Numerical characterization of the plasma arc with various Ar-CO2 mixtures

Environmental Science and Pollution Research - Plasma technology finds applications in many industrial areas. To improve the process efficiency, different plasma forming gases and their mixtures...     

Parameters affecting azoxystrobin and imidacloprid degradation in biobed substrates in the North Indian tropical environment

Abstract

This study reports degradation of azoxystrobin (AZOXY) and imidacloprid (IMIDA) in the rice straw (RS)/corn cob (CC) and peat (P)/compost (C)-based biomixtures. The effect of biomixture preconditioning (10?days incubation prior to pesticide application), pesticide concentration and moisture content was evaluated. Results suggested that conditioning of biomixture greatly affected IMIDA degradation where half-life (t_1/2) was reduced by 5–9 times. This was attributed to higher microbial biomass carbon content and dehydrogenase activity in the conditioned biomixtures. Pesticide application in the conditioned biomixture did not show any negative impact on soil microbial parameters. Both pesticides degraded at faster rate in the rice straw-based biomixtures than in the corn cob-based biomixtures. Degradation slowed down with increase in initial concentration of pesticides in biomixture and 1.6–3.0 (AZOXY) and 2.4–3.6 (IMIDA) times increase in t_1/2 values was observed. The moisture content of biomixture showed positive effect on degradation which increased when moisture content was increased from 60 to 80% water holding capacity. The effect was significant for IMIDA degradation in the corn cob-based biomixtures and AZOXY degradation in the peat biomixtures. The rice straw-based biomixtures were better in degrading AZOXY and IMIDA and can be used in biopurification systems.     

Changes in oxygen consumption and respiratory enzymes as stress indicators in an estuarine edible crab Scylla serrata exposed to naphthalene

The sublethal effect of naphthalene was studied on the physiology of a mud crab Scylla serrata. The 96 h acute toxicity of naphthalene was determined and found to be 28 mg 1(-1) (LC100), 18 mg 1(-1) (LC50), 10 mg 1(-1) (LC0) respectively. The 30 days sublethal effect (LC0) 9 mg 1(-1), 8 mg 1(-1), 10 mg 1(-1), of naphthalene was investigated in the crab S. serrata with reference to oxygen consumption and changes in the activity of respiratory enzymes. The results indicated that naphthalene caused disturbance in the normal physiology of the crab. The bioaccumulation of naphthalene was also investigated in gills, hepatopancreas, haemolymph and ovary. The consumption of oxygen increased in the naphthalene medium when compared with that of the crabs exposed to naphthalene free medium. A decreased trend in the activity of respiratory enzymes such as lactate dehydrogenase (LDH), isocitrate dehydrogenase (ICDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH), alpha-ketoglutarate dehydrogenase (alpha-KDH) and glutathione (GSH) were recorded in the hepatopancreas, ovary and gills of S. serrata for all the tested concentrations of naphthalene and the results were analyzed for their significance.     

Characterization and source identification of airborne trace metals in Singapore

Airborne particulate trace metals have important health implications. As a consequence, their concentrations are increasingly monitored in many urban locations worldwide. In this study, fine atmospheric particles (PM(2.5)) were collected in Singapore over a period of 83 consecutive days during 2000, and analysed to determine the concentration of trace elements using ICP-MS. Altogether, eighteen airborne trace metals were quantified: Al, Ag, Ba, Cd, Cr, Co, Cu, Fe, Ga, Li, Mn, Ni, Pb, Sr, Zn, V, Si, and Ti. While Li was the least abundant trace metal with a mean concentration of 0.2 ng m(-3), Zn showed the maximum mean concentration of 279.1 ng m(-3). Calculation of enrichment factors indicated that the elements Pb, Zn, Cd, V, Ni, Cr, and Cu were enriched by factors of 30 to 5000 relative to their natural abundance in crustal soil. The extent of metal pollution in the study area was assessed by comparing the measured concentrations to those reported in the literature for a selected number of urban sites in other parts of the world. Factor analysis was used to identify the major sources affecting particulate air pollution in Singapore. The sources that contribute to the loading of trace metal-bearing aerosols in the Singapore urban atmosphere include fuel oil-fired power plants, metal processing industry, land reclamation and construction activities, municipal solid waste incinerators, and traffic emissions.     

Electrocoagulation-integrated hybrid membrane processes for the treatment of tannery wastewater

Three different combinations of treatment techniques, i.e. electrocoagulation combined with microfiltration (EMR), membrane bioreactor (MBR) and electrocoagulation integrated with membrane bioreactor (hybrid MBR, (HMBR)), were analysed and compared for the treatment of tannery wastewater operated for 7 days under the constant trans-membrane pressure of 5 kPa. HMBR was found to be most suitable in performance as well as fouling reduction, with 94 % of chemical oxygen demand (COD) removal, 100 % chromium removal and 8 % improvement in percentage reduction in permeate flux compared to MBR with only 90 % COD removal and 67 % chromium removal. The effect of mixed liquor suspended solids on fouling was also investigated and was found to be insignificant. EMR was capable of elevating the flux but was not as efficient as HMBR and MBR in COD removal. Fouling reduction by HMBR was further confirmed by SEM-EDX and particle size analysis.     

Pilot-scale biopesticide production by Bacillus thuringiensis subsp. kurstaki using starch industry wastewater as raw material

Pilot-scale Bacillus thuringiensis based biopesticide production (2000 L bioreactor) was conducted using starch industry wastewater (SIW) as a raw material using optimized operational parameters obtained in 15 L and 150 L fermenters. In pilot scale fermentation process the oxygen transfer rate is a major limiting factor for high product yield. Thus, the volumetric mass transfer coefficient (K_La) remains a tool to determine the oxygen transfer capacity [oxygen utilization rate (OUR) and oxygen transfer rate (OTR)] to obtain better bacterial growth rate and entomotoxicity in new bioreactor process optimization and scale-up. This study results demonstrated that the oxygen transfer rate in 2000 L bioreactor was better than 15 L and 150 L fermenters. The better oxygen transfer in 2000 L bioreactor augmented the bacterial growth [total cell (TC) and viable spore count (SC)] and delta-endotoxin yield. Prepared a stable biopesticide formulation for field use and its entomotoxicity was also evaluated. This study result corroborates the feasibility of industrial scale operation of biopesticide production using starch industry wastewater as raw material.     

Ammonia in the atmosphere: a review on emission sources, atmospheric chemistry and deposition on terrestrial bodies

Gaseous ammonia (NH₃) is the most abundant alkaline gas in the atmosphere. In addition, it is a major component of total reactive nitrogen. The largest source of NH₃ emissions is agriculture, including animal husbandry and NH₃-based fertilizer applications. Other sources of NH₃ include industrial processes, vehicular emissions and volatilization from soils and oceans. Recent studies have indicated that NH₃ emissions have been increasing over the last few decades on a global scale. This is a concern because NH₃ plays a significant role in the formation of atmospheric particulate matter, visibility degradation and atmospheric deposition of nitrogen to sensitive ecosystems. Thus, the increase in NH₃ emissions negatively influences environmental and public health as well as climate change. For these reasons, it is important to have a clear understanding of the sources, deposition and atmospheric behaviour of NH₃. Over the last two decades, a number of research papers have addressed pertinent issues related to NH₃ emissions into the atmosphere at global, regional and local scales. This review article integrates the knowledge available on atmospheric NH₃ from the literature in a systematic manner, describes the environmental implications of unabated NH₃ emissions and provides a scientific basis for developing effective control strategies for NH₃.     

A comparative evaluation of passive and active samplers for measurements of gaseous semi-volatile organic compounds in the tropical atmosphere

The polyurethane foam (PUF) disk-based passive air samplers (PAS), mounted inside two aluminium bowls to buffer the air flow to the disk and to shield it from precipitation and sunlight, were used for the collection of atmospheric SVOCs in Singapore during April 2008–June 2008. Data obtained from PAS measurements are compared to those from active high-volume air sampling (AAS). Single factor ANOVA tests show that there were no significant differences in chemical distribution profiles between actively and passively collected samples (PAHs, F = 3.38 × 10^?8 < F_critical = 4.17 with p > 0.05; OCPs, F = 2.71 × 10^?8 < F_critical = 4.75 with p > 0.05). The average air-side mass transfer coefficient (k_A) for PAS, determined from the loss of depuration compounds such as 13C₆ – HCB (1000 ng), 13C₁₂ – 4,4′ DDT (1000 ng) and 13C₁₂ – PCB 101 (1000 ng)spiked on the disks prior to deployment, was 0.12 ± 0.04 m s^?1. These values are comparable to those reported previously in the literature. The average sampling rate was 3.78 ± 1.83 m³ d^?1 for the 365 cm² PUF disk. Throughout the entire sampling period (～68 d), most of the PAHs and all OCPs exhibited a linear uptake trend on PAS, while naphthalene, acenaphthylene, acenaphthene and fluorene reached the curvilinear phase after the first ～30 d exposure. Theoretically estimated times to equilibrium (t_eq) ranged from around one month for Acy to hundreds of years for DB(ah)A. Sampling rates, based on the time integrated active sampling-derived concentrations and masses collected by PUF disks during the linear uptake phase, were determined for all target compounds with the average values of 2.50 m³ d^?1 and 3.43 m³ d^?1 for PAHs and OCPs, respectively. More variations were observed as compared to those from the depuration study. These variation were most likely due to the difference of physicochemical properties of individual species. Lastly, multiple linear regression models were developed to estimate the log-transformed gaseous concentration of an individual compound in air based on the mass collection rate of the gaseous SVOCs measured using the PAS and the molecular weight (MW) of the particular compound for both PAHs and OCPs, respectively.     

Sublethal effect of silver and chromium in the green mussel Perna viridis with reference to alterations in oxygen uptake, filtration rate and membrane bound ATPase system as biomarkers

Perna viridis is an ideal animal for studying the impairment caused by the effects of heavy metals that are often detected in coastal areas. Preliminary bioassay tests revealed that the lethal (LC(100)), median lethal (LC(50)) and sublethal (LC(0)) concentration of silver and chromium to P. viridis were 6.5, 4.0, 2.0 mg l(-1) and 4.5, 2.5, 1.0 mg l(-1), respectively. Toxic effect of silver and chromium was evaluated in the green mussel P. viridis, with reference to oxygen consumption, filtration rate and ATPase system in laboratory experiments. These parameters were selected as the end point of sublethal stress. Oxygen consumption and filtration rates were calculated as a measure of decline in the dissolved oxygen level and algal concentration (feed) in the aquaria water, respectively. Silver and chromium affects both oxygen consumption and filtration rate significantly (P<0.01) at 96 h when compared to control. The activity of ATPases system in the gills, hepatopancreas, ovary and muscle of mussels were inhibited by silver and chromium indicating that metals exerted significant toxic effect. The inhibition of Na(+)K(+) ATPase, Ca(2+) ATPase and Mg(2+) ATPase in the mussels were significant (P<0.05) for silver and highly significant (P<0.01) for chromium, which indicates that chromium was more toxic to mussels when compared to silver. The assessment of oxygen consumption, filtration and ATPases system can thus be used as a valid biomarker in aquatic ecotoxicology studies.