Limited Aeration Research Articles

Coenzyme Q10 production in a 150-l reactor by a mutant strain of Rhodobacter sphaeroides

For the commercial production of CoQ(10), batch-type fermentations were attempted in a 150-l fermenter using a mutant strain of R. sphaeroides. Optimum temperature and initial aeration rate were found to be 30 degrees C and 2 vvm, respectively. Under optimum fermentation conditions, the maximum value of specific CoQ(10) content was achieved reproducibly as 6.34 mg/g DCW after 24 h, with 3.02 g/l of DCW. During the fermentation, aeration shift (from the adequate aeration at the early growth phase to the limited aeration in active cellular metabolism) was a key factor in CoQ(10) production for scale-up. A higher value of the specific CoQ(10) content (8.12 mg/g DCW) was achieved in fed-batch fermentation and comparable to those produced by the pilot-scale fed-batch fermentations of A. tumefaciens, which indicated that the mutant strain of R. sphaeroides used in this study was a potential high CoQ(10) producer. This is the first detailed study to demonstrate a pilot-scale production of CoQ(10) using a mutant strain of R. sphaeroides.

Characteristics and potential environmental consequence of weathered materials in the surface layer of a spontaneously combusting mine spoil stockpile

Abstract Investigation was carried out to characterize the sulfidic mine spoils in the surface layer of a spontaneously combusting waste rock stockpile. The objective was to assess its potential impacts on acid mine drainage generation. The results show that there were substantial amounts of elemental S and various sulfate minerals in the weathered materials, indicating the occurrence of significant sulfide mineral oxidation in the investigated spontaneously combusting mine spoils (SCMS). It is likely that the surfacially-occurring elemental S was derived from the deeper waste rock layers experiencing spontaneous combustion under limited aeration conditions. The significantly higher acidity, EC and SO 4 2 - concentration in the SCMS, relative to the Non-SCMS suggest that spontaneous combustion is a much faster and more powerful process driving sulfide-derived acid generation, compared to microbially-catalyzed oxidation of sulfide minerals. The export of acid sulfate materials from the spontaneously combusting waste rock stockpile not only generates severe acid mine drainage but could also act as an inducer for biologically-catalyzed oxidation of newly exposed sulfide minerals in the areas surrounding the stockpile.

Growth strategy of the pathogenic yeast Cryptococcus neoformans submerged culture under different cultivation formats

Growth patterns of Cryptococcus neoformans submerged culture in different culture volumes, intensity of agitation and types of sealing were evaluated to better understand the physiological role of hypoxia response in this yeast. When low intensity agitation was set at high culture volumes and air exchange between the cultivation vessel and external environment was not abolished completely, the cells proliferated slowly but steadily. On the other hand, when the intensity of agitation was high but the vessel was withheld from fresh air supply, the cells first proliferated rapidly, then arrested completely and finally died. Therefore, the central strategy of C. neoformans here seems to lie in its proliferation-rate adjustment to the available oxygen levels and not in its capacity to survive under anoxia. The data support the opinion that the cultures grown under limited aeration (even though not completely withheld from fresh air supply) are much closer to the real cryptococcal life in human tissues than conventional well-aerated exponential cultures.

The influence of cultural and physical conditions on the antimicrobial activity of bacteriocin produced by a newly isolated Bacillus megaterium 22 strain

Bacillus megaterium 22, a soil isolate, produced a bacteriocin that exhibited a broad range of inhibitory activity against food-spoilage microorganisms includingSalmonella typhimurium and Staphylococcus aureus. The antimicrobial activity peaked at the early stationary phase. De Man Rogosa Shrarpe (MRS) was the best medium for bacteriocin production, where growth of B. megaterium 22 for 12 - 18 h at 30oC, pH 6 - 6.5 resulted in maximum inhibitory effect on the pathogenic indicator strains. Supplemen-tation and/or replacement of medium nutrients demonstrated higher values of bacteriocin activity in the presence of 5 - 10% sucrose, 1% beef extract, and under limited aeration. Bacteriocin activity was significantly stimulated at concentrations of up to 3% NaCl, or 1% KCl. Low levels of spices (curry, red and Black pepper) synergistically stimulated the bacteriocin activity, except for garlic and rosemary where higher concentrations (1%) considerably influenced the activity. The bacteriocin was heat stable for 15 min of exposure to a wide range of temperatures, and over a pH range of 2 - 8 after 1 h of exposure. The bacteriocin was stable for up to 30 min of exposure to UV light, and when stored at 4oC for 90 days. The activity was inhibited by proteolytic enzymes and tested organic solvents. SDS-PAGE revealed that the apparent molecular weight of the partially purified bacteriocin ranged from 3.496 to 6.512 kDa. Results presented here support the idea that the bacteriocin may propose some industrial advantages that render it as a good natural food bio preservative candidate. Key words: Bacillus megaterium, antimicrobial activity, bacteriocin, biopreservation, growth media, spices, storage, indicator strains.

Genes Required for Ethanol Tolerance and Utilization inSaccharomyces cerevisiae

The yeast deletion set was screened to identify mutations impacting ethanol tolerance under limited aeration. Ethanol tolerance was correlated with growth and assessed as the ability to attain the final optical density reached by the parental strain. Of the 4,750 deletants evaluated, 175 strains showed a growth defect in the presence of 5% ethanol. Of these, 21 strains showed a severe growth defect. Growth of many of these strains improved with aeration, but five strains continued to show weak growth: <i>CLC1</i>Δ<i>, GSH1</i>Δ, <i>UME6</i>Δ<i>, TDP3</i>Δ, and <i>VPS24</i>Δ. <i>ADH1</i>Δ also showed higher levels of sensitivity to ethanol but did not grow as well as the other strains in the minimal medium used for the assay in the absence of ethanol and displayed a stronger effect of aeration. The deletion set was also screened to identify mutations affecting growth on ethanol as sole substrate and energy source. Deletants were simultaneously evaluated on lactate to define those mutations needed for growth on respiratory substrates. A total of 176 deletants conferred a growth defect on both ethanol and lactate. Many of these genes are involved in respiration, in mitochondrial ATP synthesis, or define other mitochondrial functions required for organelle integrity. An additional 165 deletants resulted in an ethanol-specific growth defect. These deletants included other mitochondrial proteins as well as genes representing several different functional families. Only 14 genes conferred a specific growth defect on lactate. No deletants were found to confer a growth defect on low sugar concentrations.

Integration of a Coagulation/Flocculation step in a biological sequencing batch reactor for COD and nitrogen removal of supernatant of anaerobically digested piggery wastewater

The supernatant from mesophilic anaerobic digestion of piggery wastewater is characterised by a high amount of COD (4.1 g COD L −1), ammonium (2.3 g NH 4 + – N L - 1 ) and suspended solids (2.5 g SS L −1). This effluent can be efficiently treated by means of a Sequencing Batch Reactor (SBR) strategy for biological COD, SS and nitrogen removal including a Coagulation/Flocculation step. Total COD and SS reduction yields higher than 66% and 74%, respectively, and a total nitrogen removal (via nitrite) of more than 98% were reached when working with HRT 2.7 days, SRT 12 days, temperature 32 °C, three aerobic/anoxic periods, without external control of pH and under limited aeration flow. The inhibition of nitrite oxidizing biomass was achieved by the working free ammonia concentration and the restricted air supply (dissolved oxygen concentration below 1 mg O 2 L −1). Since a part of the total COD was colloidal and/or refractory, a Coagulation/Flocculation step was implemented inside the SBR operating strategy to meet a suitable effluent quality to be discharged. Several Jar-Tests demonstrated that the optimal concentration of FeCl 3 was 800 mg L −1. A respirometric assay showed that this coagulant dosage did not affect the biological activity of nitrifying/denitrifying biomass.

Co-fermentation of a mixture of glucose and xylose to ethanol by Zymomonas mobilis and Pachysolen tannophilus

This research was designed to maximize ethanol production from a glucose-xylose sugar mixture (simulating a sugar cane bagasse hydrolysate) by co-fermentation with Zymomonas mobilis and Pachysolen tannophilus. The volumetric ethanol productivity of Z. mobilis with 50 g glucose/l was 2.87 g/l/h, giving an ethanol yield of 0.50 g/g glucose, which is 98% of the theoretical. P. tannophilus when cultured on 50 g xylose/l gave a volumetric ethanol productivity of 0.10 g/l/h with an ethanol yield of 0.15 g/g xylose, which is 29% of the theoretical. On optimization of the co-fermentation with the sugar mixture (60 g glucose/l and 40 g xylose/l) a total ethanol yield of 0.33 g/g sugar mixture, which is 65% of the theoretical yield, was obtained. The co-fermentation increased the ethanol yield from xylose to 0.17 g/g. Glucose and xylose were completely utilized and no residual sugar was detected in the medium at the end of the fermentation. The pH of the medium was found to be a good indicator of the fermentation status. The optimum conditions were a temperature of 30°C, initial inoculation with Z. mobilis and incubation with no aeration, inactivation of bacterium after the utilization of glucose, followed by inoculation with P. tannophilus and incubation with limited aeration.

In situ nitrogen removal from leachate by bioreactor landfill with limited aeration

The feasibility of simultaneous nitrification and denitrification in a bioreactor landfill with limited aeration was assessed. Three column reactors, simulating bioreactor landfill operations under anaerobic condition (as reference), intermittent forced aeration and enhanced natural aeration were hence established, where aerated columns passed through two phases, i.e., fresh landfill and well-decomposed landfill. The experimental results show that limited aeration decreased nitrogen loadings of leachate distinctly in the fresh landfill. In the well-decomposed landfill, the NH(4)(+)-N of the input leachate could be nitrified completely in the aerated landfill columns. The nitrifying loadings of the column cross section reached 7.9 g N/m(2)d and 16.9 g N/m(2)d in the simulated landfill columns of intermittent forced aeration and enhanced natural aeration, respectively. The denitrification was influenced by oxygen distribution in the landfill column. Intermittent existence of oxygen in the landfill with the intermittent forced aeration was favorable to denitrify the NO(2)(-)-N and NO(3)(-)-N, indicated by the high denitrification efficiency (>99%) under the condition of BOD(5)/TN of more than 5.4 in leachate; locally persistent existence of oxygen in the landfill with enhanced natural aeration could limit the denitrification, indicated by relatively low denitrification efficiency of about 75% even when the BOD(5)/TN in leachate had an average of 7.1.

Coupled anaerobic–aerobic treatment of whey wastewater in a sequencing batch reactor: proof of concept

A proof of concept was performed in order to verify if the coupling of anaerobic and aerobic conditions inside the same digester could efficiently treat a reconstituted whey wastewater at 21 degrees C. The sequencing batch reactor (SBR) cycles combined initial anaerobic phase and final aerobic phase with reduced aeration. A series of 24 h cycles in 0.5 L digesters, with four different levels of oxygenation (none, 54, 108 and 182 mgO2 per gram of chemical oxygen demand (COD)), showed residual soluble chemical oxygen demand (sCOD) of 683 +/- 46, 720 +/- 33, 581 +/- 45, 1239 +/- 15 mg L(-1), respectively. Acetate and hydrogen specific activities were maintained for the anaerobic digester, but decreased by 10-25% for the acetate and by 20-50% for the hydrogen, in the coupled digesters. The experiment was repeated using 48 h cycles with limited aeration during 6 or 16 hours at 54 and 108 mgO2gCODinitial(-1), displaying residual sCOD of 177 +/- 43, 137 +/- 38, 104 +/- 22 and 112 +/- 9 mgL(-1) for the anaerobic and the coupled digesters, respectively. The coupled digesters recovered after a pH shock with residual sCOD as low as 132 mg L(-1) compared to 636 mg L(-1) for the anaerobic digester. With regard to the obtained results, the feasibility of the anaerobic-aerobic coupling in SBR digesters for the treatment of whey wastewater was demonstrated.

Vitreoscilla hemoglobin aids respiration under hypoxic conditions in its native host

When Vitreoscilla were grown in medium containing 60mM sodium nitrite under both normal and limited aeration conditions, the levels of Vitreoscilla hemoglobin (VHb) were decreased by greater than 90%, while the levels of the terminal respiratory oxidase, cytochrome bo, were increased 350% under normal aeration and 7-23% under limited aeration. Cytochrome function, as measured by both NADH and ubiquinol oxidases for cells grown under both conditions, increased in parallel (by 150-222% and 8-56%, respectively, for the two activities). Nitrite in the medium inhibited Vitreoscilla growth at both normal and limited aeration. The inhibition of VHb at 60mM nitrite decreased whole cell respiration to the greatest degree in stationary phase for growth in limited aeration conditions, which was the most oxygen poor condition tested. These results are consistent with the originally proposed role for VHb, as an aid to respiration under hypoxic conditions.

Effect of limited aeration on the anaerobic treatment of evaporator condensate from a sulfite pulp mill

Serious inhibition was found in the regular up-flow anaerobic sludge blanket (UASB) reactor in treating the evaporator condensate from a sulfite pulp mill, which contained high strength sulfur compounds. After applying the direct limited aeration in the UASB, the inhibition was alleviated gradually and the activity of the microorganisms was recovered. The COD removal rate increased from 40% to 80% at the organic loading rate of 8kgCODm(-3)d(-1) and a hydraulic retention time of 12h. Limited aeration caused no oxygen inhibition to the anaerobic microorganisms but instigated sulfide oxidization and H(2)S removal, which was beneficial to the methanogens. The experiment confirmed the feasibility of applying limited aeration in the anaerobic reactor to alleviate the sulfide inhibition. It also proved that the anaerobic system was actually aerotolerant. SEM observation showed that the predominant microorganisms partly changed from rod-shaped methanogens to cocci after the UASB reactor was aerated.

Optimization of Biological Nitrogen Removal via Nitrite in a SBR Treating Supernatant from the Anaerobic Digestion of Municipal Solid Wastes

Two strategies (run 1 and run 2) were tested for biological nitrogen removal (BNR) of the digester supernatant of a plant treating municipal solid wastes (MSW) using a laboratory-scale sequencing batch reactor (SBR) with control of temperature. External chemical oxygen demand (COD) was added for denitrification, as not enough biodegradable COD was present. A Monod model was used to fit the NH4+−N removal. In run 1, temperature was fixed at 30 °C, and pH was fixed between 7.4 and 8.6 by the addition of NaHCO3. The hydraulic retention time (HRT) was set to 3 days, and the sludge retention time (SRT) was kept at 12 days. The cycle length was set to 8 h. Nitrate formation was avoided by temperature, pH, and limited aeration flow rate. In run 2, alkalinity was recovered with an intermediate denitrification period, thus avoiding the use of NaHCO3. The strategy consisted of alternating different aerobic−anoxic subcycles inside the operating cycle. The second strategy was found to be effective, with improved kinetics and without addition of chemicals. NH4+-N concentrations of around 360 mg L-1 day were removed with this strategy. The behavior of the SBR was modeled with a modification of Activated Sludge Model No. 1, using kinetic constants obtained in previous experiments. The model was used to predict the profiles of an optimal cycle of 6 h.

A calibration methodology and model‐based systems analysis for SBRs removing nutrients under limited aeration conditions

AbstractA methodology is proposed for the model calibration of nutrient‐removing laboratory‐scale SBRs under limited aeration. Based on in‐process measurements and influent wastewater characterization, the ASM2d model was modified by adding an organic nitrogen module incorporating a hydrolysis mechanism. After calibration, the simulation results showed that enhanced biological nutrient removal occurred during the fill period and under reduced aeration achieving so‐called ‘simultaneous nutrient removal’. A model‐based systems analysis was performed in terms of the contributions of different processes to overall oxygen, nitrogen and phosphate utilization. In each phase, simultaneously occurring biological reactions were compared using the calibrated model. According to the calibrated model, 61% of all denitrified nitrate is denitrified during the mixing/filling phase. On the other hand, 17% of all denitrified nitrate is consumed by simultaneous nitrification–denitrification during the first aerobic period. The aerobic and anoxic P‐removals were quantified as 73% and 12%, respectively. Copyright © 2006 Society of Chemical Industry

Expression of Vitreoscilla hemoglobin in Gordonia amarae enhances biosurfactant production

The gene (vgb) encoding Vitreoscilla (bacterial) hemoglobin (VHb) was electroporated into Gordonia amarae, where it was stably maintained, and expressed at about 4 nmol VHb g(-1) of cells. The maximum cell mass (OD(600)) of vgb-bearing G. amarae was greater than that of untransformed G. amarae for a variety of media and aeration conditions (2.8-fold under normal aeration and 3.4-fold under limited aeration in rich medium, and 3.5-fold under normal aeration and 3.2-fold under limited aeration in mineral salts medium). The maximum level of trehalose lipid from cultures grown in rich medium plus hexadecane was also increased for the recombinant strain, by 4.0-fold in broth and 1.8-fold in cells under normal aeration and 2.1-fold in broth and 1.4-fold in cells under limited aeration. Maximum overall biosurfactant production was also increased in the engineered strain, by 1.4-fold and 2.4-fold for limited and normal aeration, respectively. The engineered strain may be an improved source for producing purified biosurfactant or an aid to microorganisms bioremediating sparingly soluble contaminants in situ.

SHARON process evaluated for improved wastewater treatment plant nitrogen effluent quality

New stricter nitrogen effluent standards and increasing influent loads require existing wastewater treatment plans (WWTPs) to extend or optimize. At WWTPs with limited aeration capacity, limited denitrification capacity or shortage of aerobic sludge age, implementation of SHARON to improve nitrogen effluent quality can be a solution. SHARON is a compact, sustainable and cost-effective biological process for treatment of nitrogen-rich rejection waters. At WWTP Rotterdam-Dokhaven and WWTP Utrecht a SHARON has been in operation for several years. For both WWTPs the effect of SHARON on the nitrogen effluent quality has been evaluated. WWTP Rotterdam-Dokhaven has limited aeration capacity. By implementation of SHARON, the ammonia load of the effluent was reduced by 50%. WWTP Utrecht had limited denitrification capacity. The implementation of SHARON improved the effluent nitrate load by 40%. The overall TN removal efficiency increased from 65% to over 75% and strict nitrogen effluents standards (TN = 10 mg N/l) could be reached. Through modelling and supported by full scale practice it has been shown that by implementation of SHARON in combination with enhanced influent pre-treatment, the aerobic sludge age can be extended to maintain total nitrogen removal at lower temperatures.

Changes in Concentrations of Malodorous Compounds During Controlled Aeration Composting

Effects of composting on odorous chemicals in dairy manure were investigated in replicated pilot-scale studies. Three 16-day composting trials were conducted, using 205 L vessels containing 83 kg mass. Fresh or 12-day-aged manure, from lactating cows, was mixed with sawdust (3man:1saw w/w). Vessels were either aerated continuously with high (2.3 kg/hr)/low (0.8 kg/hr) air flow controlled by thermostats or intermittently on a 5 min high air flow/55 min off clock controlled cycle. Six vessel replicates were conducted on each manure/air flow treatment combination. Temperatures, air flow, O2 consumption, and CO2 production were recorded every 10 minutes. Trapped NH3 emissions were determined daily. Exhaust air was passed through water-cooled condensers to analyze emitted volatiles, and condensate volume, pH, and volatile fatty acids (VFAs) were quantified at 12 or 24 hour intervals. Solids were collected from each vessel initially, at remix at the end of day 7, and at the end of each trial (day 16) for analysis of moisture, pH, ash, C/N, and odorants. Phenolics and indolics were extracted with ethyl ether. VFAs were recovered with pH 2.0 water. Analysis was by flame or mass selective detection gas chromatography. Temperature increased most rapidly in continuously aerated vessels yet maintained a lower mean temperature (49 vs 58°C) than intermittent aeration. Both returned to near ambient temperature by day 16. Continuous aeration nearly doubled (11 vs 18 L) the amount of condensate released over 16 days. Fresh manure/sawdust mixes contained 6553, 795, 77, 51, 19, and 17μg/g of acetate, propionate, isobutyrate, isovalerate, phenol, and p-cresol. Aged manure mixes contained 9350, 3397, 2810, 445, 285, 441, 34, 176, and 18 μg/g acetate, propionate, butyrate, valerate, isobutyrate, isovalerate, phenol, p-cresol, and skatole, as well as a number of C11 to C17 fatty acids. Both aeration methods maintained conditions that resulted in the destruction of most of the odorous chemicals studied in the composting mass in 7 days with only small quantities of acetate, isobutyrate, and skatole present by the end of day 16. Continuous aeration, as opposed to intermittent, more than doubled (115 vs 55 g) the emissions of NH3-N and increased the emissions of VFAs in condensate four-fold. Whereas, limited aeration did not destroy the odorants as rapidly, they remained in the compost until destruction.

Study on performance characteristics of SBR under limited dissolved oxygen

The performance of sequence batch reactor (SBR) was studied under four different air fluxes. Special attention was paid to the operating characteristics of SBR under limited aeration or low dissolved oxygen (DO) conditions. At the air flux of 40 l/h, COD and NH 4 +-N had been removed just before the cycle was over, and during the cycle DO was about 0.5 mg/l most of the time. Operational parameters, such as DO, ORP and pH, were monitored during the whole cycle. The effect of these parameters on the removal efficiency of COD and NH 4 +-N was discussed.

Induced synchrony in Cryptococcus neoformans after release from G2-arrest.

Cryptococcus neoformans was grown first to OD 4 under moderate aeration, then diluted 2.5 times with fresh medium, and grown under limited aeration for 5 h. Oxygen concentration decreased from 5-6 mg l(-1) to 1.5 mg l(-1) 1 h after the shift to limited aeration, and remained at a similar level thereafter. In all the eleven strains examined the shift caused unbudded G(2)-arrest in more than half of the cells. In three strains more than 80% of the cells were arrested in unbudded G(2), and, therefore they were selected for synchrony experiments. After being shifted to extensive aeration again, the cells resumed growth by synchronous budding, followed by synchronous nuclear division. This method has turned out to be a good tool to prepare synchronized culture in C. neoformans, especially when a large amount of synchronized cells is needed. This is worthy of attention, since synchronous cultures after release from G(2)-arrest have not been reported yet in any yeast species.

Monitoring the corrosion susceptibility of mild steel in varied soil textures by corrosion product count technique

The corrosion susceptibilities of buried steel in natural soil and laboratory simulated buried steel in varied soil textures were monitored by weight loss and corrosion product count technique. The result shows that the corrosion product counts in these soils are in the order: clay⪢sand<loam. Adsorption dynamics revealed that Weber and Morris equation was obeyed in all soil textures studied while the applicability of Lagergren equation was limited to sandy and clay soil textures. Also, in the absence of insidious ions, fairly identical pH values, limited aeration and moisture laden, soil depth and textures were corroborated for the observed high corrosion susceptibility of the buried steel.

Production of xylitol from Candida tropicalis by using an oxidation-reduction potential-stat controlled fermentation

An on-line device, ORP (oxidation-reduction potential)-stat, was used to control glucose-feeding for enhancing xylitol conversion from D-xylose during an oxygen-limited fermentation by Candida tropicalis. The fermentation was carried out in a 5 l jar fermenter. After glucose in the medium was depleted, a switching to a limited aeration and feeding glucose controlled by ORP-stat was performed. The maximum xylitol yield was obtained under a condition at an ORP of - 180 mV and at an aeration rate of 0.2 l min(-1).