Bed Volume Research Articles

Oxygen defects of MgLa-LDH enhancing electrostatic attraction and inner-sphere complexation during phosphate adsorption from wastewater

The introduction of oxygen defects toward constructing new binding sites is a promising strategy for improving the adsorption performance of layered double hydroxide (LDH). Here, a facile and novel method for adjusting the abundance of oxygen defects by regulating the preparation pH values of MgLa-LDH was used to enhance phosphate efficient adsorption. The MgLa-LDH with high-defect-degree (ML-11) presented a larger adsorption capacity and faster mass-transfer than that of low-defect-degree LDH (ML-10). Particularly, the adsorption capacity (121.56 mg/g) and initial adsorption rate (16.25 mg/g⋅min) of ML-11 were 1.8 times and 2.6 times higher than those in ML-10 in neutral condition, respectively. Characterization results confirmed that oxygen defects played a vital role in phosphate adsorption. The promotion mechanism of oxygen defects on phosphate absorption included the enhancing electrostatic attraction via increasing surface electron density, boosting M-OH groups generated by oxygen defects, and reducing adsorption energy. Compared with ML-10, ML-11 had similar or even better resistance of coexisting anions, and regeneration performance. Furthermore, the performance of ML-11 was verified in fixed-bed column experiment with real wastewater, and the treatment bed volume of it (978.6 BV) was higher than that in ML-10 (509.7 BV). The oxygen defects method can provide a promising choice for improving the material properties of efficient phosphate removal.

Mechanistic Study of Arsenate Adsorption onto Different Amorphous Grades of Titanium (Hydr)Oxides Impregnated into a Point-of-Use Activated Carbon Block.

Millions of households still rely on drinking water from private wells or municipal systems with arsenic levels approaching or exceeding regulatory limits. Arsenic is a potent carcinogen, and there is no safe level of it in drinking water. Point-of-use (POU) treatment systems are a promising option to mitigate arsenic exposure. However, the most commonly used POU technology, an activated carbon block filter, is ineffective at removing arsenic. Our study aimed to explore the potential of impregnating carbon blocks with amorphous titanium (hydr)oxide (THO) to improve arsenic removal without introducing titanium (Ti) into the treated water. Four synthesis methods achieved 8-16 wt.% Ti loading within the carbon block with 58-97% amorphous THO content. The THO-modified carbon block could adsorb both oxidation states of arsenic (arsenate and arsenite) in batch or column tests. Modified carbon block with higher Ti and amorphous content always led to better arsenate removal, achieving arsenic loadings up to 31 mg As/mg Ti after 70,000 bed volumes in continuous flow tests. Impregnating carbon block with amorphous THO consistently outperformed impregnation using crystalline TiO2. The best-performing system (TTIP-EtOH carbon block) was an amorphous THO derived using titanium isopropoxide, ethanol, and acetic acid via sol-gel technique, aged at 80° for 18 hours and dried overnight at 60°. Comparable pore size distribution and surface area of the impregnated carbon blocks suggested that chemical properties play a more crucial role than physical and textural properties in removing arsenate via amorphous Ti-impregnated carbon block. Freundlich isotherms indicated energetically favorable adsorption for amorphous chemically synthesized adsorbents. The mass transport coefficients for the amorphous TTIP-EtOH carbon block were fitted using a pore surface diffusion model, resulting in Dsurface = 3.1×10-12 cm2/s and Dpore = 3.2×10-6 cm2/s. Impregnating the carbon block with THO enabled effective arsenic removal from water without adversely affecting the pressure drop across the unit or the carbon block's ability to remove polar organic chemical pollutants efficiently.

Removal of Na and K from aqueous solutions of Li salts

ABSTRACT The sorption properties of manganese (III, IV), the ferrocyanides sorbents to Na+ and K+ in Li salts water solutions have been studied. The sorption properties of the sorbents have been determined under batch and dynamic conditions using Li salts water solutions. The granulated sorbents, based on manganese oxide, obtained via interaction of KMnO4 and H2O2 solution, heated at 500°C, with NaOH or KOH, have the best characteristics. These sorbents are also chemically and mechanically stable for implementing them in the sorption-desorption procedure. The sorption resource of the granulated manganese oxide until the 50% breakthrough of sodium is 60 bed volumes, the potassium is 280 bed volumes. The investigated sorbents can be used in Na+ and K+ ions extraction for obtaining highly purified lithium salts.

Alpha-MnO2 nanoneedle embedded in MgO-chitosan biochar for higher removal of arsenic from groundwater: Co-effects of oxidation and adsorption

High performance and high permeability of reactive materials are crucial issues for the remedy of arsenic (As)-enriched groundwater by permeable reactive barriers. The remediation strategy integrating adsorption and oxidation has gained wide concerns due to its deep removal for As(Ⅲ). In this study, a granular bifunctional nanocomposite MgO-Chitosan-MnO2 (MgO-CS-MnO2) was fabricated as permeable reactive media for the in-situ remediation for high As groundwater. The needle structure of MnO2 could provide adequate oxidation sites, furthermore, the multilayer porous characteristic of MgO-CS could also meet higher adsorption capacity. As a result, the estimated maximal adsorption capacity of MgO-CS-MnO2 for As(Ⅲ) reached to 266.61 mg/g and 578.05 mg/g for arsenate (As(Ⅴ)), which are much higher than current similar adsorbents. The adsorption behaviors of As(Ⅲ/Ⅴ) follow pseudo-second-order kinetic model and Freundlich isotherm model, suggesting that both As(Ⅲ) and As(Ⅴ) are mainly chemisorbed onto MgO-CS-MnO2. It could perform effectively in a broad range of pH values (3−11), moreover, competing oxyanions (CO32-, NO-, and SO42-), organic matters (humic acid) and ion strength exert no significant influence towards As remediation. XPS results revealed As(Ⅲ) adsorbed onto composite completely transformed to As(Ⅴ), and removal mechanisms involved oxidation and metal-O-As(Ⅲ/Ⅴ) complexation. In addition, it can be easily regenerated and recycled maintaining an excellent adsorption and oxidative ability. Besides, Column experiment demonstrated this composite column could effectively treat 1300 and 1700 bed volume (BV) of synthetic As(Ⅲ/Ⅴ)-contaminated groundwater, respectively. Therefore, MgO-CS-MnO2 have a great potential applicability towards high As groundwater improvement as permeable reactive media.

Surface area per volumetric loading and its practical significance

The surface area of porous materials is a widely-used parameter in catalysis and adsorption. The most-commonly applied model, Brunauer–Emmett–Teller (BET), bases the parameter to the mass of material. Though the model does have its limitations, comparisons among materials are widely done to rank them from low to high surface areas, and to make correlations with other properties. However, in practical terms volume is often more appropriate since the design of reactors and adsorption columns aims at minimizing their volume. Thus, in such cases the surface areas can be better expressed per material bed volume using the bulk density. In this communication, we discuss the concept of volumetric surface area as m2/cm3MatBed, showing remarkable new insights. We applied this concept to two mesoporous silica-based materials with comparable pore size and C values. A material which was far superior in terms of conventional surface area (561 versus 227 m2/gMat), they both became comparable in terms of m2/cm3MatBed (ca. 110 both) due to the much lower density of the former material. In other words, being superior in gravimetric terms does not guarantee to be volumetrically superior. The results highlight the importance of considering the material bulk density when comparing surface areas of porous materials for applications where volume is critical.

Prototype Experiments Assessing Arsenic and Iron Removal Efficiencies through Adsorption Using Natural Skye Sand

Based on earlier batch and column experimental results, it was established that Skye sand is suitable for removing arsenic from water through adsorption. As a real-size prototype may not always replicate results from batch and column experiments, this paper presents experimental results on arsenic removal through a prototype arsenic filter using the same Skye sand used in the batch and column experiments. As arsenic-contaminated water is often associated with a high concentration of iron, which causes blockage of the filter system, this study also investigates the removal of iron from the water through the same filter media. First, several physical properties of the Skye sand were established through XRF, XRD, SEM and EDX analyses. Then, a real-size prototype was made based on an earlier design of a similar filter made of iron oxide-coated sand (IOCS). It was found that the current filter is capable of removing arsenic consistently to a level below the detection limit (0.05 µg/L) for a considerable period (up to 150 bed volumes). Additionally, the same filter is capable of removing iron to a level below the WHO-acceptable limit (0.3 mg/L). Analytical calculation suggests that the current prototype filter with Skye sand can produce arsenic-free water continuously for 600 days (100 L per day) with a feed arsenic concentration of 500 µg/L.

Sorptive removal of short-chain perfluoroalkyl substances (PFAS) during drinking water treatment using activated carbon and anion exchanger

Laboratory tests and column tests were carried out in a waterwoks to investigate the removal of short- and long-chain PFAS using activated carbon filtration and ion exchange treatment. For all adsorbents, the sorption affinity of short-chain per- and polyfluoroalkyl carboxylic acids (PFCA) was significantly lower than that of long-chain PFAS or short-chain per- and polyfluoroalkyl sulfonic acids (PFSA). In the PFAS-polluted groundwater matrix, the short-chain PFCA PFBA and PFPeA could only be sufficiently removed with activated carbon over short run times of 6000 and 11,000 bed volumes (BV), respectively. Longer PFCA with a chain length of C6 or more were removed over longer run times.The removal of short-chain PFCA using ion exchange media could also only be achieved over relatively short run times of 5000 BV for PFBA, 10,000BV for PFPeA and 18,000 BV for PFHxA. These are sometimes significantly longer than those of activated carbon. Due to the higher material costs for ion exchange media, there are nevertheless no lower operating costs when the ion exchangers are used in single-use mode. However, ion exchangers can be regenerated and then reused which can result in economic advantages compared to activated carbon filtration. However, for the extensive regeneration, especially for the elution of the long-chain PFAS, the additional use of ethanol is needed in the process. In contrast, the short-chain PFBA and PFPeA can be extracted without organic solvent from a weakly basic ion exchanger.

Phosphate removal performance and mechanism of magnesium–lanthanum-modified coal gasification coarse slag

Herein we present a novel coal gasification coarse slag (CGCS)-loaded magnesium–lanthanum bimetallic phosphate remover. The as-prepared composite (denoted ML2-CGCS) with a magnesium (Mg): lanthanum (La) molar ratio of 1:2 was found to be the best phosphate remover. The modification of CGCS with magnesium instead of lanthanum not only maintains a good phosphate adsorption capacity but also greatly reduces the cost of lanthanum-modified materials; this can save 4601 yuan per ton (in RMB). The maximum phosphate adsorption capacity was 39.22 mg/g, and 35 mg/L phosphate was nearly completely adsorbed within 180 min, exhibiting good phosphate removal capabilities. The effects of humic acid and anions demonstrated that ML2-CGCS has a good selectivity for phosphate removal. A metal leaching study showed that loading Mg–La on CGCS can reduce the lanthanum release problem of Mg–La hydroxides. Saturated ML2-CGCS can be reclaimed at least four times, and can continuously treat more than 1026 bed volumes of actual wastewater. The phosphate removal mechanism involves precipitation, electrostatic attraction, and the inner-sphere complexation. This study revealed that ML2-CGCS exhibits good selectivity, phosphate removal efficiency, and reproducibility, and it can be used to treat actual phosphate wastewater and thereby recover phosphate. This study provides a new method for the development of phosphate adsorbents while recycling CGCS.

Natural Zeolites for the Sorption of Ammonium: Breakthrough Curve Evaluation and Modeling

The excessive use of ammonium fertilizer and its associated leakage threatens aquatic environments around the world. With a focus on the treatment of drinking water, the scope of this study was to evaluate and model the breakthrough curves for NH4+ in zeolite-filled, fixed-bed columns. Breakthrough experiments were performed in single- and multi-sorbate systems with the initial K+ and NH4+ concentrations set to 0.7 mmol/L. Breakthrough curves were successfully modeled by applying the linear driving force (LDF) and Thomas models. Batch experiments revealed that a good description of NH4+ sorption was provided by the Freundlich sorption model (R2 = 0.99), while unfavorable sorption was determined for K+ (nF = 2.19). Intraparticle diffusion was identified as the rate limiting step for NH4+ and K+ during breakthrough. Compared to ultrapure water, the use of tap, river, and groundwater matrices decreased the treated bed volumes by between 25% and 69%-as measured at a NH4+ breakthrough level of 50%. The concentrations of K+ and of dissolved organic carbon (DOC) were identified as the main parameters that determine NH4+ sorption in zeolite-filled, fixed-bed columns. Based on our results, the LDF and Thomas models are promising tools to predict the breakthrough curves of NH4+ in zeolite-filled, fixed-bed columns.

Carbon Dioxide Removal from Humid Atmosphere by a Porous Hierarchical Silicoaluminophosphate/Carbon Composite Adsorbent

A chabazite-type silicoaluminophosphate (SAPO-34) was grown within the meso- and macropores of activated carbon (AC) via a confined space synthesis and functionalized via the addition of strontium(II) (i.e., Sr2+-CSAPO-34) for the selective adsorption of CO2 in the presence of humidity. The in situ growth of the SAPO phase was corroborated through SEM/EDAX, XRD, and pore size distribution profiles. About 80% of the meso- and macropores of AC were occupied by the SAPO. Sr2+-CSAPO-34 was further characterized via XRD, TGA, ICP-OES, and water contact angle measurements. A physical mixture of Sr2+-SAPO-34 and AC was also prepared to contrast against the hierarchical variant. The selectivity and capacity for trace CO2 removal were evaluated through single-component equilibrium and multicomponent fixed-bed adsorption. Bed tests (v = 200 mL min–1 and Ci = 500, 1000, or 2500 ppm) showed that the CO2 capacity remains in the presence of 90% relative humidity, with no signs of roll-up. Specifically, the uptake capacity of the Sr2+-CSAPO-34 bed for a CO2 feed content of 1000 ppm was 0.11 mmol per cm3 of bed and with a breakthrough point greater than 2000 bed volumes; this is superior compared to other adsorbents for CO2 capture under humid conditions. The Sr2+-CSAPO-34 composite bed was also subjected to various cycles upon vacuum-assisted thermal regeneration, and no decrease in adsorption capacity was observed. The adsorbent hierarchical design approach showed that a synergistic combination of hydrophobicity and enhanced adsorbate–adsorbent interactions at the physisorption level is a promising strategy for removing trace CO2 under humid conditions.

Redox-Active Polymers as Robust Electron-Shuttle Co-Catalysts for Fast Fe3+/Fe2+ Circulation and Green Fenton Oxidation.

Accelerating the rate-limiting Fe3+/Fe2+ circulation in Fenton reactions through the addition of reducing agents (or co-catalysts) stands out as one of the most promising technologies for rapid water decontamination. However, conventional reducing agents such as hydroxylamine and metal sulfides are greatly restricted by three intractable challenges: (1) self-quenching effects, (2) heavy metal dissolution, and (3) irreversible capacity decline. To this end, we, for the first time, introduced redox-active polymers as electron shuttles to expedite the Fe3+/Fe2+ cycle and promote H2O2 activation. The reduction of Fe3+ mainly took place at active N-H or O-H bonds through a proton-coupled electron transfer process. As electron carriers, H atoms at the solid phase could effectively inhibit radical quenching, avoid metal dissolution, and maintain long-term reducing capacity via facile regeneration. Experimental and density functional theory (DFT) calculation results indicated that the activity of different polymers shows a volcano curve trend as a function of the energy barrier, highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap, and vertical ionization potential. Thanks to the appropriate redox ability, polyaniline outperforms other redox-active polymers (e.g., poypyrrole, hydroquinone resin, poly(2,6-diaminopyridine), and hexaazatrinaphthalene framework) with a highest iron reduction capacity up to 5.5 mmol/g, which corresponds to the state transformation from leucoemeraldine to emeraldine. Moreover, the proposed system exhibited high pollutant removal efficiency in a flow-through reactor for 8000 bed volumes without an obvious decline in performance. Overall, this work established a green and sustainable oxidation system, which offers great potential for practical organic wastewater remediation.

Water quality impacts on sorbent efficacy for per‐ and polyfluoroalkyl substances treatment of groundwater

AbstractPer‐ and polyfluoroalkyl substances (PFAS) are a large group of synthetic compounds that have emerged as chemicals of concern in drinking water and groundwater. Typically, such waters are treated to remove PFAS by passing the water through a bed of sorbent material (e.g., activated carbon and anion exchange resins [AIX]). However, the efficacy of these sorbents varies depending on the types and concentrations of PFAS, in addition to water quality conditions such as organic matter content and conductivity (ionic strength). The choice of sorbent material to effectively treat PFAS in complex natural waters will, therefore, depend upon site water quality and PFAS conditions. To help inform these decisions, a series of evaluations using a rapid small‐scale column test approach was conducted with two sorbent materials (a granulated activated carbon [GAC] and an AIX), individually and combined, under conditions where conductivity, pH, and organic carbon concentrations were varied in a semifactorial approach. Artificial groundwater batches were prepared to meet these test conditions and spiked with six PFAS compounds (perfluorobutane sulfonic acid [PFBS], perfluorobutanoic acid [PFBA], perfluorohexane sulfonic acid [PFHxS], perfluorohexanoic acid [PFHxA], perfluorooctane sulfonic acid [PFOS], and perfluorooctanoic acid [PFOA]), passed through small columns packed with ground sorbent material for ∼30,000 bed volumes of water for single sorbent treatments and ∼20,000 bed volumes for combined sorbent treatments, during which samples of effluent were captured and analyzed to quantify breakthrough of PFAS from the sorbent materials over time. AIX was found to be more effective than GAC at removing the tested perfluoroalkyl sulfonic acids (PFBS, PFHxS, and PFOS), but GAC was similarly or more effective than AIX at removing perfluorocarboxylic acids (PFBA, PFHxA, and PFOA) under high conductivity conditions. Overall, the efficacy of AIX at removing PFAS was more strongly impacted by organic carbon and conductivity than GAC, while pH had less of an effect on either sorbent's efficacy compared to the other test conditions.

Biomass power plant integrated with a thermochemical heat storage system using a fluidized bed reactor worked by variable renewable energy: Dynamic simulation, energetic and economic analyses

This study focused on a biomass power plant (Organic Rankine Cycle: ORC, 1 MWe) integrated with a thermochemical heat storage (TCS) system as a Carnot battery. In the TCS, a fluidized bed reactor using CaO/Ca(OH)2/alumina particles was used, and steam was used as a fluidizing and reacting gas. The surplus electricity from variable renewable energy (VRE) is converted to heat and stored during daytime, and the stored energy is utilized to generate power in the evening. In this study, there were three objectives. First, process performances were compared when R245fa or R1233zd was used as a working fluid of ORC, and influences of ORC parameters such as the turbine inlet temperature, superheat temperature, and the scale of the power generation, were evaluated. In addition, effects of the fluidized bed volume and the reduction of biomass fuel combustion were also investigated. Second, a potential of the proposed process that can absorb the VRE fluctuation was evaluated by the dynamic calculation. Third, the economics of the TCS system was evaluated. Results show that the round-trip efficiency of the process using R1233zd was 8.77 %, which was slightly lower than that of the process using R245fa (8.84 %). The increases of a turbine inlet temperature led to the increase of heat recovery from the outlet steam of the TCS reactor, meanwhile, the round-trip efficiency decreased. The efficiencies of the cases changing the superheat temperature (5 → 15 °C) were slightly changed (<0.5 %). To achieve high energy efficiencies, a large-scale biomass power plant and a small-fluidized bed volume was effective. It was found that the VRE fluctuation was mostly absorbed by the TCS with a fluidized bed and ORC process. In the economic evaluations, the levelized cost of storage regarding only the TCS system was 0.92–2.37 USD/kWhe when the charging electricity cost is 0.05 USD/kWhe. LCOS also decreases to 0.50–1.14 USD/kWhe if the electricity cost is free during daytime in the future and power output is two times in a day.

Adsorptive removal of arsenic ions from contaminated water using low-cost schwertmannites and akaganéites

Schwertmannite and akaganéite have potential in treatment of arsenic contaminated waters. In this work, schwertmannite and akaganéite were synthesized by chemical and biological methods. Characterization and analysis results showed about 120 m2/g for schwertmannite spheres with a diameter of 2–5 μm (Sch-Chem) and about 0.5 μm (Sch-Bio) and 240–280 m2/g for akaganéite rod with a length of about 300–500 nm (Aka-Chem) and 150 nm (Aka-Bio). Agglomerated particle average diameters (μm) of synthesized products in solutions were 32.5, 20.6, 0.480 and 26.4, respectively. Schwertmannite and akaganéite were used to investigate arsenic adsorption behaviors in aqueous solutions by batch experiments, under various reaction times, initial arsenic and adsorbent levels, pH values, and anions (Cl−, NO3−, H2PO4−, CO32−, and SO42−). Adsorption data well fitted to pseudo-second-order rate model (R2 = 0.999), and Langmuir (R2 = 0.977–0.998) and Freundlich (R2 = 0.948–0.998) isothermal models at pH 7.0. Maximum adsorption capacities of As(III)/As(V) were 102/98.3, 110/115, 6.40/7.03 and 30.3/34.8 mg/g, respectively. Anions of SO42− and H2PO4− can affect arsenic removal efficiency. Adsorbents with pHZPC of 4.0–5.0 still had a good arsenic removal ability at pH 3.0–9.0, due to a main adsorption mechanism of anionic exchange between hydroxyl group (or sulfate) and arsenic ions. Further, schwertmannite candidates were used in arsenic removal from polluted groundwater. Breakthrough points (bed volume, mL) for Sch-Bio/Sch-Chem were about at 90/120, 70/(100–110) and 80/110 for As(III), As(V), and total As, respectively. It demonstrated that akaganéite and schwertmannite could be potentially applied in treatments of arsenic-polluted waters.

Desalination of brackish groundwater using self-regeneration hybrid ion exchange and reverse osmosis system (HSIX-RO)

The United Nations International Decade for Action on Water for Sustainable Development (2018–2028) recognized the importance of water to sustainable development and the eradication of poverty and hunger. It voiced alarm over the worsening of issues such as access to clean water, water scarcity, and wastewater as a result of increasing populations and altered climates. One of the most promising solutions to the water shortage is desalination, which can increase the available water supply beyond the currently possible limit. In this study, we analyze the performance of a unique hybrid self-regeneration ion exchange and reverse osmosis (HSIX-RO) system for the desalination of brackish groundwater. In the pretreatment step for protecting RO membrane fouling, the traditional homogenized strong acid cation exchanger (Purolite C100) and shallow shell structured strong acid cation exchanger (Purolite SSTC65) were compared for their efficiency in removing hardness cations from brackish groundwater. The fixed-bed column study concluded that C100 and SSTC65 can treat brackish water containing 250 mg L−1 Ca2+ and 10,000 mg L−1 NaCl at approximately 80 and 76 bed volumes (BVs), respectively. Studying the efficiency of RO system, it has % RO recovery of >70 % at an optimized pressure of 120 psi. An upscale self-regeneration ion exchange and RO system, i.e., HSIX-RO, that can be applied for a pilot-scale study was proposed. This proposed study suggested that HSIX-RO can be suited for the desalination of brackish groundwater with minimum use of an additional salt and can be self-sustained using an automated control. It was noted that the HSIX-RO system cannot be effectively applied to groundwater (TDS < 5000 mg L−1) nor seawater (TDS > 30,000 mg L−1) contained high Ca2+ and Mg2+ due to low regeneration efficiency and short length service runs, respectively.

Pilot-scale biofiltration of 1,4-dioxane at drinking water-relevant concentrations

1,4-Dioxane is a drinking water contaminant of emerging concern. Because conventional and many advanced drinking water treatment technologies are ineffective for 1,4-dioxane removal, cost-effective technologies for the removal of 1,4-dioxane at drinking water-relevant concentrations are needed. In this research, a gravity-fed, cometabolic biofiltration system was developed to degrade 1,4-dioxane that was spiked into coagulated, settled surface water at a concentration of ∼10 µg/L. Objectives were to determine whether cometabolic degradation of trace levels of 1,4-dioxane can be sustained using n-butane as primary substrate and whether filter media properties and empty bed contact time (EBCT) affect biofiltration efficiency. A mixed culture of bacteria derived from the Cape Fear River basin and previously enriched using isobutane served as inoculum for biologically active filters. Two granular activated carbons (GACs) with different grain sizes and one carbonaceous resin were used as attachment media, and n-butane served as the primary substrate for biologically active filters. Non-inoculated controls with the same media were evaluated in parallel to distinguish between biological and adsorptive removals of 1,4-dioxane. For the duration of the pilot study (>3 months), 1,4-dioxane was degraded in inoculated biofilters receiving n-butane. In control filters containing larger and smaller grain GAC, 1,4-dioxane broke through completely within 750 and 1250 bed volumes, respectively, corresponding to 15 to 30 days of operation at an EBCT of 30 min. 1,4-Dioxane removal increased with increasing EBCT in all biologically active filters. At an EBCT of 30 min, the biologically active GAC filter containing the larger-grain GAC removed on average 87% of 1,4-dioxane at pseudo steady-state. When the hydraulic loading rate was decreased to achieve an overall EBCT of 60 min, 1,4-dioxane was removed to <1 µg/L in the biologically active GAC filter containing the larger-grain GAC. Activity-based labeling showed the presence of catalytically active monooxygenases in backwash water from biologically active filters that degraded 1,4-dioxane. Amplicon sequencing results showed that while taxa shifted after the initial inoculation of biologically active filters, taxa in biologically active filters remained more similar to the inoculum than those in the non-inoculated control filters. Overall, results of this research demonstrate that cometabolic degradation of 1,4-dioxane at trace levels is possible for extended periods of time in inoculated biofilters that receive n-butane as primary substrate.

SiO2 nanospheres as surfactant and template in aqueous dispersion polymerizations yielding highly nanoporous resin particles

HypothesisHigh nitrogen containing resins such as poly(melamine-co-formaldehyde) (PMF) are known for their very good adsorption properties. Until now, using an ecofriendly hard-templating approach with SiO2 nanospheres in water for synthesis, only yielded either highly porous particles with diameters up to 1 µm or non-porous particles with diameters above 1 µm. Small particles cannot be used as fixed bed adsorbents in columns because of the very high pressure occurring. ExperimentsTo yield particles with high porosity and larger diameters for the use as fixed bed adsorbent, we investigated the influence of several synthesis parameters on porosity and particle morphology. FindingsFrom all variations, we proposed a mechanism for the complex interplay between the PMF prepolymer and resin species with SiO2 nanoparticles acting both as Pickering-like surfactant and template particle. With this knowledge we were able to produce a suitable column material with high specific surface area up to 260 m2/g. We then proved the application of this material for aqueous dichromate adsorption in batch, yielding a maximum capacity of 138 mg/g with recyclability. In column experiments, the contamination of 5 mg/L dichromate in water was reduced to drinking water safe levels for an influent volume equal to over 160 bed volumes.

Statistical analysis of treatment of rice mill wastewater using the aerobic inverse fluidized bed biofilm reactor (AIFBBR)

Among the different industries, the ricemill industry is identified as one of the major polluting industries because of the large amounts of effluents generated and variations in the concentration of its constituents. The current experimental study aimed to investigate the treatment of ricemill (simulated) using the aerobic inverse fluidized bed biofilm reactor (AIFBBR). Box–Behnken design (BBD) based statiscal response surface methodology (RSM) was used for the current AIFBBR-ricemill treatment system. For the evaluation of the RSM process through the BBD technique, three input variables: Influent COD (800–3200 mg/L), HRT (12–24 h), and % bed volume (15 − 45), and two output variables: %COD and %TOC removal, were selected. The effect of these chosen variables was verified by conducting 15 experiments in a multivariate system for the AIFBBR-ricemill treatment system. The quadratic polynomial models yielded a regression coefficient (R2) of 0.99 (for both COD and TOC) when the experimental data were fitted to it, which indicates the model's suitability for the process. The precision and efficiency of the model were visualized using the ANOVA and lack of fit test. The system has witnessed the maximum COD (88.95%) and TOC (95.68%) removal at optimum parameters of 2804.27 mg/L of influent COD, 23.79 h of HRT, and at a % bed volume of 44.94. Along with the COD and TOC, parameters such as nutrients (NH4+-N, PO43--P, and NO3--N), phenol, and lignin were also monitored in the present study.

Ultrafast uranium recovery from high-salinity nuclear wastewater using amine-functionalized lignin microspheres

U(VI) recovery from high-salinity nuclear wastewater remains a diffcult challenge. Accordingly, amine-functionalized lignin microspheres (AL-PEI/GMS) with high porosity, abundant functional groups, and appropriate surface area, were synthesized via a green and simple process, and used as an adsorbent for U(VI) recovery. Results illustrated that AL-PEI/GMS showed outstanding adsorption capacity for U(VI) of 250 mg/g and high selectivity of SFU(VI) > 15, 000 over a wide pH range from one to nine, preeminent regeneration performance with adsorption efficiency > 95% after 50 cycles, and desorption performance (desorption efficiency > 60% after 50 cycles). The high applicability of AL-PEI/GMS was further proven by its high U(VI) removal efficiency under various high-salinity conditions (U(VI) removal rate > 99%). Furthermore, 2553 bed volumes (BV) of the U(VI) feeding streams can be effectively treated by AL-PEI/GMS via a fixed-bed column system with an extremely high flow rate (20 mL/min), and more than 95.6% of U(VI) can be rapidly desorbed by using 12 BV of eluent solution. Furthermore, the comparatively low operational costs and overall economic feasibility further suggested the great potential of AL-PEI/GMS for U(VI) on the industrial scale. The mechanism of U(VI) adsorption on AL-PEI/GMS was further found to be chemisorption-related. This work presents an applicable approach by using amine-functionalized lignin microspheres to achieve highly ultrafast U(VI) adsorption and desorption under a high-salinity condition via a fixed-bed column system, which not only provides a feasible method to purify U-contaminated nuclear wastewater, but also successfully realizes the recycling of U(VI) from nuclear wastewater, thus resolving the increasingly serious energy crisis and protecting environment in the nuclear industry.

Experimental investigation on ex-vessel debris bed formation using low melting-point melt of binary metals

During severe accidents in a light water reactor, the core melt (corium) may relocate to the lower head and fail the reactor pressure vessel (RPV). The corium will be ejected to the reactor cavity upon the RPV failure and undergo melt coolant interactions (FCI) if the cavity is flooded with water. The FCI process does not only determines the characteristics of the resulting debris bed which are important to coolability, but also induces a steam explosion risk which may threaten containment integrity. The present study is concerned with characterization of debris bed formed from FCI of metal-rich corium failing into a deep water pool in the reactor cavity. Low melting-point metals Tin and Tin–Bismuth (20 kg) were employed as the simulant materials of metal-rich corium melt. Ten tests were carried out on the DEFOR-M test facility at KTH to investigate the effects of various parameters on debris bed formation, such as melt superheat, coolant subcooling, material. The melt jet fragmentation and fragments movement in the water pool as well as debris deposition on the pool floor were recorded by high-speed cameras. Melt sensors and weight sensors were installed to detect the period of melt jet discharge and the mass of forming debris bed. The porosity of debris bed was obtained through the debris bed volume measured by a three-dimensional laser scanner and the pore volume measured by water absorption. The final configuration of debris bed was also reconstructed through the laser scanner data, and the debris particles were sieved for their size distribution. The experimental results revealed the FCI phenomena and debris bed characteristics including configuration and porosity of debris bed as well as morphology and size distribution of debris particles under different melt superheats, coolant subcooling, materials.