Continuous Flow Fixed-bed Column Research Articles

Adaptation of breakthrough models in a continuous-flow fixed bed column: Describing and predicting 1.1.1.2-Tetrafluoroethane breakthrough curves under high moisture content

Gas mask and filter adsorber designs are mainly determined by the accurate breakthrough time calculated by fitting descriptive models to breakthrough curves in military chemistry. Currently, in most practical environments, the highly toxic fluoride gas/vapor breakthrough curves with roll-up and/or stepwise breakthrough structures in the C/C0<1.0 range usually occur, which is induced by the existence of pre-adsorbed water vapor. Common and easily modified descriptive breakthrough models have a significant shortcoming in that they are not able to simultaneously fit the above complex breakthrough curves and explain gas desorption, enhanced adsorption again, and stepwise adsorption in the competitive adsorption process. This study adapts three modified descriptive models by introducing a dimensionless breakthrough coefficient to fit roll-up and stepwise 1.1.1.2-Tetrafluoroethane (R134a) breakthrough curves under humid conditions. Results reveal that correlation coefficients between the model and R134a breakthrough data are higher than 0.98, demonstrating that the novel adaptation successfully accounted for R134a desorption, enhanced R134a adsorption again, and R134a stepwise adsorption without significantly increasing the complexity of implementing the models. Further, through relationship curves between fitting parameters and moisture contents, R134a breakthrough curves on activated carbons under a wider moisture content range were successfully predicted. It will greatly reduce the cost of toxic experimentation and improve experimental safety factors.

Aqueous arsenic(V) remediation and redox transformation of arsenic(III) to arsenic(V) using Fe3O4/Douglas fir biochar

Magnetite nanoparticles were deposited on Douglas fir biochar (Fe3O4/DFBC) using aqueous, NaOH-induced chemical co-precipitation from Fe2+/Fe3+ salt solutions. Fe3O4/DFBC was used to remediate As(V)-contaminated water. Kinetics and isotherms were studied. pH 5 was selected as the optimized pH due to low iron leaching and closeness to groundwater pH. Adsorption equilibrium was reached after 3 h, 2 h, and 1 h for 0.5, 5, and 50 mg/L initial As(V) concentrations, respectively. Adsorption was endothermic, and the Langmuir capacity was 6.33 mg/g at 25 °C. Ionic strength, impacts of Fe3O4/DFBC particle size, and competitive ion/molecule effects during As(V) adsorption were studied. Continuous-flow fixed-bed column breakthrough studies performed at 0.5, 5, and 50 mg/L of As(V) at pH 5 exhibited maximum capacities of 3.47, 3.99, and 3.72 mg/g, respectively. Aqueous potassium phosphate was used successfully for column regeneration. Fe3O4/DFBC was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Mössbauer spectroscopy before and after As(III) and As(V) adsorption. Mössbauer found the “Fe3O4” was composed of several phases. A key target was the study of simultaneous toxic As(III) adsorption and its transformation to As(V) from pH 1–13. The highest removal of As(III) and oxidized As(V) was obtained at pH 3. The relationship between iron leaching and pH was investigated and the pH-dependent surface adsorption was monitored using X-ray photoelectron spectroscopy (XPS) from pH 1 to 13. One goal of this study was to enhance the understanding of the adsorption characteristics needed for initial scaling of a treatment facility that can efficiently remediate arsenic-contaminated wastewater. Experiments were conducted using batch and fixed bed continuous flow columns to optimize adsorption process parameters under various circumstances and solution matrices. Another goal was to further establish the surface structures of the chemisorbed arsenates versus pH.

Removal of polystyrene microplastics using biochar-based continuous flow fixed-bed column.

In the realm of environmental challenges, microplastics have emerged as a pressing threat, presenting risks to both individuals and ecosystems. Conventional treatment plants are presently not equipped for effectively removing these minute contaminants. This study presents an investigation into the potential of a continuous flow biochar column, utilizing biochar derived from banana peel through a nitrogen-free slow pyrolysis process for the removal of microplastics. A systematic exploration of various parameters, including bed height, flow rate, inflow microplastic concentration, and microplastic size is undertaken to discern their impact on polystyrene removal efficiency. A peak removal efficiency of 92.16% has been achieved under specific conditions: a 6-cm bed height, a 3-mL/min flow rate, an inlet concentration of 0.05g/L, and microplastic sizes ranging from 150 to 300µm. The removal efficiency was inversely affected by flow rate while directly influenced by bed height. To deepen the understanding of polystyrene removal on biochar, a detailed characterization of the synthesized material was carried out. The removal of microplastics by banana peel biochar (BPB) is observed to be dominated by adsorption and filtration processes. The entanglement of microplastics with minuscule biochar granules, capture between particles, and entrapment in the porous system were identified as the mechanisms of removal. Leveraging the hydrophobic nature of polystyrene microplastics, interactions with the hydrophobic functional groups in BPB result in effective adsorption. This is further complemented by self-agglomeration and filtration mechanisms that synergistically contribute to the elimination of larger agglomerates. The findings thus provide a comprehensive understanding, offering hope for a more effective strategy in mitigating the environmental impact of microplastics.

Thermally-activated gelatin–chitosan–MOF hybrid aerogels for efficient removal of ibuprofen and naproxen

Nonsteroidal anti-inflammatory drugs (NSAIDs) are one of the most frequently used drugs and have been frequently detected in aquatic environments. This paper demonstrates a thermally-activated gelatin–chitosan and amine-functionalized metal–organic framework (UiO-66–NH2) aerogel (CGC–MOF), which was successfully synthesized for the efficient removal of ibuprofen (IBP) and naproxen (NPX). Various characterization tools were used to systematically analyze the microstructure and physicochemical properties of the synthesized aerogel. In addition, the effect of key reaction parameters as well as batch and continuous-flow fixed-bed column experiments were carried out to elucidate the adsorption process. Several functional groups in the biopolymer network, combined with excellent MOF properties, synergistically couple to form an adsorbent with great performance. The mesoporous aerogel activated at 200 °C (CGC–MOF200) exhibited a high specific surface area (819.6 m2/g) that is valuable in providing abundant adsorption active sites that facilitate the efficient adsorption of IBP and NPX. CGC–MOF200 exhibited an excellent removal of IBP and NPX, accounting to 99.28 % and 96.39 %, respectively. The adsorption process followed the pseudo-second-order kinetics and the Freundlich isotherm models, suggesting heterogeneous and chemisorption adsorption processes. Overall, this work provides new and valuable insights into the development of a promising biopolymer–MOF composite aerogel for environmental remediation.

High-performance Cu/Mn modified ceramsite as a persulfate activator to degrade oxytetracycline in batch Erlenmeyer flask and continuous-flow fixed-bed column systems: An exploration of its practicability and non-radical mechanisms

Persulfate non-radical oxidation have excellent catalytic capability for degrading specific contaminants in complicated water environments. Nevertheless, the preparation of high-performance activators and their application in actual water treatment in continuous flow mode are still scarce and unsatisfactory. In this work, copper-, manganese-, and copper/manganese-doped ceramsites (Cu–C, Mn–C and Cu/Mn–C), successfully fabricated through a facile impregnation-calcination approach, were characterized and evaluated for their performance to activate potassium peroxydisulfate (PDS) and degrade oxytetracycline (OTC) under different pH, ceramsite dosages, and PDS dosages. Compared with Cu–C and Mn–C, Cu/Mn–C showed the highest OTC degradation rate (0.0264 min−1) via activating PDS with an OTC removal efficiency of 98.2% in 240 min at an initial OTC concentration of 40 mg/L. The removal efficiency of OTC by Cu/Mn–C only decreased to 92.8% after 5 cycles; the activating ability of the used Cu/Mn–C was almost completely recovered through 2 h of calcination at 500 °C. The results of electron paramagnetic resonance and radical quenching suggest that singlet oxygen (1O2) was unveiled to be the dominant reactive oxygen species (ROS) for contaminant degradation, originating from the regrouping of superoxide ions or reduction of active Cu/Mn sites. Synergies between Cu and Mn species to enhance ROS yield were the primary activating mechanisms. Six possible routes of OTC decomposition were inferred. Additionally, Cu/Mn–C behaved excellently in treating an actual wastewater using a continuous flow fixed-bed reactor. It is believed that this novel Cu/Mn–C/PDS system may create a fresh path to design effective and cheap metal-ceramsite hybrid activators for degrading recalcitrant contaminants in the actual application process.

Remediation of Pb (II), Cd (II), and Zn (II) from aqueous solutions using porous (styrene-divinylbenzene)/Cu-Ni bimetallic nanocomposite microspheres: continuous fixed-bed column study.

Bimetallic nanoparticles (BNPs) have been used as a new line of defence against heavy metal contamination among several types of nanoparticles (NPs) due to their enhanced, synergistic activity. In this study, we investigated the adsorption behaviour of porous (styrene-divinylbenzene)/CuNi bimetallic nanocomposite (P(St-DVB)/CuNi BNC) in a continuous flow fixed-bed column and its ability to remove Pb (II), Cd (II), and Zn (II) ions from aqueous solutions. We examined how the initial metal concentration, flow rate, and bed height affected the adsorption characteristics. Experimental results confirmed that the adsorption capacity increased with increase in influent metal concentration and bed height and decreased with increase in flow rate. The breakthrough and the column kinetic parameters were successfully predicted with three mathematical models: Thomas, Yoon-Nelson, and Adams-Bohart models. Both Thomas and Yoon-Nelson models showed good agreement with the experimental results for all the operating conditions. Successful desorption of heavy metals from the P(St-DVB)/CuNi BNC was performed using 0.5 M NaOH solution, and it showed good reusability of the adsorbent during four adsorption-desorption cycles. The results show that P(St-DVB)/CuNi BNC are effective and low-cost adsorbents, and they can be used in real-time large-scale industrial water treatment processes for the removal of heavy metals.

Performance and cell toxicity studies for the use of graphene oxide-bimetallic oxide hybrids in the absorptive removal of Pb(II) from wastewater: fixed-bed column study with regeneration.

The current study involves the removal of Pb(II) ions from an aqueous solution using GO/Mn-Fe hybrids in a fixed bed column study. The capability of the hybrid in the Pb removal was examined using a continuous flow fixed bed column which revealed that the hybrid had the maximum adsorption capacity of 172.768mg/g at a flow rate of 2mL/min, bed height of 1cm, and influent concentration of 200mg/L. The breakthrough curves obtained from the experiments were examined using three different models, i.e., Bohart-Adams model, Thomas Model, and Yoon-Nelson model, wherein all the models showed high correlation coefficient values. Three consecutive adsorption-desorption cycles in the column yielded regeneration efficiencies of 91.71%, 88.31%, and 85.41%. The column life factor indicated that the fixed bed would have enough capacity to avoid a zero breakthrough time for up to 9 cycles, implying that GO/Mn-Fe could be used as a cheap and efficient adsorbent in the removal of Pb(II) from contaminated water. The adsorption mechanism was postulated based on the characterization of the spent adsorbent by FTIR and SEM. The phenomenon of the adsorption process can be described in accordance with the surface complex formation theory, which suggests that an increase in pH decreases the competition between metal ions and protons, favoring metal ion adsorption. The toxicity of the synthesized hybrid was evaluated on HeLa cells and compared to the toxicity of GO. Increasing the concentration of GO/Mn-Fe hybrid from 50 to 250g/mL resulted in a decrease in cell viability from 91.90 to 56.52%, whereas increasing the concentration of GO resulted in a decrease in cell viability from 61.59 to 37.19%. The study clearly demonstrates the use of GO/Mn-Fe hybrid as an adsorbent for efficient sequestration of Pb(II) ions with lower environmental toxicity.

Fixed-bed column study of phosphate adsorption using immobilized phosphate-binding protein

Bio-adsorption using high-affinity phosphate-binding proteins (PBP) has demonstrated effective phosphorus removal and recovery in batch-scale tests. Subsequent optimization of design and performance of fixed-bed column systems is essential for scaling up and implementation. Here, continuous-flow fixed-bed column tests were used to investigate the adsorption of inorganic phosphate (orthophosphate, Pi) using phosphate-binding proteins immobilized on resin (PBP–NHS) targeting Pi removal to ultra-low levels followed by recovery. Time to breakthrough decreased with higher influent Pi concentration, smaller bed volume, and higher influent flow rates. The Thomas and Yoon-Nelson breakthrough models adequately described PBP-NHS resin performance with a correlation coefficient of R2 > 0.95. The sharp S-shape of the breakthrough curves for both Pi-only solution and multi-ion solution indicated highly favorable and selective separation of Pi using PBP-NHS resin, beyond that achieved using LayneRT™, a commercial ion exchange resin. The Pi adsorption capacity of the PBP-NHS column was unaffected by competing anions, whereas capacity of the LayneRT™ column dropped by 20%. Tertiary wastewater effluent was also successfully treated in PBP-NHS column tests with a typical S-shaped breakthrough curve. Operating the fixed-bed column in multi-cycle mode evidenced the reusability of PBP-NHS resin with no significant decline in column performance. The results of this study contribute to efforts to scale up designs of PBP-NHS adsorption systems.

Polyaniline nanofibers, a nanostructured conducting polymer for the remediation of Methyl orange dye from aqueous solutions in fixed-bed column studies

Polyaniline nanofibers (PANI NFs) were synthesized and employed as potential adsorbents in a continuous flow fixed-bed column adsorption study for an organic dye, Methyl Orange (MO) removal from water. These nanostructured adsorbents were characterized using ATR-FTIR, FE-SEM, HR-TEM, TGA, BET, XRD, XPS, and the Zeta-sizer. Morphological representations from SEM and TEM analyses showed that the fibers were nanosized with diameters lower than 80 nm and an interconnected network possessing a smooth surface. The SBET of the PANI NFs was found to be 35.80 m2/g. The impact of column design parameters for instance; influent concentration, flow rate, and bed mass was investigated using pH 4 influent MO solutions optimized through batch studies. The best influent concentration, bed length, and flow rate for this study were determined as 25 mg/L, 9 cm (6 g), and 3 mL/min, respectively. The column information was fitted in Thomas, Yoon-Nelson, and Bohart-Adams models. It appeared that the Thomas and Yoon-Nelson models described the data satisfactorily. The PANI NFs were able to treat 29.16 L of 25 mg/L MO solution at 9 cm bed length. A sulfate peak in a de-convoluted sulfur spectrum using XPS verified the successful adsorption of Methyl Orange.

Fixed-Bed Column Technique for the Removal of Phosphate from Water Using Leftover Coal.

The excessive discharge of phosphate from anthropogenic activities is a primary cause for the eutrophication of aquatic habitats. Several methodologies have been tested for the removal of phosphate from aqueous solutions, and adsorption in a flow-through reactor is an effective mechanism to reduce the nutrient loading of water. This research aimed to investigate the adsorption potential of leftover coal material to remove phosphate from a solution by using continuous flow fixed-bed column, and analyzes the obtained breakthrough curves. A series of column tests were performed to determine the phosphorus breakthrough characteristics by varying operational design parameters such as adsorbent bed height (5 to 8 cm), influent phosphate concentration (10–25 mg/L), and influent flow rate (1–2 mL/min). The amorphous and crystalline property of leftover coal material was studied using XRD technology. The FT-IR spectrum confirmed the interaction of adsorption sites with phosphate ions. Breakthrough time decreased with increasing flow rate and influent phosphate concentration, but increased with increasing adsorbent bed height. Breakthrough-curve analysis showed that phosphate adsorption onto the leftover coal material was most effective at a flow rate of 1 mL/min, influent phosphate concentration of 25 mg/L, and at a bed height of 8 cm. The maximal total phosphate adsorbed onto the coal material’s surface was 243 mg/kg adsorbent. The Adams–Bohart model depicted the experimental breakthrough curve well, and overall performed better than the Thomas and Yoon–Nelson models did, with correlation values (R2) ranging from 0.92 to 0.98. Lastly, leftover coal could be used in the purification of phosphorus-laden water, and the Adams–Bohart model can be employed to design filter units at a technical scale.

Cucurbituril-Functionalized Nanocomposite as a Promising Industrial Adsorbent for Rapid Cationic Dye Removal.

A supramolecular cucurbit[6]uril (CB[6])-enriched magnetic montmorillonite (CBCM) nanocomposite was prepared and characterized. CB[6] played a prominent role as a capping agent, helping in better distribution of the nanoparticles, and as a binder between nanoparticles. Montmorillonite provided structural stability and fortified ultrafast adsorption toward dyes. Its application in the removal of cationic dyes from wastewater was systematically assessed. Process parameters such as pH, initial dye concentration, dosage, temperature, and time were optimized. Kinetics and isotherms of the process were described using pseudo-second-order kinetics and the Langmuir isotherm, respectively. CBCM exhibited rapid dye removal capacity in short reaction times with qmax of 199.20, 78.31, and 55.62 mg g–1 and K2 of 0.0281, 0.0.0823, and 0.0953 L mg–1 min–1 for crystal violet, methylene blue, and rhodamine B, respectively. Benefiting from the synergetic effects of montmorillonite surface hydrophobicity, abundant carbonyl groups of CB[6], and magnetic properties of copper ferrite, CBCM demonstrated outstanding dye removal capacity, negligible leaching at saturation, and high tolerance toward harsh conditions. This intrinsic nature is expedient in prolonged industrial operations. To demonstrate industrial viability, syringe filtration and continuous flow fixed-bed column operations were validated. The CBCM fixed-bed column demonstrated stable dye removal efficiency with 10–100 mg mL–1 dye at 10–50 mL min–1 flow rates. Utilizing the magnetic and catalytic activities of the copper ferrite nanoparticles, CBCM was recycled using a magnet, regenerated, and reused for several cycles. CB[6] remarkably improved the performance of the nanocomposite and made it suitable for different effluent treatment techniques. This may pave a sustainable way toward the efficient onsite treatment of effluent at the industrial scale.

Continuous fixed-bed column assessment for defluoridation of water using HAp-coated-limestone

A continuous flow fixed-bed column study was carried out using hydroxyapatite (HAp)-coated limestone to remove fluoride from water. The adsorbent was prepared by reacting limestone with sodium dihydrogen phosphate. The influencing conditions studied are bed mass (30, 40, 50 g), particle size (0.005-0.1, 0.1-0.2, 0.2-0.5 cm), influent flow rate (8, 16, 32 mL min−1), inlet fluoride concentration (5, 7, 10 mg L−1) and coexisting anions (Cl-, NO3-, SO42-). Results confirmed that the defluoridation capacity of the adsorbent increases with increase in bed mass but decreases with increasing flow rate and influent fluoride concentration. Among the coexisting anions, SO42- had the highest negative effect on defluoridation. It was found that the sorbent has a defluoridation capacity of 3.86 mg g−1 with bed mass of 40 g, particle size 0.1-0.2 cm, influent flow rate 8 mL min−1 and influent fluoride concentration of 5 mg L−1. The Thomas model, with better predictions for the breakthrough curves, was more capable in describing the dynamics of the fluoride adsorption process than the Adam-Bohart and Yoon-Nelson models. With a good adsorption capacity, the present adsorbent is competitive among many previously reported adsorbents. Finally, regeneration studies indicated that the fluoride-loaded sorbent can be effectively regenerated using NaOH solution.

Modification of breakthrough models in a continuous-flow fixed-bed column: Mathematical characteristics of breakthrough curves and rate profiles

In order to more completely describe mathematical characteristics of the breakthrough curve, this work defines the four parameters: Maximum specific breakthrough rate μmax, lag time λ, inflection point ti and half-operating time t50. The breakthrough models include the Bohart–Adams, Thomas, Yoon–Nelson, Clark, Wolborska and dose-response models. Attempts are made to address mathematical relationships between the breakthrough models, propose modified breakthrough models, investigate effects of model parameters on the breakthrough curve and rate profile and reveal their physical meanings. The fitting performance of the breakthrough models is verified by the adsorption of nitrate on the chitosan-Fe(III) composite. The results indicate that the model terms q0m/vc0 and a0x/uc0 are the operating time required to reach 50% breakthrough. The Clark model has the best fitting performance with high adjusted determination factor (Adj. R2 = 0.9976) and low reduced chi-squared value (χ2 = 2.70 × 10−4). In addition, an inconsistency concerning application of the Wolborska model is proposed to avoid this situation where it is repeated in subsequent publications. This work is expected to help readers better understand the breakthrough models and select the appropriate model to analyze the dynamic behaviors in a continuous-flow fixed-bed column.

Fixed-bed Column Study for Adsorption of Cadmium on Oil Palm

The spread of heavy metal pollution in the environment can lead to the contamination of crops and water for consumption. An approach to control the spread of groundwater pollution is by using a permeable reactive barrier with granular activated carbon. In this study, the adsorption of Cd(II) ions was conducted in a continuous flow fixed-bed column by using oil palm shell-derived activated carbon. The activated carbon column performance was evaluated by manipulating the activated carbon bed height, cadmium solution flow rate and influent concentration. The increase in bed height increased the amount of adsorbent used, thus increasing the total removal of Cd(II) and prolonged the lifespan of the activated carbon column. However, the increase in flow rate and influent concentration resulted in the shortened lifespan of the column. The column system with a bed height of 5.5 cm, flow rate of 2.0 mL/min and 200 mg/L influent concentration showed the best Cd(II) uptake performance in this study. The column performance were best fitted to the Thomas model and Yoon-Nelson model for the longest bed depth of 5.5 cm, all flow rates studied and highest influent concentration of 200 mg/L, with correlation coefficient greater than 0.95.

Simultaneous removal of phosphate and ammonium using salt–thermal-activated and lanthanum-doped zeolite: fixed-bed column and mechanism study

Assessment of breakthrough performance of NaCl–Thermal–LaCl3 synthetic modified zeolite continuous flow fixed-bed column on the simultaneous removal of phosphate and ammonium from simulated municipal wastewater was conducted. Variable parameters, including solution pH, bed depth, effluent flow rate, and input concentration, were examined for this study. The results indicated that the adsorption capacity increased with the increase in bed depth and input concentration and decrease of effluent flow rate for both phosphate and ammonium. Thomas and Yoon–Nelson models were found to give the better fitness to experiment data of the whole breakthrough curves, whereas Adams–Bohart model could only predict the initial part of the breakthrough using linear regression analysis. The bed depth service time model of breakthrough data showed that the time for the movement of the mass transfer zone increased with the increase in bed height and flow rate and decrease in initial concentration. Best fixed-bed column performance was obtained at high fixed bed depth, low effluent flow rate, and low initial concentration. Successful desorption and regeneration were achieved with 0.2M HCl and 0.1M NaOH. BET, scanning electron microscopy, energy dispersive X-ray spectroscopy, and FTIR and X-ray photoelectron spectra analyses confirmed that ammonium removal was mainly ascribed to exchanging with sodium in the adsorbent, and phosphate adsorption mainly followed the surface complexion mechanism; the surface hydroxyl groups played the key role. All the results proved that the column could be promising option for the simultaneous removal of phosphate and ammonium at lower concentrations.

Chromium(VI) removal from water using fixed bed column of polypyrrole/Fe3O4 nanocomposite

The adsorption of Cr(VI) using polypyrrole/Fe3O4 nanocomposite adsorbent was investigated in a continuous flow fixed-bed column. The effects of composition of the nanocomposite, adsorbent mass, influent Cr(VI) concentration and flow rate on the adsorption characteristics of adsorbent was explored at pH 2. Experimental results confirmed that the breakthrough curves were dependent on bed mass, initial Cr(VI) concentration and flow rate. Three kinetic models; Yoon–Nelson, Thomas, Bohart–Adams were applied to the experimental data to predict the breakthrough curves using linear regression and to determine the characteristic parameters of the column that are useful for process design. The Yoon–Nelson and Thomas models were found appropriate for description of the whole breakthrough curves, whereas the Bohart–Adams model could only predict the initial part of the breakthrough curves. Using environmental water, the PPy/Fe3O4 nanocomposite demonstrated its effectiveness in Cr(VI) removal below acceptable level by processing 5.04L water with initial 76.59mg/L Cr(VI) concentration using only 2g of adsorbent mass. It can be concluded therefore that PPy/Fe3O4 media provides alternative solution to ameliorate water contaminated with Cr(VI).

Phosphorus Removal and Recovery in Novel Seed Crystal Media Filter

A seed crystal medium was developed from the powder steel slag and other material in order to carry out a novel method for phosphorus removal and recovery through the crystallization process. Continuous-flow fixed-bed column experiment was conducted to investigate the phosphorus removal capacity with low P concentration (10mg/L), and the influences of HRT, Ca/P ratio and pH on the treatment efficiency were also considered. It was observed that the P concentration of filter effluent was always lower than 0.5mg/L whether under the experimental condition of pH=7 and HRT=60 min or the condition of pH=7, HRT=30min and the Ca/P ratio = 1.5. With the HRT 30min, increasing pH to 7.5 and decreasing Ca/P ratio to 1, the P concentration of filter effluent was still lower than 0.5mg/L. The XRD analysis of the sediment obtained from the filter bed proved that product formed in the phosphorus removal process was Hydroxyapatite (HAP), illustrated that the crystallization occurred in the process of P-removal. The results of this study suggest that the fixed bed - phosphorus crystallization process with seed crystal media is a promising technique for phosphorus removal and recovery.

Biosorption of arsenic from contaminated water by anaerobic biomass

The potential of an anaerobic sludge from an anaerobic wastewater treatment plant to remediate (inorganic) arsenic contaminated water was evaluated. The granular biomass was chemically modified as PO 4-biomass and Cl-biomass. The biomass was then investigated in equilibrium batch experiments and continuous flow fixed-bed column operation. Initial arsenic concentration, contact time and solution pH affected the biosorption capacity. Arsenate exhibited greater removal rates than arsenite. Adsorption data fitted better with the Langmuir than the Freundlich isotherm model. Kinetic data followed a pseudo-second-order model. In column operation, at pH 5, 90 and 220 bed volumes of water with the respective arsenate concentrations of 500 and 200 μg/L were treated. Desorption of almost 40% arsenate was achieved by using 0.5 M NaCl solution. Protein/amino acid–arsenic interaction was proposed as the dominant mechanism in the biosorption process. The arsenic–laden biomass satisfied USEPA's Toxicity Characteristic Leaching Procedure (TCLP) test and can be safely disposed of as non-hazardous waste.

Application potential of grapefruit peel as dye sorbent: Kinetics, equilibrium and mechanism of crystal violet adsorption

This study reports the sorption of crystal violet (CV) dye by grapefruit peel (GFP), which has application potential in the remediation of dye-contaminated wastewaters using a solid waste generated by the citrus fruit juice industry. Batch adsorption of CV was conducted to evaluate the effect of initial pH, contact time, temperature, initial dye concentration, GFP adsorbent dose, and removal of the adsorbate CV dye from aqueous solution to understand the mechanism of sorption involved. Sorption equilibrium reached rapidly with 96% CV removal in 60 min. Fit of the sorption experimental data was tested on the pseudo-first and pseudo-second-order kinetics mathematical equations, which was noted to follow the pseudo-second-order kinetics better, with coefficient of correlation ≥0.992. The equilibrium process was well described by the Langmuir isotherm model, with maximum sorption capacity of 254.16 mg g −1. The GFP was regenerated using 1 M NaOH, with up to 98.25% recovery of CV and could be reused as a dye sorbent in repeated cycles. GFP was also shown to be highly effective in removing CV from aqueous solution in continuous-flow fixed-bed column reactors. The study shows that GFP has the potential of application as an efficient sorbent for the removal of CV from aqueous solutions.

Hybrid biosorbent: An innovative matrix to enhance the biosorption of Cd(II) from aqueous solution

To enhance the metal removing capacity of a fungus biosorbent, a new idea of producing a hybrid biosorbent (HB) matrix by combining two different biosorbents using a simple and low-cost immobilization technique was tested for the sorption of Cd(II). The two biosorbents, used as the building block for the production of HB matrix, were the fungal biomass of Phanerochaete chrysosporium (B1) and fibrous network of papaya wood (B2). Maximum independent biosorption capacity of B1 and B2 was noted, respectively, to be 71.36 and 17.62 mg Cd(II) g −1 biosorbent. However, when two biosorbents were hybridized to form HB matrix, the combined biosorption capacity (141.63 mg Cd(II) g −1 biosorbent) was increased by 98.47, 703.80%, respectively, as compared to the ability of B1 and B2 when used alone, and by 59.17% than the sum of separate individual abilities of biosorbents B1 and B2. The kinetics of equilibrium was fast, approximately 88% of Cd(II) biosorption taking place within 30 min. Biosorption kinetics and equilibria followed the pseudo-second order kinetics and Langmuir adsorption isotherms model. HB matrix was also shown to be highly effective in removing Cd(II) from aqueous solution in a continuous flow fixed-bed column bioreactor, both in batch and repeated cycles.