High Aeration Rate Research Articles

Microtiter plate tests for segregation of bioluminescent bacteria

It has been recently shown that bioluminescence imaging can be usefully applied to provide new insights into bacterial self-organization. In this work we employ bioluminescence imaging to record images of nutrient rich liquid cultures of the lux-gene reporter Escherichia coli in microtiter plate wells. The images show that patterns of inhomogenous bioluminescence form along the three-phase contact lines. The paper analyzes the dependencies of the average number of luminous aggregates (clouds) on various environmental factors. In particular, our results show that optimal (neutral) pH and high aeration rates determine the highest mean number of clouds, and that spatiotemporal patterns do not form in the pH buffered suspensions. In addition, a sigmoidal (switch-like) dependence of the number of aggregates on the rate of aeration was observed. The obtained bioluminescence imaging data was interpreted by employing the Keller-Segel-Fisher (KSF) model of chemotaxis and logistic growth, adapted to systems of metabolically flexible (two-state) bacteria. The modified KSF model successfully simulated the observed switch-like responses. The results of the microtiter plate tests and their simulations indicate that the segregation of bacteria with different activities proceeds in the three-phase contact line region.

Effect of carbon sources on nitrous oxide emission in a modified Ludzak Ettinger process.

Effect of methanol and glycerol on nitrous oxide (N2O) emission in two laboratory-scale modified Ludzak Ettinger (MLE) processes was investigated during three distinct periods: dissolved oxygen (DO) control by intermittent aeration with a DO controller, and high and low aeration rates. N2O consumption rate in an anoxic tank and aeration mode influenced N2O emission rates from the MLE processes. In the DO control period, N2O emission rate from the glycerol-fed MLE process was higher than the methanol-fed counterpart, likely caused by a higher N2O consumption rate in an anoxic tank of the methanol-fed process. During the period of a higher aeration rate, N2O emission rates from both processes were comparable. In contrast, during the period of a lower aeration rate, N2O emission rate from the methanol-fed MLE process was higher than that from the glycerol-fed counterpart likely because of a higher degree of nitrite accumulation, corroborated by statistical analysis. N2O consumption activities of biomasses fed with the different carbon sources were distinct. However, the high activity did not necessarily result in a decrease in N2O emission rate from an aerobic tank and the effect of nitrite on the emission was stronger under the tested conditions.

Partial nitrification process by seeding aerobic and anaerobic granular sludge

In this study, the partial nitrification process was developed by seeding aerobic and anaerobic granular sludge into an airlift sequencing batch reactor. The effect of aeration rate on partial nitrifying granules was investigated at different ammonia concentrations. At a high aeration rate (1.72 cm/s), the nitrite accumulation rate of higher than 98% was accomplished. At a low aeration rate (0.12–0.26 cm/s), significant biomass detachment occurred on the surface of aerobic granular sludge whereas anaerobic granular sludge could maintain stable granular structure. Then, about 50% influent ammonium was oxidized to nitrite at dissolved oxygen concentration less than 1.5 mg/L. The Nitrosomonas in aerobic granular sludge was 16% after 30 d and was 33% after 80 d. The Nitrosomonas in anaerobic granular sludge was 3% after 50 d. Therefore, the development of partial nitrifying bacteria could be better in aerobic granular sludge.

Sewage sludge composting in a two-stage system: Carbon and nitrogen transformations and potential ecological risk assessment

The study examined how aeration rate (AR) in bioreactor (1.0 and 0.5l/minkgdm) at low C/N ratio (ca. 15–16) affected kinetics of organic matter (OM) removal, i.e. rate constant of OM removal (k) and maximum degradation of OM (A) and nitrogen evolution during sewage sludge composting. Moreover, potential ecological risk (Er) based on metal (Cd, Cr, Cu, Hg, Ni, Pb, Zn) content was evaluated. The process involved a two-stage system (bioreactor and windrow). In the bioreactor, at higher AR, k and A equaled 0.34d−1 and 101.9g/kgdm, respectively; at lower AR k was 0.38d−1, however A 1.4-fold lower. Interestingly, in the windrow, k was much higher (0.086d−1) for the biomass subjected to a lower AR, compared to 0.026d−1 at higher AR. Moreover, although at lower AR, k in the windrow was 4.4-fold lower than in the bioreactor, A was 1.15-fold higher. Total N content in mature compost was on the level 23.51–22.35g/kgdm and metal concentration showed low ecological risk (Er<16).

Stability and maturity of maize stalks compost as affected by aeration rate, C/N ratio and moisture content

To estimate the order of importance of factors affecting the stability and maturation of compost, cow feces and maize stalks were co-composted at different aeration rates AR (22, 44 and 66 L kg-1 DM . min-1) of C/N ratios (16, 19, 22), and moisture contents MC (60 %, 65 %, 70 %). A composting process was monitored by physical and chemical methods. The thermophilic phase with all treatments was long enough to meet sanitation requirements. The emitted carbon dioxide and the losses total organic carbon and total extractable carbon increased with increasing aeration rate, there was a significant difference between the treatments with low and high aeration rate, but no significant differences between those two treatments and the moderate aeration rate. The total nitrogen contents of all treatments decreased during the thermophilic phase, while it was increased after that for all treatments except T8. The compost with the highest initial C/N ratio was significantly different from the other treatments and had the highest values of humic substances, degree of humification and humification rate. The compost with the lowest initial C/N ratio was significantly different from the other treatments and had the lowest germination index (57-67%). Aeration rate was the main factor influencing compost stability, while the C/N ratio mainly contributed to compost maturity, and the moisture content had an insignificant effect on the compost quality. The recommended parameters for composting are an aeration rate of 0.44 L kg-1 DM. min-1 and a carbon to nitrogen ratio of 19 with moisture content of 60-70%.

Biotechnology Carbon Capture and Storage (CCS) by Mix-culture Green Microalgae to Enhancing Carbon Uptake Rate and Carbon Dioxide Removal Efficiency with Variation Aeration Rates in Closed System Photobioreactor

Carbon dioxide (CO2) sequestration by green microalgae is receiving increased attention in alleviating the impact of increasing CO2 in the atmosphere. The goal of this study was to explore the capacity of mixed culture green microalgae Chlorella sp, Scenedesmus obliquus, and Ankistrodesmus sp. as carbon capture and storage agent to enhance CO2 uptake rate and CO2 removal efficiency which was observed at elevated CO2 aeration rates of 2, 5, and 8 L min-1 supplied to vertical photobioreactor continuously in batch system culture. The operation condition of this research were 6.5-7.5 pH, temperature of 300C, light intensity of 4000 lux with 16 hours light period and 8 hours dark period, and high pure CO2 elevated level of 5 to 18 (concentration in %; v/v in the aeration gas) as inorganic carbon. The maximum CO2 removal efficiency of the mix culture was 59.80% when the biomass was obtained at 4.90 gL-1 and CO2 flow rate (Lmin-1) of 5 vvm in a vertical photobioreactor. The value of CO2 removal efficiency improved by almost 200% and 120% as compared to that in the low and high aeration rate (2 Lmin-1 and 8 Lmin-1) respectively. The CO2 up take rate of a mixed culture reach 979.62 mg carbon L-1day-1, which was enhancing by 3-fold in high aeration rate (8 Lmin-1). The results showed that the CO2 removal efficiency and carbon uptake rate was related to biomass concentration and aeration rate of CO2 supplied.

Effect of heterotrophic activities on nitrous oxide emission during nitrification under different aeration rates

Nitrous oxide (N2O), a greenhouse gas, can be released from both nitrification and denitrification during wastewater treatment. In this study, N2O emission under three aerobic conditions (aeration rates of 100, 250, and 500 ml/min, respectively) were examined, one with only endogenous heterotrophic activities, one with heterotrophic activities using internal stored organic carbon (polyhydroxybutyrate, PHB), and the other with heterotrophic activities using external organic carbon (acetate). Under the condition with PHB as the organic carbon, the released N2O-N to the produced oxidized nitrogen (NOx-N) was 10.0% at 100 ml/min, 3.6% at 250 ml/min, and 0.6% at 500 ml/min. Under the condition with acetate as the organic carbon, the released N2O-N to the produced NOx-N was 14.5% at 100 ml/min, 4.1% at 250 ml/min, and 0.7% at 500 ml/min. Under the condition without organic carbon, the released N2O-N to the produced NOx-N was 0.18% at 100 ml/min, 0.20% at 250 ml/min, and 0.41% at 500 ml/min. These results showed that (i) heterotrophic activities affected N2O emission during nitrification significantly; (ii) there was no significant difference in N2O emission during nitrification affected by heterotrophic activities using internal or external organic carbon; and (iii) a high aeration rate with a high dissolved oxygen concentration reduced N2O emission significantly under aerobic conditions.

Impact of loop seal structure on gas solid flow in a CFB system

In a circulating fluidized bed (CFB) boiler, loop seal is one of the most commonly used non-mechanical valves. When the solids are conveyed horizontally from the supply chamber to the recycle chamber through the horizontal section, the length of the horizontal section will cause much flow resistance, which not only influences the fan burden but also the pressure and mass balance between the furnace and the external loop.In this paper, a new structure loop seal with a slope passage connecting the supply and recycle chambers (named N-type) is described. The flow characteristic of quartz sand (Geldart-B particles) in the new loop seal was studied by comparison with the traditional loop seal (named U-type).The experimental data show that the passage design connecting the two chambers of a loop seal has an obvious effect on the gas solid flow not only in the loop seal, but also in other components in the whole loop. For the N-type loop seal, the minimum aeration rate required for the onset of solid flow is equal to the minimum fluidization velocity of the bed materials, much less than with the U-type loop seal. The solid recycling capability of the N-type loop seal is better than of U-type one at low aeration rate, but this status will be reversed at high aeration rate. A small amount of vertical aeration into the bottom of the standpipe can further improve the solid recycling capability of the N-type loop seal, by reducing the inter-particle friction and build up a higher pressure drop gradient in the standpipe. At the same time, less air bypassing upward into the cyclone through the standpipe is found for the N-type loop seal at high level of aeration rate, while, at the same condition the U-type suffers severe gas bypassing with a fluidized state in the standpipe. At last, the pressure drop of the new type loop seal is much less than the pressure drop of the traditional one with the same solid flow rate, which provides an advantage for reducing fan power and sustaining more solids in the boiler furnace.

Application of airlift bioreactor for the cultivation of aerobic oleaginous yeast Rhodotorula glutinis with different aeration rates

The high cost of microbial oils produced from oleaginous microorganisms is the major obstacle to commercial production. In this study, the operation of an airlift bioreactor is examined for the cultivation of oleaginous yeast-Rhodotorula glutinis, due to the low process cost. The results suggest that the use of a high aeration rate could enhance cell growth. The maximum biomass concentration of 25.40 g/L was observed in the batch with a 2.0 vvm aeration rate. In addition, a higher aeration rate of 2.5 vvm could achieve the maximum growth rate of 0.46 g/L h, about twice the 0.22 g/L h obtained in an agitation tank. However, an increase in tank pressure instead of the aeration rate did not enhance cell growth. The operation of airlift bioreactor described in this work has the advantages of simple operation and low energy consumption, thus making it suitable for the accumulation of microbial oils.

Biological Aerated Filter에서 유입 질소농도에 따른 아질산화 특성

The purpose of this study was to investigate the nitrification characteristics of biological aerated filter (BAF) packed with ceramic media, especially focusing on nitrite build-up during nitrification. When increasing the nitrogen load above 1.63 kgNH4 + -N/m 3 ·d, ammonium removal efficiency decreased to less than 60% and the nitrite ratio (NO2 - -N/NOx-N) of higher than 75% was achieved due to the inhibitory free ammonia (FA, NH3-N) concentration and oxygen limitation. FA inhibition, however, is not recommended strategy to promote nitrite build-up since FA concentration in the reactor is coupled with decreased ammonium removal efficiency. Nitrite ratio in the effluent was also affected by aeration rate and influent ammonium concentration. Ammonium oxidation was enhanced at a higher aeration rate regardless of influent ammonium concentration but, the nitrite ratio was dependent on both aeration rate and influent ammonium concentration. While a higher nitrite ratio was obtained when BAFs were fed with 50 mgNH 4 + -N/L of influent, the nitrite ratio significantly decreased for a greater influent concentration of 200-300 mgNH4 + -N/L. Taken together, aeration rate, influent ammonium concentration and FA concentrations kept in the BAF were found to be critical variables for nitrite accumulation in the BAF system.

Potential of aeration flow rate and bio-char addition to reduce greenhouse gas and ammonia emissions during manure composting

Aeration is an important factor influencing CO2, CH4, N2O and NH3 emissions from the composting process. Both CH4 and N2O are potent greenhouse gases (GHG) of high importance. Here, we examined the effects of high and low aeration rates together with addition of barley straw with and without bio-char on GHG and NH3 emissions from composting cattle slurry and hen manure in small-scale laboratory composters. Depending on treatment, cumulative C losses via CO2 and CH4 emissions accounted for 11.4–22.5% and 0.004–0.2% of initial total carbon, while N losses as N2O and NH3 emissions comprised 0.05–0.1% and 0.8–26.5% of initial total nitrogen, respectively. Decreasing the flow rate reduced cumulative NH3 losses non-significantly (by 88%) but significantly increased CH4 losses (by 51%) from composting of cattle slurry with barley straw. Among the hen manure treatments evaluated, bio-char addition to composting hen manure and barley straw at low flow rates proved most effective in reducing cumulative NH3 and CH4 losses. Addition of bio-char in combination with barley straw to hen manure at both high and low flow rates reduced total GHG emissions (as CO2-equivalents) by 27–32% compared with barley straw addition alone. Comparisons of flow rates showed that low flow could be an alternative strategy for reducing NH3 losses without any significant change in N2O emissions, pointing to the need for well-controlled composting conditions if gaseous emissions are to be minimised.

Designing of an Intensification Process for Biosynthesis and Recovery of Menaquinone-7

A nutritional food rich in menaquinone-7 has a potential in preventing osteoporosis and cardiovascular diseases. The static fermentation of Bacillus subtilis natto is widely regarded as an optimum process for menaquinone-7 production. The major issues for the bulk production of menaquinone-7 are the low fermentation yield, biofilm formation and the use of organic solvents for the vitamin extraction. In this study, we demonstrate that the dynamic fermentation involving high stirring and aeration rates enhances the yield of fermentation process significantly compared to static system. The menaquinone-7 concentration of 226 mg/L was produced at 1,000 rpm, 5 vvm, 40 °C after 5 days of fermentation. This concentration is 70-fold higher than commercially available food products such as natto. Additionally, it was found that more than 80% of menaquinone-7 was recovered in situ in the vegetable oil that was gradually added to the system as an anti-foaming agent. The intensification process developed in this study has a capacity to produce an oil rich in menaquinone-7 in one step and eliminate the use of organic solvents for recovery of this compound. This oil can, therefore, be used for the preparation of broad range of supplementary and dietary food products rich in menaquinone-7 to reduce the risk of osteoporotic fractures and cardiovascular diseases.

Feeding profile is not the sole factor influencing lovastatin production by Aspergillus terreus ATCC20542 in a continuous fed-batch stirred tank bioreactor

The effect of various feeding strategies with the use of glycerol and the mixture of glycerol and lactose on lovastatin biosynthesis in the continuous fed-batch stirred tank bioreactor by Aspergillus terreus ATCC20542 was studied. Within the first 24h of feeding the increase in lovastatin titre, even by 100%, compared with batch runs, was obtained. In this work, it was proved that apart from carbon substrate feeding other factors played a crucial role in lovastatin formation. These were redox potential level, air flow rate and carbonate carbon assimilation rate. Thus, their impact was also thoroughly examined. Under the conditions of the elevated redox potential, both initial and feeding carbon substrates were faster utilised, which led to the enhancement of lovastatin production. In the process with the highest redox potential levels maximum lovastatin concentration was equal to 83.8mgLOVl−1, while at the lowest redox level it did not reach 67mgLOVl−1. In turn, carbonate carbon as well as organic carbon were considerably better assimilated at the higher aeration rates, which also positively influenced lovastatin formation. All in all, there were several factors that had to occur simultaneously to achieve the satisfactory lovastatin titres.

Direct monitoring of sub-critical flux fouling in a horizontal double-end submerged hollow fiber membrane module using ultrasonic time domain reflectometry

Ultrasonic time-domain reflectometry (UTDR) as a non-invasive and real-time technique was employed to monitor the sub-critical flux fouling in a submerged hollow fiber membrane module (SHFMM) oriented horizontally. A single polyethersulfone hollow fiber membrane was used to filter 5g/L yeast suspension in the fouling experiment. The effect of aeration rate, fiber length and operating flux on the sub-critical flux fouling profiles was investigated. Results showed that the fouling distribution along fiber in the horizontal SHFMM was more uniform than that in the vertical SHFMM under the same conditions. The deposition of foulants gradually migrated from both suction ends to the middle part of fiber in the horizontal SHFMM. Further, a high aeration rate could effectively restrain the deposition of fouling, but could not completely eliminate membrane fouling. Moreover, shortening the length of horizontal SHFMM could not reduce membrane fouling. A low operating flux could effectively prevent from membrane fouling.

Production of biomass and bioactive compounds by adventitious root suspension cultures of Morinda citrifolia (L.) in a liquid-phase airlift balloon-type bioreactor

To improve root growth and production of bioactive compounds such as anthraquinones (AQ), phenolics, and flavonoids by adventitious root cultures of Morinda citrifolia, the effects of aeration rate, inoculum density, and Murashige and Skoog (MS) medium salt strengths were investigated using a balloon-type bubble bioreactor. The possible mechanisms underlying changes in activities of enzymic (superoxide dismutase, catalase, guaiacol peroxidase, ascorbate peroxidase) and nonenzymic (vitamin E) antioxidants, phenylalanine ammonia lyase, and stress levels (accumulation of hydrogen peroxide and proline, peroxidation of lipids) were also studied. Low aeration rate (0.05 vvm [air volume/culture volume/min]) accelerated accumulation of root fresh weight and dry weight (DW). High aeration rates (0.1 to 0.3 vvm) stimulated accumulation of AQ, phenolics, and flavonoids and reduced root growth. Low inoculum densities (5 and 10 g l–1) increased accumulation of those metabolites but inhibited root growth. Culture of adventitious roots with high concentrations of MS salts (1× and 1.5× MS) resulted in induction of oxidative stress that strongly inhibited root growth. Overall, an aeration rate of 0.05 vvm, 15 g l–1 inoculum density, and half-strength (0.5×) MS medium were optimal for enhancing accumulation of root dry biomass (4.38 g l–1), AQ (103.08 mg g–1 DW), phenolics (54.81 mg g–1 DW), and flavonoids (49.27 mg g–1 DW).

Use of slow glucose feeding as supporting carbon source in lactose autoinduction medium improves the robustness of protein expression at different aeration conditions

Recombinant protein expression from lac derived promoters by the autoinduction regime is based on diauxic growth of Escherichia coli on glucose and lactose. Glycerol is used as a supporting carbon source during the lactose-induced expression. While this glycerol-based formulation usually provides high cell densities, successful protein expression by autoinduction is often very dependent on correct aeration level. This complicates the reproducibility and scalability of the cultures. In this study we investigate the use of an alternative autoinduction formulation, in which the supporting carbon source is provided by fed-batch-like slow glucose feed from a biocatalytically degraded polysaccharide. The glucose feed as supporting carbon source allowed for high level of autoinduced target protein expression from T7lac promoter in E. coli BL21(DE3) and from T5lac promoter in E. coli K-12 RB791(lacIq) with lactose concentrations of 0.5–2gl−1. Cell densities and protein yields per culture volume were similar to or higher than in the glycerol-based ZYM-5052 medium. In the glycerol-based medium, protein production was adversely influenced by high aeration level, resulting in 75–90% reduction in protein yield per cell compared to more moderately aerated conditions. The glucose fed-batch medium attenuated this oxygen-sensitivity and provided robust high-yield expression also under high aeration rates. It is concluded that the slow glucose feed as supporting carbon source mitigates aeration-related scale differences in autoinduced protein expression, and combined with the benefit of high product yields this makes the fed-batch autoinduction medium ideal for high-throughput screening and scale-up of the production process.

Process Conditions Influence on Pig Slaughter House Compost Quality Under Forced Aeration

The objective of this paper was to study the influence of process conditions (aeration rate, bulking agent (BA) particle size distribution, BA incorporation ratio and process duration) on the quality (moisture, stability, disinfection as per the temperature regime and nitrogen conservation) of mechanically aerated pig slaughterhouse sludge (PSS) compost. The waste and wood chips as BA were composted in 300 L mechanically aerated reactors. The range of process conditions tested were: aeration rate from 1.68 to 13.04 L/h/kg of wet sludge; BA particle size distribution of <10 mm, 10–20 mm and 20–30 mm, and; BA:PSS incorporation ratio of 0.55–1.11 (kg of wet wood chips/kg of wet sludge). The results showed that a high aeration rate and a high BA:PSS ratio produced a faster stabilization whereas BA of small particles size distribution increased the amount of biodegradable matter and slowed down stabilization. The composting temperature regime was positively correlated to O2 consumption with a high BA:PSS ratio and a small BA particles size. A low aeration rate, without being O2 limiting, optimized the composting process since too high or too low an aeration rate favored heat losses through respectively convection and water evaporation. Water loss was positively correlated with temperature regime and a higher BA:PSS ratio as opposed to a small BA particle size distribution. Similarly, medium to high aeration rates favored water removal. The composting process duration was reduced with a high aeration rates of 6.22 or 9.8 L/h/kg of wet sludge and a high BA:PSS ratio of 1.11. Finally, process condition had no influence on compost nitrogen conservation.

Process Characterization of hCTLA4Ig Production in Transgenic Rice Cell Cultures Using a 3-L Bioreactor

Most of the technical know-how and experience of bioreactor engineering is applicable to plant cell cultures. In this study, transgenic rice cell cultures using RAmy3D promoter were used for the production of human cytotoxic T-lymphocyte antigen 4-immunoglobulin (hCTLA4Ig). In process aspect, the rice cells during production phase are strongly influenced by hydrodynamic stresses, such as shear stress and bubble burst. Therefore, the effects of agitation and aeration rates on cell growth and hCTLA4Ig production were investigated in a 3-L multi-bioreactor. By increasing over 240 rpm, the detrimental effects on cell growth and hCTLA4Ig production were observed. At an aeration rate of 0.3 vvm, relative cell viability sharply decreased 2 days earlier than those of lower aeration rates. In addition, it was confirmed that the specific yields and the specific productivity at 0.3 vvm were superior to those values at 0.05 vvm. Overall, higher aeration rate showed the improved hCTLA4Ig production in combination experiment. High aeration rates in general, however, have an undesired effect as excessive aeration was found to negatively affect the quality of hCTLA4Ig. Consequently, the hydrodynamic conditions must be tightly regulated during bioreactor operation in order to enhance hCTLA4Ig productivity and quality in transgenic rice cell cultures.

Effects of pH and microbial composition on odour in food waste composting

A major problem for composting plants is odour emission. Slow decomposition during prolonged low-pH conditions is a frequent process problem in food waste composting. The aim was to investigate correlations between low pH, odour and microbial composition during food waste composting. Samples from laboratory composting experiments and two large scale composting plants were analysed for odour by olfactometry, as well as physico-chemical and microbial composition. There was large variation in odour, and samples clustered in two groups, one with low odour and high pH (above 6.5), the other with high odour and low pH (below 6.0). The low-odour samples were significantly drier, had lower nitrate and TVOC concentrations and no detectable organic acids. Samples of both groups were dominated by Bacillales or Actinobacteria, organisms which are often indicative of well-functioning composting processes, but the high-odour group DNA sequences were similar to those of anaerobic or facultatively anaerobic species, not to typical thermophilic composting species. High-odour samples also contained Lactobacteria and Clostridia, known to produce odorous substances. A proposed odour reduction strategy is to rapidly overcome the low pH phase, through high initial aeration rates and the use of additives such as recycled compost.

Effect of CO2 supply conditions on lipid production of Chlorella vulgaris from enzymatic hydrolysates of lipid-extracted microalgal biomass residues

The hydrolysates from lipid-extracted microalgal biomass residues (LMBRs) were used as a source of nutrients for the cultivation of Chlorella vulgaris for lipid production under various CO2 supply conditions, including different CO2 concentrations and aeration rates. Both parameters had a significant effect on lipid production. A CO2 concentration of 5% was found to be most suitable for microalgal growth. Microalga grew best at a CO2 aeration rate of 0.5vvm. At this rate, biomass concentration and lipid productivity were at a maximum of 3.83gL−1 and 157mg L−1d−1, respectively, but decreased at lower or higher aeration rates. The present results showed that LMBRs utilization was effective in microalgal lipid production under suitable CO2 supply conditions.