Large Discharge Volume Research Articles

Ar-Kr resonance energy transfer in He/Ar/Kr optically pumped rare gas laser medium

High metastable density is one of the research hotspots of optically pumped rare gas laser (OPRGL). Considering that the Ar metastable state energy level is only 20 cm<sup>–1</sup> different from the Kr excited state 5p[3/2]<sub>2</sub>, argon gas is added to the He/Kr discharge system. Owing to the long lifetime of the Ar metastable state atoms, through the collision resonance energy transfer process of Ar(4s[3/2]<sub>2</sub>)→Kr(5p[3/2]<sub>2</sub>), the purpose of supplementing and increasing the metastable density of Kr (Kr<sup>*</sup>) can be realized. In the case of obtaining the same metastable density, the pressure of the discharge power source is reduced, and a new idea is provided for further obtaining a high metastable density in a large discharge volume. In this work, the experimental analysis is carried out from the perspectives of spectral diagnosis and measurement of metastable density by laser absorption spectroscopy. The results show that the peak of radiative transition line of Kr high energy level atoms participating in the collision to the metastable state energy level is significantly enhanced after adding argon, and the tail signal of the transition line is extended within one discharge cycle. Under the gas conditions of 100 mbar, 1% Kr and 12.5% Ar, the peak value of the spectral line can be enhanced by about 10 times, and the tail signal of the transition line can be extended from 0.6 μs to 14.25 μs. At the same time, the density of Kr metastable energy level atoms is measured under different Ar content. Under the gas conditions of 100 mbar, 15% Ar and 1% Kr, the density of Kr<sup>*</sup> increases from 4.94×10<sup>11</sup> cm<sup>–3</sup> to 6.96×10<sup>12</sup> cm<sup>–3</sup>. At low pressure, the absorption linewidth of Kr metastable atoms narrows with the increase of Ar content. Under the gas condition of 600 mbar and 1% Kr, when the content of Ar is increased to 5%, the peak density of Kr<sup>*</sup> increases from 4.69×10<sup>13</sup> cm<sup>–3</sup> to 5.79×10<sup>13</sup> cm<sup>–3</sup>, i.e. the increment is 20%. Although the enhancement of metastable-atom-generation at high pressure is not so significant as those at low pressure, an increasing trend can still be observed. The results verify that the Kr metastable atoms generated in each discharge period can be supplemented by Ar-Kr resonance energy transfer.

The fate of microplastics in wastewater treatment plants: An overview of source and remediation technologies

Microplastics (MPs) in everyday consumer products have paved the way for high MPs concentrations in wastewater. Wastewater treatment plants (WWTP)s are the significant focal points for MP pollution, as millions of MP particles with varying characteristics enter WWTPs through the sewage systems of urban areas. Although the units in the WWTPs are not primarily designed to target MPs specifically, researchers have reported a large amount of microplastic removal from various units of WWTPs. The scientific community has remarkably studied various conventional and advanced treatment methods to remediate MPs and nanoplastics (NPs) from wastewater. This review aims to provide comprehensive knowledge about the source of MPs and NPs in wastewater, their composition, toxic effects, and remediation from treatment units of the WWTPs. The WWTPs comprise several physical, chemical, and biological treatment processes broadly categorized into three key stages: primary, secondary, and tertiary. The interaction of MPs and NPs with these processes have also been reviewed. Literature indicates that the WWTPs can separate more than 90% of MPs from wastewater. However, despite low concentrations of MPs in the treated effluent, large discharge volumes contribute to millions of MPs/NPs into the environment. Also, the separated MPs/NPs re-enter the environment through sludge applied on land. The paper also discusses the application of various advanced wastewater treatment technologies and their efficacies in remediating microplastics. Finally, the paper also highlights the research gaps where additional exploration is required, providing a new perspective on developing policies for controlling microplastic pollution.

Numerical investigation on indicated power and discharge process of three different discharge methods of swing compressor

Pressure variation during the discharge process is important to the discharge flow loss and indicated power of swing compressor. Due to the small effective discharge area and the large discharge volume flow rate at the beginning of discharge process, pressure shoots up to a high value, which is 25%-35% higher than the nominal discharge pressure. Using a suitable discharge method is beneficial to reduce the maximum pressure and indicated power. This paper presents a numerical model to study the indicated power and pressure variation of three different discharge methods. The power consumption per revolution has been discussed to analyze the discharge flow loss. And the effects of over-compression, under-compression and operation speed have been analyzed. Simulation results show that the errors of indicated power are within 3% and the errors of mass flow rates are within 2%, which proves that the accuracy of the presented model is good enough. Furthermore, the major reason affecting the discharge flow loss is the effective discharge area rather than over-compression or under-compression. And compared with the discharge port with valve, the discharge port without valve has a larger effective discharge area. Adding discharge port without valve in swing compressor can reduce the indicated power.

Elevated river discharge enhances the immigration of juvenile catadromous and amphidromous fishes into temperate coastal rivers.

Anthropogenic alterations to river flow regimes threaten freshwater biodiversity globally, with potentially disproportionate impacts on species that rely on flow cues to trigger critical life history processes, such as migration for diadromous fishes. This study investigates the influence of river discharge on the abundance of juvenile fish moving into rivers by four temperate catadromous or amphidromous species (common galaxias Galaxias maculatus, spotted galaxias Galaxias truttaceus, climbing galaxias Galaxias brevipinnis and the threatened Australian grayling Prototroctes maraena). Fyke netting or fishway trapping was used to catch juvenile fish moving from estuaries into freshwater in five coastal waterways in south-eastern Australia during the spring migratory period. There was a positive relationship between the probability of high catch rates and mean discharge in September. We also found a positive relationship between discharge and the number of recruits captured 22-30 days later in a flow stressed system. In addition, day-of-year had a strong influence on catch rates, with the peak abundance of juveniles for three species most likely to occur midway through the sampling period (spotted galaxias in October, climbing galaxias in late October and Australian grayling in late October and early November). Our study shows that higher magnitudes of river discharge were associated with increased catches of juvenile catadromous and amphidromous fishes. With a limited supply of environmental water, environmental flows used to enhance immigration of these fishes may be best targeted to maintain small amounts of immigration into freshwater populations in waterways or years when discharges are low and stable. When there are natural, large discharge volumes, relatively large numbers of juvenile fish can be expected to enter coastal waterways and during these times environmental flows may not be required to promote immigration.

Modelling and optimisation of the biogas yield after hybrid alkaline-ultrasonic pre-treatment in the early stages of anaerobic digestion of pot ale to shorten the processing time

Whiskey distillery wastewater (pot ale) is classified as a high organic content wastewater and its year-long large discharge volume makes it a suitable substrate for anaerobic digestion from environmental and economical perspectives. Prior to anaerobic digestion, a hybrid alkaline-ultrasonic pre-treatment was performed in order to alter the lignocellulosic structure of the pot ale. Effects of alkaline dose (0–3M NaOH), amplitude ratio (40–100%) and exposure time (1–3h) of ultrasonic pre-treatment on CH4, CO2 and H2S generation within the first 2 days of anaerobic digestion were investigated at a lab scale batch reactor. Response surface methodology (RSM) was adopted as a process modelling and optimisation tool. Significant enhancements in the hydrolysis rate constant and methane yield were achieved in the early stages of digestion. The highest methane yield of the first 2 days digestion was 333±5mL/g VS after implementation of ultrasonic pre-treatment at 70 % amplitude for 3h in isolation leading to 48±4.4 and 56±3.5 % reduction in chemical and biological oxygen demand respectively. The optimum pre-treatment conditions according to combined numerical and graphical optimisation, to maximise CH4 yield while minimising the H2S generation was identified as 40 % amplitude ratio, 1–2.5h exposure time and 0 – 0.6M NaOH.

Dissipation of Pesticide Residues on Grapes and Strawberries Using Plasma-Activated Water

In this study, we present a novel atmospheric air plasma discharge for the generation of plasma-activated water (PAW), with the aim of reducing pesticide residues on fresh fruit. For this purpose, a large discharge volume pin-to-plate cold plasma reactor was employed. The pesticide-spiked grapes and strawberries were processed with varying PAW concentrations to study their efficacies for pesticide degradation combined with an evaluation of any induced changes in key nutritional and quality attributes. The results suggest that the reduction of chlorpyrifos was 79% on grapes and 69% on strawberries while that of carbaryl was 86% on grapes and 73% on strawberries, respectively. The degradation of pesticides in PAW is due to the generation of metastable reactive species including nitrates, nitrites, and hydrogen peroxide. The high oxidation potential and acidic environment of this PAW are proposed as important actors for pesticide dissipation. In addition to the effective pesticide reductions obtained, there were no significant changes in the key physical attributes (color and firmness) of the treated samples and only slight changes in the ascorbic acid levels observed for both strawberries and grapes. This study points to the effective potential of PAW for chemical decontamination of fruit while maintaining important quality and nutritional parameters.

Industrial waste lignin as an antifouling coating for the treatment of oily wastewater: Creating wealth from waste

Treatment of oily wastewater is of paramount importance to prevent unbearable water pollution caused by large discharge volume from industrial and household activities. Membrane technology is an effective oily wastewater treatment technology. However, it suffers from fouling if the membrane element is not modified to possess anti-oil-fouling propensity. Here, we converted an agro-industrial waste into an asset by coating hydrophilic sulfonated kraft lignin on polyethersulfone (PES) membrane using layer-by-layer (LbL) assembly. The polyelectrolytes used in the LbL process were lignin as a polyanion and poly (diallyldimethylammonium chloride) (pDAC) as a polycation. The effects of polyelectrolyte concentration and the number of coating bilayers were examined to fabricate a membrane with an enhanced anti-fouling propensity and minimal loss in permeation performance. The membrane with the highest anti-fouling performance was obtained by coating 3 pDAC/lignin bilayers with 2 wt% concentration of the individual polyelectrolyte solution. This membrane demonstrated a low flux decline of 23.1%, and a high flux recovery ratio of 93.8% when was utilized for the filtration of the n-hexadecane-in-water emulsion as synthetic oily wastewater. The pristine PES membrane showed a flux decline of 44.2%, and the flux recovery ratio of 75.9% under similar test conditions. The improvement in anti-fouling properties of the LbL-assembled membrane was achieved due to its higher underwater oleophobicity (22.6° ± 0.5°) as compared to the pristine PES membrane (71.1° ± 0.7°). The present study opens up a new paradigm to develop anti-fouling membranes by using hydrophilic industrial waste lignin in LbL surface modification of conventional polymeric membranes for oily wastewater treatment.

Investigation of characteristics of discharge pressure pulsation in a twin-screw refrigeration compressor

In this paper, characteristics of discharge pressure pulsation in a twin-screw refrigeration compressor are investigated. A thermodynamic model is developed and validated using data from a comprehensive experimental study. This validated model is then applied to investigate effects of key parameters including condensing temperature, compressor rotational speed, super-feed pressure, part-load operation, and design parameters on the discharge pressure pulsation. The results showed that the discharge pressure pulsation was mainly due to periodic variations of mass and energy flow from the working volumes to the discharge chamber. As the condensing temperature increased or decreased from the design condition, the compressor was in either over- or undercompression leading to an increase in the amplitude of the pressure pulsation. The gas super-feed pressure could increase the pressure pulsation at condensing temperatures below the design value and reduce the pressure pulsation at condensing temperatures above the design value. The analysis also demonstrated that the pressure pulsation was lower at part-load conditions. However, the compressor rotational speed increased both the amplitude and frequency of the pressure pulsation. Theoretical analysis of design parameters indicated that a large discharge volume with a high number of lobes could lower the pressure pulsation. These analyses provide useful information for the compressor design and optimization.

Modeling of plasma transport and negative ion extraction in a magnetized radio-frequency plasma source

Negative ion sources for fusion are high densities plasma sources in large discharge volumes. There are many challenges in the modeling of these sources, due to numerical constraints associated with the high plasma density, to the coupling between plasma and neutral transport and chemistry, the presence of a magnetic filter, and the extraction of negative ions. In this paper we present recent results concerning these different aspects. Emphasis is put on the modeling approach and on the methods and approximations. The models are not fully predictive and not complete as would be engineering codes but they are used to identify the basic principles and to better understand the physics of the negative ion sources.

High CO2 evasion during floods in an Australian subtropical estuary downstream from a modified acidic floodplain wetland

Dissolved CO2 dynamics associated with flooding and postflood recovery were investigated in the lower estuary of the Richmond River and a tributary draining an acidic wetland. Heavy rains (up to 133 mm d−1) resulted in large discharge volumes (up to 250 × 106 m3 d−1) flushing the estuary in less than a day. Maximum values of the partial pressure of CO2 ( PCO2, 2006 Pa or 19,801 μatm) occurred during the postflood recovery period. High PCO2 values were related to the transport of floodplain metabolic products via surface runoff and groundwater as well as the low pH (4.22) of waters draining a modified wetland with coastal acid sulphate soils. Aerobic respiration alone could not explain the high concentrations of CO2 in the estuary and an area of low buffering developed in the 0–20 salinity range. PCO2 was correlated with freshwater discharge in the Richmond River main channel (R2 = 0.82; p 0.05; n = 7). Air-water fluxes of CO2 were at the high end of the range for aquatic systems (maximum 1413 mmol C m−2 d−1, mean 252 mmol C m−2 d−1). This study highlights the large spatiotemporal variability of PCO2, the importance of episodic flooding events, the role of adjacent modified acidic wetlands, and the role of groundwater discharge as a source of CO2 to estuaries. Global estimates of CO2 air-water fluxes in estuaries may be under estimated due to the lack of high-resolution data to capture short-term episodic events (e.g., flooding), in tropical and subtropical areas.

Assessing the performance and cost of oil spill remediation technologies

Abstract Oil spills are an especially challenging chemical contamination event to remediate. Predicting the fate and effects of spilled oil is a formidable task, complicated by its complex chemical composition and the potential for catastrophically large discharge volumes. The proper choice of cleanup technique is equally complex, and depends on a host of factors, including oil type, spill location, spill size, weather, and local regulations and standards. This paper aims to provide a broad review of the current technologies used to remediate oil spills, and the context in which they operate. The chemical characteristics of an oil spill are discussed, including implications for transport modeling, and impacts that arise from short-term and chronic toxicity. The most common remediation technologies (mechanical recovery, dispersants, and in-situ burning) are reviewed, as are emerging technologies (hydrophobic meshes). A comparative analysis is performed on these methods by calculating a maximum oil encounter rate for each device, which is a performance characteristic critical to planning a response effort. Finally, a review of cleanup cost estimation techniques is used to assess the cost-effectiveness of remediation methods. Analysis shows that waiving the legal penalty for recovered oil can result in significant cost savings for the liable party, and may drive improvements in recovery-focused technologies. The authors suggest continued research into improving oil spill recovery methods and understanding the fate of individual compounds in the spilled oil. This will both minimize potential environmental damages, and reduce the uncertainty of their impacts.

Fracture flow and groundwater compartmentalization in the Rollins Sandstone, Lower Mesaverde Group, Colorado, USA

This paper presents a site-specific conceptual model of groundwater flow in fractured damage zones associated with faulting in a package of sedimentary rocks. The model is based on the results of field and laboratory investigations. Groundwater and methane gas inflows from fault-fracture systems in the West Elk coal mine, Colorado, USA, have occurred with increasing severity. Inflows of 6, 160 and 500 L s−1 discharged almost instantaneously from three separate faults encountered in mine workings about 460 m below ground level. The faults are about 600 m apart. The δ 2H and δ 18O compositions of the fault-related inflow waters and the hydrodynamic responses of each fault inflow indicate that the groundwaters discharge from hydraulically isolated systems. 14C data indicate that the groundwaters are as much as 10,500 years old. Discharge temperatures are geothermal (≈30°C), which could indicate upwelling from depth. However, calculations of geothermal gradients, analysis of solute compositions of groundwater in potential host reservoirs, geothermometer calculations, and results of packer testing indicate that the fractured groundwater reservoir is the Rollins Sandstone (120 m thick) directly beneath the coal seams. The packer test also demonstrates that the methane gas is contained in the coal seams. A geothermal gradient of 70–80°C km−1, related to an underlying intrusion, is probably responsible for the slightly elevated discharge temperatures. Large discharge volumes, as great as 8.2×105 m3 from the 14 South East Headgate fault (14 SEHG), rapid declines in discharge rates, and vertical and horizontal permeability (matrix permeability generally <0.006 Darcy) indicate fracture flow. An in-mine pumping test demonstrates that the 14 SEHG fault has excellent hydraulic communication with fractures 50 m from the fault. Aeromagnetic data indicate that the faults are tectonically related to an igneous body that is several thousand meters below the coal seams. Exploratory drilling has confirmed a fourth fault, and two additional faults are projected, based on the aeromagnetic data. The conceptual model describes a series of parallel, hydraulically separate groundwater systems associated with fault-specific damage zones. The faults are about 600 m apart. Groundwater stored in fractured sandstone is confined above and below by clayey layers.

The development of a spatially uniform fast ionization wave in a large discharge volume

A high-voltage nanosecond breakdown in the form of a fast ionization wave (FIW) has been obtained and investigated in a large discharge volume (of 40 l). For various regimes in the air pressure range -4 Torr the velocity of breakdown front propagation and energy absorption by the plasma were measured. A high level of spatial uniformity and reproducibility of the discharge was demonstrated. The possibility of propagation of FIWs in electrodeless systems was shown. It is demonstrated that the FIW propagates quasi-spherically in a free-boundary space until the reduced electric field in the wavefront is close to or exceeds the electron run-away threshold, otherwise the FIW loses its homogeneity and becomes transformed into a streamer corona discharge.

Comparative hydrological behaviour of forested and cleared catchments in southeastern Australia

The effects of clearing on the hydrology of small upland catchments were evaluated on two experimental catchments; one vegetated by natural remnant eucalypt forest and the other completely cleared of forest and maintained in grassland for over 80 yrs. The hydraulic properties of soils in both catchments were measured. The grassland catchment generated high-peak stormflows and large discharge volumes irrespective of antecedent soil moisture conditions, whereas the forest catchment gave little runoff provided the antecedent soil water content was below 60% of the available storage capacity. Subsurface (0.1–0.4 m) hydraulic conductivities of the grassland soils were about half those of the undisturbed forest at slope positions above the depression areas, and even less in the depressions, and this produced the differences in runoff behaviour of the two catchments. Water table responses to rainfall in the two catchments indicated that continuous macropore pathways for preferential water movement contributed to rapid rises and falls in forest water tables, but these pathways appeared to be absent under grassland. Impermeable depression areas in the grassland catchment generated much of the runoff from the catchment, so that it behaved as if it were constantly in an advanced stage of saturation. In contrast, the depression areas under forest were relatively permeable and therefore runoff was delayed until the soils became wet, provided hydrophobic conditions had not developed. Runoff from a 277 km 2 catchment, containing almost equal proportions of forest and grassland and with comparable topography to the two experimental catchments, was analysed to demonstrate that findings from the two small catchments could be used to interpret the hydrological behaviour of the large catchment. The implications of these results for the future management of forested landscapes are discussed.

Crossed-tube fluid-ballasted electrode pair for EDL applications

The design and operational features of a fluid-ballasted electrode structure for a high powered EDL CO(2) laser are described. This new device incorporates a crossed-tube geometry and as such is much simpler and inexpensive to fabricate than previous multielement or pin electrodes. Hot boundary layer formation at the electrode surfaces is minimized by a ducted flow-through feature also incorporated into the structure. This further assists in suppression of glow-to-arc transitions. The modular design used allows easy scaling to very large discharge volumes. A 40-liter cw CO(2) laser discharge system has recently been developed using this simplified crossed-tube fluid-ballasted electrode pair concept.

Construction and Operation of a Double-Discharge TEA CO2 Laser

We have operated a double-discharge transversely excited atmospheric pressure (TEA) CO2 laser with a Marx bank system at high output energies and efficiencies over a large discharge volume. The typical laser energy output is approximately 17 J/liter at an efficiency of 24% and a pulse-to-pulse variation of less than 10%. The parameters that govern the operation of the system are discussed.