High Aeration Research Articles

Gas exchange in maize as a function of aeration porosity in a cohesive soil

Due to their physical characteristics, cohesive soils of either low or high aeration porosity can intensify limitations on plant cultivation. With the hypothesis that moist cohesive horizons where the soil has not yet reached a hard to extremely hard consistency may present a level of aeration porosity that affects gas exchange in maize plants, the aim of this study was to understand the influence of a cohesive horizon at different levels of aeration porosity on gas exchange in maize. The experiment was conducted in Fortaleza in the state of Ceara in a screened and covered environment, in a completely randomised block design with five levels of aeration porosity (AP) (0.04, 0.06, 0.09, 0.11 and 0.13 m3 m-3) and six replications, giving a total of 30 experimental units. The variables under analysis were intrinsic permeability (Kair) and gas exchange. Increases in AP afforded an increase in Kair. The AP of 0.04 and 0.13 m3 m-3 reflected in lower values for the photosynthetic rate (A) (24.54 and 25.50 μmol CO2 m2 s-1 respectively) and internal CO2 concentration (140.72 and 118.66 µmol mol-1 respectively). With the increase in AP, stomatal conductance and transpiration were reduced by 18% and 13.6% respectively, while the increase in instantaneous carboxylation efficiency was 19%, and intrinsic water use efficiency, 21%. It was concluded that variations in aeration porosity in cohesive soils affected gas exchange in maize plants. The AP of 0.04 and 0.13 m3 m-3 reduced the value of A due to non-stomatal and stomatal limitations respectively.

Numerical study of hydrodynamic characteristics in a moving bed biofilm reactor

The moving bed biofilm reactor (MBBR) has certain advantages, such as high wastewater treatment efficiency, low maintenance and operating costs, and simple operation. It has emerged as a valuable option for small decentralized facilities. The filling ratio, aeration mode and aeration intensity are the main factors that affect the performance of MBBRs in wastewater treatment. However, the information that concerns the used criteria that pertain to the process design for the MBBR is not adequate. In this study, a three dimensional computational fluid dynamics (CFD) model was constructed and the maximum error was only 1.98%, which was much smaller than the traditional 2D-CFD model. The filling ratio, aeration mode and aeration intensity of MBBR were optimized by CFD model from the point of view of fluid mechanics. The results show that the fluidization performance of the filling is the best under the one-side aeration mode with 30% filling ratio. The cost-performance ratio of the reactor with 30% filling ratio was 1.53, 25% and 35% filling ratio were only 1.17 and 1.14 respectively. Increasing the aeration intensity could improve the fluidization performance. However, the effect of high aeration intensity on the fluidization performance of the carrier was limited and the energy consumption increased greatly. The results revealed that when the aeration intensity increased from 0.07 min−1 to 0.13 min−1, the proportion of the carrier area increased by 16.56%. The proportion of the carrier area with an aeration rate of 0.20 min−1 was only 4.23%, which is higher than 0.13 min−1. The main factors that control the fluidization of the carrier were the range of the flow zone and the flow velocity of the liquid. Increasing the range of the flow zone could facilitate the flow of the carriers. The critical value of the flow velocity of the liquid in the flow zone was 0.04 m/s. These results could guide the optimization design of the filling ratio and the aeration conditions and provide a theoretical basis for the application of MBBR.

Optimizing vertical flow aerated steel slag filter system with nitrifiers bacteria for nutrients' removal from domestic wastewater: a pilot study

AbstractBACKGROUNDThe present study aimed to optimize the removal efficiency of ammonia nitrogen (NH3‐N) and total kjeldhal nitrogen (TKN) from domestic wastewater as a function of hydraulic loading rates (HLRs) (0.16–5.44 m3 m–3 day–1) and the aeration rate (3, 5 and 10 L min–1) in a vertical flow aerated steel slag filter (VFASSF) system with nitrifier bacteria. The nitrifier bacterial cell morphology was determined using scanning electron microscopy (SEM) analysis.RESULTSThe HLRs affected the performance of the VFASSF in removing TKN and NH3‐N from domestic wastewater. The optimal air flow rate for removing NH3‐N and TKN was recorded with 10 L min–1 and HLR 2.72 m3 m–3 day–1, at which the removal efficiency was >91% compared to 90% and 88% with 3 L min–1 and 5 L min–1 air flow rate, respectively. The high removal was a consequence of the high aeration which enhances the nitrification process performed by the nitrifying bacteria in the VFASSF.CONCLUSIONSThese findings reflected the applicability of VFASSF in the treatment and removal of nutrients from domestic wastewater. © 2020 Society of Chemical Industry

Characteristics of oxygen mass transfer and its impact on pollutant removal performance and microbial community structure in an aerobic fluidized bed biofilm reactor for treatment of municipal wastewater

A laboratory-scale aerobic fluidized bed biofilm reactor (AFBBR) was established to evaluate the oxygen mass transfer (OMT) process and its impact on municipal wastewater treatment performance. Aeration rates had different effects on the OMT of the wastewater and biofilm. In the wastewater, oxygenation performance, oxygen uptake rate (OUR), and volumetric OMT coefficient (kLa) improved under high aeration rates. However, within the biofilm, the OMT process under the aeration rate of 0.096 L/(min·L) were higher than under other conditions [0.064 L/(min·L) and 0.128 L/(min·L)]. The denitrifying bacteria (DNB) abundance under the aeration rate of 0.096 L/(min·L) were improved so that total nitrogen (TN, 66.98 ± 4.23%) and ammonia nitrogen (NH4+-N, 74.70 ± 2.30%) removal were higher than those under other aeration conditions. These results showed that suitable aeration could improve wastewater treatment efficiency through changing the OMT process and microbial community structure.

Filterability of Polysulfone Membrane in a Tilted Panel System for Activated Sludge Filtration

Membrane bioreactors (MBRs) are established technology for treatment of domestic and industrial wastewater because they offer a small footprint and high quality of effluent, in addition to lower excess sludge. However, their widespread applications are still limited by higher expenditure for compensating for membrane fouling. In this study, polysulfone (PSF)-based ultrafiltration membranes were developed and integrated with a tilted panel system for fouling control in activated sludge filtration. The results show an enhanced performance of filtration system thanks to the mutual advantage of the tilted panel system and the membrane properties. Both membranes showed a clear trend of higher permeability with respect to the tilted panel parameters, namely, higher tilting angle, higher aeration rate, and shorter intermittent/switching period. PSF-1 (1 wt% polyethylene glycol (PEG) additive) shows significantly better performance than PSF-3 (3 wt% PEG additive) although their mean flow pore size, structural properties, and contact angle do not differ significantly. PSF-1 shows superior filterability performance of about 45% for panel tilting angles of 20° at an aeration rate of 1.8 L·min−1, and 11% for a switching period of 1 min compared with PSF-3. The key property enhancing the performance of the PSF-1 is its narrower distribution of pore size. Overall results suggest that an optimum system could be achieved by optimizing both the filtration system and the membrane material properties.

The net energy ratio of microalgae biofuels production based on correlated cultivation parameters in flat plate photobioreactors

The net energy ratio (NER) of microalgae biofuels depends fundamentally on assumptions of operational energy demand and biomass yield. However, for the NER calculation, it has not previously been considered that these parameters are related. This study derives a correlation between these values from published experimental data on flat plate photobioreactors and uses it to calculate the NER. The found correlation is adapted to outdoor conditions, and the energy demand throughout the life cycle for cultivation and biogas production is added. Results show that an asymptotic correlation between the aeration rate and the photosynthetic efficiency hampers net energy output. Maximising the biomass output requires a disproportionately high aeration rate, and thus operational energy demand. Best NER is obtained at low aeration rates, however the biomethane yield at these rates cannot compensate for the total energy demand throughout the life cycle. A NER of 3.6 is calculated. Sensitivity analysis on further technological improvements, such as more efficient energy supply, reduces the NER to 1.8. A comparison of assumptions from seven previous life cycle analyses demonstrates that NER below one results from incomplete system boundaries, or unrelated parameters for operational energy demand and biomass yield. Our findings help to explain contradictory results in previous studies, and will improve the quality of future NER analyses.

Effects of operating parameters on salinity accumulation in a bioelectrochemically-assisted osmotic membrane bioreactor

Salinity accumulation in osmotic membrane bioreactors (OMBRs) is one of the key challenges, which can be mitigated in situ by reverse-fluxed solute transport through integration of bioelectrochemical systems (BES). The effects of several key operating parameters on salinity accumulation were investigated. Salinity accumulation depended on balance between reversal solute flux (RSF) and reverse-fluxed ammonium (RFA) transport, which was driven by electrical migration and concentration diffusion. DS concentration was the primary factor influencing RSF, and the lowest DS concentration exhibited the minimum solute leakage. Aeration played a vital role in RFA transport, and a higher aeration helped to enhance RFA transport. Increased current generation (i.e., influent flow rate of 0.5 mL min−1 and external resistance of 5.0 Ω) contributed to RFA migration. The lack of electrolyte addition in catholyte contributed to RFA diffusion. These optimal parameters encourage the further development of an effective strategy for salinity mitigation in BES-based OMBR technology.

ВЛИЯНИЕ ЗАГРЯЗНЕНИЙ СТОЧНЫХ ВОД НА БИОЦЕНОЗ АКТИВНОГО ИЛА

Wastewater from agro-industrial complexes is rich in organic components. Biological method is considered to be the most universal for their purification. It provides a high rate of biodegradation of pollution. But due to the high concentration of incoming pollutants, activated sludge microbiome can reduce its cleaning ability. High aeration rate is required for the effective decomposition of such compounds, since aerobic microorganisms predominate in the activated sludge. Under real conditions, the time for the oxidation of these substances by microbial communities is often insufficient. This imbalance between incoming organic matter and oxidized activated sludge microbiota leads to the growth of filamentous bacteria, which is one of the reasons of activated sludge swelling. The influence of high concentrations of pollutants in wastewater on a consortium of microorganisms of activated sludge was investigated to eliminate this negative factor. Physical and chemical composition of the wastewater was carried out according to standard methods. The composition of the activated sludge bacteriocenosis and pig intestine microbiome were determined by standard methods of inoculation in liquid and solid nutrient media. A correlation between the decrease in the concentration of pollutants and regeneration of activated sludge biocenosis has been established. A 59.8% decrease in the overall level of COD contamination of source effluents led to an increase in the number of flocculating microorganisms by 41.7%. Deep destruction of amine nitrogen (99%) and phosphorus (71.4%) was observed due to the activation of heterotrophic microorganisms.

Effects of carbon-based additives and ventilation rate on nitrogen loss and microbial community during chicken manure composting.

Aerobic composting is a sustainable method for chicken manure recycling, while its unsuitable porosity and carbon to nitrogen ratio (C/N) may result in high nitrogen loss and incomplete composting. With the aim to investigate the effects of carbon-based additives and two ventilation rates on chicken manure composting and microbial community, two series of treatments were set up for chicken manure composting, in order to investigate their effects on the biodegradation process, ammonia (NH3) emission, nitrogen loss, physiochemical properties and microbial community. The results showed that additives and ventilation rates set in the current study influenced the carbon dioxide (CO2) production from the 2nd week and also the physiochemical parameters during the entire process, while no inhibitory effect on the maturity were observed. With woody peat as additive, the NH3 emission amount and nitrogen loss rate were shown as 15.86 mg and 4.02%, less than those in other treatments, 31.08–80.13 mg and 24.26–34.24%, respectively. The high aeration rate increased the NH3 emission and nitrogen loss, which were varied when the additives were different. The terminal restriction fragment length polymorphism (T-RFLP) results showed that the additives and the ventilation rates changed the microbial community, while the prominent microbial clones belonged to the class of Bacilli and Clostridia (in the phylum of Firmicutes), and Alphaproteobacteria, Deltaproteobacteria and Gammaproteobacteria (in the phylum of Proteobacteria). Bacillus spp. was observed to be the most dominant bacteria in all the composting stages and treatments. It was concluded that woody peat could improve chicken manure composting more than other additives, especially on reducing nitrogen loss, meanwhile 0.18 L‧min-1‧kg-1 DM was suitable for various additives. Therefore, suitable additive and aeration rate could be used in practical application, which could significantly reduce nitrogen loss without influence on the compos maturity process.

Exploring the optimized strategy in the nitritation-anammox biofilm process for treating low ammonium wastewater

The main challenge for achieving the simultaneous nitritation, anammox and denitrification (SNAD) process is to optimize the concentrations of nitrite and dissolved oxygen (DO). This study explored the performance of SNAD biofilm reactor under three operational strategies. At Stage 1, 2 and 3, the average concentrations of DO were 0.7, 2.7 and 5.2 mg/L, respectively. The peak concentrations of NO2–-N in the sequencing batch reactor (SBR) cycle were 5.3, 6.0 and 2.7 mg/L, respectively. The average removal rates of total inorganic nitrogen (TIN) were 0.30, 0.42 and 0.22 kg N/m3/d, respectively. Protein (PN) was the dominant extracellular polymeric substance (EPS) content on the SNAD biofilm. The PN concentration remained stable while the polysaccharide (PS) concentration changed rapidly under different operational strategies. High-throughput sequencing analysis indicated that high DO and long aeration period condition could lead to a slight decrease in the abundances of denitrifying bacteria and anammox bacteria.

Mechanism of nutrient removal enhancement in low carbon/nitrogen wastewater by a novel high-frequency micro-aeration/anoxic (HMOA) mode

In this study, a novel high-frequency micro-aeration/anoxic (HMOA) mode with a high aeration frequency (15 times/h) and short aeration duration (Taer = 1 h/cycle) was proposed. Compared with continuous aeration modes, the highest nitrogen and phosphorus removal efficiencies were achieved in the sequencing batch reactor (SBR) under HMOA mode when treating wastewater with carbon/nitrogen (C/N) ratios of 4.5 (85% and 97%, respectively) and 3 (77% and 75%, respectively). Metagenomic analysis was utilized to analyse the microbial metabolic mechanism under the HMOA mode. The results showed that under the HMOA mode, the enhanced transduction and metabolism pathways of nitrate, nitrite, oxygen, phosphorus and acetate provided favourable nutritional conditions for the proliferation of denitrifiers and phosphorus accumulating organisms (PAOs), and simultaneously strengthened the survival capacity of nitrifiers under low dissolved oxygen (DO) conditions. In addition, genes involved in carbon metabolism were upregulated by the HMOA mode, which further increased the utility of carbon sources for denitrifier and PAO metabolism. Consequently, the limited carbon source could be fully utilized in nitrogen and phosphorus removal, which improved the efficiency of treating low C/N wastewater. This study proposed a potential aeration mode for microbial metabolism regulation to enhance nutrient removal in biological wastewater treatment processes.

Hydroelasticity effects on water-structure impacts

Local and global loadings, which may cause the local damage and/or global failure and collapse of offshore structures and ships, are experimentally investigated in this study. The research question is how the elasticity of the structural section affects loading during severe environmental conditions. Two different experiments were undertaken in this study to try to answer this question: (i) vertical slamming impacts of a square flat plate, which represents a plate section of the bottom or bow of a ship structure, onto water surface with zero degree deadrise angle; (ii) wave impacts on a truncated vertical wall in water, where the wall represents a plate section of a hull. The plate and wall are constructed such that they can be either rigid or elastic by virtue of a specially designed spring system. The experiments were carried out in the University of Plymouth’s COAST Laboratory. For the cases considered here, elasticity of the impact plate and/or wall has an effect on the slamming and wave impact loads. Here the slamming impact loads (both pressure and force) were considerably reduced for the elastic plate compared to the rigid one, though only at high impact velocities. The total impact force on the elastic wall was found to reduce for the high aeration, flip-through and slightly breaking wave impacts. However, the impact pressure decreased on the elastic wall only under flip-through wave impact. Due to the elasticity of the plates, the impulse of the first positive phase of pressure and force decreases significantly for the vertical slamming impact tests. This significant effect of hydroelasticity is also found for the total force impulse on the vertical wall under wave impacts.Graphic abstractHydroelasticity effects on water-structure impacts: a impact pressures on dropped plates; b impact forces on dropped plates; c, d, e, f wave impact pressures on the vertical walls; g wave impact forces on the vertical walls; h wave force impulses on the vertical walls: elastic wall 1 vs. rigid wall (filled markers); elastic wall 2 vs. rigid wall (empty markers)

Image processing for hydraulic jump free-surface detection: coupled gradient/machine learning model

High-frequency oscillations and high surface aeration, induced by strong turbulence, make water depth measurement for hydraulic jumps a persistently challenging task. The investigation of hydraulic jump behaviour continues to be an important research theme, particularly with regards to the stilling basin design. Reliable knowledge of time-averaged and extreme values along a depth profile can help develop an adequate design of a stilling basin, improve safety, and aid the understanding of the jump phenomenon. This paper presents an attempt to mitigate certain limitations of existing depth measurement methods by adopting a non-intrusive computer vision-based approach to measuring the water depth profile of a hydraulic jump. The proposed method analyses video data in order to detect the boundary between the air–water mixture and the laboratory flume wall. This is achieved by coupling two computer vision methods: (1) analysis of the vertical image gradients, and (2) general-purpose edge detection using a deep neural network model. While the gradient analysis technique alone can provide adequate results, its performance can be significantly improved in combination with a neural network model which incorporates a ‘human-like’ vision within the algorithm. The model coupling reduces the likelihood of false detections and improves the overall detection accuracy. The proposed method is tested in two experiments with different degrees of jump aeration. Results show that the coupled model can reliably and accurately capture the instantaneous depth profile along the jump, with low sensitivity to image noise and flow aeration. The coupled model presented fewer false detections than the gradient-based model, and offered consistent performance in regions of high as well as low aeration. The proposed approach allows for automated detection of the free-surface interface and expands the potential of computer vision-based measurement methods in hydraulics.

Turbulence and self-similarity in highly aerated shear flows: The stable hydraulic jump

Hydraulic jumps are oftentimes encountered in natural and human-made environments. The transition from supercritical to subcritical flow involves large energy dissipation rates and substantial air entrainment, preventing the use of monophasic flow measurement instrumentation. This paper presents an experimental study of a stable hydraulic jump with a Froude number of 4.25, utilizing novel intrusive phase-detection probe techniques and image-based velocimetry from a side perspective. Turbulence estimations were obtained for the impinging region and the roller region of the jump including Reynolds stresses, turbulent integral scales and velocity fluctuation spectra. The velocity spectra fulfilled a - 5/3 slope in the inertial subrange, despite the high aeration of the flow. Overall, the collected data is of particular interest for high-fidelity numerical model validation and the study represents an advancement in air-water flow research enabled by the latest experimental developments for multiphase flows.

Municipal wastewater treatment by semi-continuous and membrane algal-bacterial photo-bioreactors

Conventional wastewater treatment systems demand a high cost mechanical aeration. Using algal-bacterial systems helps to reach a cost-efficient treatment method by eliminating mechanical aeration, since algae produce the oxygen needed for treatment process. In this study, two groups of experiments were performed for domestic wastewater treatment processes. For the first group, semi-continuous microalgae-bacterial photo-bioreactors were cultivated. Chlorella Vulgaris and activated sludge (AS) were used as microalgae and bacterial inoculums, respectively. The effect of different algae and AS ratios on the chemical oxygen demand (COD), N-NH4+ and P-PO43− removal was studied. The removal efficiency of COD was above 93 % for the three tested algae and AS inoculum ratios (5:1, 1:1, and 1:5). The reactor with algae: AS inoculum ratio of 5:1 achieved the highest final N-NH4+ and P-PO43− removal efficiencies (88.0 ± 1.0 % and 84.0 ± 1.0 %, respectively). Furthermore, the highest biomass concentration (1.96 g L-1 from initial amount of 0.3 g L-1) was observed in the reactor with algae: AS ratio of 5:1. The ratio of 5:1 (algae: AS) was found as the optimum ratio which promoted the cooperation between microalgae and AS for nutrient removal. For the second group of experiments, the optimum ratio of 5:1 (algae: AS) was used in a membrane bioreactor, and the results showed that this reactor enhanced the final removal efficacies from 88 to 98 % and from 84 to 89 % for N-NH4+ and P-PO43-, respectively.

Improve biotransformation of crude glycerol to ethanol of Enterobacter aerogenes by two-stage redox potential fed-batch process under microaerobic environment

Ethanol production from crude glycerol under microaerobic condition was optimized. The aeration rate in the reactor was controlled using redox potential (ORP) as to replace a conventional oxygen sensor that became insensitive at low oxygen concentration. The performance of Enterobacter aerogenes TISTR1468 in a batch reactor using a simple medium (crude glycerol and tuna condensate (GT) medium) was evaluated on various aeration strategies: continuous aeration at 0.5 vvm; controlled aeration at −350 mV and −400 mV ORP; and no aeration. The 72-h batch fermentation showed that a more reductive environment (lower aeration and ORP value) increased ethanol concentration and yield, but decreased the ethanol productivity. No-aeration fermentation with the lowest ORP value achieved the highest ethanol production (18.78 g L−1) and yield (0.94 g-ethanol.g-glycerol−1). A more oxidative environment (higher aeration and ORP value) fasten the specific growth rate (μ), but ethanol concentration and yield decreased. The optimum specific ethanol production rate (qp) and glycerol consumption rate occurred at ORP of −400 mV and −350 mV, respectively. When the ORP was very low, the μ decreased following substrate depletion, but this phenomenon was not observed at higher ORP value, an evident that adequate oxygen supply could maintain cell viability.Fed-batch with two-stage aeration strategy (−350 mV and −400 mV ORP) acquired higher ethanol production (30.31 g L−1) than fed-batch with single-stage aeration (25.95 g L−1) and batch process (12.33 g L−1).This study has revived the potential of crude glycerol biotransformation to ethanol and opened up opportunities for optimization of related microaerobic systems other than ethanol.

Patterned Membrane in an Energy-Efficient Tilted Panel Filtration System for Fouling Control in Activated Sludge Filtration.

A membrane bioreactor enhances the overall biological performance of a conventional activated sludge system for wastewater treatment by producing high-quality effluent suitable for reuse. However, membrane fouling hinders the widespread application of membrane bioreactors by reducing the hydraulic performance, shortening membrane lifespan, and increasing the operational costs for membrane fouling management. This study assesses the combined effect of membrane surface corrugation and a tilted panel in enhancing the impact of air bubbling for membrane fouling control in activated sludge filtration, applicable for membrane bioreactors. The filterability performance of such a system was further tested under variable parameters: Filtration cycle, aeration rate, and intermittent aeration. Results show that a combination of surface corrugation and panel tilting enhances the impact of aeration and leads to 87% permeance increment. The results of the parametric study shows that the highest permeance was achieved under short filtration–relaxation cycle of 5 min, high aeration rate of 1.5 L/min, and short switching period of 2.5 min, to yield the permeances of 465 ± 18, 447 ± 2, and 369 ± 9 L/(m2h bar), respectively. The high permeances lead to higher operational flux that helps to lower the membrane area as well as energy consumption. Initial estimation of the fully aerated system yields the energy input of 0.152 kWh/m3, much lower than data from the full-scale references of <0.4 kWh/m3. Further energy savings and a lower system footprint can still be achieved by applying the two-sided panel with a switching system, which will be addressed in the future.

Effect of aeration rates on enzymatic activity and bacterial community succession during cattle manure composting

In order to explore changes in microbial enzyme activity and bacterial community, a 60-day composting experiment was conducted using cattle manure and straw under aeration rates of 0.45, 0.68, and 0.90 L min−1 kg−1 fresh weight. High aeration rate increased the cellulase, urease, alkaline and acid phosphatase activities, but decreased that of invertase and catalase. Cellulase, alkaline phosphatase and catalase were the main enzymes that affected the composting process. Microbial analysis showed that high aeration rate increased the uniformity of bacterial community in thermophilic phase, but decreased that in mature phase. Different aeration rate affected the bacterial community structure and further influenced the relationship between enzyme and functional bacteria. Regulating the temperature, moisture content and EC in specific phases to affect bacterial community succession could provide guidance for improving maturity of composting.

Gas exchanges and growth of maize as affected by aeration porosity and soil compaction

Based on the hypothesis that less than 10% aeration porosity is sufficient to ensure plant development, the objective of this study was to evaluate the effect of levels of aeration porosity and soil density on the gas exchange and growth of maize plants. The experiment was conducted in a greenhouse, in randomized blocks in a 2 × 5 factorial arrangement: two densities (1.6 and 1.7 Mg m-3) and five aeration porosities (0.07, 0.08, 0.09, 0.10 and 0.12 m3 m-3), with five replicates. The interaction between the factors did not have an effect on the analyzed variables. Aeration porosity had a significant effect on photosynthesis, stomatal conductance, relative chlorophyll index (SPAD), plant height and biomass production, whose data were fitted by quadratic models. The highest aeration porosity reduced conductance by 11%, followed by 7% reduction in photosynthesis and 6.4% in SPAD. Aeration porosities lower than 0.10 m3 m-3 did not cause significant reduction in the values of gas exchange and growth of maize. At soil density of 1.7 Mg m-3, photosynthesis, SPAD, chlorophyll b, total chlorophyll and carotenoids were higher, but with no increments in biomass and leaf area. It is concluded that aeration porosities greater than 0.10 m3 m-3 are more limiting to plants due to changes in soil attributes, such as penetration resistance and water content. The highest contents of chlorophyll b and carotenoids at the highest density are acclimatization responses to the stress condition.

Investigation of antifouling properties of polypropylene/TiO2 nanocomposite membrane under different aeration rate in membrane bioreactor system

This paper presents the results of aeration rate effect on antifouling properties of polypropylene (PP)/TiO2 nanocomposite membrane in membrane bioreactor (MBR) system in order to oil refinery wastewater treatment. For this purpose, three levels of aeration rate with specific aeration demand per membrane area (SADm) of 0.5, 1, and 1.5 m3/m2h was used. According to the obtained results, PP nanocomposite membrane showed high hydrophilicity, porosity, and high flux compared to neat PP membrane. Also, either low or high aeration rate had a negative influence on permeability and antifouling properties of neat PP and nanocomposite membranes. The analysis of fouling mechanism for both membranes based on Hermia’s model revealed that the cake formation is dominant mechanism for lower aeration rate while by increasing aeration rate, all models couldn’t predict experimental data. Meanwhile, by increasing aeration rate, chemical oxygen demand (COD) removal for activated sludge and both membranes decreased and increased, respectively.