Bench-scale Tests Research Articles

Correlations between Bench-Scale and Large-Scale Extinction Metrics for Firefighting Foams

Locally weighted regressions (LWR) were calculated between MIL-PRF-24385 1.8 m diameter pool fire extinction results and various 19 cm pool fire metrics, as compiled in a recent database. The goal: to define correlations between bench and large-scale foam fire extinction experiments to improve bench-scale experiments to more rapidly screen the firefighting potential of environmentally-friendly foams. Bench-scale metrics included the area under the curve (AUC) for extinction time versus foam flow rate profiles, the average extinction times at binned foam flow rate ranges, and CO2-based extinction times, determined through tunable diode laser absorption spectroscopy (TDLAS) measurements above the pool fire. When cross-validation was implemented within the LWR algorithm, the AUC values, CO2-based extinction times, and extinction times for a flow rate-bin > 1500 ml/min showed the best correlations to large-scale data; however, the R2 values were all below 0.6, indicating a low level of correlation. Although differences between active versus passive firefighter and foam generation methods exist between the two scales, data accuracy and limited data are likely contributing the most to low R2 values. The LWR correlations are promising and can be improved with accurate data, providing confidence in bench-scale testing despite diminished radiation intensity and turbulence associated with larger fires.

Multiscale insights into polyamide membrane fouling during reverse osmosis of rare earth wastewater

The rare earth elements (REEs) industrial wastewater is characterized by high ammonium nitrogen and low-strength organic compounds. Reverse osmosis (RO) process is effective for the REEs wastewater treatment. However, membrane fouling deteriorated the RO process. In this work, the fouling mechanism during RO process of REEs wastewater was elucidated via multiscale methods. A series of bench-scale fouling tests with simulated REEs wastewater containing high NH4+–N and different concentrations of 2-ethylhexyl phosphonic acid mono-(2-ethylhexyl) ester (P507) were performed with a commercial RO membrane to evaluate the fouling extent of the RO process. A critical P507 concentration (0.25 mg L−1) was observed where the fouling pattern changed qualitatively. When the P507 concentration was lower than 0.25 mg L−1, the relative flux increased and the membrane surface became more hydrophilic. When P507 reached this critical point, severe fouling occurred accompanied with a more hydrophobic membrane surface. Multiscale simulations [i.e., molecular dynamics (MD) and dissipative particle dynamics (DPD)] revealed that the fouling layer network varied with P507 concentration. This work provides in-depth insights into membrane fouling mechanism in the REEs wastewater, and has enlightening significance for fouling control strategies and the innovation of anti-fouling membrane materials.

Efficient flotation separation approach of apatite from calcite for phosphate up-grading using phosphorylated starch macromolecules as a selective depressant

Physico-chemical similarities of surface proprieties of calcite and apatite make their separation challenging. Effective flotation separation requires sustainable depressants to mitigate environmental consequences associated with traditional chemical reagents. Here, for the first time we explore the potential of phosphorylated starch (PS) derived from potato waste as a green and effective depressant. Starch was modified using a straightforward phosphorylation process, resulting in PS with a remarkable charge density exceeding 6000 mmol kg−1. The PS was then evaluated for its ability to depress apatite, enhancing the separation efficiency of apatite from calcite in phosphate rock beneficiation via reverse flotation. Micro-flotation experiments revealed PS's distinct depression effect on apatite while minimally impacting calcite. Floatability rates of apatite and calcite were 90.45 % and 92.68 %, respectively. Introducing 10 mg/g PS drastically reduced apatite recovery to <19 %, while calcite recovery remained at 78.80 %. The bench-scale flotation tests demonstrated an upgrading of the phosphate rock to 70,64 % Bone Phosphate of Lime (BPL) with a yield of 89,41 %. Mechanistic studies employing zeta potential (ZP), and wettability analysis elucidated the depression mechanism. Apatite retained hydrophilicity post-PS addition and conditioning with ester, while calcite-acquired hydrophobicity even in the presence of PS. Furthermore, PS exhibited substantial adsorption onto the apatite surface through chemical reactions involving the phosphate groups and the activated calcium sites on the apatite. Overall, PS stands out as a promising, eco-friendly, and remarkably efficient depressant for separating apatite from calcite through flotation.

Electrochemically assisted remediation of a highly chlorinated organic polluted sludge: A full-scale case study

Electrochemical technology has emerged as an effective method to remediate soils in a laboratory environment. However, its practical application is often challenging due to the complexity of adopting small-scale parameters and identifying all the potential problems during the operation of electrokinetic plants. Here, a prototype demonstration in a space environment (Technology Readiness Level 7) is reported to remediate a 5 × 5 m2 plot of a leachate pond from a landfill containing dense sludge contaminated with chlorinated organic compounds. Bench-scale tests (50 kg per mock-up) were initially carried out to evaluate the effects of the key parameters (electric field, surfactants, and electrode materials) and demonstrated the feasibility of reducing contaminant concentrations in the sludge through dehalogenation and volatilisation. The average electro-osmotic flux was 0.23 cm day−1, comparable to that reported for silty soils. Iron electrodes enhanced electrokinetic water transport and reduced acidification, while glassy carbon electrodes increased water volatilisation, acidity near the anode, and dehalogenation of chlorinated hydrocarbons. Based on these findings, the full-scale design and operating conditions were selected. After 590 h of operation, the total pollutant concentration was reduced by 34 %, mainly due to volatilisation, using a sequence of six iron-electrode arrays at 1 V cm−1, which increased the sludge temperature over 60 °C. An evaporation rate of 0.021 cm d−1 and an electro-osmotic flux of 0.62 cm d−1 were achieved, consistent with the bench tests. These findings demonstrate the potential of electrokinetic plants for the remediation of sludges and provide expertise applicable to future remediation at other contaminated sites.

High recovery design of reverse osmosis process with high permeate water quality and low wastewater discharge for ultra-pure water production

Ultra-pure water (UPW) for electronic industry is produced via many unit processes including reverse osmosis (RO), pretreatments, membrane degasifier, and ion exchange processes. Generally, 2-pass RO system is adopted in UPW production process to remove ionic and organic matters to meet water quality requirements of post-treatments. Since RO concentrate occupies most of wastewater discharged from UPW production process, high recovery design is beneficial to reduce wastewater discharge. According to the solution-diffusion model, permeate concentrations increase at higher feed concentrations, which may limit to increase RO recovery. Interestingly, the bench-scale 2-pass RO test using five commercial membrane modules revealed permeate concentrations were not affected by feed concentrations below a critical value (35 mg/L as NaCl in this work). This means the first-pass RO recovery can be increased without decreasing permeate water quality as far as second-pass RO feed concentrations are below the critical values. Various 2-pass UPW-RO system designs (250 mg/L as NaCl of feed concentration) were analyzed using an industrial RO system simulator to investigate the effect of the first- and second-pass recovery. The simulation works found that increasing the first- and second-pass recovery decreased wastewater discharge, energy consumption, and the number of membrane modules without degrading permeate water quality.

Bench scale and pilot plant flotation tests with phosphate rock from the Alto Paranaíba Region/MG, Brazil

This paper highlights the significant advances in phosphate recovery in the Alto Paranaíba region, Minas Gerais, as a result of collaboration between RJMG and the local mining industry. The applied methodology focused on the development and use of the innovative AGEM B plant collector, going from laboratory tests to pilot plant tests. The results demonstrated the superiority of AGEM B compared to standard collectors, where a 14.1% increase in P2O5 recovery and a 40% reduction in collector dosage were observed. On a pilot scale, the average P2O5 content in the rougher tailings was 1.66 ± 0.29%, 38.40% lower than that obtained with the collector used by the mining company (a fatty acid) which presented an average content of 2.69 %. The average P2O5 content in the recleaner concentrate was 32.15 ± 2.59%, 8.27% higher than that obtained with fatty acid (average of 35.05%). Increases of 43.59% in mass recovery (average of 11.20 ± 1.31%) and 36.28% in metallurgical recovery (average of 71.00 ± 4.82%) were observed. This work highlights the importance of innovation and strategic collaboration to overcome challenges in mineral processing, recommending the use of AGEM B on an industrial scale for better efficiency and sustainability in the phosphate recovery process.

Performance and economic viability assessment of a novel CO2 adsorbent for manufacturing and integration with coal power plants

This study assesses the performance and economic feasibility of a novel CO2 adsorbent for post-combustion capture in DOE/NETL’s 650 MWnet SubC PC power plant (case B11B). Bench-scale tests showed an initial adsorption capacity of 16.3 wt%, which decreased to 12.1 wt% after 41 adsorption–desorption cycles due to induced particle aggregation by over-humidification. With a conservative adsorption capacity of 8.8 wt% and 695 adsorption–desorption cycles, an adsorbent replenishment rate of 10 tonnes/h is necessary to capture 90% of CO2. The breakeven sale price of the adsorbent produced at this rate is $1,293/tonne, which is 40 to 80 times lower than prices for K2CO3 adsorbents reported in the literature (e.g., K2CO3/TiO2, K2CO3/ZrO2) while providing better capture performances. Sensitivity analysis reveals that increasing the plant production rate from 10 to 40 tonnes/h reduces the sale price by 8%. The study also compares the CO2 capture cost to Cansolv, an integrated solvent-based technology. The novel adsorbent requires 2.4 GJ/tonne of CO2 for regeneration, lower than Cansolv’s 2.7 GJ/tonne. With conservative performance estimates, the capture cost is $54/tonne of CO2, slightly higher than Cansolv’s $45/tonne. To achieve lower or comparable capture costs to Cansolv, the adsorbent should meet one of the following conditions at a commercial scale: minimum 950 cycles, 16 wt% capture capacity, 50% of the adsorbent recovery, or a reduced cost to $646/tonne by upscaling the manufactury to 75 tonnes/h.

High-Performance Crown Ether-Modified Membranes for Selective Lithium Recovery from High Na+ and Mg2+ Brines Using Electrodialysis

The challenge of efficiently extracting Li+ from brines with high Na+ or Mg2+ concentrations has led to extensive research on developing highly selective separation membranes for electrodialysis. Various studies have demonstrated that nanofiltration membranes or adsorbents modified with crown ethers (CEs) such as 2-OH-12-crown-4-ether (12CE), 2-OH-18-crown-6-ether (18CE), and 2-OH-15-crown-5-ether (15CE) show selectivity for Li+ in brines. This study aims to develop high-performance cation exchange membranes (CEMs) using CEs to enhance Li+ selectivity and to compare the performance of various CE-modified membranes for selective electrodialysis. The novel CEM (CR671) was modified with 12CE, 18CE, and 15CE to identify the optimal CE for efficient Li+ recovery during brine electrodialysis. The modification process included polydopamine (PDA) treatment and the deposition of polyethyleneimine (PEI) complexes with the different CEs via hydrogen bonding. Interfacial polymerization with 1,3,5-benzenetricarbonyl trichloride-crosslinked PEI was used to create specific channels for Li+ transport within the modified membranes (12CE/CR671, 15CE/CR671, and 18CE/CR671). The successful application of CE coatings and Li+ selectivity of the modified membranes were verified through Fourier-transform infrared spectroscopy, zeta-potential measurements, and electrochemical impedance spectroscopy. Bench-scale electrodialysis tests showed significant improvements in permselectivity and Li+ flux for all three modified membranes. In brines with high Na+ and Mg2+ concentrations, the 15CE/CR671 membrane demonstrated more significant improvements in permselectivity compared to the 12CE/CR671 (3.3-fold and 1.7-fold) and the 18CE/CR671 (2.4-fold and 2.6-fold) membranes at current densities of 2.3 mA/cm2 and 2.2 mA/cm2, respectively. At higher current densities of 14.7 mA/cm2 in Mg2+-rich brine and 15.9 mA/cm2 in Na+-rich brine, the 15CE/CR671 membrane showed greater improvements in Li+ flux, approximately 2.1-fold and 2.3-fold, and 3.2-fold and 3.4-fold compared to the 12CE/CR671 and 18CE/CR671 membranes. This study underscores the superior performance of 15CE-modified membranes for efficient Li+ recovery with low energy demand and offers valuable insights for advancing electrodialysis processes in challenging brine environments.

A new experimental method to study the flame inhibition performance of low concentration halogenated gas

The minimum fire extinguishing concentration is a key index for the development of next generation chemical clean fire extinguishing gases, which is usually got by the cup-burner. The fire suppression performance of low concentration of chemical gas is hard to be understood by the available methods. In this work, the fundamental acknowledgement of steady flame surface attacking mechanism by halon functional group is newly discussed by conducting a series of bench scale tests with a cylindrical channel under a varied fluorinated gases. The characteristics of flame propagation under differentiated air atmosphere environmental conditions is obtained. The influence of fluorine-containing gas flow rate on flame propagation speed is clarified. A dimensionless relationship including atomic radius, bond length, polarization degree, molar mass and molar volume are proposed to describe the influence of low concentration of fluorine-containing gas on flame propagation speed. It provides an insight for the understanding of the flame inhibition performance of low concentration halogenated gas.

An innovative deformation coordination method for analyzing distortion effects on box girders

A deformation coordination method is proposed in this study to account for the distortion effects on a box girder. The differential equation for distortion in vertical web box girders is derived based on the deformation coordination condition of the distortion angle, considering both external loads and internal forces. Subsequently, a comparative analysis is conducted to explore the similarities and differences between the differential equations derived from the proposed deformation coordination method, the plate element analysis method and the total potential energy variation method. The accuracy of the proposed approach is verified through bench-scale tests and numerical simulations. The findings indicate that the derived governing distortion differential equation and distortion attenuation coefficients in the proposed method align with those obtained from the plate element analysis method and the total potential energy variational method, which enhances the applicability to allow for the distortion equations to be obtained simply by calculating the distortion displacements. The analytical findings regarding the distortion warping normal stresses on the cross-sections of the box girders demonstrate favorable correspondence with the experimental results, displaying an acceptable error ranging from − 0.3% to 5.4%. Moreover, the peak of distortion warping normal stresses on the mid-span cross-section increases with higher span-to-depth ratios and height-to-thickness ratios of the web. Consequently, augmenting the thickness of the box wall proves to be an effective means of reducing the distortion effect in box girders.

Understanding the Catalytic Effect on the CO2 Regeneration Performance of Amine Aqueous Solutions

To address the high energy consumption of the carbon capture and storage process in the shipping industry, the effects of several commonly used commercial catalysts, such as HZSM-5-25, γ-Al2O3, and SiO2, as well as a self-prepared catalyst, Zr-HZSM-5-25, on the regeneration of MEA solution and MEA + MDEA mixed solution were investigated in this paper. The results showed that Zr-HZSM-5-25 had the best catalytic effect on the regeneration process of the MEA aqueous solution, which could increase the instantaneous maximum CO2 regeneration rate of the MEA-rich solution by about 8.25% and the average regeneration rate by about 5.28%. For the MEA + MDEA mixed solution, the reaction between tertiary amine MDEA and CO2 produced a large amount of HCO3− in the reaction system, which could accelerate the release of CO2 to a large extent, which resulted in the catalytic effect of the Zr-HZSM-5-25 catalyst on the regeneration process of the mixed amine solution being significantly lower than that on the single MEA solution, with an increase of 4.91% in the instantaneous maximum regeneration rate. This instantaneous maximum regeneration rate was only increased by 4.91%. While Zr-HZSM-5-25 showed a better performance in the bench-scale test, it reduced CO2 regeneration energy consumption by 7.3%.

Mitigating municipal solid waste fouling in biofuel conversion via screw surface modifications

Municipal solid waste (MSW)'s 40–60 % carbon content makes it a feedstock for biofuel production via pyrolysis. One challenge in the conversion process is MSW fouling due to thermal decomposition. The accumulated deposit on the injection screw often leads to plugging and constriction. This study examined the morphology and composition of the MSW fouling deposit and conducted a thermal simulation to understand the temperature gradience of the injection screw. Surface modifications including smoothening and anti-adhesion coating were proposed for the injection screw to address the deposit problem. For evaluating the candidate mitigations, a bench-scale fouling test was developed with the gas environment, temperature, and sliding speed relevant to the contact interface between the MSW particles and the screw. Results suggested that a smoother screw surface could reduce the grip and a non-metallic coating with a lower surface energy could decrease adhesion, consequently leading to less fouling. Specifically, reducing the roughness from 2 to 0.6 and then to 0.2 μm proportionally decreased the amount of deposit, and the diamond-like-carbon, CrN, and NiCr–CrC composite coatings effectively hindered the fouling process. This study provides fundamental insights into the MSW fouling and proof-of-concept of potential mitigations through the screw surface modification.

Effectiveness of advanced oxidation process for the pretreatment of mixed agrofood industrial wastewater from Nablus City, Palestine

ABSTRACT Food processing industries generate complex effluent with high levels of organic and inorganic contaminants. Without proper treatment, significant operational, environmental, and public health issues may arise. This study aimed to assess the Fenton reaction’s efficacy as an advanced oxidation process (AOP), to treat mixed dairy and slaughterhouse effluent from Nablus city. Bench-scale tests showed inadequate results (45.2% COD removal) because of high pollution levels (COD: 15400 -18,100 mg L−1). Further tests have combined the Fenton process with three pre-treatment methods: (A) coagulant addition, (B) settling, and (C) flocculent application. Fenton’s process with flocculent achieved significant removal of organic (88.4% COD; 84.1% TKN) and inorganic (91.0% TSS; 62.4% TS) contaminants under optimised conditions (H2O2/COD ratio 2:1, H2O2/Fe + 2 ratio 10:1, pH = 3). Treated wastewater from trial (C) let meeting local regulatory standards with COD levels below 2,000 mg/l.

Demulsification of steam-assisted gravity drainage (SAGD) emulsions under high temperature and high pressure: Effects of emulsion breaker and reverse emulsion breaker dosages

Effective treatment of complex emulsions formed during steam-assisted gravity drainage (SAGD) production is crucial for oil/water separation and subsequent processing. However, it remains challenging due to the complexity of SAGD emulsions, and there are only very limited studies on demulsification under simulated SAGD conditions. This study systematically characterized the comprehensive properties of a fresh field SAGD emulsion with about 84.6 % water and 15.4 % bitumen, and then achieved effective demulsification under a simulated SAGD condition at 135 °C and 60 psi via adding a poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) copolymer (as a model emulsion breaker or EB) combined with a branched polyethylenimine (PEI, as a model reverse emulsion breaker or REB) in a bench-scale bottle test setup. The effects of EB and REB dosages on the demulsification of the SAGD emulsion were evaluated based on the properties of the separated phases. Dynamic interfacial tension, zeta potential, and coalescence time were measured to reveal the demulsification mechanisms of EB and REB. The highly interface-active EB facilitated oil dehydration by displacing the natural interface-active species at the interfaces, disrupting the rigid interfacial films and promoting water droplet coalescence, while the cationic REB aided water de-oiling by neutralizing oil droplet surface charges, disrupting the rigid interfacial films and promoting the approach and coalescence of oil droplets in aqueous media. This work has improved the understanding of SAGD emulsion characteristics, the effects of EB and REB dosages on the demulsification performance, and the underlying demulsification mechanisms in SAGD operations. The results provide useful insights for developing effective and cost-efficient chemical approaches to address challenging emulsion issues in oil production.

Concentration of goethitic slimes by comprehensively exploring a ternary Collector-Frother flotation reagent and ultrasound dispersion

The recovery of elements of interest from tailings has been increasingly studied to reduce their generation and mitigate disposal risks, and in iron ore production the reality is no different. This work presents a comprehensive assessment of parameters in bench scale tests for two innovative possible solutions for recovering iron minerals contained in ultrafine tailings: a new collector reagent formulation composed of a mixture of amidoamine, etheramine and a frother, without the need of applying a depressant in reverse cationic flotation, preceded by the application of ultrasound as a tool for physical particle dispersion. The new collector presented better results than its constituents separately. The presence of a frother in its composition helps diminishing water recovery and entrainment. The main limiting factor for enhancing the quality of the concentrate is the fraction of alumina in the feed. Molecular simulations gave initial insights on the mechanisms behind the new collector and the gangue minerals interaction. The application of ultrasound at alkaline pH promotes better particle dispersion ensuring sufficient exposed surfaces for selective adsorption of the new collector. The influence of the intensity and residence time applied at the sonication step, as well as the percentage of solids are evaluated. The study shows that it is possible to increase the metallurgical recovery by 6 % for a difficult to process, goethite-rich slimes sample with 51% Fe from the Iron Quadrangle in Brazil.

The Tube Furnace with Online Mass Loss Measurement as a New Bench Scale Test for Pyrolysis

In this paper, a new gram scale experiment with well characterised boundary conditions is proposed for pyrolysis experiments. The set-up consists of a tube furnace, based on ISO19700, with a newly designed concept for a balance within the oven, allowing for online mass loss measurements. Samples with a length up to 50 cm can be investigated in this apparatus. The oven allows for experiments at fixed temperatures or at fixed heating rates, under controlled atmosphere, w.r.t. gas composition and flow rate. A thorough characterisation of the set-up is presented, including aspects like reproducibility of the heating rate or the precision of the balance. The functionality of the balance has been demonstrated with calcium carbonate (CaCO3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{3}$$\\end{document}) experiments. This material was chosen because it decomposes in a single reaction, which only releases CO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}. This allows for comparison between the mass loss rate of the balance and the CO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document} production rate, measured by a gas analyser. Results for two different heating rates: 3 K/min and 5 K/min and for different masses (25 g and 8.5 g) are presented. The two measurement methods are in excellent agreement. Finally, the data obtained from the new experimental set-up is compared to results from thermogravimetric analyser (TGA) experiments.

THE EFFECT OF AIRGAP THICKNESS ON THERMAL PROTECTIVE PERFORMANCE IN HEAT RESISTANT CLOTHING

The thermal protective performance is provided by thermal protective clothing worn by people who work in high temperature environments and is highly influenced by air gaps. In this paper, effect of air gap thickness on thermal protective performance as indicated by the time before degree burn were investigated. 3 layers of thermal protective clothing with 3 types of fabrics that have been selected will be tested using an experimental method. The research will be conducted through experimental tests using the fabric level method on a bench-scale test apparatus which is equipped with 4 thermocouples and using gas torch as a heat source. The air gap located between the layers of thermal protective clothing will be varied with different thickness in a vertical orientation. The size of the air gap used varies from 01 mm, 2.51 mm, 51 mm, and 7.51 mm. The results show that the temperature distribution in each layer of clothing from the outer shell to the thermal linear has decreased. In addition, time before degree burn which is an indicator on thermal protective performance shows a positive effect on the addition of air gap thickness where the optimum air gap thickness is shown at 7.5 mm variation. It is hoped that the results of this research can be a source or useful information in mechanical engineering, especially in the fields of thermal comfort and fire safety.

Quantification of hydraulic characteristics and validation of CFD simulation of subsurface flow constructed wetlands using tracer

The analysis of residence time distributions (RTDs) is of great significance in the hydraulic characterization of subsurface flow constructed wetlands (SSF-CWs), and tracer experiments and simulations are generally used methods to obtain RTDs. This study developed a computational fluid dynamics (CFD) model involving two tracer tracking approaches in order to understand and quantify the flow behavior in SSF-CW. To validate the CFD model, RTDs were obtained from bench-scale impulse response tests with finite-constant injection of tracer, and the hydraulic indexes were corrected by introducing tracer injection time and nominal residence time in the formulae. The shape similarities of RTDs between the CFD model, the gamma model and observation were evaluated by a dynamic time warping algorithm, where the CFD model incorporating advection, diffusion and dispersion processes had the highest shape similarity (0.94–0.98). The proposed CFD model gave the tracer the same velocity field as the fluid, characterizing more accurate hydraulic indexes compared to the gamma model. The CFD model is appropriate for design optimization prior to full-scale construction since it saves time and is environmentally benign. It also gives visualization of the tracer trajectory, which aids in understanding contaminant fate and transport within the SSF-CW.

Development and performance evaluation of active insulation systems using solid-state thermal switches

Traditional building envelopes have passive insulation systems that cannot respond to dynamic changes in the environment. An Active Insulation System (AIS) consists of Active Insulation Materials (AIMs) that dynamically vary the thermal conductivity of the insulation system. Several researchers have evaluated the impact of AIS on building thermal and energy performance by using simulation tools. Up to 70% savings in annual heating and cooling energy and significant reductions in peak demand have been predicted for some climates with wall systems employing AIS. However, materials and assembly development still need a cost-effective product that achieves the required performance. In this study, we present the process of developing an AIS that we will install in a test hut for its performance evaluation. Minimum performance criteria of the AIS system are developed based on R-low/R-high ratio, required time and efficiency to switch states, and cost estimates. The following steps during this study are creating the concept to meet the requirements, predicting the performance via simulations, developing the experimental setup for bench-scale testing, and finally, constructing a full-scale wall assembly and monitoring the performance when exposed to environmental chamber tests. The selected approach uses off-the-shelf products to create an AIS that can switch R-value between 0.98 ft2·°F·h/BTU (0.173 m2·K/W) and 5.81 ft2·°F·h/BTU (1.02 m2·K/W) and have a switching time of less than one minute between R-high and R-low.

Techno-economic comparison of flocculation combined with dissolved air flotation versus sedimentation for microalgae harvesting

Microalgae are a promising new source of biomass but the harvesting method needs to optimised to reduce the production cost. In a two-step harvesting process, the bulk water is removed via flocculation (first step) followed by complete dewatering using centrifugation (second step). Flocs can be separated from the bulk water using either gravity sedimentation or dissolved air flotation (DAF). DAF requires a more complex setup and demands more energy than sedimentation, but it is faster and generates a sludge with a higher dry matter content. This study aims to compare the performance of DAF and sedimentation in laboratory experiments and then estimates the cost for a 100-hectare farm using sedimentation versus DAF for harvesting (step-1) and using a decanter centrifuge (step-2) for dewatering. Chlorella vulgaris was the model species and poly(dimethylaminoethyl methacrylate) (pDMAEMA) was synthesised and used as the flocculant. In bench-scale testing, sedimentation and DAF achieved maximum harvesting efficiencies of 87 % and 98 %, respectively. Sedimentation was slow and generated a sludge with low solids content (1.1 %). DAF achieved a fast separation and generated a sludge with 3× higher solids content of 3.4 %. When estimating the costs of biomass harvesting at 100-hectare scale, DAF was found to have higher capital and operating expenditure than sedimentation. However, when combining harvesting with the dewatering step in a two-stage harvesting-dewatering system, the total capital and operating expenditure was projected to be 20–38 % and 10–18 % cheaper, respectively, than sedimentation. This is due to the faster separation, higher sludge solids content, and greater separation efficiencies obtained via DAF than sedimentation. Hence, DAF is recommended over sedimentation for harvesting microalgae. Importantly, this study showcases that contrary to conventional belief, flocculation–DAF is cheaper than flocculation–sedimentation for large-scale algal harvesting.