Search Results (14)

Dyes are widely used in various industries, but their removal from wastewater remains a challenge due to their resistance to biodegradation. While substantial research exists regarding the removal of individual dyes, there is much less about the removal of their mixtures. The aim of the research was to determine the possibility of using the immobilised mycelium of Pleurotus ostreatus strains to remove three-component mixtures of dyes from different classes. Efficiency of the removal in the continuously aerated reactor was similar to that obtained in a periodically aerated reactor and was over 90% at the end of each cycle. Despite the addition of subsequent portions of dyes, no increase in the toxicity of post-process samples was observed, and even a decrease in zootoxicity was noticed. The results of the study therefore indicate that an immobilised biomass can be used to remove the dyes, without the need to constantly inject air into the reactor. Full article

Chlorella sp. was cultivated in a closed system using PET bottles (5 L) and with the continuous injection of air and commercial gas (98% CO₂) and in simulated conditions (15% CO₂, 73% N₂, and 12% O₂). The culture medium was prepared using well water and mining wastewater, the cultivation period occurred in a 10-day cycle, and the cell growth curves were evaluated through cell counting using a Neubauer chamber. The cultivation was carried out under the following conditions: temperature at 22 °C to 25 °C; aeration rate with commercial and simulated CO₂ gas at 0.01 vvm; and synthetic air containing 0.042% CO₂. The dry biomass productivity was 0.81 g·L⁻¹·day⁻¹ and the maximum CO₂ fixation rate was 0.90 g·L⁻¹·day⁻¹ when the microalgae were cultivated with a continuous flow of simulated waste gas and a culture medium composed of wastewater. The percentages of macromolecules obtained in the biomass cultivated in wastewater reached 20.95%, 26.48%, and 9.3% for lipids, proteins, and carbohydrates, respectively. Full article

Microbial biosurfactants are considered environmentally friendly alternatives to synthetic surfactants in numerous applications. One of the main bottlenecks to their widespread use is the lack of effective processes for their production on an industrial scale. Biosurfactant production using conventional aerated bioreactors results in excessive foaming due to the combination of air injection and their tensioactive properties. A not widely explored approach to overcome this problem is the development of foam-free production processes, which require the identification and characterization of appropriate microorganisms. Bacillus licheniformis EL3 was evaluated for biosurfactant production under oxygen-limiting conditions in a bioreactor, using a mineral medium containing glucose as a carbon source and NaNO₃ and NH₄Cl as nitrogen sources. After optimizing the operational conditions, glucose concentration, and inoculum strategy, B. licheniformis EL3 produced 75 ± 3 mg biosurfactant/L in 43 h. The purified biosurfactant exhibited exceptional surface active properties, with minimum surface tension values (29 mN/m) and a critical micelle concentration (27 mg/L) similar to those achieved with commercial surfactin. Furthermore, biosurfactant yield per substrate (Y_P/S = 0.007 g biosurfactant/g glucose) was similar to the figures reported for Bacillus subtilis strains grown in similar conditions, whereas biosurfactant yield per biomass (Y_P/X = 0.755 g biosurfactant/g biomass) and specific biosurfactant productivity (q_BS = 0.018 g biosurfactant/(g biomass × h)) were almost three times higher when compared to previous reports. The results obtained indicate that B. licheniformis EL3 is a promising candidate for the development of foam-free biosurfactant production processes at an industrial scale. Full article

Aerated drip irrigation is rendered as a new water-saving irrigation method based on drip irrigation technology, which is endowed with the function of effectively alleviating the problem of rhizosphere hypoxia in crop soil, enhancing the utilization rate of water and fertilizer; as a result, it improves the harvest and quality of crops. However, clogged emitters are important indexes, among others, that pose an influence to the service effect and life duration of drip irrigation systems. At present, the working principle and mechanism of the influence of air feeding on the blockage of drip irrigation emitters remain unclear. Therefore, based on the two gas filling methods of the micro/nano bubble generator and Venturi injector, the dynamic change process for the average flow ratio of an air-filled drip irrigation emitter was studied by the method of emitter plugging test. 16S rRNA sequencing was used to analyze the microbial diversity of the emitter plugs. The results show that the air injection can pose influence on the clogging procedure of drip irrigation emitters, and more importantly, it makes the distribution of blocked emitters more uniform, thus improving the uniformity of the system. Different filling methods have different effects on the blockage of the emitter. Among them, the blockage time of drip irrigation system under the micro/nano aerated drip irrigation (MAI) mode is 5.73 times longer than that under unaerated drip irrigation (UVI), and similarly, Venturi gas drip irrigation (VAI) is close to that under UVI. The filling method changed the microbial diversity of the blockage in the emitter. Among them, the number of operational taxonomic unit (OTU) unique to MAI was 2.1 times that of UVI, and the number of OTU unique to VAI was 1.3 times that of UVI. Meanwhile, gas addition will inhibit the growth of Nitrospirae and Proteobacteria microbial communities and promote the growth of Firmicutes and Actinobacteria microbial communities. Furthermore, the increase in microbial extracellular polymer in the plugging material of the emitter was inhibited and the plugging process of the emitter was slowed down. The research results are of great significance in the disclosure of the clogging mechanism of drip irrigation emitter and constructing the green, anti-blockage technology of aerated drip irrigation. Full article

Iron oxidation and removal from groundwater is a necessary and costly process in drinking water production. In most cases, iron removal is done via aeration, succeeded by precipitation. Most systems for aeration are based on increasing the interfacial area via injecting air in the system or spraying. Both methods have disadvantages, like clogging and formation of aerosols. In this study, a new vortex-based flow-through reactor consisting of a cylindrical tank with an impeller located at the bottom was studied regarding its aeration and iron oxidation capabilities in groundwater. During the aeration experiments, the flow rate, impeller rotation and aerated volume were varied. A nondimensional constant α was proposed to relate the system’s physical characteristics and its aeration capabilities, expressed in dissolved oxygen and system volumetric mass transfer coefficient (K_La). Three distinct operational regimes were defined: formation, complete and bubble regime. These regimes showed very specific characteristics regarding the air–water interface structure and the area to volume ratio, resulting in different aeration capabilities and iron oxidation efficiency values. The system presented K_La values similar to commercially available aeration systems, especially inside the bubble regime. By using dimensionless coefficients, the presented analysis provided the basis for the design of continuous impeller aeration and oxidation systems of arbitrary size. Full article

The fluidized particle-in-tube solar receiver concept is promoted as an attractive solution for heating particles at high temperature in the context of the next generation of solar power tower. Similar to most existing central solar receivers, the irradiated part of the system, the absorber, is composed of tubes in which circulate the fluidized particles. In this concept, the bottom tip of the tubes is immersed in a fluidized bed generated in a vessel named the dispenser. A secondary air injection, called aeration, is added at the bottom of the tube to stabilize the flow. Contrary to risers, the particle mass flow rate is controlled by a combination of the overpressure in the dispenser and the aeration air velocity in the tube. This is an originality of the system that justifies a specific study of the fluidization regimes in a wide range of operating parameters. Moreover, due to the high value of the aspect ratio, the particle flow structure varies along the tube. Experiments were conducted with Geldart Group A particles at ambient temperature with a 0.045 m internal diameter and 3 m long tube. Various temporal pressure signal processing methods, applied in the case of classical risers, are applied. Over a short acquisition time, a cross-reference of the results is necessary to identify and characterize the fluidization regimes. Bubbling, slugging, turbulent and fast fluidization regimes are encountered and the two operation modes, without and with particle circulation, are compared. Full article

Airlift pumps can be used in the aquaculture industry to provide aeration while concurrently moving water utilizing the dynamics of two-phase flow in the pump riser. The oxygen mass transfer that occurs from the injected compressed air to the water in the aquaculture systems can be experimentally investigated to determine the pump aeration capabilities. The objective of this study is to evaluate the effects of various airflow rates as well as the injection methods on the oxygen transfer rate within a dual injector airlift pump system. Experiments were conducted using an airlift pump connected to a vertical pump riser within a recirculating system. Both two-phase flow patterns and the void fraction measurements were used to evaluate the dissolved oxygen mass transfer mechanism through the airlift pump. A dissolved oxygen (DO) sensor was used to determine the DO levels within the airlift pumping system at different operating conditions required by the pump. Flow visualization imaging and particle image velocimetry (PIV) measurements were performed in order to better understand the effects of the two-phase flow patterns on the aeration performance. It was found that the radial injection method reached the saturation point faster at lower airflow rates, whereas the axial method performed better as the airflow rates were increased. The standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE) were calculated and were found to strongly depend on the injection method as well as the two-phase flow patterns in the pump riser. Full article

The intermittent nature of most renewable energy sources requires their coupling with an energy storage system, with pumped storage hydropower (PSH) being one popular option. However, PSH cannot always be constructed due to topographic, environmental, and societal constraints, among others. Underground pumped storage hydropower (UPSH) has recently gained popularity as a viable alternative and may utilize abandoned mines for the construction of the lower reservoir in the underground. Such underground mines may have complex geometries and the injection/pumping of large volumes of water with high discharge could lead to uneven water level distribution over the underground reservoir subparts. This can temporarily influence the head difference between the upper and lower reservoirs of the UPSH, thus affecting the efficiency of the plant or inducing structural stability problems. The present study considers an abandoned slate mine in Martelange in Southeast Belgium as the lower, underground, reservoir of an UPSH plant and analyzes its hydraulic behavior. The abandoned slate mine consists of nine large chambers with a total volume of about 550,000 m³, whereas the maximum pumping and turbining discharges are 22.2 m³/s. The chambers have different size and they are interconnected with small galleries with limited discharge capacity that may hinder the flow exchange between adjacent chambers. The objective of this study is to quantify the effect of the connecting galleries cross-section and the chambers adequate aeration on the water level variations in the underground reservoir, considering a possible operation scenario build upon current electricity prices and using an original hydraulic modelling approach. The results highlight the importance of adequate ventilation of the chambers in order to reach the same equilibrium water level across all communicating chambers. For fully aerated chambers, the connecting galleries should have a total cross-sectional area of at least 15 m² to allow water flow through them without significant restrictions and maintain similar water level at all times. Partially aerated chambers do not attain the same water level because of the entrapped air; however, the maximum water level differences between adjacent chambers remain relatively invariant when the total cross-sectional area of the connecting galleries is greater than 8 m². The variation of hydraulic roughness of the connecting galleries affects the water exchange through small connecting galleries but is not very influential on water moving through galleries with large cross-sections. Full article

This study aims to monitor the biological processes ongoing in a hydrocarbon polluted soil. The experiments were carried out at a laboratory scale by measuring the evolution of its geophysical electromagnetic parameters. Time-domain reflectometry (TDR) probes were used to measure dielectric permittivity and electrical conductivity in columns of sandy soil artificially contaminated with diesel oil (V_oil/V_tot = 0.19). To provide aerobic conditions suitable for the growth of microorganisms, they were hydrated with Mineral Salt Medium for Bacteria. One mesocosm was aerated by injecting air from the bottom of the column, while the other had only natural aeration due to diffusion of air through the soil itself. The monitoring lasted 105 days. Geophysical measurements were supported by microbiological, gas chromatographic analyses, and scanning electron microscope (SEM) images. Air injection heavily influenced the TDR monitoring, probably due to the generation of air bubbles around the probe that interfered with the probe–soil coupling. Therefore, the measurement accuracy of geophysical properties was dramatically reduced in the aerated system, although biological analyses showed that aeration strongly supports microbial activity. In the non-aerated system, a slight (2%) linear decrease of dielectric permittivity was observed over time. Meanwhile, the electrical conductivity initially decreased, then increased from day 20 to day 45, then decreased again by about 30%. We compared these results with other researches in recent literature to explain the complex biological phenomena that can induce variations in electrical parameters in a contaminated soil matrix, from salt depletion to pore clogging. Full article

Hydrogen sulfide (H₂S) is a corrosive trace gas present in biogas produced from anaerobic digestion systems that should be removed to reduce engine-generator set maintenance costs. This study was conducted to provide a more complete understanding of two H₂S scrubbers in terms of efficiency, operational and maintenance parameters, capital and operational costs, and the effect of scrubber management on sustained H₂S reduction potential. For this work, biogas H₂S, CO₂, O₂, and CH₄ concentrations were quantified for two existing H₂S scrubbing systems (iron-oxide scrubber, and biological oxidation using air injection) located on two rural dairy farms. In the micro-aerated digester, the variability in biogas H₂S concentration (average: 1938 ± 65 ppm) correlated with the O₂ concentration (average: 0.030 ± 0.004%). For the iron-oxide scrubber, there was no significant difference in the H₂S concentrations in the pre-scrubbed (450 ± 42 ppm) and post-scrubbed (430 ± 41 ppm) biogas due to the use of scrap iron and steel wool instead of proprietary iron oxide-based adsorbents often used for biogas desulfurization. Even though the capital and operating costs for the two scrubbing systems were low (<$1500/year), the lack of dedicated operators led to inefficient performance for the two scrubbing systems. Full article

A field study was conducted in 2016–2017 and 2017–2018 to evaluate the effects of air injection into an irrigation stream during the subsurface drip irrigation (SDI) process on the nutritional values and productivity of potato grown in clay loam soil. Two irrigation treatments (non-aerated and aerated) and six fertilizer applications (chicken, cow, rabbit, compost, mineral, and chicken + biochar) were compared. In the first growing season, the maximum yield occurred under aerated treatment with cow fertilizer (36.25 ton ha⁻¹), while the minimum yield occurred under non-aerated treatment with chicken fertilizer (24.00 ton ha⁻¹). On the other hand, the maximum and minimum yields in the second growing season were 35.00 and 24.74 ton ha⁻¹ under aerated and non-aerated treatments with cow fertilizer, respectively. Maximum water productivity was achieved under aerated treatment with cow fertilizer (10.04 and 9.13 kg m⁻³ for the first and second growing seasons, respectively), while minimum water productivity was achieved under the non-aerated treatment with chicken + biochar fertilizer (5.91 and 5.26 kg m⁻³ for the first and second growing seasons, respectively). Fertilization using aerated treatment yielded the best results and the highest coupling after air injection, compared with the traditional methods of adding soil fertilizer without aeration. The plant growth parameters significantly increased following aeration relative to non-aerated treatments for all fertilizer applications in both growing seasons. Air injection into the soil for potatoes, unsurprisingly, not only benefitted the crop by increasing the soil–air exchange rate but also promoted water infiltration rates and nutrient absorption and reduced drainage water, thus increasing water productivity and reducing the overall irrigation requirements. Full article

China is now accelerating the development of an ecological engineering for carbon sequestration in coastal mariculture environments to cope with climate change. Artificial upwelling as the ecological engineering can mix surface water with bottom water and bring rich nutrients to the euphotic zone, enhance seaweed growth in the oligotrophic sea area, and then increase coastal carbon sequestration. However, one of the major obstacles of the artificial upwelling is the high energy consumption. This study focused on the development of energy management technology for air-lift artificial upwelling by optimizing air injection rate. The fundamental principle underlying this technology is that the mode and intensity of air injection are adjusted from the feedback of information on velocity variation in tidal currents, illumination, and temperature of the surface layer. A series of equations to control air injection was derived based on seaweed growth and solar power generation. Although this finding was originally developed for the air-lift artificial upwelling, it also can be used in other areas of engineering, such as water delivery, aeration, and oxygenation. The simulations show that using a variable air injection rate can lift more nitrogen nutrients of 28.2 mol than using a fixed air injection rate of 26.6 mol, mostly with the same energy cost. Using this control algorithm, the changed temperature and dissolved oxygen profiles prove the effective upwelling in the experiments and the average weights of kelp are 33.1 g in the experimental group and 10.1 g in the control group. The ecological engineering was successfully increasing crop yield for carbon sequestration in coastal mariculture environments. Full article

After irrigation in intensive vegetable cultivation, the soil is filled with water leading to reduced oxygen content of the soil air which will affect vegetable growth and soil N₂O emission. In this study, the effect of aerated irrigation and residue biochar on soil N₂O emission, yield, and ion uptake of komatsuna grown in Andosol was explored. The experiment included four treatments; control (tap water irrigation), aerated water irrigation, pruning residue biochar with tap water irrigation, and a combination of aerated irrigation and biochar. The results showed that aerated irrigation had no effect on plant growth, but it also increased N₂O emission by 12.3% for several days after planting. Plant ion uptake was not affected by aerated irrigation. Biochar amendment increased shoot dry weight and significantly reduced soil N₂O emission by 27.9% compared with the control. Plant uptake of N and K also increased with biochar. This study showed that pruning residue biochar has the potential to mitigate N₂O emission while increasing vegetable growth and plant nutrient uptake. However, the study soil, Andosol, already has high soil porosity with low bulk density. Thus, further injection of air through irrigation showed no effect on plant growth but increased N₂O emission, hence soil aeration was not a limiting factor in Andosol. Full article

As the water passes through a restriction in a pipe, it forms a vacuum at the end of the restriction. A hole bored into the pipe at a point where this vacuum occurs will cause air to be drawn into the main flow. One example of this mechanism is seen in the venturi tube. When a minimal amount of differential pressure exists between the inlet and outlet sides of the venturi tube, a vacuum occurs at suction holes of the venturi tube. Venturi aeration is a method of aeration that has become popular in recent years. In present paper, air injection rates of venturi tubes are analyzed using Computational Fluid Dynamics modeling. These analyses are carried out by means of the program FLUENT V6.2 that uses finite volume theory. There is a good agreement between the measured air injection rates and the values computed from FLUENT CFD program. Full article