Intense Aeration Research Articles

Monoculture and Mixed Culture of Pacific White Shrimp Litopenaeus vannamei and Tiger Shrimp Penaeus monodon in Biofloc System: A Comparative Study

The microbial modification method known as Biofloc Technology (BFT) has been used regularly in prawn culture operations lately. The primary component of BFT culture systems, microbial Biofloc, is responsible for improving water quality, supplementing natural nutrition, and encouraging the growth and welfare of grown prawns. An attempt has been made to investigate the effects of adding probiotics (Bacillus licheniformis and Lactobacillus rhamnosus) and the Biofloc system on water quality parameters and the performance of shrimp Litopenaeus vannamei and Penaeus monodon. Various external carbon sources, such as molasses and tapioca flour combinations, were used for the development of Bioflocs in the present study both under monoculture and mixed culture operations. Experimental diets comprising one control, one supplemented with probiotics and bioflocs (combinations of tapioca flour and molasses developed with varying external carbon sources), and both monoculture and mixed culture operations of Litopenaeus vannamei and Penaeus monodon were used in feeding trail experiments for about 120 days. Because mixtures of both Probiotics and Bioflocs were added, all the water quality indicators remained in optimal condition and provided resistance and protection against Candidate species of cultivation. Along with acting as a food supplement for prawns, intense mechanical aeration also promotes the microbial community's breakdown of toxic nitrogen and other pollutants. Productivity rates increased dramatically as a result. Therefore, BFT is an effective pathogen replacement, preserves ideal water quality, and boosts the growth and survival of prawns from L. vannamei and P. monodon. Probiotics and Bioflocs are used in combination in this work to maintain good water quality metrics and P. monodon and L. vannamei growth performance.

O2-enriched microbial activity with pH-sensitive solvo-chemical and electro-chlorination strategy to reclaim critical metals from the hazardous waste printed circuit boards

An innovative process integration for the sustainable recovery of critical metals from waste printed circuit boards (WPCBs) is demonstrated. In the acid pre-treatment of WPCBs, > 95% of highly toxic metals lead and tin could dissolve after 240 min of contact in 4.0 mol L−1 HNO3. Thereafter, the microbial activity of Sulfobacillus thermosulfidooxidans (strain RDB) under intense aeration is found favorable for base metals’ liberation. ~92% copper, 89% nickel, and 93% zinc get extracted at the optimal condition of O2-mixed-aeration, 30%; pulp density, 10 g L−1; aeration rate, 0.5 L min−1; sulfur dosage, 2%; temperature, 45 °C; and duration, 21 days. Quantitative separation of base metals is achieved using ketoxime as a function of equilibrium pH that yielding pH0.5 order: Cu (1.45) < Ni (5.7) < Zn (8.1). The residual gold from WPCBs is uniquely leached (~99% efficiency) in brine solution (2.0 mol L−1 NaCl) under the electro-chlorination rate, 0.62 mmol min−1; dissolution pH, 1.0; pulp density, 20 g L−1; temperature, 30 °C; and time, 60 min. Subsequently, gold from brine solution is solvated with tri-butyl-phosphate at pHeq, ≤ 0.5, forming [2(RP=O)·HAuCl4·H2O]¯ complex in the organic phase. Finally, > 99% of high-purity gold is stripped from loaded organic while contacting ammoniacal thiosulfate solution in two-stages of counter-current flow.

The Influence of Temperature Changes in Activated Sludge Processes on Ibuprofen Removal Efficiency

Abstract The article presents results regarding the ibuprofen reduction rate at three various temperature values (8, 18 and 28 °C) which were conducted using a static test in accordance with the PN-C-04645 ‘Water and wastewater. Evaluation of partial biodegradation of anionic and non-ionic surface active substances. Initial test’ standard. A single study cycle including the analysis of ibuprofen degradation rate in specific temperature variants lasted 24 h. The activated sludge for tests was obtained from the aeration zone of a bioreactor localized in the Central Wastewater Treatment Plant in Poznan City (Poland), which was used for inoculation (1 g/dm3) of sterile samples with the medium and ibuprofen (10 mg/dm3) after appropriate pre-treatment (intense aeration for 5 h). The analysis procedure included the separation and concentration of analytes from biodegradation samples by means of solid phase extraction (SPE) and subsequent determination with high performance liquid chromatography coupled with mass spectrometry (LC-MS/MS) using an UltiMate 3000 RSLC liquid chromatogram (Dionex, USA) with a tandem API 4000 QTRAP mass spectrometer (Biosystem, MDS Sciex, USA). Both literature review as well as the conducted initial studies confirmed that the removal of ibuprofen proceeds more rapidly at higher temperature values. A higher retention rate also enhanced the reduction of ibuprofen concentration. A decrease of its concentration was observed after 24 h, which reached 40 and 50 % for temperature values of 8 and 18 °C, accordingly, whereas the highest reduction by approx. 65 % was noted at 28 °C.

Temporal trends in live foraminiferal assemblages near a pollution outfall on the Levant shelf

Long and short term effects of activated sewage sludge input on live benthic foraminiferal assemblages of the shallow shelf off Palmachim, Israel were examined at three stations along the eutrophic gradient. Over ten years from 2003 to 2012, foraminiferal abundance decreased dramatically by >50% in all stations. In 2012, new species were found near the discharge point, relative abundance of the dominant species decreased and in-sediment depth increased. In the remote stations the dominant species failed to bloom seasonally. Each year, dispersion of sludge was accompanied by intense current activity, aeration, and periodic local sediment transport, reintroducing species from nearby. Storm frequency was notably high in 2012. The decrease in numbers over time despite seasonal amelioration indicates that the constant OM input is a permanent source of environmental stress. Aside from this stress, natural variability, changes in Nile input, or a hidden impact of long-term climate change may play a role.

Aeration and Foam Control in Baker's Yeast Production: Mapping Patents.

A key ingredient in the baking industry, baker's yeast must be produced under strict controlled conditions. High yields of baker's yeast cannot be attained unless a huge quantity of air is injected into fermentation vats. This review of 245 patent specifications shows that inventors have paid much attention to the distribution of fine air bubbles in order to optimize oxygen transfer to the yeast cells. Technical solutions to reduce energy costs associated with aeration are also proposed. Intense aeration caused foaming problems, so mechanical destruction of foam was first proposed until inventions on specific chemical antifoams were patented. In recent years, the development of cheaper and more efficient foam control techniques has remained an issue. Aeration during yeast growth in tanks impairs its fermentative activity in anaerobic bread dough. Since the beginning of the 20th century, massive adoption of air-grown fed-batch baker's yeast probably encouraged sugar addition to stimulate yeast gassing activity in pan bread characterized by high loaf volume, especially those prepared under short dough fermentation conditions.

Interaction between free-surface aeration and total pressure on a stepped chute

Stepped chutes have been used as flood release facilities for several centuries. Key features are the intense free-surface aeration of both prototype and laboratory systems and the macro-roughness caused by the stepped cavities. Herein the air bubble entrainment and turbulence were investigated in a stepped spillway model, to characterise the interplay between air bubble entrainment and turbulence, and the complicated interactions between mainstream flow and cavity recirculation motion. New experiments were conducted in a large steep stepped chute (θ=45°, h=0.10m, W=0.985m). Detailed two-phase flow measurements were conducted for a range of discharges corresponding to Reynolds numbers between 2×105 and 9×105. The total pressure, air–water flow and turbulence properties were documented systematically in the mainstream and cavity flows. Energy calculations showed an overall energy dissipation of about 50% regardless of the discharge. Overall the data indicated that the bottom roughness (i.e. stepped profile) was a determining factor on the energy dissipation performance of the stepped structure, as well as on the longitudinal changes in air–water flow properties. Comparative results showed that the cavity aspect ratio, hence the slope, has a marked effect on the residual energy.

Tolerance and Avoidance Characteristics of Prenant's Schizothoracin Schizothorax prenanti to Total Dissolved Gas Supersaturated Water

AbstractWhen water is allowed to spill over a hydroelectric dam, the intense aeration and pressure in the deep plunge‐pool produced by the high‐volume discharge generates water supersaturated with total dissolved gases (TDGs) in areas downstream from the dam, which can cause gas bubble disease (GBD) in fish and threaten their survival. Experiments were conducted to measure the acute lethality, intermittent exposure, horizontal avoidance, and vertical avoidance of Prenant's Schizothoracin Schizothorax prenanti related to TDG supersaturation. The fish were placed in different tanks containing TDG‐supersaturated water at a maximum water depth of 35 cm, and the resulting median lethal times (LT50) determined for the fish were 23.88, 9.66, 8.74, 8.03, 4.61, 3.48, and 2.81 h when the TDG supersaturation levels were 120, 125, 130, 135, 140, 145, and 150%, respectively. The LT50 values of the fish in continuous exposure conditions were not significantly different from the LT50 values of fish subjected to intermittent exposure (F = 2.72, df = 9,10, P = 0.07). In all of the avoidance experiments, Prenant's Schizothoracin exhibited varying degrees of horizontal escape from and strong vertical avoidance of TDG‐supersaturated water. These results provide important information that can be used in operational processes at hydropower stations in China and contribute fundamental data for the establishment of water‐related environmental standards for this and similar species.Received November 1, 2014; accepted May 8, 2015

Methods to reduce bacterial contamination of recycling cooling systems of a CHPP

Bacterial contamination of circulating and make-up water of the nonconjugated recycling cooling system with evaporative cooling towers of thermal power plants is studied. The nonconjugated recycling cooling system of Naberezhnochelninskaya CHP Plant was selected as the object of study. It was found that circulating water of recycling cooling is highly contaminated with aerobic heterotrophic bacteria. At the same time, make-up water for the cooling system from the Kama River is moderately polluted with anaerobic bacteria. Measurements of biological contamination in different parts of the recycling cooling system showed that populations of colonies of microorganisms abruptly decreases in turbine condensers, which is probably indicative of their death and deposition on the heat transfer surface of the condenser. Calculation using a special program showed that biological contamination of the recycling cooling system poses the greatest risks for clogging of the equipment (seven points on a nine-point scale), its corrosion (two points), and damage to the health of personnel (two points). Rapid development of aerobic bacteria apparently occurs under elevated temperature and intense aeration of water in the cooling tower. It is suggested to periodically monitor the recycling cooling system for biological pollution and to set a timetable for bactericidal treatment of circulating water depending on the level of its bacterial contamination.

Experimental Study of Turbulent Fluctuations in Hydraulic Jumps

AbstractIn an open channel, the transformation from a supercritical flow into a subcritical flow is a rapidly varied flow with large turbulent fluctuations, intense air entrainment, and substantial energy dissipation called a hydraulic jump. New experiments were conducted to quantify its fluctuating characteristics in terms of free-surface and two-phase flow properties for a wide range of Froude numbers (3.8<F1<8.5) at relatively large Reynolds numbers (2.1×104<R<1.6×105). The time-averaged free-surface profile presented a self-similar profile. The longitudinal movements of the jump were observed, showing both fast and very slow fluctuations for all Froude numbers. The air–water flow measurements quantified the intense aeration of the roller. Overall the present findings demonstrated the strong interactions between the jump roller turbulence and free-surface fluctuations.

Effect of aeration regime on N2O emission from partial nitritation-anammox in a full-scale granular sludge reactor

N2O emission from wastewater treatment plants is high of concern due to the strong environmental impact of this greenhouse gas. Good understanding of the factors affecting the emission and formation of this gas is crucial to minimize its impact. This study addressed the investigation of the N2O emission dynamics in a full-scale one-stage granular sludge reactor performing partial nitritation-anammox (PNA) operated at a N-loading of 1.75 kg NH4+–N m−3 d−1. A monitoring campaign was conducted, gathering on-line data of the N2O concentration in the off-gas of the reactor as well as of the ammonium and nitrite concentrations in the liquid phase. The N2O formation rate and the liquid N2O concentration profile were calculated from the gas phase measurements. The mean (gaseous) N2O–N emission obtained was 2.0% of the total incoming nitrogen during normal reactor operation. During normal operation of the reactor under variable aeration rate, intense aeration resulted in higher N2O emission and formation than during low aeration periods (mean N2O formation rate of 0.050 kg N m−3 d−1 for high aeration and 0.029 kg N m−3 d−1 for low aeration). Accumulation of N2O in the liquid phase was detected during low aeration periods and was accompanied by a relatively lower ammonium conversion rate, while N2O stripping was observed once the aeration was increased. During a dedicated experiment, gas recirculation without fresh air addition into the reactor led to the consumption of N2O, while accumulation of N2O was not detected. The transition from a prolonged period without fresh air addition and with little recirculation to enhanced aeration with fresh air addition resulted in the highest N2O formation (0.064 kg N m−3 d−1). The results indicate that adequate aeration control may be used to minimize N2O emissions from PNA reactors.

α-Acetolactate overexpression from glucose in the diacetyl producer Lactococcus lactis ssp. lactis bv. diacetylactis B2103, a natural mutant lacking α-acetolactate decarboxylase

We investigated the effects of the oxygen supply rate on the activity of pyruvate metabolic pathways and their end products, the lactatedehydrogenase (LDH), pyruvateformiatelyase (PFL), pyruvatedehydrogenase (PDH) and acetolactatesynthase (ALS) pathways, in the Lactococcus lactis ssp. lactis bv. diacetylactis strain B2103/74. We found that this culture, apart from inactivated α-acetyldecarboxylase, also possesses a unique natural capacity to overexpress α-acetolactate (AL) up to 25–28 mM. Our search for similar properties among the diacetilicus bv. strains showed that this ability is quite rare. We identified a single additional strain, 7590 from the National Russian Collection of Industrial Microorganisms (NRCIM-7590), which displayed a similar capacity. However, unlike B2103/74, NRCIM-7590 has an active α-acetolactate decarboxylase and therefore can only produce acetoin. AL overexpression took place under conditions of intense aeration (KLa ≥ 90–120 h−1), and the composition of the medium played a decisive role in AL productivity. We found that AL overproduction is determined by a diversion of a portion of pyruvate flow from the LDH to the PDH and ALS pathways. We further found that all additional pyruvate, supplied from LDH, is utilized exclusively by the ALS pathway because of the restricted capacity of the PDH pathway. This shift in pyruvate metabolism in the B2103/74 strain, from LDH to PDH and ALS pathways, is associated with the initiation of an oxidation reaction that reduces oxygen to H2O and sequesters NADH from the LDH pathway in the process. A specific manifestation of this reaction in B2103/74 and NRCIM-7590 cultures, which results in a profound shift of the pyruvate metabolism towards the production of α-acetolactate, is due to the function of a potent oxidative system that shifts 75–80% of NADH flow from LDH to the oxidative pathway, resulting in the regeneration of NAD+. The nature of this oxidative system is not known. Based on our studies, we propose that the structure of the newly discovered oxidative system is similar to a simple transmembrane electron transport chain.

Maximum stable drop size measurements indicate turbulence attenuation by aeration in a 3 m3 aerated stirred tank

In this study, break-up controlled drop dispersion experiments in a 3m3 pilot scale reactor with 1.2m inner diameter are presented that allow a correlation of the maximum local energy dissipation rate in stirred reactors with intense aeration. Experiments with two different setups of 6-bladed Rushton turbine impellers with diameters of d=0.41m (d/DR=0.34) and d=0.51m (d/DR=0.43) in a 3 impeller configuration were conducted. The results from experiments without aeration are well in agreement with the existing literature on drop dispersion. The results from experiments with aeration indicate a strong attenuation of turbulence intensity in stirred tank reactors by the presence of air. The ratio between maximum and volume-averaged energy dissipation rate was reduced by aeration by 64% for the d/DR=0.34 impeller and by 52% for the d/DR=0.43 impeller when compared with unaerated operating conditions on the basis of equal volumetric power input. The value of the aeration rate had no measurable effect in the range of aeration rates applied, which was between 0.1vvm (volume of gas/volume liquid/minute) and 1vvm.

Detection of anaerobic processes and microorganisms in immobilized activated sludge of a wastewater treatment plant with intense aeration

Attached activated sludge from the Krasnaya Polyana (Sochi) wastewater treatment plant was studied after the reconstruction by increased aeration and water recycle, as well as by the installation of a bristle carrier for activated sludge immobilization. The activated sludge biofilms developing under conditions of intense aeration were shown to contain both aerobic and anaerobic microorganisms. Activity of a strictly anaerobic methanogenic community was revealed, which degraded organic compounds to methane, further oxidized by aerobic methanotrophs. Volatile fatty acids, the intermediates of anaerobic degradation of complex organic compounds, were used by both aerobic and anaerobic microorganisms. Anaerobic oxidation of ammonium with nitrite (anammox) and the presence of obligate anammox bacteria were revealed in attached activated sludge biofilms. Simultaneous aerobic and anaerobic degradation of organic contaminants by attached activated sludge provides for high rates of water treatment, stability of the activated sludge under variable environmental conditions, and decreased excess sludge formation.

Measurement of maximum stable drop size in aerated dilute liquid–liquid dispersions in stirred tanks

Turbulence intensity, or hydromechanical stress, is a controlling parameter in many industrially relevant processes. Especially fermentation processes are often characterized by intense aeration and agitation, operating conditions for which the measurement of turbulence intensity is extremely difficult. Since the maximum stable drop diameter in a break-up controlled dispersion is directly correlated with turbulence intensity, the measurement of drop sizes can enable an indirect access to the intensity of turbulence under such operating conditions. This work presents the constraints and the development of a method for the measurement of maximum stable drop size in aerated liquid–liquid dispersions in stirred tanks for the purpose of characterizing turbulence intensity. Continuous and dispersed phase properties were selected to achieve a break-up controlled dispersion with negligible coalescence. This was accomplished mainly by applying a dilute dispersion, a low ionic strength and by incorporating a dispersed phase, paraffin oil, with a negative spreading coefficient. The negative spreading coefficient prevents coalescence due to drop–bubble interactions for aerated operating conditions. It was demonstrated that the off-line measured drop size distributions are representative for the conditions in the bioreactor and are not altered by sample handling. The sampling and measurement procedure was found to be highly reproducible with a standard deviation for the maximum stable drop size for independent experiments of approximately 10%. Relevant constraints for the application of the method in large-scale experiments were discussed and accounted for during method development to allow a later application in production scale equipment.

Turbulence and aeration in hydraulic jumps: free-surface fluctuation and integral turbulent scale measurements

In an open channel, a change from a supercritical to subcritical flow is a strong dissipative process called a hydraulic jump. Herein some new measurements of free-surface fluctuations of the impingement perimeter and integral turbulent time and length scales in the roller are presented with a focus on turbulence in hydraulic jumps with a marked roller. The observations highlighted the fluctuating nature of the impingement perimeter in terms of both longitudinal and transverse locations. The results showed further the close link between the production and detachment of large eddies in jump shear layer, and the longitudinal fluctuations of the jump toe. They highlighted the importance of the impingement perimeter as the origin of the developing shear layer and a source of vorticity. The air–water flow measurements emphasised the intense flow aeration. The turbulent velocity distributions presented a shape similar to a wall jet solution with a marked shear layer downstream of the impingement point. The integral turbulent length scale distributions exhibited a monotonic increase with increasing vertical elevation within 0.2 < Lz/d1 < 0.8 in the shear layer, where Lz is the integral turbulent length scale and d1 the inflow depth, while the integral turbulent time scales were about two orders of magnitude smaller than the period of impingement position longitudinal oscillations.

Investigation of long-term operation and biomass activity in a membrane bioreactor system

The aim of this work was to evaluate the long-term performance of a Membrane Bioreactor (MBR) that operated continuously for 2.5 years and to assess membrane fouling and biomass activity under various operating conditions. Furthermore, a method for the characterisation of influent wastewater was developed based on its separation into various fractions. The MBR system operated at the solids retention times (SRT) of 10, 15, 20 and 33 days. The increase of SRT resulted in a decrease of the fouling rate associated with the reduction of extracellular polymeric substances. Moreover, the SRT increase resulted in a significant reduction of the Oxygen Uptake Rate (OUR) due to the lower availability of substrate and in a notable decrease of the maximum OUR since high SRT allowed the development of slower growing microorganisms. Biomass consisted of small flocs due to extensive deflocculation caused by intense aeration. Finally, the method developed for wastewater characterisation is straightforward and less time consuming than the usual method that is employed.

Regulation of metabolic pathways in sulfobacilli under different aeration regimes

A comparative study of the activities of the enzymes of carbon metabolism from the cells of moderately thermophilic chemolithotrophic bacteria Sulfobacillus sibiricus (strains N1 and SSO) and Sulfobacillus thermosulfidooxidans subsp. asporogenes (strain 41) was carried out grown in a high layer of medium without forced aeration and cells grown with intense aeration. Limited air access to the growing S. sibiricus N1 cells resulted in switching from the pentose phosphate pathway of glucose metabolism to the Entner-Doudoroff pathway while the Embden-Meyerhof-Parnas pathway persisted. Irrespective of the level of the aeration, in the cells of S. sibiricus SSO and S. thermosulfidooxidans subsp. asporogenes 41, degradation of the glucose occurred via the Entner-Doudoroff and pentose phosphate metabolic pathways, respectively, as well as via the Embden-Meyerhof-Parnas pathway. Prolonged growth of S. sibiricus, strains N1 and SSO, in a high layer of the medium without forced aeration led to the repression of synthesis of most of the tricarboxylic acid cycle (TCA cycle) enzymes, in particular dehydrogenases, as well as of some carboxylases including RuBisCO. The traits of carbon metabolism in various strains of Sulfobacillus under conditions of oxygen deficiency are discussed.

Weathering of gasification and grate bottom ash in anaerobic conditions

The effect of anaerobic conditions on weathering of gasification and grate bottom ash were studied in laboratory lysimeters. The two parallel lysimeters containing the same ash were run in anaerobic conditions for 322 days, after which one was aerated for 132 days. The lysimeters were watered throughout the study and the quality of leachates and changes in the binding of elements into ash were observed. The results show that organic carbon content and initial moisture of ashes are the key parameters affecting the weathering of ashes. In the grate ash the biodegradation of organic carbon produced enough CO 2 to regulate pH. In contrast the dry gasification ash, containing little organic carbon, was not carbonated under anaerobic conditions and the pH decreased only after aeration was started. During the aeration the CO 2 absorption capacity was not reached, indicating that intense aeration would be needed to fully carbonate gasification ash. The results indicate that in common weathering practice the main emissions-reducing processes are leaching and carbonation due to CO 2 from biodegradation. The results of the aeration study suggest that the role of atmospheric CO 2 in the weathering process was insignificant.

Municipal waste sludge digestion in an autothermal aerobic sequencing batch reactor

An autothermal aerobic sequencing batch process for sludge digestion and "class A" biosolids production was developed. The process was tested in laboratory and pilot scale size up to 150 PE, which can be considered a full scale size in some cases. In this process the maximum temperatures of 61.2 degrees C and 60.2 degrees C were achieved in laboratory scale in pilot scale equipment, respectively. The degradation efficiency of total chemical oxygen demand of sludge was between 50 and 70%. Similar results were achieved using pure oxygen in laboratory scale and oxygen/air mixture 1:1 by volume. The reactor scale greatly affects the achievement of thermophilic temperature. In smaller sizes the convective heat losses are the prevailing heat sink and the process is unable to produce enough heat to reach thermophilic temperature. Larger systems produce excess heat and can be installed with less intense aeration systems. The limit of air aeration system is at the size of about 500 PE.

PERFORMANCE OF A HIGH‐RATE/HIGH‐SHEAR ACTIVATED SLUDGE BIOREACTOR TREATING BIODEGRADABLE WASTEWATER

A high‐rate activated sludge (HRAS) bioreactor with high shear venturi aeration was operated in the laboratory at various organic loading rates to evaluate chemical oxygen demand (COD) removal efficiency and sludge production. Organic loading rates two orders of magnitude higher than conventional activated sludge loading were investigated in the modified HRAS reactor for a period of 41 weeks. Filtered COD removal efficiency varied from 81 to 92 % for organic loading rates of 3 to 85 kg COD m−3 d−1. Observed sludge yield was determined to be 0.10–0.25 g TSS produced g−1 COD removed, under hydraulic and solids retention times (SRTs) approaching less than two hours and two days, respectively. Observed sludge yield actually declined as loading increased and SRT decreased. It was concluded that high‐shear forces created in the reactor due to intense aeration at high volumetric organic loading rates increased substrate utilization rate, improved filtered COD removal efficiency, and kept sludge yields relatively low (despite the very low operating SRTs).