Aeration Time Research Articles

Performance Upgrading Evaluation of the Anaerobic Baffled Reactor by Integrating Aerobic Media Filter for Municipal Wastewater Treatment

Background & Aims of the Study: Anaerobic baffled reactor (ABR) is one of the low-cost wastewater treatment systems; however, it has some limitations, such as insufficient standard nutrient outflow. Accordingly, it should be studied and developed. This research aims to determine the efficiency of a five-sectional reactor pilot and to upgrade it with an integrated aerated media filter in the reactor (integrated reactor) for municipal wastewater treatment. Materials and Methods: This study was performed on a laboratory scale with field conditions in the Khoy City wastewater treatment plant. The ABR reactor operated for 270 days with a hydraulic retention time (HRT) of 48, 36, 24, and 18 hours, respectively. The Integrated anaerobic baffled reactor (IABR) was operated for 35 days with 24 hours of HRT, i.e., aeration time of 5 hours. The reactors were fed in line from the inflowing wastewater to the treatment plant. A 24-hour combined sampling was performed 224 times from the inflow and outflow of the system, and volatile suspended solids, total kjeldahl nitrogen (TKN), total phosphorus (TP), biochemical oxygen demand (BOD), chemical oxygen demand (COD), and Total Suspended Solids (TSS) parameters were measured and compared with the effluent disposal standard. Results: The launch of ABR lasted 105 days, and its helpful operation lasted 200 days. In 18 to 48 hours, the reactor removed 79% to 91% of COD, 9% to 20% of TKN, 19% to 30% of phosphorus, and 89% to 94% of TSS. The IABR reached the effluent disposal standard in terms of TSS, BOD, COD, and phosphorus under 24 hours HRT, i.e., aeration time of 5 hours, and increased the COD removal efficiency by 6% compared to ABR under 24 hours HRT and the same conditions. Conclusion: By integrating the final aerobic media filter in ABR while reducing the required HRT by 50%, its efficiency in achieving the effluent disposal standards increased compared to ABR. Therefore, this system can be used to treat municipal wastewater.

Operational parameters optimization for remediation of crude oil-polluted water in floating treatment wetlands using response surface methodology

The application of floating treatment wetlands (FTWs) is an innovative nature-based solution for the remediation of polluted water. The rational improvement of water treatment via FTWs is typically based on multifactorial experiments which are labor-intensive and time-consuming. Here, we used the response surface methodology (RSM) for the optimization of FTW’s operational parameters for the remediation of water polluted by crude oil. The central composite design (CCD) of RSM was used to generate the experimental layout for testing the effect of the variables hydrocarbon, nutrient, and surfactant concentrations, aeration, and retention time on the hydrocarbon removal in 50 different FTW test systems planted with the common reed, Phragmites australis. The results from these FTW were used to formulate a mathematical model in which the computational data strongly correlated with the experimental results. The operational parameters were further optimized via modeling prediction plus experimental validation in test FTW systems. In the FTW with optimized parameters, there was a 95% attenuation of the hydrocarbon concentration, which was very close to the 98% attenuation predicted by the model. The cost-effectiveness ratio showed a reduction of the treatment cost up to $0.048/liter of wastewater. The approach showed that RSM is a useful strategy for designing FTW experiments and optimizing operational parameters.

Solving hindered groundwater dynamics in restored tidal marshes by creek excavation and soil amendments: A model study

Groundwater fluxes in tidal marshes largely control key ecosystem functions and services, such as vegetation growth, soil carbon sequestration, and nutrient cycling. In tidal marshes restored on formerly embanked agricultural land, groundwater fluxes are often limited as compared to nearby natural marshes, as a result of historical agricultural soil compaction. To improve the functioning of restored tidal marshes, knowledge is needed on how much certain design options can optimize soil-groundwater interactions in future restoration projects. Based on measured data on soil properties and tidally induced groundwater dynamics, we calibrated and evaluated a 2D vertical model of a creek-marsh cross-section, accounting for both saturated and unsaturated groundwater flow and solute transport in a variably saturated groundwater flow model. We found that model simulations of common restoration practices such as soil amendments (increasing the depth of porous soil on top of the compact layer) and creek excavation (increasing the creek density) increase the soil aeration depth and time, the drainage depth and the solute flux, and decrease the residence time of solutes in the porewater. Our simulations indicate that increasing the depth to the compact layer from 20 cm to 40 cm, or increasing the creek density from 1 creek to 2 creeks along a 50 m marsh transect (while maintaining the total creek cross-sectional area), in both cases more than doubles the volume of water processed by the marsh soil. We discuss that this may stimulate nutrient cycling. As such, our study demonstrates that groundwater modelling can support the design of marsh restoration measures aiming to optimize groundwater fluxes and related ecosystem services.

Electrical generation and methane emission from an anoxic riverine sediment slurry treated by a two-chamber microbial fuel cell.

A two-chamber slurry microbial fuel cell (SMFC) was constructed using black-odorous river sediments as substrate for the anode. We tested addition of potassium ferricyanide (K3[Fe(CN)6]) or sodium chloride (NaCl) to the cathode chamber (0, 50, 100, 150, and 200mM) and aeration of the cathode chamber (0, 2, 4, 6, and 8h per day) to assess their response on electrical generation, internal resistance, and methane emission over a 600-h period. When the aeration time in the cathode chamber was 6h and K3[Fe(CN)6] or NaCl concentrations were 200mM, the highest power densities were 6.00, 6.45, and 6.64 mW·m-2, respectively. With increasing K3[Fe(CN)6] or NaCl concentration in the cathode chamber, methane emission progressively decreased (mean ± SD: 181.6 ± 10.9 → 75.5 ± 9.8mg/m3·h and 428.0 ± 28.5 → 157.0 ± 35.7mg/m3·h), respectively, but was higher than the reference having no cathode/anode electrodes (~ 30mg/m3·h). Cathode aeration (0 → 8h/day) demonstrated a reduction in methane emission from the anode chamber for only the 6-h treatment (mean: 349.6 ± 37.4 versus 299.4 ± 34.7mg/m3·h for 6h/day treatment); methane emission from the reference was much lower (85.3 ± 26.1mg/m3·h). Our results demonstrate that adding an electron acceptor (K3[Fe(CN)6]), electrolyte solution (NaCl), and aeration to the cathode chamber can appreciably improve electrical generation efficiency from the MFC. Notably, electrical generation stimulates methane emission, but methane emission decreases at higher power densities.

Insight on Exogenous Calcium/Magnesium in Weakening Pyrite Floatability with Prolonged Pre-Oxidation: Localized and Concomitant Secondary Minerals and Their Depression Characteristics

In this study, we investigated the localized and concomitant precipitation of calcium (Ca)/magnesium (Mg)-bearing species and iron oxides/oxyhydroxides, and their depression characteristics to the pyrite floatability in flotation process at pH 9 and pH 10.5 with prolonged pre-oxidation. Contrary to the depression characteristics at pH 9, the incipient (within aeration times of 30 min) depression of pyrite floatability in Ca/Mg-bearing solutions was more obvious at pH 10.5, while the subsequent decline was only slightly when the pre-oxidation time was expanded to 120 min and 360 min. The competitive adsorption among Ca/Mg-bearing species and potassium amyl xanthate (PAX, C6H11OS2K, collector) at specific sites onto the pyrite surface was demonstrated by the regularly decreased zeta potential of the pyrite surface pretreated in Ca/Mg-bearing solutions. Further scanning electron microscopy-energy dispersive spectrometry demonstrated the concomitant secondary Ca/Mg/Fe-bearing precipitates on the pyrite surface. X-Ray photoelectron spectroscopy suggested strong reprecipitation of iron oxides/oxyhydroxides on the pyrite surface via acid–base complexation among Ca/Mg hydroxy species and iron hydroxy species. Incipient occupation efficiency of specific reaction sites by Ca/Mg-bearing species, which were mainly controlled by the metastable distribution of Ca/Mg hydroxy species and their electrostatic affinity with pyrite surface, was the crucial factor that influenced the competitive adsorption of xanthate and pyrite floatability. More obvious incipient depression at pH 10.5 rather than at pH 9 contributed to more effective Ca/Mg-bearing species and their higher affinity to pyrite surface at pH 10.5. The localized and concomitant precipitation of secondary Ca/Mg/Fe-bearing species leads to a slightly increased hydrophilic coverage upon the pyrite surface, thus a slowly decreased pyrite floatability with increasing pre-oxidation time.

Study on radius of influence of groundwater circulation well in the field experiment

In recent years, groundwater circulation wells (GCW) have gradually become a research hotspot as an In-situ remediation technology. This technology reduces the construction of gas phase extraction wells and saves underground space compared to the traditional Air sparging (AS) remediation technology, the remediation process involves both volatile removal and microbial degradation. This study fully combines the background conditions of an organic contamination site and designs a positive circulation airflow lift circulation well. By analyzing the diffusion law of chloride tracer with aeration time and the changes of water level and water pressure of the monitoring well, it is known that the influence radius of the circulation well can be stabilized at 5.00 m when the aeration volume is 10 L/min. It not only has an essential demonstration significance for the development of groundwater circulation well remediation technology, but also provides reference process parameters for subsequent applications in type site remediation engineering applications.

Hydrodynamic Cavitation: Its optimization and potential application in treatment of Pigment Industry Wastewater

Paper presents the application of Hydrodynamic Cavitation technique in reduction of Chemical Oxygen Demand (of Chemical Oxygen Demand (COD) and its various fractions from the Pigment Industry wastewater. Orifice plate with dimension of single hole of 1.5 mm is used in this study. The sample were analyzed at different pressures of 2 bar, 3 bar, 4 bar, 5 bar and 6 bar at different time intervals of 30 min, 60 min, 90 min, 120 min and 180 min. The optimum time and inlet pressure for maximum COD reduction is obtained at 5 bar and 120 min. The samples are analyzed in two stages. In stage first stage, samples are treated with hydrodynamic cavitation only and filtered thereafter. Both the unfiltered and filtered samples were analyzed for various parameters such as COD (filtered and unfiltered), BOD (filtered and unfiltered), TDS and pH. In stage two, the samples are treated with aeration for optimum time followed by Hydrodynamic Cavitation. The optimum time of aeration was obtained at 36 hrs. Response Surface Methodology was used to check the sensitivity of the Hydrodynamic Cavitation set up. Optimization using RSM provided optimum results with desirability 0.798 when pressure was at 5 bar and time of reaction was 120 min.

Comparative Study on Using Various Recovery Stimulation Methods to Boost Nitrification Recovery in SBRs Inhibited by Hazardous Events

A system consisting of six SBR units was operated in parallel for three phases to investigate the impacts of salinity shock and anaerobic and aerobic starvation on the activated sludge process stability and effects of various recovery stimulation methods on the subsequent recovery period. Different recovery strategies were applied in each SBR unit, including natural recovery, adding bio-accelerators, a stepwise increase feed strategy, a stepwise strategy coupled with bio-accelerators dosing, extended aeration time, and extended aeration time coupled with bio-accelerators dosing. It was concluded that the combination of stepwise strategy and dosing bio-accelerators showed the most efficiency in boosting system recovery after being subjected to NaCl shock and starvation. The boosting effect of the stepwise strategy alone was slightly better in recovery after NaCl shock. Furthermore, extending the aeration rate could bring more positive effects when resuscitating the system after long-term anaerobic starvation. For the unit that only received dosing of bio-accelerators during the recovery period, it could be concluded that there was a specific time requirement for the bio-accelerators to take effect significantly, as the impact of bio-accelerators on the beginning days of recovery periods was very slight. In contrast, adjusting operational regimes such as stepwise increased feed volume or extending aeration time could significantly boost the SBRs from the first recovery days. Hence, highly effective recovery efficiency could be achieved by coupling dosing bio-accelerators with other operational adjustment methods, especially stepwise strategies.

Improvement of batch and continuous ethanol fermentations from sweet sorghum stem juice in a packed bed bioreactor by immobilized yeast cells under microaeration

Microaeration during ethanol fermentation from sweet sorghum stem juice (SSJ) by immobilized Saccharomyces cerevisiae NP01 was investigated in a tubular packed bed bioreactor to improve ethanol production. In batch fermentation from SSJ containing 230 g/L of total sugars, aeration time and its rate were optimized using a factorial design. The highest ethanol concentration (PE) and productivity (QP) was 106.9 g/L and 1.78 g/L·h, respectively, with sugar consumption (SC) of 89.9% under an aeration rate of 0.35 vvm for 12 h. In continuous ethanol fermentation under an aeration rate of 0.05 vvm, the initial sugar concentration and dilution rate were optimized for high values of SC, PE and QP using response surface methodology. The optimal conditions for continuous fermentation were an initial sugar concentration of 160 g/L and a dilution rate of 0.05 h−1, yielding satisfactory experimental values of SC, PE and QP values at 90.8%, 75.4 g/L and 3.72 g/L·h, respectively.

Effects of temperature shocks on the formation and characteristics of soluble microbial products in an aerobic activated sludge system

The present study investigated the impacts of temperature shocks on the generation of soluble microbial products (SMPs) in an aerobic activated sludge system, focusing on biopolymers and low molecular weight (LMW) substances that significantly impact the effluent quality. The results indicated that raising the temperature increased SMP production. At 25 and 35 °C, all size fractions of SMPs increased linearly with the aeration time, and biopolymers comprised a large proportion of SMPs. At 5 and 15 °C, in contrast, only biopolymers increased linearly with the aeration time, and LMW substances were the predominant fraction of SMPs. The reduced bio-utilization of SMPs with an increase in temperature was associated with the decreased relative abundance of LMW substances, which is supported by the assimilable organic carbon bioassay measurements. The mass of the biopolymers for the SMPs and extracellular polymeric substances (EPS) was balanced at all temperatures, wherein a negative correlation was observed, indicating that increased SMPs in the water phase led to a decrease in EPS. The results of the reactive oxygen species (ROS) and toxicity assays confirmed that the immune defense reaction of the bacteria (induced by ROS) was the key factor for variations in LMW substances in the SMPs and EPS under temperature stresses.

Control of aeration time in the aniline degrading-bioreactor with the analysis of metagenomic: Aniline degradation and nitrogen metabolism

The strategy of adjusting aeration time (5 h/6 h/7 h) was applied to the sequential batch reactors to optimize the treatment of aniline wastewater (600 mg/L) conveniently and economically. Three reactors degraded aniline effectively. The nitrogen removal ability of system with 6 h aeration time was better, performing the similar denitrification property as 5 h and nitrification performance as 7 h. Meanwhile, longer aeration time potentially damaged the sludge structure. The metagenomic analysis explained the micro-mechanism for the better performance of the system with 6 h aeration time. Appropriate aeration time was conducive to the enrichment of synergistic microflora, including aniline degrading-bacteria, heterotrophic nitrifiers and denitrifiers. Then, the tilt of environmental resources to these floras in the system was beneficial to the maximum value utilization of living substrates. Accordingly, these bacteria were more closely related to genes, resulting in higher expression of functional genes in the system.

Energy savings with a biochemical oxygen demand (BOD)- and pH-based intermittent aeration control system using a BOD biosensor for swine wastewater treatment

Intermittently aerated activated sludge processes save energy by minimizing the total aeration time per day without deteriorating effluent water quality. Swine wastewater contains high, often widely fluctuating concentrations of biochemical oxygen demand (BOD) and nitrogen. BOD-based aeration control would therefore be a useful method to reduce the energy demands of aeration, but requires a reliable BOD sensor for swine wastewater. In this study we developed a novel approach for BOD- and pH-based intermittent aeration control (BAC) using a BOD biosensor based on exoelectrogenic bacteria and tested it at four swine wastewater treatment plants. This BAC system reduced aeration energy in the plants by 15–36% compared to fixed aeration cycle operations while maintaining low concentrations of BOD and total nitrogen in the effluent. The energy saved per wastewater volume was 477–1012 kWh/m3/yr, equivalent to a reduction of 2.2–7.0 t-CO2/m3/yr in greenhouse gas emissions. The biosensor was equipped with an internet connection to allow for remote monitoring of water quality data with a smartphone, saving labour in the operational management of the plants. Aquabacterium and the aerobic denitrifier Thauera were detected as the predominant genera in the activated sludge.

Model construction and application for effluent prediction in wastewater treatment plant: Data processing method optimization and process parameters integration

Wastewater treatment based on the activated sludge process is complex process, which is easily affected by influent quality, aeration time and other factors, leading to unstable effluent. Facing increasingly stringent sewage discharge standards in China, it is necessary to build a prediction model for early warning of effluent quality. In this study, nine machine learning algorithms were adopted to construct models for the prediction of effluent Chemical Oxygen Demand (COD). In order to improve the prediction accuracy of the models, model optimization was conducted by introducing the hysteresis condition [Hydraulic Retention Time (HRT) of 18 h], data processing method (K-FOLD) and process parameters [dissolved oxygen (DO), sludge return ratio (SRR) and mixed liquid suspended solids (MLSS)]. Results showed that both K-Nearest Neighbour (KNN) and Gradient Boosting Decision Tree (GBDT) displayed excellent prediction effects, the best results of MAPE, RMSE and R2 were 7.34%/1.29/0.92(COD, KNN). The optimized models were further applied to the prediction of effluent total phosphorus (TP), total nitrogen (TN) and pH. The MAPE/RMSE/R2 were 7.43%/0.92/0.93(TN, GBDT), 17.81%/0.19/0.99(TP, KNN), 0.53%/0.16/0.99 (pH, KNN) respectively, indicating high prediction accuracy. The change and comparison of modeling conditions provide a new insight to wastewater prediction models. In addition, this study is close to the actual application scenario of WWTPs operation and management, also laying a foundation for the reverse regulation of energy saving and consumption reduction of wastewater treatment plants (WWTPs).

Development of a cost‐effective and portable aeration freezing system for germplasm cryopreservation for eastern oysters and other aquatic species

The goal was to develop a cost-effective and portable freezing system for germplasm cryopreservation of fish and shellfish. The objectives were to: (1) identify components for construction of a portable freezing system by evaluating the affecting factors of cooling rates; (2) generate a range of cooling rates through adjusting different variables; (3) compare cooling profiles generated by the aeration freezing system and a commercial programmable freezer, and (4) verify the effectiveness of the aeration freezing system by cryopreserving sperm of eastern oysters Crassostrea virginica. An aeration freezing system was constructed using a Styrofoam box as cooling chamber and an innovative aeration unit to create nitrogen vapour. A wide range of cooling rates (1.5–32.1°C/min) were achieved by combinations of sample position at 2, 5, or 10 cm above liquid nitrogen surface, the temperature of nitrogen vapour (−150 or −180°C), and aeration time of liquid nitrogen (0, 1, 2 min, or continuity). Compared to a programmable freezer, the aeration freezing system generated cooling profiles with significantly higher temperature for ice nucleation initiation. No difference in post-thaw sperm motility of eastern oysters were found between samples cooling in the aeration freezing system or a programmable freezer. Cooling rates of 10 or 15°C/min from 4°C to −80°C yielded the highest post-thaw sperm motility regardless of the cooling devices. The aeration freezing system developed in this study has the potential for high-throughput sample processing, and the design allows easy construction by multiple users.

Stability and nutrients removal performance of a Phanerochaete chrysosporium-based aerobic granular sludge process by step-feeding and multi A/O conditions

A Phanerochaete chrysosporium-based aerobic granular sludge (PC-AGS) was developed by inoculating fungal mycelial pellets into a lab-scale aerobic granular sequencing batch reactor (AGSBR). A strategy using step-anaerobic feeding coupled with multi A/O conditions was adopted. The results showed that the removal efficiencies for total phosphorus (TP) and total inorganic nitrogen (TIN) were 94.56 ± 2.92% and 75.20 ± 7.74%, respectively, under relatively low aeration time. Compared with original AGS, the content of extracellular proteins for PC-AGS obviously increased from 18.61 to 41.44 mg/g MLSS by the end of phase I. Moreover, the mature granules had a larger size and better stability during the 100 days operation. Furthermore, the analysis of microbial diversity detected many key functional groups in PC-AGS granules that were beneficial to nutrients removal. This work demonstrated that the addition of fungal pellets not only enhanced the removal performance, but also improved the stability of the AGS system.

Experimental study on the influence of aerated gas pressure and confining pressure on low-rank coal gas adsorption process

To deeply study the variation characteristics of the gas content in the process of gas adsorption for coal samples under different gas pressures and confining pressures, low-field nuclear magnetic resonance technology was used to carry out experimental research on the gas adsorption of coal. The relationship between the T2 spectrum amplitude integral and the gas quantity was analyzed. The results show the following: (1) When the samples were inflated for 11 h at each gas pressure point (0.31, 0.74, 1.11, and 1.46 MPa), after ∼5 h of adsorption, the amount of adsorbed gas exceeded 85.0% of the total adsorption capacity; additionally, as the adsorption time increased, the amount of adsorbed gas gradually tended to stabilize. When the gas pressure was >1 MPa, the amount of adsorbed gas exceeded 90.0% of the total adsorption capacity; Higher the pressure of aerated gas, greater the gas pressure gradient or concentration gradient on the surface of the coal sample and the greater the driving force for gas molecules to seep or diffuse into the coal sample. (2) When the samples were inflated for 11 h at each confining pressure point (3, 4, 5, and 7 MPa), the adsorbed gas increased by ∼85.0% of the total adsorbed gas in the first 5 h. When the pressure was <5 MPa, the amount of adsorbed gas exceeded 85.0% of the total amount of adsorption; that is, the increase in adsorbed gas was the largest at ∼5 h in the adsorption process for the columnar coal sample under different confining pressures, and the increase was ∼5.0% from 7–11 h. When the large pores in the coal sample closed, the amount of gas that seeped into the deep part of the coal sample within the same aeration time was reduced.

Application research of internal electrolysis as pre-treatment for berberine wastewater biodegradation

The composition of the berberine wastewater is complicated with high concentration of chemical oxygen demand (COD). Because it is hard to be degraded by traditional biochemical treatment and causes serious environmental pollution. The applicability of internal electrolysis to improve the biodegradability of berberine wastewater to be treated biologically was investigated. The wastewater was originated from a factory producing berberine. Treatability studies were conducted under laboratory conditions in order to determine the operational conditions to enhance the biodegradation of the wastewater.The major operational conditions, such as the initial pH, the second stage pH, the volume ratio of iron-carbon microelectrolysis filler to waste water and aeration time were investigated in the paper. The result of the experiment shows that the initial pH 2.0-2.5, second stage pH 9, the best volume ratio of iron-carbon micro-electrolysis packing and wastewater is 1:1 and the the residence time control in 120 minutes are the best operating parameters on the berberine wastewater treatment.

The effectiveness of increasing the amount of Return Activated Sludge (RAS) in wastewater with a combination biofilter system on bulking parameters

Control of industrial wastewater treatment is very important to produce good effluent. Secondary processing is the heart of wastewater treatment. The problem that often occurs in secondary processing using activated sludge is bulking in the mixed liquor. Various studies on bulking have been done. The optimal aeration time is 3 hours to remove bulking in the mixed liquor caused by S.Natans bacteria. This research aims to determine the effectiveness of the addition of the amount of Return Activated Sludge (RAS) in wastewater with a combination biofilter system on bulking parameters. The method used is experimental in the laboratory. The research design used a completely randomized design. The variation of the test that will be carried out is the addition of the Return Activated sludge variation test to determine the effectiveness of adding RAS to wastewater with a biofilter combination system on bulking parameters. The experiment was repeated 3 times, resulting in 27 treatments. To test bulking, it is tested using the parameters SVI (Sludge Volume Index), DO, MLSS (Mixed Liquor Suspended Solid), and BOD. The results showed that the addition of Return Activated Sludge in wastewater was very effective in a combination biofilter system against bulking parameters.

Effects of Lung Injury on Regional Aeration and Expiratory Time Constants: Insights From Four-Dimensional Computed Tomography Image Registration.

Rationale: Intratidal changes in regional lung aeration, as assessed with dynamic four-dimensional computed tomography (CT; 4DCT), may indicate the processes of recruitment and derecruitment, thus portending atelectrauma during mechanical ventilation. In this study, we characterized the time constants associated with deaeration during the expiratory phase of pressure-controlled ventilation in pigs before and after acute lung injury using respiratory-gated 4DCT and image registration.Methods: Eleven pigs were mechanically ventilated in pressure-controlled mode under baseline conditions and following an oleic acid model of acute lung injury. Dynamic 4DCT scans were acquired without interrupting ventilation. Automated segmentation of lung parenchyma was obtained by a convolutional neural network. Respiratory structures were aligned using 4D image registration. Exponential regression was performed on the time-varying CT density in each aligned voxel during exhalation, resulting in regional estimates of intratidal aeration change and deaeration time constants. Regressions were also performed for regional and total exhaled gas volume changes.Results: Normally and poorly aerated lung regions demonstrated the largest median intratidal aeration changes during exhalation, compared to minimal changes within hyper- and non-aerated regions. Following lung injury, median time constants throughout normally aerated regions within each subject were greater than respective values for poorly aerated regions. However, parametric response mapping revealed an association between larger intratidal aeration changes and slower time constants. Lower aeration and faster time constants were observed for the dependent lung regions in the supine position. Regional gas volume changes exhibited faster time constants compared to regional density time constants, as well as better correspondence to total exhaled volume time constants.Conclusion: Mechanical time constants based on exhaled gas volume underestimate regional aeration time constants. After lung injury, poorly aerated regions experience larger intratidal changes in aeration over shorter time scales compared to normally aerated regions. However, the largest intratidal aeration changes occur over the longest time scales within poorly aerated regions. These dynamic 4DCT imaging data provide supporting evidence for the susceptibility of poorly aerated regions to ventilator-induced lung injury, and for the functional benefits of short exhalation times during mechanical ventilation of injured lungs.

Experimental Investigation of a Pilot-Scale Concerning Ex-Situ Bioremediation of Petroleum Hydrocarbons Contaminated Soils

The soil samples were taken from the site of a former oil products depot from an industrial area (Romania). The soil samples taken were analyzed from a physical and chemical point of view: texture, pH, soil micronutrient content, metals concentration and petroleum hydrocarbon concentration (PHCs). The soil contaminated with total petroleum hydrocarbon (TPH (4280 mg kg−1) was disposed in the form of a pile (L × W × H: 3000 × 1400 × 500 mm). Experiments on a pilot-scale were conducted over 12 weeks at constant pH (7.5–8), temperature (22–32 °C), nutrient contents C/N/P ratio 100/10/1, soil aeration time (8 h/day) and moisture (30%). Samples were taken every two weeks for the monitoring of the TPH and the microorganisms content. During the experiment, microorganisms were added (Pseudomonas and Bacillus) every two weeks. Results of the analyses regarding the concentration of PHCs were revealed a linear decrease of the concentration of PHCs after only two weeks of treatment. This decrease in concentration was also achieved in the following weeks. Following the analysis performed on the model at the pilot scale regarding the depollution process, it can be concluded that a soil contaminated with petroleum hydrocarbons can be efficiently depolluted by performing an aeration of 8 h/day, adding microorganisms Pseudomonas and Bacillus to ensure the conditions for increasing in the total number of germs (colony forming units–CFU) from 151 × 105 to 213 × 107 CFU g−1 soil, after 12 weeks of soil treatment—the depollution efficiency achieved is 83%.