Impacts of bioreactor operating parameters on removal efficiency, biodegradation rate, molecular distribution, and toxicity of commercial naphthenic acids.

Effects of naphthenic acids (NAs) concentration (50-200 mg NA L-1; 35-140 mg TOC L-1) and loading rate (1.4-1249 mg NA L-1 h-1; 1-874 mg TOC L-1 h-1) on removal efficiency, removal rate, and molecular distribution of NAs, and effluent toxicity were evaluated for biodegradation of commercial NAs mixture in circulating packed bed bioreactors (CPBBs). Increase of NAs concentration and loading rate (shorter residence times) increased the removal rate, while removal efficiency initially declined and then stabilized. The maximum biodegradation rates for 50, 100, 150, and 200 mg NA L-1 were 128.0, 321.7, 430.2, and 630.0 mg TOC L-1 h-1 at loading rates of 218.5, 455.6, 673.5 and 874.0 mg TOC L-1 h-1, respectively, with removal efficiencies of 58.6, 70.6, 63.9 and 72.1%. Analysis of influent and treated effluents with gas chromatography-mass spectrometry showed that molecular weight and cyclicity (C and Z numbers) affected the biodegradation, with low molecular weight acyclic NAs (C = 6-12) were the most amenable to biodegradation and those with intermediate and high molecular weights (C = 13-22) and moderate cyclicity (Z = - 4, - 6) were the most recalcitrant. In the biofilm, Proteobacteria and Actinobacteria were the most abundant phyla, and Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria were the dominant classes. Toxicity analyses with Artemia salina and Vibrio fischeri (Microtox) showed that high influent concentrations and loading rates (short residence times) led to higher NAs residual concentration and effluent toxicity. To design and operate large-scale CPBBs, intermediate loading rates and residence times that result in high removal efficiency, reasonable removal rates, and low toxicity are recommended.

Co-biodegradation of naphthenic acids in anoxic denitrifying biofilm reactors.

Anoxic co-biodegradation of linear and cyclic naphthenic acids (NAs) namely octanoic acid, trans-4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA), cis- and trans-4-methyl-1-cyclohexane-acetic acids (cis-4MCHAA and trans-4MCHAA) was investigated in denitrifying biofilm reactors. In all evaluated compositions, co-biodegradation of NAs was coupled to denitrification, with octanoic acid showing the fastest biodegradation rate (1180.4 mg L-1 h-1 at loading rate of 1180.4 mg L-1 h-1), followed by trans-4MCHCA (398.1 mg L-1 h-1 at loading rate of 435.8 mg L-1 h-1), trans-4MCHAA (25.7 mg L-1 h-1 at loading rate of 221.7 mg L-1 h-1), and cis-4MCHAA (5.3 mg L-1 h-1 at loading rate of 16.9 mg L-1 h-1). Biodegradation of octanoic acid and trans-4MCHCA were not influenced by the presence of recalcitrant NAs (cis- and trans-4MCHAA). Co-biodegradation of cis- and trans-4MCHAA with octanoic acid, trans-4MCHCA, or their combination enhanced the biodegradability of these recalcitrant NAs, with the positive impact being more pronounced for trans-4MCHCA. Finally anoxic co-biodegradation of NAs under denitrifying conditions proceeded at rates that were faster than the aerobic rates obtained in similar mixtures. Anoxic biodegradation, therefore, is an effective alternative for in situ treatment of oil sands process water in anoxic stabilization ponds amended with nitrate, or as an ex situ treatment approach in denitrifying bioreactors whereby the cost and technical challenges of aeration are eliminated.

Biodegradation of surrogate naphthenic acids and electricity generation in microbial fuel cells: bioelectrochemical and microbial characterizations.

Waters contaminated with naphthenic acids (NAs) and associated tailings are one of the major environmental challenges associated with the processing of oil sands and production of heavy oil. In the current work biodegradation of linear and cyclic naphthenic acids, namely octanoic acid and 4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA), individually and in mixture were evaluated in microbial fuel cells (MFCs). In batch MFCs with single rod electrodes and freely suspended bacteria, biodegradation rate increased as NA initial concentration increased from 100 to 250 mg L-1 with no further improvement when a concentration of 500 mg L-1 was evaluated. During the co-biodegradation, diauxic microbial growth and preferential use of octanoic acid were observed. Moreover, the presence of octanoic acid enhanced the biodegradation of trans-4MCHCA. In the continuous flow MFCs with granular graphite electrodes and biofilm, increases in NA concentration and loading rate led to higher biodegradation rates and improvement of electrochemical output. Furthermore, MFC operated with octanoic acid outperformed its counterpart that was fed with trans-4MCHCA, with the maximum biodegradation rate, current and power densities for octanoic acid and trans-4MCHCA being 49.9 and 36.5 mg L-1 h-1, 6000.0 and 4296.3 mA m-3, and 963.0 and 481.5 mW m-3, respectively. Co-biodegradation of NAs in continuous flow MFCs with biofilm acclimated to octanoic acid or trans-4MCHCA revealed development of distinctly different microbial communities, simultaneous biodegradation of NAs albeit at faster rates for octanoic acid, and superior performance of MFC with the biofilm developed with trans-4MCHCA.

A systematic review of consumer preference for e-cigarette attributes: Flavor, nicotine strength, and type.

OBJECTIVE: Systematic review of research examining consumer preference for the main electronic cigarette (e-cigarette) attributes namely flavor, nicotine strength, and type. METHOD: A systematic search of peer-reviewed articles resulted in a pool of 12,933 articles. We included only articles that meet all the selection criteria: (1) peer-reviewed, (2) written in English, and (3) addressed consumer preference for one or more of the e-cigarette attributes including flavor, strength, and type. RESULTS: 66 articles met the inclusion criteria for this review. Consumers preferred flavored e-cigarettes, and such preference varied with age groups and smoking status. We also found that several flavors were associated with decreased harm perception while tobacco flavor was associated with increased harm perception. In addition, some flavor chemicals and sweeteners used in e-cigarettes could be of toxicological concern. Finally, consumer preference for nicotine strength and types depended on smoking status, e-cigarette use history, and gender. CONCLUSION: Adolescents could consider flavor the most important factor trying e-cigarettes and were more likely to initiate vaping through flavored e-cigarettes. Young adults overall preferred sweet, menthol, and cherry flavors, while non-smokers in particular preferred coffee and menthol flavors. Adults in general also preferred sweet flavors (though smokers like tobacco flavor the most) and disliked flavors that elicit bitterness or harshness. In terms of whether flavored e-cigarettes assisted quitting smoking, we found inconclusive evidence. E-cigarette users likely initiated use with a cigarette like product and transitioned to an advanced system with more features. Non-smokers and inexperienced e-cigarettes users tended to prefer no nicotine or low nicotine e-cigarettes while smokers and experienced e-cigarettes users preferred medium and high nicotine e-cigarettes. Weak evidence exists regarding a positive interaction between menthol flavor and nicotine strength.

Biodegradation of phenol in batch and continuous flow microbial fuel cells with rod and granular graphite electrodes.

Phenol biodegradation was evaluated in batch and continuous flow microbial fuel cells (MFCs). In batch-operated MFCs, biodegradation of 100-1000 mg L-1 phenol was four to six times faster when graphite granules were used instead of rods (3.5-4.8 mg L-1 h-1 vs 0.5-0.9 mg L-1 h-1). Similarly maximum phenol biodegradation rates in continuous MFCs with granular and single-rod electrodes were 11.5 and 0.8 mg L-1 h-1, respectively. This superior performance was also evident in terms of electrochemical outputs, whereby continuous flow MFCs with granular graphite electrodes achieved maximum current and power densities (3444.4 mA m-3 and 777.8 mW m-3) that were markedly higher than those with single-rod electrodes (37.3 mA m-3 and 0.8 mW m-3). Addition of neutral red enhanced the electrochemical outputs to 5714.3 mA m-3 and 1428.6 mW m-3. Using the data generated in the continuous flow MFC, biokinetic parameters including µm, KS, Y and Ke were determined as 0.03 h-1, 24.2 mg L-1, 0.25 mg cell (mg phenol)-1 and 3.7 × 10-4 h-1, respectively. Access to detailed kinetic information generated in MFC environmental conditions is critical in the design, operation and control of large-scale treatment systems utilizing MFC technology.

Biokinetic evaluation of fatty acids degradation in microbial fuel cell type bioreactors.

Biodegradations of Na-lactate and Na-acetate were evaluated in microbial fuel cell (MFC) type bioreactors. Increase in lactate concentration from 1,000 to 5,000 mg L(-1) enhanced the biodegradation rate from 4.6 to 23.9 mg L(-1) h(-1). Sequential batch operation of MFC enhanced the lactate biodegradation rate. With acetate, neither increase in concentration nor sequential operation had a marked effect. Maximum power and current densities in MFCs operated batch-wise with lactate and acetate were 3.30 and 2.28 mW m(-2), and 48.2 and 40.2 mA m(-2), respectively. In the MFC operated continuously, increase in lactate loading rate caused the biodegradation rate to pass through maximum value of 1,668.2 mg L(-1) h(-1) (residence time: 1.2 h). Open circuit potential, power and current densities for continuous operation were 700 mV, 8.10 mW m(-2) and 43.0 mA m(-2), respectively. Using the experimental data, kinetic models for microbial growth and biodegradation of lactate and acetate in the MFC were developed.

Ammonia loading rate: an effective variable to control partial nitrification and generate the anaerobic ammonium oxidation influent.

Anaerobic ammonium oxidation (ANAMMOX) is an innovative process for the treatment of ammonia-contaminated waters. ANNAMOX is usually preceded by a nitrifying step in which ammonia is partially oxidized to nitrite. The effectiveness of the overall process depends on control of the nitrification and creation of a suitable influent for ANAMMOX. In this work, impacts of ammonia concentration and loading rate on partial nitrification and composition of the resulting effluent were investigated in continuous stirred tank (CSTR) and biofilm reactors fed with various ammonia concentrations (17.6-61.5 mM; 299-1045 ppm). Regardless of ammonia concentration, loading rates from 3.1 to 5.4mM/h in the CSTR and 6.4-12.1 mM/h in the biofilm reactor generated effluents with nitrite to ammonia ratios of 1.2 +/- 0.3 (suitable ANAMMOX influent). Under these conditions, the highest ammonia loading and nitrite production rates in the CSTR and biofilm reactors were 5.4 and 2.5 mM/h (HRT: 3.7 h) and 12.1 and 6.5 mM/h (HRT: 1.6 h), respectively. Results reveal that ammonia loading rate can be used effectively to achieve suitable ANAMMOX influent without the need for precise control of dissolved oxygen (DO). Considering the difficulty in regulating DO in large-scale systems and the need for the nitrifying process to be flexible with respect to various ammonia concentrations, the loading rate appears to be a practical option to control partial nitrification. Verifying the range of ammonia loading rates that generate ANAMMOX influent allows operation of the nitrifying step with any level of ammonia in the feed, with the proper loading rate achieved through adjustment of hydraulic residence time.

Biodegradation of a surrogate naphthenic acid under denitrifying conditions.

Extraction of bitumen from the shallow oil sands generates extremely large volumes of waters contaminated by naphthenic acid which pose severe environmental and ecological risks. Aerobic biodegradation of NA in properly designed bioreactors has been investigated in our earlier works. In the present work, anoxic biodegradation of trans-4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA) coupled to denitrification was investigated as a potential ex situ approach for the treatment of oil sand process waters in bioreactors whereby excessive aeration cost could be eliminated, or as an in situ alternative for the treatment of these waters in anoxic stabilization ponds amended with nitrate. Using batch and continuous reactors (CSTR and biofilm), effects of NA concentration (100-750mgL(-1)), NA loading rate (up to 2607.9mgL(-1)h(-1)) and temperature (10-35°C) on biodegradation and denitrification processes were evaluated. In the batch system biodegradation of trans-4MCHCA coupled to denitrification occurred even at the highest concentration of 750mgL(-1). Consistent with the patterns reported for aerobic biodegradation, increase in initial concentration of NA led to higher biodegradation and denitrification rates and the optimum temperature was determined as 23-24°C. In the CSTR, NA removal and nitrate reduction rates passed through a maximum due to increases in NA loading rate. NA loading rate of 157.8mgL(-1)h(-1) at which maximum anoxic NA and nitrate removal rates (105.3mgL(-1)h(-1) and 144.5mgL(-1)h(-1), respectively) occurred was much higher than those reported for the aerobic alternative (NA loading and removal rates: 14.2 and 9.6mgL(-1)h(-1), respectively). In the anoxic biofilm reactor removal rates of NA and nitrate were dependent on NA loading rate in a linear fashion for the entire range of applied loading rates. The highest loading and removal rates for NA were 2607.9 and 2028.1mgL(-1)h(-1), respectively which were at least twofold higher than the values reported for the aerobic biofilm reactor. The highest nitrate removal rate coincided with maximum removal rate of NA and was 3164.7mgL(-1)h(-1).

Evaluation of sulfur-based autotrophic denitrification and denitritation for biological removal of nitrate and nitrite from contaminated waters.

Sulfur-based autotrophic denitrification and denitritation were investigated using an oil reservoir culture. In batch system nitrate up to 20 mM was reduced with concomitant sulfate production. With 20 mM nitrate, reduction of produced nitrite did not occur which was contrary to that under heterotrophic conditions. Reduction of nitrite as the sole substrate occurred even at 50 mM. When both sulfur and acetate were present, only acetate was used as the electron donor. In the continuous biofilm reactor maximum nitrate and nitrite removal rates of 17.3 and 13.2 mM/h, much higher than literature values, were achieved at residence times of 0.4 and 0.6 h, respectively. Bicarbonate functioned effectively as carbon source and alkaline, and eliminated the problems associated with lime addition. Based on these and our earlier findings the highest nitrate and nitrite removal rates are achieved under heterotrophic conditions with acetate, followed by autotrophic rates with sulfide, and then elemental sulfur.

Batch and continuous biodegradation of three model naphthenic acids in a circulating packed-bed bioreactor.

Generation of process waters contaminated by naphthenic acids is a serious environmental concern associated with processing of the oil sands. This together with the necessity for sustainable use of water highlights the need for development of effective technologies such as bioremediation for treatment of these contaminated waters. In this work, a circulating packed bed bioreactor and a culture developed in our laboratory were used to study batch and continuous biodegradation of trans-4-methyl-cyclohexane carboxylic acid (trans-4MCHCA), a mixture of cis- and trans-4-methyl-cyclohexane acetic acid (4-MCHAA), and mixture of these three naphthenic acids. Experimental results revealed that the biodegradability of the naphthenic acids was influenced by both carbon number and the spatial arrangement of the alkyl side branch. The maximum biodegradation rate of trans-4MCHCA observed during the continuous operation (209 mg/Lh at a residence time of 0.15 h) was significantly higher than those reported for CSTR and packed-bed bioreactors. The biodegradation rates of cis- and trans-4-MCHAA were much lower than trans-4MCHCA, with the maximum biodegradation rates determined for the two isomers being 4.2 and 7.8 mg/Lh, respectively (residence time: 3.3 h).

Biological removal of nitrate by an oil reservoir culture capable of autotrophic and heterotrophic activities: kinetic evaluation and modeling of heterotrophic process.

Kinetics of heterotrophic denitrification was investigated using an oil reservoir culture with the ability to function under both autotrophic and heterotrophic conditions. In the batch system nitrate at concentrations up to 30 mM did not influence the kinetics but with 50mM slower growth and removal rates were observed. A kinetic model, representing the denitrification as reduction of nitrate to nitrite, and subsequent reduction of nitrite to nitrous oxides and nitrogen gas was developed. The value of various kinetic coefficients, including maximum specific growth rate, saturation constant, yield and activation energy for nitrate and nitrite reductions were determined by fitting the experimental data into the developed model. In continuous bioreactors operated with 10 or 30 mM nitrate, complete removal of nitrate (no residual nitrite) and linear dependency between nitrate loading and removal rates were observed for loading rates up to 0.21 and 0.58 mM h(-1), respectively. The highest removal rates of 0.31 and 0.94 mM h(-1) observed at loading rates of 0.42 mM h(-1) and 1.26 mM h(-1), with corresponding removal percentages of nitrate and total nitrogen being 75.4, 54.4%, and 74.4 and 17.9%, respectively. Developed kinetic model predicted the performance of the continuous bioreactors with accuracy.

Biodegradation kinetics of 1,4-benzoquinone in batch and continuous systems.

Combining chemical and biological treatments is a potentially economic approach to remove high concentration of recalcitrant compounds from wastewaters. In the present study, the biodegradation of 1,4-benzoquinone, an intermediate compound formed during phenol oxidation by chlorine dioxide, was investigated using Pseudomonas putida (ATCC 17484) in batch and continuous bioreactors. Batch experiments were conducted to determine the effects of 1,4-benzoquinone concentration and temperature on the microbial activity and biodegradation kinetics. Using the generated data, the maximum specific growth rate and biodegradation rate were determined as 0.94 h(-1) and 6.71 mg of 1,4-benzoquinone l(-1) h(-1). Biodegradation in a continuous bioreactor indicated a linear relationship between substrate loading and biodegradation rates prior to wash out of the cells, with a maximum biodegradation rate of 246 mg l(-1) h(-1) observed at a loading rate of 275 mg l(-1) h(-1) (residence time: 1.82 h). Biokinetic parameters were also determined using the steady state substrate and biomass concentrations at various dilution rates and compared to those obtained in batch cultures.

Evaluation of autotrophic and heterotrophic processes in biofilm reactors used for removal of sulphide, nitrate and COD.

Microbial cultures originated from an oil reservoir were used in three biofilm reactors and effects of sulphide and nitrate loading rates and molar loading ratio on the removal of sulphide, nitrate and acetate, and composition of end products were investigated. Application of biofilms improved sulphide and nitrate removal rates significantly when compared with freely suspended cells. Maximum sulphide and nitrate removal rates under autotrophic conditions were 30.0 and 24.4 mM h(-1), respectively (residence time: 0.5h). Oxidation of acetate occurred only at nitrate to sulphide molar loading ratios around 0.7 or higher when nitrate was present at levels higher than that required for oxidation of sulphide to sulphur. Conversion of sulphide to sulphate increased from 0% to 66% as nitrate to sulphide molar loading ratio was increased from 0.34 to 3.98. The highest nitrate and acetate removal rates in the bioreactor operated under heterotrophic conditions were 183.2 and 88.0 mM h(-1), respectively (residence time: 0.8h).

Scale up of diesel oil biodegradation in a baffled roller bioreactor.

Diesel oil is a suitable substance to represent petroleum contamination from accidental spills in operating and transportation facilities. Using a microbial culture enriched from a petroleum contaminated soil, biodegradation of diesel oil was carried out in 2.2, 55, and 220 L roller baffled bioreactors. The effects of bioreactor rotation speed (from 5 to 45 rpm) and liquid loading (from 18% to 73% of total volume) on the biodegradation of diesel oil were studied. In the small scale bioreactor (2.2L), the maximum rotation speed of 45 rpm resulted in the highest biodegradation rate with a first order biodegradation kinetic constant of 0.095 d(-1). In the larger scale bioreactors, rotation speed did not affect the biodegradation rate. Liquid loadings higher than 64% resulted in reduced biodegradation rates in the small scale bioreactor; however, in the larger roller bioreactors liquid loading did not affect the biodegradation rate. Biodegradation of diesel oil at 5 rpm and 73% loading is recommended for operating large scale roller baffled bioreactors. Under these conditions, high diesel oil concentrations up to 50 gL(-1) can be bioremediated at a rate of 1.61 gL(-1)d(-1).

Simultaneous biodesulphurization and denitrification using an oil reservoir microbial culture: Effects of sulphide loading rate and sulphide to nitrate loading ratio.

Biooxidation of sulphide under denitrifying conditions is a key process in control of souring in oil reservoirs and in treatment of gas and liquids contaminated with sulphide and nitrate. In this work, biooxidation of sulphide was studied using a representative culture originated from an oil reservoir. Effects of sulphide concentration, sulphide to nitrate molar ratio, and loading rates of sulphide and nitrate on their removal rates and composition of the end products were investigated. In the batch system sulphide removal rate passed through a maximum as sulphide concentration was increased from 2.1 to 16.3mM, with the highest rate (2.06mMh(-1)) observed with 10.7mM sulphide. Nitrate removal was coupled to sulphide oxidation and the highest removal rate was 1.05mMh(-1). In the continuous bioreactors fed with 10 and 5, 15 and 7.5, and 20 and 10mM sulphide and nitrate, cell wash-out occurred as dilution rate was increased above 0.15, 0.13 and 0.08h(-1), respectively. Prior to cell wash-out linear increases in sulphide and nitrate removal rates were observed as loading rate was increased. The highest sulphide and nitrate removal rates of 2.0 and 0.92mMh(-1) were obtained in the bioreactor fed with 15mM sulphide and 7.5mM nitrate at loading rates of 2.1 and 0.93mMh(-1), respectively. Short residence times and high sulphide to nitrate ratios promoted the formation of sulphur, a desired end product for ex situ treatment of contaminated streams. Combination of long residence times and low sulphide to nitrate ratios, which favours formation of sulphate, is the suitable strategy for in situ removal of H(2)S from oil reservoirs.

Laboratory, semi-pilot and room scale study of nitrite and molybdate mediated control of H(2)S emission from swine manure.

The effects of manure age on emission of H(2)S and required level of nitrite or molybdate to control these emissions were investigated in the present work. Molybdate mediated control of H(2)S emission was also studied in semi-pilot scale open systems, and in specifically designed chambers which simulated swine production rooms. With fresh 1-, 3- and 6-month old manures average H(2)S concentration in the headspace gas of the closed systems were 4856+/-460, 3431+/-208, 1037+/-98 ppm and non-detectable, respectively. Moreover, the level of nitrite or molybdate required to control the emission of H(2)S decreased as manure age increased. In the semi-pilot scale open system and chambers, average H(2)S concentration at the surface of agitated fresh manure were 831+/-26 and 88.4+/-5.7 ppm, respectively. Furthermore, 0.1-0.25 mM molybdate was sufficient to control the emission of H(2)S. A cost study for an average size swine operation showed that the cost of treatment with molybdate was less than 1% of the overall production cost for each market hog.

Biodegradation kinetics of trans-4-methyl-1-cyclohexane carboxylic acid.

Naphthenic acids are a complex mixture of organic compounds which naturally occur in crude oil. Low molecular weight components of the naphthenic acids are known to be toxic in aquatic environments and there is a need to better understand the factors controlling the kinetics of their biodegradation. In this study, a relatively low molecular weight naphthenic acid compound (trans-isomer of 4-methyl-1-cyclohexane carboxylic acid) and a microbial culture developed in our laboratory were used to study the biodegradation of this naphthenic acid and to evaluate the kinetics of the process in batch cultures. The initial concentration of trans-4-methyl-1-cyclohexane carboxylic acid (50-750 mg l(-1)) did not affect the maximum specific growth rate of the bacteria at 23 degrees C (0.52 day(-1)) to the maximum biodegradable concentration (750 mg l(-1)). The maximum yield observed at this temperature and at a neutral pH was 0.21 mg of biomass per milligram of substrate. Batch experiments indicated that biodegradation can be achieved at low temperatures; however, the biodegradation rate at room temperature (23 degrees C) and neutral pH was 5 times faster than that observed at 4 degrees C. Biodegradation at various pH conditions indicated a maximum specific growth rate of 1.69 day(-1) and yield (0.41 mg mg(-1)) at a pH of 10.

Scale-up impacts on mass transfer and bioremediation of suspended naphthalene particles in bead mill bioreactors.

Scale-up effects on mass transfer and bioremediation of suspended naphthalene particles have been studied in 20 and 58L bead mill bioreactors and compared to data generated earlier with a laboratory scaled bioreactor. The bead mill bioreactor performance with respect to naphthalene mass transfer rate was dependent on the size and loading of the inert particles, as well as the rotational speed of the roller apparatus. The optimum operating conditions were found to be 15mm glass beads at a loading of 50% (total volume of particles/working volume of bioreactor: v/v%) and a bioreactor rotational speed of 50rpm. The highest naphthalene mass transfer coefficients obtained in the large scale system under these optimum conditions (19.6 and 22.4h(-1) for 20 and 58L vessels, respectively) were higher than those determined previously in a 2.5L bead mill bioreactor (0.7h(-1)). The acute toxicity tests indicated that the bioreactor effluent was less toxic than the untreated naphthalene suspension. Biodegradation rates obtained in these large scale bead mill bioreactors under optimum conditions (36-37.4mgL(-1)h(-1)) were higher than those achieved in the control bioreactors of similar sizes (11.4 and 11.6mgL(-1)h(-1)) but were slower than those previously determined in a 2.5L bead mill bioreactor (59-61.5mgL(-1)h(-1)). The limitation of oxygen in the large scale systems and damage of the bacterial cells due to the crushing effects of the large beads are likely contributing factors in the lower observed biodegradation rates. The optimum conditions with respect to naphthalene mass transfer might not necessarily translate to optimum performance with regard to bioremediation.

Control of H2S emission from swine manure using Na-nitrite and Na-molybdate.

Biogenic production of hydrogen sulphide (H2S) in oil reservoirs (souring) has been shown to be controlled effectively using nitrite and molybdate salts. In the present work the effects of addition of nitrite and molybdate on reducing the emission of H2S from swine manure slurry was investigated in the laboratory and semi-pilot scale systems. Addition of 80 mM nitrite or 2 mM molybdate (final concentration in the manure slurry) to fresh manure in the laboratory scale closed systems (125 mL and 4 L) reduced the concentration of H2S in the headspace gas from 1500 microL L(-1) to 10 microL L(-1) which maintained during the remaining period of trials (40-60 days). With aged manure, similar results were achieved with a lower level of nitrite (10 mM). Simultaneous or sequential additions of nitrite and molybdate to fresh manure had similar effects. Contrary to the systems simulating biological conditions in oil reservoirs in which simultaneous addition of nitrite and molybdate has been reported to have a synergistic effect, no synergism was observed when nitrite and molybdate were added to the manure simultaneously. Experiments with fresh manure slurry in the semi-pilot scale systems (200 L) confirmed the effectiveness of this approach in which addition of 80 mM nitrite or 2 mM molybdate or a combination of 80 mM nitrite and 2 mM molybdate decreased the concentration of the H2S in the headspace gas from an initial value of 500 microL L(-1) to a low level in the range 2-25 microL L(-1) and maintained these low levels during the remaining period of trials (16 days). The concentration of ammonia (NH3) in the headspace gas of the treated systems was similar to that observed in the control system (untreated), indicating that the treatment did not have an effect on the level of present NH3. Although the addition of nitrite or molybdate reduced emissions of H2S from swine manure and the associated health and safety concerns, it had little impact on the intensity of odour in the headspace gas samples from the semi-pilot scale system.

Corrosion risk associated with microbial souring control using nitrate or nitrite.

Souring, the production of hydrogen sulfide by sulfate-reducing bacteria (SRB) in oil reservoirs, can be controlled through nitrate or nitrite addition. To assess the effects of this containment approach on corrosion, metal coupons were installed in up-flow packed-bed bioreactors fed with medium containing 8 mM sulfate and 25 mM lactate. Following inoculation with produced water to establish biogenic H(2)S production, some bioreactors were treated with 17.5 mM nitrate or up to 20 mM nitrite, eliminating souring. Corrosion rates were highest near the outlet of untreated bioreactors (up to 0.4 mm year(-1)). Nitrate (17.5 mM) eliminated sulfide but gave pitting corrosion near the inlet of the bioreactor, whereas a high nitrite dose (20 mM) completely eliminated microbial activity and associated corrosion. More gradual, step-wise addition of nitrite up to 20 mM resulted in the retention of microbial activity and localized pitting corrosion, especially near the bioreactor inlet. We conclude that: (1) SRB control by nitrate or nitrite reduction shifts the corrosion risk from the bioreactor outlet to the inlet (i.e. from production to injection wells) and (2) souring treatment by continuous addition of a high inhibitory nitrite dose is preferable from a corrosion-prevention point of view.