Regeneration Of Granular Activated Carbon Research Articles

Thermal transformations of perfluorooctanoic acid (PFOA): Mechanisms, volatile organofluorine emissions, and implications to thermal regeneration of granular activated carbon

Thermal treatment is effective for the removal of perfluorooctanoic acid (PFOA). However, how temperatures, heating methods, and granular activated carbon (GAC) influence pyrolysis of PFOA, and emission risks are not fully understood. We studied thermal behaviors of PFOA at various conditions and analyzed gaseous products using real-time detection technologies and gas chromatography-mass spectrometry (GC-MS). The thermal decomposition of PFOA is surface-mediated. On the surface of quartz, PFOA decomposed into perfluoro-1-heptene and perfluoro-2-heptene, while on GAC, it tended to decompose into 1 H-perfluoroheptane (C7HF15). Neutral PFOA started evaporating around 100 ℃ without decomposition in ramp heating. During pyrolysis, when PFOA was pre-adsorbed onto GAC, it was mineralized into SiF4 and produced more than 45 volatile organic fluorine (VOF) byproducts, including perfluorocarbons (PFCs) and hydrofluorocarbons (HFCs). The VOF products were longer-chain (hydro)fluorocarbons (C4-C7) at low temperatures (< 500 ℃) and became shorter-chain (C1-C4) at higher temperatures (> 600 ℃). PFOA transformations include decarboxylation, VOF desorption, further organofluorine decomposition and mineralization in ramp heating of PFOA-laden GAC. Decarboxylation initiates at 120 ℃, but other processes require higher temperatures (>200 ℃). These results offer valuable information regarding the thermal regeneration of PFAS-laden GAC and further VOF control with the afterburner or thermal oxidizer.

Regeneration of perfluorooctane sulfonic acid (PFOS) loaded granular activated carbon using organic/inorganic mixed solutions

Public concern about poly- and perfluoroalkyl substances (PFAS) in the environment has been raised due to their potential toxicity and environmental endurance. Adsorption using granular activated carbon (GAC) is a widespread strategy to remove PFAS. Herein, regeneration of PFAS-saturated GAC was studied and organic/inorganic mixed solutions were used to regenerate exhausted GAC. Optimization experiments revealed that a regenerant solution consisting of 0.1 mol/L HCl in ethanol with a 30-min residence time effectively regenerated PFAS-saturated GAC. The results showed that even after the fifth usage cycle, the proposed regeneration method can efficiently regenerate the PFAS-saturated GAC. Identification of the regeneration mechanism indicated that the regeneration process can be attributed to physical displacement and solubilization of PFAS from exhausted GAC. Additionally, BET analysis of PFAS-saturated and regenerated GACs revealed an increase in total pore volume and BET surface area in regenerated GACs, demonstrating the suggested method’s regeneration capabilities.

Sustainable application of surfactants in soil remediation: Selective pollutants adsorption and hydrogen peroxide-driven adsorbent regeneration

The uncontrolled disposal of the liquid lindane wastes have led to the formation of dense non-aqueous phase liquids (DNAPL), consisting of 28 chlorinated organic compounds (COCs), contaminating soil and groundwater. Surfactant-enhanced aquifer remediation is proposed as technology to treat these sites. However, the polluted emulsion generated must be manged on-site. In this work a two-step process is applied to treat emulsion composed of E-Mulse® 3 (4 g·L−1) as surfactant and a DNAPL (2 gCOCs·L−1). In the first, the COCs were selectively adsorbed in a granular activated carbon (GAC) column with Fe (II) previously adsorbed (10–20mg·g-1) onto the carbon surface, recovering an aqueous phase with surfactant for their reuse. In the second step, the spent GAC was regenerated with a 40 g·L−1 solution of hydrogen peroxide fed to the column at 2 mL·min−1 to promote the oxidation of the COCs adsorbed in the GAC. The kinetic and adsorption model in a multisolute (surfactant and DNAPL) system has been proposed. Five successive cycles of regeneration/adsorption have been successfully applied in the column process. About 50 % of the COCs were retained from the emulsion, and more than 70 % of the surfactant was recovered. The consumption of unproductive oxidants decreased with the number of regeneration cycles. The water effluent obtained after regeneration of GAC did not present chlorinated compounds desorbed and nontoxic by-products generated, such as short-chain acids.

Regeneration of granular activated carbon adsorbent by peroxymonosulfate activation with MnO2/MnFe2O4

The regeneration of spent adsorbent is crucial in terms of environmental and economic aspects. In this study, MnO2/MnFe2O4 was synthesized by an impregnation-precipitation method and investigated as a peroxymonosulfate (PMS) catalyst for the regeneration of granular activated carbon (GAC) after adsorption of ofloxacin (OFL). MnO2/MnFe2O4 exhibited high catalytic activity for the regeneration of GAC with PMS, and the adsorbed OFL was effectively removed from GAC surface. Singlet oxygen was found to be the dominant reactive species in this process, while O2•− and SO4•− participated in the degradation of intermediates. At neural pH, the regeneration efficiency of the spent GAC after the adsorption of OFL, tetracycline hydrochloride, ciprofloxacin and methylene blue reached 100 %, 100 %, 87.2 % and 84.2 %, respectively. MnO2/MnFe2O4 and GAC exhibited good stability and reusability in this process, and the regeneration efficiency was still above 90 % in the fifth cycle. The results suggest the potential application of PMS activation with magnetic catalyst in the regeneration of GAC after adsorption of organic pollutants.

Peroxymonosulfate activation with CuOX/MnFe2O4 for the regeneration of granular activated carbon after adsorption of organic pollutants

Adsorption is a cost-effective technology for the removal of refractory organic pollutants, and the regeneration of the spent adsorbent is crucial in terms of environmental and economic aspects. Herein, CuOX/MnFe2O4 was synthesized by a two-step precipitation method and investigated as a peroxymonosulfate (PMS) catalyst for the regeneration of granular activated carbon (GAC) saturated with ofloxacin. The influences of reaction conditions on the regeneration of GAC with CuOX/MnFe2O4-PMS and the possible mechanism were explored. The results showed that CuOX/MnFe2O4 exhibited high catalytic activity for the regeneration of GAC via the high mineralization of the adsorbed ofloxacin. Singlet oxygen was the dominant reactive species for organics removal, while O2•− and SO4•− also made a contribution to the degradation of organic intermediates. Under the optimized conditions, the regeneration efficiency of the spent GAC reached 98%, 89%, 87% and 85% for ofloxacin, ciprofloxacin, Orange II and methylene blue, respectively. Moreover, CuOX/MnFe2O4 and GAC exhibited high stability and good reusability in this process, suggesting the potential application of this regeneration technology for removing refractory organic pollutants.

Regeneration of Granulated Spent Activated Carbon with 1,2,4-Trichlorobenzene Using Thermally Activated Persulfate.

Chlorinated organic compounds (COCs) are persistent organic pollutants often found in groundwater near industrial sites or in industrial wastewaters. Adsorption into activated carbon is a common strategy to remediate these waters, but spent activated carbon results in a toxic residue to manage. To avoid the transport of the chlorinated compounds out of the site, the in-situ regeneration of the spent activated carbon can be considered for reuse to implement a circular economy. In this work, the regeneration of a commercial granular activated carbon (GAC) has been carried out using thermally activated sodium persulfate (TAP). GAC was previously saturated in 1,2,4-trichlorobenzene (124-TCB) as the model compound. The initial adsorption value was 350 mg124-TCB·gGAC–1. First, the nonproductive consumption of sodium persulfate was studied at different temperatures using nonsaturated GAC. Then, the regeneration of the saturated GAC (5 g) was studied by an aqueous solution (166 mM) of TAP (1 L) at a temperature range from 20 to 80 °C. The possible recovery of the adsorption capacity was studied after 3 h of treatment in three successive adsorption–regeneration cycles at the selected temperature (60 °C). The physicochemical changes of the GAC were also investigated before and after the regeneration treatments. The results evidence the significant deposition of sulfate on the GAC after each treatment of regeneration, which avoids the recovery of the initial adsorption capacity. Therefore, each regeneration cycle was necessarily followed by a washing step at 60 °C to remove this sulfate. After that, the regeneration treatment achieved a stable and high recovery of the initial adsorption capacity of about 48.2%.

Extending granular activated carbon (GAC) bed life: A column study of in-situ chemical regeneration of pesticide loaded activated carbon for water treatment

In-situ chemical regeneration of granular activated carbon (GAC) may represent an advantageous alternative to conventional off-site thermal regeneration in water treatment applications. The performance of chemical regeneration of carbon exhausted by metaldehyde and isoproturon was investigated using rapid small-scale column tests, performed using a sequence of pesticide adsorption and chemical regeneration cycles with a novel alkaline-organic regenerant solution. A fresh regenerant solution was able to achieve 82% and 45% regeneration of carbon exhausted by metaldehyde and isoproturon, respectively. After the first regeneration, the performance declined slightly to 79%, and to 36% after the fourth regeneration. A comparison using a thermally regenerated (operational) carbon suggested that chemical regeneration was more beneficial for carbon exhausted by metaldehyde. The regenerant solution has a potential to be re-used multiple times, thereby minimizing the amount of waste chemicals generated. A series of carbon characterization tests showed that chemical regeneration did not alter the surface area, pore size distribution and surface chemistry of the carbon. As part of the evaluation, the adsorption thermodynamics of virgin and chemically regenerated carbons were determined using isothermal titration calorimetry to evaluate the adsorption behaviour of the pesticides on the carbon samples. The relatively high regeneration efficiency achieved by chemical regeneration, and minimal deleterious effect to the physico-chemical properties of the carbon, demonstrated the beneficial potential of this process as an alternative to conventional thermal regeneration of GAC.

Thermal Regeneration of Spent Granular Activated Carbon Presents an Opportunity to Break the Forever PFAS Cycle.

Extensive use of per- and polyfluoroalkyl substances (PFAS) has caused their ubiquitous presence in natural waters. One of the standard practices for PFAS removal from water is adsorption onto granular activated carbon (GAC); however, this approach generates a new waste stream, i.e., PFAS-laden GAC. Considering the recalcitrance of PFAS molecules in the environment, inadequate disposal (e.g., landfill or incineration) of PFAS-laden GAC may let PFAS back into the aquatic cycle. Therefore, developing approaches for PFAS-laden GAC management present unique opportunities to break its forever circulation within the aqueous environment. This comprehensive review evaluates the past two decades of research on conventional thermal regeneration of GAC and critically analyzes and summarizes the literature on regeneration of PFAS-laden GACs. Optimized thermal regeneration of PFAS-laden GACs may provide an opportunity to employ existing regeneration infrastructure to mineralize the adsorbed PFAS and recover the spent GAC. The specific objectives of this review are (i) to investigate the role of physicochemical properties of PFAS on thermal regeneration, (ii) to assess the changes in regeneration yield as well as GAC physical and chemical structure upon thermal regeneration, and (iii) to critically discuss regeneration parameters controlling the process. This literature review on the engineered regeneration process illustrates the significant promise of this approach that can break the endless environmental cycle of these forever chemicals, while preserving the desired physicochemical properties of the valuable GAC adsorbent.

Simple and eco-friendly thermal regeneration of granular activated carbon from the odour control system of a full-scale WWTP: Study of the process in oxidizing atmosphere

Adsorption by granular activated carbon (GAC) is an efficient, reliable, and well-established technique for treating malodours in wastewater treatment plants (WWTPs). However, when the lifespan of GAC is over, it becomes a hazardous industrial waste, which is mostly discarded in landfills. In the framework of a sustainable economy, this work proposes an oxidative thermal regeneration of GAC from the odour control system of an urban WWTP for reuse, mainly as an odour adsorbent in WWTPs, avoiding the use of high-cost inert atmosphere and complex additional post-treatments. In this sense, GAC, from two deodorization points of the abovementioned facility, the pretreatment header (P1 sample) and sludge dewatering (P2 sample), has been characterized in depth, both before and after its regeneration. Previous characterization has shown that GAC regeneration conditions depend on the nature of adsorbed odorants after the same operating time, while post-regeneration characterization has proven the recovery of the GAC’s original properties. Thus, specific surface area (SBET) values above 550 m2/g have been reached for both P1 and P2, considerably exceeding the pristine sample (P0) value of 406 m2/g. Furthermore, the microporous structure was also recovered in both samples, highlighting the case of the almost non-porous P1 sample, whose micropore volume exceeded 1.27 times the value of the P0 sample (0.180 cm3/g) after regeneration. On the basis of the above, and taking into account the good regeneration efficiencies reached (72–98%), the oxidative thermal regeneration at temperatures no higher than 350 °C can be a simple and sustainable alternative to revalue GAC used in WWTPs.

Hybrid electrochemical-granular activated carbon system for the treatment of greywater

Three-dimensional (3D) flow-through electrochemical reactor filled with granular activated carbon (GAC) was employed for the treatment of greywater. Polarization of GAC by the electric field, without the direct contact with the terminal current feeders, resulted in oxidant production and degradation of the adsorbed/electrosorbed contaminants. This in turn enabled electrochemical regeneration of GAC and an improved performance compared to a conventional two-dimensional (2D) electrochemical system. The synergy between electrooxidation and GAC adsorption enhanced the performance of the 3D system by up to 21% and 23% in terms of COD and TOC removal, respectively, compared to the summed up performances of GAC and 2D electrochemical systems operating separately. In long-term operation of the 3D system with a previously saturated GAC, the regeneration efficiency of GAC was increased from 42 to 65% over 31 consecutive runs. Disinfection efficiency was evaluated using Escherichia coli (E. coli), spores of Clostridium perfringens (SCP) and somatic coliphages (SOMCPH) as model organisms for pathogenic bacteria, protozoan surrogate and viruses, respectively. GAC could not remove any of the abovementioned microbial indicators. 2D and 3D electrochemical systems achieved similar log removals of E. coli (4.6–5.1 log), SCP (0.1–0.6 log) and SOMCPH (3.2–3.3 log). However, the proportions of viable cells from the total cells adsorbed onto the GAC was reduced from 72% to 22% when an electric field was applied, further confirming that electrochemical polarization of GAC caused the killing of the adsorbed microorganisms. Simultaneous adsorption/electrosorption and electrocatalysis in the GAC packed bed lowered the energy consumption from 46 kWh kg COD−1 removed in conventional 2D system, to 30 kWh kg COD−1 removed in the 3D electrochemical system, thus enabling significant savings in the operational costs.

Evaluation of Water Treatment Efficiency according to Number of Regeneration of GACs For Efficient Operation of GAC Process

This study was conducted to evaluate the effect of increasing the number of regenerated granular activated carbon (GAC) on the adsorption efficiency of DOC and THMs from 2011 to 2016. As increase the number of regeneration times, the apparent density, hardness and I2 number were decreased, and the ash was increased. Average breakthrough period of virgin GAC for DOC (C/C0 = 0.8) was about 8 months and each GAC basin (300 m3) adsorbed about 4,246 kg of DOC. The regenerated GACs reached to breakthrough 7 to 10 months and these GACs have 3,514~4,656 kg/basin adsorption capacity. The average THMs breakthrough (C/C0 = 1.0) period of virgin GAC was about 7 months and each basin adsorbed 60.6 kg of THMs. 1st and 2nd and more regenerated GACs had 44.8 kg/basin, 21.6 kg/basin and 10.8 kg/basin adsorption capacity respectively. To determine the optimum regeneration times, 6th regenerated GAC has almost same degree of adsorbing DOC capacity of virgin GAC that means it is difficult to determine the appropriate regeneration times for DOC, on the other hands for THMs, 2nd regenerated GAC’s adsorption capacity has one thirds of virgin GAC of that and more 4th regenerated GAC has only one sixths of virgin of that, therefore, more two times of regenerated GAC needs to be considered for THMs removal. Key words: Granular Activated Carbon (GAC), Regeneration, Regeneration Times, Trihalomethanes (THMs), Dissolved Organic Carbon (DOC), Breakthrough

Persulfate/electrochemical/FeCl2 system for the degradation of phenol adsorbed on granular activated carbon and adsorbent regeneration

A novel method was developed for phenol degradation and the regeneration of phenol-saturated granular activated carbon (GAC) in bench-scale tests. The degree of phenol degradation in solutions was as high as 75.3% when using persulfate/electrochemical/FeCl2 (PS/Electro/Fe) system under optimal conditions (1000 mg/L Na2S2O8 and 500 mg/L FeCl2 at 15 V). Based on these results, the regeneration of phenol-saturated GAC was then examined by the PS/Electro/Fe method. The highest regeneration efficiency of 58.2% was obtained when 30 g phenol-saturated GAC was treated in 1000 mg/L FeCl2 and 2000 mg/L PS at an applied voltage of 22.5 V. The effects of electric voltage and initial PS concentrations on the regeneration efficiency were examined in detail for the PS/Electro/Fe system. Considering the practical application of this method, multiple regenerations and reuse cycles of the phenol-saturated GAC were conducted, affording a regeneration efficiency of more than 40% after 3 cycles in practice.

Catalytic polymer-clay composite for enhanced removal and degradation of diazinon

It is well established that organophosphate pesticides, such as diazinon, pose environmental and health risks. Diazinon is prone to rapid acidic hydrolysis, forming the less toxic compound 2-isopropyl-6-methyl-4-pyrimidinol (IMP). In this study, diazinon surface catalyzed hydrolysis was achieved by its adsorption to a composite, based on protonated poly (4-vinyl-pyridine-co-styrene) (HPVPcoS) and montmorillonite (MMT) clay. The adsorption affinity and kinetics of diazinon to HPVPcoS-MMT were significantly higher than those obtained to the deprotonated PVPcoS-MMT, emphasizing the importance of hydrogen bonding. Correspondingly, diazinon filtration by HPVPcoS-MMT columns was highly efficient (100% for 100 pore volumes), while filtration by columns of PVPcoS-MMT or granular activated carbon (GAC) reached only 55% and 85%, respectively. Regeneration of HPVPcoS-MMT by pH increase was demonstrated and sorbent reuse was successful, whereas regeneration and reuse of GAC and PVPcoS-MMT were inefficient. Proton transfer from HPVPcos-MMT to diazinon, investigated by FTIR analysis, supports the suggested mechanism of surface catalyzed hydrolysis. These findings demonstrate the applicability of such bi-functional sorbents, to adsorb and degrade pollutants, for efficient water treatment.

Residual organic fluorinated compounds from thermal treatment of PFOA, PFHxA and PFOS adsorbed onto granular activated carbon (GAC)

Perfluorooctanoic acid (PFOA), perfluorohexanoic acid (PFHxA) and perfluorooctane sulfonate (PFOS) adsorbed onto granular activated carbon (GAC) were thermally treated in N2 gas stream. The purpose was to assess the fate of perfluoroalkyl and polyfluoroalkyl substances (PFASs) during thermal regeneration of GAC, which had been used for water treatment. Mineralized F, residual PFASs including short-chained species, and volatile organic fluorine (VOF) were determined. In a temperature condition of 700 °C, VOF were 13.2, 4.8, and 5.9 % as for PFOA, PFHxA, and PFOS. However, the VOF decreased to 0.1 %, if the GAC and off-gas were kept at 1000 °C. No PFASs remained in GAC at 700–1000 °C; at the same time, short-chained PFASs were slightly detected in the aqueous trapping of off-gas at 800 and 900 °C conditions. The destruction of PFASs on GAC could be perfect if the temperature is higher than 700 °C; however, the process is competitive against volatile escape from GAC. Destruction in gaseous phase needs a temperature as high as 1000 °C. Destruction of PFASs on the surface of GAC, volatile escape from the site, and thermolysis in gas phase should be considered, as to thermal regeneration of GAC.

Regeneration of Acid Orange 7 Exhausted Granular Activated Carbon Using Pulsed Discharge Plasmas**supported by National Natural Science Foundation of China (No. 21207052), China Postdoctoral Science Foundation (No. 20110491353) and Jiangsu Planned Projects for Postdoctoral Research Funds, China (No. 1102116C)

In this paper, a pulsed discharge plasma (PDP) system with a multi-needle-to-plate electrodes geometry was set up to investigate the regeneration of acid orange 7 (AO7) exhausted granular activated carbon (GAC). Regeneration of GAC was studied under different conditions of peak pulse discharge voltage and water pH, as well as the modification effect of GAC by the pulse discharge process, to figure out the regeneration efficiency and the change of the GAC structure by the PDP treatment. The obtained results showed that there was an appropriate peak pulse voltage and an optimal initial pH value of the solution for GAC regeneration. Analyses of scanning electron microscope (SEM), Boehm titration, Brunauer-Emmett-Teller (BET), Horvath-Kawazoe (HK), and X-ray Diffraction (XRD) showed that there were more mesopore and macropore in the regenerated GAC and the structure turned smoother with the increase of discharge voltage; the amount of acidic functional groups on the GAC surface increased while the amount of basic functional groups decreased after the regeneration process. From the result of the XRD analysis, there were no new substances produced on the GAC after PDP treatment.

Ultrasound-assisted regeneration of granular activated carbon saturated by 4-chlorophenol in batch-loop reactor

The present work reports an investigation for examining the use of low-frequency ultrasound (20 kHz) as an inventive technique for the regeneration of granular activated carbon (GAC) saturated by 4-chlorophenol (4-CP) in batch-loop reactor. The effects of experimental conditions such as the amount of adsorbent (0.05–0.4 g), intensity of ultrasound irradiation (20–35%), temperature (25–55°C), flow rate (3–30 mL/min) and total volume of regenerating solution (200–300 mL), NaOH (0.01–0.1 N), ethyl alcohol (10–60%) and mixture of NaOH, and ethanol on the regeneration process were examined. The obtained results show that the amount of 4-CP desorption decreased with increasing the amount of adsorbent and intensity of ultrasonic irradiation. The desorption gradually increased with the increase in temperature and flow rate and total volume of regenerating solution. Using NaOH or/and ethyl alcohol as regenerating solutions causes an improvement in the desorption of 4-CP from GAC. The regeneration of spent GAC by ultrasonic irradiation is due to the generation of physical and thermal effects of ultrasound. It can be concluded that desorption by ultrasound can be an alternative technique to classical methods used for the regeneration of exhausted GAC.

Regeneration of exhausted granular activated carbon by low frequency ultrasound in batch reactor

The aim of the present work is to investigate the use of low frequency ultrasound (20 kHz) for the desorption of 4-chlorophenol (4-CP) from granular activated carbon (GAC) in batch reactor. The influence of experimental conditions such as amount of adsorbent, acoustic power, pulsed ultrasound, temperature, concentrations of NaOH, ethyl alcohol, and salt and saturating gases on the desorption was examined. The obtained results show that continuous wave ultrasound was more effective than pulsed modulation. The desorption was enhanced with the rise in temperature from 15 to 45°C and was reduced in the presence of salt (NaCl) and saturating gases such as argon and nitrogen. The regeneration of GAC was increased with increasing the concentration of NaOH from 0.01 to 0.1M and decreased afterward. The desorption increased with increasing the ethanol percentage. Using different mixtures of ethanol and NaOH at various concentrations, it has been shown that these regenerating mixtures improve the desorption of 4-CP. A mixture of 30% ethanol and 0.1M NaOH produces a synergistic effect and a significant intensification of desorption. The findings revealed the potential to regenerate exhausted GAC by ultrasonic irradiation.

UV-activated persulfate oxidation and regeneration of NOM-Saturated granular activated carbon

A new method of ultraviolet light (UV) activated persulfate (PS) oxidation was investigated to regenerate granular activated carbon (GAC) in drinking water applications. The improvements in iodine and methylene blue numbers measured in the GAC after ultraviolet- (UV) activated persulfate suggested that the GAC preloaded with natural organic matter (NOM) was chemically regenerated. An experimental matrix for UV-activated persulfate regeneration included a range of persulfate doses and different UV wavelengths. Over 87% of the initial iodine number for GAC was restored under the optimum conditions, perfulfate dosage 60 g/L and UV exposure 1.75 × 104 mJ/cm2. The persulfate dosages had little effect on the recovery of the methylene blue number, which was approximately 65%. Persulfate activation at 185 nm was superior to activation at 254 nm. UV activation of persulfate in the presence of GAC produced acid, lowering the solution pH. Higher persulfate concentrations and UV exposure resulted in greater GAC regeneration. Typical organic and inorganic byproducts (e.g., benzene compounds and sulfate ions) were measured as a component of treated water quality safety. This study provides a proof-of-concept that can be used to optimize pilot-scale and full-scale UV-activated persulfate for regeneration of NOM-saturated GAC.

Desorption of bisphenol-A (BPA) and regeneration of BPA-spent granular activated carbon using ultrasonic irradiation and organic solvent extraction

Desorption of bisphenol-A (BPA) from granular activated carbon (GAC) by ultrapure water and regeneration of BPA-spent GAC using ultrasonic irradiation and organic solvent extraction are investigated in this paper. The results showed that the pseudo-second-order kinetic model more appropriately described the BPA desorption pattern, and BPA desorption well followed the classical Arrhenius equation at a temperature range of 288–308 K with an activation energy of −56.47 kJ mol−1. Desorption rates of BPA were significantly favored by increasing acoustic intensity within a range of 17–100W at 20 kHz frequency. Certain fraction of methanol or ethanol, particularly methanol, in the extraction solution enhanced the BPA desorption from the spent GAC. The optimal volumetric fraction of methanol in the extraction solution was 75% at which 80% of BPA on the spent GAC was desorbed within 400 min. A synergetic enhancement could be observed when ultrasonic irradiation was coupled with methanol for the GAC regeneration, and the regeneration efficiency was improved with the increasing irradiation intensity. Results demonstrate that the proposed ultrasonic irradiation and organic solvent extraction technology is a promising alternative to regenerate the spent GAC with BPA.

Electrochemical Regeneration of Zn-Saturated Granular Activated Carbon from Electroplating Wastewater Plant

An electrically assisted regeneration (EAR) process was used to assess the effectiveness of regenerating exhausted granular activated carbon (GAC) preloaded with electroplating wastewater containing hyper Zn concentration at a concentration of 950.5 mg L −1 (1.45 × 10 −2 mol L −1 ). The electrochemical rege-neration process supplied with direct current was controlled at a constant voltage of 5.0 V. Two regeneration methods were tested and compared: first, acid washing (pH 1.0) and, second, electrically assisted acid washing. Results showed that the Zn adsorption capacity of GAC regenerated by EAR was significantly higher than that of GAC regenerated by acid washing. The effectiveness of the Zn desorbing efficiency from GAC was enhanced by electric current in the electrochemical regeneration process. Using the EAR method, a regeneration efficiency of 88.3% was observed for GAC, whereas using acid regeneration, the efficiency was only 25.3%. These observations reveal that EAR could be a potential alternative to acid washing for the regeneration of GAC saturated with Zn.