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Employing floating treatment wetlands (FTWs) and constructed wetlands (CWs) is one of the most eco-friendly strategies for the bioremediation of water contaminants. Here, the efficiency of FTWs and CWs was compared for the degradation of phenanthrene-contaminated water for the first time. The FTWs and CWs were established by vegetated Phragmites australis in phenanthrene (1000 mg L−1)-contaminated water. Both wetlands were augmented with a bacterial consortium of four bacterial strains: Burkholderia phytofirmans PsJN, Pseudomonas anguiliseptica ITRI53, Arthrobacter oxydans ITRH49, and Achromobacter xylosoxidans ITSI70. Overall, the wetlands removed 91–93% of the phenanthrene whilst the augmentation of the bacterial strains had a synergistic effect. In comparison, the CWs showed a better treatment efficiency, with a 93% reduction in phenanthrene, a 91.7% reduction in the chemical oxygen demand, an 89% reduction in the biochemical oxygen demand, and a 100% reduction in toxicity. The inoculated bacteria were found growing in the shoots, roots, and water of both wetlands, but were comparatively better adapted to the CWs when compared with the FTWs. Similarly, the plants vegetated in the CWs exhibited better growth than that observed in the FTWs. This study revealed that the FTWs and CWs vegetated with P. australis both had promising potential for the cost-effective bioremediation of phenanthrene-contaminated water.

Textile wastewater treatment generates sludge that needs to be disposed of safely. The cost of sludge management is 50% of the total treatment cost of the wastewater. To reduce the expense, the sludge can be repurposed as a valuable resource by extracting extracellular polymeric substance (EPS). EPS contains polysaccharides, proteins, and humic substances, which are surface-active substances that act as potential biosurfactants. In this study, we investigated sludges (sludge 1 and sludge 2) from two different textile industries for EPS production. The results showed a maximum EPS yield of 179 mg/g-activated sludge from the wastewater from sludge 2. The EPS from textile wastewater activated sludge had a protein/carbohydrate ratio of 0.27-0.56, lower than that of municipal activated sludge. This difference is due to variations in nitrogen/carbon ratio in these wastewaters. Based on the biosurfactant activity test, EPS from both textile wastewaters could lower the water surface tension to around 60 mN/m and emulsify olive oil better than Tween 20 and 80. However, only EPS from sludge 2 showed better xylene emulsification than EPS from sludge 1 due to the difference in humic acid content.

This paper reviews recent developments in membrane biosorption and focuses on features and performance of different configurations of membrane biosorption. Biofilm formation, its role, and optimization in biosorption application as well as challenges and strategies for future applications are also discussed. Biosorption has gained increasing attention for wastewater treatment process due to its advantages of high separation efficiency, environmentally friendly, high availability of biomass, and low cost. In addition, biosorbents are reusable since they can be regenerated by employing a wash solution. This also provides the possibility of recovering valuable sorbed components from the concentrated wash solution. It has been demonstrated in several studies that membrane can be used to improve the performance of sorption processes. Membrane biosorption displays interesting features including higher process efficiency and smaller footprint. The membrane enhances contact between the biosorbent and the sorbate (pollutant) resulting in an improved sorption kinetic. Membrane also helps to remove priority pollutant from a wastewater by providing a selective extraction and avoids the mixing between the biosorbent and wastewater. In addition, membrane can improve the contact between gas stream and biosorbent for gas removal from a waste gas stream. It is also possible for supplying bubble-less aeration which improves the biological growth of the biosorbent. Some reported studies show that combined membrane biosorption may allow one to achieve pollutant removal up to three times of the single biosorption process. However, there are several challenges that need to be addressed for membrane biosorption application, including diffusion limitation in membrane and uncontrolled biofilm formation. Therefore, it is imperative to identify membranes with appropriate characteristics as well as biofilm control strategies.

Anaerobic digestion plays an important role in the gastrointestinal tract and in organic waste treatment. Thermodynamic analysis based on the reaction Gibbs free energy can be used to predict the favorability of some reactions occurring during anaerobic digestion. In this study, we used a thermodynamic approach to evaluating reactions and stoichiometric coefficients of the anaerobic process of in vitro rumen microbiota. The favorability of glucose, butyrate, propionate, and hydrogen utilizations was analyzed by calculating the Gibbs free energy change of each reaction. A previously published Gibbs free energy dissipation method was also used to calculate stoichiometric coefficients of the total metabolism reaction of glucose and hydrogen utilization. For glucose utilization in which the metabolism follows several different pathways, the fraction of glucose following each pathway is estimated by considering the number of electron transfer attributed throughout the catabolism reaction. Glucose utilization always occurs in the system, and the syntrophic correlation among butyrate, propionate, and hydrogen utilizations run well with propionate utilization following the alternative pathway that yields lower hydrogen. The approach applied in this research significantly reduces the stoichiometric coefficients that must be predicted in kinetic modeling. To verify the calculation result, the yield coefficients obtained were then applied in the previous mechanistic model of in vitro rumen microbiota, and the results were compared to the experimental data from literature.

The separation process between 5-hydroxymethylfurfural (HMF) and trace glucose in glucose conversion is important in the biphasic system (aqueous&ndash, organic phase), due to the partial solubility property of HMF in water. In addition, the yield of HMF via the dehydration reaction of glucose in water is low (under 50%) with the use of Br&oslash, nsted acid as a catalyst. Therefore, this study was conducted to optimize the production and separation of products by using a new hydrophobic ionic liquid (IL), which is more selective than water. The new IL (1,3-dibutyl-2-(2-butoxyphenyl)-4,5-diphenyl imidazolium iodide) [DBDIm]I was used as a solvent and was optimized for the dehydration reaction of glucose to make a more selective separation of HMF, levulinic acid (LA), and formic acid (FA). [DBDIm]I showed high performance as a solvent for glucose conversion at 100 &deg, C for 120 min, with a yield of 82.2% HMF, 14.9% LA, and 2.9% FA in the presence of sulfuric acid as the Br&oslash, nsted acid catalyst.

Proteins are one of the primary building blocks that have significant functional properties to be applied in food and pharmaceutical industries. Proteins could be beneficial in their concentrated products or isolates, of which membrane-based filtration methods such as ultrafiltration (UF) encompass application in broad spectra of protein sources. More importantly, selective enrichment by UF is of immense interest due to the presence of antinutrients that may dominate their perspicuous bioactivities. UF process is primarily obstructed by concentration polarization and fouling; in turn, a trade-off between productivity and selectivity emerges, especially when pure isolates are an ultimate goal. Several factors such as operating conditions and membrane equipment could leverage those pervasive contributions; therefore, UF protocols should be optimized for each unique protein mixture and mode of configuration. For instance, employing charged UF membranes or combining UF membranes with electrodialysis enables efficient separation of proteins with a similar molecular weight, which is hard to achieve by the conventional UF membrane. Meanwhile, some proposed strategies, such as utilizing ultrasonic waves, tuning operating conditions, and modifying membrane surfaces, can effectively mitigate fouling issues. A plethora of advancements in UF, from their membrane material modification to the arrangement of new configurations, contribute to the quest to actualize promising potentials of protein separation by UF, and they are reviewed in this paper.

In this study, imidazole derivative-based new ionic liquids were investigated as corrosion inhibitors. These new ionic liquids (ILs) are 1,3-dipropyl-2-(2-propoxyphenyl)-4,5-diphenylimidazole iodide (IL1) and 1,3-dibutyl-2-(2-butoxyphenyl)-4,5-diphenylimidazole iodide (IL2). The corrosion inhibition effects of two new ILs were observed on carbon steel in brackish water media (1% NaCl solution). Carbon steel coupons were exposed to 1% NaCl solution with various concentrations of ILs. Corrosion inhibition effects were tested by the electrochemical impedance spectroscopy (EIS) method and the Tafel method at various temperatures ranging from 25 &deg, C to 55 &deg, C. The results showed that ILs have potential as corrosion inhibitors and the adsorption mechanisms of IL1 and IL2 on carbon steel surfaces were also determined, which followed the Langmuir adsorption isotherm model. Acquisition of ∆Gads values of IL1 and IL2 were &minus, 35.04 and &minus, 34.04 kJ/mol, respectively. The thermodynamic data of the ILs show that semi-chemical and or physical adsorptions occurred on carbon steel surfaces.

Ionic liquid (IL) demonstrates better performance as a solvent in the biomass conversion process than conventional organic solvents. This study focuses on the application of new hydrophobic imidazolium-based IL as a solvent in biomass conversion process. A novel IL, namely, 1,3-dipropyl-2-(2-propoxyphenyl)-4,5-diphenylimidazolium iodide ([DPDIm]I), was synthesized and subsequently used as a solvent for biomass conversion to produce levulinic acid (LA) and Formic Acid (FA). The performance of [DPDIm]I supported by H2SO4 as a solvent was shown by cellulose conversion into 94.23% of LA and 18.85% of FA at the optimum conditions of 140 °C temperature and the reaction time of two hours. A reusability test revealed the performance of [DPDIm]I as a solvent that can be recycled up to five times for biomass conversion.

The eastern subterranean termite (EST) Reticulitermes flavipes is an insect pest in the USA. Like all wood-feeding termites (WFT), EST relies on a complex system of microbes to meet its nutritional requirements. The microbiome of WFT is stable, but the relative abundance of bacteria changes depending on diet. The purpose of this study was to explore the microbial diversity within EST collected in Thibodaux and St. Francisville, LA and detect differences based on diet and location to determine if the microbiome has a strict structure. It was found that taxa did not differ much between nearby colonies, but relative abundance is impacted by the wood in the diet. Half of bacteria from the gut of termites on nuttall oak were Bacteroidales, of which 22.7% were members of the family Porphyromonadaceae. 44% of bacteria from termites on red maple were Spirochaetes. All Spirochaetes were members of the genus Treponema. Elusimicrobia, a phylum found exclusively within termites and wood-feeding cockroaches was not abundant in either St. Francisville colony. Taxa differed more between termite colonies from different locations, but the mircobiome of St. Francisville colonies appeared to begin diverging at the family level. Overall, the microbiome was typical of termites, harboring cellulolytic protozoa, nitrogen-fixing bacteria, acetogenic Spirochaetes, and methanogenic archaeans. This has implications in microbial ecology because the organisms are changing, but the function, digestion of lignocellulose, is not. A bacterium was isolated and identified from termite gut as Acinetobacter tandoii from our previous studies degraded various phenolics, including phenol, nitrophenol, dinitrophenol, trinitrophenol, and toluene.

Hydrolysis of lignocellulosic materials into simple sugar plays an important role in biorefinery. Hemicellulosic sugars from the hydrolysis of lignocellulosic materials could be used in xylitol production. However, xylanase activity during hydrolysis process is affected by activators and inhibitors that may present in the reaction system. The pretreatment process was reported to produce compounds that may affect the enzymatic hydrolysis process, such as furans, aliphatic acid, and aromatics. The purpose of this study was to investigate the inhibition effect of these potential inhibitors on xylanase activity. Three groups of potential inhibitors were evaluated including, furan, aliphatic acid, and hydrolysis-fermentation products. The result showed that ethanol, vanillin, and formic acid gave the highest inhibition effect from each group. Ethanol competed with xylanase competitively. Vanillin showed non-competitive inhibition. Formic acid performed mixed-inhibition by reducing maximum hydrolysis rate and giving varied Michaelis constant values at different concentrations.

Combining bioreactor and membrane, known as a membrane bioreactor (MBR), has been considered as an attractive strategy to solve the limitations of conventional activated sludge process, such as biological instability, poor sludge quality, and low concentration of mixed liquor suspended solid. Unlike the other MBRs, extractive membrane bioreactor (EMBR) focuses on enhancing the efficiency of wastewater treatment through toxic compounds extraction by using a selective membrane. Even though EMBR has been successfully demonstrated in wastewater and waste gas treatment by several studies, it still faces some obstacles such as biofilm formation and low selectivity of the membrane towards a specific component. Appropriate biofilm formation control strategies and membrane with high selectivity are needed to solve those problems. This paper reviews EMBR including its potential applications in wastewater treatment, denitrification process, and waste gas treatment. In addition, challenges and outlook of EMBR are discussed.

In order to improve the water quality in shrimp aquaculture operated under low-salinity conditions, a sequencing batch reactor (SBR) was tested for treatment of the wastewater. This water from the backwash of a single-bead filter from the Waddell Mariculture Center, South Carolina, contained high concentrations of carbon and nitrogen and was successfully treated using the SBR. By operating the reactor sequentially in aerobic, anoxic and aerobic modes, nitrification and denitrification were achieved, as well as removal of carbon. Specifically, the initial chemical oxygen demand (COD) concentration of 1201 mg l −1 was reduced to 32 mg l −1 within 8 days of reactor operation. Ammonia in the sludge was nitrified within 3 days. The denitrification of nitrate was achieved by the anoxic process and total removal of nitrate was observed.

A laboratory study was conducted to determine whether tetryl (2,4,6-trinitrophenlymethylnitramine) contaminated soil could be bioremediated using a sequencing batch soil slurry reactor (SBR) operated under anoxic–aerobic sequence. The results indicated that tetryl was co-metabolically converted to aniline under anoxic conditions with molasses as the growth substrate. The gas chromatographic/mass spectrometric analysis of the soil slurry showed various metabolites, identified as trinitrobenzeneamine, dintrobenzenediamine, nitroaniline and aniline. Aniline was not metabolized further under anoxic conditions. When the soil slurry reactor was operated under aerobic conditions, the aniline concentration was reduced to below the detection limit (0.05 ppm). This metabolic conversion of tetryl is probably of value in the treatment of tetryl-contaminated soil and ground water, such as those found at the Joliet army ammunition plant site in Illinois and the Iowa army ammunition plant site in Burlington, Iowa.

Metabolism of nitroaromatic compounds by a Klebsiella pneumoniae isolated from a regional wetland was studied. When it was grown with nitrophenol as the sole nitrogen source, the isolate had the metabolic capability of transforming nitrophenol to phenol; however, it did not use nitrophenol as the sole carbon source. The metabolic pathway showed that the K. pneumoniae reduced the nitro group to an amino group forming aminophenol as a major metabolite. This aminophenol was oxidatively deaminated to phenol. For every mole of nitrophenol metabolized, 1 mol of phenol was produced and the phenol did not undergo further metabolism. The isolate also used several other nitroaromatic compounds including nitrotoluenes and nitrobenzenes as its nitrogen source. Even though this organism did not degrade the nitroaromatics completely, it may be useful in degrading nitroaromatics in contaminated soil and water containing other aromatic degraders in a syntrophic condition in nature.

The biodegradation of No. 2 diesel fuel under anaerobic conditions was investigated using anaerobic soil slurry reactors. Soil samples were collected from a diesel spill site, where the diesel spill has migrated to vadose zone. The purpose of this study was to find out which of the various groups of anaerobic bacteria present in the study site will degrade the petroleum hydrocarbons in the soil. The various anaerobic groups included sulfate-, nitrate-reducing, methanogenic, and mixed electron acceptor conditions. The results indicated enhanced biodegradation of diesel fuel under all conditions compared to no electron-supplemented reactor (passive bioremediation). However, the rate of diesel degradation was the highest under mixed electron acceptor conditions followed in order by sulfate-, nitrate-reducing, and methanogenic conditions. Under mixed electron acceptor condition, 80.5% removal of diesel fuel was achieved within 290 days. While under sulfate-reducing condition 55% degradation of diesel fuel was observed for the same period. This study showed that the mixed heterogeneous microbial population of the contaminated site has the metabolic capability to degrade diesel fuel.

Samples of subgingival dental tissues were examined for the presence of methanogenic activities. Using enrichment cultures, methanogenic activities were detected in 9 of 17 individuals. A mesophilic, Gram-positive, irregular coccoid methanogen, which showed close resemblance to a Methanosarcina sp., was isolated from one sample collected from a patient with type IV periodontal pocket (the periodontal pocket is a space bounded by the tooth on one side and by ulcerated epithelium lining the soft tissue wall on the other). The isolate used methanol, methylamine, acetate, and H(2)-CO(2) as the sole source of carbon. However, the isolate was unable to use formate and trimethylamine as growth substrates. The organism had an optimum pH of 6.5 and an optimum temperature of 37 degrees C. The isolate not only used ammonia, but also used nitrate as a nitrogen source. The niche of this methanogen in periodontal pockets may be to carry out terminal oxidation of simple organic compounds such as methanol and acetate produced by other obligate anaerobes present in periodontal pockets. This methanogen may also play a vital role in interspecies hydrogen transfer, as demonstrated by its use of H(2)-CO(2) as a substrate. The isolate produced significant amount of methane in vitro.

A laboratory in situ composting study was conducted as a possible alternative method for the current practice of open air burning of post-harvest sugarcane residue by sugarcane farmers. In situ composting of the sugarcane residue by the indigenous bacteria and fungi was accelerated using molasses as an initial substrate. A one-time application of molasses boosted the soil microbial population. which started to decompose the ligno-cellulosic fractions of the residue. The study showed significant differences in several parameters among the control and molasses applied treatments, namely, visual decomposition of residue, bacterial and fungal population, soil pH, cellulose content, cellulase activity. and soil organic matter. Further study is needed to refine the process for the future application of this technology as a possible alternative to the current practice of open air burning of sugarcane residue by farmers.

Soil in some parts of the Iowa Army Ammunition Plant in Burlington, Iowa, was contaminated with cyclotetramethyleneter-anitramine, commonly known as high melting explosive (HMX). A laboratory treat-ability study was conducted to find out the ability of the native soil bacteria present in the contaminated site to degrade HMX. The results indicated that the HMX can be removed effectively from soil by native soil bacteria through a co-metabolic process. Molasses, identified as an effective co-substrate, is inexpensive, and this factor makes the treatment system cost-effective. The successful operation of aerobic-anoxic soil slurry reactors in batch mode with HMX-contaminated soil showed that the technology can be scaled up for field demonstration. The HMX concentration in the contaminated soil was decreased by 97% in 4 months of reactor operation. The advantage of the slurry reactor is its simplicity of operation. The method needs only mixing and the addition of molasses as co-substrate.

The biotransformation of trichloroethylene (TCE) under various electron acceptor conditions was investigated by using enrichment cultures developed from the anaerobic digester sludge of Thibodaux sewage treatment plant. The results indicated that TCE was biotransformed under sulfate reducing, methanogenic, nitrate reducing, iron reducing, and fermenting conditions. However, the rates of TCE removal varied among the conditions studied. The fastest removal of TCE (100% removal in 9 days) was observed under mixed electron acceptor conditions, followed in order by methanogenic, fermenting, iron reducing, sulfate reducing, and nitrate reducing conditions. Under mixed electron acceptor conditions, the TCE was converted to ethene, which was further metabolized. Under sulfate and nitrate reducing conditions, the major metabolites produced from TCE metabolism were cis and trans dichloroethylene (DCE). Under methanogenic, iron reducing, and fermenting conditions, cis and trans DCE and ethene were produced from TCE metabolism. This study showed evidence for TCE metabolism in a mixed microbial population system similar to any contaminated field sites, where heterogeneous microbial population exists.

This research paper presents two bioremediation technologies for the treatment of explosives-contaminated soil. The technologies include soil slurry reactor, and in situ bioremediation. Both bioremediation technologies showed promising results and these treatment methods used co-metabolic process with molasses as a co-substrate for bacterial growth. The soil slurry reactor removed the explosive contaminants present in the soil within three weeks of incubation period. The in situ treatment method also removed all the explosives present in the soil, but the treatment time was approximately 12 months. Each of the bioremediation methods described in this study has advantages and disadvantages. The major advantage in the soil slurry reactor method is the short treatment time, but the disadvantage is that it is labor intensive and expensive due to the excavation of soil, operation of slurry reactors, and post-treatment costs. The in situ treatment method has the advantage of lower treatment costs, but the disadvantage is the treatment time, which is considerably longer.

A laboratory study was conducted to determine whether tetryl can be biodegraded by native soil bacteria under soil-slurry conditions with molasses as cosubstrate. A 2-L laboratory reactor was set up with a 15% (weight/volume) slurry of contaminated soil in deionized water. The soil slurry was mixed continuously at 80 r/min. Molasses at 0.3% (volume/volume) was added weekly as a cosubstrate. A no-carbon control reactor was also set up without molasses addition. The concentration of tetryl in the soil was monitored periodically. The results showed 100% removal of tetryl from the soil within 3 months of operation. In the no-carbon control, no significant degradation of tetryl was observed. The gas chromatographic/mass spectrometric analysis of the aqueous phase of the soil slurry showed metabolites identified as trinitro-n-methylaniline, trinitrobenzeneamine, dinitrobenzenediamine, nitroaniline, and aniline. None of these metabolites persisted more than a week after they appeared in the reactor system. The parameters relevant to biodegradation and process control, such as pH, dissolved oxygen, bacterial counts, and metabolites produced in the reactor, are discussed.

Four laboratory-scale anaerobic baffled reactors (with two, three, four, and five chambers, respectively) were used to successfully treat whole swine waste. The baffled reactors did an excellent job of trapping the small diameter, methane-containing particles of proteins, cellulose, hemicellulose, and lipids. Solids retention times of 25, 30, 36, and 42 days were achieved with a corresponding hydraulic retention time of 14 days for two-, three-, four- and five-chamber anaerobic baffled reactors, respectively. COD reductions ranged from 70 to 78% among all the reactors studied. Maximum methane production was observed in the reactors with four and five chambers with a value of 0.59 and 0.62 l/g of volatile solids added at a loading of 4 g VS/l/day, respectively.

The successful operation of an aerobic/anoxic laboratory-scale soil slurry reactor showed that soil contaminated with 2,4,6-trinitrotoluene (TNT) and hexahydro-l,3,5-trinitro-l,3,5-triazine (RDX) could be treated in batches or semicontinuously. Batch treatment resulted in the transformation of TNT. Semicontinuous treatment resulted in complete degradation of TNT. In addition to removing TNT, the slurry reactor also removed contaminants such as trinitrobenzene, 2,4-dinitrotoluene, RDX, and octahydro-l,3,5,7-tetranitro-l,3,5,7-tetraazocine (HMX). Radiolabeled TNT incubated with reactor biomass showed that 23% of [{sup 14}C]TNT was mineralized, 27% was converted to biomass, and 8% was adsorbed onto the soil. The rest of the [{sup 14}C]TNT was accounted for as metabolites, including a ring cleavage product identified as 2,3-butanediol. Increasing the frequency of soil addition from once to two or three times weekly did not affect the TNT removal rates. The soil slurry reactor also maintained the bacterial population fairly well, needing only 0.3% molasses as a cosubstrate.

A laboratory study was conducted to study the feasibility of removing explosives in contaminated soil under anaerobic conditions. Anaerobic enrichment cultures were prepared from soil samples under various electron-accepting conditions, namely, sulfate-reducing, methanogenic, and nitrate-reducing conditions. The sulfate-reducing condition was very effective in removing all of the explosive compounds from the soil. The sulfate-reducing consortium removed 100% of 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitrobenzene (TNB) within 10–15 days of incubation and removed 75 to 95% of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocine (HMX), within 21 days of incubation. The consortium used explosive compounds as the nitrogen source, however, it did not use these compounds as the sole carbon source. The various metabolites obtained from TNT metabolism were 4-amino-2,6-dinitrotoluene (4-A-2,6-DNT), 2,4-diamino-6-nitrotoluene (2,4- d -6-NT), and 2-methyl pentanoic acid. This sulfate-reducing consortium was further studied for its usefulness in removing TNT at the contaminated site. The results showed that the consortium can remove TNT under 5% and 10% soil slurry conditions. This laboratory study demonstrated that under anaerobic conditions, sulfate-reducing bacteria can be useful in the bioremediation of contaminated soil with TNT and other explosives.

In recent years, research on microbial degradation of explosives and nitroaromatic compounds has increased. Most studies of the microbial metabolism of nitroaromatic compounds have used aerobic microorganisms. Ecological observations suggest that sulfate-reducing and methanogenic bacteria might metabolize nitroaromatic compounds under anaerobic conditions if appropriate electron donors and electron acceptors are present in the environment, but this ability had not been demonstrated until recently. Few review papers exist, and those deal mainly with aerobic bacterial degradation of explosives; none deals with anaerobic bacteria. In this paper, we review the anaerobic metabolic processes in the degradation of explosives and nitroaromatic compounds under sulfate-reducing and methanogenic conditions.

Swine manure contains diverse groups of aerobic and anaerobic bacteria. An anaerobic bacterial consortium containing sulfate-reducing bacteria (SRB) and acetate-utilizing methanogenic bacteria was isolated from swine manure. This consortium used phenol as its sole source of carbon and converted it to methane and CO2. The sulfate-reducing bacterial members of the consortium are the incomplete oxidizers, unable to carry out the terminal oxidation of organic substrates, leaving acetic acid as the end product. The methanogenic bacteria of the consortium converted the acetic acid to methane. When a methanogen inhibitor was used in the culture medium, phenol was converted to acetic acid by the SRB, but the acetic acid did not undergo further metabolism. On the other hand, when the growth of SRB in the consortium was suppressed with a specific SRB inhibitor, namely, molybdenum tetroxide, the phenol was not degraded. Thus, the metabolic activities of both the sulfate-reducing bacteria and the methanogenic bacteria were essential for complete degradation of phenol.

This research presented a bench-scale investigation of an innovative approach to land farming for the bioremediation of 2,4,6-trinitrotoluene (TNT)-contaminated soils. Molasses, which contains sugar, nitrogen, vitamins, and minerals, was used as cosubstrate and this process combines several advantages of conventional land farming with the use of molasses for the biological degradation of TNT and its derivatives. In the optimum treatment, contaminated soil was amended with shredded grass and managed in an operating cycle where it was alternatively flooded with a dilute molasses solution, then drained, passively aerated, and finally tilled when moisture conditions were optimum. Soil TNT concentrations in all treatments receiving molasses were reduced from approximately 4,000-mg/kg levels initially to less than 100 mg/kg in 12 months, and to less than 1 mg/kg in the optimum treatment in this same time. Concentrations of the primary metabolic intermediates and bacterial populations were also tracked. Radiolabeling studies confirmed that the biomass enhanced by the treatments could mineralize approximately 20% of [14C] from a contaminant spike after 22 d. A shredded grass amendment in the optimum treatment was shown to increase moisture retention during aeration phases. The results of this bench-scale study are promising with regard to transferring the process to full-scale applications.

In earlier studies (Boopathy et al. 1994a, 1994b), soil bacteria present in a TNT-contaminated site removed 2,4,6-trinitrotoluene (TNT). In this study the optimum conditions for the most efficient removal of TNT is discussed. The results suggest that the soil bacterial consortium has an optimal pH range of 6-7. Maximum growth was observed at pH 7. However, the TNT removal rate was higher at pH 6. Studies of the effects of temperature showed that the bacterial consortium had maximum metabolic activity at 20 to 22 degrees C (ambient temperature). At a higher temperature (37 degrees C) the TNT removal rate dropped significantly. The consortium could not use TNT as a nitrogen source but required the addition of ammonium. Optimal growth occurred with 0.25 g/L of ammonium chloride. Growing cells removed TNT significantly faster rates than resting cells or cell-free extract. The operation of soil slurry reactors with the optimal conditions suggested that TNT can be removed effectively from the contaminated sites. These environmental conditions established as optimal can be used to improve the efficiency of large-scale soil slurry reactors for the treatment of soil contaminated with TNT.

In situ bioremediation of soil contaminated with explosives was studied using columns packed with contaminated soil. Several operating strategies were investigated, including continuous flooding of the soil column with dilute molasses or succinate solution, and periodic operating cycles consisting of flooding followed by draining and aeration. Two control columns were also used, which were flooded with deionized water. All of the soil columns that received molasses solution degraded 2,4,6-trinitrotoluene (TNT) and other explosive contaminants present in the soil. However, the most efficient removal of contaminants in terms of TNT removal rates was achieved by the soil column that was operated periodically with flooding with molasses solution, followed by draining and aeration. The columns that received succinate as co-substrate did not perform well. In control columns with deionized water, there was no removal of TNT. Results of this study will aid in improving the design and operation of field-scale bioremediation systems.

A sulfate-reducing bacterium isolated from a creek sediment and capable of metabolizing TNT (2,4,6-trinitrotoluene) using sulfate and nitrate as electron acceptors was tentatively characterized as Desulfovibrio desulfuricans strain A. The isolate was unable to use TNT as the sole source of carbon. TNT degradation was accomplished by a co-metabolic process using pyruvate as the main substrate. Two different metabolic steps were employed by this isolate under different electron-accepting conditions. Under sulfate-reducing conditions, TNT was reduced to 4-amino-2,6-dinitrotoluene, 2-amino-4,6-dinitrotoluene and 2,4-diamino-6-nitrotoluene. In contrast, under nitrate-reducing conditions, these amino compounds were not produced, instead, butyric acid was identified as the major metabolite of TNT metabolism. This organism also used a wide variety of other carbon sources, including ethanol, lactate, succinate, formate and malate. The isolate contained the electron-carrier desulfoviridin and used sulfate, nitrate, and thiosulfate as electron acceptors. The isolate had an optimal temperature of 25°C and an optimal pH of 6.8 and used ammonium chloride, nitrate and glutamate as nitrogen sources. The characteristic features of the sulfate-reducing bacterium closely resembled those of Desulfovibrio desulfuricans.

A mesophilic, Gram positive (Gram +ve), irregular coccoid methanogen, which showed close resemblance to a Methanosarcina sp., was isolated from swine manure. Acetate or methanol or H 2 + CO 2 served as a substrate for methanogenesis in a mineral salt medium. The isolate did not use formate as a growth substrate. The organism had an optimum pH of 6.8 and an optimum temperature of 37°C. The isolate used ammonia as a nitrogen source. The role of this methanogen in the swine manure is the terminal oxidation of simple organic compounds like acetate to CO 2 and methane. In an earlier report, a sulfate-reducing bacterium (SRB) isolated from swine manure that converted phenol to acetic acid was described (Boopathy, 1995). The methanogen described in this paper was isolated from the same swine manure sample. In a microbial ecology scenario these two anaerobic bacteria (methanogen and SRB) could co-exist together and degrade phenol to CO 2 and methane.

A sulfate-reducing bacterium isolated from swine manure used phenol as its sole source of carbon and energy. Sulfate was used as the electron acceptor. The major end product of phenol metabolism was acetic acid. For every mole of phenol degraded, almost 2 moles of acetic acid were produced. Acetic acid was not degraded further to CO 2 , indicating that this sulfate-reducing bacterium (SRB) is an incomplete oxidizer unable to carry-out the terminal oxidation of organic compounds. The SRB isolate also used p-chlorophenol as the sole source of carbon and energy. However, it did not use the chlorophenolic compounds containing two or more chlorine atoms, dichlorophenol and pentachlorophenol.

The metabolism of trinitrobenzene by a Pseudomonas consortium was studied. The Pseudomonas consortium used trinitrobenzene as a sole source of nitrogen, but not as a sole source of carbon. Trinitrobenzene was metabolized within 60 h of incubation. The main intermediates produced were dinitroaniline, 1,5-dinitrobenzene, nitroaniline, 5-nitrobenzene, and ammonia. The ammonia concentration in the culture medium increased during the course of incubation. Nearly stoichiometric amounts of 1,5-dinitrobenzene and 5-nitrobenzene were produced by the consortium. During trinitrobenzene metabolism by this bacterial consortium, the trinitrobenzene was first reduced to an amino compound, dinitroaniline. This intermediate was reductively deaminated with the release of ammonia into the culture medium and production of 1,5-dinitrobenzene. By the same mechanism, 1,5-dinitrobenzene was further converted to 5-nitrobenzene, which was not metabolized further, even after 60 days of incubation. This pathway is believed to be novel in that an aerobic bacterial consortium uses the nitroaromatic compound as its nitrogen source but leaves the ring intact. The bacterial consortium studied could be used in a syntrophic culture system with other 5-nitrobenzene-degrading bacteria to remove trinitrobenzene completely from soil and water at contaminated sites.Key words: trinitrobenzene, aniline, nitrobenzene, biodegradation, transformation.

The transformation of several nitroaromatic compounds by a newly isolated methanogenic bacterium, Methanococcus sp. (strain B) was studied. The presence of nitroaromatic compounds (0.5 mM) viz., nitrobenzene, 2,4-dinitrobenzene, 2,4,6-trinitrobenzene, 2,4-dinitrophenol, 2,4-dinitrobenzene, and 2,6-dinitrotoluene in the culture medium did not inhibit growth of the isolate. The bacteria grew rapidly and reached stationary phase within seven days of incubation. All the nitroaromatic compounds tested were 80 to 100% transformed by the bacterium to amino compounds by a reduction process. The isolate did not use the nitroaromatic compounds as the sole source of carbon or nitrogen. The transformation of nitroaromatic compounds by this isolate was compared to that of other methanogenic bacteria. Out of five methanogens studied, only Methanococcus deltae and Methanococcus thermolithotrophicus could transform the nitroaromatic compounds; however, the transformation rates were significantly less than that of the new isolate Methanococcus sp. (strain B). The nitroaromatic compounds were not transformed by Methanosarcina barkeri, Methanobacterium thermoautotrophicum, and Methanobrevibacter ruminantium.

An aerobic bacterial consortium was shown to degrade 2,4,6-trinitrotoluene (TNT). At an initial concentration of 100 ppm, 100% of the TNT was transformed to intermediates in 108 h. Radiolabeling studies indicated that 8% of [14C]TNT was used as biomass and 3.1% of [14C]TNT was mineralized. The first intermediates observed were 4-amino-2,6-dinitrotoluene and its isomer 2-amino-4,6-dinitrotoluene. Prolonged incubation revealed signs of ring cleavage. Succinate or another substrate—e.g., malic acid, acetate, citrate, molasses, sucrose, or glucose—must be added to the culture medium for the degradation of TNT. The bacterial consortium was composed of variousPseudomonas spp. The results suggest that the degradation of TNT is accomplished by co-metabolism and that succinate serves as the carbon and energy source for the growth of the consortium. The results also suggest that this soil bacterial consortium may be useful for the decontamination of environmental sites contaminated with TNT.

Four Pseudomonas spp. were isolated from a soil consortium enriched from soil contaminated with 2,4,6-trinitrotoluene (TNT). All four species extensively transformed TNT. The rate of transformation varied among species. In isolate 4, 100% of TNT (100 ppm) was transformed in 4 days. The TNT transformation was achieved by the four isolates through a co-metabolic process with a succinate co-substrate. The four isolates produced NO 2 − from TNT. The maximum NO 2 − production, observed for isolate 1, was equal to 30% of the NO 2 − available from the nitro groups of TNT. For other isolates the NO 2 − production varied from 10 to 16%. The radiolabeling studies showed signs ring cleavage. Isolate 3 used 13% of 14 C-TNT to make cellular material, and isolate 4 converted 6% of 14 C-TNT to biomass. The production of 14 C-CO 2 was observed for all four isolates, but the amount of 14 C-CO 2 produced was quite low: isolate 4 produced 14 C-CO 2 from approximately 1% of 14 C-TNT. The rate of degradation of TNT intermediates was very slow, reflecting possible difficulties in metabolizing the intermediates of TNT to CO 2 . The main intermediates were identified as 4-amino-2,6-dinitrotoluene and 2-amino-4,6-dinitrotoluene.

An attempt has been made to study the anaerobic removal of 2,4,6-trinitrotoluene (TNT) under different electron accepting conditions by a soil bacterial consortium. The results indicated that among the differenf electron acceptors studied (sulfate, nitrate, and carbon dioxide), significanf TNT removal was observed under nitrate reducing conditions. When there was no electron acceptor in the medium, TNT was not removed even after 60 days of incubation. Under nitrate reducing conditions, 82% of TNT was removed from the original concentration of 100 ppm of TNT. Under sulfate reducing conditions, approximately 30% of TNT was removed. When carbon dioxide was used as electron acceptor and H 2 as electron donor, TNT was removed by 35%

Viable counts and activities of sulfate-reducing bacteria (SRB) and methanogenic bacteria were determined in the oral cavities of eight volunteers. Of these, seven harbored viable SRB populations, and six harbored viable methanogenic bacterial populations. Two volunteers classified as type III periodontal patients had both SRB and methanogenic bacteria. Six separate sites were sampled: posterior tongue, anterior tongue, mid-buccal mucosa, vestibular mucosa, supragingival plaque, and subgingival plaque. The SRB was found in all areas in one volunteer, and it was mostly present in posterior tongue, anterior tongue, supragingival, and subgingival plaques in many volunteers. The methanogenic bacteria were mostly found in supragingival and subgingival plaques. The activities of sulfate reduction and methane production were determined in randomly selected isolates.

Samples of subgingival dental tissues were examined for the presence of sulfate-reducing bacteria (SRB). Using enrichment cultures, SRBs were detected in 9 of 17 individuals. A pure culture of SRB was obtained from one sample collected from a patient with type IV periodontal disease. The characterization of this isolate showed that it belongs to the genus Desulfovibrio. The isolate used pyruvate, lactate, glucose, fructose, and ethanol as the sole source of carbon. However, the isolate was unable to use acetate and methanol as a carbon source, indicating it as an incomplete oxidizer unable to carry out the terminal oxidation of substrates. Apart from using sulfate as electron acceptor, the isolate also used thiosulfate and nitrate as an electron acceptor. It has the ability to use a variety of nitrogen sources, including ammonium chloride, nitrate, and glutamate. The optimum growth temperature of the isolate was 37°C and the optimum pH for growth was 6.8. The SRB isolate contained the electron carrier desulfoviridin. The numbers of SRB in the mouth are assumed to be limited by sulfate. Potential sources of sulfate in the subgingival area include free sulfate in pocket fluid and glycosaminoglycans and sulfur-containing amino acids from periodontal tissues.Key words: sulfate-reducing bacteria, periodontal pocket, Desulfovibrio, subgingival tissues, electron acceptor.

The biotransformation of carbon tetrachloride (CT) under various electron acceptor conditions was investigated using enrichment cultures developed from the anaerobic digester sludge of Thibodaux sewage treatment plant. The results indicated that CT was biotransformed under sulfate-reducing, methanogenic, nitrate-reducing, iron-reducing, fermenting, and mixed electron acceptor conditions. However, the rates of CT removal varied among the conditions studied. The fastest removal of CT (100% removal in 12 days) was observed under mixed electron acceptor conditions followed in order by sulfate-reducing, methanogenic, fermenting, iron-reducing, and nitrate-reducing conditions. Under mixed electron acceptor conditions, the CT was converted to methyl chlorides, which was further metabolized. Under sulfate, iron, nitrate-reducing, and methanogenic conditions, the major metabolite produced from CT metabolism was chloroform (CF). Under fermenting conditions, methylene chloride was produced from CT metabolism. This study showed evidence for CT metabolism in a mixed microbial population system similar to many contaminated field sites where a heterogeneous microbial population exists.

Methanogenesis from furfural by defined mixed cultures was studied. Under sulfate-reducing conditions, a Desulfovibrio strain was used as the furfural-degrading species producing acetic acid. This sulfate-reducing bacterium (SRB) Desulfovibrio strain B is an incomplete oxidizer, unable to carry out the terminal oxidation of organic substrates, leaving acetic acid as the end product. Introduction of acetate-utilizing methanogenic archaeon Methanosarcina barkeri 227 converted acetic acid to methane. This well-defined mixed consortium used furfural as its sole source of carbon and converted it to methane and CO(2). In the mixed culture, when a methanogen inhibitor was used in the culture medium, furfural was converted to acetic acid by the Desulfovibrio strain B, but acetic acid did not undergo further metabolism. On the other hand, when the growth of Desulfovibrio in the consortium was suppressed with a specific SRB inhibitor, namely molybdate, furfural was not degraded. Thus, the metabolic activities of both Desulfovibrio strain B and M. barkeri 227 were essential for the complete degradation of furfural.