Regeneration Of Activated Carbon Research Articles

Advanced Oxidation Processes for Activated Carbon Regeneration: From Fundamental to Application

Advanced Oxidation Processes for Activated Carbon Regeneration: From Fundamental to Application

Equilibrium adsorption of diethyl ketone on activated carbon in a supercritical CO2 environment: Measurements and thermodynamic modeling

This study focuses on the equilibrium adsorption of diethyl ketone, a VOC widely used in the printing industry, on activated carbon in a supercritical CO2 environment at pressures in the range of 10 MPa to 20 MPa and temperatures between 313 K and 353 K, which provides a wider range of equilibrium adsorption data for diethyl ketone under different pressure and temperature conditions and allows a comparative analysis with other ketone VOCs. It is found that the equilibrium adsorption of diethyl ketone on activated carbon exceeds that of methyl ethyl ketone, probably due to differences in their respective affinities for activated carbon and their different volatilities in a supercritical fluid context. The Dubinin-Astakhov model was used to interpret the data and showed an average relative deviation of approximately 3.8 % between modeled and observed values. Additional analysis of the model parameters influenced by CO2 density and VOC characteristics was performed to gain a better insight into the adsorption dynamics and to contribute to the design and improvement of the activated carbon regeneration process.

Experimental Study on the Preparation of Lignin-Based Activated Carbon and the Adsorption Performance for Phenol.

Biomass waste and wastewater are important wastes in the process of industrialization, which need to be effectively treated and utilized. In this work, an innovative method of collaborative treatment of biomass waste and phenol-containing wastewater is proposed. Biomass waste was used to produce activated carbon (AC), and then AC was used for phenol removal in wastewater treatment. Two kinds of typical biomass waste material, namely, coconut shell and lignin, were used. Physical activation (steam activation) and chemical activation methods were compared. Results show that steam activation is an effective method for coconut shell AC production. The largest Brunauer-Emmett-Teller (BET) surface area was 1065 m2/g at 800 °C. Chemical activation could produce AC samples with higher BET specific surface area. The lignin AC with K2CO3 activation has the largest BET surface of 1723.8 m2/g at 800 °C. FTIR results indicated that K2CO3 activation could greatly enhance the formation of surface oxygen-containing functional groups. Both coconut shell AC and lignin AC samples show excellent performance for phenol removal. The highest phenol removal efficiency for coconut shell AC and lignin AC are 96.87% and 98.22%, respectively. Adsorption kinetic analysis show that the pseudo-first-order kinetic model is able to describe the adsorption characteristics of phenol in wastewater treatment. Recycling properties show that regeneration of lignin AC could maintain high adsorption performance for phenol.

Removal of malachite green from water: Comparison of adsorption in a residue-derived AC versus photocatalytic oxidation with TiO2 and study of the adsorption-photocatalysis synergy

The literature rarely compiles studies devoted to the removal of pollutants in aqueous media comparing adsorption and photocatalytic degradation, and does not pay enough attention to the analysis of combined adsorption-photocatalytic oxidation processes. In the present manuscript, the removal of malachite green (MG) from aqueous solutions has been investigated in three different sustainable scenarios: i) adsorption on activated carbon (AC) derived from a residue, luffa cylindrica, ii) photocatalytic oxidation under simulated solar light using titanium dioxide (TP) and iii) combined adsorption-photocatalytic oxidation using TP-AC (70/30 wt./wt.) under simulated solar light. The study has revealed that in the three scenarios and studied conditions, the total removal of this endocrine-disrupting dye from the solution takes place in the assayed time, 2 h, in some cases just in a few minutes. MG adsorption in the AC is a very fast and efficient removal method. MG photocatalytic oxidation with TP also occurs efficiently, although the oxidized MG is not totally mineralized. MG removal using the TP-AC composite under simulated solar light occurs only slightly faster to the MG adsorption in the AC, being adsorption the dominating MG removal mechanism for TP-AC. Thus, more than 90% of the removed MG with TP-AC under simulated solar light is adsorbed in this carbon-containing composite. The obtained results highlight the interest in adsorption, being the selection of the most suitable removal method dependent on several factors (i.e., the cost of the AC regeneration, for adsorption, or the toxicity of the intermediate oxidation species, for photooxidation).Paying attention to MG photooxidation with TiO2, comparison of two working photodegradation schemes shows that the direct photodegradation of MG from solution, avoiding any initial dark equilibrium period, is more efficient from a time perspective. The use of scavengers has proved that MG photodegradation occurs via an oxidation mechanism dominated by superoxide anion radicals.

Enabling in situ electro-regeneration systems for PFOA-laden spent activated carbon adsorbents reuse

Adsorption is the main commercially used water treatment technology to remove per-and polyfluoroalkyl substances (PFAS) from water. Despite the high performance of this physical separation treatment, the endpoint of this technology is the production of PFAS-laden spent activated carbon. So far, several regeneration techniques have been used for spent activated carbon. However, activated carbon regeneration techniques remain challenging due to a limited understanding of cost/benefit analysis. In the present study, we developed the first proof of concept in situ electro-regeneration technique for the regeneration of perfluorooctanoic acid (PFOA, as a model long chain PFAS compound) laden-F400 using electro-assisted up-flow rapid small-scale column test (RSSCT) setup. The laboratory column experiments were conducted exploring sequential adsorption and electro-regeneration cycles. The results showed that the electro-regeneration of saturated F400 reinstated up to ∼60% of initial capacity. After the 1st regeneration cycle, the regeneration efficiency of spent F400 remained similar following 4 consecutive adsorption/regeneration cycles. The calculated operational cost for electro-regeneration was 0.70 kWh/kg, which is more competitive than current regeneration techniques. Overall, this novel proof-of-concept approach can be used as a promising alternative regeneration technique to existing ones to minimize waste PFAS-laden adsorbents in landfills and decrease the amount of CO2 emissions associated with the incineration of these sorbents.

Towards net-zero: CO2 capture and biogas purification through electric potential swing desorption to achieve SDGs 7 and 13

Currently, the potential of biomethane derived from biogas is substantial, positioning it to fulfill a considerable share of the United Kingdom’s total energy needs. The primary challenge associated with raw biogas lies in purifying it to produce biomethane, a process that necessitates the removal of carbon dioxide and hydrogen sulfide. Among the various methods, adsorption of activated carbon (AC) stands out as a particularly effective and cost-efficient approach for converting biogas into biomethane, provided that the regeneration of AC proves economically viable. In this research, a segment of activated carbon was utilized to assess the adsorption properties when exposed to a gas mixture of CO2, H2S, and N2 within a regenerative activated carbon setup. This investigation encompassed the analysis of adsorption and desorption behaviors, process capacities, and the impact of regeneration. To enhance the adsorption of CO2, electro-conductive polymers (ECPs) were incorporated into the AC samples, leading to an extension in breakthrough time. Subsequent to adsorption, the electric potential swing desorption (EPSD) was employed for in situ regeneration of activated carbon samples, involving potentials of up to 30 V. The findings exhibited that the newly introduced EPSD technique considerably diminished desorption durations for both H2S and CO2. Moreover, it successfully rejuvenated the accessible adsorption sites, resulting in reduced desorption times compared to the initial breakthrough time during adsorption. Consequently, the EPSD system proves to be a promising candidate for in situ regeneration of activated carbon to eliminate CO2 and H2S from biogas. Notably, this approach offers inherent advantages over conventional methods including thermal swing adsorption (TSA) and pressure swing adsorption (PSA) in terms of regeneration. The demonstrated method underscores the potential for more efficient and economically viable cycles of adsorption and desorption, thereby enhancing the overall biogas-to-biomethane conversion process to achieve SDGs 7 and 13 for clean and green energy applications.

Regeneration of granular activated carbon clogged in the treatment of leachates.

Landfill leachates are highly contaminated liquids and complex to treat. Two of the processes which are promising for the treatment are the advanced oxidation and adsorption methods. With the combination of the Fenton and adsorption methods, practically all the organic load of leachates can be removed; however, this combination of processes is limited due to the soon clogging of adsorbent material, which leads to high operation costs. In the present work, the results of the regeneration of clogged activated carbon are shown after the application of the Fenton/adsorption process in leachates. This research consisted of four stages: sampling and leachate characterization, clogging of the carbon through the Fenton/adsorption process, carbon regeneration through the oxidative Fenton process, and lastly, evaluation of regenerated carbon adsorption through jar and column tests. In the experiments, HCl 3M was used, and different concentration of hydrogen peroxide (0.15M, 0.2M, 0.25M) were tested at different times (16h and 30h). The activated carbon regeneration through the Fenton process and the optimal peroxide dosage was 0.15M for 16h. The regeneration efficiency was obtained from comparing the adsorption efficiency between regenerated and virgin carbon, reaching 98.27% and can be applied up to 4 times without losing regeneration efficiency. These results prove that it is possible to restore the clogged activated carbon adsorption capacity during the Fenton/adsorption process.

Highly active and stable CuxFey/AC-H catalysts with CuFe2O4 for NO reduction by CO in the presence of H2O and SO2 under regeneration gas

For industrial flue gas, the synergistic removal of NOx and CO pollutants is in high demand but still has not been realized due to the presence of O2. We propose firstly that activated carbon regeneration gas provides suitable O2-free conditions for NO reduction by CO, but high contents of 5% SO2 and 5% H2O affect the catalyst activity. Here, we report a bimetallic modified catalyst CuxFey/AC-H that exhibits high catalytic activity under the abovementioned conditions due to the high amount of CuFe2O4. By regulating the Cu/Fe ratio, the formation of CuFe2O4 active sites is promoted, which improves the redox properties, adsorption and activation capacity of NO, the ratio of high valence metal, and content of synergistic oxygen vacancies. Based on in situ DRIFTS and fixed-bed FTIR/MS combined platform, it was found that the side reaction of H2O with the intermediate of −NCO forms NH3 above 250 °C and with CO forms H2 above 400 °C·NH3 and H2 provide additional reaction pathways of Fast-SCR and H2-SCR to significantly improve the reaction activity with 92.0% of NO conversion at 450 °C and 108,000 mL g−1h−1 on Cu2Fe2/AC-H. According to DFT calculations, CuFe2O4 active sites provide the high binding energy of sulfation, and then Cu2Fe2/AC-H demonstrates excellent activity and long-term stability with 72.2% of NO conversion at high contents of SO2 and H2O for 48 h. And CuxFey/AC-H provides great potential prospects for the application of NO reduction by CO under activated carbon regeneration gas.

The Electro-Fenton Process for Caffeine Removal from Water and Granular Activated Carbon Regeneration

The electro-Fenton process (EF) has faced major challenges, including mass transfer limitations. When the targeted pollutants are present in water at very low concentrations, the degradation kinetics are slower than desired, which leads to high energy consumption. To overcome this drawback, coupled adsorption on activated carbon (AC) and the EF process can be performed. Therefore, the compounds can be preconcentrated on AC before elimination by the EF process. As such, in this study, batch experiments were conducted using low-cost granular activated carbon (GAC) packed in a stainless-steel mesh for the adsorption of caffeine. Once saturated, GAC is used as a cathode during the EF process, where the adsorption capacity is regenerated. This approach allows the regeneration of the AC for multiple cycles and the degradation of the desorbed compounds. The EF process was studied to this end, for the purposes of the removal of caffeine as a model compound. The main goals of this work are (i) to study the removal of caffeine from water in three different matrices and (ii) to regenerate GAC by using the EF process. The results reported in this study show that it is possible to achieve caffeine degradation up to 95%, 100%, and 100%, and a mineralization up to 70%, 72%, and 76% in pure water, simulated wastewater, and wastewater effluent, respectively. In the regeneration process, total elimination of the desorbed caffeine was achieved, and a regeneration efficiency of 50% was obtained for the first cycle. The results confirm the ability of the EF process to achieve regeneration of AC loaded with caffeine.

Micropollutants Removal from Water and Activated Carbon Regeneration by Combining Adsorption and Electro-Fenton

The presence of micropollutants in municipal wastewater effluents is a topic of major concern, as these pollutants end up in surface and ground waters. Currently, adsorption on activated carbon (AC) is used to remove these recalcitrant compounds. When saturated, the AC is generally either thermally regenerated or disposed of. Thermal regeneration is expensive and negatively affects the structure and adsorptive properties of the AC.Over the last decade, considerable attention has been directed towards the electrochemical advanced oxidation processes (eAOPs), due to their ability to remove a large range of organic pollutants from water even at very low concentrations [1]. eAOPs rely on the in-situ generation of powerful oxidants, such as HO• by electron transfer at the anode surface. However, these processes are limited by mass transfer and require high energy consumption.In this study, combined adsorption on granular activated carbon (GAC) and electro Fenton process (EF) is applied. The purpose of this coupled process is to overcome the mass transfer issue by pre-concentrating the compounds on AC and proposing a new AC regeneration method. During the EF the AC can directly be used as a cathode. Due to the electrostatic repulsions and oxidation process, the compounds are desorbed from the AC and oxidized by the HO• generated in the bulk. Material and Methods The adsorption cycles and EF experiments were performed in batch mode using deionized water (DW) and simulated wastewater (SWW) with caffeine as a model compound. Similar experimental steps and conditions as described in [2] are followed, using 1g of GAC, with pH=3, Fe2+= 0.15 mM, Na2SO4= 50mM, and a current intensity of 200 mA. To assess the degradation and mineralization of the caffeine, HPLC and TOC measurements were used, respectively. The regeneration efficiency was calculated by comparing the adsorption capacity of the AC after each regeneration cycle with its initial adsorption capacity. Results and Conclusions The efficiency of the process was discussed as regards (i) desorption of organic compounds and regeneration efficiency in DW and SWW, (ii) degradation and mineralization of organic compounds, and (iii) stability of GAC for several successive regeneration cycles. During the regeneration, over 80% of desorbed caffeine was degraded and 75% was mineralized due to the formed HO• by Fenton reaction and at the BDD anode surface (Fig.1). Furthermore, a recovery of the AC adsorption capacity by up to 50 % in PW and 37% in SWW was observed. These regeneration percentages decreased to 25% during the second cycle and then remained stable during the third and the fourth cycle. The incomplete regeneration is most likely due to remaining caffeine molecules at the AC [3], or a blockage of the carbon adsorption sites by formed degradation molecules. Hence, a longer treatment time might lead to higher efficiency. These hypotheses will be taken into consideration in future work to draw a clear conclusion on the regeneration phenomenon. The similar regeneration efficiencies and mineralization rates obtained during the 2nd,3rd, and 4th cycles indicate the stability of the GAC electrode.In conclusion, the results from this study illustrate that combined adsorption and EF is a suitable process for the removal of caffeine and regeneration of AC. The advantage of such a process is that part of the AC can be regenerated while over 75% of the desorbed compounds from the AC are mineralized, thus avoiding toxic effluents. This process is currently implemented as a continuous e-cell for sequential adsorption and EF regeneration.

The enhancement mechanism of the microwave-assisted toluene desorption for activated carbon regeneration based on the constructive interference

Reducing energy consumption is a crucial issue in adsorbent regeneration process, while regulating temperature distribution during regeneration is expected to solve this problem. In this study, we propose a novel enhancement mechanism based on the enhanced constructive interference for microwave-assisted regeneration of the activated carbons via a facile method for preparing activated carbons. We prepared activated carbons with similar adsorption characteristics (qe ≈ 0.20 g g−1 with a toluene concentration of 376 mg m−3) and different dielectric properties (29.96 < εr' < 84.18 and 20.21 < εr'' < 36.36) to investigate the effect of dielectric properties on microwave-assisted regeneration. Moreover, we obtained a high regeneration efficiency (>95%) and reduced energy consumption (∼50% of maximum value) in AC-450 with an input power of 40 W. A series of experiments and numerical simulations revealed that the reduced energy consumption was due to the enhanced constructive interference governed by dielectric properties. Further, a decreased dimensionless parameter affected by dielectric properties, fp, can enhance constructive interference. In summary, this work proposes an enhancement mechanism based on the enhanced constructive interference for microwave heating technology and provides a facile method for reducing energy consumption in microwave-assisted regeneration.

Environment–Energy–Economy Analysis and Related Technical Transition Strategies for Spent Activated Carbon Regeneration in China

Spent activated carbon (AC) regeneration attracts growing interests due to the increased waste amounts and limited AC resources. Herein, environment–energy–economy performances of four spent AC regeneration technologies demonstrated in China were compared with conventional incineration via life cycle assessment (LCA), energy-efficiency analysis (EEA), and environmental life-cycle costing. Their energy efficiencies are lower than 42%, which should be improved. Tradeoffs between environmental and economic performances found such as tunnel kiln regeneration technology were handled by integrating both performances with emission monetization model by internalizing environmental externalities as economic metric. Results indicated that microwave and rotary-kiln regeneration are preferred and break even in 2 years even with externalities. Potential pollution migration (in air–water–human medium) analysis illustrates that technical-sustainable transition from spent AC incineration to regeneration may relieve GHG emissions but add human risks due to dioxins and heavy metal emitted. Regeneration rate and energy use are sensitive to environmental and economic result.

Degradation of ampicillin by combined process: Adsorption and Fenton reaction

When disposed incorrectly, antibiotics can cause complex effects on environmental matrices, such as bacterial resistance. In this context, the present work investigated the degradation and mineralization of the β -lactam antibiotic ampicillin (AMP) applying a combined treatment of Fenton reaction and adsorption onto granular activated carbon (GAC). Adsorption parameters of contact time (10–210 min) and GAC dosage (5–50 g L − 1 ) were evaluated, as well as adsorption kinetics. Both in Fenton reaction and combined process, the influence of H 2 O 2 and Fe + 2 concentrations were evaluated, using five combinations of H 2 O 2 /Fe + 2 : 300/60 μ M, 300/80 μ M, 400/70 μ M, 500/60 μ M and 500/80 μ M. Finally, because of the combined process, GAC regeneration was investigated in 3 cycles. Best adsorption conditions were determined as 150 minutes of contact time and GAC concentration of 20 g L −1 , reaching 57% of AMP removal and adsorbed amount of 0.58 mg g − 1 . All Fenton experimental conditions led to a complete degradation of AMP within 1 min, suggesting the generation rate of hydroxyl radicals was faster in the first minutes of reaction. In the combined process, similar results for degradation were found. A higher mineralization (83%) and GAC regeneration (85%) was reached at H 2 O 2 /Fe + 2 = 500 / 80 μ M, indicating the influence of H 2 O 2 and Fe + 2 concentrations. GAC regeneration efficiency for the 3 cycles were, respectively, 84%, 71% and 49%. Thus, the results demonstrate the combined process of Fenton reaction and GAC adsorption is a feasible treatment reaching high mineralization. • The combined process of adsorption and Fenton is a feasible treatment for effluents containing ampicillin reaching high mineralization. • Generation rate of hydroxyl radicals was faster in the first minutes of reaction. • Fenton promotes the granular activated carbon regeneration.

Treating High COD Dyeing Wastewater via a Regenerative Sorption-Oxidation Process Using a Nano-Pored Activated Carbon.

Nowadays, the structural complexity of dyes used in the textile industry and the widely adopted water-saving strategy in the dyeing processes often fail plants’ biological wastewater treatment units due to chemical oxygen demand (COD) overload. To alleviate this problems, this study investigated a regenerable adsorption–oxidation process to treat dyeing wastewater with COD around 10,000 mg/dm3 using a highly nano-pored activated carbon (AC) as a COD adsorbent, followed by its regeneration using hydrogen peroxide as an oxidizing reagent. In addition to studying AC’s COD adsorption and oxidation performance, its operational treatment conditions in terms of temperature and pH were assessed. The results firstly demonstrated that about 50–60% of the COD was consistently adsorbed during the repeated adsorption operation before reaching AC’s maximum adsorption capacity (qmax) of 0.165 g-COD/g-AC. The optimal pH and temperature during adsorption were 4.7 and 25 °C, respectively. Secondly, AC regeneration was accomplished by using an initial peroxide concentration of 2.5% (by wt %) and EDTA-Fe of 2.12 mmole/dm3. The reuse of the regenerated ACs was doable. Surprisingly, after the first AC regeneration, the COD adsorption capacity of the regenerated AC even increased by ~7% with respect to the virgin AC. Thirdly, the results of a five-consecutive adsorption–regeneration operation showed that a total of 0.3625 g COD was removed by the 5 g AC used, which was equivalent to an adsorption capacity (q) of 0.0725 (= 0.3625/5) g-COD/g-AC during each adsorption stage. Based on the obtained results, a regenerable COD adsorption–oxidation process using a nano-pored AC to treat the high-textile-COD wastewater looks promising. Thus, a conceptual treatment unit was proposed, and its potential benefits and limitations were addressed.

Study on sulfur migration and carbon consumption during regeneration of SO2-loaded activated carbon: Effect of alkali/alkaline earth metals

Activated carbon (AC) has emerged as a new technology with promising application prospects for environment friendly SO2 removal, and the thermal regeneration process of SO2-loaded AC is the key step to realize adsorbent circulation and sulfur recovery. Herein, the synergistic effects of alkali/alkaline earth metals in ash on sulfur migration and carbon consumption were studied based on fixed bed adsorption and thermal regeneration. The experimental results showed that the adsorption atmosphere has a significant effect on gas desorption. In the temperature range of 150–850 °C, SO2 was the cause of excessive CO2 release during regeneration compared with non-adsorbed AC. Among them, the carbon consumption caused by CO2 release in the relatively low temperature range (150–500 °C) was mainly due to the regeneration reaction of chemisorbed SO2. The carbon consumption in the relatively high temperature range (500–850 °C) was mainly related to the Ca-based sulfate formed in the adsorption process, which was reduced during heating to release CO2. This study elucidates the synergistic effect of ash on the sulfur migration and carbon consumption in the process of regeneration, which provides a deeper understanding of the AC flue gas desulfurization and regeneration process.

A review about microwave regeneration technology of waste activated carbon

Activated carbon (AC) can concentrate and transfer pollutants using its own adsorption capacity. Waste AC is a kind of solid waste, its adsorption capacity of pollutants is greatly reduced after adsorption saturation. If handled improperly, it will cause secondary pollution to the environment. Therefore, it is necessary to regenerate the waste AC to restore its adsorption performance and reduce environmental pollution and resource waste. Microwave regeneration technology is of great research value because of its low energy consumption, time saving and high efficiency. Based on the characteristics of microwave heating and regeneration mechanism, this paper summarizes the advantages of microwave regeneration compared with conventional heating regeneration, and the application status of microwave technology in the regeneration of waste AC was reviewed. The influence of different types of pollutants adsorbed by AC, the change of control conditions for microwave regeneration of AC and the characteristics of AC itself on microwave regeneration were briefly described. And the development direction of microwave regeneration of AC in the future is also prospected.

Long-term performance of granular activated carbon electrode system for the removal of amoxicillin

Three-dimensional electrode reactor, packed with conductive particles, is more cost-effective than traditional two-dimensional electrode reactor. In this study, granular activated carbon (GAC) was applied as particle electrode, then the long-term performance on amoxicillin (AMX) removal and activated carbon regeneration of the GAC particle electrode oxidation process (GAC EOP) was investigated, and the GAC adsorption process (GAC ADS) was carried out for comparison. Both of them ran continuously to remove AMX. Because of the regeneration effect of electrochemical action, the GAC EOP showed a more stable physisorption capacity than GAC ADS, with less change in micropore volume, pore size distribution and surface morphology of GAC. The result of XPS revealed the AMX chemisorption mechanism: the carbonyl (CO) and phenolic hydroxyl (OH) on activated carbon combined with carboxyl (COOH) and ammonium group (NH3+) on AMX, respectively. Correspondingly, the content of CO and OH on GAC fell significantly during the GAC ADS. However, due to the chemical bond regeneration effect of electrolysis, noticeable declines were not observed in GAC EOP, which ensured the stable chemisorption capacity of this system. It was shown that during the 50 consecutive runs, the AMX removal in GAC EOP was always higher than 60%. Even the removal efficiency showed an upward tendency, with the average value reached 86.1% and 99.1% in the 31–40 and 41–50 run times respectively. It was because of the rising specific surface area of GAC and the effect of electro-polarization, which made it more meaningful to explore the long-term performance of three-dimensional electrode reactor.

A Pilot Study of a Hybrid Process Involving In Situ Regenerated Activated Carbon, Membrane Separation and Advanced Oxidation for Water Pollution Abatement

The assessment of a pilot-scale hybrid system coupling powdered activated carbon (PAC) adsorption with membrane ultrafiltration (UF), in respect of activated carbon regeneration and organic micropollutant removal, was investigated in this study. Field tests with two adsorbents (i.e. a commercial PAC and a PAC-Fe(II) composite), conducted in the premises of Thessaloniki Water Treatment Plant, demonstrated the high efficiency of the combined PAC/UF process. Regeneration efficiencies varying between approximately 95% and 110%, complete diclofenac (DCF) degradation and rather moderate mineralization (TOC removal) rates of up to 47%, can be achieved by UVC/H2O2 or photo-Fenton oxidation after 4 hours of treatment; this performance is attributed to the in situ generation of reactive oxidant species by photolysis of H2O2, which seems to enhance the process effectiveness. Among the two adsorbent materials tested, composite PAC-Fe(II) exhibited a higher DCF adsorption capacity than the original PAC, probably due to the improved chemisorption and/or the electrostatic attractive interactions between the negatively charged DCF molecules and the positively charged iron species, at neutral pH. Furthermore, a rather insignificant effect of PAC-Fe(II) loading on the regeneration efficiency was observed. The advantages of totally controlled H2O2 dosages and short operating times render the hybrid PAC/UF system a promising alternative to conventional and advanced drinking water purification methods.

Prolonged lifetime of biological activated carbon filters through enhanced biodegradation of melamine

Micropollutants can be removed in Biological Activated Carbon (BAC) filters through biodegradation, besides adsorption, when the conditions are favorable. In the present study, we build upon previous work on melamine biodegradation and activated carbon regeneration in batch experiments and assess the efficiency of this process in continuous flow lab-scale BAC filters. Melamine is frequently detected at low concentrations in surface water and is used here as a model micropollutant. BAC filters were inoculated with melamine degrading biomass and the contribution of biodegradation to melamine removal was assessed. Furthermore, we tested the effect of an additional carbon source (methanol) and the effect of contact time on melamine removal efficiency. We demonstrate that inoculation of activated carbon filters with melamine degrading biomass increases melamine removal efficiency by at least 25%. When an additional carbon source (methanol) is supplied, melamine removal is almost complete (up to 99%). Finally, through a nitrogen mass balance, we demonstrate that around 60% of the previously adsorbed melamine desorbs from the BAC surface when biodegradation rates in the liquid phase increase. Melamine desorption resulted in a partial recovery of the adsorption capacity.

Polyvinyl alcohol-montmorillonite composites for water purification: Analysis of clay mineral cation exchange and composite particle synthesis

Municipal and residential water purification rely heavily on activated carbon (AC), but regeneration of AC is costly and cannot be performed at the point-of-use. Clay minerals (CMs) comprise a class of naturally abundant materials with known capacities for analyte adsorbance. However, the gel-forming properties of CMs in aqueous suspension pose problems for these materials being used in water-purification. In this study, we have taken three main steps to optimize the use of CMs in these applications. First, we produced several variants of montmorillonite CMs to evaluate the effect of interstitial cation hydrophobicity on the ability of the CM to uptake charge-carrying organic pollutants. These variants include CMs with the following cations: sodium, hexyl(triphenyl)phosphonium, hexyadecyl(triphenyl)phosphonium, and hexyl(tributyl)phosphonium. Second, we synthesized polymer–clay mineral composite films composed of polyvinyl alcohol (PVA), crosslinked in the presence of a CM variant. These films were evaluated for their ability to uptake malachite green (MG). Finally, we developed a one-pot synthetic method for the generation of polymer–clay particles for use in a continuous column process. We synthesized polymer–clay mineral particles using the highest performing CM (based on the film experiments) and evaluated the equilibrium capacity and kinetics of MG uptake from solution.