Mechanistic study of microbial control of hydrogen sulfide production in oil reservoirs

Microbial control of biogenic production of hydrogen sulfide in oil fields was studied in a model system consisting of pure cultures of the nitrate-reducing, sulfide-oxidizing bacterium (NR-SOB) Thiomicrospira sp. strain CVO and the sulfate-reducing bacterium (SRB) Desulfovibrio sp. strain Lac6, as well as in microbial cultures enriched from produced water of a Canadian oil reservoir. The presence of nitrate at concentrations up to 20 mM had little effect on the rate of sulfate reduction by a pure culture of Lac6. Addition of CVO imposed a strong inhibition effect on production of sulfide. In the absence of added nitrate SRB we were able to overcome this effect after an extended lag phase. Simultaneous addition of CVO and nitrate stopped the production of H2S immediately. The concentration of sulfide decreased to a negligible level due to nitrate-dependent sulfide oxidation activity of CVO. This was not prevented by raising the concentration of Na-lactate, the electron donor for sulfate reduction. Similar results were obtained with enrichment cultures. Enrichments of produced water with sulfide and nitrate were dominated by CVO, whereas enrichments with sulfate and Na-lactate were dominated by SRB. Addition of an NR-SOB enrichment to an SRB enrichment inhibited the production of sulfide. Subsequent addition of sufficient nitrate caused the sulfide concentration to drop to zero. A similar response was seen in the presence of nitrate alone, although after a pronounced lag time, it was needed for emergence of a sizable CVO population. The results of the present study show that two mechanisms are involved in microbial control of biogenic sulfide production. First, addition of NR-SOB imposes an inhibition effect, possibly by increasing the environmental redox potential to levels which are inhibitory for SRB. Second, in the presence of sufficient nitrate, NR-SOB oxidize sulfide, leading to its complete removal from the environment. Successful microbial control of H2S in an oil reservoir is crucially dependent on the simultaneous presence of NR-SOB (either indigenous population or injected) and nitrate in the environment.

Impact of nitrate-mediated microbial control of souring in oil reservoirs on the extent of corrosion

The effect of microbial control of souring on the extent of corrosion was studied in a model system consisting of pure cultures of the nitrate-reducing, sulfide-oxidizing bacterium (NR-SOB) Thiomicrospira sp. strain CVO and the sulfate-reducing bacterium (SRB) Desulfovibrio sp. strain Lac6, as well as in an SRB consortium enriched from produced water from a Canadian oil reservoir. The average corrosion rate induced by the SRB consortium (1.4 g x m(-2) x day(-1)) was faster than that observed in the presence of strain Lac6 (0.2 g x m(-2) x day(-1)). Examination of the metallic coupons at the end of the tests indicated a uniform corrosion in both cases. Addition of CVO and 10 mM nitrate to a fully grown culture of Lac6 or the SRB consortium led to complete removal of sulfide from the system and a significant increase in the population of CVO, as determined by reverse sample genome probing. In the case of the SRB consortium addition of just nitrate (10 mM) had a similar effect. When grown in the absence of nitrate, the consortium was dominated by Desulfovibrio sp. strains Lac15 and Lac29, while growth in the presence of nitrate led to dominance of Desulfovibrio sp. strain Lac3. The addition of CVO and nitrate to the Lac6 culture or nitrate to the SRB consortium accelerated the average corrosion rate to 1.5 and 2.9 g x m(-2) x day(-1), respectively. Localized corrosion and the occurrence of pitting were apparent in both cases. Although the sulfide concentration (0.5-7 mM) had little effect on corrosion rates, a clear increase of the corrosion rate with increasing nitrate concentration was observed in experiments conducted with consortia enriched from produced water.

Control of biogenic H(2)S production with nitrite and molybdate

The effects of the metabolic inhibitors, sodium nitrite and ammonium molybdate, on production of H(2)S by a pure culture of the sulfate-reducing bacterium (SRB) Desulfovibrio sp. strain Lac6 and a consortium of SRB, enriched from produced water of a Canadian oil field, were investigated. Addition of 0.1 mM nitrite or 0.024 mM molybdate at the start of growth prevented the production of H(2)S by strain Lac6. With exponentially growing cultures, higher levels of inhibitors, 0.25 mM nitrite or 0.095 mM molybdate, were required to suppress the production of H(2)S. Simultaneous addition of nitrite and molybdate had a synergistic effect: at time 0, 0.05 mM nitrite and 0.01 mM molybdate, whereas during the exponential phase, 0.1 mM nitrite and 0.047 mM molybdate were sufficient to stop H(2)S production. With an exponentially growing consortium of SRB, enriched from produced water of the Coleville oil field, much higher levels of inhibitors, 4 mM nitrite or 0.47 mM molybdate, were needed to stop the production of H(2)S. The addition of these inhibitors had no effect on the composition of the microbial community, as shown by reverse sample genome probing. The results indicate that the efficiency of inhibitors in containment of SRB depends on the composition and metabolic state of the microbial community.

Particle size effects in bioleaching of pyrite by acidophilic thermophile Sulfolobus metallicus (BC)

The effect of mineral particle size on the bioleaching of pyrite by the acidophilic thermophile Sulfolobus metallicus was investigated in a batch bioreactor. Decreasing the particle size from a mean diameter of 202 micron (size fraction: 150-180 micron) to a mean diameter of 42.5 micron (size fraction: 25-45 micron) enhanced the bioleaching rate from 0.05 kg m(-3) h(-1) to 0.098 kg m(-3) h(-1). The particle size distribution of the mineral in this range did not influence the morphology and growth kinetics of the cells. The values of specific growth rate (mu) and yield factor (Y) were 0.018-0.025 h(-1) and 0.67x10(11)-1.45x10(11) cells (g iron)(-1), respectively. Decreasing the particle size of the mineral to a mean diameter of 6.40 micron (size fraction <25 micron) adversely influenced the activity of the cells. The presence of fine particles apparently damaged the structure of the cells, resulting in their inability to oxidise pyrite.

The influence of constitutional variables on orthogonal electrocardiograms of normal women

Correlations between 276 orthogonal electrocardiographic measurements and constitutional variables were made in 450 normal women, aged 18 to 90 years. Advancing age led to decreases in amplitudes, left QRS axis shift, rightward and superior displacement of the ST segment, and anterior shift of the T wave. QZ was absent in 1% of normal women over age 40. In the oldest subjects, Ry amplitude was 71% and RZ amplitude was 80% of the respective values in the youngest group. Whereas QRS amplitude decreases with age leveled off at the sixth decade of life, they continued to old age for ST-T measurements. Men revealed steeper age trends than women. Blacks had larger QRS amplitudes and smaller Q/R ratios than whites. Stratification of electrocardiographic criteria according to age, sex, and race appears essential for routine interpretations and for epidemiological studies where new events, such as myocardial infarcts, need to be differentiated from normal age trends.

Clinical study of ticrynafen. A new diuretic, antihypertensive, and uricosuric agent

In a double-blind study, 20 hypertensive patients were randomly assigned to a six-week regimen of either ticrynafen or hydrochlorothiazide. Blood pressure was significantly reduced with both medications, although most patients required an increase in dosage from 250 to 500 mg ticrynafen daily. Whereas the serum uric acid level rose moderately in the hydrochlorothiazide-treated patients, it fell strikingly to less than half of the pretreatment level in patients treated with ticryafen. Body weight decreased slightly in both groups, as did serum potassium levels. Blood urea nitrogen and serum creatinine levels rose slightly in both groups. The magnitude of these changes was not significantly different between the two groups. Use of ticryafen was well tolerated. Ticryafen appears to be a useful new antihypertensive agent because of its unique combination of diuretic, antihypertensive, and hypouricemic effects.