Purging Period Research Articles

A new approach for eliminating off-flavors from RAS fish, as part of the normal grow-out period

A new concept is presented for eliminating off-flavor from cold-water RAS-grown fish, while feeding, and as a part of the normal grow-out period. The technology is based on disconnecting the nitrification biofilter, and instead passing the water through an electrolysis system, which both oxidizes the ammonia and disinfects the water, while also removing the off-flavor compounds from the water, which thereby results in the purging of the fish. The purging period was expected to last up to 2 weeks and the fish are fed throughout it. Laboratory and pilot plant experiments were performed to prove the new concept. Lab experiments included quantification of the removal of MIB and geosmin by electrooxidation and stripping, together and separately, in the presence and absence of organic matter. A pilot plant experiment was performed using Rainbow trout to determine the rate at which the off-flavor compounds were removed from the water and the fish flesh (both skin and muscle were tested). The results show that the treatment process eliminated off-flavors in the water after ∼7 days and that the fish were below taste and odor threshold for geosmin and MIB after a maximum of 11 days. Detachment from the biofilter and the fact that the water was vigorously disinfected during the electrooxidation step guaranteed that no further off-flavor compounds would be generated during the operation. Aquacultural-management assessment indicates that RAS farms can increase both their annual production and their income by more than 10%, by implementing the suggested concept as part of the grow-out period.

Sensor Array System Based on Electronic Nose to Detect Borax in Meatballs with Artificial Neural Network

The categorization of odors utilizing gas sensor arrays with various meatball borax concentrations has been studied. The samples included meatballs with a borax content of 0.05%, 0.10%, 0.15%, 0.20%, and 0.25% (%mm) and meatballs without any borax. Six TGS gas sensors with a baseline of 10 seconds, a detecting period of 120 seconds, and a purging period of 250 seconds make up the gas sensor array used in this work. Artificial neural networks (ANNs) and principal component analysis (PCA), which are beneficial for feature extraction and classification, are used to handle the collected data based on machine learning approaches. Two models were produced by the data analysis: model 1, which only used the PCA approach, and model 2, which only used the ANN methodology. 90.33% is the total variance value of PC from model 1. In addition, the multilayer perceptron artificial neural network (ANN-MLP) technique for model 2 yielded accuracy values of 95%.

Quantification of N and C cycling during aerobic composting, including automated direct measurement of N2, N2O, NO, NH3, CO2 and CH4 emissions

Closing the carbon (C) and nitrogen (N) balance has yet to be achieved in aerobic bioprocess due to current methodological drawbacks in the frequency of sampling and detection and the challenge in direct measurement of instantaneous N2 emission. To address this issue, a novel system was developed enabling simultaneous and online determination of gaseous C and N species (N2, N2O, NO, NH3, CO2 and CH4) from aerobic composting at a high frequency of 120 times·d−1. A helium‑oxygen gas mixture was used to replace the air in the system to enable direct measurement of N2 emission, and three different gas exchange methods were assessed in their ability to minimize atmospheric background N2: 1) the N2-free gas purging method; 2) one cycle of the evacuation-refilling procedure; 3) one cycle of evacuating and refilling followed by N2-free gas purging. Method 3 was demonstrated as an optimum N2-removal method, and background N2 concentrations decreased to ~66 μmol·mol−1 within 11.6 h. During the N2-free gas purging period, low temperature incubation at 15 °C reduced CO2, CH4, NO, N2O and NH3 losses by 80.5 %, 41-fold, 10-fold, 11,403-fold and 61.4 %, respectively, compared with incubation at 30 °C. Therefore, a fast and low-perturbation N2 removal method was developed, namely the evacuating/refilling-low temperature purging method. Notably, all C and N gases exhibited large within-day variations during the peak emission period, which can be addressed by high-frequency measurement. Based on the developed method, up to 97.8 % of gaseous C and 95.6 % of gaseous N losses were quantified over a 43-day compost incubation, with N2 emission accounting (on average) for 5.8 % of the initial total N. This system for high frequency measurement of multiple gases (including N2) provides a novel tool for obtaining a deeper understanding of C and N turnover and more accurate estimation of reactive N and greenhouse gas emissions during composting.

Two-Dimensional simulation of purge processes for dead-ended H2/O2 proton exchange membrane fuel cell

ABSTRACT Proton exchange membrane fuel cells (PEMFCs) with the dead-ended anode (DEA) and dead-ended cathode (DEC) can achieve high utilization of hydrogen and oxygen but also cause the accumulation of liquid water in the cell and performance degradation. In this study, a two-dimensional multiphase transient PEMFC model is developed to investigate the purge strategy of the PEMFC with DEA and DEC. This model is well validated with the experimental data. The simulation results show that the voltage increases to a certain extent at the beginning of the dead-ended operation and then decreases gradually. During the purging period, the voltage reaches a peak value and then decreases. Therefore, the optimal purge duration is defined as the purge stops when the voltage reaches the maximum value, and the optimal purge duration decreases with the increase of scavenging velocity and increases with the increase of voltage drop rate, however, the energy efficiency under the optimal purge duration is not the highest. Besides, compared with the purging anode and cathode operation, the peak value of the purging cathode operation decreases gradually. Compared with the counter-flow operation, the co-flow operation leads to earlier purging moment, larger ohmic resistance, and voltage decay rate. The excessive accumulation of liquid water leads to a more poor uniformity of the local current density distribution. The purging cathode and counter-flow operation is the most ideal purge strategy during short-time operation, due to the highest energy efficiency about 52.3%, the second-highest output performance, and the second-longest purge interval about 180.01 s.

Impact of different mechanical ventilation strategies for night purging on indoor air quality in public buildings

Night-time ventilation has been used in non-residential buildings to enhance indoor air quality before occupied periods. However, many hypotheses exist on how this ventilation should be used. A typical choice has been to shut down the ventilation after occupancy and restart the ventilation again 2 hours before occupancy. Another option has been to ventilate the buildings continuously. In this study, the shut-down, continuous, and intermittent ventilation strategies were compared by evaluating indoor air quality. The daily occupied-hour ventilation was kept as usual. Each test case lasted for 2 weeks. Indoor air quality was assessed by measuring TVOC concentrations. Also, the thermal conditions, carbon dioxide, and pressure differences over the building envelope and over the air distribution devices were measured. The results show that the averaged TVOC concentrations were at the same level in the mornings with all those ventilation strategies. The evening concentrations reached a minimum level after a 2-hour purging period. TVOC concentrations were higher during the day than at night. This reveals that space usage had the largest effect on TVOC concentrations. The results indicate that a 2-hour purging is enough to cleanse indoor air before occupancy, and therefore the continuous night-time ventilation is not necessary.

On the degree of oxygen of metal bath with upper blow in the LD converter

The reasons and the degree of the existing assimilation by the converter bath of the blast stream of oxidizing gas (oxygen) for refining the melt during the purging period have been considered. It has been shown that the degree of oxygen absorption from the blast of a metal bath is related to the fact that the peripheral part of the oxygen jet is reflected lengthwise from the exit section of the nozzles to the surface of the metallic melt because of the converter gases counterflows in the converter gas space and the slag layer. As this takes place the degree of oxygen uptake due to these factors is reduced by 5-35% depending on the regime parameters, on the design of the blowing devices, the portable properties of supersonic jets in the high-temperature gas cavity of the converter with counter flows of converter gases and melt, on the height of the tuyere position above the metallic melt and etc. The assimilation process is also influenced by the interaction of the gas jet with the liquid melt at the top injection, which is different for different intensity of blasting and the height of the location of the lance - laminar, transient or turbulent. It is shown that the existing mode of transferring disturbances from the surrounding atmosphere into the jet affects the regime of gas interaction with the melt. Appropriate analytical relationships for the determination and examples of calculation of the degree of oxygen assimilation by a metal melt in 160-t and 350-t converters of the upper blast during the interaction of oxidant flows with converter gases and slagmetallic melt are given. It has been found that during the main blowing time, the degree of oxygen uptake increases with increasing blast intensity, oxidizer speed in the effective (isobaric) section, with increasing characteristic sizes (diameters) of the nozzles and reducing their number, with lowering the tuyere and decreasing the distance from the root of the escaping jets to the metal surface bath

Performance degradation of a proton exchange membrane fuel cell with dead-ended cathode and anode

Proton exchange membrane fuel cells with dead-ended cathodes and anodes can simplify the fuel cell system and reduce costs. An experiment was performed to determine the performance degradation characteristics of Proton exchange membrane fuel cells with dead-ended cathodes and anodes. The effects of operating temperature and pressure differences between the cathode and the anode on the purging period were investigated in detail. The performance and cyclic voltammetry before and after the dead-ended operation were analyzed and compared. After the experiment, the membrane electrode assembly was cut to analyze the catalytic layer cross-section membrane morphology by scanning electron microscopy. The results showed that during operation, the fuel cell performance gradually decreases until the setting value, and then quickly recovers when the cathode outlet solenoid valve is triggered during a purging cycle. The dead-ended operating period decreases with an increase in operating temperature but increases with an increase in the pressure difference between the cathode and the anode. Flooding occurs easily in a Proton exchange membrane fuel cell with a dead-ended cathode and anode, causing performance degradation. Moreover, it may cause a decrease in the electrochemical surface area of the catalyst layer. The scanning electron microscopy images showed that both the upper and middle regions of the catalyst layers remained unchanged, whereas the downstream region corroded and become thinner in the dead-ended mode after 60 h.

Optimization of groundwater sampling approach under various hydrogeological conditions using a numerical simulation model

This study presents a numerical model based on field data to simulate groundwater flow in both the aquifer and the well-bore for the low-flow sampling method and the well-volume sampling method. The numerical model was calibrated to match well with field drawdown, and calculated flow regime in the well was used to predict the variation of dissolved oxygen (DO) concentration during the purging period. The model was then used to analyze sampling representativeness and sampling time. Site characteristics, such as aquifer hydraulic conductivity, and sampling choices, such as purging rate and screen length, were found to be significant determinants of sampling representativeness and required sampling time. Results demonstrated that: (1) DO was the most useful water quality indicator in ensuring groundwater sampling representativeness in comparison with turbidity, pH, specific conductance, oxidation reduction potential (ORP) and temperature; (2) it is not necessary to maintain a drawdown of less than 0.1m when conducting low flow purging. However, a high purging rate in a low permeability aquifer may result in a dramatic decrease in sampling representativeness after an initial peak; (3) the presence of a short screen length may result in greater drawdown and a longer sampling time for low-flow purging. Overall, the present study suggests that this new numerical model is suitable for describing groundwater flow during the sampling process, and can be used to optimize sampling strategies under various hydrogeological conditions.

Investigation of the purging effect on a dead-end anode PEM fuel cell-powered vehicle during segments of a European driving cycle

The dynamic performance of the PEM fuel cell is one of the key factors for successful operation of a fuel cell-powered vehicle. Maintaining fast time response while keeping stable and high stack performance is of importance, especially during acceleration and deceleration. In this paper, we evaluate the transient response of a PEM fuel cell stack with a dead-end anode during segments of a legislated European driving cycle together with the effect of purging factors. The PEM fuel cell stack comprises of 24 cells with a 300cm2 active catalyst area and operates at a low hydrogen and air pressure. Humidified air is supplied to the cathode side and the dry hydrogen is fed to the anode. The liquid coolant is circulated to the stack and the radiator to maintain the thermal envelope throughout the stack. The stack performance deterioration over time is prevented by utilizing the purging, which removes the accumulated water and impurities. The effect of purging period, purging duration, coolant flow rate and cathode stoichiometry are examined with regard to the fuel cell’s transient performance during the driving cycle. The results show that a low purging duration may avoid the undesired deceleration at a high current, and a high purging period may sustain a better performance over time. Moreover, the coolant flow rate is found to be an important parameter, which affects the stack temperature–time response of the cooling control and the stack performance, especially at high operating currents.

A Factorial Study to Investigate the Purging Effect on the Performance of a Dead‐End Anode PEM Fuel Cell Stack

AbstractThis paper presents an experimental investigation of the effect of hydrogen purging time period and duration on the performance of a proton exchange membrane (PEM) fuel cell stack with a dead‐end anode. The objective is to develop a better understanding of the interactions between the purging parameters and the cathode air‐stoichiometry. It employs a full factorial approach for three factors (purging period, purging duration and air‐stoichiometry) with two levels and three replications. The study is performed on a 300 cm2, 24‐cell PEM fuel cell stack with the rated power of 1.5 kW. The stack was operated with water cooling, fully humidified air and dry hydrogen at the ambient pressure. The results showed that the stack performance is significantly influenced by the interactions of the purging parameters and the cathode air‐stoichiometry. The least square model was utilized to determine the optimum values of these parameters with regard to the stack performance and hydrogen utilization. For the present stack, the optimum values of parameters were: purging period of 3 min, purging duration of 4 s and the cathode air‐stoichiometry of 200%.

Fillet quality changes as a result of purging of common carp (Cyprinus carpio L.) with special regard to weight loss and lipid profile

Purging is a very important part of the rearing process for common carp (Cyprinus carpio L.) in Central Europe and is commonly conducted between October and December. Fish are kept in clear water without feeding in order to empty the gut, decrease the entrail proportion and eliminate possible tainted flavour. This leads to weight loss and stored fat mobilisation. This study investigated the effect of a purging period of up to 70days on lipid content and quality of common carp flesh. Four-year-old, market-size carp (weight 1700–2600g) from three different production systems (C: cereal supplemented; P: linseed/rapeseed pellet supplemented; N: natural feed) were sampled every 14days for weight, fillet yield and lipid analysis. Fillet yield was highest after 14days and decreased thereafter. Throughout the experiment, fillet fat content decreased continuously in groups C and P, but remained stable in group N. Initially, carp from groups C and P mainly metabolised monounsaturated fatty acids (MUFAs), but with prolonged starvation fish from all groups started to metabolise more polyunsaturated fatty acids (PUFAs). After 70days of purging, all groups showed almost identical saturated FA (SFA), MUFA and PUFA values. Our conclusion is that carp are able to metabolise selected FA for their energy needs when they are in good condition and have surplus fat stores. However, when body fat content is low, they may metabolise all FA types equally to sustain metabolic functions.

Preparation of Datex-Ohmeda Aestiva® and Aisys® anaesthetic machines for use in malignant hyperthermia susceptible patients

Preparation of anaesthesia machines for use by malignant hyperthermia susceptible patients requires purging the machines of halogenated anaesthetic agents. The endpoint of this process is to reach a gas concentration of 5 ppm or less, which has been arbitrarily chosen as the safe limit of exposure to avoid triggering a malignant hyperthermia event. We examined the washout characteristics of sevoflurane and desflurane from the Datex-Ohmeda Aestiva Anaesthesia System and Aisys Anaesthesia Carestation anaesthetic machines. The machines were contaminated for two hours using either sevoflurane 2 vol% or desflurane 6 vol%. At the end of the priming period, the patient breathing circuit and reservoir bag, carbon dioxide absorbent, sampling line and test lung were replaced with uncontaminated components. During the test period, machines were purged using oxygen flows of 10 l/minute. The average time to reach 5 ppm with the Aestiva machines was 51 minutes with sevoflurane and 71 minutes with desflurane. The average time to reach 5 ppm for the Aisys machines was 55 minutes with sevoflurane and 69 minutes with desflurane. All configurations of machines and anaesthetic gases demonstrated a rebound effect in agent concentration above 5 ppm when the fresh gas flow was subsequently reduced from 10 to 2 l/minute. Aestiva and Aisys anaesthetic machines require a prolonged period to adequately purge them of halogenated volatile anaesthetic agent. The rebound effect poses a serious concern, suggesting that after the purging period, fresh gas flows of 10 l/minute should be maintained for the duration of anaesthesia care of the malignant hyperthermia susceptible patient.

Dietary Exposure of Fathead Minnows to the Explosives TNT and RDX and to the Pesticide DDT using Contaminated Invertebrates

Explosive compounds have been released into the environment during manufacturing, handling, and usage procedures. These compounds have been found to persist in the environment and potentially promote detrimental biological effects. The lack of research on bioaccumulation and bioconcentration and especially dietary transfer on aquatic life has resulted in challenges in assessing ecological risks. The objective of this study was to investigate the potential trophic transfer of the explosive compounds 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) using a realistic freshwater prey/predator model and using dichlorodiphenyltrichloroethane (DDT), a highly bioaccumulative compound, to establish relative dietary uptake potential. The oligochaete worm Lumbriculus variegatus was exposed to 14C-labeled TNT, RDX or DDT for 5 hours in water, frozen in meal-size packages and subsequently fed to individual juvenile fathead minnows (Pimephales promelas). Fish were sampled for body residue determination on days 1, 2, 3, 4, 7, and 14 following an 8-hour gut purging period. Extensive metabolism of the parent compound in worms occurred for TNT but not for RDX and DDT. Fish body residue remained relatively unchanged over time for TNT and RDX, but did not approach steady-state concentration for DDT during the exposure period. The bioaccumulation factor (concentration in fish relative to concentration in worms) was 0.018, 0.010, and 0.422 g/g for TNT, RDX and DDT, respectively, confirming the expected relatively low bioaccumulative potential for TNT and RDX through the dietary route. The experimental design was deemed successful in determining the potential for trophic transfer of organic contaminants via a realistic predator/prey exposure scenario.

Freeze–purged–desorption method for quantitative evaluation of CO 2-solubility in polymeric films

A new experimental method, named as freeze–purged–desorption (FPD) method, to evaluate quantitatively the amount of gases sorbed in polymeric films, has been developed by using carbon dioxide gas and five different films (low density polyethylene: LDPE, polypropylene: PP, polystyrene: PS, polyacrylonitrile copolymer: PAN, polycarbonate: PC). The FPD method consisted of three operational periods of time based on the stepwise change in the system temperatures, the freeze periods of sorbed CO 2 at −196°C, the purging period of atmospheric CO 2 at −78°C and the desorption period of the freezed CO 2 in the film at −9°C. The evaluated values for LDPE, PP, PS, PAN and PC were 0.310, 0.65, 3.90, 0.098 and 6.90 (cm 3(STP)/cm 3 atm), respectively, which were about 20–40% higher than the reference values. The validity of the method was reconfirmed by a good reproducibility of the desorption curves of sorbed gases referring to a blank curve obtained from the non-porous glass beads.

Evaluation of methods to remove ammonia interference in marine sediment toxicity tests

AbstractAmmonia naturally accumulates to high concentrations in nonsurficial marine sediments. It can also interfere and confound interpretation of toxicity from persistent anthropogenic chemicals in tests with laboratory amphipods. Renewal of overlying water has become a standardized procedure to decrease pore‐water ammonia. Our objective was to propose an alternative technique for decreasing pore‐water ammonia concentrations. Sediment samples with ammonia concentrations of 70 and 155 mg/L were purged of toxic concentrations in pore‐water ammonia using the existing procedure of performing two renewals of overlying water per day. A thin‐layer technique, which involved increasing the sediment surface area during the purging period, decreased the ammonia concentration by as much as 4.5‐fold faster than the conventional purging protocol. Minimal decreases in concentrations of polycyclic aromatic hydrocarbons, heavy metals, and total organic carbon were found among all the purging techniques. Toxicity tests with the marine amphipod Ampelisca abdita suggest that minimizing the time required to purge a sediment of ammonia is critical in maintaining the integrity of the sample. The thin‐layer purging technique appears to be an effective method of decreasing pore‐water ammonia concentrations in sediments before laboratory toxicity testing with amphipods.

An experimental investigation of saline intrusion in a long sea outfall

The discharge and subsequent dispersion of wastewater through long sea outfalls is often inhibited by the intrusion of saline receiving water into the outfall diffiiser. Until recently, numerical modelling of intrusion and purging of saline water has been limited to one-dimensional (1-D) and enhanced 1-D models, which do not adequately describe the complex hydrodynamic processes generated within these devices. Recent research [1] has resulted in the development of a two-dimensional (2-D) numerical model to simulate the internal hydraulics of a long sea outfall with a saline intrusion. The model, which was developed using the FLUENT computational fluid dynamics (CFD) package, is designed to reproduce the effects of buoyancy and stratification, so that the interaction between the saline sea water and the effluent may be more accurately predicted. In this paper, details of an experimental investigation to assess the performance of the numerical model are presented. The investigation used a 1 in 30 scale model of a typical modern outfall difiuser discharging, under simplified conditions, into still receiving waters. Information is provided on model scaling, experimental facilities, instrumentation, and measurement procedures. The paper documents the results of an initial test series, in which discharge was permitted through only one of the outfall's four vertical risers. The results include measurements of velocity and water density within the model outfall as the conditions change from a steady state with the outfall fully intruded, through the transitory purging period, to normal operation. A brief overview of the numerical modelling technique is provided and a comparison of the results obtained using the physical and numerical models is presented. Advances in Fluid Mechanics III, C.A. Brebbia & M. Rahman (Editors) © 2000 WIT Press, www.witpress.com, ISBN 1-85312-813-9

Implications of gut purging for tissue residues determined in bioaccumulation testing of sediment with Lumbriculus variegatus

AbstractBioaccumulation test procedures using the oligochaete Lumbriculus variegatus have been developed as a means of evaluating the accumulation of chemicals from freshwater sediments. To avoid including chemicals associated with gut contents as part of the measured tissue residue, a 24‐h period of purging in clean water after the uptake phase of the test has been recommended. While purging acts to reduce bias from gut contents, it also has the potential to introduce bias caused by depuration of chemicals from tissues. In this paper, a series of model calculations are used to assess the expected sensitivity of measured residues of nonionic organic chemicals to the presence of sediment in the gut and to varying lengths of purging. If organisms are not purged, the predicted influence of gut contents on measured residue is not large (generally <20%) when a biota‐sediment accumulation factor (BSAF) of one is assumed. However, if BSAFs substantially less than one apply, projected errors increase to 30‐fold or more. To derive a better estimate of the time required for L. variegatus to clear the gut of sediment, a sediment purging experiment was conducted; results indicate that >98% of sediment had cleared the gut in 6 h (half‐life = 0.98 h). Based on these results and model analyses, a much shorter purging period of 6 h, rather than 24 h, is suggested as a reasonable guideline for many test applications.

Regular and relayed heteronuclear correlations by a single two‐dimensional experiment involving an RF gradient

AbstractIn order to achieve a better suppression of signals arising from protons non‐bonded to the considered heteronucleus, two (π/4) proton pulses are used in the HMQC sequence: one, at the very beginning, replaces the classical (π/2) pulse and the other is at the end of the sequence. In addition, a spin‐lock purging period improves the elimination process. This novel sequence is shown to provide the conventional heteronuclear correlations and, in addition, relayed homonuclear (proton–proton) correlations. A simple methodology capable of sorting out both types of correlations is proposed. However, this procedure entails a sensitivity loss by a factor of two.

Monitoring Krypton-85 During Three Mile Island Unit 2 Purging

The Penn State noble gas monitor played an important role in measuring environmental levels of /sup 85/Kr during the purging of the Three Mile Island Unit 2 primary containment. It filled a gap in the U.S. Environmental Protection Agency monitoring program, which existed between their real time monitors and their cryogenic gas chromatographic separation technique. During the 15-day purging period, the system analyzed a total of 124 samples, of which 37 were quantified to contain /sup 85/Kr in concentrations ranging from 3 X 10/sup 4/ to 1.5 X 10/sup 6/ pCi/m/sup 3/. The maximum whole body beta dose rate was found to be 0.28 mrem/h.