Raj Boopathy

Soils contaminated with explosives: Environmental fate and evaluation of state-of- the-art remediation processes (IUPAC Technical Report)*

An explosion occurs when a large amount of energy is suddenly released. This energy may come from an over-pressurized steam boiler, from the products of a chemical reaction involving explosive materials, or from a nuclear reaction that is uncontrolled. In order for an explosion to occur, there must be a local accumulation of energy at the site of the explosion, which is suddenly released. This release of energy can be dissipated as blast waves, propulsion of debris, or by the emission of thermal and ionizing radiation. Modern explosives or energetic materials are nitrogen-containing organic compounds with the potential for self-oxidation to small gaseous molecules (N2, H2O, and CO2). Explosives are classified as primary or secondary based on their susceptibility of initiation. Primary explosives are highly susceptible to initiation and are often used to ignite secondary explosives, such as TNT (2,4,6-trinitrotoluene), RDX (1,3,5-trinitroperhydro-1,3,5-triazine), HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane), and tetryl (N-methyl-N-2,4,6-tetranitro-aniline).

Biodegradation of Crude Oil from the BP Oil Spill in the Marsh Sediments of Southeast Louisiana, USA

The significant challenges presented by the April 20, 2010 explosion, sinking, and subsequent oil spill of the Deepwater Horizon drilling platform in Canyon Block 252 about 52 miles southeast of Venice, LA, USA greatly impacted Louisiana’s coastal ecosystem including the sea food industry, recreational fishing, and tourism. The short-term and long-term impact of this oil spill are significant, and the Deepwater Horizon spill is potentially both an economic and an ecological disaster. Microbes present in the water column and sediments have the potential to degrade the oil. Oil degradation could be enhanced by biostimulation method. The conventional approach to bioremediation of petroleum hydrocarbon is based on aerobic processes. Anaerobic bioremediation has been tested only in a very few cases and is still considered experimental. The currently practiced conventional in situ biorestoration of petroleum-contaminated soils and ground water relies on the supply of oxygen to the subsurface to enhance natural aerobic processes to remediate the contaminants. However, anaerobic microbial processes can be significant in oxygen-depleted subsurface environments and sediments that are contaminated with petroleum-based compounds such as oil-impacted marshes in Louisiana. The goal of this work was to identify the right conditions for the indigenous anaerobic bacteria present in the contaminated sites to enhance degradation of petroleum hydrocarbons. We evaluated the ability of microorganisms under a variety of electron acceptor conditions to degrade petroleum hydrocarbons. Researched microbial systems include sulfate-, nitrate-reducing bacteria, and fermenting bacteria. The results indicated that anaerobic bacteria are viable candidates for bioremediation. Enhanced biodegradation was attained under mixed electron acceptor conditions, where various electron-accepting anaerobes coexisted and aided in degrading complex petroleum hydrocarbon components of marsh sediments in the coastal Louisiana. Significant degradation of oil also occurred under sulfate-reducing and nitrate-reducing conditions.

Bactericidal and ammonia removal activity of silver ion-exchanged zeolite

The antimicrobial activity of silver-zeolite against Escherichia coli, Vibrio harveyi, Vibrio cholerae and Vibrio parahaemolyticus was examined in liquid medium and agar well diffusion assays. The minimum inhibitory concentration for silver ion-exchanged zeolite against E. coli and V. harveyi was 40 μg/ml, and 50-60 μg/ml for V. cholerae and V. parahaemolyticus. The diameter of the inhibition zones for E. coli, V. harveyi, V. cholerae and V. parahaemolyticus, respectively, increased from 0.5 to 2.3 cm, 0.6 to 2.4 cm, 0.3 to 1.65 cm and 0.3 to 1.7 cm with increasing concentrations of silver ion-exchanged zeolite from 10 to 400 μg. Silver-zeolite removed 20-37% ammonia from aqueous solutions. This study suggests that silver ion-exchanged zeolite could impact disease and environmental management in shrimp aquaculture.

Effect of food-grade surfactant on bioremediation of explosives-contaminated soil

The use of native soil bacteria to biodegrade explosives-contaminated soil under co-metabolic conditions has been demonstrated. The addition of food-grade surfactants could improve the process by enhancing the rates of explosives desorption from soil, thereby increasing the bioavailability of explosives for microbial degradation. The objective of this study was to decrease residence time in the slurry reactor, thereby increasing output and reducing clean-up costs. In this study, Tween 80 (monooleate), served not only as a surfactant but also as the carbon substrate for the soil microorganisms. Four 2l soil slurry reactors were operated in batch mode with soil containing 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). The results indicated that TNT and RDX were removed in all reactors except the control (no added carbon source). The reactor enriched with surfactant and molasses performed better than reactors with either molasses or surfactant alone. The TNT and its metabolite, 4-amino-2,6-dinitrotoluene were removed faster in the reactor with surfactant plus molasses (35 days) than in the reactor with molasses alone as carbon source (45 days). A radiolabeling study of the mass balance of TNT in the slurry reactors showed substantial mineralization of TNT to CO2.

Presence of antibiotic resistance genes in a sewage treatment plant in Thibodaux, Louisiana, USA

Increasing uses and disposals of antibiotics to the environment have increased emergence of various antibiotic resistance. One of the sources for the spread of antibiotic resistance is wastewater treatment plant, where bacteria and antibiotics can come in contact and can acquire antibiotics resistance. There are very few studies on this subject from a small town sewage treatment plant. Therefore, this study was conducted using raw sewage as well as treated sewage from a sewage treatment plant in Thibodaux in rural southeast Louisiana in USA. Samples were collected monthly from the Thibodaux sewage treatment plant and the presence of antibiotic resistance genes was monitored. The study showed the presence of antibiotic resistance genes in both raw and treated sewage in every month of the study period. The genetic transformation assay showed the successful transformation of methicillin resistant gene, mecA to an antibiotic sensitive Staphylococcus aureus, which became antibiotic resistant within 24h.

Effect of Orange Oil Extract on the Formosan Subterranean Termite (Isoptera: Rhinotermitidae)

Abstract The Formosan subterranean termite,Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), accidentally brought into the United States, has become a major urban pest, causing damage to structures and live trees. Because of increasing restrictions on the use of conventional termiticides, attention is focused on finding safer alternative methods for termite management. Oil from citrus peel, referred to here as orange oil extract (OOE), contains ≈92%d-limonene, and it is generally known to be toxic to insects. In laboratory experiments, 96 and 68% termites were killed in 5 d when OOE at 5 ppm (vol:vol) was dispensed from the top or bottom, respectively, with termites held at the opposite end of a tight-fitting plastic container. Apart from high mortality, workers exposed to vapor consumed significantly less filter paper than controls. However, when termites were exposed to OOE vapor, even at 10 ppm, in the void of a model wall, there was very little mortality. Termites did not tunnel through glass tubes filled with sand treated with 0.2 or 0.4% OOE. Sand treated with OOE was extracted each week for 8 wk to determine the remaining amount ofd-limonene. Results indicated that there was a sharp decline in the quantity ofd-limonene during the first 3 wk to a residual level that gradually decreased over the remaining period. With a suitable method of application and in combination with other control practices, OOE can be effectively used for the control of subterranean termites.

Accelerated decomposition of sugarcane crop residue using a fungal–bacterial consortium

A fungal–bacterial consortium provided by Sybron Chemicals, Inc. was used in a laboratory study in an e2ort to accelerate the decomposition of post-harvest sugarcane residue. The consortium includes the fungus Ceriporiopsis subvermispora and bacterium Cellulomonas sp., which were chosen for their cellulolytic capabilities and Azospirillum brasilense, which was chosen because it is a nitrogen-4xing bacterium. Study results indicated that the consortium sprayed over the residue and mixed in soil supplemented with 0.3% molasses showed a signi4cant di2erence for several parameters. Those measurable di2erences included visual decomposition of residue, bacterial and fungal populations, soil pH, nitrogen, and available phosphorous when compared to control and the treatment in which the consortium was sprayed over the residue but not mixed. This study indicates that this fungal–bacterial consortium may accelerate the decomposition of post-harvest sugarcane residue provided the residue is mixed with soil. Further study is necessary to re4ne the process for the future application of this consortium as a possible alternative to the current practice of open air burning of sugarcane residue by farmers. ? 2002 Elsevier Science Ltd. All rights reserved.

Use of formic acid to control vibriosis in shrimp aquaculture

Luminous vibriosis is a shrimp disease that causes major economic losses in shrimp industry as a result of massive shrimp kills due to bacterial infection caused by Vibrio species. Use of antibiotics to control Vibrio in shrimp aquaculture is not allowed in the United States and so it is necessary to develop an alternative pathogen control method for shrimp production. Short-chain fatty acids have been used as food preservatives for a long time. Organic acids are commonly added in feeds in animal production, such as chicken, pig, and cattle. In this study, growth inhibition effects of formic acid on five selected Vibrio species, namely Vibrio alginolyticus, Vibrio cholerae, Vibrio harveyi, Vibrio parahaemolyticus and Vibrio vulnificus were studied. The Vibrio bacteria were grown on both solid and liquid media using Muller-Hinton agar and alkaline peptone water, respectively, with various concentrations of formic acid. Bacterial growth was monitored in the liquid media using optical density method. The results showed significant inhibition of growth of all five Vibrio species by formic acid at low concentration. The effective concentration (EC50) values were calculated for all five Vibrio species, which were less than 0.039% of formic acid. The results are encouraging to supplement formic acid in the shrimp feed as a control mechanism to reduce Vibrio outbreak in shrimp aquaculture system.

Biodegradation of 2,4,6-trinitrotoluene (TNT) under sulfate and nitrate reducing conditions*

Anaerobic degradation of 2,4,6-trinitrotoluene (TNT) was studied under sulfate- and nitrate-reducing conditions using enrichment cultures developed from a TNT-contaminated soil from the Louisiana Army Ammunition Plant (LAAP) in Minden, Louisiana, USA. The soil samples were enriched using mineral salt media with either nitrate or sulfate as electron acceptors in the presence of TNT under strict anaerobic conditions. The enriched samples were experimented with TNT as either the sole source of carbon or nitrogen and also under co-metabolic conditions with molasses as co-substrate. The results revealed that TNT was removed under both electron acceptor conditions. However, the TNT degradation efficiency was significantly higher under sulfate-reducing conditions than the nitrate-reducing conditions. Under sulfate-reducing conditions, TNT removal was faster when molasses was used as co-substrate. The metabolic analysis showed that TNT was mineralized and the major end product was acetic acid, CO2, and ammonia. A soil slurry reactor with TNT-contaminated soil showed more than 90% of TNT removal within 60 days of incubation.

Combined biological and chemical pretreatment method for lignocellulosic ethanol production from energy cane

Abstract The process of converting lignocellulosic biomass to ethanol involves pretreatment to disrupt the complex of lignin, cellulose, and hemicellulose, freeing cellulose and hemicellulose for enzymatic saccharification and