Fenton degradation of dialkylphthalates: products and mechanism

Contamination of wastewater by organic pollutants is a major worldwide issue. For instance plastic additives such as phthalates are found in wastewater. Efficient techniques are thus needed to clean wastewaters. The Fenton reaction involving H₂O₂ and Fe(II) salts can be used to treat polluted water. During the Fenton reaction pollutants are decomposed directly by hydroxyl radicals. In some cases toxic by-products are produced. Here dimethyl phthalate, diethyl phthalate, and dipropyl phthalate by-products formed during the Fenton reaction were studied. Fenton degradation of selected phthalates yielded numerous transformation products such as hydroxylated phthalates. The hydroxylation reaction occurred at the aromatic ring of phthalates and yielded mono- and dihydroxylated phthalates. For monohydroxylated phthalate, 3-hydroxy- and 4-hydroxydialkylphthalates are the main transformation products. In addition to hydroxylated derivatives, aliphatic chain degraded mono- and dihydroxylated phthalates were also detected.     

Preliminary Study of Non-woven Composite: Effect of Needle Punching and Kenaf Fiber Loadings on Non-woven Thermoplastic Composites Prepared From Kenaf and Polypropylene Fiber

Non-woven composites were produced using kenaf (bast) fiber and polypropylene (PP) fiber. The effects of needle punching process, number of needle and kenaf fiber loadings on the properties of non-woven composite were studied. The aspect ratio of kenaf fiber was also measured in this study. The aspect ratio of most of kenaf fiber used was in the range of 200–400. The results indicated that the mechanical strength of the non-woven composite was significantly influenced by the percentage of kenaf fiber. This may due to the evenly mixed kenaf and PP fibers during carding process prior to the mechanical interlocking by needle punching process. The tensile strength, modulus and toughness were enhanced with the incorporation of carded and needle punched fibers. The number of needle used in needle punching process had a significant effect on the strength of the composite. This was evident in SEM micrograph where composite prepared from carded to needle punched non-woven web showed better wettability as compared to composite prepared from carded non-woven web only. However, no significant difference was observed in water absorption and thickness swelling tests for composites prepared with different number of needles.     

BETR global--a geographically-explicit global-scale multimedia contaminant fate model

We present two new software implementations of the BETR Global multimedia contaminant fate model. The model uses steady-state or non-steady-state mass-balance calculations to describe the fate and transport of persistent organic pollutants using a desktop computer. The global environment is described using a database of long-term average monthly conditions on a 15° × 15° grid. We demonstrate BETR Global by modeling the global sources, transport, and removal of decamethylcyclopentasiloxane (D5).     

The influence of storage on the morphology and physiology of phthalic acid-degrading aerobic granules

The precultured aerobic granules with special degradabilities could be used as a feasible bioseed for enhancement of aerobic granulation systems. In practice, the storage stability, physicochemical characteristics, and recovering efficiency of granules are crucial for a long-distance transportation and successful application. In this study, phthalic acid (PA)-degrading aerobic granules were cultivated and stored for 8 wk at 4 °C. The granular size, settling ability as well as structure integrity was found stable during the storage period. It was observed that the upper 1/3 part of granules stored in the reagent bottle turned to black color, while the lower 2/3 part granules did not significantly change color (brown–yellow) after the 8-wk storage. The black and brown–yellow color PA-degrading granules were manually separated and re-inoculated into two identical sequencing batch reactors for reviving the PA degradation capability. After a 7 d operation, both black and yellow granules restored their activities to the levels before storage, in terms of total organic carbon removal efficiency (100%), specific oxygen uptake rate (59 mg g VSS⁻¹ h⁻¹), and adenosine triphosphate content (0.016 mg g VSS⁻¹). This study demonstrated that aerobic granules grown on a complex substrate could tolerate storage conditions and rapidly restored their bioactivities toward the target pollutant. The results also shed the light on the future application of precultured aerobic granules with unique functions for biodegradation and bioremediation purpose.     

Control of mercury vapor emissions from combustion flue gas

GOAL, SCOPE AND BACKGROUND: Mercury (Hg) emission from combustion flue gas is a significant environmental concern due to its toxicity and high volatility. A number of the research efforts have been carried out in the past decade exploiting mercury emission, monitoring and control from combustion flue gases. Most recently, increasing activities are focused on evaluating the behavior of mercury in coal combustion systems and developing novel Hg control technologies. This is partly due to the new regulatory requirement on mercury emissions from coal-fired combustors to be enacted under the U.S. Title III of the 1990 Clean Air Act Amendments. The aim of this review work is to better understand the state-of-the-art technologies of flue gas mercury control and identify the gaps of knowledge hence areas for further opportunities in research and development. MAIN FEATURES: This paper examines mercury behaviors in combustion systems through a comprehensive review of the available literature. About 70 published papers and reports were cited and studied. RESULTS AND DISCUSSION: This paper summarizes the mechanisms of formation of mercury containing compounds during combustion, its speciation and reaction in flue gas, as well as subsequent mobilization in the environment. It also provides a review of the current techniques designed for real-time, continuous emission monitoring (CEM) for mercury. Most importantly, current flue gas mercury control technologies are reviewed while activated carbon adsorption, a technology that offers the greatest potential for the control of gas-phase mercury emissions, is highlighted. CONCLUSIONS AND RECOMMENDATIONS: Although much progress has been achieved in the last decade, techniques developed for the monitoring and control of mercury from combustion flue gases are not yet mature and gaps in knowledge exist for further advancement. More R&D efforts are required for the effective control of Hg emissions and the main focuses are identified.     

Ozonation of metoprolol in aqueous solution: ozonation by-products and mechanisms of degradation

This study investigated the degradation pathway of metoprolol, a widely used β-blocker, in the ozonation via the identification of generated ozonation by-products (OPs). Structure elucidation of OPs was performed using HPLC coupled with quadrupole time-of-flight high-resolution mass spectrometry. Seven OPs were identified, and four of these have not been reported elsewhere. Identified OPs of metoprolol included aromatic ring breakdown by-products; aliphatic chain degraded by-products and aromatic ring mono-, di-, and tetrahydroxylated derivatives. Based on the detected OPs, metoprolol could be degraded through aromatic ring opening reaction via reaction with ozone (O₃) and degradation of aliphatic chain and aromatic ring via reaction with hydroxyl radical (?OH).     

Kinetic studies of the degradation of parabens in aqueous solution by ozone oxidation

Ozone degradation of a mixture containing methylparaben, ethylparaben, propylparaben, butylparaben and benzylparaben was carried out in aqueous solution. The degradation followed the pseudo-first-order kinetic model and occurs with two ozonation stages with the observed rate constants of second stage ozonation, k _obs2, being higher than the observed rate constants in first stage, k _obs1. The k _obs1 of parabens was found to increase exponentially whilst k _obs2 was found to maximize at 35°C. Both k _obs1 and k _obs2 were found to decrease exponentially with respect to the initial concentration of parabens. Both pH and ozone dose showed positive effects on the rate of degradation. It was also observed that an ozone dose of 0.67 g/h resulted in the removal of 99% of parabens in 12 min, and also the removal of 61 and 32% of chemical oxygen demand (COD) and total organic carbon (TOC), respectively, in 3 h of ozonation time for a 500 μM of solution of parabens.     

Contamination time effect on lead and cadmium fractionation in a tropical coastal clay

The capability of a tropical coastal clay to immobilize lead (Pb) and cadmium (Cd) was investigated in laboratory batch sorption tests conducted under acidic, neutral, and slightly alkaline conditions. The contact time was extended to 65 d. The distribution of Pb and Cd among various sorbed phases was examined using a sequential extraction technique. The sorbed phases were fractionated into the exchangeable, carbonate, reducible, organic, and residual fractions. There were only small changes in the total Pb and Cd sorption beyond a 1-d sorption period. The metal fractionation results show that the amount of Pb and Cd in various fractions changed with sorption time, and the changes were pH-dependent. These changes could be attributed to mineral dissolution and transformation or redistribution of the sorbed phases. Transformation of the sorbed phases resulted in increasing Pb and Cd retention in the more persistent fractions with time, at the expense of reductions in the loosely bound fractions. Nevertheless, Pb and Cd fractionation in the solid phase appeared to reach equilibrium within the 65-d sorption period. These Pb and Cd fractionation results reflect the effect of contamination time on the heavy metal lability and bioavailability in the subsurface environment.     

Media Factors Affecting the Performance of Upflow Anaerobic Packed-Bed Reactors

Numerous studies have demonstrated that anaerobic packed-bed reactors (APBRs) containing media such as clay chip, small stone, and porous plastic modules are effective for treating a variety of organic wastes. Most of these studies focused on the treatment capabilities of the processes, yet little work was done about the factors affecting their designs and performance. This paper presents the results of a study on a laboratory scale APBR system examining the significance of media factors such as media roughness, specific surface area, porosity and pore size on treatment performance. The results showed that media roughness and pore size were more important over surface area on the reactor performance. Within the same media porosity, pore size plays a more significant role than surface area in term of COD removal efficiency. The study indicates that the ability of a support medium to retain biomass either as suspended growth entrapped in the void space, or by attachment to the media surface is a significant consideration in an upflow APBR. A testing protocol for measuring methane gas produced by the suspended biomass using a batch serum bottle technique was developed and presented in this study. The method involved measurements of hourly methane production and instantaneous TOC concentration from the suspended biological solids extracted from various reactor heights. The proportion of methane production associated with the suspended biomass was as high as 58% at organic loading rate of 16 g COD/L.day. The results suggest that media pore size and porosity play a significant role in the performance of upflow APBRs.     

The distribution of polynuclear aromatic hydrocarbons in ambient air particulates in Singapore

Ambient air particulates were collected using high volume samplers at seven locations throughout Singapore. The particulates were analyzed for eleven polynuclear aromatic hydrocarbons (PAH) using high performance liquid chromatography (HPLC) with fluorescence detection. Several sample preparation techniques were used to determine which method would yield the most PAHs from the bulk sample matrix. PAH profiles (standardised against the concentration of benzo(a)pyrene) were obtained to characterise the different sampling sites chosen.