas/particle partitioning under some conditions. In addition to these uncertainties, the significant PM overpredictions by PMCAMx may be attributed to the lack of wet removal for PM and a likely underprediction in the vertical mixing during the daytime.     

Relationships Between Nitrogen Transformation Rates and Gene Abundance in a Riparian Buffer Soil

Denitrification is a critical biogeochemical process that results in the conversion of nitrate to volatile products, and thus is a major route of nitrogen loss from terrestrial environments. Riparian buffers are an important management tool that is widely utilized to protect water from non-point source pollution. However, riparian buffers vary in their nitrate removal effectiveness, and thus there is a need for mechanistic studies to explore nitrate dynamics in buffer soils. The objectives of this study were to examine the influence of specific types of soluble organic matter on nitrate loss and nitrous oxide production rates, and to elucidate the relationships between these rates and the abundances of functional genes in a riparian buffer soil. Continuous-flow soil column experiments were performed to investigate the effect of three types of soluble organic matter (citric acid, alginic acid, and Suwannee River dissolved organic carbon) on rates of nitrate loss and nitrous oxide production. We found that nitrate loss rates increased as citric acid concentrations increased; however, rates of nitrate loss were weakly affected or not affected by the addition of the other types of organic matter. In all experiments, rates of nitrous oxide production mirrored nitrate loss rates. In addition, quantitative polymerase chain reaction (qPCR) was utilized to quantify the number of genes known to encode enzymes that catalyze nitrite reduction (i.e., nirS and nirK) in soil that was collected at the conclusion of column experiments. Nitrate loss and nitrous oxide production rates trended with copy numbers of both nir and 16s rDNA genes. The results suggest that low-molecular mass organic species are more effective at promoting nitrogen transformations than large biopolymers or humic substances, and also help to link genetic potential to chemical reactivity.     

羧酸盐型双子表面活性剂的合成及性能研究

以月桂酰氯、乙二胺与丁二酸酐为原料合成了一种羧酸盐型双子(gemini)表面活性剂。采用IR、1 HNMR对中间产物和目标产物进行结构表征,并考察了合成所得羧酸盐型gemini表面活性剂的表面活性。结果表明:合成产物即为目标产物。合成产物的临界胶束浓度为0.027mmol/L,比普通单链表面活性剂低2～3个数量级,表面张力最低可降至29.5mN/m。     

Chromium exhibits adverse effects at environmental relevant concentrations in chronic toxicity assay system of nematode Caenorhabditis elegans

Here we investigated whether the assay system (10-d) in Caenorhabditis elegans can be used to evaluate chronic toxicity of chromium (Cr(VI)) at environmental relevant concentrations ranging from 5.2 μg L⁻¹ to 260 μg L⁻¹. The results indicated that lethality, locomotion behavior as revealed by head thrash, body bend, and forward turn, metabolism as revealed by pumping rate and mean defecation cycle length, intestinal autofluorescence, and ROS production were severely altered in Cr chronically exposed nematodes at environmental relevant concentrations. The most surprising observations were that head thrash, body bend, intestinal autofluorescence, and ROS production in 13 μg L⁻¹ Cr exposed nematodes were significantly influenced. The observed adverse effects of Cr on survival, locomotion behavior, and metabolism were largely due to forming severe intestinal autofluorescence and ROS production. Therefore, our findings demonstrate the usefulness of chronic toxicity assay system in C. elegans in evaluating the chronic toxicity of toxicants at environmental relevant concentrations.     

The OH-induced degradation mechanism of 4-chloro-2-methylphenoxyacetic acid (MCPA) with two forms in the water: a DFT comparison

The initial degradation mechanisms of OH and 4-chloro-2-methylphenoxyacetic acid (MCPA) including molecular form and anionic form are studied at the MPWB1K/6-311+G(3df, 2p)//MPWB1K/6-31+G(d, p) level. Possible reaction pathways of H-atom abstraction and OH addition are considered in detail. By result comparison analysis, it is found that the reaction mechanisms for OH and two forms of MCPA are different, and most reactions for anionic MCPA are easier than those for molecular MCPA. For H-atom abstraction reactions, the calculated energies show that OH abstracting H-atom from -CH₃ group of molecular MCPA is the most kinetically favorable process; the potential energy surface for anionic MCPA indicates that H-atom in -CH₂ group is slightly easier to be abstracted than that in -CH₃ group. For OH addition reactions, the addition of OH to the C1 site is the initial step for molecular MCPA and the predominant product is 4-chloro-2-methylphenol (denoted P3), while the C4 site is the most reactive site for anionic MCPA and the primary product results from the hydroxylation of the aromatic ring, which is in good agreement with the experimental observation. In additional, results from PCM calculations show that most reactions in water phase are more kinetically favorable than those in gas phase, though the mechanisms discussed above will not be changed.     

Chronic toxicity of copper on embryo development in Chinese toad, Bufo gargarizans

This study examined the effects of copper exposure on embryonic development of Chinese toad, Bufo gargarizans. Firstly, the LC₅₀ values from 24 to 96 h of exposure were 3.61 × 10⁻⁶ M, by means of a 4 d toxicity test with B. gargarizans embryos. Secondly, Chinese toad embryos were exposed to 10⁻⁹-10⁻⁶ M copper from mid gastrula stage to operculum completion stage. Measurements included mortality, tadpole weight, tadpole total length, growth retardation, duration of different embryo stages and malformation. Embryonic survival was not affected by copper. Relative to control tadpoles, significantly decreased weight and total length were found at 10^-9-10^-6 M reduced percentage of the embryos in right operculum stage after 10 d exposure to copper and reduced percentage of embryos in operculum completion stage after 12 d exposure to copper were also observed. Moreover, the duration of embryonic development increased at neural, circulation and operculum development stage in copper-treated groups. For the scanning microscope and histological observation, the abnormalities were malformation of wavy dorsal fin, flexural tail, curvature body axis, yolk sac oedema and reduced pigmentation in the yolk sac. Histopathological changes in olfactory, retinal epithelium and skin were also observed. DNA strand breaks exposed to the copper were analyzed by DNA ladder. In conclusion, copper induced toxic effects on B. gargarizans embryos. The present study indicated chronic toxicity tests may provide more accurate way in formulating the “safe levels” of heavy metals to amphibian.     

Ozonation as an advanced oxidant in treatment of bamboo industry wastewater

The present study employed ozonation process to treat the bamboo industry wastewater (BIWW). The impact of ozone dosage and initial organic concentration on color, COD and TOC removal rates were studied along with characterization of the major organics in raw and treated wastewater. The results suggested the ozone dosage of 3.15 g h⁻¹ (concentration 52.5 mg L⁻¹) was suitable for the treatment. After 25 min ozonation of 1 L raw wastewater, the color, COD and TOC removal efficiencies were 95%, 56% and 40%, respectively, with an influent COD concentration of 835 mg L⁻¹. The ratio of kg O₃ kg⁻¹ COD at 3.15 g h⁻¹ was 2.8 (<3), revealing that ozonation was a cost effective process for tertiary treatment of BIWW. Longer oxidization time was required to achieve similar results for raw wastewater with higher COD concentration. The chromatogram from gel permeation chromatography revealed that ozonation resulted in the breakdown of high molecular weight compounds into lower molecular weight components but could not completely mineralize the organic matter. The majority of these compounds were identified in both raw and ozonated samples via GC-MS analysis. In addition to ester derivatives as the main intermediates of ozonation, 1-chloroctadecane, methyl stearate, benzophenone and α-cyperone were identified as the by-products of ozonation.